x°/EPA Inventory of U.S. Greenhouse Gas
Emissions and Sinks: 1990-2002
430R04003
•^:9P?^,.' V|fp%'
-------
How to obtain copies
You can electronically download this document on the U.S. EPA's homepage at .
Released for printing: April 15, 2004
Emissions of Greenhouse Gases
The photographs on the front and back cover of this report represent the six major sectors into which U.S. greenhouse
gas emissions have been allocated for analytical purposes. These sectors are defined by the IPCC and used in this report
for international reporting and standardized methodological reasons, and are represented by each chapter in this report as
Energy, Industrial Processes, Solvent and Other Product Use, Agriculture, Land-Use Change and Forestry, and Waste.
Energy: Transportation accounts for approximately 30 percent of emissions from the energy sector,
which have been steadily increasing from 1990 through 2002 due to several factors, including an
increased demand for travel. While transportation emissions result primarily from combustion
of petroleum for use in highway vehicles, they are also generated from airplanes, boats, trains,
and other equipment.
Waste: The waste sector exhibits a decrease in emissions between 1990 and 2002, due to an
increase in the amount of landfill methane collected and combusted at landfills. Within this sector,
landfills account for the majority of emissions, with wastewater treatment and human sewage
also contributing.
Industrial Processes: There are more than 20 specific industrial processes from which greenhouse
gas emissions are estimated in the United States. Emissions covered in this sector exclude the
use of energy consumed during industrial processes, as these emissions are accounted for in the
energy sector. Cement manufacturing is a large source of CO2 emissions within this sector.
Agriculture: Nitrous oxide emissions from agricultural soils dominate this sector, followed by
emissions of CH4 and N2O from livestock due to enteric fermentation and manure management.
Smaller quantities of CH4 and N2O emissions are derived from rice cultivation and field burning
of agricultural residues.
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
\ WASHINGTON, D.C. 20460
OFFICE OF
The U.S. Environmental Protection Agency, in cooperation with other federal agencies,
has prepared the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002. The
estimates of emissions and removals contained in this report, along with future updates, will be
used to monitor and track the progress of the United States in meeting our commitments under
the United Nations Framework Convention on Climate Change (UNFCCC).
In accordance with a decision of the Conference of Parties to the UNFCCC (Decision
3/CP.5), this inventory complies with the UNFCCC Reporting Guidelines on Annual Inventories
(FCCC/CP/1999/7). Adherence to these guidelines ensures that national inventories are well
documented, consistently prepared, and as accurate and complete as possible. The assumptions
and methodologies used in this report have been clearly explained, and are based on the Revised
1996IPCC Guidelines for National Greenhouse Gas Inventories and the IPCC Report on Good
Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories.
Each year, advances in scientific understanding and availability of underlying data allow
us to improve the quality and comprehensiveness of the inventory. Some of this year's advances
include improved estimates for iron and steel production, carbon dioxide consumption, the
substitution of ozone depleting substances, electrical transmission and distribution, manure
management, agricultural soil management, and the changes in forest carbon stocks. Also,
included for the first time this year are new emissions data on abandoned underground coal
mines.
Another notable change to this year's report is the new report structure, which conforms
with the new UNFCCC reporting requirements for inventory reports.
We hope that these improvements make this document more useful, and appreciate the
comments and suggestions we have received from numerous reviewers in both the scientific
community and the general public.
sy R. Jjlolmstead
Assistant Adnunistrator
Internet Address (URL)« htl
SecjchHj/Recycla&ia • Printed wftn V«g*tabta OH Based Inks on Racycied Paper (Minimum 50% Poslconsum«f content)
-------
-------
INVENTORY OF U.S. GREENHOUSE GAS
EMISSIONS AND SINKS:
1990 - 2002
APRIL 15,2004
U.S. Environmental Protection Agency
1200 Pennsylvania Ave., N.W.
Washington, DC 20460
U.S.A.
-------
-------
Acknowledgments
"The Environmental Protection Agency would like to acknowledge the many individual and organizational contributors
I to this document, without whose efforts this report would not be complete. Although the complete list of researchers,
government employees, and consultants who have provided technical and editorial support is too long to list here, EPA's
Office of Atmospheric Programs would like to thank some key contributors and reviewers whose work has significantly
improved this year's report.
Work on fuel combustion and industrial process emissions was led by Leif Hockstad and Lisa Hanle. Work on energy
and waste sector methane emissions was directed by Elizabeth Scheehle, while work on agriculture sector emissions was
directed by Tom Wirth and Joe Mangino. Tom Wirth led the preparation of the chapter on Land-Use Change and Forestry.
Work on emissions of HFCs, PFCs, and SF6 was directed by Deborah Schafer and Dave Godwin. Veronika Pesinova and
John Hall directed the work on mobile combustion.
Within the EPA, other Offices also contributed data, analysis and technical review for this report. The Office of
Transportation and Air Quality and the Office of Air Quality Planning and Standards provided analysis and review for several
of the source categories addressed in this report. The Office of Solid Waste and the Office of Research and Development
also contributed analysis and research.
The Energy Information Administration and the Department of Energy contributed invaluable data and analysis on
numerous energy-related topics. The U.S. Forest Service prepared the forest carbon inventory, and the Department of
Agriculture's Agricultural Research Service and the Natural Resource Ecology Laboratory at Colorado State University
contributed leading research on nitrous oxide and carbon fluxes from soils.
Other government agencies have contributed data as well, including the U.S. Geological Survey, the Federal Highway
Administration, the Department of Transportation, the Bureau of Transportation Statistics, the Department of Commerce,
the National Agricultural Statistics Service, the Federal Aviation Administration, and the Department of Defense.
We would also like to thank Marian Martin Van Pelt, Randall Freed, and their staff at ICF Consulting's Climate and
Atmospheric Policy Practice, including John Venezia, Katrin Peterson, Leonard Crook, Sarah Percy, Diana Pape, Meg Walsh,
Bill Cowart, Ravi Kantamaneni, Robert Lanza, Deanna Lekas, Caren Mintz, Kamala Jayaraman, Jeremy Scharfenberg, Matt
Stanberry, Vanessa Melendez, Rebecca LePrell, Philip Groth, Beth Moore, and Michael Grant for synthesizing this report
and preparing many of the individual analyses. Eastern Research Group, Raven Ridge Resources, and Arcadis also provided
significant analytical support.
-------
The United States Environmental Protection Agency (EPA) prepares the official U.S. Inventory of Greenhouse Gas
Emissions and Sinks to comply with existing commitments under the United Nations Framework Convention on Climate
Change (UNFCCC).1 Under decision 3/CP.5 of the UNFCCC Conference of the Parties, national inventories for UNFCCC
Annex I parties should be provided to the UNFCCC Secretariat each year by April 15.
In an effort to engage the public and researchers across the country, the EPA has instituted an annual public review and
comment process for this document. The availability of the draft document is announced via Federal Register Notice and
is posted on the EPA web site.2 Copies are also mailed upon request. The public comment period is generally limited to
30 days; however, comments received after the closure of the public comment period are accepted and considered for the
next edition of this annual report.
' See Article 4(1 )(a) of the United Nations Framework Convention on Climate Change .
See .
ii
-------
Table of Contents
Acknowledgments i
Table of Contents Hi
List of Tables, Figures, and Boxes v
Tables v
Figures xi
Boxe xii
Executive Summary ES-1
ES.l. Background Information ES-1
ES.2. Recent Trends in U.S. Greenhouse Gas Emissions and Sinks ES-3
ES.3. Overview of Source and Sink Emission Trends ES-6
ES.4. Other Information ES-18
1. Introduction
1.1. Background Information 1-2
1.2. Institutional Arrangements 1-7
1.3. Inventory Process 1-7
1.4. Methodology and Data Sources 1-11
1.5. Key Sources 1-12
1.6. Quality Assurance and Quality Control 1-14
1.7. Uncertainty and Limitations of Emission Estimates 1-15
1.8. Completeness 1-17
1.9. Organization of Report 1-17
2. Trends in Greenhouse Gas Emissions
2.1. Recent Trends in U.S. Greenhouse Gas Emissions 2-1
2.2. Emissions by Economic Sector 2-7
2.3. Ambient Air Pollutant Emissions 2-13
3. Energy
3.1. Carbon Dioxide Emissions from Fossil Fuel Combustion (IPCC Source Category 1A) 3-3
3.2. Carbon Stored in Products from Non-Energy Uses of Fossil Fuels (IPCC Source Category 1A) 3-19
3.3. Stationary Combustion (excluding CO2) (IPCC Source Category 1A) 3-23
3.4. Mobile Combustion (excluding CO2) (IPCC Source Category 1 A) 3-28
3.5. Coal Mining (IPCC Source Category IBla) 3-39
3.6. Abandoned Underground Coal Mines (IPCC Source Category IBla) 3-42
3.7. Petroleum Systems (IPCC Source Category lB2a) 3-46
3.8. Natural Gas Systems (IPCC Source Category lB2b) 3-49
3.9. Municipal Solid Waste Combustion (IPCC Source Category 1A5) 3-52
3.10. Natural Gas Flaring and Ambient Air Pollutant Emissions from Oil and Gas Activities
(IPCC Source Category 1B2) 3-56
3.11. International Bunker Fuels (IPCC Source Category 1: Memo Items) 3-58
3.12. Wood Biomass and Ethanol Consumption (IPCC Source Category 1 A) 3-63
Hi
-------
4. Industrial Processes
4.1. Iron and Steel Production (IPCC Source Category 2C1) 4-4
4.2. Cement Manufacture (IPCC Source Category 2A1) 4-7
4.3. Ammonia Manufacture and Urea Application (IPCC Source Category 2B1) 4-9
4.4. Lime Manufacture (IPCC Source Category 2A2) 4-12
4.5. Limestone and Dolomite Use (IPCC Source Category 2A3) 4-15
4.6. Soda Ash Manufacture and Consumption (IPCC Source Category 2A4) 4-18
4.7. Titanium Dioxide Production (IPCC Source Category 2B5) 4-20
4.8. Phosphoric Acid Production (IPCC Source Category 2A7) 4-21
4.9. Ferroalloy Production (IPCC Source Category 2C2) 4-24
4.10. Carbon Dioxide Consumption (IPCC Source Category 2B5) 4-26
4.11. Petrochemical Production (IPCC Source Category 2B5) 4-29
4.12. Silicon Carbide Production (IPCC Source Category 2B4) 4-30
4.13. Nitric Acid Production (IPCC Source Category 2B2) 4-31
4.14. Adipic Acid Production (IPCC Source Category 2B3) 4-33
4.15. Substitution of Ozone Depleting Substances (IPCC Source Category 2F) 4-35
4.16. HCFC-22 Production (IPCC Source Category 2E1) 4-37
4.17. Electrical Transmission and Distribution (IPCC Source Category 2F7) 4-38
4.18. Aluminum Production (IPCC Source Category 2C3) 4-41
4.19. Semiconductor Manufacture (IPCC Source Category 2F6) 4-45
4.20. Magnesium Production and Processing (IPCC Source Category 2C4) 4-48
4.21. Industrial Sources of Ambient Air Pollutants 4-50
5. Solvent and Other Product Use
5.1. Nitrous Oxide Product Usage (IPCC Source Category 3D) 5-1
5.2. Ambient Air Pollutants from Solvent Use 5-2
6. Agriculture
6.1. Enteric Fermentation (IPCC Source Category 4A) 6-2
6.2. Manure Management (IPCC Source Category 4B) 6-5
6.3. Rice Cultivation (IPCC Source Category 4C) 6-12
6.4. Agricultural Soil Management (IPCC Source Category 4D) 6-17
6.5. Field Burning of Agricultural Residues (IPCC Source Category 4F) 6-23
7. Land-Use Change and Forestry
7.1. Changes in Forest Carbon Stocks (IPCC Source Category 5A) 7-2
7.2. Changes in Carbon Stocks in Urban Trees (IPCC Source Category 5A5) 7-11
7.3. Changes in Agricultural Soil Carbon Stocks (IPCC Source Category 5D) 7-13
7.4. Changes in Yard Trimming and Food Scrap Carbon Stocks in Landfills (IPCC Source Category 5E) 7-22
8. Waste
8.1. Landfills (IPCC Source Category 6A1) 8-2
8.2. Wastewater Treatment (IPCC Source Category 6B) 8-5
8.3. Human Sewage (Domestic Wastewater) (IPCC Source Category 6B) 8-8
8.4. Waste Sources of Ambient Air Pollutants 8-10
9. Other
10. Recalculations and Improvements
References
iv
-------
List of Tables, Figures, and Boxes
Tables
Table ES-1: Global Warming Potentials (100 Year Time Horizon) Used in this Report ES-3
Table ES-2: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg CO2 Eq.) ES-4
Table ES-3: Annual Change in CO2 Emissions from Fossil Fuel Combustion for Selected Fuels and
Sectors (Tg CO2 Eq. and Percent) ES-6
Table ES-4: U.S. Sources of CO2 Emissions and Sinks (Tg CO2 Eq.) ES-8
Table ES-5: CO2 Emissions from Fossil Fuel Combustion by End-Use Sector (Tg CO2 Eq.) ES-9
Table ES-6: U.S. Sources of CH4 Emissions (Tg CO2 Eq.) ES-13
Table ES-7: U.S. Sources of Nitrous Oxide Emissions (Tg CO2 Eq.) ES-15
Table ES-8: Emissions of MFCs, PFCs, and SF6 (Tg CO2 Eq.) ES-17
Table ES-9: Emissions of Ozone Depleting Substances (Gg) ES-19
Table ES-10: U.S. Greenhouse Gas Emissions Allocated to Economic Sectors (Tg CO2 Eq.) ES-20
Table ES-11: U.S Greenhouse Gas Emissions by Economic Sector and Gas with Electricity-Related
Emissions Distributed (Tg CO2 Eq.) ES-21
Table ES-12: Recent Trends in Various U.S. Data (Index 1990 = 100) and Global Atmospheric CO2
Concentration ES-22
Table ES-13: Emissions of NOX, CO, NMVOCs, and SO2 (Gg) ES-23
Table 1-1: Global atmospheric concentration (ppm unless otherwise specified), rate of concentration
change (ppb/year) and atmospheric lifetime (years) of selected greenhouse gases 1-3
Table 1-2: Global Warming Potentials and Atmospheric Lifetimes (Years) Used in this Report 1-7
Table 1-3: Comparison of 100 Year GWPs 1-8
Table 1-4: Effects on U.S. Greenhouse Gas Emission Trends Using IPCC SAR and TAR GWP Values
(TgC02Eq.) 1-8
Table 1 -5: Comparison of Emissions by Sector using IPCC SAR and TAR GWP Values (Tg CO2 Eq.) 1-9
Table 1-6: Key Source Categories for the United States (1990-2002) Based on Tier 1 Approach 1-14
Table 1-7: IPCC Sector Descriptions 1-17
Table 1-8: List of Annexes 1-18
Table 2-1: Annual Change in CO2 Emissions from Fossil Fuel Combustion for Selected Fuels and
Sectors (Tg CO2 Eq. and Percent) 2-2
Table 2-2: Recent Trends in Various U.S. Data (Index 1990 = 100) and Global Atmospheric CO2
Concentration 2-4
Table 2-3: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg CO2 Eq.) 2-5
Table 2-4: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Gg) 2-6
Table 2-5: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks by Chapter/IPCC
Sector (Tg CO2 Eq.) 2-7
Table 2-6: U.S. Greenhouse Gas Emissions Allocated to Economic Sectors (Tg CO2 Eq. and Percent of
Total in 2002) 2-9
Table 2-7: Electricity Generation-Related Greenhouse Gas Emissions (Tg CO2 Eq.) 2-8
Table 2-8: U.S Greenhouse Gas Emissions by "Economic Sector" and Gas with Electricity-Related
Emissions Distributed (Tg CO2 Eq.) and percent of total in 2002 2-11
Table 2-9: Transportation-Related Greenhouse Gas Emissions (Tg CO2 Eq.) 2-12
Table 2-10: Emissions of NOX, CO, NMVOCs, and SO2 (Gg) 2-14
Table 3-1: Emissions from Energy (Tg CO2 Eq.) 3-2
Table 3-2: Emissions from Energy (Gg) 3-3
Table 3-3: CO2 Emissions from Fossil Fuel Combustion by Fuel Type and Sector (Tg CO2 Eq.) 3-4
Table 3-4: Fossil Fuel Carbon in Products (Tg CO2 Eq.)* 3-5
Table 3-5: CO2 Emissions from International Bunker Fuels (Tg CO2 Eq.)* 3-7
-------
Table 3-6: CO2 Emissions from Fossil Fuel Combustion by End-Use Sector (Tg CO2 Eq.) 3-7
Table 3-7: CO2 Emissions from Fossil Fuel Combustion in Transportation End-Use
Sector (Tg CO2 Eq.) 3-9
Table 3-8: Carbon Intensity from Direct Fossil Fuel Combustion by Sector (Tg CO2 Eq./QBtu) 3-13
Table 3-9: Carbon Intensity from all Energy Consumption by Sector (Tg CO2 Eq./QBtu) 3-14
Table 3-10: Uncertainty Estimates for CO2 from Fossil Fuel Combustion by Fuel Type and Sector 3-17
Table 3-11: 2002 Non-Energy Use (NEU) Fossil Fuel Consumption, Storage, and Emissions 3-20
Table 3-12: Storage and Emissions from NEU Fossil Fuel Consumption (Tg CO2 Eq.) 3-21
Table 3-13: Quantitative Uncertainty Estimates for Carbon Stored in Products (Tg C) and Carbon Storage
Factor (Percent) 3-22
Table 3-14: CH4 Emissions from Stationary Combustion (Tg CO2 Eq.) 3-24
Table 3-15: N2O Emissions from Stationary Combustion (Tg CO2 Eq.) 3-24
Table 3-16: CH4 Emissions from Stationary Combustion (Gg) 3-25
Table 3-17: N20 Emissions from Stationary Combustion (Gg) 3-25
Table 3-18: NOX, CO, and NMVOC Emissions from Stationary Combustion in 2002 (Gg) 3-26
Table 3-19: Quantitative Uncertainty Estimates for CH4 and N2O Emissions from Stationary
Combustion, Including Biomass (Tg CO2 Eq. and Percent) 3-27
Table 3-20: CH4 Emissions from Mobile Combustion (Tg CO2 Eq.) 3-29
Table 3-21: N2O Emissions from Mobile Combustion (Tg CO2 Eq.) 3-30
Table 3-22: CH4 Emissions from Mobile Combustion (Gg) 3-30
Table 3-23: N2O Emissions from Mobile Combustion (Gg) 3-31
Table 3-24: NOX Emissions from Mobile Combustion (Gg) 3-31
Table 3-25: CO Emissions from Mobile Combustion (Gg) 3-32
Table 3-26: NMVOC Emissions from Mobile Combustion (Gg) 3-33
Table 3-27: Quantitative Uncertainty Estimates for CH4 and N2O Emissions from Highway Vehicles
(Tg CO2 Eq. and Percent) 3-38
Table 3-28: CH4 Emissions from Coal Mining (Tg CO2 Eq.) 3-40
Table 3-29: CH4 Emissions from Coal Mining (Gg) 3-40
Table 3-30: Coal Production (Thousand Metric Tons) 3-41
Table 3-31: Quantitative Uncertainty Estimates for CH4 Emissions from Coal Mining
(TgCO2Eq. and Percent) 3-42
Table 3-32: CH4 Emissions from Abandoned Coal Mines (Tg CO2 Eq.) 3-43
Table 3-33: CH4 Emissions from Abandoned Coal Mines (Gg) 3-43
Table 3-34: Range of Uncertainty Estimates for CH4 Emissions from Abandoned Underground
Coal Mining (Tg CO2 Eq. and Percent) • 3-45
Table 3-35: CH4 Emissions from Petroleum Systems (Tg CO2 Eq.) 3-46
Table 3-36: CH4 Emissions from Petroleum Systems (Gg) 3-47
Table 3-37: Range of Uncertainty Estimates for CH4 Emissions from Petroleum Systems
(Tg CO2 Eq. and Percent) 3-48
Table 3-38: CH4 Emissions from Natural Gas Systems (Tg CO2 Eq.) 3-49
Table 3-39: CH4 Emissions from Natural Gas Systems (Gg) 3-49
Table 3-40: Range of Uncertainty Estimates for CH4 Emissions from Natural Gas Systems
(Tg CO2 Eq. and Percent) 3-51
Table 3-41: CO2 and N2O Emissions from Municipal Solid Waste Combustion (Tg CO2 Eq.) 3-52
Table 3-42: CO2 and N2O Emissions from Municipal Solid Waste Combustion (Gg) 3-53
Table 3-43: NOX, CO, and NMVOC Emissions from Municipal Solid Waste Combustion (Gg) 3-53
Table 3-44: Municipal Solid Waste Generation (Metric Tons) and Percent Combusted 3-54
-------
Table 3-45: Range of Uncertainty Estimates for CO2 from Municipal Solid Waste Combustion
(Tg CO2 Eq. and Percent) 3-54
Table 3-46: U.S. Municipal Solid Waste Combusted, as Reported by EPA and BioCycle (Metric Tons) 3-55
Table 3-47: CO2 Emissions from On-Shore and Off-Shore Natural Gas Flaring (Tg CO2 Eq.) 3-57
Table 3-48: CO2 Emissions from On-Shore and Off-Shore Natural Gas Flaring (Gg) 3-57
Table 3-49: NOX, NMVOCs, and CO Emissions from Oil and Gas Activities (Gg) 3-57
Table 3-50: Volume Flared Offshore (MMcf) and Fraction Vented and Flared (Percent) 3-57
Table 3-51: Total Natural Gas Reported Vented and Flared (Million Ft3) and Thermal Conversion
Factor (Btu/Ft3) 3-58
Table 3-52: Emissions from International Bunker Fuels (Tg CO2 Eq.) 3-60
Table 3-53: Emissions from International Bunker Fuels (Gg) 3-60
Table 3-54: Aviation Jet Fuel Consumption for International Transport (Million Gallons) 3-61
Table 3-55: Marine Fuel Consumption for International Transport (Million Gallons) 3-61
Table 3-56: CO2 Emissions from Wood Consumption by End-Use Sector (Tg CO2 Eq.) 3-63
Table 3-57: CO2 Emissions from Wood Consumption by End-Use Sector (Gg) 3-64
Table 3-58: CO2 Emissions from Ethanol Consumption 3-64
Table 3-59: Woody Biomass Consumption by Sector (Trillion Btu) 3-64
Table 3-60: Ethanol Consumption 3-66
Table 3-61: CH4 Emissions from Non-Combustion Fossil Sources (Gg) 3-65
Table 3-62: Formation of CO2 through Atmospheric CH4 Oxidation (Tg CO2 Eq.) 3-65
Table 4-1: Emissions from Industrial Processes (Tg CO2 Eq.) 4-2
Table 4-2: Emissions from Industrial Processes (Gg) 4-3
Table 4-3: CO2 and CH4 Emissions from Iron and Steel Production (Tg CO2 Eq.) 4-4
Table 4-4: CO2 and CH4 Emissions from Iron and Steel Production (Gg) 4-5
Table 4-5: CH4 Emission Factors for Coal Coke, Sinter, and Pig Iron Production 4-5
Table 4-6: Production and Consumption Data for the Calculation of CO2 and CH4 Emissions from
Iron and Steel Production (Thousand Metric Tons) 4-6
Table 4-7: Quantitative Uncertainty Estimates for CO2 and CH4 Emissions from Iron and Steel
Production (Tg. CO2 Eq. and Percent) 4-7
Table 4-8: CO2 Emissions from Cement Production* 4-8
Table 4-9: Cement Production (Gg) 4-8
Table 4-10: Quantitative Uncertainty Estimates for CO2 Emissions from Cement Manufacture
(Tg CO2 Eq. and Percent) 4-9
Table 4-11: CO2 Emissions from Ammonia Manufacture 4-10
Table 4-12: CO2 Emissions from Urea Application 4-10
Table 4-13: Ammonia Production 4-11
Table 4-14: Urea Production 4-11
Table 4-15: Urea Net Imports 4-11
Table 4-16: Quantitative Uncertainty Estimates for CO2 Emissions from Ammonia Manufacture
and Urea Application (Tg CO2Eq. and Percent) 4-12
Table 4-17: Net CO2 Emissions from Lime Manufacture 4-13
Table 4-18: CO2 Emissions from Lime Manufacture (Gg) 4-13
Table 4-19: Lime Production and Lime Use for Sugar Refining and PCC (Thousand Metric Tons) 4-14
Table 4-20: Hydrated Lime Production (Thousand Metric Tons) 4-14
Table 4-21: Quantitative Uncertainty Estimates for CO2 Emissions from Lime Manufacture
(Tg CO2 Eq. and Percent) 4-15
Table 4-22: CO2 Emissions from Limestone & Dolomite Use (Tg CO2 Eq.) 4-16
vii
-------
Table 4-23: CO2 Emissions from Limestone & Dolomite Use (Gg) 4-16
Table 4-24: Limestone and Dolomite Consumption (Thousand Metric Tons) 4-16
Table 4-25: Dolomitic Magnesium Metal Production Capacity (Metric Tons) 4-17
Table 4-26: Quantitative Uncertainty Estimates for CO2 Emissions from Limestone and Dolomite Use
(Tg CO2 Eq. and Percent) 4-17
Table 4-27: CO2 Emissions from Soda Ash Manufacture and Consumption 4-18
Table 4-28: CO2 Emissions from Soda Ash Manufacture and Consumption (Gg) 4-18
Table 4-29: Soda Ash Manufacture and Consumption (Thousand Metric Tons) 4-19
Table 4-30: Quantitative Uncertainty Estimates for CO2 Emissions from Soda Ash Manufacture and
Consumption (Tg CO2 Eq. and Percent) 4-19
Table 4-31: CO2 Emissions from Titanium Dioxide 4-20
Table 4-32: Titanium Dioxide Production 4-20
Table 4-33: Quantitative Uncertainty Estimates for CO2 Emissions from Titanium Dioxide
Production (Tg CO2 Eq. and Percent) ..4-21
Table 4-34: CO2 Emissions from Phosphoric Acid Production 4-22
Table 4-35: Phosphate Rock Domestic Production, Exports, and Imports (Thousand Metric Tons) 4-23
Table 4-36: Chemical Composition of Phosphate Rock (percent by weight) 4-23
Table 4-37: Quantitative Uncertainty Estimates for CO2 Emissions from Phosphoric Acid Production
(Tg CO2 Eq. and Percent) 4-24
Table 4-38: CO2 Emissions from Ferroalloy Production 4-25
Table 4-39: Production of Ferroalloys (Metric Tons) 4-25
Table 4-40: Quantitative Uncertainty Estimates for CO2 Emissions from Ferroalloy Production
(Tg CO2 Eq. and Percent) 4-26
Table 4-41: CO2 Emissions from Carbon Dioxide Consumption 4-27
Table 4-42: Carbon Dioxide Consumption 4-28
Table 4-43: Quantitative Uncertainty Estimates for CO2 Emissions from Carbon Dioxide
Consumption (Tg CO2 Eq. and Percent) 4-28
Table 4-44: CH4 Emissions from Petrochemical Production 4-29
Table 4-45: Production of Selected Petrochemicals (Thousand Metric Tons) 4-30
Table 4-46: Quantitative Uncertainty Estimates for CH4 Emissions from Petrochemical
Production (Tg CO2 Eq. and Percent) 4-30
Table 4-47: CH4 Emissions from Silicon Carbide Production 4-31
Table 4-48: Production of Silicon Carbide 4-31
Table 4-49: N2O Emissions from Nitric Acid Production 4-31
Table 4-50: Nitric Acid Production 4-32
Table 4-51: Quantitative Uncertainty Estimates for N2O Emissions from Nitric Acid Production
(Tg CO2 Eq. and Percent) 4-32
Table 4-52: N2O Emissions from Adipic Acid Production 4-33
Table 4-53: Adipic Acid Production 4-34
Table 4-54: Quantitative Uncertainty Estimates for N2O Emissions from Adipic Acid Production
(Tg CO2 Eq. and Percent) 4-34
Table 4-55: Emissions of MFCs and PFCs from ODS Substitution (Tg CO2 Eq.) 4-35
Table 4-56: Emissions of HFCs and PFCs from ODS Substitution (Mg) 4-35
Table 4-57: Quantitative Uncertainty Estimates for HFC and PFC Emissions from ODS Substitution
(Tg CO2 Eq. and Percent) 4-36
Table 4-58: HFC-23 Emissions from HCFC-22 Production 4-37
Table 4-59: HCFC-22 Production 4-38
viii
-------
Table 4-60: Quantitative Uncertainty Estimates for HFC-23 Emissions from HCFC-22 Production
(Tg CO2 Eq. and Percent) 4-38
Table 4-61: SF6 Emissions from Electric Power Systems and Original Equipment Manufactures
(TgC02Eq.) 4-39
Table 4-62: SF6 Emissions from Electric Power Systems and Original Equipment Manufactures (Gg) 4-39
Table 4-63: Quantitative Uncertainty Estimates for SF6 Emissions from Electrical Transmission
and Distribution (Tg CO2 Eq. and Percent) 4-40
Table 4-64: CO2 Emissions from Aluminum Production 4-42
Table 4-65: PFC Emissions from Aluminum Production (Tg CO2 Eq.) 4-42
Table 4-66: PFC Emissions from Aluminum Production (Gg) 4-42
Table 4-67: Production of Primary Aluminum 4-43
Table 4-68: Quantitative Uncertainty Estimates for CO2 Emissions from Aluminum Production
(TgC02Eq.) 4-44
Table 4-69: Quantitative Uncertainty Estimates for PFC Emissions from Aluminum Production
(Tg CO2 Eq. and Percent) 4-44
Table 4-70: PFC, HFC, and SF6 Emissions from Semiconductor Manufacture (Tg CO2 Eq.) 4-46
Table 4-71: PFC, HFC, and SF6 Emissions from Semiconductor Manufacture (Mg) 4-46
Table 4-72: Quantitative Uncertainty Estimates for HFC, PFC, and SF6 Emissions from
Semiconductor Manufacture (Tg CO2 Eq. and Percent) 4-47
Table 4-73: SF6 Emissions from Magnesium Production and Processing 4-48
Table 4-74: SF6 Emission Factors (kg SF6 per metric ton of magnesium) 4-48
Table 4-75: Quantitative Uncertainty Estimates for SF6 Emissions from Magnesium Production
and Processing (Tg CO2 Eq. and Percent) 4-49
Table 4-76: 2002 Potential and Actual Emissions of HFCs, PFCs, and SF6 from Selected Sources
(TgC02Eq.) 4-51
Table 4-77: NOX, CO, and NMVOC Emissions from Industrial Processes (Gg) 4-50
Table 5-1: N2O Emissions from Solvent and Other Product Use 5-1
Table 5-2: N2O Emissions from Nitrous Oxide Product Usage 5-1
Table 5-3: N2O Production (Thousand Metric Tons) 5-2
Table 5-4: Quantitative Uncertainty Estimates for N2O Emissions from Nitrous Oxide Product
Usage (Tg CO2 Eq. and Percent) 5-3
Table 5-5: Emissions of NOX, CO, and NMVOC from Solvent Use (Gg) 5-4
Table 6-1: Emissions from Agriculture (Tg CO2Eq.) 6-1
Table 6-2: Emissions from Agriculture (Gg) 6-2
Table 6-3: CH4 Emissions from Enteric Fermentation (Tg CO2 Eq.) 6-2
Table 6-4: CH4 Emissions from Enteric Fermentation (Gg) 6-3
Table 6-5: Quantitative Uncertainty Estimates for CH4 Emissions from Enteric Fermentation
(Tg CO2 Eq. and Percent) 6-5
Table 6-6: CH4 and N2O Emissions from Manure Management (Tg CO2 Eq.) 6-7
Table 6-7: CH4 andN2O Emissions from Manure Management (Gg) 6-7
Table 6-8: Quantitative Uncertainty Estimates for CH4 and N2O Emissions from Manure
Management (Tg CO2 Eq. and %) 6-10
Table 6-9: CH4 Emissions from Rice Cultivation (Tg CO2 Eq.) 6-14
Table 6-10: CH4 Emissions from Rice Cultivation (Gg CH4) 6-14
Table 6-11: Rice Areas Harvested (Hectares) 6-15
Table 6-12: Quantitative Uncertainty Estimates for CH4 Emissions from Rice Cultivation
(Tg CO2 Eq. and Percent) 6-17
Table 6-13: N2O Emissions from Agricultural Soil Management (Tg CO2 Eq.) 6-18
ix
-------
Table 6-14: N2O Emissions from Agricultural Soil Management (Gg N2O) 6-18
Table 6-15: Direct N2O Emissions from Managed Soils (Tg CO2 Eq.) 6-18
Table 6-16: Direct N2O Emissions from Pasture, Range, and Paddock Livestock Manure
(TgC02Eq.) 6-19
Table 6-17: Indirect N2O Emissions (Tg CO2 Eq.) 6-19
Table 6-18: Quantitative Uncertainty Estimates of N2O Emissions from Agricultural Soil
Management (Tg CO2 Eq. and Percent) 6-23
Table 6-19: Emissions from Field Burning of Agricultural Residues (Tg CO2 Eq.) 6-24
Table 6-20: Emissions from Field Burning of Agricultural Residues (Gg)* 6-25
Table 6-21: Agricultural Crop Production (Thousand Metric Tons of Product) 6-26
Table 6-22: Percentage of Rice Area Burned by State 6-26
Table 6-23: Percentage of Rice Area Burned in California 6-26
Table 6-24: Key Assumptions for Estimating Emissions from Agricultural Residue Burning 6-27
Table 6-25: Greenhouse Gas Emission Ratios 6-27
Table 6-26: Quantitative Uncertainty Estimates for CH4 and N2O Emissions from Field Burning
of Agricultural Residues (Tg CO2 Eq. and Percent) 6-28
Table 7-1: Net CO2 Flux from Land-Use Change and Forestry (Tg CO2 Eq.) 7-2
Table 7-2: Net CO2 Flux from Land-Use Change and Forestry (Tg C) 7-2
Table 7-3: Net Changes in Carbon Stocks in Forest and Harvested Wood Pools, and Total Net
Forest Carbon Flux (Tg CO2 Eq.) 7-4
Table 7-4: Net Changes in Carbon Stocks in Forest and Harvested Wood Pools, and Total Net
Forest Carbon Flux (Tg C) 7-5
Table 7-5: Carbon Stocks in Forest and Harvested Wood Pools (Tg C) 7-5
Table 7-6: Carbon Stocks in Forest Soils (Tg C) 7-5
Table 7-7: Net Flux from Urban Trees (Tg CO2 Eq. and Tg C) 7-11
Table 7-8: Carbon Stocks (Metric Tons C), Annual Carbon Sequestration (Metric Tons C/yr), Tree
Cover (Percent), and Annual Carbon Sequestration per Area of Tree Cover (kg C/m cover-yr)
for Ten U.S. Cities 7-12
Table 7-9: Quantitative Uncertainty Estimates for CO2 Emissions from Changes in Carbon Stocks in
Urban Trees (Tg CO2 Eq. and Percent) ". 7-13
Table 7-10: Net CO2 Flux from Agricultural Soils (Tg CO2 Eq.) 7-17
Table 7-11: Net Carbon Flux from Agricultural Soils (Tg C) 7-17
Table 7-12: Quantities of Applied Minerals (Thousand Metric Tons) 7-19
Table 7-13: Quantitative Uncertainty Estimates for CO2 Flux from Agricultural Soil Carbon Stocks
(Tg CO2 Eq. and Percent) 7-20
Table 7-14: Net Changes in Yard Trimming and Food Scrap Stocks (Tg CO2 Eq.) 7-23
Table 7-15: Net Changes in Yard Trimming and Food Scrap Stocks (Tg C) 7-23
Table 7-16: Moisture Content (%), Carbon Storage Factor, Initial Carbon Content (%), Proportion of
Initial Carbon Sequestered (%), and Half-Life (years) for Landfilled Yard Trimmings and
Food Scraps 7-24
Table 7-17: Carbon Stocks in Yard Trimmings and Food Scraps (Tg of C) 7-25
Table 8-1: Emissions from Waste (Tg CO2 Eq.) 8-1
Table 8-2: Emissions from Waste (Gg) 8-1
Table 8-3: CH4 Emissions from Landfills (Tg CO2 Eq.) 8-2
Table 8-4: CH4 Emissions from Landfills (Gg) 8-3
Table 8-5: Quantitative Uncertainty Estimates for CH4 Emissions from Landfills
(Tg CO2 Eq. and Percent) 8-4
Table 8-6: CH4 Emissions from Domestic and Industrial Wastewater Treatment (Tg CO2 Eq.) 8-5
-------
Table 8-7: CH4 Emissions from Domestic and Industrial Wastewater Treatment (Gg) 8-6
Table 8-8: U.S. Population (Millions) and Wastewater BOD Produced (Gg) 8-6
Table 8-9: U.S. Pulp and Paper, Meat and Poultry, and Vegetables, Fruits and Juices Production
(Million Metric Tons) 8-7
Table 8-10: Quantitative Uncertainty Estimates for CH4 Emissions from Wastewater Treatment
(Tg CO2 Eq. and Percent) 8-7
Table 8-11: N2O Emissions from Human Sewage 8-8
Table 8-12: U.S. Population (Millions) and Average Protein Intake (kg/Person/Year) 8-9
Table 8-13: Quantitative Uncertainty Estimates for N2O Emissions from Human Sewage
(Tg CO2 Eq. and Percent) 8-10
Table 8-14: Emissions of NOX, CO, and NMVOC from Waste (Gg) 8-10
Table 10-1: Revisions to U.S. Greenhouse Gas Emissions (Tg CO2 Eq.) 10-2
Table 10-2: Revisions to Net CO2 Sequestration from Land-Use Change and Forestry (Tg CO2 Eq.) 10-3
Figures
Figure ES-1: U.S. Greenhouse Gas Emissions by Gas ES-3
Figure ES-2: Annual Percent Change in U.S. Greenhouse Gas Emissions ES-3
Figure ES-3: Absolute Change in U.S. Greenhouse Gas Emissions Since 1990 ES-3
Figure ES-4: 2002 Greenhouse Gas Emissions by Gas ES-5
Figure ES-5: 2002 Sources of CO2 ES-7
Figure ES-6: 2002 U.S. Fossil Carbon Flows (Tg CO2 Eq.) ES-7
Figure ES-7: 2002 U.S. Energy Consumption by Energy Source ES-8
Figure ES-8: U.S. Energy Consumption (Quadrillion Btu) ES-8
Figure ES-9: 2002 CO2 Emissions from Fossil Fuel Combustion by Sector and Fuel Type ES-9
Figure ES-10: 2002 End-Use Sector Emissions of CO2 from Fossil Fuel Combustion ES-10
Figure ES-11: 2002 Sources of CH4 ES-13
Figure ES-12: 2002 Sources of N2O ES-16
Figure ES-13: 2002 Sources of HFCs, PFCs, and SF6 ES-18
Figure ES-14: Emissions Allocated to Economic Sectors ES-20
Figure ES-15: Emissions with Electricity Distributed to Economic Sectors ES-21
Figure ES-16: U.S. Greenhouse Gas Emissions Per Capita and Per Dollar of Gross Domestic Product ES-22
Figure 2-1: U.S. Greenhouse Gas Emissions by Gas 2-1
Figure 2-2: Annual Percent Change in U.S. Greenhouse Gas Emissions 2-1
Figure 2-3: Absolute Change in U.S. Greenhouse Gas Emissions Since 1990 2-2
Figure 2-4: U.S. Greenhouse Gas Emissions Per Capita and Per Dollar of Gross Domestic Product 2-4
Figure 2-5: U.S. Greenhouse Gas Emissions by Chapter/IPCC Sector 2-7
Figure 2-6: Emissions Allocated to Economic Sectors 2-8
Figure 2-7: Emissions with Electricity Distributed to Economic Sectors 2-10
Figure 3-1: 2002 Energy Chapter Greenhouse Gas Sources 3-1
Figure 3-2: 2002 U.S. Fossil Carbon Flows (Tg CO2 Eq.) 3-2
Figure 3-3: 2002 U.S. Energy Consumption by Energy Source 3-4
Figure 3-4: U.S. Energy Consumption (Quadrillion Btu) 3-4
Figure 3-5: 2002 CO2 Emissions from Fossil Fuel Combustion by Sector and Fuel Type 3-5
Figure 3-6: Annual Deviations from Normal Heating Degree Days for the United States (1949-2002) 3-6
Figure 3-7: Annual Deviations from Normal Cooling Degree Days for the United States (1949-2002) 3-6
Figure 3-8: Aggregate Nuclear and Hydroelectric Power Plant Capacity Factors in the United States
(1973-2002) 3-6
XI
-------
Figure 3-9: 2002 End-Use Sector Emissions of CO2 from Fossil Fuel Combustion 3-7
Figure 3-10: Motor Gasoline Retail Prices (Real) 3-8
Figure 3-11: Motor Vehicle Fuel Efficiency 3-8
Figure 3-12: Industrial Production Indexes (Index 1997=100) 3-10
Figure 3-13: Heating Degree Days 3-11
Figure 3-14: Cooling Degree Days 3-11
Figure 3-15: Electricity Generation Retail Sales by End-Use Sector 3-11
Figure 3-16: U.S. Energy Consumption and Energy-Related CO2 Emissions Per Capita and
Per Dollar GDP 3-14
Figure 3-17: Mobile Source CH4 and N2O Emissions 3-29
Figure 4-1: 2002 Industrial Processes Chapter Greenhouse Gas Sources 4-1
Figure 6-1: 2002 Agriculture Chapter Greenhouse Gas Sources 6-1
Figure 6-2: Direct and Indirect N2O Emissions from Agricultural Soils 6-17
Figure 7-1: Forest Sector Carbon Pools and Flows 7-3
Figure 7-2: Estimates of Forest Carbon Flux in Major Pools 7-6
Figure 7-3: Average Carbon Density in the Forest Tree Pool in the Conterminous U.S.
During 2003 7-6
Figure 7-4: Estimates of Forest Carbon Flux in Major Pools: Comparison of New Estimates with
those in Previous Inventory 7-10
Figure 7-5: Net Annual CO2 Flux, per Hectare, From Mineral Soils Under Agricultural Management,
1990-1992 7-15
Figure 7-6: Net Annual CO2 Flux, per Hectare, From Mineral Soils Under Agricultural Management,
1993-2002 7-15
Figure 7-7: Net Annual CO2 Flux, per Hectare, From Organic Soils Under Agricultural Management,
1990-1992 7-16
Figure 7-8: Net Annual CO2 Flux, per Hectare, From Organic Soils Under Agricultural Management,
1993-2002 7-16
Figure 8-1: 2002 Waste Chapter Greenhouse Gas Sources 8-1
Boxes
Box ES-1: Emissions of Ozone Depleting Substances ES-19
Box ES-2: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data ES-22
Box ES-3: Sources and Effects of Sulfur Dioxide ES-24
Box 1-1: The IPCC Third Assessment Report and Global Warming Potentials 1-8
Box 1-2: IPCC Good Practice Guidance 1-11
Box 2-1: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data 2-4
Box 2-2: Methodology for Aggregating Emissions by Economic Sector 2-13
Box 2-3: Sources and Effects of Sulfur Dioxide 2-14
Box 3-1: Weather and Non-Fossil Energy Effects on CO2 from Fossil Fuel Combustion Trends 3-6
Box 3-2: Carbon Intensity of U.S. Energy Consumption 3-13
Box 3-3: Biogenic Emissions and Sinks of Carbon 3-51
Box 3-4: Formation of CO2 through Atmospheric CH4 Oxidation 3-65
Box 4-1: Potential Emission Estimates of HFCs, PFCs, and SF6 4-51
xii
-------
Executive Summary
Central to any study of climate change is the development of an emissions inventory that identifies and quantifies
a country's primary anthropogenic1 sources and sinks of greenhouse gases. This inventory adheres to both 1)
a comprehensive and detailed methodology for estimating sources and sinks of anthropogenic greenhouse gases, and 2)
a common and consistent mechanism that enables signatory countries to the United Nations Framework Convention on
Climate Change (UNFCCC) to compare the relative contribution of different emission sources and greenhouse gases to
climate change. Moreover, systematically and consistently estimating national and international emissions is a prerequisite
for accounting for reductions and evaluating mitigation strategies.
In 1992, the United States signed and ratified the UNFCCC. The ultimate objective of the UNFCCC is "to achieve, in
accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere
at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved
within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is
not threatened and to enable economic development to proceed in a sustainable manner."2
Parties to the Convention, by ratifying, "shall develop, periodically update, publish and make available.. .national inventories
of anthropogenic emissions by sources and removals by sinks of all greenhouse gases not controlled by the Montreal Protocol,
using comparable methodologies..."3 The United States views this report as an opportunity to fulfill these commitments.
This chapter summarizes the latest information on U.S. anthropogenic greenhouse gas emission trends from 1990
through 2002. To ensure that the U.S. emissions inventory is comparable to those of other UNFCCC Parties, the estimates
presented here were calculated using methodologies consistent with those recommended in the Revised 1996IPCC Guidelines
for National Greenhouse Gas Inventories (IPCC/UNEP/OECD/IEA 1997) and the IPCC Good Practice Guidance and
Uncertainty Management in National Greenhouse Gas Inventories (IPCC 2000). The structure of this report is consistent
with the new UNFCCC guidelines for inventory reporting.4 For most source categories, the IPCC methodologies were
expanded, resulting in a more comprehensive and detailed estimate of emissions.
ES.1. Background Information
Naturally occurring greenhouse gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and
ozone (O3). Several classes of halogenated substances that contain fluorine, chlorine, or bromine are also greenhouse gases, but
they are, for the most part, solely a product of industrial activities. Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons
(HCFCs) are halocarbons that contain chlorine, while halocarbons that contain bromine are referred to as bromofluorocarbons (i.e.,
1 The term "anthropogenic", in this context, refers to greenhouse gas emissions and removals that are a direct result of human activities or are the result
of natural processes that have been affected by human activities (IPCC/UNEP/OECD/IEA 1997).
2 Article 2 of the Framework Convention on Climate Change published by the UNEP/WMO Information Unit on Climate Change. See .
Article 4( 1 )(a) of the United Nations Framework Convention on Climate Change (also identified in Article 12). Subsequent decisions by the Conference
of the Parties elaborated the role of Annex I Parties in preparing national inventories. See .
4 See .
Executive Summary ES-1
-------
halons). As stratospheric ozone depleting substances, CFCs,
HCFCs, and halons are covered under the Montreal Protocol
on Substances that Deplete the Ozone Layer. The UNFCCC
defers to this earlier international treaty. Consequently,
Parties are not required to include these gases in their national
greenhouse gas inventories.5 Some other fluorine-containing
halogenated substances—hydrofluoro.carbons (HFCs),
perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)—do
not deplete stratospheric ozone but are potent greenhouse
gases. These latter substances are addressed by the UNFCCC
and accounted for in national greenhouse gas inventories.
There are also several gases that do not have a direct
global warming effect but indirectly affect terrestrial and/or
solar radiation absorption by influencing the formation or
destruction of other greenhouse gases, including tropospheric
and stratospheric ozone. These gases include carbon monoxide
(CO), oxides of nitrogen (NOX), and non-methane volatile
organic compounds (NMVOCs). Aerosols, which are extremely
small particles or liquid droplets, such as those produced by
sulfur dioxide (SO2) or elemental carbon emissions, can also
affect the absorptive characteristics of the atmosphere.
Although the direct greenhouse gases CO2, CH4, and
N2O occur naturally in the atmosphere, human activities
have changed their atmospheric concentrations. Since the
pre-industrial era (i.e., ending about 1750), concentrations
of these greenhouse gases have increased by 31, 150, and
16 percent, respectively (IPCC 2001).
Beginning in the 1950s, the use of CFCs and other
stratospheric ozone depleting substances (ODSs) increased
by nearly 10 percent per year until the mid-1980s, when
international concern about ozone depletion led to the
entry into force of the Montreal Protocol. Since then, the
production of ODSs is being phased out. In recent years,
use of ODS substitutes such as HFCs and PFCs has grown
as they begin to be phased in as replacements for CFCs and
HCFCs. Accordingly, atmospheric concentrations of these
substitutes have been growing (IPCC 2001).
Global Warming Potentials
Gases in the atmosphere can contribute to the greenhouse
effect both directly and indirectly. Direct effects occur when
the gas itself absorbs radiation. Indirect radiative forcing
occurs when chemical transformations of the substance
produce other greenhouse gases, when a gas influences
the atmospheric lifetimes of other gases, and/or when a
gas affects atmospheric processes that alter the radiative
balance of the earth (e.g., affect cloud formation or albedo).6
The IPCC developed the Global Warming Potential (GWP)
concept to compare the ability of each greenhouse gas to trap
heat in the atmosphere relative to another gas.
The GWP of a greenhouse gas is defined as the ratio of
the time-integrated radiative forcing from the instantaneous
release of 1 kg of a trace substance relative to that of 1 kg of
a reference gas (IPCC 2001). Direct radiative effects occur
when the gas itself is a greenhouse gas. The reference gas
used is CO2, and therefore GWP-weighted emissions are
measured in teragrams of CO2 equivalent (Tg CO2Eq.).7 All
gases in this executive summary are presented in units of Tg
CO2 Eq. The relationship between gigagrams (Gg) of a gas
and Tg CO2 Eq. can be expressed as follows:
Tg CO2 Eq = (Gg of gas) x (GWP) x / Tg
U,OOOGg
The UNFCCC reporting guidelines for national
inventories were updated in 2002,8 but continue to require
the use of GWPs from the IPCC Second Assessment Report
(SAR). This requirement is so that current estimates of
aggregated greenhouse gas emission for 1990 to 2002 are
consistent with estimates developed prior to the publication
of the IPCC Third Assessment Report (TAR). Therefore,
to comply with international reporting standards under the
UNFCCC, official emission estimates are reported by the
U.S. using SAR GWP values. All estimates are provided
throughout the report in both CO2 equivalent and unweighted
units. A comparison of emission values use the SAR GWPs
versus the TAR GWPs can be found in Chapter 1 and in more
detail in Annex 6.1. The GWP values used in this report are
listed in Table ES-1.
Global warming potentials are not provided for CO,
NOX, NMVOCs, SO2, and aerosols because there is no
agreed-upon method to estimate the contribution of gases that
are short-lived in the atmosphere, spatially variable, or have
only indirect effects on radiative forcing (IPCC 1996).
5 Emissions estimates of CFCs, HCFCs, halons and other ozone-depleting substances are included in this document for informational purposes.
6 Albedo is a measure of the Earth's reflectivity; see the Glossary (Annex 6.8) for definition.
7 Carbon comprises 12/44ths of carbon dioxide by weight.
8
See .
ES-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table ES-1: Global Warming Potentials (100 Year Time
Horizon) Used in this Report
Figure ES-1
ES.2. Recent Trends in U.S.
Greenhouse Gas Emissions
and Sinks
In 2002, total U.S. greenhouse gas emissions were
6,934.6 Tg CO2 Eq.9 Overall, total U.S. emissions have
risen by 13 percent from 1990 to 2002, while the U.S. gross
domestic product has increased by 42 percent over the same
period (BEA 2004). Emissions rose slightly from 2001 to
2002, increasing by 0.7 percent (50.7 Tg CO2 Eq.). The
following factors were primary contributors to this increase:
1) moderate economic growth in 2002, leading to increased
demand for electricity and fossil fuels, and 2) much hotter
summer conditions in 2002, causing an increase in electricity
use for air-conditioning.
Figure ES-1 through Figure ES-3 illustrate the overall
trends in total U.S. emissions by gas, annual changes,
and absolute change since 1990. Table ES-2 provides a
detailed summary of U.S. greenhouse gas emissions and
sinks for 1990 through 2002.
U S Gippnnouse Gas Emissions by Gas
• HFCs, PFCs, & SF,
• Nitrous Oxide
• Methane
6,687 6,764 6790 6,853 Jjjgj 6,884 MM
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Figure ES-2
Annual Percent Change in U S Greenhouse Gas Emissions
3.1%
2.7%
0.7%
-3% J
Figure ES-3
Absolute Change in U S Greenhouse Gas
Emissions Since 1990
80S
Estimates are presented in units of teragrams of carbon dioxide equivalent (Tg CO2 Eq.), which weight each gas by its Global Warming Potential, or
GWP, value. (See section on Global Warming Potentials, Chapter 1.)
Executive Summary ES-3
-------
Table ES-2: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg C02 Eq.)
ES-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Figure ES-4 illustrates the relative contribution of the
direct greenhouse gases to total U.S. emissions in 2002.
The primary greenhouse gas emitted by human activities
in the United States was CO2, representing approximately
83 percent of total greenhouse gas emissions. The largest
source of CO2, and of overall greenhouse gas emissions,
was fossil fuel combustion. Methane emissions, which
have steadily declined since 1990, resulted primarily from
decomposition of wastes in landfills, natural gas systems,
and enteric fermentation associated with domestic livestock.
Agricultural soil management and mobile source fossil fuel
combustion were the major sources of N2O emissions. The
emissions of substitutes for ozone depleting substances and
emissions of HFC-23 during the production of HCFC-22
were the primary contributors to aggregate HFC emissions.
Electrical transmission and distribution systems accounted
for most SF6 emissions, while the majority of PFC emissions
resulted as a by-product of primary aluminum production.
As the largest source of U.S. greenhouse gas emissions,
CO2 from fossil fuel combustion has accounted for a nearly
constant 80 percent of global warming potential (GWP)
weighted emissions since 1990. Emissions from this source
category grew by 17 percent (796.3 Tg CO2Eq.) from 1990
to 2002 and were responsible for most of the increase in
national emissions during this period. From 2001 to 2002,
these emissions increased by 52.2 Tg CO2 Eq. (0.9 percent),
slightly lower than the source's average annual growth rate
of 1.3 percent from 1990 through 2002. Historically, changes
in emissions from fossil fuel combustion have been the
dominant factor affecting U.S. emission trends.
Changes in CO2 emissions from fossil fuel combustion are
influenced by many long-term and short-term factors, including
population and economic growth, energy price fluctuations,
technological changes, and seasonal temperatures. On an
annual basis, the overall consumption of fossil fuels in the
United States generally fluctuates in response to changes in
general economic conditions, energy prices, weather, and the
availability of non-fossil alternatives. For example, in a year
with increased consumption of goods and services, low fuel
prices, severe summer and winter weather conditions, nuclear
plant closures, and lower precipitation feeding hydroelectric
dams, there would likely be proportionally greater fossil fuel
consumption than a year with poor economic performance,
high fuel prices, mild temperatures, and increased output from
nuclear and hydroelectric plants.
Figure ES-4
2002 Greenhouse Gas Emissions by Gas
HFCs, PFCs & SFt
N,0
CH,
83.4%
In the longer-term energy consumption patterns respond
to changes that affect the scale of consumption (e.g.,
population, number of cars, and size of houses), the efficiency
with which energy is used in equipment (e.g., cars, power
plants, steel mills, and light bulbs) and consumer behavior
(e.g., walking, bicycling, or telecommuting to work instead
of driving).
Energy-related CO2 emissions also depend on the type of
fuel or energy consumed and its carbon intensity. Producing
a unit of heat or electricity using natural gas instead of coal,
for example, can reduce the CO2 emissions because of the
lower carbon content of natural gas. Table ES-3 shows annual
changes in emissions during the last six years for coal,
petroleum, and natural gas in selected sectors.
Emissions from fuel combustion resumed a modest
growth in 2002, slightly less than the average annual growth
rate since 1990. There were a number of reasons behind this
increase. The U.S. economy experienced moderate growth,
recovering from weaker conditions in 2001. Prices for fuels
remained at or below 2001 levels; the cost of natural gas,
motor gasoline, and electricity were all lower—triggering an
increase in demand for fuel. In addition, the United States
experienced one of the hottest summers on record, causing a
significant increase in electricity use in the residential sector
as the use of air-conditioners increased. Partially offsetting
this increased consumption of fossil fuels, however, were
increases in the use of nuclear and renewable fuels. Nuclear
facilities operated at the highest capacity on record in 2002.
Furthermore, there was a considerable increase in the use
of hydroelectric power in 2002 after a very low output the
previous year.
Executive Summary ES-5
-------
Table ES-3: Annual Change in C02 Emissions from Fossil Fuel Combustion for Selected Fuels and Sectors
(Tg C02 Eq. and Percent)
.. „ ... ;.-4#
•te* - ia n - us? .. * 'TTW* «',--•«"»• -3'^aut vv.
i-: •-1-1,3 9%i ,.j^Br
-• *7.8 --7*-'-'
>/«*^£^|- ^,5 4%'-,.4*:': -^It.'
~w,0 4%- • j$£-.-"-at-:
1.7 1% ; -jav^.
-54 -4% ;•• :ti: a%-
--4* 7.7
*-S% 4J
-4,9., -4%" -3J
^S T * saf *
rW*/ * , r^pe . -.
3%
3%
-2%
t%
Other significant trends in emissions from additional
source categories over the thirteen-year period from 1990
through 2002 included the following:
• Carbon dioxide emissions from waste combustion in-
creased by 7.9 Tg CO2 Eq. (72 percent), as the volume
of plastics and other fossil carbon-containing materials
in municipal solid waste grew.
• Net CO2 sequestration from land use change and forestry
decreased by 267.1 Tg CO2 Eq. (28 percent), primarily due
to a decline in the rate of net carbon accumulation in forest
carbon stocks. This decline largely resulted from a decrease
in the estimated rate of forest soil sequestration caused by
a slowing rate of increase in forest area after 1997.
• Methane emissions from coal mining dropped by 29.7
Tg CO2 Eq. (36 percent) as a result of the mining of less
gassy coal from underground mines and the increased
use of methane collected from degasification systems.
• Nitrous oxide emissions from agricultural soil man-
agement increased by 24.5 Tg CO2 Eq. (9 percent) as
crop and forage production, manure production, and
fertilizer consumption rose.
• Aggregate HFC and PFC emissions resulting from
the substitution of ozone depleting substances (e.g.,
CFCs) increased by 91.4 Tg CO2 Eq. This increase
was significantly offset, however, by reductions in
PFC emissions from aluminum production (12.9 Tg
CO2 Eq. or 71 percent), reductions in emissions of
HFC-23 from the production of HCFC-22 (15.2 Tg
CO2 Eq. or 43 percent), and reductions of SF6 from
electric power transmission and distribution systems
(14.5 Tg CO2 Eq. or 49 percent). Reductions in PFC
emissions from aluminum production resulted from
both industry emission reduction efforts and lower do-
mestic aluminum production. HFC-23 emissions from
the production of HCFC-22 decreased because a re-
duction in the intensity of emissions from that source
offset an increase in HCFC-22 production. Reduced
emissions of SF6 from electric power transmission
and distribution systems are primarily the result of
higher purchase prices for SF6 and efforts by industry
to reduce emissions.
Overall, from 1990 to 2002, total emissions of CO2 and
N2O increased by 780.0 Tg CO2 Eq. (16 percent) and 22.7
Tg CO2 Eq. (6 percent), respectively, while CH4 emissions
decreased by 44.6 Tg CO2 Eq. (7 percent). During the same
period, aggregate weighted emissions of HFCs, PFCs, and
SF6 rose by 47.3 Tg CO2 Eq. (52 percent). Despite being
emitted in smaller quantities relative to the other principal
greenhouse gases, emissions of HFCs, PFCs, and SF6 are
significant because many of them have extremely high global
warming potentials and, in the cases of PFCs and SF6, long
atmospheric lifetimes. Conversely, U.S. greenhouse gas
emissions were partly offset by carbon sequestration in
forests, trees in urban areas, agricultural soils, and landfilled
yard trimmings and food scraps, which was estimated to be
10 percent of total emissions in 2002.
ES.3. Overview of Source
and Sink Emission Trends
Carbon Dioxide Emissions
The global carbon cycle is made up of large carbon
flows and reservoirs. Billions of tons of carbon in the form
ES-6 Inventory of U.S. Greonhouso Gas Emissions and Sinks: 1990-2002
-------
Figure ES-5
2002 Sources of C0
Fossil Fuel Combustion
Iran and Steel Production
Cement Manufacture
Waste Combustion
Ammonia Production and Urea Application
Lime Manufacture
Limestone and Dolomite Use
Natural Gas Flaring
Aluminum Production
Soda Ash Manufacture and Consumption
Titanium Uioxide Production
| 5,611.0
Phosphoric Acid Consumption |
Ferroalloys |
Carbon Dioxide Consumption |
COZ as a Portion
of all Emissions
^^^^83.
ff
10 40
Tg CO, Eq
of CO2 are absorbed by oceans and living biomass (i.e.,
sinks) and are emitted to the atmosphere annually through
natural processes (i.e., sources). When in equilibrium,
carbon fluxes among these various reservoirs are roughly
balanced. Since the Industrial Revolution, this equilibrium
of atmospheric carbon has been disrupted. Atmospheric
concentrations of CO2 have risen about 31 percent (IPCC
Figure ES-6
2001), principally because of fossil fuel combustion, which
accounted for 97 percent of total U.S. CO2 emissions in 2002.
Globally, approximately 23,300 Tg of CO2 were added to
the atmosphere through the combustion of fossil fuels at the
end of the 1990s, of which the United States accounted for
about 24 percent.10 Changes in land use and forestry practices
can also emit CO2 (e.g., through conversion of forest land to
agricultural or urban use) or can act as a sink for CO2 (e.g.,
through net additions to forest biomass).
Figure ES-5 and Table ES-4 summarize U.S. sources
and sinks of CO2. Figure ES-6 shows the flow of carbon in
the U.S. economy. The remainder of this section discusses
CO2 emission trends in greater detail.
Energy
Energy-related activities, primarily fossil fuel
combustion, accounted for the vast majority of U.S. CO2
emissions for the period of 1990 through 2002. In 2002,
approximately 86 percent of the energy consumed in the
United States was produced through the combustion of fossil
fuels. The remaining 14 percent came from other energy
2002 U.S. Fossil Carbon Flows (Tg C02 Eq.)
Coal Emissions
2,006
Natural Gas Emissions
1,196
NEU Emissions 121
Petroleum Emissions
2,409
Note: Totals may not sum due to independent rounding.
The "Balancing Item" above accounts for the statistical imbalances
and unknowns in the reported data sets combined here.
NEU=Non-EnergyUse
NG=Natural Gas
10 Global CO2 emissions from fossil fuel combustion were taken from Marland et al. (2002) .
Executive Summary ES-7
-------
Table ES-4: U.S. Sources of C02 Emissions and Sinks (Tg C02 Eq.)
Figure ES-7
Figure ES-8
2002 U.S. Energy Consumption by Energy Source
6.0% Renewable
8.3% Nuclear
22.8% Coal
23.6% Natural Gas
39.1% Petroleum
U.S Energy Consumption (Quadrillion Btu)
Total Energy
E 60
20 -
Renewable & Nuclear
z a
ai o»
Sin to r- eo
o» o> o> o>
o» at 01 at at
sources such as hydropower, biomass, nuclear, wind, and
solar energy (see Figure ES-7 and Figure ES-8). A discussion
of specific trends related to CO2 emissions from energy
consumption is presented below.
Fossil Fuel Combustion (5,611.0 Tg C02 Eq.)
As fossil fuels are combusted, the carbon stored in them is
emitted almost entirely as CO2. The amount of carbon in fuels
per unit of energy content varies significantly by fuel type. For
example, coal contains the highest amount of carbon per unit of
energy, while petroleum and natural gas have about 25 percent
and 45 percent less carbon than coal, respectively. From 1990
through 2002, petroleum supplied the largest share of U.S.
energy demands, accounting for an average of 39 percent of
total energy consumption. Natural gas and coal followed in
ES-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table ES-5: C02 Emissions from Fossil Fuel Combustion by End-Use Sector (Tg C02 Eq.)
End-Use Sector
Transportation
Combustion
Electricity
Industrial
Combustion
Electricity
Residential
Combustion
Electricity
Commercial
Combustion
Electricity
U.S. Territories
Total
1990
1,461.2
1,458.2
3.0
1,638.5
966.6
671,9
925.5
339.6
585.9
755.7
224.2
531.6
33.7
4,814.7
Electricity Generation 1,792.4
1996
1,607.8
1,604.8
3.0
1,769.6
1,045.9
723.7
1,053.1
388.9
664.2
838.3
237.0
601.3
41.3
5,310.1
1997
1,617.8
1,614.8
3.1
1,800.7
1,058.4
742.3
1,043.5
370.6
673.0
879.4
237.2
642.2
42.6
5,384.0
1998
1,648.0
1,644.9
3.1
1,778.4
1,018.1
760.3
1,047.5
338.6
708.9
895.9
219.7
676.2
42.6
5,412.4
1999
1,706.1
1,702.9
3.2
1,768.4
1,001.9
766.4
1,066.5
359.3
707.3
904.2
222.3
681.9
43.7
5,488.8
2000
1,753.0
1,749.6
3.4
1,782.5
999.7
782,8
1,127.5
379.3
748,3
964.6
237.1
727,5
45.9
5,673.6
2001
1,734.1
1,730.6
3.5
1,687.5
970.8
716,7
1,117.5
386.9
750.7
974.6
227.3
747.3
45.0
5,558.8
2002
1,767.5
1,764.4
3.2
1,677.1
955.8
721.3
1,149.2
373.1
776.2
970.6
231.2
739.4
46,5
5,611.0
1,992.2 2,060.5 2,148.5 2,158.7 2,261.9 2,218.2 2,240.1
Note: Totels may not sum due to independent rounding. Combustion-related emissions from electricity generation are allocated based on aggregate
national electricity consumption by each end-use sector.
order of importance, accounting for an average of 24 and 23
percent of total energy consumption, respectively. Petroleum
was consumed primarily in the transportation end-use sector,
the vast majority of coal was used by electric power generators,
and natural gas was consumed largely in the industrial and
residential end-use sectors.
Emissions of CO2 from fossil fuel combustion increased
at an average annual rate of 1.3 percent from 1990 to 2002.
The fundamental factors influencing this trend include (1)
a growing domestic economy over the last 11 years, and
(2) significant growth in emissions from transportation
activities and electricity generation. Between 1990 and 2002,
CO2 emissions from fossil fuel combustion increased from
4,814.7 Tg CO2 Eq. to 5,611.0 Tg CO2 Eq.—a 17 percent
total increase over the twelve-year period.
The four major end-use sectors contributing to CO2
emissions from fossil fuel combustion are industrial,
transportation, residential, and commercial. Electricity
generation also emits CO2, although these emissions are
produced as they consume fossil fuel to provide electricity
to one of the four end-use sectors. For the discussion below,
electricity generation emissions have been distributed to each
end-use sector on the basis of each sector's share of aggregate
electricity consumption. This method of distributing
emissions assumes that each end-use sector consumes
electricity that is generated from the national average mix of
fuels according to their carbon intensity. In reality, sources of
electricity vary widely in carbon intensity. By assuming the
same carbon intensity for each end-use sector's electricity
consumption, for example, emissions attributed to the
residential end-use sector may be underestimated, while
emissions attributed to the industrial end-use sector may
be overestimated. Emissions from electricity generation
are also addressed separately after the end-use sectors have
been discussed.
Note that emissions from U.S. territories are calculated
separately due to a lack of specific consumption data for the
individual end-use sectors. Table ES-5, Figure ES-9, and
Figure ES-10 summarize CO2 emissions from fossil fuel
combustion by end-use sector.
Figure ES-9
2002 CO; Emissions from Fossil Fuel
Combustion by Sector and Fuel Type
2,000
1,500 -
1,000 -
500 -
0 -
Relative Contribution
by Fuel Type
I Natural Gas
(Petroleum
•Coal
Executive Summary ES-9
-------
Figure ES-10
2002 End Use Sector Emission*
of CO, trom Fossil fuel Combustion
I From Electricity
Consumption
I From Direct Fossil
Fuel Combustion
ff
Transportation End-Use Sector. Transportation
activities (excluding international bunker fuels) accounted for
31 percent of CO2 emissions from fossil fuel combustion in
2002.'' Virtually all of the energy consumed in this end-use
sector came from petroleum products. Just over half of the
emissions resulted from gasoline consumption for personal
vehicle use. The remaining emissions came from other
transportation activities, including the combustion of diesel
fuel in heavy-duty vehicles and jet fuel in aircraft.
Industrial End-Use Sector. Industrial CO2 emissions,
resulting both directly from the combustion of fossil fuels and
indirectly from the generation of electricity that is consumed
by industry, accounted for 17 percent of CO2 from fossil fuel
combustion in 2002. About half of these emissions resulted
from direct fossil fuel combustion to produce steam and/or
heat for industrial processes. The other half of the emissions
resulted from consuming electricity for motors, electric
furnaces, ovens, lighting, and other applications.
Residential and Commercial End-Use Sectors. The
residential and commercial end-use sectors accounted
for 7 and 4 percent, respectively, of CO2 emissions from
fossil fuel combustion in 2002. Both sectors relied heavily
on electricity for meeting energy demands, with 68 and
76 percent, respectively, of their emissions attributable to
electricity consumption for lighting, heating, cooling, and
operating appliances. The remaining emissions were due to
the consumption of natural gas and petroleum for heating
and cooking.
Electricity Generation. The United States relies on
electricity to meet a significant portion of its energy demands,
especially for lighting, electric motors, heating, and air
conditioning. Electricity generators consumed 35 percent of
U.S. energy from fossil fuels and emitted 40 percent of the
CO2 from fossil fuel combustion in 2002. The type of fuel
combusted by electricity generators has a significant effect on
their emissions. For example, some electricity is generated with
low CO2 emitting energy technologies, particularly non-fossil
options such as nuclear, hydroelectric, or geothermal energy.
However, electricity generators rely on coal for over half of
their total energy requirements and accounted for 93 percent
of all coal consumed for energy in the United States in 2002.
Consequently, changes in electricity demand have a significant
impact on coal consumption and associated CO2 emissions.
Waste Combustion (18.8 Tg C02 Eq.)
The burning of garbage and non-hazardous solids,
referred to as municipal solid waste, as well as the burning
of hazardous waste, is usually performed to recover energy
from the waste materials. Carbon dioxide emissions arise
from the organic (i.e., carbon) materials found in these
wastes. Within municipal solid waste, many products contain
carbon of biogenic origin, and the CO2 emissions from their
combustion are accounted for under the Land-Use Change
and Forestry chapter. Several components of municipal solid
waste, such as plastics, synthetic rubber, synthetic fibers, and
carbon black, are of fossil fuel origin, and are included as
sources of CO2 emissions.
Natural Gas Flaring (5.3 Tg C02 Eq.)
The flaring of natural gas from oil wells results in the
release of CO2 emissions. Natural gas is flared from both on-
shore and off-shore oil wells to relieve rising pressure or to
dispose of small quantities of gas that are not commercially
marketable. In 2002, flaring accounted for approximately
0.1 percent of U.S. CO2 emissions.
Biomass Combustion (207.1 Tg C02 Eq.)
Biomass refers to organically-based carbon fuels (as
opposed to fossil-based). Biomass in the form of fuel wood and
wood waste was used primarily in the industrial sector, while the
transportation sector was the predominant user of biomass-based
fuels, such as ethanol from corn and woody crops.
1' If emissions from international bunker fuels are included, the transportation end-use sector accounted for 33 percent of U.S. emissions from fossil fuel
combustion in 2002.
ES-10 Inventory of U.S. Greenhouse Gas Emissions ana* Sinks: 1990-2002
-------
Although these fuels do emit CO2 in the long run
the CO2 emitted from biomass consumption does not
increase atmospheric CO2 concentrations if the biogenic
carbon emitted is offset by the growth of new biomass. For
example, fuel wood burned one year but re-grown the next
only recycles carbon, rather than creating a net increase in
total atmospheric carbon. Net carbon fluxes from changes
in biogenic carbon reservoirs in wooded or croplands
are accounted for in the estimates for Land-Use Change
and Forestry. As a result, CO2 emissions from biomass
combustion have been estimated separately from fossil fuel-
based emissions and are not included in the U.S. totals.
The consumption of wood biomass in the industrial,
residential, electric power, and commercial sectors accounted
for 68, 17, 7, and 2 percent of gross CO2 emissions from
biomass combustion, respectively. Ethanol consumption in the
transportation sector accounted for the remaining 6 percent.
Industrial Processes
Emissions are produced as a by-product of many
non-energy-related activities. For example, industrial
processes can chemically transform raw materials, which
often release waste gases such as CO2. The processes
that emit CO2 include iron and steel production, cement
manufacture, ammonia manufacturing and urea application,
lime manufacture, limestone and dolomite use, soda ash
manufacture and consumption, aluminum production,
titanium dioxide production, phosphoric acid production,
ferroalloy production, and CO2 consumption. Carbon dioxide
emissions from these sources were approximately 147.3 Tg
CO2 Eq. in 2002, accounting for about 3 percent of total
CO2 emissions.
Iron and Steel Production (54.4 Tg C02 Eq.)
Pig iron is the product of combining iron oxide (i.e., iron
ore) and sinter with metallurgical coke in a blast furnace. The
pig iron production process, as well as the thermal processes
used to create sinter and metallurgical coke result in the
emission of CO2. Some of the pig iron is transformed into
steel using a variety of specialized steel making furnaces that
allow the emission of additional CO2. The majority of CO2
emissions from the iron and steel processes come from the
production of coke for use in pig iron creation, with smaller
amounts evolving from the removal of carbon from pig iron
used to produce steel.
Cement Manufacture (42.9 Tg C02 Eq.)
Clinker is an intermediate product in the formation of
finished Portland and masonry cement. Heating calcium
carbonate (CaCO3) in a cement kiln forms lime and CO2.
The lime combines with other materials to produce clinker,
and the CO2 is released into the atmosphere.
Ammonia Manufacture and Urea Application (17.7 Tg C02 Eq.)
In the United States, roughly 98 percent of synthetic
ammonia is produced by catalytic steam reforming of natural
gas, and the remainder is produced using naphtha (i.e., a
petroleum fraction) or the electrolysis of brine at chlorine
plants (EPA 1997). The two fossil fuel-based reactions
produce carbon monoxide and hydrogen gas. This carbon
monoxide is transformed into CO2 in the presence of a
catalyst. The CO2 is generally released into the atmosphere,
but some of the CO2, together with ammonia, is used as a
raw material in the production of urea [CO(NH2)2], which
is a type of nitrogenous fertilizer. The carbon in the urea
that is produced and assumed to be subsequently applied
to agricultural land as a nitrogenous fertilizer is ultimately
released into the environment as CO2.
Lime Manufacture (12.3 Tg C02 Eq.)
Lime is used in steel making, construction, flue gas
desulfurization, and water and sewage treatment. It is
manufactured by heating limestone (mostly calcium carbonate,
CaCO3) in a kiln, creating quicklime (calcium oxide, CaO) and
CO2, which is normally emitted to the atmosphere.
Limestone and Dolomite Use (5.8 Tg C02 Eq.)
Limestone (CaCO3) and dolomite (CaMg(CO3)) are
basic raw materials used in a wide variety of industries,
including construction, agriculture, chemical, and metallurgy.
For example, limestone can be used as a purifier in refining
metals. In the case of iron ore, limestone heated in a blast
furnace reacts with impurities in the iron ore and fuels,
generating CO2 as a by-product. Limestone is also used in
flue gas desulfurization systems to remove sulfur dioxide
from the exhaust gases.
Aluminum Production (4.2 Tg C02 Eq.)
Carbon dioxide is emitted when alumina (aluminum
oxide, A12O3) is reduced to aluminum. The reduction of
the alumina occurs through electrolysis in a molten bath
of natural or synthetic cryolite. The reduction cells contain
a carbon lining that serves as the cathode. Carbon is also
Executive Summary ES-11
-------
contained in the anode, which can be a carbon mass of paste,
coke briquettes, or prebaked carbon blocks from petroleum
coke. During reduction, some of this carbon is oxidized and
released to the atmosphere as CO2.
Soda Ash Manufacture and Consumption (4.1 Tg C02 Eq.)
Commercial soda ash (sodium carbonate, Na2CO3)
is used in many consumer products, such as glass, soap
and detergents, paper, textiles, and food. During the
manufacturing of soda ash, some natural sources of sodium
carbonate are heated and transformed into a crude soda ash,
in which CO2 is generated as a by-product. In addition, CO2
is often released when the soda ash is consumed.
Titanium Dioxide Production (2.0 Tg C02 Eq.)
Titanium dioxide (TiO2) is a metal oxide manufactured
from titanium ore, and is principally used as a pigment. It is
used in white paint and as a pigment in the manufacture of
white paper, foods, and other products. Two processes, the
chloride process and the sulfate process, are used for making
TiO2. Carbon dioxide is emitted from the chloride process,
which uses petroleum coke and chlorine as raw materials.
Phosphoric Acid Production (1.3 Tg C02 Eq.)
Phosphoric acid is a basic raw material in the production
of phosphate-based fertilizers. The phosphate rock consumed
in the United States originates from both domestic mines,
located primarily in Florida, North Carolina, Idaho, and Utah,
and foreign mining operations in Morocco. The primary use
of this material is as a basic component of a series of chemical
reactions that lead to the production of phosphoric acid, as
well as the by-products CO2 and phosphogypsum.
Carbon Dioxide Consumption (1.3 Tg C02 Eq.)
Many segments of the economy consume CO2, including
food processing, beverage manufacturing, chemical processing,
and a host of industrial and other miscellaneous applications.
Carbon dioxide may be produced as a by-product from the
production of certain chemicals (e.g., ammonia), from select
natural gas wells, or by separating it from crude oil and natural
gas. For the most part, the CO2 used in these applications is
eventually released to the atmosphere.
Ferroalloy Production (1.2 Tg C02 Eq.)
Carbon dioxide is emitted from the production of several
ferroalloys. Ferroalloys are composites of iron and other
elements such as silicon, manganese, and chromium. When
incorporated in alloy steels, ferroalloys are used to alter the
material properties of the steel. Ferroalloy emissions have been
decreasing since 1999, due to decreases in production. Overall,
from 1990 ferroalloy emissions have decreased 12 percent.
Land-Use Change and Forestry
When humans alter the terrestrial biosphere through land
use, changes in land use, and land management practices,
they also alter the natural carbon fluxes between biomass,
soils, and the atmosphere. Forest management practices,
tree planting in urban areas, the management of agricultural
soils, and landfilling of yard trimmings have resulted in a net
uptake (sequestration) of carbon in the United States, which
offset about 10 percent of total U.S. gross CO2 emissions
in 2002. Forests (including vegetation, soils, and harvested
wood) accounted for approximately 87 percent of total
2002 sequestration, urban trees accounted for 8 percent,
agricultural soils (including mineral and organic soils and the
application of lime) accounted for 3 percent, and landfilled
yard trimmings and food scraps accounted for 1 percent of the
total sequestration in 2002. The net forest sequestration is a
result of net forest growth and increasing forest area, as well
as a net accumulation of carbon stocks in harvested wood
pools. The net sequestration in urban forests is a result of net
tree growth in these areas. In agricultural soils, mineral soils
account for a net carbon sink that is approximately one and
a third times larger than the sum of emissions from organic
soils and liming. The mineral soil carbon sequestration is
largely due to conversion of cropland to permanent pastures
and hay production, a reduction in summer fallow areas in
semi-arid areas, an increase in the adoption of conservation
tillage practices, and an increase in the amounts of organic
fertilizers (i.e., manure and sewage sludge) applied to
agriculture lands. The landfilled yard trimmings and food
scraps net sequestration is due to the long-term accumulation
of yard trimming carbon and food scraps in landfills.
Methane Emissions
According to the IPCC, CH4 is more than 20 times as
effective as CO2 at trapping heat in the atmosphere. Over the
last two hundred and fifty years, the concentration of CH4
in the atmosphere increased by 150 percent (IPCC 2001).
Experts believe that over half of this atmospheric increase
was due to emissions from anthropogenic sources, such as
landfills, natural gas and petroleum systems, agricultural
ES-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
activities, coal mining, wastewater treatment, stationary and
mobile combustion, and certain industrial processes (see
Figure ES-11 and Table ES-6).
Landfills (193.0 Tg C02Eq.)
Landfills are the largest anthropogenic source of CH4
emissions in the United States, accounting for approximately
32 percent of total CH4 emissions in 2002. In an environment
where the oxygen content is low or zero, anaerobic bacteria
can decompose organic materials, such as yard waste,
household waste, food waste, and paper, resulting in the
generation of CH4 and biogenic CO2. Site-specific factors,
such as waste composition, moisture, and landfill size,
influence the level of methane generation.
Methane emissions from U.S. landfills have decreased
by 8 percent since 1990. The generally declining emission
estimates are a result of two offsetting trends: (1) the amount of
municipal solid waste in landfills contributing to CH4 emissions
has increased, thereby increasing the potential for emissions;
and (2) the amount of landfill gas collected and combusted by
landfill operators has also increased, thereby reducing emissions.
Additionally, a regulation promulgated in March 1996 requires
the largest U.S. landfills to begin collecting and combusting their
landfill gas to reduce emissions of NMVOCs.
Natural Gas and Petroleum Systems (145.0 Tg C02 Eq.)
Methane is the major component of natural gas. Fugitive
emissions of CH4 occur throughout the production, processing,
Table ES-6: U.S. Sources of CH4 Emissions (Tg C02 Eq.)
Figure ES-11
2002 Sources of CH.
Landfills
Natural Gas Systems
Enteric Fermentation
Coal Mining
Manure Management ^H
Wastewater Treatment H
Petroleum Systems H
Rice Cultivation I
Stationary Sources I
Mobile Sources I
Abandoned Coal Mines I
Petrochemical Porduction I
Iron and Steel Production I
Agricultural Residue Burning I
Silicon Carbide Production <0.05
CH, as a Portion
of all Emissions
8.6%
©
50
100 150 200
Tg CO, Eq
transmission, and distribution of natural gas. Because natural
gas is often found in conjunction with petroleum deposits,
leakage from petroleum systems is also a source of emissions.
Emissions vary greatly from facility to facility and are largely
a function of operation and maintenance procedures and
equipment conditions. In 2002, CH4 emissions from U.S.
natural gas systems accounted for 121.8 Tg CO2 Eq., or
approximately 20 percent of U.S. CH4 emissions.
Petroleum is often found in the same geological structures
as natural gas, and the two are often retrieved together. Crude
Note:
Executive Summary ES-13
-------
oil is saturated with many lighter hydrocarbons, including
methane. When the oil is brought to the surface and processed,
many of the dissolved lighter hydrocarbons (as well as water)
are removed through a series of high-pressure and low-
pressure separators. The remaining hydrocarbons in the oil
are emitted at various points along the system. Methane
emissions from the components of petroleum systems
generally occur as a result of system leaks, disruptions, and
routine maintenance. In 2002, emissions from petroleum
systems were 23.2 Tg CO2 Eq., or just under 4 percent of
U.S. CH4 emissions.
Enteric Fermentation (114.4 Tg C02 Eq.)
During animal digestion, CH4 is produced through the
process of enteric fermentation, in which microbes residing
in animal digestive systems break down food. Ruminants,
which include cattle, buffalo, sheep, and goats, have the
highest CH4 emissions among all animal types because they
have a rumen, or large fore-stomach, in which CH4-producing
fermentation occurs. Non-ruminant domestic animals, such
as pigs and horses, have much lower CH4 emissions. In 2002,
enteric fermentation was the source of about 19 percent of
U.S. CH4 emissions, and more than 71 percent of the CH4
emissions from agriculture. From 1990 to 2002, emissions
from this source decreased by 3 percent. Emissions from
enteric fermentation have been generally decreasing since
1995, primarily due to declining dairy cow and beef cattle
populations as a result of improved efficiency in milk and
beef production.
Coal Mining (52.2 Tg C02 Eq.)
Produced millions of years ago during the formation of
coal, CH4 trapped within coal seams and surrounding rock
strata is released when the coal is mined. The quantity of CH4
released to the atmosphere during coal mining operations
depends primarily upon the type of coal and the method
and rate of mining.
Methane from surface mines is emitted directly to the
atmosphere as the rock strata overlying the coal seam are
removed. Because CH4 in underground mines is explosive
at concentrations of 5 to 15 percent in air, most active
underground mines are required to vent this methane,
typically to the atmosphere. At some mines, CH4-recovery
systems may supplement these ventilation systems. Recovery
of CH4 in the United States has increased in recent years.
During 2002, coal mining activities emitted 9 percent of U.S.
CH4 emissions. From 1990 to 2002, emissions from this
source decreased by 36 percent due to increased use of the
CH4 collected by mine degasification systems and a general
shift toward surface mining.
Manure Management (39.5 Tg C02 Eq.)
The decomposition of organic animal waste in an
anaerobic environment produces CH4. The most important
factor affecting the amount of CH4 produced is how the
manure is managed, because certain types of storage and
treatment systems promote an oxygen-free environment.
In particular, liquid systems tend to encourage anaerobic
conditions and produce significant quantities of CH4, whereas
solid waste management approaches produce little or no
CH4. Higher temperatures and moist climatic conditions also
promote CH4 production.
Emissions from manure management were about 7
percent of U.S. CH4 emissions in 2002 and 24 percent of the
CH4 emissions from the agriculture sector. From 1990 to 2002,
emissions from this source increased by 27 percent. The bulk
of this increase was from swine and dairy cow manure, and
is attributed to the shift in the composition of the swine and
dairy industries towards larger facilities. Larger swine and
dairy farms tend to use liquid management systems.
Wastewater Treatment (28.7 Tg C02 Eq.)
Wastewater from domestic sources (i.e., municipal
sewage) and industrial sources is treated to remove soluble
organic matter, suspended solids, pathogenic organisms and
chemical contaminants. Soluble organic matter is generally
removed using biological processes in which microorganisms
consume the organic matter for maintenance and growth.
Microorganisms can biodegrade soluble organic material
in wastewater under aerobic or anaerobic conditions, with
the latter condition producing CH4. During collection and
treatment, wastewater may be accidentally or deliberately
managed under anaerobic conditions. In addition, the sludge
may be further biodegraded under aerobic or anaerobic
conditions. Untreated wastewater may also produce CH4 if
contained under anaerobic conditions. In 2002, wastewater
treatment was the source of approximately 5 percent of U.S.
CH4 emissions.
Stationary and Mobile Combustion (11.1 Tg C02 Eq.)
In 2002, stationary and mobile combustion were
responsible for CH4 emissions of 6.9 and 4.2 Tg CO2 Eq.,
ES-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
respectively. The majority of CH4 emissions from stationary
combustion resulted from the burning of wood in the
residential end-use sector. The combustion of gasoline in
highway vehicles was responsible for the majority of the
CH4 emitted from mobile combustion.
Rice Cultivation (6.8 Tg C02 Eq.)
Most of the world's rice, and all of the rice in the United
States, is grown on flooded fields. When fields are flooded,
anaerobic conditions develop and the organic matter in the
soil decomposes, releasing CH4 to the atmosphere, primarily
through the rice plants. In 2002, rice cultivation was the source
of 1 percent of U.S. CH4 emissions, and about 4 percent of U.S.
CH4 emissions from agriculture. Emission estimates from this
source have decreased about 4 percent since 1990.
Abandoned Coal Mines (4.1 Tg C02 Eq.)
Coal mining activities result in the emission of CH4 into
the atmosphere. However, the closure of a coal mine does
not correspond with an immediate cessation in the release
of emissions. Following an initial decline, abandoned mines
can liberate CH4 at a near-steady rate over an extended period
of time, or, if flooded, produce gas for only a few years. In
2002, the emissions from abandoned coal mines constituted
less than 1 percent of U.S. CH4 emissions.
Petrochemical and Silicon Carbide Production (1.5 Tg C02 Eq.)
Small amounts of CH4 are released during the production of
five petrochemicals: carbon black, ethylene, ethylene dichloride,
styrene, and methanol. These production processes resulted in
emissions of 1.5 Tg CO2 Eq. in 2002. Methane is also emitted
from the production of silicon carbide, a material used as an
industrial abrasive. In 2002, silicon carbide production resulted
in emissions of less than 0.1 Tg CO2 Eq.
Iron and Steel Production (1.0 Tg C02 Eq.)
Pig iron is the product of combining iron oxide (i.e., iron
ore) and sinter with metallurgical coke in a blast furnace. The
pig iron production process, as well as the thermal processes
used to create sinter and metallurgical coke result in the
emission of CH4. In 2002, iron and steel production resulted
in 1.0 Tg CO2 Eq. of CH4 emissions with the majority of the
emissions coming from the pig iron production process.
Field Burning of Agricultural Residues (0.7 Tg C02 Eq.)
Burning crop residue releases a number of greenhouse
gases, including CH4. Because field burning is not a
common debris clearing method used in the United States, it
was responsible for only 0.1 percent of U.S. CH4 emissions
in 2002.
Nitrous Oxide Emissions
Nitrous oxide is produced by biological processes that
occur in soil and water and by a variety of anthropogenic
activities in the agricultural, energy-related, industrial, and
waste management fields. While total N2O emissions are much
lower than CO2 emissions, N2O is approximately 300 times
more powerful than CO2 at trapping heat in the atmosphere.
Since 1750, the atmospheric concentration of N2O has risen by
approximately 16 percent (IPCC 2001). The main anthropogenic
activities producing N2O in the United States are agricultural
soil management, fuel combustion in motor vehicles, manure
management, nitric acid production, human sewage, and
stationary fuel combustion (see Figure ES-12 and Table ES-7).
Table ES-7: U.S. Sources of Nitrous Oxide Emissions (Tg C02 Eq.)
Source
Agricultural Soil Management
Mobile Sources
Manure Management
Nitric Acid
Human Sewage
Stationary Sources
Adipic Acid
N2Q Product Usage
Field Burning of Agricultural Residues
Waste Combustion
international Bunker Fuels * :
Total' .
* Emissions from International Bunker Fuels are not Included in totals.
Note: Totals may not sum due to Independent rounding.
199$
288.1
60.7
17.0
20.7
14.2
13.9
17.0
4.5
0.4
0.4
0,9
436.9
1997
293.2
60.3
17.3
21.2
14.4
14.0
10.3
4.8
0.4
0.4
7,0
436.3
1998
294.2
59,6
17.3
20.9
14.7
13.8
6.0
4.8
0.5
0.3
1.0
432.1
1999
292.1
58.6
17.4
20.1
15.2
13.9
5.5
4.8
0.4
0.3
0.9
428.4
2000
289.7
57.4
17.7
19.6
15.3
14.4
6.0
4.8
0.5
0.4
0.9
425.8
2001
288.6
55.0
18.0
15.9
15.4
13.9
4.9
4.8
0.5
0.4
0.9
417.3
2002
287.3
52.9
17.8
16.7
15.6
14.0
5.9
4.8
0.4
0.4
0.8
415.8
Executive Summary ES-15
-------
Figure ES-12
2002 Sources of N,0
Agricultural Soil Management
Mobile Sources
Manure Management |^^
Nitric Acid ^B
Human Sewage m
Stationary Sources ^^|
Adipic Acid |
N,0 Product Usage |
Agricultural Residue Burning | <1.0
Waste Combustion I <1.0
287.3
N20 as a Portion
of all Emissions
6.0%
0 10 20 30 40 50 60 70
Tg CO, EQ
Agricultural Soil Management (287.3 Tg C02 Eq.)
Nitrous oxide is produced naturally in soils through
microbial processes of nitrification and denitrification.
A number of anthropogenic activities add to the amount
of nitrogen available to be emitted as N2O by microbial
processes. These activities may add nitrogen to soils either
directly or indirectly. Direct additions occur through the
application of synthetic and organic fertilizers; production of
nitrogen-fixing crops and forages; the application of livestock
manure, crop residues, and sewage sludge; cultivation of
high-organic-content soils; and direct excretion by animals
onto soil. Indirect additions result from volatilization and
subsequent atmospheric deposition, and from leaching and
surface run-off of some of the nitrogen applied to or deposited
on soils as fertilizer, livestock manure, and sewage sludge.
In 2002, agricultural soil management accounted for
69 percent of U.S. N2O emissions. From 1990 to 2002,
emissions from this source increased by 9 percent as
fertilizer consumption, manure production, and production
of nitrogen-fixing and other crops rose.
Stationary and Mobile Combustion (66.9 Tg C02 Eq.)
Nitrous oxide is a product of the reaction that occurs
between nitrogen and oxygen during fuel combustion. Both
mobile and stationary combustion emit N2O, and the quantity
emitted varies according to the type of fuel, technology, and
pollution control device used, as well as maintenance and
operating practices. For example, some types of catalytic
converters installed to reduce motor vehicle pollution can
promote the formation of N2O.
In 2002, N2O emissions from mobile combustion were
52.9 Tg CO2 Eq. (13 percent of U.S. N2O emissions), while
stationary combustion accounted for 14.0 Tg CO2 Eq. (3
percent). From 1990 to 2002, combined N2O emissions
from stationary and mobile combustion increased by 6
percent, due to increased fuel consumption by both mobile
and stationary sources.
Manure Management (17.8 Tg C02 Eq.)
Nitrous oxide is produced as part of microbial
nitrification and denitrification processes in managed and
unmanaged manure. Unmanaged manure is addressed under
the discussion of agricultural soil management. Total N2O
emissions from managed manure systems in 2002 accounted
for 4 percent of U.S. N2O emissions. From 1990 to 2002,
emissions from this source category increased by 10 percent,
primarily due to increases in swine and poultry populations
over the same time period.
Nitric Acid Production (16.7 Tg C02 Eq.)
Nitric acid production is an industrial source of N2O
emissions. Used primarily to make synthetic commercial
fertilizer, this raw material is also a major component in the
production of adipic acid and explosives.
Virtually all of the nitric acid manufactured in the United
States is produced by the oxidation of ammonia, during
which N2O is formed and emitted to the atmosphere. In
2002, N2O emissions from nitric acid production accounted
for 4 percent of U.S. N2O emissions. From 1990 to 2002,
emissions from this source category decreased by 6 percent
with the trend in the time series closely tracking the changes
in production.
Human Sewage (Domestic Wastewater) (15.6 Tg C02 Eq.)
Domestic human sewage is usually mixed with other
household wastewater, which includes shower drains, sink
drains, washing machine effluent, etc., and transported by a
collection system to either a direct discharge, an on-site or
decentralized or centralized wastewater treatment system.
After processing, treated effluent may be discharged to a
receiving water environment (e.g., river, lake, estuary, etc.),
applied to soils, or disposed of below the surface. Nitrous
oxide may be generated during both nitrification and
denitrification of the nitrogen present, usually in the form
of urea, ammonia, and proteins. Emissions of N2O from
treated human sewage discharged into aquatic environments
ES-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
accounted for4 percent of U.S. N2O emissions in 2002. From
1990 to 2002, emissions from this source category increased
by 22 percent.
Adipic Acid Production (5.9 Tg C02 Eq.)
Most adipic acid produced in the United States is used
to manufacture nylon 6,6. Adipic acid is also used to produce
some low-temperature lubricants and to add a "tangy" flavor
to foods. Nitrous oxide is emitted as a by-product of the
chemical synthesis of adipic acid.
In 2002, U.S. adipic acid plants emitted 1 percent of
U.S. N2O emissions. Even though adipic acid production has
increased, by 1998 all three major adipic acid plants in the
United States had voluntarily implemented N2O abatement
technology. As a result, emissions have decreased by 61
percent since 1990.
N20 from Product Usage (4.8 Tg C02 Eq.)
Nitrous oxide is used in carrier gases with oxygen to
administer more potent inhalation anesthetics for general
anesthesia and as an anesthetic in various dental and veterinary
applications. As such, it is used to treat short-term pain, for
sedation in minor elective surgeries and as an induction
anesthetic. The second main use of N2O is as a propellant in
pressure and aerosol products, the largest application being
pressure-packaged whipped cream. In 2002, N2O emissions
from product usage constituted approximately 1 percent of
U.S. N2O emissions. From 1990 to 2002, emissions from
this source category increased by 11 percent.
Field Burning of Agricultural Residues (0.4 Tg C02 Eq.)
Large quantities of agricultural crop residues are
produced by farming activities, some of which is disposed
by burning in the field. Field burning of crop residues is a
source of N2O, which is released during combustion. Because
Table ES-8: Emissions of HFCs, PFCs, and SF6 (Tg C02 Eq.)
field burning is not a common method of agricultural residue
disposal in the United States, emissions from this source are
minor, representing 0.1 percent of U.S. N2O emissions.
Waste Combustion (0.4 Tg C02 Eq.)
Combustion is used to manage about 7 to 17 percent of
the municipal solid wastes generated in the United States.
Almost all combustion of municipal solid waste in the United
States occurs at waste-to-energy facilities where energy is
recovered. Most of the organic materials in municipal solid
waste are of biogenic origin (e.g., paper, yard trimmings),
with some components, such as plastics, synthetic rubber, and
synthetic fibers, of fossil origin, which together accounted for
emissions of 0.1 percent of U.S. N2O emissions in 2002.
HFC, PFC, and SF6 Emissions
HFCs and PFCs are families of synthetic chemicals
that are being used as alternatives to the ODSs, which are
being phased out under the Montreal Protocol and Clean Air
Act Amendments of 1990. HFCs and PFCs do not deplete
the stratospheric ozone layer, and are therefore acceptable
alternatives under the Montreal Protocol.
These compounds, however, along with SF6, are
potent greenhouse gases. In addition to having high
global warming potentials, SF6 and PFCs have extremely
long atmospheric lifetimes, resulting in their essentially
irreversible accumulation in the atmosphere once emitted.
Sulfur hexafluoride is the most potent greenhouse gas the
IPCC has evaluated.
Other emissive sources of these gases include HCFC-22
production, electrical transmission and distribution systems,
semiconductor manufacturing, aluminum production, and
magnesium production and processing. Figure ES-13 and
Table ES-8 present emission estimates for HFCs, PFCs, and
SF6, which totaled 138.2 Tg CO2 Eq. in 2002.
Source
Total
1990
Substitution of Qa»e Depleting Substances ;>|K3fJ
HCFC-22 Production^ . 35,0.
EtoettcrtTransmlssfcn.awfDfeWWton , '.'••'28.2,;'
Aluminum Productai 18.1
Semiconductor Manufacture 2.9
Magnesium Production and Processing 5,4
90.0
Note: Totals may not sum due to independent rounding.
1186
35J
311
24,3
12.5
5.5
6,5
114.9
1187
46.4
30.0
21.7
11.0
6.3
6-.3
121.7
1998
5tj
40.2
17.1
11
5J
135.7
1999
65.8
30.4
16.4
8.9
„ 7.2
6.0
134.8
2008
. 75.1
29.8
, 15.9
&3
3.2
139.1
2001
83.4
19.8
15.6
4.0
4.5
2.5
121.7
2002
91.7
19.8
14.8
5.2
4.4
2.4
138.2
Executive Summary ES-17
-------
Figure ES-13
2002 Sources of MFCs. PFCs. and SFfi
Substitution of Ozone Depleting Substances
HCFC-22 Production
Electrical Transmission and Distribution
Semiconductor Manufacture
Aluminum Production
I
I
MFCs, PFCs, and
SF, as a Portion
of all Emissions
2.0%
Magnesium Production and Processing
0 20 40 60 80 100
Tg CO, Eq
Substitution of Ozone Depleting Substances (91.7 Tg C02 Eq.)
The use and subsequent emissions of MFCs and PFCs
as substitutes for ODSs have increased from small amounts
in 1990 to account for 66 percent of aggregate HFC, PFC,
and SF6 emissions. This increase was in large part the result
of efforts to phase-out CFCs and other ODSs in the United
States, especially the introduction of HFC-134a as a CFC
substitute in refrigeration and air-conditioning applications.
In the short term, this trend is expected to continue, and
will likely accelerate in the next decade as HCFCs, which
are interim substitutes in many applications, are themselves
phased-out under the provisions of the Copenhagen
Amendments to the Montreal Protocol. Improvements in the
technologies associated with the use of these gases and the
introduction of alternative gases and technologies, however,
may help to offset this anticipated increase in emissions.
HCFC-22 Production (19.8 Tg C02 Eq.)
HFC-23 is a by-product of the production of HCFC-22.
Emissions from this source have decreased by 43 percent
since 1990. The HFC-23 emission rate (i.e., the amount of
HFC-23 emitted per kilogram of HCFC-22 manufactured)
has declined significantly since 1990, although production
has been increasing.
Electrical Transmission and Distribution Systems
(14.8TgC02Eq.)
The primary use of SF6 is as a dielectric in electrical
transmission and distribution systems. Fugitive emissions
of SF6 occur from leaks in and servicing of substations and
circuit breakers, especially from older equipment. Estimated
emissions from this source decreased by 49 percent since
1990, primarily due to higher SF6 prices and industrial efforts
to reduce emissions.
Semiconductor Manufacturing (4.4 Tg C02 Eq.)
The semiconductor industry uses combinations of HFCs,"
PFCs, SF6 and other gases for plasma etching and to clean
chemical vapor deposition tools. Emissions from this source
category have increased with the growth in the semiconductor
industry and the rising intricacy of chip designs. However,
the growth rate in emissions has slowed since 1997, and
emissions actually declined between 1999 and 2002. This
later reduction is due to the implementation of PFC emission
reduction methods, such as process optimization.
Aluminum Production (5.2 Tg C02 Eq.)
During the production of primary aluminum CF4 and
C2F6 are emitted as intermittent by-products of the smelting
process. These PFCs are formed when fluorine from the
cryolite bath combines with carbon from the electrolyte
anode. Emissions from aluminum production have decreased
by 71 percent between 1990 and 2002 due to emission
reduction efforts by the industry and falling domestic
aluminum production.
Magnesium Production (2.4 Tg C02 Eq.)
Sulfur hexafluoride is also used as a protective cover
gas for the casting of molten magnesium. Emissions from
primary magnesium production and magnesium casting
have decreased by 55 percent since 1990. Emissions have
decreased since 1999; due to a decrease in the quantity
of magnesium die cast and the closure of a U.S. primary
magnesium production facility.
ES.4. Other Information
Emissions by Economic Sector
Throughout this report, emission estimates are grouped
into six sectors (i.e., chapters) defined by the IPCC:
Energy, Industrial Processes, Solvent Use, Agriculture,
Land-Use Change and Forestry, and Waste. While it is
important to use this characterization for consistency with
UNFCCC reporting guidelines, it is also useful to allocate
emissions into more commonly used sectoral categories.
ES-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Box ES-1: Emissions of Ozone Depleting Substances
of man-made compounds includes CFCs, halons, methyl chloroform,
have a
duftit the 20* eenfciry. This family
methyl bromide, and HCFCs. These substances
States furtheredIts cownttnent t
Under these arnendments, the Unted States commtted to
TheWFTOreporttogpWeiiesdor^
the Monirea/ Protocol. Nevertheless, estimates for several Class I arid Class II ODSs are provided in Table ES-9fc»r Wormafcnat purposes.
Compounds are grouped by class according to their ozone depleting potenflal. Class I compounds are the prtrory QDSs; Class B (ampounds
include partially haiogenated chlorine compounds (i.e., HCFCs), some <
these HCFC compounds are only partially haiogenated, 1
therefore, pose only one-tent! to one-hundredth the threat to stratospheric ozone compared to CFCs.
ft should be noted that Ihe effects of these compounds on raoTaBve forcing are not provided. Although many ODSs have relatively high
direct 6WPs, their indirect effects from the destruction of ozone—also a greenhouse gas— are believed to have negative radiaflve forcing
effects, and terete could s^nlfleantfy reduce the overall magnitude of fiefr radiative forcing effects. Given TO uncertainfe surrounding the
net effect of these gases, emissions are reported on an unweighted basis,
Table ES-9: Emissions of Ozone Depleting Substances (Gg)
Compound
Class 1
CFC-11
CFC-12
CFC-113
CFC-114
CFC-115
Carbon Tetrachloride
Methyl Chloroform
Halon-1211
Halon-1301
Class II
HCFC-22
HCFG-123
HCFC-124
HCFC-141b
HCFC-142b
HCFC-225ea/cb
1990
28,6
155.5
59.4
5.1
4.5
4.3
222.5
4-
4
37.1
4-
4
1.1
2.2
4
1996
8.2
83.6
+
0.5
2.9
22.2
8.7
4
0.5
55.3
1.3
3.4
5.7
3.4
4
1987
7.8
72.9
+
0.6
2.4
22.6
4-
4
. 0.5
59.1
1.5
3.9
6.3
3.7
4
1998
7.2
60.2
+
0.5
1.8
23.1
+
4
0.5
62.8
1.8
4,3
6.9
4.1
+
1999
6.6
50.7
+
+
1.6
23.5
+
+ •
0.5
65.9
2.0
4.3
7.6
4.4
+
2QM
16.1
43.0
4-
+
1.5
24.0
4-
4-
0.5
73.7
2.2
4.6
7,7
4.8
4-
2001
1§.8
35,1
+
4-
1,4
24.5
4-
4-
0.5
78.3
2,4
4.4
7.6
5.1
4-
2002
15.4
28.6
+
+
1.3
25.0
4-
4-
0.5
78.0
2.6
4.2
7.1
5.5
4-
Source: EPA, Office of Atmospheric Programs
4 Does not exceed 0.05 Gg
This section reports emissions by the following economic
sectors: Residential, Commercial, Industry, Transportation,
Electricity Generation, and Agriculture, and U.S. Territories.
Table ES-10 summarizes emissions from each of these
sectors. Figure ES-14 shows the trend in emissions by sector
from 1990 to 2002.
Using this categorization, emissions from electricity
generation accounted for the largest portion (33 percent)
of U.S. greenhouse gas emissions in 2002. Transportation
activities, in aggregate, accounted for the second largest
portion (27 percent). Emissions from industry accounted
for 19 percent of U.S. greenhouse gas emissions in 2002. In
Executive Summary ES-19
-------
Table ES-10: U.S. Greenhouse Gas Emissions Allocated to Economic Sectors (Tg C02 Eq.)
Sector
Electricity generation
Transportation
Industry
Agriculture
Commercial
Residential
U.S. Territories
Total
Land-Use Change and Forestfy
Net Emissions (Sources and Sinks)
1990 1
1,843.9 1
1,513,4 I
1,437.4 1
482.8 1
472.2 1
345.6 1
33.8 1
6,1294 I
(957,9) 1
5,171.3 I
• 1996
• 2,047.0
I 1,683.7
1 1,493.2
I 520.8
I 497.4
1 403.8
I 41.4
1 6,687.3
1 (1,055.2)
1 5,632.1
1997
2,113.2
1,698.6
1.495J
532.6
496.7
385.1
42.7
6,764.4
(821.0)
5,943.5
1998
2,118,3
1,732.9
1,454,6
534 3
477.2
352:4
42,0
6.780J
(76S.8)
MiMT.
1999
2,2flft7
1,794.7
t4140
534,7
484J
373.6
; 43.S
;iBjs£i:?
|675,i)r
t,*mt
2000
2,309.1
1,844.8
1,418.5
520,7
505.1
394,0
48.1
7,f|8J
(6»2>;
6,348.2
2001
2^65,5
1,827.0;
1,353.1
519,3
492.2
381.7
45.2
«,«83J
(68SJ)
6,194.1
2002
2,286.8
1,861,4
1,331,9
519.8
500.4
387.7
46.6
6,934.6
(690.7)
6,243.8
Note: Totals may not sum, Emissions inetode COg, CH* BFCs, PFCs, and SF8.
See Table 2-6 for more detailed data.
Figure ES-14
Emissions Allocated to Economic Sectors
2,500
2,000
• 1,500 -
, 1,000
500
0
Electricity Generation
Commercial^ Agriculture
\ Residential
Year
contrast to electricity generation and transportation, emissions
from industry have declined over the past decade, as structural
changes have occurred in the U.S. economy (i.e., shifts from
a manufacturing based to a service-based economy), fuel
switching has occurred, and efficiency improvements have
been made. The remaining 21 percent of U.S. greenhouse gas
emissions were contributed by the residential, agriculture,
and commercial economic sectors, plus emissions from
U.S. Territories. Residences accounted for about 6 percent,
and primarily consisted of CO2 emissions from fossil fuel
combustion. Activities related to agriculture accounted for
roughly 7 percent of U.S. emissions; these emissions were
dominated by N2O emissions from agricultural soils instead
of CO2 from fossil fuel combustion. The commercial sector
accounted for about 7 percent of emissions, while U.S.
territories accounted for 1 percent.
Carbon dioxide was also emitted and sequestered by a
variety of activities related to forest management practices,
tree planting in urban areas, the management of agricultural
soils, and landfilling of yard trimmings.
Electricity is ultimately consumed in the economic sectors
described above. Table ES-11 presents greenhouse gas emissions
from economic sectors with emissions related to electricity
generation distributed into end-use categories (i.e., emissions
from electricity generation are allocated to the economic sectors
in which the electricity is consumed). To distribute electricity
emissions among end-use sectors, emissions from the source
categories assigned to electricity generation were allocated to the
residential, commercial, industry, transportation, and agriculture
economic sectors according to retail sales of electricity.n These
source categories include CO2 from fossil fuel combustion and
the use of limestone and dolomite for flue gas desulfurization,
CO2 and N2O from waste combustion, CH4 and N2O from
stationary sources, and SF6 from electrical transmission and
distribution systems.
When emissions from electricity are distributed among
these sectors, industry accounts for the largest share of U.S.
greenhouse gas emissions (30 percent) in 2002. Emissions
from the residential and commercial sectors also increase
substantially due to their relatively large share of electricity
consumption (e.g., lighting, appliances, etc.). Transportation
activities remain the second largest contributor to emissions.
In all sectors except agriculture, CO2 accounts for more than
75 percent of greenhouse gas emissions, primarily from the
combustion of fossil fuels. Figure ES-15 shows the trend in
these emissions by sector from 1990 to 2002.
12 Emissions were not distributed to U.S. territories, since the electricity generation sector only includes emissions related to the generation of electricity
in the 50 states and the District of Columbia.
ES-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table ES-11: U.S Greenhouse Gas Emissions by Economic Sector and Gas with Electricity-Related Emissions Distributed
(TgC02Eq.)
Sector
Industry
Transportation
Commercial
Residential
Agriculture
U.S, Territories
Total
Land-Use Change and Forestry
Net Emissions (Sources and Sinks)
1990
2.067J
1,516.5
1,019.0
948.4
543.7
33.8
6,118.1
(957.9)
5,171.3
See Table 2-8 for more detailed data.
I 1996
2,210.8
" 1,«ft7.
1,003.7
1,062.4
592,4
• 414'
| 6MiM
a«8& ,
1 5,632.1
1917
2,236.7
1,701.6
1,138.0
1,057.1
588.3
42.7
6,764.4
,{«2tO)
5,943.5
1998
2,210.4
1,736.0
1,149.4
1,057.1
594.8
42.8
6,790.5
(705.8)
6,084.7
1899
2,179.5
1,797.9
1,166.0
1,080.0
585.3
43.8
6,852.5
(675.8)
6,176,8
2809
2,197.9
1,848.1
1,229.3
1,139.0
577.9
46.1
7,038.3
(690.2)
6,348.2
2001
2,063,4
1,830.4
1,232.9
1,125.6
586.3
45.2
*MM\
(6«9.7)
6,184.1
2002
2,047.9
1,864.5
1,234.3
1,158.1
583.1
46.6
6,934.6
1690.7)
6,243,8
Ambient Air Pollutant Emissions
In the United States, CO, NOX, NMVOCs, SO2 are referred
to as "ambient air pollutants," as termed in the Clean Air Act.
These pollutants do not have a direct global warming effect, but
indirectly affect terrestrial radiation absorption by influencing
the formation and destruction of tropospheric and stratospheric
ozone, or, in the case of SO2, by affecting the absorptive
characteristics of the atmosphere. Carbon monoxide is produced
when carbon-containing fuels are combusted incompletely.
Nitrogen oxides (i.e., NO and NO2) are created by lightning,
fires, fossil fuel combustion, and in the stratosphere from N2O.
NMVOCs—which include hundreds of organic compounds
that participate in atmospheric chemical reactions (i.e., propane,
butane, xylene, toluene, ethane and many others)—are emitted
primarily from transportation, industrial processes, and non-
industrial consumption of organic solvents. In the United States,
SO2 is primarily emitted from coal combustion for electric
power generation and the metals industry.
Ambient air pollutants are regulated under the Clean Air
Act in an effort to protect human health and the environment.
These gases also indirectly affect the global climate by either
acting as short-lived greenhouse gases or reacting with other
chemical compounds in the atmosphere to form compounds
that are greenhouse gases. Unlike the other ambient air
pollutants, sulfur-containing compounds emitted into the
atmosphere affect the Earth's radiative budget negatively;
therefore, it is discussed separately.
One important indirect climate change effect of NMVOCs
and NOX is their role as precursors for tropospheric ozone
formation. They can also alter the atmospheric lifetimes of
other greenhouse gases. Another example of ambient air
Figure ES-15
Emissions with Electricity Distributed to Economic Sectors
2,500 n
2,000-
«, 1,500-
UJ
o
u
" 1,000-
500
Industrial
Commercial -
———
Residential'
Agriculture
Note: Does not include U.S. territories.
pollutant formation into greenhouse gases is carbon monoxide's
interaction with the hydroxyl radical—the major atmospheric
sink for methane emissions—to form CO2. Therefore, increased
atmospheric concentrations of CO limit the number of hydroxyl
molecules (OH) available to destroy methane.
Since 1970, the United States has published estimates
of annual emissions of ambient air pollutants (EPA 2003).13
Table ES-13 shows that fuel combustion accounts for the
majority of emissions of these gases. Industrial processes—
such as the manufacture of chemical and allied products,
metals processing, and industrial uses of solvents—are also
significant sources of CO, NOX and NMVOCs.
Quality Assurance and Quality Control
(QA/QC)
The United States seeks to continually improve the
quality, transparency and credibility of the Inventory of
13
NOX and CO emission estimates from field burning of agricultural residues were estimated separately, and therefore not taken from EPA (2003).
Executive Summary ES-21
-------
Box ES-2: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data
Total emissions can be compared to other economic and social indices to highlight changes overtime. These comparisons include: 1)
emissio
per unit of fossil fuel co
unit of electricity consumption, I
greenhouse gas emissions in 2002; 4) emissions per unit of total gross domestic pWduet as a measure of national economic activity; or
5) emissions per capita. '_ •;'.-..
Table ES-12 provides daft on various statistics related to U.S. greenhouse gas emissions normalized to 1990 as a baseline year.
Greenhouse gas emissions in the U.S. have grown at an average annual rate of 1.0 percent since 1990. This rate is slower than that for total
energy or fossil fuel consumption and much slower than thatfor either electricity consumption or overall gross domestic product. Total U.S.
greenhouse gas emisstons nave atee grewnfoomstow^tttan national (KpjIaftonsteeliW^l^pSvlljVChwraM, globalafrnospheric
COz concentraBons—a functfen ol many complex anthropogenic and natural processes—are irw»asir% at 0,4 percent per year.
Table ES-12: Recent Trends in Various U.S. Data (Index 1990 = 100) and Global Atmospheric C02 Concentration
Variable
Greenhouse Gas Emissions8
Energy Consumption"
Fossil Fuel Consumption"
Electricity Gonsurnpfion6
GDF
Population"
im
99
100
99
102
100
101
jm
101
101
102
102
103
103
1993
103
103
104
106
106
104
1994
105
105
106
109
110
105
1995
106
108
107
112
113
107
1996
109
111
111
115
117
108
199?
110
112
112
117
122
109
1998
111
112
113
121
127
111
199»
112
114
1.14
124
133
112
2000
115
117
117
128
138
113
2001
112
114
115
126
139
114
2002
113
115
115
129
142
116
Growth
Rate1
10%
1.2%
1.2%
2.2%
3,0%
1.2%
Atmospheric CO, Concentration8 100 101 101 101 102 102 103 104 104 : 104 105 105 0.4%
a GWP weighted values
b Energy content weighted values {HA 2003)
c Gross Domestic Product in chained 2000 dollars (SEA 2004)
d (U.S. Census Bureau 2003)
e Mauna Loa Observatory, Hawaii (Keeling and Whorf 2003)
1 Average annual growth rate
Figure ES-16
U.S. Greenhouse Gas Emissions Per Capita and
Per Dollar of Gross Domestic Product
Real GDP^
Population
Emissions per capita
Emissions per $GDP
U.S. Greenhouse Gas Emissions and Sinks. To assist in
these efforts, the United States recently implemented a
systematic approach to QA/QC. While QA/QC has always
been an integral part of the U.S. national system for Inventory
development, the procedures followed for the current
inventory have been formalized in accordance with the QA/
QC plan and the UNFCCC reporting guidelines.
ES-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table ES-13: Emissions of NOX, CO, NMVOCs, and S02 (Gg)
Gas/Activity
1996 189? 1999
2001 2002
&$w
9,540
11,714
126
;" ':i*:
Z** ' tjujj -'
-' ' ' • *> Q
K:'V, •!?*•
104,063 '
jji 0.^8^8
[•: IKSiQi
c •"'' •' 3E1
H-^828;;
r 3i016
•\ '-'.--I
- '•.-.747
:::,;::>
fvfriiti-
[-. 1,018
8,306
V 433
::304
, 1,997
4,969
NA
158
18,082
14,746
I 649
I 504
29
953
I 1
NA
\ 1
22,289
9,578
11,768
130
140
634
3
34
3
181,182
3,927
90,284
333
2,668
3,153
1
761
5
16*994
1,016
7,928
442
313
2,038
5,100
NA
157
17,091
15,104
659
312
29
985
1
NA
1
tim
9,419
11,592
130
145
635
3
35
3
98,976
3,927
87,940
332
2,826
3,163
1
781
5
16,483
1,016
7,742
440
328
2,047
4,671
NA
161
17,189
15,191
665
310
30
991
1
NA
1
21,341
8,716
11,582
113
142
748
3
34
3
95,464
4,941
84,574 ;
152
2,833
2,145
46
760
14
16,246
1,312
7,658
376
326
1,890
4,533
NA
151
16,813
14,073
701
275
29
933
1
NA
1
28,817
81228
11,395
115
149
992
3
35
. •:••• 3:,
mm-
-"4,188";'
83,6811
152
2,«14
2,214 ;
45
784
, . 14
15,418
1,088
7^30
348
332
1,845
4,422
NA.
153
14,882
12,883
632
279
29
977
1
NA
1
2f,14V
*.7,8f6V<'
11,254
117
149
•'- .755';:
, -,'3.-' '
,/ ';.>." 35'^.-
:/V;; "3:,;. ..'
100,653
':'.'i^j(|9>:'>;
."-SJ6j?(j8!v
;;';"f§3. '•
•'•.•2^9'-"'
-• • "2,32? • ' ',
44
762
14 .
1l,t4»
1,087
6,800
357
333
1,829
4,584
m
158
14,324
12J67
-. ,«ae":'
• 281 -
' , m
1,008
' - "1 '
NA
1 :
19,849
7;542
11,852
118
'149
-: 649
. - -: "• 3
•v ' 33
: v 3
92,541
4iS61
agoea
; ,153
-3,294
2,304
44
706
15
14886
1,147
6,771
348
333
1,818
4,420
NA
, 158
18,889
11,805
634
m
••••': 30
930
1
NA
1
+ Does not exceed 0.5 Gg
Uncertainty in and Limitations
of Emission Estimates
While the current U.S. emissions inventory provides a
solid foundation for the development of a more detailed and
comprehensive national inventory, there are uncertainties
associated with the emission estimates. Some of the current
estimates, such as those for CO2 emissions from energy-
related activities and cement processing, are considered to
have low uncertainties. For some other categories of emissions,
however, a lack of data or an incomplete understanding of
how emissions are generated increases the uncertainty
associated with the estimates presented. Acquiring a better
understanding of the uncertainty associated with inventory
estimates is an important step in helping to prioritize future
work and improve the overall quality of the Inventory.
Recognizing the benefit of conducting an uncertainty
analysis, the UNFCCC reporting guidelines follow the
recommendations of the IPCC Good Practice Guidance
and Uncertainty Management in National Greenhouse Gas
Inventories (hereafter referred to as the IPCC Good Practice
Guidance) and require that countries provide single point
estimates for many source and sink categories.
Currently, a qualitative discussion of uncertainty is
presented for all source and sink categories. Within the
discussion of each emission source, specific factors affecting
the uncertainty surrounding the estimates are discussed. Most
sources also contain a quantitative uncertainty assessment, in
accordance with the new UNFCCC reporting guidelines.
Executive Summary ES-23
-------
Box ES-3: Sources and Effects of Sulfur Dioxide
, by providing surfaces for
totwe jjarts. The
The second Indirect «ffeet is it» tewler«y af fl» fKteeiion Hi
thickness. Although still highly uncertain, the radiative forcing estimates
be negative, as is the combined radiative forcing of the two (IPCC 2001).
the atmosphere, its radiatwr torcft^ J^mcte m ft^ uncertain.
by increasing cloud lifetime and
in
ES-24 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
1. Introduction
This report presents estimates by the United States government of U.S. anthropogenic greenhouse gas emissions
and sinks for the years 1990 through 2002. A summary of these estimates is provided in Table 2-3 and Table 2-4
by gas and source category in the Trends in Greenhouse Gas Emissions chapter. The emission estimates in these tables are
presented on both a full molecular mass basis and on a Global Warming Potential (GWP) weighted basis in order to show
the relative contribution of each gas to global average radiative forcing.1 This report also discusses the methods and data
used to calculate these emission estimates.
In June of 1992, the United States signed, and later ratified in October, the United Nations Framework Convention on
Climate Change (UNFCCC). The ultimate objective of the UNFCCC is "to achieve, in accordance with the relevant provisions
of the Convention, stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous
anthropogenic interference with the climate system. Such a level should be achieved within a time-frame sufficient to allow
ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic
development to proceed in a sustainable manner."2'3
Parties to the Convention, by ratifying, "shall develop, periodically update, publish and make available...national
inventories of anthropogenic emissions by sources and removals by sinks of all greenhouse gases not controlled by the
Montreal Protocol, using comparable methodologies..."4 The United States views this report as an opportunity to fulfill
these commitments under the UNFCCC.
In 1988, preceding the creation of the UNFCCC, the World Meteorological Organization (WMO) and the United
Nations Environment Programme (UNEP) jointly established the Intergovernmental Panel on Climate Change (IPCC).
The charter of the IPCC is to assess available scientific information on climate change, assess the environmental and socio-
economic impacts of climate change, and formulate response strategies (IPCC 1996). Underworking Group 1 of the IPCC,
nearly 140 scientists and national experts from more than thirty countries collaborated in the creation of the Revised 1996
IPCC Guidelines for National Greenhouse Gas Inventories (IPCC/UNEP/OECD/IEA 1997) to ensure that the emission
inventories submitted to the UNFCCC are consistent and comparable between nations. The IPCC accepted the Revised
1996 IPCC Guidelines at its Twelfth Session (Mexico City, 11-13 September 1996). This report presents information in
accordance with these guidelines. In addition, this inventory is in accordance with the IPCC Good Practice Guidance and
Uncertainty Management in National Greenhouse Gas Inventories, which further expanded upon the methodologies in the
Revised 1996 IPCC Guidelines.
1 See the section below entitled Global Warming Potentials for an explanation of GWP values.
2 The term "anthropogenic," in this context, refers to greenhouse gas emissions and removals that are a direct result of human activities
or are the result of natural processes that have been affected by human activities (IPCC/UNEP/OECD/IEA 1997).
3 Article 2 of the Framework Convention on Climate Change published by the UNEP/WMO Information Unit on Climate Change. See
.
Introduction 1-1
-------
Overall, this inventory of anthropogenic greenhouse gas
emissions provides a common and consistent mechanism
through which Parties to the UNFCCC can estimate emissions
and compare the relative contribution of individual sources,
gases, and nations to climate change, and is a prerequisite for
accounting for reductions and evaluating possible mitigation
strategies. The structure of this report is consistent with the
current UNFCCC Guidelines on Reporting and Review
(UNFCCC 2003).
1.1. Background Information
Greenhouse Gases
Although the Earth's atmosphere consists mainly of
oxygen and nitrogen, neither plays a significant role in
enhancing the greenhouse effect because both are essentially
transparent to terrestrial radiation. The greenhouse effect is
primarily a function of the concentration of water vapor,
carbon dioxide (CO2), and other trace gases in the atmosphere
that absorb the terrestrial radiation leaving the surface
of the Earth (IPCC 1996). Changes in the atmospheric
concentrations of these greenhouse gases can alter the
balance of energy transfers between the atmosphere, space,
land, and the oceans.5 A gauge of these changes is called
radiative forcing, which is a simple measure of changes
in the energy available to the Earth-atmosphere system
(IPCC 1996). Holding everything else constant, increases
in greenhouse gas concentrations in the atmosphere will
produce positive radiative forcing (i.e., a net increase in the
absorption of energy by the Earth).
Climate change can be driven by changes in the
atmospheric concentrations of a number ofradiatively active
gases and aerosols. We have clear evidence that human
activities have affected concentrations, distributions and life
cycles of these gases (IPCC 1996).
Naturally occurring greenhouse gases include water
vapor, CO2, methane (CH4), nitrous oxide (N2O), and
ozone (O3). Several classes of halogenated substances that
contain fluorine, chlorine, or bromine are also greenhouse
gases, but they are, for the most part, solely a product
of industrial activities. Chlorofluorocarbons (CFCs) and
hydrochlorofluorocarbons (HCFCs) are halocarbons that
contain chlorine, while halocarbons that contain bromine
are referred to as bromofluorocarbons (i.e., halons). As
stratospheric ozone depleting substances, CFCs, HCFCs,
and halons are covered under the Montreal Protocol on
Substances that Deplete the Ozone Layer. The UNFCCC
defers to this earlier international treaty. Consequently,
Parties are not required to include these gases in national
greenhouse gas inventories.6 Some other fluorine-containing
halogenated substances—hydrofluorocarbons (HFCs),
perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)—do
not deplete stratospheric ozone but are potent greenhouse
gases. These latter substances are addressed by the UNFCCC
and accounted for in national greenhouse gas inventories.
There are also several gases that, although they do
not have a commonly agreed upon direct radiative forcing
effect, do influence the global radiation budget. These
tropospheric gases include carbon monoxide (CO), nitrogen
dioxide (NO2), sulfur dioxide (SO2), and tropospheric
(ground level) O3. Tropospheric ozone is formed by two
precursor pollutants, volatile organic compounds (VOCs)
and nitrogen oxides (NOX) in the presence of ultraviolet
light (sunlight). Aerosols are extremely small particles or
liquid droplets that are often composed of sulfur compounds,
carbonaceous combustion products, crustal materials
and other human induced pollutants. They can affect the
absorptive characteristics of the atmosphere. Comparatively,
however, the level of scientific understanding of aerosols is
still very low (IPCC 2001).
Carbon dioxide, CH4, and N2O are continuously emitted
to and removed from the atmosphere by natural processes
on Earth. Anthropogenic activities, however, can cause
additional quantities of these and other greenhouse gases
to be emitted or sequestered, thereby changing their global
average atmospheric concentrations. Natural activities such
as respiration by plants or animals and seasonal cycles of
plant growth and decay are examples of processes that only
cycle carbon or nitrogen between the atmosphere and organic
biomass. Such processes, except when directly or indirectly
perturbed out of equilibrium by anthropogenic activities,
generally do not alter average atmospheric greenhouse gas
concentrations over decadal timeframes. Climatic changes
5 For more on the science of climate change, see NRC (2001).
6 Emissions estimates of CFCs, HCFCs, halons and other ozone-depleting substances are included in this document for informational
purposes.
1-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 1-1: Global atmospheric concentration (ppm unless otherwise specified), rate of concentration change
(ppb/year) and atmospheric lifetime (years) of selected greenhouse gases
Atmospheric Variable
Pre-industrial atmospheric concentration
Atmospheric concentration"
Rate of concentration changed
Atmospheric Lifetime
C02
280
372.3
1.5e
5-200'
CH4
0.722
1.729-1.843°
0.0076
129
N20
0.270
0.317-0.318°
0.0008
1148
SF6a
0
4.7-4,8
0.24
3,200
CF4°
40
80
1.0
> 50,000
Source: Current atmospheric concentrations for C02, CH4, N20, and SF6 are from Biasing and Jones (2003). All other data is from IPCC (2001).
a Concentrations in parts per trillion (ppt) and rate of concentration change in ppl/year.
b Concentration for SF6 was measured in 2001; concentration for CF4 was measured in 2000. Concentrations for all other gases were measured in 2002.
cThe low and high endpoints of the range represent concentrations from Tasmania, a mid-latitude Southern-Hemisphere site, and Ireland, a mid-latitude
Northern-Hemisphere site, respectively.
" Rate is calculated over the period 1990 to 1999.
e Rate has fluctuated between 0.9 and 2.8 ppm per year for C02 and between 0 and 0.013 ppm per year for CH4 over the period 1990 to 1999.
' No single lifetime can be defined for C02 because of the different rates of uptake by different removal processes.
8 This lifetime has been defined as an "adjustment time" that takes into account the indirect effect of the gas on its own residence time.
resulting from anthropogenic activities, however, could
have positive or negative feedback effects on these natural
systems. Atmospheric concentrations of these gases, along
with their rates of growth and atmospheric lifetimes, are
presented in Table 1-1.
A brief description of each greenhouse gas, its sources,
and its role in the atmosphere is given below. The following
section then explains the concept of GWPs, which are
assigned to individual gases as a measure of their relative
average global radiative forcing effect.
Water Vapor (H2O). Overall, the most abundant and
dominant greenhouse gas in the atmosphere is water vapor.
Water vapor is neither long-lived nor well mixed in the
atmosphere, varying spatially from 0 to 2 percent (IPCC
1996). In addition, atmospheric water can exist in several
physical states including gaseous, liquid, and solid. Human
activities are not believed to affect directly the average
global concentration of water vapor, but, the radiative
forcing produced by the increased concentrations of other
greenhouse gases may indirectly affect the hydrologic cycle.
While a warmer atmosphere has an increased water holding
capacity, increased concentrations of water vapor affects the
formation of clouds, which can both absorb and reflect solar
and terrestrial radiation. Aircraft contrails, which consist of
water vapor and other aircraft emittants, are similar to clouds
in their radiative forcing effects (IPCC 1999).
Carbon Dioxide. In nature, carbon is cycled between
various atmospheric, oceanic, land biotic, marine biotic,
and mineral reservoirs. The largest fluxes occur between
the atmosphere and terrestrial biota, and between the
atmosphere and surface water of the oceans. In the
atmosphere, carbon predominantly exists in its oxidized
form as CO2. Atmospheric CO2 is part of this global
carbon cycle, and therefore its fate is a complex function
of geochemical and biological processes. Carbon
dioxide concentrations in the atmosphere increased from
approximately 280 parts per million by volume (ppmv) in
pre-industrial times to 372.3 ppmv in 2001, a 33 percent
increase (IPCC 2001 and Biasing and Jones 2003).7'8 The
IPCC definitively states that "the present atmospheric CO2
increase is caused by anthropogenic emissions of CO,"
(IPCC 2001). The predominant source of anthropogenic
CO2 emissions is the combustion of fossil fuels. Forest
clearing, other biomass burning, and some non-energy
production processes (e.g., cement production) also emit
notable quantities of CO2.
In its second assessment, the IPCC also stated that "[t]he
increased amount of carbon dioxide [in the atmosphere] is
leading to climate change and will produce, on average, a
global warming of the Earth's surface because of its enhanced
greenhouse effect—although the magnitude and significance
of the effects are not fully resolved" (IPCC 1996).
7
The pre-industrial period is considered as the time preceding the year 1750 (IPCC 2001).
8 Carbon dioxide concentrations during the last 1,000 years of the pre-industrial period (i.e., 750-1750), a time of relative climate stability,
fluctuated by about ±10 ppmv around 280 ppmv (IPCC 2001).
Introduction 1-3
-------
Methane. Methane is primarily produced through
anaerobic decomposition of organic matter in biological
systems. Agricultural processes such as wetland rice
cultivation, enteric fermentation in animals, and the
decomposition of animal wastes emit CH4, as does the
decomposition of municipal solid wastes. Methane is also
emitted during the production and distribution of natural
gas and petroleum, and is released as a by-product of coal
mining and incomplete fossil fuel combustion. Atmospheric
concentrations of CH4 have increased by about 150 percent
since pre-industrial times, although the rate of increase
has been declining. The IPCC has estimated that slightly
more than half of the current CH4 flux to the atmosphere is
anthropogenic, from human activities such as agriculture,
fossil fuel use, and waste disposal (IPCC 2001).
Methane is removed from the atmosphere through a
reaction with the hydroxyl radical (OH) and is ultimately
converted to CO2. Minor removal processes also include
reaction with chlorine in the marine boundary layer, a soil
sink, and stratospheric reactions. Increasing emissions of
CH4 reduce the concentration of OH, a feedback that may
increase the atmospheric lifetime of CH4 (IPCC 2001).
Nitrous Oxide. Anthropogenic sources of N2O emissions
include agricultural soils, especially production of nitrogen-
fixing crops and forages, the use of synthetic and manure
fertilizers, and manure deposition by livestock; fossil fuel
combustion, especially from mobile combustion; adipic
(nylon) and nitric acid production; wastewater treatment and
waste combustion; and biomass burning. The atmospheric
concentration of N2O has increased by 17 percent since 1750,
from a pre-industrial value of about 270 ppb to 318 ppb in
2002, a concentration that has not been exceeded during
the last thousand years. Nitrous oxide is primarily removed
from the atmosphere by the photolytic action of sunlight in
the stratosphere (IPCC 2001).
Ozone. Ozone is present in both the upper stratosphere,9
where it shields the Earth from harmful levels of ultraviolet
radiation, and at lower concentrations in the troposphere,10
where it is the main component of anthropogenic pho-
tochemical "smog." During the last two decades, emissions
of anthropogenic chlorine and bromine-containing
halocarbons, such as CFCs, have depleted stratospheric
ozone concentrations. This loss of ozone in the stratosphere
has resulted in negative radiative forcing, representing
an indirect effect of anthropogenic emissions of chlorine
and bromine compounds (IPCC 1996). The depletion of
stratospheric ozone and its radiative forcing was expected to
reach a maximum in about 2000 before starting to recover,
with detection of such recovery not expected to occur much
before 2010 (IPCC 2001).
The past increase in tropospheric ozone, which is also
a greenhouse gas, is estimated to provide the third largest
increase in direct radiative forcing since the pre-industrial
era, behind CO2 and CH4. Tropospheric ozone is produced
from complex chemical reactions of volatile organic
compounds mixing with NOX in the presence of sunlight.
Ozone, CO, SO2, nitrogen dioxide (NO2) and paniculate
matter are included in the category referred to as "ambient
air pollutants" in the United States under the Clean Air
Act11 and its subsequent amendments. The tropospheric
concentrations of ozone and these other pollutants are short-
lived and, therefore, spatially variable.
Halocarbons, Perfluorocarbons, and Sulfur
Hexafluoride. Halocarbons are, for the most part, man-made
chemicals that have both direct and indirect radiative forcing
effects. Halocarbons that contain chlorine (CFCs, HCFCs,
methyl chloroform, and carbon tetrachloride) and bromine
(halons, methyl bromide, and hydrobromofluorocarbons
(HBFCs)) result in stratospheric ozone depletion and
are therefore controlled under the Montreal Protocol on
Substances that Deplete the Ozone Layer. Although CFCs
and HCFCs include potent global warming gases, their
net radiative forcing effect on the atmosphere is reduced
because they cause stratospheric ozone depletion, which
itself is an important greenhouse gas in addition to shielding
the Earth from harmful levels of ultraviolet radiation.
" The stratosphere is the layer from the troposphere up to roughly 50 kilometers. In the lower regions the temperature is nearly constant
but in the upper layer the temperature increases rapidly because of sunlight absorption by the ozone layer. The ozone-layer is the part of
the stratosphere from 19 kilometers up to 48 kilometers where the concentration of ozone reaches up to 10 parts per million.
10 The troposphere is the layer from the ground up to 11 kilometers near the poles and up to 16 kilometers in equatorial regions (i.e., the
lowest layer of the atmosphere where people live). It contains roughly 80 percent of the mass of all gases in the atmosphere and is the
site for most weather processes, including most of the water vapor and clouds.
11 [42 U.S.C § 7408, CAA § 108]
1-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Under the Montreal Protocol, the United States phased
out the production and importation of halons by 1994 and
of CFCs by 1996. Under the Copenhagen Amendments
to the Protocol, a cap was placed on the production
and importation of HCFCs by non-Article 512 countries
beginning in 1996, and then followed by a complete phase-
out by the year 2030. While ozone depleting gases covered
under the Montreal Protocol and its Amendments are not
covered by the UNFCCC; they are reported in this inventory
under Annex 6.2 for informational purposes.
HFCs, PFCs, and SF6 are not ozone depleting
substances, and therefore are not covered under the Montreal
Protocol. They are, however, powerful greenhouse gases.
HFCs are primarily used as replacements for ozone depleting
substances but also emitted as a by-product of the HCFC-
22 manufacturing process. Currently, they have a small
aggregate radiative forcing impact, but it is anticipated that
their contribution to overall radiative forcing will increase
(IPCC 2001). PFCs and SF6 are predominantly emitted from
various industrial processes including aluminum smelting,
semiconductor manufacturing, electric power transmission
and distribution, and magnesium casting. Currently, the
radiative forcing impact of PFCs and SF6 is also small,
but they have a significant growth rate, extremely long
atmospheric lifetimes, and are strong absorbers of infrared
radiation, and therefore have the potential to influence
climate far into the future (IPCC 2001).
Carbon Monoxide. Carbon monoxide has an indirect
radiative forcing effect by elevating concentrations of CH4
and tropospheric ozone through chemical reactions with
other atmospheric constituents (e.g., the hydroxyl radical,
OH) that would otherwise assist in destroying CH4 and
tropospheric ozone. Carbon monoxide is created when
carbon-containing fuels are burned incompletely. Through
natural processes in the atmosphere, it is eventually oxidized
to CO2. Carbon monoxide concentrations are both short-lived
in the atmosphere and spatially variable.
Nitrogen Oxides. The primary climate change effects of
nitrogen oxides (i.e., NO and NO2) are indirect and result
from their role in promoting the formation of ozone in the
troposphere and, to a lesser degree, lower stratosphere,
where it has positive radiative forcing effects.! 3 Additionally,
NOX emissions from aircraft are also likely to decrease CH4
concentrations, thus having a negative radiative forcing
effect (IPCC 1999). Nitrogen oxides are created from
lightning, soil microbial activity, biomass burning (both
natural and anthropogenic fires) fuel combustion, and,
in the stratosphere, from the photo-degradation of N2O.
Concentrations of NOX are both relatively short-lived in the
atmosphere and spatially variable.
Nonmethane Volatile Organic Compounds (NMVOCs).
Nonmethane volatile organic compounds include substances
such as propane, butane, and ethane. These compounds
participate, along with NOX, in the formation of tropospheric
ozone and other photochemical oxidants. NMVOCs
are emitted primarily from transportation and industrial
processes, as well as biomass burning and non-industrial
consumption of organic solvents. Concentrations of
NMVOCs tend to be both short-lived in the atmosphere and
spatially variable.
Aerosols. Aerosols are extremely small particles or liquid
droplets found in the atmosphere. They can be produced by
natural events such as dust storms and volcanic activity, or by
anthropogenic processes such as fuel combustion and biomass
burning. Aerosols affect radiative forcing differently than
greenhouse gases, and their radiative effects occur through
direct and indirect mechanisms: directly by scattering and
absorbing solar radiation; and indirectly by increasing droplet
counts that modify the formation, precipitation efficiency,
and radiative properties of clouds. Aerosols are removed from
the atmosphere relatively rapidly by precipitation. Because
aerosols generally have short atmospheric lifetimes, and
have concentrations and compositions that vary regionally,
spatially, and temporally, their contributions to radiative
forcing are difficult to quantify (IPCC 2001).
The indirect radiative forcing from aerosols is typically
divided into two effects. The first effect involves decreased
droplet size and increased droplet concentration resulting
12 Article 5 of the Montreal Protocol covers several groups of countries, especially developing countries, with low consumption rates of
ozone depletion substances. Developing countries with per capita consumption of less than 0.3 kg of certain ozone depleting substances
(weighted by their ozone depletion potential) receive financial assistance and a grace period of ten additional years in the phase-out of
ozone depleting substances.
13 NOX emissions injected higher in the stratosphere, primarily from fuel combustion emissions from high altitude supersonic aircraft,
can lead to stratospheric ozone depletion.
Introduction 1-5
-------
from an increase in airborne aerosols. The second effect
involves an increase in the water content and lifetime
of clouds due to the effect of reduced droplet size on
precipitation efficiency (IPCC 2001). Recent research has
placed a greater focus on the second indirect radiative forcing
effect of aerosols.
Various categories of aerosols exist, including
naturally produced aerosols such as soil dust, sea salt,
biogenic aerosols, sulfates, and volcanic aerosols, and
anthropogenically manufactured aerosols such as industrial
dust and carbonaceous14 aerosols (e.g., black carbon, organic
carbon) from transportation, coal combustion, cement
manufacturing, waste incineration, and biomass burning.
The net effect of aerosols on radiative forcing is believed
to be negative (i.e., net cooling effect on the climate),
although because they remain in the atmosphere for only days
to weeks, their concentrations respond rapidly to changes in
emissions.15 Locally, the negative radiative forcing effects
of aerosols can offset the positive forcing of greenhouse
gases (IPCC 1996). "However, the aerosol effects do not
cancel the global-scale effects of the much longer-lived
greenhouse gases, and significant climate changes can still
result" (IPCC 1996).
The IPCC's Third Assessment Report notes that "the
indirect radiative effect of aerosols is now understood to also
encompass effects on ice and mixed-phase clouds, but the
magnitude of any such indirect effect is not known, although
it is likely to be positive" (IPCC 2001). Additionally, current
research suggests that another constituent of aerosols, black
carbon, may have a positive radiative forcing (Jacobson
2001). The primary anthropogenic emission sources of black
carbon include diesel exhaust and open biomass burning.
Global Warming Potentials
A GWP is a quantified measure of the globally averaged
relative radiative forcing impacts of a particular greenhouse
gas (see Table 1-2). It is defined as the ratio of the time-
integrated radiative forcing from the instantaneous release of
1 kg of a trace substance relative to that of 1 kg of a reference
gas (IPCC 2001). Direct radiative effects occur when the
gas itself absorbs radiation. Indirect radiative forcing occurs
when chemical transformations involving the original gas
produces a gas or gases that are greenhouse gases, or when
a gas influences other radiatively important processes such
as the atmospheric lifetimes of other gases. The reference
gas used is CO2, and therefore GWP weighted emissions are
measured in teragrams of CO2 equivalent (Tg CO2Eq.)16 The
relationship between gigagrams (Gg) of a gas and Tg CO2
Eq. can be expressed as follows:
Tg C02 Eq = (Gg of gas) x (GWP) x / Tg
, 1,000 Gg)
where,
Tg CO2 Eq. = Teragrams of Carbon Dioxide Equivalent
Gg = Gigagrams (equivalent to a thousand
metric tons)
GWP = Global Warming Potential
Tg = Teragrams
GWP values allow for a comparison of the impacts of
emissions and reductions of different gases. According to the
IPCC, GWPs typically have an uncertainty of ±35 percent.
The parties to the UNFCCC have also agreed to use GWPs
based upon a 100-year time horizon although other time
horizon values are available.
Greenhouse gas emissions and removals should be
presented on a gas-by-gas basis in units of mass... In
addition, consistent with decision 2/CP.3, Parties should
report aggregate emissions and removals of greenhouse
gases, expressed in CO2 equivalent terms at summary
inventory level, using GWP values provided by the IPCC
in its Second Assessment Report... based on the effects of
greenhouse gases over a 100-year time horizon.^
14 Carbonaceous aerosols are aerosols that are comprised mainly of organic substances and forms of black carbon (or soot)
(IPCC 2001).
15 Volcanic activity can inject significant quantities of aerosol producing sulfur dioxide and other sulfur compounds into the stratosphere,
which can result in a longer negative forcing effect (i.e., a few years) (IPCC 1996).
'6 Carbon comprises 12/44ths of carbon dioxide by weight.
'^ Framework Convention on Climate Change; ; 1 November 2002; Report of the Conference
of the Parties at its eighth session; held at New Delhi from 23 October to 1 November 2002; Addendum; Part One: Action taken by the
Conference of the Parties at its eighth session; Decision 18/CP.8; Communications from Parties included in Annex I to the Convention:
Guidelines for the Preparation of National Communications by Parties Included in Annex I to the Convention, Part 1: UNFCCC reporting
guidelines on annual inventories; p. 7. (UNFCCC 2003)
1-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 1-2: Global Warming Potentials and
Atmospheric Lifetimes (Years) Used in this Report
GO? ••/
N.,0
we«t3.
m
•HRMS2B
1,3ft}
6,500
r,m
;;P» 1S86)
b The GWP of CH4 includes the direct effects and those indirect effects
due to the production of tropospheric ozone and stratospheric water
vapor. The indirect effect due to the production of C02 is not included.
Greenhouse gases with relatively long atmospheric
lifetimes (e.g., CO2, CH4, N2O, HFCs, PFCs, and SF6)
tend to be evenly distributed throughout the atmosphere,
and consequently global average concentrations can be
determined. The short-lived gases such as water vapor, carbon
monoxide, tropospheric ozone, ozone precursors (e.g., NOX,
and NMVOCs), and tropospheric aerosols (e.g., SO2 products
and carbonaceous particles), however, vary regionally, and
consequently it is difficult to quantify their global radiative
forcing impacts. No GWP values are attributed to these
gases that are short-lived and spatially inhomogeneous in
the atmosphere.
1 .2. Institutional Arrangements
The U.S. Environmental Protection Agency (EPA), in
cooperation with other U.S. government agencies, prepares
the Inventory of U.S. Greenhouse Gas Emissions and Sinks.
A wide range of agencies and individuals are involved in
supplying data to, reviewing, or preparing portions of the
U.S. Inventory — including federal and state government
authorities, research and academic institutions, industry
associations, and private consultants.
Within EPA, the Office of Atmospheric Programs (OAP)
is the lead office responsible for the emission calculations
provided in the Inventory, as well as the completion of the
National Inventory Report and the Common Reporting
Format tables. The Office of Transportation and Air Quality
(OTAQ) is also involved in calculating emissions for the
Inventory. While the U.S. Department of State officially
submits the annual Inventory to the UNFCCC, EPA's
OAP serves as the focal point for questions and comments
on the U.S. Inventory. The staff of OAP and OTAQ
coordinates the annual methodological choice, activity
data collection, and emission calculations at the individual
source category level. Within OAP, an Inventory coordinator
compiles the entire Inventory into the proper reporting
format for submission to the UNFCCC, and is responsible
for the collection and consistency of cross-cutting issues
in the Inventory.
Several other government agencies contribute to the
collection and analysis of the underlying activity data
used in the Inventory calculations. Formal relationships
exist between EPA and other U.S. agencies that provide
for the provision of official data for use in the Inventory.
The U.S. Department of Energy's Energy Information
Administration provides national fuel consumption data
and the U.S. Department of Defense provides military fuel
consumption and bunker fuels. Informal relationships also
exist with other U.S. agencies to provide activity data for
use in EPA's emission calculations. These include: the U.S.
Department of Agriculture, the U.S. Geological Survey,
the Federal Highway Administration, the Department of
Transportation, the Bureau of Transportation Statistics,
the Department of Commerce, the National Agricultural
Statistics Service, and the Federal Aviation Administration.
Academic and research centers also provide activity data
and calculations to EPA, as well as individual companies
participating in voluntary outreach efforts with EPA.
Finally, the U.S. Department of State officially submits the
Inventory to the UNFCCC each April.
1.3. Inventory Process
EPA has a decentralized approach to preparing the
Inventory, which consists of a National Inventory Report
(NIR) and Common Reporting Format (CRF) tables. The
Inventory coordinator at EPA is responsible for compiling
Introduction 1-7
-------
Box 1-1: The IPCC Third Assessment Report and Global Warming Potentials
The IPCC recently pblisbed its ThW Assessment Report (TAR), providing fte most cwiertaiid«orr^Ww8ive sdenttfic assesswent of cBmate
change. Within this report, the GWPs of several gases were revised relative to the IPCC's Sewnd Asse^aiBt Reporj |SAR), and (^ SWPs have
been calculated for an expanded set of gases. Since the SAR, the IPCC has applied an improved calculation of C02 radiative forcing and an improved
C02 response function (presented in WMO 1999). The GWPs are drawn from WMO (1999) and th«.SAR, with updates for flwse casss where
significantly different new laboratory or radiative transfer results have been published. Additionally, the atmospheric lifetimes of some gases have been
recalculated. Because the revised radiative forcing of C02 is about 12 percent lower than that in the SAR, iifa GWPs of the other gases relative to C02
tend to be larger, taking into account revisions in lifetimes. In addition, the values for radiative forcing and lifetimes nave been calculated tor a variety
of halocarbons, which were not presented in the SAR. Table 1 -3 presents the new GWPs, relative to those presented in the SAR.
Table 1-3: Comparison of 100 Year GWPs
Gas
C02
CH4*
N20
HFC-23
HFC-32
HFC-125
HFC-134a
HFC-143a
HFC-1523
HFC-227ea
HFC-236fa
HFC-4310mee
CF4
C2F6
C^io
C6Fi4
SF6
SAR
1
21
310
11,700
650
2,800
1,300
3,800-
140
2,900
6,300
1,300
6,500
9,200
7,000
7,400
23,900
TAR
1
23
296 '
12,000
550
3,400
1,300
4,300
120
3,500
9,400
1,500
5,700
11,900
8,600
9,000
22,200
CD
NC
2
{14}
300
(100)
. 600
NC
500
(20)
600
3, tOO
200
(800)
2,700
1,600
1,600
(1,700)
taupe
NC
10%
(5%)
3%
(15%)
21%
NC
13%
(14%)
21%
49%
15%
(12%)
29%
23%
22%
(7%)
Source: (IPCC 2001)
NC (No Change)
Note: Parentheses indicate negative values.
The GWP of CH4 includes the direct effects and those indirect effects due to the production of tropospneric ozone and stratospheric water vapor. The indirect effect
due to the production of C02 is not included.
Although the GWPs have been updated by the IPCC, this report uses GWPs from the SAR. The UNFCCC reporting guidelines for national inventories18
were updated in 2002 but continue to require the use of GWPs from the SAR so that current estimates of aggregate greenhouse gas emissions for 1990
through 2002 are consistent and comparable with estimates developed prior to the publication of the TAR. Therefore, to comply with international reporting
standards under the UNFCCC, official emission estimates are reported by the United States using SAR GWP values. For informational purposes, emission
estimates that use the updated GWPs are presented below and in even more detail in Annex 6.1. Overall, these revisions to GWP values do not have a
significant effect on U.S. emission trends, as shown in Table 1-4. All estimates provided throughout this report are also presented in unweighted unite.
Table 1 -4: Effects on U.S. Greenhouse Gas Emission Trends Using IPCC SAR ami TAR GWP Values (Tg C02 Eq.)
Change from 1990 to 2002 Revisions to Annual Estimates
Gas SAR TAR 1990 2002
C02
CH4
N20
HFCs, PFCs, and SF6
Total
Percent Change
780.0
(44.6)
22.7
47.3
805.4
13.1%
780.0
(48.8)
21.6
46.9
799.8
13.0%
0
61.2
(17.8)
(2.6)
40.9
. 0.7%
0
57.0 •,'
(18.8)
(3.0)
35.2 •
0.5%
Note: Parentheses indicate negative values. Totals may not sum due to Independent rounding.
See .
1-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 1-5 below shows a comparison of total emission estimates by sector using both the IPCC SAR and TAR SWP values. For most sectors,
the change in emissions was minimal. The effect on emissions from waste was by far the greatest (an average of 8.7 percent), due the predominance
of CH4 emissions in this sector. Emissions from all other sectors were comprised of mainly C02 or a mix of gases, which moderated the effect of
the changes.
Table 1-5: Comparison of Emissions by Sector using IPCC SAR and TAR GWP Values (Tg C02Eq.)
Sector
1990
Energy
SAR SWP (Used In Inventory) 5,144.5
TAR SWP 5,165.3
Difference (%) 0:4%
297.4
293.6
(1.3%)
4.3
4.1
(4.5%)
436.0
438.4
0.5%
(957.9)
(957.9)
0.0%
246.9
268.6
8.8%
SAR SWP (Used in Inventory)
TAR SWP
Difference {%)
Solvent and Otter Product Use
SAR SWP (Used In Inventory)
TAR SWP
Difference (%)
Agriculture
SAR SWP (Used In Inventory)
TAR SWP
Difference (%)
Land-Use Change and Forestry
SAR SWP (Used In Inventory)
TAR SWP
Difference (%)
Waste
SAR SWP (Used In Inventory)
TAR SWP
Difference (%)
Net Emissions (Sources and Sinks)
SAR GWP (Used In Inventory) 5,171.3
TAR SWP 5,212.2
Difference (%) 0.8%
NC (No change)
Note: Parentheses Indicate negative values. Totals may not sum due to Independent rounding.
1996
5,646.4
5,665.4
0.3%
318.3
314.1
(1.3%)
4.5
4.3
(4.5%)
468.3
470.0
0.4%
(1,055.2)
(1,055.2)
0.0%
249.9
271.7
8.7%
5,632.1
5,670.3
0.7%
1997
5,716.6
5,735.3
0.3%
324.1
320.5
(1.1%)
4.8
4.6
(4.5%)
473.8
475.3
0.3%
(821.0)
(821.0)
0.0%
245.2
266.6
8.7%
5,943.5
5,981.2
0.6%
1998
5,738.6
5,757.1
0.3%
331.9
329.1
(0.9%)
4.8
4.6
(4.5%)
476.2
477.7
0.3%
(705.8)
(705.8)
0.0%
239.0
259.7
8.7%
6,084.7
6,122.3
0.6%
1999
5,806.1
5,823.8
0.3%
326.2
322.6
(1.1%)
4.8
4.6
(4.5%)
474.2
475.9
0.3%
(675.8)
(675.8)
0.0%
241.2
262.0
8.6%
6,176.8
6,213.1
0.6%
2000
5,991.4
6,009.3
0.3%
329.3
325.6
(1.1%)
4.8
4.6
(4.5%)
469.9
471.4
0.3%
(690.2)
(690.2)
0.0%
243.0
264.0
8.6%
6,348.2
6,384.7
0.6%
2001
5,871.9
5,889.7
0.3%
301.9
298.3
(1.2%)
4.8
4.6
(4.5%)
468.6
470.1
0.3%
(689.7)
(689.7)
0.0%
236.8
257.2
8.6%
6,194.1
6,230.1
0.6%
2002
5,914.8
5,932.0
0.3%
310.7
307.0
(1.2%)
4.8
4.6
(4.5%)
467.1
468.6
0.3%
(690.7)
(690.7)
0.0%
237.2
257.7
8.6%
6,243.8
6,279.1
0.6%
all emission estimates, and ensuring consistency and
quality throughout the NIR and CRF tables. Emission
calculations for individual sources are the responsibility
of individual source leads, who are most familiar with
each source category.and the unique characteristics of its
emissions profile. The individual source leads determine
the most appropriate methodology and collect the best
activity data to use in the emission calculations, based
upon their expertise in the source category, as well as
coordinating with researchers and contractors familiar
with the sources. A multi-stage process for collecting
information from the individual source leads and producing
the Inventory is undertaken annually to compile all
information and data.
Introduction 1-9
-------
Methodology Development, Data
Collection, and Emissions and Sink
Estimation
Source leads at EPA collect input data and, as necessary,
evaluate or develop the estimation methodology for the
individual source categories. For most source categories,
the methodology for the previous year is applied to the
new "current" year of the Inventory, and Inventory analysts
collect any new data or update data that have changed from
the previous year. If estimates for a new source category are
being developed for the first time, or if the methodology is
changing for an existing source category (e.g., the United
States is implementing a higher Tiered approach for that
source category), then the source category lead will develop
a new methodology, gather the most appropriate activity
data and emission factors (or in some cases direct emission
measurements) for the entire time series, and conduct a
special source-specific peer review process involving relevant
experts from industry, government, and universities.
Once the methodology is in place and the data are
collected, the individual source leads calculate emissions and
sink estimates. The source leads then update or create the
relevant text and accompanying annexes for the Inventory.
Source leads are also responsible for completing the relevant
sectoral background tables of the Common Reporting Format,
conducting quality assurance and quality control (QA/QC)
checks, and uncertainty analyses, where appropriate.
Summary Spreadsheet Compilation and
Data Storage
The Inventory coordinator at EPA collects the source
categories' descriptive text and Annexes, and also aggregates
the emission estimates into a summary spreadsheet that
links the individual source category spreadsheets together.
This summary sheet contains all of the essential data in one
central location, in formats commonly used in the Inventory
document. In addition to the data from each source category,
national trend and related data is also gathered in the summary
sheet for use in the Executive Summary, Introduction, and
Recent Trends sections of the Inventory report. Electronic
copies of each year's summary spreadsheet, which contains
all the emission and sink estimates for the United States, are
kept on a central server at EPA under the jurisdiction of the
Inventory coordinator.
National Inventory Report Preparation
The NIR is compiled from the sections developed
by each individual source lead. In addition, the Inventory
coordinator prepares a brief overview of each chapter that
summarizes the emissions from all sources discussed in
the chapters. The Inventory coordinator then carries out a
key source analysis for the Inventory, consistent with the
IPCC Good Practice Guidance and in accordance with
the reporting requirements of the UNFCCC. Also at this
time, the Introduction, Executive Summary, and Recent
Trends sections are drafted, to reflect the trends for the
most recent year of the current Inventory. The analysis of
trends necessitates gathering supplemental data, including
weather and temperature conditions, economic activity and
gross domestic product, population, atmospheric conditions,
and the annual consumption of electricity, energy, and fossil
fuels. Changes in these data are used to explain the trends
observed in greenhouse gas emissions in the United States.
Furthermore, specific factors that affect individual sectors
are researched and discussed. Many of the factors that affect
emissions are included in the Inventory document as separate
analyses or side discussions in boxes within the text. Text
boxes are also created to examine the data aggregated in
different ways than in the remainder of the document, such
as a focus on transportation activities or emissions from
electricity generation. The document is prepared to match
the specification of the UNFCCC reporting guidelines for
National Inventory Reports.
Common Reporting Format Table
Compilation
The CRF tables are compiled from individual tables
completed by each individual source lead, which contain
source emissions and activity data. The Inventory coordinator
integrates the source data into the complete CRF tables for
the United States, assuring consistency across all sectoral
tables. The summary reports for emissions, methods, and
emission factors used, the overview tables for completeness
and quality of estimates, the recalculation tables, the notation
key completion tables, and the emission trends tables are then
completed by the Inventory coordinator. Internal automated
quality checks on the CRF tables, as well as reviews by the
source leads, are completed for the entire time series of CRF
tables before submission.
1-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Box 1-2: IPCC Good Practice Guidance
In response to a request by Parties in 1998 to tie United Nations Framework Convention on Climate Change (UNFCCC), the Inter-
governmental Panel on Climate Change (JPC$ prepared and published a report on Inventory good practice. The report, eriffltei Good
Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories (IPCC Good Practice Guid^^
witt) extensive participation of experts from the United States and many other countries.19 It focuses on providing direction to countries
to produce emission estimates that are as accurate and transparent as possible, with the feast possible uncertainty. In addition, the IPCC
Good Practice Guidance was designed as a tool to complement the methodologies suggested In the Revised 1996 IPCC Guidelines for
National Greenhouse Gas Inventories (IPCC Guidelines). ' V^; \
In order to obtain these goals,/PCC Good Pracf/ceGu/yance gives specific guidance in the following areas:
• Selection of the most appropriate esBmato raetjiirf, wl^
• Implementation of quality control and quality assurance measures
* Proper assessment and documentation of data and information
• Quantification of uncertainties for most source categories
The IPCC accepted ihe Land Use, Land-Use Chang*, and Foresiif (LULUCF) Good Practice fiufdance report in 2003 and Parties will
be required to implement Its guidance beginning with the 2005 Inventory submission.
QA/QC and Uncertainty
QA/QC and uncertainty analyses are supervised by
the QA/QC coordinator, who has general oversight over
the implementation of the QA/QC plan and the overall
uncertainty analysis for the Inventory (see section on QA/QC
and Uncertainty, below). The QA/QC coordinator works
closely with the source leads to ensure a consistent QA/QC
plan and uncertainty analysis is implemented across all
inventory sources. The inventory QA/QC plan, detailed in
a following section, is consistent with the quality assurance
procedures outlined by EPA.
Expert and Public Review Periods
During the Expert Review period, a first draft of the
document is sent to a select list of technical experts outside
of EPA. The purpose of the Expert Review is to encourage
feedback on the methodological and data sources used in
the current Inventory, especially for sources which have
experienced any changes since the previous Inventory.
Once comments are received and addressed, a second
draft of the document is released for public review by
publishing a notice in the U.S. Federal Register and posting
the document on the EPA Web site. The Public Review
period allows for a 30 day comment period and is open to
the entire U.S. public.
Final Submittal to UNFCCC and Document
Printing
After the final revisions to incorporate any comments
from the Expert Review and Public Review periods, EPA
prepares the final National Inventory Report and the ac-
companying Common Reporting Format Tables. The U.S.
Department of State sends the official submission of the
U.S. Inventory to the UNFCCC. The document is then
formatted for printing, posted online, printed by the U.S.
Government Printing Office, and made available for the
general public.
1.4. Methodology and Data Sources
Emissions of greenhouse gases from various source and
sink categories have been estimated using methodologies that
are consistent with the Revised 1996 IPCC Guidelines for
National Greenhouse Gas Inventories (IPCC/UNEP/OECD/
IEA 1997). To the extent possible, the present report relies
on published activity and emission factor data. Depending
on the emission source category, activity data can include
fuel consumption or deliveries, vehicle-miles traveled, raw
material processed, etc. Emission factors are factors that
relate quantities of emissions to an activity. For some sources,
IPCC default methodologies and emission factors have been
See
Introduction 1-11
-------
employed. However, for most emission sources, the IPCC
methodologies were expanded and more comprehensive
methods were applied.
Inventory emission estimates from energy consumption
and production activities are based primarily on the latest
official fuel consumption data from the Energy Information
Administration (EIA) of the U.S. Department of Energy and
augmented with additional data where available. Emission
estimates for NOX, CO, and NMVOCs were obtained, except
where noted, from preliminary data (EPA 2003). In their
final iteration, these data will be published on the National
Emission Inventory (NEI) Air Pollutant Emission Trends
web site, which provides the latest estimates of regional
and national emissions of local air pollutants. Emissions
of these pollutants are estimated by the EPA based on
statistical information about each source category, emission
factors, and control efficiencies. While the EPA's estimation
methodologies for local air pollutants are conceptually similar
to the IPCC recommended methodologies, the large number
of sources EPA used in developing its local air pollutant
estimates makes it difficult to reproduce the methodologies
from EPA (2003) in this inventory document. In these
instances, the references containing detailed documentation
of the methods used are identified for the interested reader.
For agricultural sources, the EPA local air pollutant emission
estimates were supplemented using activity data from other
agencies. Complete documentation of the methodologies
and data sources used is provided in conjunction with the
discussion of each source and in the various annexes.
Emissions from fossil fuels combusted in civilian and
military ships and aircraft engaged in the international
transport of passengers and cargo are not included in U.S.
totals, but are reported separately as international bunkers in
accordance with IPCC reporting guidelines (IPCCAJNEP/
OECD/IEA 1997). Carbon dioxide emissions from fuel
combusted within U.S. territories, however, are included in
U.S. totals.
The UNFCCC reporting guidelines require countries to
complete a "top-down" reference approach for estimating
CO2 emissions from fossil fuel combustion in addition to
their "bottom-up" sectoral methodology. This estimation
method uses alternative methodologies and different data
sources than those contained in that section of the Energy
chapter. The reference approach estimates fossil fuel
consumption by adjusting national aggregate fuel production
data for imports, exports, and stock changes rather than
relying on end-user consumption surveys (see Annex 4). The
reference approach assumes that once carbon-based fuels
are brought into a national economy, they are either saved
in some way (e.g., stored in products, kept in fuel stocks,
or left unoxidized in ash) or combusted, and therefore the
carbon in them is oxidized and released into the atmosphere.
Accounting for actual consumption of fuels at the sectoral
or sub-national level is not required.
1.5. Key Sources
The IPCC's Good Practice Guidance (IPCC 2000)
defines a key source category as a "[source category] that
is prioritized within the national inventory system because
its estimate has a significant influence on a country's total
inventory of direct greenhouse gases in terms of the absolute
level of emissions, the trend in emissions, or both."20 By
definition, key source categories include those sources that
have the greatest contribution to the absolute level of national
emissions. In addition, when an entire time series of emission
estimates is prepared, a thorough investigation of key source
categories must also account for the influence of trends of
individual source categories. Therefore, a trend assessment is
conducted to identify source categories for which significant
uncertainty in the estimate would have considerable effects
on overall emission trends. This analysis culls out source
categories that diverge from the overall trend in national
emissions. Finally, a qualitative evaluation of key source
categories is performed to capture any categories that were
not identified in either of the quantitative analyses.
A Tier 1 approach, as defined in the IPCC's Good
Practice Guidance (IPCC 2000), was implemented to
identify the key source categories for the United States.
Using this approach, a number of key source categories were
identified based on an assessment of their absolute emission
level and/or trend in emissions.
20 See chapter 7 "Methodological Choice and Recalculation" in IPCC (2000) < http://www.ipcc-nggip.iges.or.jp/public/gp/gpgaum.htm>.
1-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Due to the relative quantity of CO2 emissions from fossil
fuel combustion—particularly from mobile combustion in
road vehicles and stationary combustion of coal, gas, and
oil—these sources contributed most to this year's level
assessment. Additionally, the following sources were the
largest contributors to the level assessments for each year
(listed in descending order as they appear in recent years):
• Direct N2O from agricultural soils;
• CH4 from solid waste disposal sites;
• CO2 emissions from mobile combustion in the
aviation sector;
• Fugitive emissions from natural gas operations;
• CH4 from enteric fermentation in domestic livestock;
• Indirect N2O emissions from nitrogen used in
agriculture;
• CO2 emissions from iron and steel production;
• Fugitive emissions from coal mining;
• N2O emissions from mobile combustion in road
vehicles; and
• CO2 emissions from cement production.
The remaining key sources identified under the level
assessment varied by year. The following six source
categories were determined to be key using the level
assessment for only part of the complete time series:
• HFC and PFC emissions from substitutes for ozone
depleting substances (1996 to 2002);
• CO2 emissions from mobile combustion in the marine
sector (1990-1997, 1999-2000, 2002);
• HFC-23 emissions from HCFC-22 manufacture (1990,
1995, 1996, 1998);
• SF6 emissions from electrical equipment (1990-1994);
• CH4 emissions from manure management (1991 -1999,
2001); and
• CH4 emissions from wastewater handling (1995).
Although other sources have fluctuated by greater
percentages since 1990, by virtue of their size, CO2 emissions
from mobile combustion from road vehicles and stationary
combustion of coal and oil are the greatest contributors to
the overall trend for 2002. The fourth largest contributor to
the overall trend in 2002—moving ahead of CO2 emissions
from stationary combustion of gas—is emissions from
substitutes for ozone depleting substances (ODSs). These
emissions have grown quickly with the phase out of ODS
under the Montreal Protocol.
Two additional source categories with trends of note
are fugitive emissions from coal mining and PFC emissions
from aluminum manufacturing, which decreased from
1990 through 2002 by approximately 36 and 71 percent,
respectively. Reductions in emissions from coal mining are
primarily due to EPA's voluntary coalbed methane capture
program and the mining of less gassy coal than in previous
years. PFC emissions have decreased primarily as a result of
emission reduction activities by the aluminum industry.
The remaining source categories that were identified as key
sources based solely on a trend assessment are listed below.
• Fugitive emissions from oil operations;
• N2O emissions from adipic acid production; and
• CO2 emissions from waste incineration.
In addition to conducting Tier 1 level and trend
assessments, a qualitative assessment of the source categories,
as described in the IPCC's Good Practice Guidance (IPCC
2000), was conducted to capture any key sources that were
not identified by either quantitative method. Two additional
key sources were identified using this qualitative assessment.
A brief discussion of the reasoning for the qualitative
designation is given below:
• International bunker fuels are fuels consumed for
aviation or marine international transport activities,
and emissions from these fuels are reported separately
from totals in accordance with IPCC guidelines. If these
emissions were included in the totals, bunker fuels would
qualify as a key source according to the Tier 1 approach.
The amount of uncertainty associated with estimation of
emissions from international bunker fuels also supports
the qualification of this source category as key.
• Non-energy uses of fossil fuels represent a significant
percentage of the total carbon inventory, and the fact that
small changes in storage factors for these non-energy
uses may result in large changes in storage and emissions
qualifies this source category as key.
Table 1 -6 presents the key source categories for the United
States based on the Tier 1 approach using emissions data in this
report, and ranked according to their sector and global warming
potential-weighted emissions in 2002. The table also indicates
the criteria used in identifying these source categories (i.e., level,
trend, and/or qualitative assessments). Please see Annex 1 for
additional information regarding the key source categories in the
United States and the methodologies used to identify them.
Introduction 1-13
-------
Table 1-6: Key Source Categories for the United States (1990-2002) Based on Tier 1 Approach
IPCC Source Categories
Gas
Level Trend
2002 Emissions
G02 Emissions from Stationary Combustion - Goal
Mobile CombusitoB: Road ^Qt«
C02 Emissions from Senary Cornli^toi ~Sas
C02 Emissions from Stationary Combustion -Oil
MooileGamtjysfloE AvMp - ,
Fugitive Emissions from Natural Gas Operations
Fugitive Emissions from Coal Mining & Handling
Mobile Combustion:: IferJos
MoWte Comowste: Roatf & Wrer
Fugitive Emissions from Oil Operations
Intemttional Sunter ftjeteB
Non-Eflergy Use Of Fos^l FueP
Industrial Processes
Emissions from Substitutes for Ozone Depleting Substances
Cft Emissions Jtorn!r« aft SJs$ Bwlpflori
G0? lirpsicws frfm Gemeflt Produrton
HFC-23 ErissWisfroni HCFC€2 Mawifattire
SF6f missions from ftetteal fqWpment
NgQ EmissiOfiis from Ad^te AiW Produ«?ton
PFC Emissions from Ataminum ProAiirjtion
Agriculture
Direct fiy) Emissions fromAgrtcuttefal Soils
CH4 Emissions from Enteric Fermentation in Domestic Livestock
Indirect N20 Emissions from Nitrogen Used in Agriculture
CH4 Emissions from Manure Manapfneflt
Waste
CH4 Emissions from Solid Waste Disposal Sites
CH4 Emissions from Wastewater Treatment
C02 Emissions from Waste Incineration
Subtotal ot Key Source Emissions
Total Emissions
Percent of Total
G02 / / „•-'••"
C02 ^ ^
co2 s .'/••••
G02 / •
C02 / V
CH4 / /
CH4 / / \
C02 /
N20 /
GH4 -/..••
Several /
C02 /
Several / /
C02 / /
C02 S ".•/'
HFCs / /
SF6 / .'
-------
• The plan includes expert review as well as QC—for
both the inventory estimates and the Inventory (which is
the primary vehicle for disseminating the results of the
inventory development process). In addition, the plan
provides for public review of the Inventory.
• The QC process includes both Tier 1 (general) and
Tier 2 (source-specific) quality controls and checks, as
recommended by IPCC Good Practice Guidance.
• Investigations of secondary data quality and source-spe-
cific quality checks (Tier 2 QC) are considered in parallel
and coordination with the uncertainty assessment; the
development of protocols and templates provides for
more structured communication and integration with the
suppliers of secondary information.
• The plan contains record-keeping provisions to track
what procedures have been followed, and the results
of the QA/QC and uncertainty analysis, and contains
feedback mechanisms for corrective action based on
the results of the investigations, thereby providing
for continual data quality improvement and guided
research efforts.
• The plan is designed so that QA/QC procedures are
implemented throughout the whole inventory develop-
ment process—from initial data collection, through
preparation of the emission estimates, to publication of
the Inventory.
• The plan includes a schedule for multi-year
implementation.
• The plan promotes and involves coordination and in-
teraction within the EPA, across Federal agencies and
departments, state government programs, and research
institutions and consulting firms involved in supply-
ing data or preparing estimates for the inventory. The
QA/QC plan itself is intended to be revised and reflect
new information that becomes available as the program
develops, methods are improved, or additional support-
ing documents become necessary. For example, the
availability of new information or additional detail on
techniques or procedures for checking the quality of
data inputs or emission calculations could necessitate
revising the procedures in the Procedures Manual or
preparing a background paper expanding on procedures
to be used.
The quality checking and control activities described
in the U.S. QA/QC plan occur throughout the inventory
process; QA/QC is not separate from, but is an integral part
of, preparing the inventory. Quality control—in the form of
both good practices (such as documentation procedures) and
checks on whether good practices and procedures are being
followed—is applied at every stage of inventory development
and document preparation. In addition, quality assurance
occurs at two stages—an expert review and a public review.
While both phases can significantly contribute to inventory
quality, the public review phase is also essential for promoting
the openness of the inventory development process and the
transparency of the inventory data and methods.
QA/QC procedures guide the process of ensuring
inventory quality by describing data and methodology
checks, developing processes governing peer review and
public comments, and developing guidance on conducting
an analysis of the uncertainty surrounding the emission
estimates. The QA/QC procedures also include feedback
loops and provide for corrective actions that are designed to
improve the inventory estimates over time.
In addition, based on the national QA/QC plan for
the Inventory, source-specific QA/QC plans have been
developed for a limited number of sources. These plans
follow the procedures outlined in the national QA/QC plan,
tailoring the procedures to the specific text and spreadsheets
of the individual sources. For the current Inventory, source-
specific plans have been developed and implemented for
the majority of sources within the Energy and Industrial
Process sectors.
Throughout this Inventory, a minimum of a Tier 1 QA/
QC analysis has been undertaken. Where QA/QC activities
for a particular source go beyond the minimum Tier 1 level,
further explanation is provided within the respective source
category text.
1.7. Uncertainty and Limitations of
Emission Estimates
Uncertainty estimates are an essential element of a
complete and transparent emissions inventory. Uncertainty
information is not intended to dispute the validity of the
inventory estimates, but to help prioritize efforts to improve
the accuracy of future inventories and guide future decisions
on methodological choice. While the U.S. Inventory calculates
its emission estimates with the highest possible accuracy,
uncertainties are associated to a varying degree with the
Introduction 1-15
-------
development of emission estimates for any inventory. Some
of the current estimates, such as those for CO2 emissions
from energy-related activities and cement processing, are
considered to have minimal uncertainty associated with them.
For some other categories of emissions, however, a lack of
data or an incomplete understanding of how emissions are
generated increases the uncertainty surrounding the estimates
presented. Despite these uncertainties, the UNFCCC reporting
guidelines follow the recommendation in the Revised 1996
IPCC Guidelines for National Greenhouse Gas Inventories
(IPCC/UNEP/OECD/IEA 1997) and require that countries
provide single point estimates for each gas and emission
or removal source category. Within the discussion of each
emission source, specific factors affecting the uncertainty
associated with the estimates are discussed.
The IPCC methodologies provided in the Revised 1996
IPCC Guidelines represent baseline methodologies for a
variety of source categories, and many of these methodologies
continue to be improved and refined as new research and data
become available. This report uses the IPCC methodologies
when applicable, and supplements them with other available
methodologies and data where possible. The United States
realizes that additional efforts are still needed to improve
methodologies and data collection procedures. Specific areas
requiring further research include:
• Incorporating excluded emission sources. Quantitative
estimates for some of the sources and sinks of green-
house gas emissions are not available at this time. In
particular, emissions from some land-use activities and
industrial processes are not included in the inventory
either because data are incomplete or because method-
ologies do not exist for estimating emissions from these
source categories. See Annex 5 for a discussion of the
sources of greenhouse gas emissions and sinks excluded
from this report.
• Improving the accuracy of emission factors. Further
research is needed in some cases to improve the ac-
curacy of emission factors used to calculate emissions
from a variety of sources. For example, the accuracy
of current emission factors applied to CH4 and N2O
emissions from stationary and mobile combustion is
highly uncertain.
• Collecting detailed activity data. Although methodologies
exist for estimating emissions for some sources, problems
arise in obtaining activity data at a level of detail in which
aggregate emission factors can be applied. For example,
the ability to estimate emissions of SF6 from electrical
transmission and distribution is limited due to a lack of
activity data regarding national SF6 consumption or aver-
age equipment leak rates.
The IPCC provides good practice guidance on two
approaches—Tier 1 and Tier 2—to estimating uncertainty for
individual source categories. The Tier 1 method is a spreadsheet-
based analysis that estimates uncertainties by using the error
propagation equation. The spreadsheet employs uncertainty
ranges for activity data and emission factors consistent with
the sectoral good practice guidance. The Tier 2 uncertainty
estimation methodology employs the Monte Carlo Stochastic
Simulation technique. The principle of Monte Carlo analysis
is to select random values of emission factor and activity data
from within their individual probability density functions,
and to calculate the corresponding emission values. Tier 2
uncertainty analysis was applied wherever data and resources
permitted. Consistent with the Good Practice Guidance, over
a multi-year timeframe, the United States expects to continue
to improve the uncertainty estimates presented in this report
and add quantitative estimates of uncertainty where none
currently exist. See Annex 7, Uncertainty, of this report for
further details on the U.S. process for estimating uncertainties
associated with emission estimates and for a more detailed
discussion of the limitations of the current analysis and plans
for improvement.
While there are two types of estimation uncertainty,
parameter uncertainty and model uncertainty, the Tier
1 and Tier 2 approaches were applied only to estimate
parameter uncertainty of emission estimates. Parameter
uncertainty refers to the uncertainty associated with
quantifying the parameters used as inputs (e.g., activity data
and emission factors) to the emission estimation models.
Model uncertainty refers to the uncertainty associated with
developing mathematical equations or models to characterize
the emission and/or removal processes. Model uncertainties
can be evaluated by comparing the model results with the
results of other models that are developed to characterize the
same emission generation process and through sensitivity
analysis. Model uncertainties for some sources are identified,
but not evaluated.
Emissions calculated for the U.S. Inventory reflect
current best estimates; in some cases, however, estimates
are based on approximate methodologies, assumptions, and
1-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
incomplete data. As new information becomes available in
the future, the United States will continue to improve and
revise its emission estimates.
1.8. Completeness
This report, along with its accompanying CRF tables,
serves as a thorough assessment of the anthropogenic sources
and sinks of greenhouse gas emissions for the United States
for the time series 1990 through 2002. Although this report
is intended to be comprehensive, certain sources have been
identified yet excluded from the estimates presented for various
reasons. Generally speaking, sources not accounted for in this
Inventory are excluded due to data limitations or a lack of
thorough understanding of the emission process. The United
States is continually working to improve upon the understanding
of such sources and seeking to find the data required to estimate
related emissions. As such improvements are made, new
emission sources are quantified and included in the Inventory.
For a complete list of sources excluded, see Annex 5.
1.9. Organization of Report
In accordance with the Revised 1996IPCC Guidelines
for National Greenhouse Gas Inventories (IPCC/UNEP/
OECD/IEA 1997), and the 2003 UNFCCC Guidelines on
Reporting and Review (UNFCCC 2003), this Inventory of
U.S. Greenhouse Gas Emissions and Sinks is segregated
into six sector-specific chapters, listed below in Table 1-7. In
addition, chapters on Trends in Greenhouse Gas Emissions
Table 1-7: IPCC Sector Descriptions
and Other information to be considered as part of the U.S.
Inventory submission are included.
Within each chapter, emissions are identified by the
anthropogenic activity that is the source or sink of the
greenhouse gas emissions being estimated (e.g., coal mining).
Overall, the following organizational structure is consistently
applied throughout this report:
Chapter/IPCC Sector: Overview of emission trends for each
IPCC-defined sector:
Source category: Description of source pathway and
emission trends.
Methodology: Description of analytical methods
employed to produce emission estimates and
identification of data references, primarily for activity
data and emission factors.
Uncertainty: A discussion and quantification of the
uncertainty in emission estimates and a discussion
of time-series consistency.
QA/QC and Verification: A discussion on steps taken
to QA/QC and verify the emission estimates, where
beyond the overall U.S. QA/QC plan, and any key
findings.
Recalculations: A discussion of any data or meth-
odological changes necessitating a recalculation of
previous years' emission estimates, and the impact
of the recalculation on the emission estimates, if
applicable.
Planned Improvements: A discussion on any source-
specific planned improvements, if applicable.
Chapter/IPCC Sector
Activities Included
Energy
Industrial Processes
Solvent and Other Product Use
Agriculture
Land-Use Change and Forestry
Waste
Emissions of al greenhouse gases resulting from stalonary and mobile energy acttvWes
including fuel combustion and fugitive fuel emissions.
By-product or fugitive emissions of greenhouse gases from industtal processes not directly
related to energy activities such as fossil fuel combustion. ;
Emissions, of primarily NMVOCs resulting from fte use of solvents and ly) from
product usage.
Anthropogenic emissions from agricultural activities except fuel combustion, which is
addressed under Energy.
Emissions and removals of C02 from forest management, other land-use activities, and
land-use change,
Emissions from waste management activities,
Source: (IPCC/UNEP/OECD/IEA1997)
Introduction 1-17
-------
Special attention is given to CO2 from fossil fuel transportation), as well as the electricity generation sector,
combustion relative to other sources because of its share of is treated individually. Additional information for certain
emissions relative to other sources and its dominant influence source categories and other topics is also provided in several
on emission trends. For example, each energy consuming Annexes listed in Table 1-8.
end-use sector (i.e., residential, commercial, industrial, and
Table 1-8: List of Annexes
ANNEX 1 Key Source Analysis
ANNEX 2 Methodology and Data for
'- .".-2Li/ ' "''"
C02 Emissions from Fossil Fuel
.... •.•„•_;•.-23.;:'I
ANNEX 3 Methodological Descriptions for Additional Source of Shtfc Categories
Methodology for Estimating CH4 Emissions from Natural Gas Systems
3.12. Methodology for Estimating Net Changes in Forest Carbon Stocks
ppM||iiipnQ^ppiHl«wiN^^
Substances
1-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
2. Trends in Greenhouse Gas
Emissions
2.1. Recent Trends in U.S. Greenhouse Gas Emissions
In 2002, total U.S. greenhouse gas emissions were 6,934.6 teragrams of carbon dioxide equivalent (Tg CO2 Eq.)1
(13.0 percent above 1990 emissions). Emissions rose slightly from 2001 to 2002, increasing by 0.7 percent (50.7 Tg
CO2 Eq.). The following factors were primary contributors to this increase: 1) moderate economic growth in 2002, leading
to increased demand for electricity and fossil fuels, 2) much hotter summer conditions in 2002—in fact, one of the hottest
summers on record—causing an increase in electricity use for air conditioning. (See the following section for an analysis
of emission trends by general economic sectors.) Figure 2-1 through Figure 2-3 illustrate the overall trends in total U.S.
emissions by gas, annual changes, and absolute changes since 1990.
As the largest source of U.S. greenhouse gas emissions, carbon dioxide (CO2) from fossil fuel combustion has accounted
for a nearly constant 80 percent of global warming potential (GWP) weighted emissions since 1990. Emissions from this source
category grew by 17 percent (796.3 Tg CO2Eq.) from 1990 to 2002 and were responsible for most of the increase in national
emissions during this period. From 2001 to 2002, these emissions increased by 52.2 Tg CO2 Eq. (0.9 percent), slightly lower
than the source's average annual growth rate of 1.3 percent from 1990 through 2002. Historically, changes in emissions from
fossil fuel combustion have been the dominant
factor affecting U.S. emission trends.
Changes in CO2 emissions from fossil
fuel combustion are influenced by many
long-term and short-term factors, including
population and economic growth, energy
price fluctuations, technological changes, and
seasonal temperatures. On an annual basis,
the overall consumption of fossil fuels in the
United States generally fluctuates in response to
changes in general economic conditions, energy
prices, weather, and the availability of non-
fossil alternatives. For example, in a year with
increased consumption of goods and services,
low fuel prices, severe summer and winter
weather conditions, nuclear plant closures, and
lower precipitation feeding hydroelectric dams,
Figure 2-1
U.S. Greenhouse Gas Emissions by Gas
8,000 -
7,000 -
6,000
_ 5,000 -
IU
3 4,000 -
ff
3,000
2,000 -
1,000 -
0 -
I MFCs, PFCs, & SF,
I Nitrous Oxide
I Methane
I Carbon Dioxide
6,884 6,935
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Estimates are presented in units of teragrams of carbon dioxide equivalent (Tg CO2 Eq.), which weight each gas by its Global Warming Potential, or
GWP, value. (See section on Global Warming Potentials, Chapter 1.)
Trends in Greenhouse Gas Emissions 2-1
-------
Figure 2-2
Annual Percent Change in U.S. Greenhouse Gas Emissions
3.1%
2.7%
0.7%
there would likely be proportionally greater fossil fuel
consumption than a year with poor economic performance,
high fuel prices, mild temperatures, and increased output
from nuclear and hydroelectric plants.
In the longer-term, energy consumption patterns
respond to changes that affect the scale of consumption (e.g.,
population, number of cars, and size of houses), the efficiency
with which energy is used in equipment (e.g., cars, power
plants, steel mills, and light bulbs) and consumer behavior
(e.g., walking, bicycling, or telecommuting to work instead
of driving).
Energy-related CO2 emissions also depend on the type of
fuel or energy consumed and its carbon intensity. Producing
a unit of heat or electricity using natural gas instead of coal,
for example, can reduce the CO2 because of the lower carbon
content of natural gas. Table 2-1 shows annual changes in
Figure 2-3
Absolute Change in U.S. Greenhouse Gas Emissions
Since 1990
emissions during the last six years for coal, petroleum, and
natural gas in selected sectors.
In 1998, warm winter temperatures contributed to a
significant drop in residential and commercial natural gas
consumption. This drop in emissions from natural gas used
for heating was offset by two factors: 1) electric utility
emissions, which increased in part due to a hot summer and
its associated air conditioning demand; and 2) increased
motor gasoline consumption for transportation.
In 1999, the increase in emissions from fossil fuel
combustion was driven largely by growth in petroleum
consumption for transportation. In addition, residential
and commercial heating fuel demand partially recovered
as winter temperatures dropped relative to 1998, although
temperatures were still warmer than normal.2 These increases
were offset, in part, by a decline in emissions from electric
Table 2-1: Annual Change in C02 Emissions from Fossil Fuel Combustion for Selected Fuels and Sectors
(Tg C02 Eq. and Percent)
Sector
Electricity Generation
Electricity Generation
Electricity Generation
Transportation*
Residential
Commercial
Industrial
Industrial
AH Sectors"
Fuel Type
Coat
Natural Gas
Petroleum
Petroleum
Natural Gas
Natural Gas
Coal
Natural Gas
All Fuels"
1997 to 1998 1998 to 1999
29.1
29.1
29.8
36.2
-23.7
-10.8
-8.1
-11.9
28.4
2%
13%
40%
2%
-9%
-6%
-6%
-2%
1%
§.9
11.9
-7.8
57,5
10.0
1,7
-§J5
-17.9
78.4
0%
5%
-7%
4%
.: 4%
1%
-4%
•4%
t%
1999to200fl
88.0
20.8
-5,6
46.9
13.9
9.0
1.6
7.S
184.7
5%
8%
-6%
3%
5%
5%
1%
2%
3%
2000102001
-81.9
8.4
9.8
-17.4
-10.9
-9.3
-4.9
-39.7
-114.8
-3%
3%
-11%
-1%
4%
-5%
-4%:
-8%.
-2%
2001 to 2002
39.9
10.0
^•27,9
32.5
7.7
4.3
-3.0
-10.4
52.2
2%
3%
-28%
2%
3%
3%
-2%
-2%
1%
3 Excludes emissions tan International Bunker Fuels.
" Includes fuels and sectors not shown In table.
2 Normals are based on data from 1971 through 2000 (EIA 2003b).
2-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
power producers due primarily to: 1) an increase in net
generation of electricity by nuclear plants which reduced
demand from fossil fuel plants; and 2) moderated summer
temperatures compared to the previous year—thereby
reducing electricity demand for air conditioning.
Emissions from fuel combustion increased considerably
in 2000, due to several factors. The primary reason for the
increase was the robust U.S. economy, which produced
a high demand for fuels—especially for petroleum in the
transportation sector—despite increases in the price of
both natural gas and petroleum. Colder winter conditions
relative to the previous year triggered a rise in residential
and commercial demand for heating. Additionally, electricity
generation became more carbon intensive as coal and natural
gas consumption offset reduced hydropower output.
In 2001, economic growth in the United States slowed
considerably for the second time since 1990, contributing
to a decrease in CO2 emissions from fossil fuel combustion,
also for the second time since 1990. A significant reduction
in industrial output contributed to weak economic growth,
primarily in manufacturing, and led to lower emissions from
the industrial sector. Several other factors also played a role
in this decrease in emissions. Warmer winter conditions
compared to 2000, along with higher natural gas prices,
reduced demand for heating fuels. Additionally, nuclear
facilities operated at a very high capacity, offsetting electricity
produced from fossil fuels. Since there are no greenhouse
gas emissions associated with electricity production from
nuclear plants, this substitution reduces the overall carbon
intensity of electricity generation.
Emissions from fuel combustion resumed a modest
growth in 2002, slightly less than the average annual growth
rate since 1990. There were a number of reasons behind this
increase. The U.S. economy experienced moderate growth,
recovering from weak conditions in 2001. Prices for fuels
remained at or below 2001 levels; the cost of natural gas,
motor gasoline, and electricity were all lower-triggering an
increase in demand for fuel. In addition, the United States
experienced one of the hottest summers on record, causing a
significant increase in electricity use in the residential sector
as the use of air-conditioners increased. Partially offsetting
this increased consumption of fossil fuels, however, were
increases in the use of nuclear and renewable fuels. Nuclear
facilities operated at the highest capacity on record in 2002.
Furthermore, there was a considerable increase in the use
of hydroelectric power in 2002 after a very low output the
previous year.
Other significant trends in emissions from additional
source categories over the thirteen-year period from 1990
through 2002 included the following:
• Carbon dioxide emissions from waste combustion in-
creased by 7.9 Tg CO2 Eq. (72 percent), as the volume
of plastics and other fossil carbon-containing materials
in municipal solid waste grew.
• Net CO2 sequestration from land use change and forestry
decreased by 267.1 Tg CO2 Eq. (28 percent), primarily
due to a decline in the rate of net carbon accumulation
in forest carbon stocks. This decline largely resulted
from a decrease in the estimated rate of forest soil
sequestration caused by a slowing rate of increase in
forest area after 1997.
• Methane (CH4) emissions from coal mining dropped
by 29.7 Tg CO2 Eq. (36 percent) as a result of the min-
ing of less gassy coal from underground mines and the
increased use of methane collected from degasification
systems.
• Nitrous oxide emissions from agricultural soil manage-
ment increased by 24.5 Tg CO2 Eq. (9 percent) as crop
and forage production, manure production, and fertilizer
consumption rose.
• Aggregate hydrofluorocarbon (HFC), perfluorocarbon
(PFC) emissions resulting from the substitution of ozone
depleting substances increased by 91.4 Tg CO2 Eq. This
increase was significantly offset, however, by reductions
in PFC emissions from aluminum production (12.9 Tg
CO2 Eq. or 71 percent), reductions in emissions of HFC-
23 from the production of HCFC-22 (15.2 Tg CO2 Eq.
or 43 percent), and reductions of sulfur hexafluoride
(SF6) from electric power transmission and distribution
systems (14.5 Tg CO2 Eq. or 49 percent). Reductions
in PFC emissions from aluminum production resulted
from both industry emission reduction efforts and lower
domestic aluminum production. HFC-23 emissions from
the production of HCFC-22 decreased because a reduc-
tion in the intensity of emissions from that source offset
an increase in HCFC-22 production. Reduced emissions
of SF6 from electric power transmission and distribution
systems are primarily the result of higher purchase prices
for SF6 and efforts by industry to reduce emissions.
Trends in Greenhouse Gas Emissions 2-3
-------
Box 2-1: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data
Total emissions can be compared to other economic and social indices to highlight changes over time. These comparisons include: 1) emissions
per unit of aggregate energy consumption, because energy-related activities are the largest sources of emissions; 2} emissions pet unit of fossil fuel
consumption, because almost all energy-related emissions involve the combustion of fossil fuels; 3) emissions per unit of electricity consumption,
because the electric power industry—utilities arrt nonutilities combined—was the largest source of U.S. greenhouse gas emissions in 2002; 4)
emissions per unit of total gross domestic product as a measure of national economic activity; or 5) emissions per capita.
Table 2-2 provides data on various statistics related to U.S. greenhouse gas emissions normalized to 1990 as a baseline year, Greenhouse gas
emissions in tie United States have grown at an average annual rate of t .0 percent since 1990. This rate is slower than that for total energy or fossil
fuel consumption and much slower than that for either electricity consumption or overall gross domestic product. Total U ,S. greenhouse gas emissions
have also grown more slowly than national populate sinee 1990 (see Figure 2-4). Qveral, gtobaf artwspjtetto (% &w»*a8
complex anthropogenic and natural processes—are increasing at 0.4 percent per year.
Table 2-2: Recent Trends in Various U.S. Data (Index 1990 = 100) and Global Atmospheric C02 Concentration
Variable
Greenhouse Gas Emissions1
Energy Consumption6
Fossil Fuel Consumption6
Electricity Consumption6
SDF
Population11
Atmospheric C02 Concentration8
1991
99
100
99
102
100
101
100
1992
101
101
102
102
• 103
103
101
1993
103
103
104
106
106
104
101
1994
105
105
106
109
110
105
101
1995
106
108
107
112
113
107
102
1996
109
111
111
115
117
108
102
199?
110
112
112
117
122
109
103
1tJt
111
111 '-
113
121
127
111
104
1999
112
114
114
124
133
112
104
2000
115
117
117
128
138
113
104
2001
112
114
115
If 6
139
114
10S
Growth
2002 Rate1
113 te%
115, «%
115 1.2%
121 2J%
142 3.8%
116 1.2%
'• tfll 0.4%
aGWP weighted values
b Energy content weighted values (EIA 2003a)
c Gross Domestic Product in chained 2000 (Mars PEA 2004)
d (U.S. Census Bureau 2003)
e Mauna Loa Observatory, Hawaii (Keeling and Whorf 2003)
f Average annual growth rate
Figure 2-4
U.S. Greenhouse Gas Emissions Per Capita and
Per Dollar of Gross Domestic Product
Source: BEA (2004), U.S. Census Bureau (2003), and emission
estimates in this report.
2-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 2-3: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg C02 Eq.)
Gas/Source
COZ
Fossil Kiel Combustion
Iron and Steel Production
Cement Manufacture
Waste Combustion
Ammonia Production and Urea Application
Lime Manufacture
Limestone and Dolomite Use
Natural Gas Flaring
Aluminum Production
Soda Ash Manufacture and Consumption
Itanium DieSde Production
Phosphoric Acid Production
Carbon Dioxide Consumption
Ferraateys
Land-U$e Change and fcresfty fSM)8
International Buntoer Fuels"
8 iomass Combustion"
CM4
• Landfills
Natural Gas Systems
Enteric Fermentation
Coal Mining
Manure Msnaflem$nt
Wastewater Treatment
Petroleum Systems
Stationary Sources
RiceCuivatfon
Mobil Sources
Abandoned Coal Mines
Petrochemical Production
Iron and Steel Production
Field Burning of Agricultural Residues
Silicon Carbide Production
International Bunker fi/e/s*
H*0
Agricultural Soil Management
Mobile Sources
Manure Management
NfWcAeW
Human Sewage
Stationary Sources
AdipfcActd
N20 Product Usage
Field Burning of Agricultural Residues
Waste Combustion
Internaflonal Bunker fi/efe4
MFCs, PFCs, and SF6
Substitution of Ozone Depleting Substances
HCFC-22 Production
Electrical Transmission and Distribution
Aluminum Production
Semiconductor Manufacture
Magnesium Production and Processing
Total
Net Emissions (Sources and Sinks)
1990
5,002.3
4,814.7
85.4
33,3
10.9
19.3
11.2
5.5
5.8
6.3
4,1
1.3
1.5
0.9
2.0
(957.9)
113,9
216.7
642,7
210.0
122.0
117.9
81.9
31.0
24.1
28.9
8.2
7.1
5.0
3.4
1.2
1.3
0.7
+
0.2
393.2
262.8
50.7
16.2
17.8
12.8
12.6
15.2
4.3
0.4
0.4
1.0
90.9
0.3
35.0
29.2
18.1
2.9
5.4
6,129.1
5,171.3
1996
5,498.5
5,310.1
WJ
37.1
17.2
28.3
13.5
7.8
8.5
5.6
. 4.2
1.7
1.6
0.8
2.0
(fM2)
162.3
244.3
637,8
208.8
127.4
120.5
13.2
34.6
26.9
25.6
8.8
7.0
4.8
6.0
1.6
1.3
0.8
'+.
0.1
436.9
288.1
60.7
17.0
20.7
14.2
13.9
17.0
4.5
0.4
0.4
0.9
114.9
35.0
31.1
24.3
12.5
5.5
6.5
6,687.3
5,632.1
1917
5,577.6
5,384.0
71.9
38.3
17.8
20.7
13.7
7.2
7.9
5.6
4.4
1.8
1.5
0.8
2.0
(827.0)
709,9
233.2
628.8
203.4
126.1
118.3
62.6
36.3
27.4
25.5
7.8
7.5
4.7
5.6
1.6
1.3
0.8
+
0.1
436.3
293.2
60.3
17.3
21.2
14.4
14.0
10.3
4.8
0.4
0.4
1.0
121.7
46.4
30.0
21.7
11.0
6.3
6.3
6,764.4
5,943.5
1998
5,602.5
5,412.4
67.4
39.2
17.1
21.9
13.9
7.4
6.6
5.8
4.3
1.8
1.6
0.9
2.0
(705.8)
115.1
217.2
620.1
196.6
124.5
116.7
62.8
38.8
27.7
25.0
7.2
7.9
4.5
4.8
1.7
1.2
0.8
+
0.2
432.1
294.2
59.6
17.3
20.9
14.7
13.8
6.0
4.8
0.5
0.3
1.0
135.7
56.5
40.2
17.1
9.0
7.1
5.8
6,790.5
6,084.7
1999
5,676.3
5,488.8
64.4
40.0
17.6
20.6
13.5
8.1
6.9
5.9
4.2
1.9
1.5
0.9
2.0
(675.8)
105.3
222.3
613.1
197.8
120.9
116.6
58.9
38.6
28.2
23.7
7.5
8.3
4.5
4.4
1.7
1.2
0.8
+
0.1
428.4
292.1
58.6
17.4
20.1
15.2
13.9
5.5
4.8
0.4
0.3
0.9
134.8
65.8
30.4
16.4
8.9
7.2
6.0
6,852.5
6,176.8
2000
5,859.0
5,673.6
65.7
41.2
18.0
19.6
13.3
6.0
5.8
5.7
4.2
1.9
1.4
1.0
1.7
(690.2)
101.4
226.8
614.4
199.3
125.7
115.7
56.2
38.0
28.4
23.5
7.7
7.5
4.4
4.4
1.7
1.2
0.8
+
0.1
425.8
289.7
57.4
17.7
19.6
15.3
14.4
6.0
4.8
0.5
0.4
0.9
139.1
75.1
29.8
15.9
8.9
6.3
3.2
7,038.3
6,348.2
2001
5,731.8
5,558.8
59.1
41.4
18.8
16.2
123
5.7
5.4
4.1
4.1
1.9
1.3
0.8
1.3
(689.7)
97.9
204.4
605.1
193.2
124.9
114.3
55.6
38.8
28.1
23.5
7.2
7.6
,4.3
4.2
1.4
1.1
0.8
+
0.1
417.3
288.6
55.0
18.0
15.9
15.4
13.9
4.9
4.8
0.5
0.4
0.9
129.7
83.4
19.8
15.6
4.0
4.5
2.5
6,883.9
6,194.1
2002
5,782.4
5fi110
54.4
42.9
18.8
17.7
12.3
5.8
5.3
4.2
4.1
2.0
1.3
1.3
1.2
(690.7)
86.8
207.1
598.1
193.0
121.8
114.4
52.2
39.5
28.7
23.2
6.9
6.8
4.2
4.1
1.5
1.0
0.7
+
0.?
415.8
287.3
52.9
17.8
16.7
15.6
14.0
5.9
4.8
0.4
0.4
0.8
138.2
91.7
19.8
14.8
5.2
4.4
2.4
6,934.6
6,243.8
+ Does not exceed 0.05 Tg CO-, Eq.
a Sinks are only included in net emissions total, and are based partially on projected activity data. Parentheses indicate negative values (or sequestration).
b Emissions from International Bunker Fuels and Biomass Combustion are not included in totals.
Note: Totals may not sum due to independent rounding.
Trends in Greenhouse Gas Emissions 2-5
-------
Table 2-4: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Gg)
Gas/Source
Fossil Fuel CoKitHfSfJon
Iron and Steel Produetai
Cement Manufacture ,
Waste Combustion
Ammonia Production and Urea Application
Lime Manufacture
Limestone and Dolomite Use
Natural Gas Raring
Aluminum Production
Soda Ash Manufacture and Consumption
Titanium Dioxide Production
Phosphoric Acid Production
Carbon Dioxide Consumption
Ferroalloys
Land-Use Change and Forestry (Slnkf
International Bunker Fuels6
Biomass Combustion
GH4
Landfills
Natural Gas Systems
Enteric Fermentation
Coal Mining
Manure Management
Wastewater Treatment
Petroleum Systems
Stationary Sources
Rice Cultivation
Mobile Sources
Abandoned Coal Mines
Petrochemical Production
Iron and Steel Production
Field Burning of Agricultural Residues
Silicon Carbide Production
International Bunker Fuels'1
M20
Agricultural Soil Management
Mobile Sources
Manure Management
Nitric Acid
Human Sewage
Stationary Sources
Adipic Acid
N20 Product Usage
Field Burning of Agricultural Residues
Waste Combustion
International Bunker Fuels"
MFCs, PFCs, and SF6
Substitution of Ozone Depleting Substances
HCFC-22 Production6
Electrical Transmission and Distribution'1
Aluminum Production
Semiconductor Manufacture
Magnesium Production and Processing* "
S02
NO*
CO
NMVOCs
13*485
7,817
8,529
0,580
4,239
1,657
1,551
:; 783
1,954
- §,412
: 1,723 4,tl4
1,382
- 993
1,719
mm
mires
28,815
9,202
5,946
5,443
2,648
1,849
1,339
1,118
344
364
205
200
S.41S
5,757
8,551
2,805
9,491
5,985
5,509
2,677
1,807
1,350
1,119
367
357
210
211
80
57
38
1
6
22,860
138,680
20,937
17,091 17,189 18,013
22,284 21,963 21,199
101,138 98,983 95,471
16,994 16,403 16,245
M
M
3
1
M
M
+
14,802
20,555
m,m
15,418
M
M
2
1
M
M
•f
14324
20,048
100,661
15,148
2002
54,411
: 42,898
18,781
17,652
12,304
5,836
5,299
4,223
4,139
1,997
1,339
1,272
1,237
(890,723;
86,845
207,097
28,482
9,192
5,801
5,450
2,487
1,879
1,365
1,104
328
325
201
196
72
47
34
1,341
927
171
58
54
50
45
19
15
1
1
3
M
M
2
1
M
M
+
13,669
19,849
92,541
14,996
+ Does not exceed 0.5 Gg.
M Mixture of multiple gases
a Sinks are not included in C02 emissions total, and are based partially on projected
activity data.
b Emissions from International Bunker Fuels and Biomass Combustion are not
included in totals.
cHFC-23 emitted
Note: Tobls may not sum due to independent rounding.
Note: Parentheses indicate negative values (or sequestration).
2-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 2-5: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks by Chapter/IPCC Sector (Tg C02 Eq.)
Chapter/IPCC Sector
Energy
Industrial Processes
Solvent and Other Product Use
Agriculture
Land-Use Change and Forestry (Sink)*
Waste
Total
Net Emissions (Sources and Sinks)
1 990 1
5,144* 1
297.4 1
4.3 1
436.0 1
(957.9) 1
246.9 1
6,129.1 I
5,1?t3 1
I 1996
1 5,646.4
• 318.3
1 4.5
I 468.3
1 (1,055,2)
I 249.9
I 6,687 J
1 5,632.1
1tf7
5,716.6
3241
4.8
473.8
(821.0)
245.2
6,764.4
5,943.5
1W8
5,731.6
331.9
4.8
476.2
(705.8)
239.0
6,790.5
6,084.7
«9t
5,806.1
326.2
4.8
474.2
(675.8)
241.2
6,852.5
6,176.8
200ft
5,991.4
329.3
4.8
469.9
(690.2)
243.0
7,036,3
6,348.2
2801
5,§7tJ
301.9
4.8
468,6
(689,7)
23J.&
6,883.9
6,184,1
2002
5,814,8
310.7
4.8
467.1
PQJ)
237.2
6,134.6
6,243.8
* Sinks are only included in net emissions total, and are based partially on projected activity date.
Note: Totals may not sum due to independent rounding.
Note: Parentheses indicate negative values (or sequestration).
Overall, from 1990 to 2002, total emissions of CO2 and
N2O increased by 780.0 Tg CO2 Eq. (16 percent) and 22.7
Tg CO2 Eq. (6 percent), respectively, while CH4 emissions
decreased by 44.6 Tg CO2 Eq. (7 percent). During the same
period, aggregate weighted emissions of HFCs, PFCs, and
SF6 rose by 47.3 Tg CO2 Eq. (52 percent). Despite being
emitted in smaller quantities relative to the other principal
greenhouse gases, emissions of HFCs, PFCs, and SF6 are
significant because many of them have extremely high global
warming potentials and, in the cases of PFCs and SF6, long
atmospheric lifetimes. Conversely, U.S. greenhouse gas
emissions were partly offset by carbon sequestration in
forests, trees in urban areas, agricultural soils, and landfilled
yard trimmings, which was estimated to be 10 percent of
total emissions in 2002.
As an alternative, emissions of all gases can be totaled
for each of the IPCC sectors. Over the thirteen year period
of 1990 to 2002, total emissions in the Energy, Agriculture,
Industrial Processes, and Solvent and Other Product
Use sectors climbed by 770.3 Tg CO2 Eq. (15 percent), 31.0
Tg CO2 Eq. (7 percent), 13.3 Tg CO2 Eq. (4 percent), and
0.5 Tg CO2 Eq. (11 percent), respectively, while emissions
from the Waste sector decreased 9.6 Tg CO2 Eq. (4 percent).
Over the same period, estimates of net carbon sequestration
in the Land-Use Change and Forestry sector declined by
267.1 Tg CO2Eq. (28 percent).
Table 2-3 summarizes emissions and sinks from all U.S.
anthropogenic sources in weighted units of Tg CO2Eq., while
unweighted gas emissions and sinks in gigagrams (Gg) are
provided in Table 2-4. Alternatively, emissions and sinks are
aggregated by chapter in Table 2-5 and Figure 2-5.
Figure 2-5
U.S. Greenhouse Gas Emissions by Chapter/IPCC Sector
Industrial Processes
Waste
2.2. Emissions by Economic Sector
Throughout this report, emission estimates are grouped
into six sectors (i.e., chapters) defined by the IPCC: Energy,
Industrial Processes, Solvent Use, Agriculture, Land-Use
Change and Forestry, and Waste. While it is important to
use this characterization for consistency with UNFCCC
reporting guidelines, it is also useful to allocate emissions
into more commonly used sectoral categories. This section
reports emissions by the following "economic sectors":
Residential, Commercial, Industry, Transportation,
Electricity Generation, and Agriculture, as well as U.S.
Territories. Using this categorization, emissions from
electricity generation accounted for the largest portion
(33 percent) of U.S. greenhouse gas emissions in 2002.
Transportation activities, in aggregate, accounted for the
Trends in Greenhouse Gas Emissions 2-7
-------
Table 2-6: U.S. Greenhouse Gas Emissions Allocated to Economic Sectors (Tg C02 Eq. and Percent of Total in 2002)
Sector/Source
Electricity Generation
C02 from Fossil Fuel Combustion
Waste Combustion6
Transmission & Distribution0
Stationary Combustion11
Limestone and Dolomite Use
Transportation
C02 from Fossil Fuel Combustion
Mobile Combustion11
Substitution of ODSe
Industry
C02 from Fossil Fuel Combustion
Natural Gas Systems
Iron and Steel Production*
Coal Mining
Cement Manufacture
Petroleum Systems
HCFC-22 Productions'
Ammonia Manufacture
Nitric Acid
Lime Manufacture
Substitution of ODSe
Aluminum Production11
Adipic Acid
Stationary Combustion6
Natural Gas Flaring
N20 Product Usage
Semiconductor Manufacture6
Soda Ash Manufacture and Consumption
Abandoned Coal Mines
Limestone and Dolomite Use
Magnesium Production and Processing0
Titanium Dioxide Production
Petrochemical Production
Phosphoric Acid Production
Carbon Dioxide Consumption
Ferroalloys
Silicon Carbide Production
Agriculture
Agricultural Soil Management
Enteric Fermentation
Manure Management/1
C02 from Fossil Fuel Combustion
Rice Cultivation
Field Burning of Agricultural Residues'1
Mobile Combustion"
Stationary Combustion"
Commercial
C02 from Fossil Fuel Combustion
Stationary Combustion"1
Substitution of ODSe
Landfills
1990
1,843.9
1,792.4
11.3
29.2
8.2
2.8
1,513.4
1,458.2
55.2
+
1,437.4
920.3
122.0
86.7
81.9
33.3
28.9
35.0
19.3
17.8
11.2
+
24.4
15.2
5.7
5.8
4.3
2.9
4.1
3.4
2.8
5.4
1.3
1.2
1.5
0.9
2.0
+
482.8
262.8
117.9
47.2
46.3
7.1
1.1
0.4
+
472.2
224.2
1.1
+
210.0
1996
2,047.0
1,992.2
17.6
24.3
9.1
3.9
1,683.7
1,604.8
65.0
13.9
1,493.2
993.9
127.4
69.6
63.2
37.1
25.6
31.1
20.3
20.7
13.5
2.8
18.0
17.0
6.3
8.5
4.5
5.5
4.2
6.0
3.9
6.5
1.7
1.6
1.6
0.8
2.0
+
520.8
288.1
120.5
51.6
52.0
7.0
1.2
0.4
+
497.4
237.0
1.2
9.3
208.8
1997
2,113.2
2,060.5
18.1
21.7
9.3
3.6
1,698.6
1,614.8
64.4
19.4
1,495.5
1,000.1
126.1
73.1
62.6
38.3
25.5
30.0
20.7
21.2
13.7
4.0
16.6
10.3
6.4
7.9
4.8
6.3
4.4
5.6
3.6
6.3
1.8
1.6
1.5
0.8
2.0
+
532.6
293.2
118.3
53.6
58.3
7.5
1.2
0.5
+
496.7
237.2
1.2
13.1
203.4
1998
2,196.3
2,148.5
17.4
17.1
9.6
3.7
1,732.9
1,644.9
63.6
24.4
1,454.6
960.5
124.5
68.6
62.8
39.2
25.0
40.2
21.9
20.9
13.9
5.1
14.8
6.0
6.0
6.6
4.8
7.1
4.3
4.8
3.7
5.8
1.8
1.7
1.6
0.9
2.0
+
534.3
294.2
116.7
56.1
57.6
7.9
1.2
0.5
+
477.2
219.7
1.1
17.4
196.6
1999
2,206.7
2,158,7
18.0
16.4
9.6
4.0
1,794.7
1,702.9
62.6
29.3
1,414.0
942.0
120.9
65.5
58.9
40.0
23.7
30.4
20.6
20.1
13.5
6.4
14.8
5.5
6.0
6.9
4.8
7.2
4.2
4.4
4.0
6.0
1.9
1.7
1.5
0.9
2.0
+
534.7
292.1
116.6
56.0
59.9
• 8.3
1.2
0.5
+
484.9
222.3
1.2
20.3
197.8
2000
2,309.1
2,261.9
18.3
15.9
10.0
3.0
1,844.8
1,749.6
61.4
33.8
1,418.5
949.3
125.7
66.9
56.2
41.2
23.5
29.8
19.6
19.6
13.3
7.5
14.6
6.0
6.0
5.8
4.8
6.3
4.2
4.4
3.0
3.2
1.9
1.7
1.4
1.0
1.7
+
520.7
289.7
115.7
55.7
50.4
7.5
1.2
0.4
+
505.1
237.1
1.2
23.8
199.3
2001
2,265.5
2,218.2
19.1
15.6
9.8
2.9
1,827.0
1,730.6
58.9
37.4
1,353.1
920.5
124.9
60.1
55.6
41.4
23.5
19.8
16.2
15.9
12.8
8.5
8.1
4.9
5.6
5.4
4.8
4.5
4.1
4.2
2.9
2.5
1.9
1.4
1.3
0.8
1.3
+
519.3
288.6
114.3
56.8
50.2
7.6
1.2
0.4
+
492.2
227.3
1.1
27.1
193.2
2W2
2,286.8
2,240.1
19.1
14.8
9.9
2.9
1,861.4
1,764.4
56,7
40.4
1,331.9
903.6
121.8
55.4
52.2
42.9
23.2
19.8
17.7
16.7
12.3
9.9
9.4
5.9
5J
5.3
4.8
4.4
4.1
4.1
2.9
2.4
2.0
1.5
1.3
1.3
1.2
+
519.8
287.3
114.4
57.3
52.2
6.8
1.1
0.5
+
500.4
231.2
1.1
30.8
193.0
PBreenP
38.0%
32.3%
0.3%
0.2%
0.1%
0.0%
26.8%
25.4%
0.8%
0.6%
19.2%
13.0%
1.8%
0.8%
0.8%
0.6%
0.3%
0.3%
0.3%
0.2%
0.2%
0.1%
0.1%
0.1%
0.1%
0.1%
0.1%
0.1%
0.1%
0.1%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
7.5%
4.1%
1.7%
0.8%
0.8%
0.1%
0.0%
0.0%
0.0%
7.2%
3.3%
0.0%
0.4%
2.8%
2-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 2-6: U.S. Greenhouse Gas Emissions Allocated to Economic Sectors (Tg C02 Eq. and Percent of Total in 2002)
(Continued)
Sector/Source
Human Sewage
Wastewater Treatment
Residential
C02 from Fossil Fuel Combustion
C02 from Fossil Fuel Combustion
Total
Sinks
Forests
Urban Trees
Agricultural Soils
LawWed Yard Tftwufcis
Net Emissions (Soun
;es and Sinks)
1990
,12*'
24.1
345.6
339.6:
.5,7
0.3
sat
8,1293
(887.8)
(846,6}
(58,7)
(28.5):
(26 J)
§,171.3
1996
; 14.2
- 26,9
403.8
388,9
V 5J
;: 9.0
414
41.4
6,687.3
.: (964.1)
, CS8J)
(19,0)
•:•'• $3,4)
i$e.i
1997
14.4
27.4
385.1
370,6
4,6
9,9
42.7
6,764.4
I8ii jw
(58.7)
(19.3)
(12,9)
5,943.5
1998
14.7
27.7
352.4
338.6
4.2
9,6
42,8
42.8
8?796,l
f»5,8>
(617.8)
, (58.7)
(16.9)
(12.4)
6,084.7
1999
15,2
28.2
3734
359.3
4.5
9.8
43.8
43.8
6,852.5
(675.8)
(588.4)
(58.7)
(17,3)
(11-3)
6,176.8
2000
15.3
28.4
394.0
379.3
4.7
10.1
48.1
46.1
7,938.1
(690.2)
(602.3)
(58.7)
(19.0)
(10.1)
6,348.2
2001
28;t
381,7
366,9
4.4
'"103
m
6,883.9
(689.7)
(600,2)
(58.7)
(20,7)
(10,2)
8,194.1
2002
15,6
28J
m.i
373.1
4.0
: m
46.6
46 M
6,934.6
{698.7}
(600,8)
(58.7)
(21.2)
(10.1)
6,243.8
Percent3
0.2%
5.8%
. 5,4%
0.1%
0.2%
9.7%
0,7%
198.8%
-18.8%
-8.7%
-0.8%
-0.3%
-0.1%
98.0%
Note: Includes * emissions ol C02> CH4,8$, HFCs, PFCs, aret &£ Parentheses indicate negative values (or sequestration). Totals my not sum due to
Does not eweed 0,05 Tg C02 Et). or 0.05%.
a Percent of total emissions to year 2002.
6 includes both COa and N20.
c Remitted.
6 May inc We a mbtture of MFCs, PFCs, and SF6.
f Includes both CH4 and C02.
»HFC-23«nWed.
ft Includes boft C02 and PFCs.
second largest portion (27 percent). Additional discussion
and data on these two economic sectors is provided below.
Emissions from industry accounted for 19 percent
of U.S. greenhouse gas emissions in 2002. In contrast to
electricity generation and transportation, emissions from
industry have declined over the past decade, as structural
changes have occurred in the U.S. economy (i.e., shifts
from a manufacturing base to a service-based economy),
fuel switching has occurred, and efficiency improvements
have been made. The residential, agriculture, commercial
economic sectors, and U.S. territories contributed the
remaining 21 percent of emissions. Residences accounted
for approximately 6 percent, and primarily consisted of CO2
emissions from fossil fuel combustion. Activities related to
agriculture accounted for roughly 7 percent of U.S. emissions,
but unlike all other economic sectors these emissions were
dominated by non-CO2 emissions. The commercial sector
accounted for about 7 percent of emissions, while U.S.
territories accounted for 1 percent of total emissions.
Carbon dioxide was also emitted and sequestered by a
variety of activities related to forest management practices,
tree planting in urban areas, the management of agricultural
soils, and landfilling of yard trimmings.
Table 2-6 presents a detailed breakdown of emissions
from each of these economic sectors by source category, as
Figure 2-6
Emissions Allocated to Economic Sectors
2,500 -.
2,000 -
S 1,500
0
» 1,000 •
500
Electricity Generation — . .
. — Transportation _
Commercial Agriculture
^Residential
3i— ogfo^-iacor-coo>Oi— CM
na>o>o>0>a>Q>a>a>a>ooo
no>a>0>a>0>a>a>a>a>ooo
Year
Note: Does not include territories.
Trends in Greenhouse Gas Emissions 2-9
-------
they are defined in this report. Figure 2-6 shows the trend in
emissions by sector from 1990 to 2002.
Emissions with Electricity Distributed to
Economic Sectors
It can also be useful to view greenhouse gas emissions
from economic sectors with emissions related to electricity
generation distributed into end-use categories (i.e.,
emissions from electricity generation are allocated to the
economic sectors in which the electricity is consumed).
The generation, transmission, and distribution of electricity,
which is the largest economic sector in the United States,
accounted for 33 percent of total U.S. greenhouse gas
emissions in 2002. Emissions increased by 24 percent since
1990, as electricity demand grew and fossil fuels remained
the dominant energy source for generation. The electricity
generation sector in the United States is composed of
traditional electric utilities as well as other entities, such
as power marketers and nonutility power producers. The
majority of electricity generated by these entities was
through the combustion of coal in boilers to produce high-
pressure steam that is passed through a turbine. Table 2-7
provides a detailed summary of emissions from electricity
generation-related activities.
To distribute electricity emissions among economic
end-use sectors, emissions from the source categories
assigned to the electricity generation sector were allocated
to the residential, commercial, industry, transportation, and
agriculture economic sectors according to retail sales of
electricity (EIA 2003a and Duffield 2004). These three source
categories include CO2 from fossil fuel combustion, CH4
and N2O from stationary sources, and SF6 from electrical
transmission and distribution.3
When emissions from electricity are distributed among
these sectors, industry accounts for the largest share of
U.S. greenhouse gas emissions (30 percent). Emissions
from the residential and commercial sectors also increase
substantially due to their relatively large share of electricity
consumption. Transportation activities remain the second
largest contributor to emissions. In all sectors except
agriculture, CO2 accounts for more than 75 percent of
greenhouse gas emissions, primarily from the combustion
of fossil fuels.
Table 2-7: Electricity Generation-Related Greenhouse Gas Emissions (Tg C02 Eq.)
Gas/Fuel Type or Source
G)02 from Fossil Fuel Combustion
Coal
Natural Gas
Petroleum
Waste Combuste
1990
1,806,1
1,792.4
1,515.9
176.0
100,1
0.4
10,9
Limestone and Dolomite Use
'
Stationary Combustion*
Waste Combustion
Electrical Transmission and Distribution
Total
0.6 =
8.0
7.6
0.4
29.2
29.2
1.843J
Note: Totals may not sum due to independent rounding.
* Includes only stationary combustion emissions related to the generation of electricity.
[ 1996
2,013.3
1,992.2
17???
204.9
64.7
0.4
17.2
L 3.9
b- 0.6
r 0,6
8.9
8.5
0.4
24.3
24.3
| 2,8*7.0
1997
2,081.9
2,060.5
1,767.4
218.9
73.7
0.4
17.8
3.6
0.6
0.6
9.1
8.7
0.4
21.7
• 21.7
2,113.2
1998
2,169.3
2,148.5
1,796.6
248.0
103.5
0.4
17.1
3.7
0.7
0.7
9.3
8.9
0.3
17.1
17.1
2,196.3
1999
2,180.4
2,158.7
1,802.5
259,9
95,9
0.4
t7.6
4.0
0.7
0.7
9.3
8.9
0.3
16.4
16.4
2,206,7
2000
2,282.9
2,261.9
1,890.5
280.7
90.4
0.4
18.0
3.0
0.7
0.7
9.7
9.3
0.4
15.1
15,9
2,309,1
2001
2,239.8
2,218.2
1,828,6
289,1
100.1
0.4
18.8
2.9
0.7
0.7
8.4
9,1
0.4
15*
15,6
2,265.5
2002
2,261.8
2,240.1
1,868.4
299.1
72.2
0.3
18.8
2.9
0.7
0.7
9.6
9,2
0.4
14J
148
2,286.8
Emissions were not distributed to U.S. territories, since the electricity generation sector only includes emissions related to the generation of electricity
in the 50 states and the District of Columbia.
2-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 2-8: U.S Greenhouse Gas Emissions by "Economic Sector" and Gas with Electricity-Related Emissions
Distributed (Tg C02 Eq.) and percent of total in 2002
Sector/Gas
«i»8!«a:|*tlt?.
2000 2001 2002 Percent3
^,i^|ii»sji»v;v;:; ::'s
'•'''^'••^.^•Y^.
'.':^^V->^;\< '••/:.
•''•'^MV.-;;:,/^;:
; ,:iF%^,'-iWJ:p^
Elec*fcil^iatkl : ;
' G02 <•''"•. ''/'A: ':
CH4
NjjO
SFg ;.;; . .;/.;,;;:,
Transportation
Direct Emissions
C02
CH4 •' ....'•''•• :' V"
N20 ^
. HFCs"
Electte^Related
CQ^v' ":.'••; : : -
CH4 •''.••• ••:••'•'•.,.•.
'. tp -'•"' '.'••.•• '..-''•'
;^';;;;,;;.: ;•
Commercial
OteefettiSsfens
....«VY:':•'..; ::::/
PH4 ; •:.'•
N20
HFCs
Electrics-Related
CQ2 ',•'••-" >
CH4
NzO
SF6 ,: • •.
Residential
Direct Emissions
C02
CH4
N20
MFCs
Efectrictty-Related
C02
CH4
N20
SF6
Agriculture
Direct Emissions
C02
CH4
N20
Electricity-Related
iMsiif
•m«ai?
'2255
' .741 J
•;;S:iSf'
*;fsHI
iAfe||;
'•I^S^
:^^:
ii^l
i*i;'
•%i
?®P-
||||lir;
^•'1^''
:5'"|lli:
Sl7|;
Sv^s;'
1}574«|:1
^'.«jv
<«:'.-""wi'-
'^.•r.-s.r
Slftjjl,
?^^
:':*|B44.9:
v^,:-4.fJ:
'$•'^59,6;
fe"\2^|
f-^-iisti.-
f;'";:'ii:
^'':•„*•-+••
: '^^>
:i'';^|
-•"•'ff
;-^;5;;;
^TS^tef
*• '.:0;2'
•'•:••'"-S^.
:'-"'^'
•'*$&»'•'
1,794.7
':1|02$
,'• '^3.9-
•-•;-f|M
.-V--!^.-
..V/-3.2,
'-•"•ii1
:?J!|*iiC
vli#^
:^Iflf:
<'^i^f.
•^?^?
-?if|i*
'•*Xjj$'
.:<••-•&:
••/:'.^*;.:
:-W^-:
:*'t1tff.f;
'4|i.i'
> ^:;:l&:
••'':'^'
;M3jj$
'-r:"%4
/V:V0S
'If^fi
^ii^Ci}!
;Siiil
li||p«-||2i>:
||^?SS||||'
Mlgs
^v^;|f
;K;lp
'r»|pi
':Wif':
;'t»M|i
^r^p^
• --i|ii.
^•••^i*'
''^(^'
»v'V.^>
^3||?!
••'•-'#
^iS||i
spipff
"Illli;"
:tflli;;
• i'.5: if •
'.^i^ii;
'^'M-
';s::ft:
i-r ';|,r;
;::;i!1%;
•lipw»'
;;-2il!%-
•2f.4%^
; o.^%
•;:ij%"
^8%
60.9
iiif;
itt:5
*• !,•-.; j'l'i-' ".'-;-,:'
i2»|S.;?
v-iife
;-^li^
•|j^$-
Hsll^;
":?tt^
- ,"'' ; '• "' •-. ••
m»:
\-M-\
vS«^
'4lii:/;'
'&&'•'•
•'••:.&-
7i>'.
9A
:'6il6:;
'8472'"
:v:;;ft2:
. ? i9^'"
' XW'
592.4
^520,8
v:Ht-^
162,9
iosj
:;^71.6-'
:;f;;S^i''
IP?:
"s ;'?>* %?£<*; '•"•
6fti?;
siiW>
w&
l:-'M$y,
^:fmm^
l$%%;:
'••.-•/ ;b^-
:^«:
/...••;,*•>;
1|ft;1::
^•:l^i;
3fO.§
3.7
IX)
9,9
672;0.
662.1
0.2
2.9
6J
588.3
532.6
58.3
163.0
311.3
55.6
'«&{£*•
*;ii*ifa
??47i2"
% 211.7':
22571
15.0
:=:;':'11.4.'
/';'B72.2;.
863.9
I 0.2
2.8
:> "5.2'
i'^1"
3514
338.6
3.3
0.9
9.6
704.7
696.0
0.2
3.0
5.5
594.8
534.3
57.6
164.3
312.4
60.5
1 ''>§*:';•
''$ji&>
''•^*&&'
>-M^
: 226.8
'''•:: 1$$)
20.3
681.0
67^9 ;
'':•'. .-6&-':
. :" ^at-
'.'-. 54,
I^IB
373.8
359.3
3.5
0.9
m
706.4
898.0
0.2
3.0
•. . 5.2:'
585.3
534.7
59.9
164.4
310.3
50,6
^m
•>$K
^.mm>
\:?&&'<
.^•3$$'
•::*?%£$>
';C7lis'^
S-H?
'^"3.tf:;
;,:o|,
;1».ft§
l'.*:aj^:
^ -3793-
.^l7:':
.•'.-.-, .M-:
;< 1W'
;/•"«$•
'-••736J5':
' ^-^
•?:':'.-ii:;-
•-"viar
'^ :^*:.
-:S20l7;'
^":"'5fti;:
162.1
308.3
57.2
'^y-K^'Sg
»'•;•., 'i23i.i95,S,A
i?lli
:*lli):
•v^SZ*'-:
^|#k^r;
v:$fci.-
f.;J^^
:: ^'f
!^^^
'MiiiS-
;>/^S
'^Tiitfi
• ?^§i;:
•] '^/\&'
i';"-.";*(S;l
:.v}y*iar:
"VI3i3r
;;-^;0}2,
;:-.--:¥i%:
:;^^ti
f'iiiij
'--sis:3'
-M'SOif:
16117
307.4
67.1
-5:!**-
-------
Table 2-8: U.S Greenhouse Gas Emissions by "Economic Sector" and Gas with Electricity-Related Emissions
Distributed (Tg C02 Eq.) and percent of total in 2002 (continued)
Sector/Gas
C02
CH4
N20
SF6
U.S. Territories
C02
Total
6,129
1996
i: :: ,70.4
*• " . 4-
f\ 0-3
• 0.8
^41.4
•:-• 41.4
6,68?,3
1997
54.8
+
0.2
0.6
42.7
42.7
6,764.4
1998
59.8
+
0.3
0.5
42.8
42.8
6,790.5
1999
50-0
• +
0,2
0.4
43.8
43.8
6.852.5
2000
.'864'
1 '' -f;
0.2
0.4
46.1
46.1
7,038.3
2001
66.3
. '• ,-K '
0.3
0.5, -
45J
45:8
6,883.9
2002
62.7 :
, • +
=' 0.3
, 0,4
46.6
,;,,46j..
6,934j|
Percent3
'. 0:9%
••i!-' +.
+
. '• +
fl.7%
••'.;fl,7%
100:0%
Note: Emissions from electricity generation are allocated based on aggregate electricity consumption in each end-use sector, : "• " ;
Totals may not sum due to independent rounding. "•.-.•;''"
+ Does not exceed 0.05 TgC02Eq. or 0.05 percent .
aPercents for year 2002. ,
"Includes primarily HFC-134a.
Box 2-2: Methodology for Aggregating Emissions by Economic Sector
In order to aggregate emissions by economic sector, source category emission estimates were generated according to the
methodologies outlined in the appropriate sections of this report. Those emissions, then, were simply reallocated into economic
sectors. In most cases, the IPCC subcategories distinctly fit into an apparent economic sector category. Several exceptions
exist, and the methodologies used to disaggregate these subcategories are described below:
• Agricultural C02 Emissions from Fossil Fuel Combustion, and non-C02 emissions from Stationary and Mobile Combustion.
Emissions from on-farm energy use were accounted for in the Energy chapter as part of the industrial and transportation end-use
sectors. To calculate agricultural emissions related to fossil fuel combustion, energy consumption estimates were obtained from
economic survey data from the U.S. Department of Agriculture (Duffield 2004) and fuel sales date (SA1991 through 2003). To
avoid double counting, emission estimates of C02 from fossil fuel combustion and non-CQj from stationary and mobile sources
were subtracted from the industrial economic sector, although some of these fuels may have been originally accounted for under
the transportation end-use sector.
• Landfills, Wastewater Treatment, and Human Sewage. CH4 emissions from landfills and wastewater treatment, as well as N20
emissions from human sewage, were allocated to the commercial sector.
• Waste Combustion. C02 and N20 emissions from waste combustion were allocated completely to the electricity generation
sector since nearly all waste combustion occurs in waste-to-energy facilities. .; ,
• Limestone and Dolomite Use. C02 emissions from limestone and dolomite use are allocated to the electricity generation
(50 percent) and industrial (50 percent) sectors, because 50 percent of the total emissions for this source are used In flue gas
desulfurization. .
• Substitution of Ozone Depleting Substances. All greenhouse gas emissions resulting from the substitution of, ozone depleting
substances were placed in the industrial economic sector, with the exception of emissions from domestic, 'commercial, mobile and
transport refrigeration/air-conditioning systems were placed in the residential, commercial, and transportationsectors, respectively.
Emissions from non-MDI aerosols were attributed to the residential economic sector. ,
Table 2-8 presents a detailed breakdown of emissions
from each of these economic sectors, with emissions from
electricity generation distributed to them. Figure 2-7 shows
the trend in these emissions by sector from 1990 to 2002.
Transportation
Transportation activities accounted for 27 percent of
U.S. greenhouse gas emissions in 2002. Table 2-9 provides
a detailed summary of greenhouse gas emissions from
2-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 2-9: Transportation-Related Greenhouse Gas Emissions (Tg C02 Eq.)
Gas/Vehicle Type
COZ
Passenger Cars ..
Light-Duty Trucks
Other Trucks
Buses .
Ships amr Boats . ',
Locomotives. ...
Other" : , '. ,.•
International Bunker TUeJsft
k •• "•-' ""•''.'.', ' '
Passenger Cars
Light-Duty Trucks .
Other Trucks ana Buses
Aircraft , " ' ;
Ships andJoats
Locomotives , ; ...;
Other* , - .Y'. -'/, _ ,-'.
InternattonalBunker Fuelsfr
Aircraft ;^:>:.: ...;>--';!:
Other4- y^;? --...i ;;:-.'
Internal oraunker, f uW
c Emissions from International
4 *
1997
1998
1999 2000 2001
2002
P 1,607.8
; ,590.1
r ,, 404.0
|-'C242.5 '•
&-:V ;8,1;
pv'..~iSQ.2\'
BV-> ;.;47,8
E& ' 32.3
&&':*$&'. '
||r':'.:4:8: .
p-^-2,0
&.-.;-, -1A
E-'.'; , • 04
p; 0.1 .
fe/jv.;j};1-
feS;^0.2~.
J§iV:jw
Iff ::33:f • '
f|;V;'21yt' '
1,617.8
588.2
416.2
254.3
8.4
178.9
' 33.4
. 32,2
106,3
106.1 .
47
2.0
1.7
0.4
- , 0.2
, 0.1
., 0.1
, 0.2
0.1
60.3
.32,6 .
' 21.1
1,648,0
608.0
427.8
264,3
8.6
180.8
'.. 27.1
32.8
98.6
103.8
4.5
2.0
1.7
0.4
0.1
•+
, 0.1,
0.2
0.2
59J
: 32.3
20.6
1,706.1
619.1
446.4
276.2
9.6
186.7
38,1
34.1
95.8
102.7
4.5
1.9
1.6
0.5
0.2
0.1
. 0.1
0.2
:0,1"..
58.6
, 31.2,
20,4, .
1,753.0
621,7
450.1
286.6 •••
9.5,
193;2;;
59.1 V
34.0,
98,8
102^2
4.4:
1.9
1.5
0.5
0.2
UT
0.1
0.2
0.1
57.4
,30,2
: ,19J,
1,734.1
623.3 -.
453.4
289;2-:,
'.'•:,. *;,8J-^;'';
:f-!:-:-1§^C f
'• .:':,1'.3?'.'£v;;
' '..3-*34."6'"'''--
,> 104.2:
.... S&.5
," •''' 4,3 •
.. 1.9
1-5
0.5
0,1 :
0,1
0;1
, 0.2
... 0.1
55itf
28v&..
":-.'J$.\, •
1,767.5
636,9
465.5
,,S2,4
'''- -.' :'8.3:~
: 177.6
'-'• 52:4
: 33.5
..V 101,0
86.8.
4^
1.8
1.4
0.5
0.1
, 0.1
0.1
0.2
0,1
52.9
V . 27.4
. .18.2
17
0.3
0.3
0.6
1.0
19.4
;13;8
1:8
0.2
,0.3,
1.0
24:4
17.4
7,0
s,g
1:8
0.3;
0.3:
ae
o;6
20.8,
, '.ftS-'
t.798.4
:^r/;S.','iU-
Qjf :':::;,/,e.7
&9f-":v 0.8
etfeumptiofi: : -.;
r, pprte,
9, aflrteutturaitnactiiftery, 1
240 ,26.7: , 28.8
transportation-related activities. Total emissions in Table
2-9 differ slightly from those shown in Table 2-8 primarily
because the table below includes all transportation activities,
including those that had been counted under the Agriculture
economic sector.
From 1990 to 2002, transportation emissions rose by
23 percent due, in part, to increased demand for travel and
the stagnation of fuel efficiency across the U.S. vehicle
fleet. Since the 1970s, the number of highway vehicles
registered in the United States has increased faster than
the overall population, according to the Federal Highway
Administration (FHWA). Likewise, the number of miles
driven (up 33 percent from 1990 to 2002) and the gallons
of gasoline consumed each year in the United States have
increased steadily since the 1980s, according to the FHWA
and Energy Information Administration, respectively. These
increases in motor vehicle usage are the result of a confluence
of factors including population growth, economic growth,
urban sprawl, low fuel prices, and increasing popularity of
sport utility vehicles and other light-duty trucks that tend
Trends in Greenhouse Gas Emissions 2-13
-------
Figure 2-7
Emissions with Electricity Distributed to Economic Sectors
2,500
2,000
. 1,500
' 1,000
500
Industrial
Transportation..
Commercial -
•^
Residential'
Agriculture
ssssssss
o>o>a>o>a>a>o>o>
Note: Does not include territories.
to have lower fuel efficiency. A similar set of social and
economic trends has led to a significant increase in air travel
and freight transportation by both air and road modes during
the 1990s.
Almost all of the energy consumed for transportation
was supplied by petroleum-based products, with nearly two-
thirds being related to gasoline consumption in automobiles
and other highway vehicles. Other fuel uses, especially diesel
fuel for freight trucks and jet fuel for aircraft, accounted for
the remainder. The primary driver of transportation-related
Box 2-3: Sources and Effects of Sulfur Dioxide
emissions was CO2 from fossil fuel combustion, which
increased by 21 percent from 1990 to 2002. This rise in CO2
emissions, combined with increases of 40.4 Tg CO2 Eq. in
HFC emissions and 2.3 Tg CO2 Eq. in N2O emissions over
the same period, led to an increase in overall emissions from
transportation activities of 23 percent.
2.3. Ambient Air Pollutant Emissions
In the United States, carbon monoxide (CO), nitrogen
oxides (NOX), nonmethane volatile organic compounds
(NMVOCs), and sulfur dioxide (SO2) are referred to as
"ambient air pollutants," as termed in the Clean Air Act.
These pollutants do not have a direct global warming effect,
but indirectly affect terrestrial radiation absorption by
influencing the formation and destruction of tropospheric
and stratospheric ozone, or, in the case of SO2, by
affecting the absorptive characteristics of the atmosphere.
Carbon monoxide is produced when carbon-containing
fuels are combusted incompletely. Nitrogen oxides (i.e.,
NO and NO2) are created by lightning, fires, fossil fuel
combustion, and in the stratosphere from nitrous oxide
(N2O). NMVOCs—which include hundreds of organic
compounds that participate in atmospheric chemical
reactions (i.e., propane, butane, xylene, toluene, ethane and
Sulfur dto^te I^Og) em$ed Into the atmosphere through natural and antjifqpogeWc processes fffects the Earth's radiatJve budget
thrpuflri ifes p)fQt0^hernical transformaiion Into sulfate aerosols ip^ean.(jj seller radiation from the sun back to space, thereby
reducjng t«e radWion reachto^
{e.g.,i#p>e^df%^
can be considered in two parts. The first indirect effect is the aerosols' tendency to decrease water droplet size and Increase water
droplet,|KfeeitlpSl]i hi ffia^osphere.fhe sej3oW^r^3|pi|!s|fti^ of the fBdiicflonln ciojjd droplet,slze to affect
precipitation by increasing cloud lifetime and thickness. Although still highly uncertain, the radiative forcing estimates from both the
first atid the s^ond;jnd|ect^ct m believed Jo be:nei^awasJs%e6^Blriid radiative forcing'of jfie two (IRCC 2001). However,
becauseSpite ^Irrtv0d an^ forcing lltipaeti ar« highiy uncertain,
,:,^._ ^:^^i -i^:i^ir^;--^-.^^ ^.^li-jfe^-^^^Ji^i^^j^^ c^,^,^^^^^!,, &C[^ an(j
as;fte primary
chronic respiratory diseases. Once S02 is emittedjt is chemically transformed in the atmosphere and
source of add rilnVBfl^aiJstMliisf harmful effect, flia JMe|$t0s has [regulated 802 emissions In tfte Glean Mr &
-------
Table 2-10: Emissions of NOX, CO, NMVOCs, and S02 (Gg)
Gas/Activity
NO,
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Waste Combusflon
Industrial Processes
Solvent Use
Field Burning of Agricultural Residues
Waste
CO
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Waste Combustion
Industrial Processes
Solvent Use
Field Burning of Agricultural Residues
Waste
NMVOCs
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Waste Combustion
Industrial Processes
Solvent Use
Field Burning of Agricultural Residues
'Waste
S02
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Waste Combustion
Industrial Processes
Solvent Use
Field Burning of Agricultural Residues
Waste
nm
9,884
12,134:
•13|1
«a.)
-. 76t:|
28^!
•*3
m^mj
4,999:
119,482;]
302;
~W]
4,124
4'!
685-J
28,8fW
10,933 ~\
555''
222
2,426;
5^?:i1
NA:<
673,|
20,936
18,4871
7931
390
39
1,306:
NA
0
Source: (EPA 2003) except for estimates torn field burning of agricultural residues.
+ Does not exceed 0.5 Gg
NA (Not Available)
Note: Totals may not sum due to Independent rounding.
| 1996
22,368
; 9,540
11,714
|>:" 126
p-135
R m
I ;-' .':' g
32
/' 3
iH«3
3,935
93,409
321
['., 2,628
3,016
I ^
747
5
17,184
1,018
I 8,306
| 433
304
f, 1,997
[4,969
; m
|l«J»2
1 14,746
649
I 304
I 29
f 953
i 1
r NA
I 1
1tW
22,289
9,578
11*768
.130
140
634
3
, 34
3
101,132
3,927
90,284
333
2,668
3,153
1
761
5
16,994
1,016
7,928
442"
313
2,038
5,100
NA
157
17,891
15,104
659
312
29
985
1
NA
1
1990
21,961
9,419
11,592
130
145
635
3
35
3
98,976
3,927
87,940
332
2,826
3,163
1
781
5
16,403
1,016
7,742
440
326
2,047
4.671
NA
161
17,189
15,191
665
310
30
991
1
NA
1
1999
21,341
8,718
11,582
113
142
748.
.. 3
34
3
95,464
4,941
84,574
152
2,833
2,145
46
760
14
16,245
1,312
7,658'
376
326
1,890
4,533
MA
151
16,013
14,073
701
275
29
933
1
NA
1
2099
20,917
8,228
11,395
,115
149
'".*»'
•• "3
35
• 3
93,965
4,163
83,680
1S2
2,914
2,214
45
784
14
15,418
1,088
7,230
348
332
1$4§
4,422
NA:
113
14,802
12J83
632
278
29
977
1
NA
1
2*1
20,141
T.826
11,254
U1?
"' :-: f49
•V?55;
;."• '" j,.
35
,..- g
100,653
.-•*$»
9^268
.153
2,118
2,327
44
762
14
15,148
1,087
8,800
'•. 357
333
1,829
-•. 4;i$4<'
- NA
' 158
14,324
12^87
636
281
30
1,008
1
NA
1
2002
19,849
,7,542
11,352
118
7 149
'.";',> «49-
;'";- . 3
33
3
92,541
3,961
82,063
153
3,294
2,304
44
706
15
14,996
1,147
6,771
348
333
1,818
, 4,420
NA'
158
13,669
11,805
634
268
30
930
1
NA
1
many others)—are emitted primarily from transportation,
industrial processes, and non-industrial consumption of
organic solvents. In the United States, SO2 is primarily
emitted from coal combustion for electric power generation
and the metals industry.
Ambient air pollutants are regulated under the Clean Air
Act in an effort to protect human health and the environment.
These gases also indirectly affect the global climate by either
acting as short-lived greenhouse gases or reacting with other
chemical compounds in the atmosphere to form compounds
that are greenhouse gases. Unlike the other ambient air
pollutants, sulfur-containing compounds emitted into the
atmosphere affect the Earth's radiative budget negatively;
therefore, it is discussed separately.
Trends in Greenhouse Gas Emissions 2-15
-------
One important indirect climate change effect of Since 1970, the United States has published estimates
NMVOCs and NOX is their role as precursors for tropospheric of annual emissions of ambient air pollutants (EPA 2003).4
ozone formation. They can also alter the atmospheric Table 2-10 shows that fuel combustion accounts for the
lifetimes of other greenhouse gases. Another example of majority of emissions of these gases. Industrial processes—
ambient air pollutant formation into greenhouse gases is such as the manufacture of chemical and allied products,
carbon monoxide's interaction with the hydroxyl radical— metals processing, and industrial uses of solvents—are also
the major atmospheric sink for methane emissions—to form significant sources of CO, NOX and NMVOCs.
CO2. Therefore, increased atmospheric concentrations of CO
limit the number of hydroxyl molecules (OH) available to
destroy methane.
NOX and CO emission estimates from field burning of agricultural residues were estimated separately, and therefore not taken from EPA (2003).
2-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
3. Energy
Energy-related activities were the primary sources of U.S. anthropogenic greenhouse gas emissions, accounting for 85
percent of total emissions on a carbon equivalent basis in 2002. This included 97,36, and 16 percent of the nation's
carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions, respectively. Energy-related CO2 emissions alone
constituted 81 percent of national emissions from all sources on a carbon equivalent basis, while the non-CO2 emissions
from energy-related activities represented a much smaller portion of total national emissions (4 percent collectively).
Emissions from fossil fuel combustion comprise the vast majority of energy-related emissions, with CO2 being the
primary gas emitted (see Figure 3-1). Globally, approximately 24,240 Tg CO2 were added to the atmosphere through the
combustion of fossil fuels in 2000, of which the United States accounted for about 23 percent (see Figure 3-2).] Due to the
relative importance of fossil fuel combustion-related CO2 emissions, they are considered separately, and in more detail than
other energy-related emissions. Fossil fuel combustion also emits CH4 and N2O, as well as ambient air pollutants such as
nitrogen oxides (NOX), carbon monoxide (CO), and non-methane volatile organic compounds (NMVOCs). Mobile fossil
fuel combustion was the second largest source of N2O emissions in the United States, and overall energy-related activities
were collectively the largest source of these ambient air pollutant emissions.
Energy-related activities other than fuel combustion, such as the production, transmission, storage, and distribu-
tion of fossil fuels, also emit greenhouse gases. These emissions consist primarily of fugitive CH4 from natural gas
systems, petroleum systems, and coal mining. Smaller quantities of CO2, CO, NMVOCs, and NOX are also emitted.
The combustion of biomass and biomass-based fuels
also emits greenhouse gases. Carbon dioxide emissions
from these activities, however, are not included in national
emissions totals because biomass fuels are of biogenic
origin. It is assumed that the carbon released during the
consumption of biomass is recycled as U.S. forests and
crops regenerate, causing no net addition of CO2 to the
atmosphere. The net impacts of land-use and forestry
activities on the carbon cycle are accounted for in the
Land-Use Change and Forestry chapter. Emissions of other
greenhouse gases from the combustion of biomass and
biomass-based fuels are included in national totals under
stationary and mobile combustion. „ 20 40 60 80 100 m 140
Tg CO, En
Figure 3-1
2002 Energy Chapter Greenhouse Gas Sources
Fossil Fuel Combustion
Natural Gas Systems
Mobile Sourcs
Coal Mining
Petroleum Systems
Stationary Systems
Waste Combustion
Natural Gas Flaring
I 5,611
Energy as a
portion of
all emissions
85.4%
Global CO2 emissions from fossil fuel combustion were taken from Marland et al. (2003) .
Energy 3-1
-------
Figure 3-2
2002 U.S. Fossil Carbon Flows (Tg C02 Eq.)
International
Bunkers
Coal Emissions
2,006
Natural Gas Liquids,
Liquefied Refinery Gas,
& Other Liquids
182 ^
Petroleum
1,650
Note: Totals may not sum due to independent rounding.
The "Balancing Item" above accounts for the statistical imbalances
and unknowns in the reported data sets combined here.
NEU=Non-Energy Use
NG=NaturalGas
Natural Gas Emissions
1,196
NEU Emissions 121
Petroleum Emissions
2,409
Table 3-1: Emissions from Energy (Tg C02 Eq.)
Gas/Source
Waste Combustion
Natural Gas Flaring
.Simass-Bltanal*
Carbon Stored in Products*
CH4
Natural Gas Systems
Coal Mirang
Petroleum Systems
Stationary Sources
Mobile Sources;.
Abandoned Coal Mines
International Bunker Fuels*
HzQ
Mobile Sources
Waste Combustion
International Bunker Fuels*
Total
1996
5,335.8
|fiai
17.2
8.5
238,8
102.3
5.5
241.2
235.6
127.4
63.2
: 2S.fi
8;8
4.8
8.0
0,1
7SJ
60.7
43*9
0:4
• r ^ .
1997
5,409.6
5,384.0
17.8
7.9
226.3
109.9
7.0
246.8
232.3
126.1
62.6
25.5.
7.8
4.7
1 .<: 5.6
0.1
74.7
, fflj
14.0
0.4
1.0
1998
5,436.1
5,412.4
17.1
. 6.6
209.5
115.1
7.7
260.1
228.8
124.5
62.8
25.0
7.2
4.5
4.8
0.2
73.8
59.6
13.8
0.3
1.0
1999
5,51 3.4
5,488.8
17.6
6.9
214.3
105.3
8.0
271,2
219.9
120.9
58.9
23.7
7.5
4.5
4.4
0.1
72.9
58,6
13.9
0.3
0.9
2000
5,697.3
5,673,6
18.0
5.8
217.6
101.4
9.2
259.0
222.0
125.7
56.2
23.5
7.7
4.4
4.4
0.1
na.
57,4
14:4
0.4
0.9
2001
5,583.0
5,558.8
18.8
5.4
194.7
97.9
9.7
257.1
219.7
124.9
55.6
23.5
7:2
4.3
4.2
0.1
69.3
55.0
13.9
0.4.
0.9
2002
5,635.1
5,611.0
18.8
5.3
195.6
86.8
11.5
260.6
212.9
121.8
52.2
23.2
6.9
4.2
4.1
0.1
67,3
52.9
14.0
0.4
0.8
5.646.4 5,716.6 5.738.6 5,806.1 5.991.4 5,871.9 5,914.8
Note: Totals may not sum due to independent rounding.
3-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-2: Emissions from Energy (Gg)
Gas/Source
C02
Fossil Fuel Combustion
Waste Combustion ,
Natural Gas Flaring
Biomass-Wood*
International Bunker Fuels*
Biomass-Ethanol*
Carton Stored in Products*-
CH4
Natural Gas Systems
Coal Mining
Petroleum Systems
Stationary Sources
Mobile Sources
Abandoned Coal Mines
International Bunker Fuels*
N20
Mobile Combustion
Stationary Combustion
Waste Combustion
International Bunker Fuels *
1990
4,831,390
4,814,660
10,919
5,810
212347
113,368
4,155:
199,266
11,875
5,811
3,900
1,375
391
236
162
8
205
163
41
1
3
1998
5,335,789
5,310,067
17,193
8,529
238,794
102,271
5,511
241,225
11,220
6,065
3,008
1,218
418
227
283
. 6
242
196
45
1
3
1997
.5,409,639
5,384,005
17,761
7,874
-mM"-'
-*&*»,.
:.e,ri'-
mm
11,060
: 6,005
" 2,983
1,215
36§
- 222
266
' 'i',"7
241
194
45
1
.-'•" J.
1998
5,436,054
•5,41,2,394
17,094
6,566
• 2109,4m
- 774094-
7,711
260,069
10,896
5,929
2,989
1,190
344
217
228
7
238
192
45
1
"•- 3
1999
5,813,403
5,488,829
17,632
6,943
274323
105,297
8,077
271,222
10,470
5,757
2,805
1,129
355
213
211
6
235
189
45
. 1
3
2000
1,697,322
5,673,575
17,979
5,769
277,577
m,m
9,i88
2S9M1
10,569
5,985
2,677
1,119.
367
210
211
6
233
185
47
1
3
2001
5,582,976
5,558,784
18,781
5,412
194,871
, 9?,B69;
.'---TO;';
2&M
10,462
5,94(5
2,648
1,118
344
205
200
5
223
177
45
1
3
2002
5,635,055
5,610,976
18,781
.5,299
195,624
86,845
• 11,473
260,600
10,118
5,801
. 2,487
, 1,104
, 328
201
196
4
217
171
45
1
3
* These values are presented for Informational purposes only and are not IncWed or are already accounted for in totals.
Note: Totals may not sum due to independent rounding, ,
Table 3-1 summarizes emissions for the Energy chapter
in units of teragrams of CO2 equivalent (Tg CO2 Eq.), while
unweighted gas emissions in gigagrams (Gg) are provided in
Table 3-2. Overall, emissions due to energy-related activities
were 5,914.8 Tg CO2 Eq. in 2002, an increase of 15 percent
since 1990.
3.1. Carbon Dioxide Emissions from
Fossil Fuel Combustion (IPCC Source
Category 1 A)
Carbon dioxide emissions from fossil fuel combustion
in 2002 increased slightly (0.9 percent) from the previous
year. A growing economy, combined with lower natural gas
and motor gasoline prices and a much hotter summer and
cooler winter resulted in a higher demand for fuels and a
consequent rise in emissions. In 2002, CO2 emissions from
fossil fuel combustion were 5,611.0 Tg CO2 Eq., or 16.5
percent above emissions in 1990 (see Table 3-3).2
Trends in CO2 emissions from fossil fuel combustion are
influenced by many long-term and short-term factors. On a year-
to-year basis, the overall demand for fossil fuels in the United
States and other countries generally fluctuates in response to
changes in general economic conditions, energy prices, weather,
and the availability of non-fossil alternatives. For example, in a
year with increased consumption of goods and services, low fuel
prices, severe summer and winter weather conditions, nuclear
plant closures, and lower precipitation feeding hydroelectric
dams, there would likely be proportionally greater fossil fuel
consumption than a year with poor economic performance,
high fuel prices, mild temperatures, and increased output from
nuclear and hydroelectric plants.
Longer-term changes in energy consumption patterns,
however, tend to be more a function of aggregate societal
trends that affect the scale of consumption (e.g., population,
number of cars, and size of houses), the efficiency with which
energy is used in equipment (e.g., cars, power plants, steel
mills, and light bulbs), and social planning and consumer
behavior (e.g., walking, bicycling, or telecommuting to work
instead of driving).
Carbon dioxide emissions also depend on the source of
energy and its carbon intensity. The amount of carbon in fuels
varies significantly by fuel type. For example, coal contains
the highest amount of carbon per unit of useful energy.
Petroleum has roughly 75 percent of the carbon per unit of
An additional discussion of fossil fuel emission trends is presented in the Recent Trends in U.S. Greenhouse Gas Emissions section of the
Introduction chapter.
Energy 3-3
-------
Table 3-3: C02 Emissions from Fossil Fuel Combustion by Fuel Type and Sector (Tg C02 Eq.)
Fuel/Sector
Coal
Residential
Commercial
Industrial
Transportation
Electricity Generation
U.S. Territories
Natural Gas
Residential
Commercial
Industrial
Transportation
Electricity Generation
U.S. Territories
Petroleum
Residential
Commercial
Industrial
Transportation
Electricity Generation
U.S. Territories
Geothermal*
Total
1,
1996 1997
1998
20l|tt
1.6
Priis
SV/-NE
^4322.2
^0^
jmz
S>fS8.9
103,1
SA.V54.3
1,927.8
1.S
12.2
145:8
NE
1,767.4
0.9
'i2te6
270.2
. 174.3
496.1
41.1
218.9
, NO
2,255.2
98.9
50.7
- 416.6
1,573.6
73,7
41.6
6.4
-•"•'1,2 '
,8.7,
: 137J:
"35.1'
248.Q-
m,
2,28SJ7
90,9
47.5
396,8
1tJ3.5-
41,7
0.4
139,8
't;;1?5.9
f ••-. '}:V$3[:$y.
'--259.9' :• ';28t7:.'::'
:..-;• NO •• 'ft?.'.'. ,
2,358.4 2,403.0
.'..107J
, 299.1
2,409.4
",=104.7
:52.7
-•-,406.1
"«*",
5,384.0 51412.4:
NE (Not estimated)' .•:.'
NO (Not occurring) ',,.,• , -
+ Does not exceed 0.05 Tg 002 Eq. •","".-.'• .'---" - ••. -"'! / " • ". .
* Although not technically a fossil iuel, pofltermaf Btiepfc-related GOj emisstoim are includes for reporting purposes.
Note: Totals may not sum due to independent raufidir& ;
energy as coal, and natural gas has only about 55 percent.3
Producing a unit of heat or electricity using natural gas
instead of coal can reduce the CO2 emissions associated with
energy consumption, and using nuclear or renewable energy
sources (e.g., wind) can essentially eliminate emissions (see
Box 3-2).
Figure 3-3
2002 U.S. Energy Consumption by Energy Source
I 6.0% Renewable
8.3% Nuclear
22.8% Coal
23.6%
Natural Gas
39.1%
Petroleum
In the United States, 86 percent of the energy consumed in
2002 was produced through the combustion of fossil fuels such
as coal, natural gas, and petroleum (see Figure 3-3 and Figure
3-4). The remaining portion was supplied by nuclear electric
power (8 percent) and by a variety of renewable energy sources
(6 percent), primarily hydroelectric power (EIA 2003a).
Figure 3-4
U.S. Energy Consumption (Quadrillion Btu)
120
100
f 60
e
" 40
e1
«
£ 20-
0J
Renewable & Nuclear
S S
S S
' Based on national aggregate carbon content of all coal, natural gas, and petroleum fuels combusted in the United States.
3-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Specifically, petroleum supplied the largest share of domestic
energy demands, accounting for an average of 39 percent of
total energy consumption from 1990 through 2002. Natural gas
and coal followed in order of importance, accounting for 24
and 23 percent of total consumption, respectively. Petroleum
was consumed primarily in the transportation end-use sector,
the vast majority of coal was used in electricity generation,
and natural gas was broadly consumed in all end-use sectors
except transportation (see Figure 3-5) (EIA 2003a).
Fossil fuels are generally combusted for the purpose
of producing energy for useful heat and work. During the
combustion process, the carbon stored in the fuels is oxidized
and emitted as CO2 and smaller amounts of other gases,
including CH4, CO, and NMVOCs.4 These other carbon
containing non-CO2 gases are emitted as a by-product of
incomplete fuel combustion, but are, for the most part,
eventually oxidized to CO2 in the atmosphere. Therefore,
except for the soot and ash left behind during the combustion
process, all the carbon in fossil fuels used to produce energy
is eventually converted to atmospheric CO2.
For the purpose of international reporting, the IPCC
(IPCC/UNEP/OECD/IEA 1997) recommends that particular
adjustments be made to national fuel consumption statistics.
Certain fossil fuels can be manufactured into plastics, asphalt,
lubricants, or other products. A portion of the carbon consumed
for these non-energy products can be stored (i.e., sequestered)
indefinitely. To account for the fact that the carbon in these fuels
ends up in products instead of being combusted (i.e., oxidized and
released into the atmosphere), the fraction of fossil fuel-based
carbon in manufactured products is subtracted from emission
estimates. (See the Carbon Stored in Products from Non-Energy
Uses of Fossil Fuels section in this chapter.) The fraction of this
carbon stored in products that is eventually combusted in waste
Table 3-4: Fossil Fuel Carbon in Products (Tg C02 Eq.)*
Figure 3-5
2002 C02 Emissions from Fossil Fuel Combustion
by Sector and Fuel Type
2,000
. 1,500
' 1,000
500-
o-
Relative Contribution
by Fuel Type
• Natural Gas
• Petroleum
• Coal
incinerators or combustion plants is accounted for in the Waste
Combustion section of this chapter.
According to the UNFCCC reporting guidelines, CO2
emissions from the consumption of fossil fuels for aviation
and marine international transport activities (i.e., international
bunker fuels) should be reported separately, and not included
in national emission totals. Estimates of carbon in products
and international bunker fuel emissions for the United States
are provided in Table 3-4 and Table 3-5.
End-Use Sector Consumption
An alternative method of presenting CO2 emissions is to
allocate emissions associated with electricity generation to the
sectors in which it is used. Four end-use sectors were defined:
industrial, transportation, residential, and commercial.5 For
the discussion below, electricity generation emissions have
been distributed to each end-use sector based upon the sector's
share of national electricity consumption. This method of
Sector
1990
Industrial
Transportation
Territories
Total
199.3
1996
239,5
1.1
0,6
241,2
1997
245,0
1,2
0.7
246.8
1998
258.1
1.2
0,7
260.1
1999
269,1
1.2
0,8
271.2
2000
256.7
1,2
1.1
259.0
2001
254.9
1.1
1.0
257.1
2002
258.4
1.1
1.1
260.6
* See Carbon Stored in Products from Non^Energy Uses of Fossil Fuels section for additional detail.
Note: Totals may not sum due to independent rounding.
See the sections entitled Stationary Combustion and Mobile Combustion in this chapter for information on non-CO2 gas emissions from fossil fuel
combustion.
See Glossary (Annex 6.8) for more detailed definitions of the industrial, residential, commercial, and transportation end-use sector, as well as electricity
generation.
Energy 3-5
-------
Box 3-1: Weather and Non-Fossil Energy Effects on CO, from Fossil Fuel Combustion Trends
In 2002, weather conditions became cooler In the winter, out much warmer in the summer. Heating degree days in the United States were 5
percent betow normal (see Figure 3-6} while eoolthg degree days in 2002 were 15 percent above normal (see Rgure 3-7) (EfA 2003e),6 Slightly
cooler winter conditions and a reduction In natural gas prices of 28 percent ted to an increase in demand for heating fuels. In the summer of
2002—one of the hottest summers on record—the U.S. demand for electricity for air conditioning increased.
Figure 3-6
Annual Deviations from Normal Heating Degree Days for the United States (1949-2002)
II
fl
II
a
15 -i
=5 10
I 5
0
-5
-10
-15 J
Normal
(4,576 Heating Degree Days)
1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002
Figure 3-7
Annual Deviations from Normal Cooling Degree Days for the United States (1949-2002)
20
99% Confidence
Normal
(1,193 Cooling Degree Days)
1950 1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998
2002
Although no new U.S. nuclear power plants have been con-
structed in recent years, the utilization (i.e., capacity factors7) of exist-
ing plants reached record levels in 2002, reaching 90 percent. This
increase in utilization translated into an increase in electricity output
by nuclear plantsof approximately 1 percent in 2002. In comparison,
electricity output by hydroelectric power plants increased significantly
in 2002 by approximately 22 percent. Nevertheless, electricity gener-
ated by nuclear plants in 2002 provided approximately 3 times as
much of the energy consumed in the United States as hydroelectric
plants (EIA 2003a). Aggregate nuclear and hydroelectric power plant
capacity factors since 1973 are shown in Figure 3-8.
Figure 3-8
Aggregate Nuclear and Hydroelectric Power Plant
Capacity Factors in the United States (1973-2002)
100
S S £ £
^ Degree days are relative measurements of outdoor air temperature. Heating degree days are deviations of the mean daily temperature below 65° F, while
cooling degree days are deviations of the mean daily temperature above 65° F. Heating degree days have a considerably greater affect on energy demand and
related emissions than do cooling degree days. Excludes Alaska and Hawaii. Normals are based on data from 1971 through 2000. The variation in these normals
during this time period was ±10 percent and ±14 percent for heating and cooling degree days, respectively (99 percent confidence interval).
7 The capacity factor is denned as the ratio of the electrical energy produced by a generating unit for a given period of time to the electrical energy that could
have been produced at continuous full-power operation during the same period (EIA 2003b).
3-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-5: C02 Emissions from International Bunker Fuels (Tg C02 Eq.)*
Vehicle Mode
Aviation
Marine
1«S7 1988
2«1 2182
55J
54.6
57.2
57.9
58,9
46,4
60J
40,9
59,4
38.5
1*3,9
18U 11i,t 185J 101.4
97J
Table 3-6: C02 Emissions from Fossil Fuel Combustion by End-Use Sector (Tg C02 Eq.)
59.1
27.7
86.8
End-Use Sector
Transportation
Combustion
Electricity
Industrial
Combustion
Electricity
Residential
Combustion
Electricity
Commercial
Combustion
Electricity
U.S. Territories
Total
Electricity Generation
1998
1,461.2
1,458.2
3.0
1,638.5
966.6
671.9
925.5
339.6
585.9
755J
224.2
531.6
33.7
4,814.7
1,792.4
1996
1,807,8
1,604.8
ao
t.TfitJ
1,045.$
723.7
1,053.1
!388J
6645
838.3
237.0
601.3
41.3
1997
1,617.8
1,614.8
3.1
1,800.7
t,058.4
742,3
1,043.5
370.6
673.0
879.4
237.2
642,2
42.6
1998
1,648.0
1,644.9
3.1
1,778.4
1,018.1
760.3
1,047.5
338.6
708.9
895.9
219.7
676.2
42.6
1999
1,788.1
1,702.9
3.2
1,768.4
1,001.9
766.4
1,068.5
359.3
707.3
904.2
222.3
681.9
43.7
2000
1,753.8
1,749.6
3.4
1,782.5
999.7
782.8
1,127.5
379.3
748.3
964.6
237.1
727.5
45.9
2001
1,734.1
1,730.6
3.5
1,687,5
970.8
716.7
1,117.5
366.9
750.7
974.6
227.3
747.3
45.0
2002
1,787.5
1,764.4
3.2
1,677.1
955.8
721.3
1,149.2
373.1
776.2
970.6
231.2
739.4
46.5
5.310.1 5,384.0 5,412.4 5,488.8 5,673.6 5,558.8 5,611.0
1,992.2 2,060.5 2,148.5 2,158.7 2^61.9 2ff8.2 2J40.1
Note: Totals may not sum due to Independent rounding. Emissions from fossil fuel combustion by electricity generation are allocated based on aggregate
national electricity consumption by each end-use sector.
distributing emissions assumes that each sector consumes
electricity generated from an equally carbon-intensive mix
of fuels and other energy sources. In reality, sources of
electricity vary widely in carbon intensity (e.g., coal versus
wind power). By giving equal carbon-intensity weight to
each sector's electricity consumption, emissions attributed to
one end-use sector may be somewhat overestimated, while
emissions attributed to another end-use sector may be slightly
underestimated. After the end-use sectors are discussed,
emissions from electricity generation are addressed separately.
Emissions from U.S. territories are also calculated separately
due to a lack of end-use-specific consumption data. Table 3-6
and Figure 3-9 summarize CO2 emissions from direct fossil
fuel combustion and pro-rated electricity generation emissions
from electricity consumption by end-use sector.
Transportation End-Use Sector
The transportation end-use sector accounted for the
largest share (approximately 32 percent) of CO2 emissions
Figure 3-9
2002 End-Use Sector Emissions of C02
from Fossil Fuel Combustion
from fossil fuel combustion.8 Almost all of the energy
consumed in the transportation sector was petroleum-
based, with nearly two-thirds being gasoline consumption
in automobiles and other highway vehicles. Other fuel
uses, especially diesel fuel for freight trucks and jet fuel for
aircraft, accounted for the remainder.9
' Note that electricity generation is actually the largest emitter of C02 when electricity is not distributed among end-use sectors.
See Glossary (Annex 6.8) for a more detailed definition of the transportation end-use sector.
Energy 3-7
-------
Carbon dioxide emissions from fossil fuel combustion
for transportation increased by 21 percent from 1990 to 2002,
to 1,767.5 Tg CO2 Eq. The growth in transportation end-
use sector emissions has been relatively steady, excluding
a 4.0 percent single year increase in 1999 and a 1.2 percent
decrease in 2001. Like overall energy demand, transportation
fuel demand is a function of many short and long-term factors.
In the short term only minor adjustments can generally be
made through consumer behavior (e.g., not driving as far for
summer vacation). However, long-term adjustments such as
vehicle purchase choices, transport mode choice and access
(i.e., trains versus planes), and urban planning can have a
significant impact on fuel demand.
In 2002, CO2 emissions from the transportation sector
increased by approximately 2 percent. The slight increase in
vehicle fuel demand is primarily due to a growing economy,10
as well as a 7 percent decrease in the price of motor gasoline
in 2002 (see Figure 3-10).
Since 1990, travel activity in the United States has
grown more rapidly than population, with a 16 percent
increase in vehicle miles traveled per capita. In the meantime,
improvements in the average fuel efficiency of the U.S. vehicle
fleet stagnated after increasing steadily since 1976 (FHWA
1996 through 2002). The average miles per gallon achieved by
the U.S. vehicle fleet has remained fairly constant since 1991.
This trend is due, in part, to the increasing dominance of new
motor vehicle sales by less fuel-efficient light-duty trucks and
sport-utility vehicles (see Figure 3-11).
Figure 3-10
Motor Gasoline Retail Prices (Real)
1977
1982
1987
1992
1997 2002
Table 3-7 provides a detailed breakdown of CO2 emissions
by fuel category and vehicle type for the transportation end-
use sector. Fifty-eight percent of the emissions from this
end-use sector in 2002 were the result of the combustion
of motor gasoline in passenger cars and light-duty trucks.
Diesel highway vehicles and jet aircraft were also significant
contributors, accounting for 15 and 13 percent of CO2 emissions
from the transportation end-use sector, respectively.11
Industrial End-Use Sector
The industrial end-use sector accounted for 30 percent
of CO2 emissions from fossil fuel combustion. On average,
57 percent of these emissions resulted from the direct
consumption of fossil fuels for steam and process heat
production. The remaining 43 percent was associated with
their consumption of electricity for uses such as motors,
electric furnaces, ovens, and lighting.
The industrial end-use sector includes activities such as
manufacturing, construction, mining, and agriculture.12 The
largest of these activities in terms of energy consumption
is manufacturing, which was estimated in 1998 to have
accounted for about 84 percent of industrial energy
consumption (EIA 2001a). Just six industries—Petroleum,
Chemicals, Primary Metals, Paper, Food, and, finally, Stone,
Clay, and Glass products—represent 83 percent of total
manufacturing energy use.
In theory, emissions from the industrial end-use sector
should be highly correlated with economic growth and
Figure 3-11
Motor Vehicle Fuel Efficiency
All Motor Vehicles
10 J
1972 1977 1982 1987 1992 1997 2002
10 Gross domestic product increased 2.2 percent between 2001 and 2002 (BEA 2004).
These percentages include emissions from bunker fuels.
1 See Glossary (Annex 6.8) for a more detailed definition of the industrial end-use sector.
3-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-7: C02 Emissions from Fossil Fuel Combustion in Transportation End-Use Sector (Tg C02 Eq.)
Fuel/Vehicle Type 1990
Gasoline
AutomobBes
Light Trucks .
Other Trucks
Buses
Motorcycles
Boats (Recreational)
Agricultural Equipment
Construcfjon EtjuJpwW8
Distillate Fuel Oil (Diesel)
AutomobBes
Light-Duty Trucks
Other Trucks
Buses
Locomotives
Ships & Boats
Agricultural Equipment
Construction Equipment
Ships (Bunkers)
Jet Fuel
Commercial Aircraft
Military Aircraft
General Aviation Aircraft
Otter Aircraft"
Aircraft punters)
Aviation Gasoline
General Aviation Aircraft
Residual Fuel Oil
Ships & Boats0
Ships (Bunkers)0
Natural Gas
Automobiles
Light Trucks
Buses
Pipeline
LPG
Light Trucks
Other Trucks
Buses
Electricity
Buses
Rail
Pipeline
Lubricants
Total (Including Bunkers)"
Total (Excluding Bunkers)"
955.2
593.9
297.3
39;8,
1:6
1.7
11.2
7.0
2.7
285.1
6.0
8.5
156.0
5.5
27.1
13.3
24.8
12,4
11.4
220.4
118.2
34.8
6.3
14.6
46.6
3.1
3.1
79.3
23.4
55.8
35.9
4-
4-
41
35.9
1.4
0.5
0.8
4-
3.9
4-
0.6
2.4
11.7
1,575,1
1,461.2
| 1996
1,834.9
585.4
391.5
35.8
0.9
1.7
8.5
7.8
• 2.4
323.7
4.6
12.0
206.2
7.2
31.7
14.7
25.8
13,2
8.3
229.8
124.9
23.1
5.8
23.9
52,2
2.6
2,6
66.4
24.6
L. .-41 At
I • 384
••»•"••
4-
0.1
38.7
9.9
0.4
0.5
4
3.9
4
0.6
2.4
I 10.9
1,719.1
I 1,887.8
1997
1,942.5
583.6
402.8
34.4
0.7
: -. 1,7
8.3
8.3
2.5
338.4
4.5
12.9
219.4
7.5
,31.6
14.4
25.6
13.4
9.1
232.1
129.4
21.0
6.1
19.7
55.9
2J
2.7
55,5
10.6
.-.., 44J
:'v. -'414 '
'' -v 4-
4.
0.2
40.9
9.8
0.4
0.4
4-
3.1
4-
0.7
2.4
11.5
1,727.7
1,617.8
1998
1,872.9
603.7
414.3
34.6
0.7
1.7
8.1
7.7
2.0
348.4
4.3
13.0
229.1
7.7
.32.1
12.8
23.8
14.0
11.5
235.6
131.4
21.5
7.7
17.7
57.2
2.4
2.4
52.6
6.2
46.4
35.1
4-
4-
0.2
34.9
1.0
0.4
0.6
4-
3.1
4-
0.6
2.5
12,0
1,763.1
1,648.8
1999
1,099.9
614.9
432.1
33.7
0.7
1.8
9.3
5.9
1.5
382.2
4.2
13.9
2419
8.7
33.5
15.1
22.7
13.9
8.2
242.9
136.4
20.6
9.2
17.9
58.9
2.7
2.7
51.9
13.7
382,
35.6
4
4
0.3
35.3
0.8
0.3
0.5
4- '
3.2
4-
0.7
2.5
12.1
1,811.4
1,786.1
2889
1.185J
617.7
435.8
33.4
0,6
1.8
9,6
5.6
i.e
374.9
4.0
14.1
252.8
8.4
33.3
15.0
24.9
15.3
6.2
251.2
140.6
21.0
9.5
19J
60.5
2.5
2.5
69.2
34.6
• .,• 34,6,;; =„
,\ ,,3§it:;;7
' s. ' 4,' '• '
4-
0.4
35.0
8.7
0.3
0.4
4-
3.4
4-
0.7
2.6
Itt
1,814.4
1,753,8
2881
1,1112.
619.4
438.6
3t.§
0.5
t,6
8.4
, 8,8
4,3
383.2
3J
145
257.1
7.9
33.8
16.3
27.4
17.1
5.2
249.4
132.8
22.8
8.9
16.5
59.4
2.4
2.4
41.7
12.4
....'.;-v3&&>.;
• .;,i«MLv
1 "' ''"+' "
4i
0.5
33.4
8.8
0.3
0.5
4-
3.5
4-
0.8
2.7
11 J
1,832.0
1,734.1
2882
1*138.7
633.4
450.9
316
0.4
1.6
, 9.2
7.1
4.5
379.0
3.5
14.2
260.3
7.5
32.8
15.9
25.5
14.3
5.1
234.4
121.7
20.5
9.6
23.4
59.1
2.3
2.3
49,9
,27.3
.•/:/,$2»6
*;V"'-jl|i2
, . .. \q_
4-
0.5
34.7
9.9
0.3
0.5
4
3.2
4
0.7
2.4
18.8
1,854.4
1,787.5
+ Does not exceed 0.05 T0 COa Eq.
Note: Totals may not aim (Jus to independent rounding.,
a The large increase In emissions from gasoline construction equipment is due primarily to a change in FHWA methodology in estimating gasoline
consumption by non-road sources, rather than from a significant increase In use of construction equipment
b Including but not limited to fuel blended with heating oils and fuel used for chartered aircraft flights.
c Fluctuations in emission estimates from the combustion of residual fuel oil are currently unexplained, but may be related to data collection problems.
d Official estimates exclude emissions from the combustion of both aviation and marine international bunker fuels; however, estimates including
international bunker fuel-related emissions are presented for informational purposes.
industrial output, but heating of industrial buildings and
agricultural energy consumption is also affected by weather
conditions.13 In addition, structural changes within the U.S.
economy that lead to shifts in industrial output away from
Some commercial customers are large enough to obtain an industrial price for natural gas and/or electricity and are consequently grouped with the
industrial end-use sector in U.S. energy statistics. These misclassifications of large commercial customers likely cause the industrial end-use sector to
appear to be more sensitive to weather conditions.
Energy 3-9
-------
energy intensive manufacturing products to less energy
intensive products (e.g., from steel to computer equipment)
also have a significant affect on industrial emissions.
From 2001 to 2002, total industrial production and
manufacturing output were reported to have decreased
by 0.6 and 0.5 percent, respectively (FRB 2003). Output
declined for the Primary Metals, Paper, and Stone, Clay,
and Glass industries, but increased for Petroleum Refineries,
Chemicals, and Food (see Figure 3-12).
Despite the growth in industrial output (44 percent)
and the overall U.S. economy (42 percent) from 1990 to
2002, emissions from the industrial end-use sector increased
only slightly (by 2 percent). The reasons for the disparity
between rapid growth in industrial output and stagnant
growth in industrial emissions are not entirely clear. It is
likely, though, that several factors have influenced industrial
emission trends, including: 1) more rapid growth in output
from less energy-intensive industries relative to traditional
manufacturing industries, 2) improvements in energy
efficiency; and 3) a lowering of the carbon intensity of
fossil fuel consumption as industry shifts from its historical
Figure 3-12
Industrial Production Indexes (Index 1997 = 100)
130 -
110 -
90 -
70
Total excluding Computers,
Communications Equip.,_and
Semiconductors
Total
Industrial
110
90 -
70 -
110 -
90
70 J
Stone, Clay & Glass Products
Petroleum Refineries
Primary Metals
reliance on coal and coke to heavier usage of natural gas. In
2002, carbon dioxide emissions from fossil fuel combustion
and electricity use within the industrial end-use sectors were
1,677.1 Tg CO2 Eq., or 0.6 percent below 2001 emissions.
These lowered emissions correlate with the decrease in
manufacturing output.
Industry was the largest user of fossil fuels for non-
energy applications. Fossil fuels can be used for producing
products such as fertilizers, plastics, asphalt, or lubricants
that can sequester or store carbon for long periods of time.
Asphalt used in road construction, for example, stores carbon
essentially indefinitely. Similarly, fossil fuels used in the
manufacture of materials like plastics can also store carbon,
if the material is not burned. The amount of carbon contained
in industrial products made from fossil fuels rose 31 percent
between 1990 and 2002, to 258.4 Tg CO2 Eq.14
Residential and Commercial End-Use Sectors
The residential and commercial end-use sectors
accounted for an average 20 and 17 percent, respectively,
of CO2 emissions from fossil fuel combustion. Both end-
use sectors were heavily reliant on electricity for meeting
energy needs, with electricity consumption
for lighting, heating, air conditioning, and
operating appliances contributing to about 68
and 76 percent of emissions from the residential
and commercial end-use sectors, respectively.
The remaining emissions were largely due
to the direct consumption of natural gas and
petroleum products, primarily for heating and
cooking needs. Coal consumption was a minor
component of energy use in both of these end-
use sectors. In 2002, CO2 emissions from fossil
fuel combustion and electricity use within the
residential and commercial end-use sectors
were 1,149.2 Tg CO2 Eq. and 970.6 Tg CO2
Eq., respectively.
Since 1990, emissions from residences
and commercial buildings have increased
relatively steadily, unlike those from the
industrial sector, which experienced sizeable
reductions during the economic downturns of
1991 and 2001 (see Table 3-6). This difference
See the Carbon Stored in Products in Non-Energy Uses of Fossil Fuels for a more detailed discussion. Also, see Waste Combustion in the Waste chapter
for a discussion of emissions from the incineration or combustion of fossil fuel-based products.
3-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Figure 3-13
Figure 3-14
120!
110
100
90(1
80 J
Heating Degree Days1
Normal
(5,424 Heating Degree Days)
exists because short-term fluctuations in energy consumption
in these sectors are correlated more with the weather than by
prevailing economic conditions. In the long-term, both end-
use sectors are also affected by population growth, regional
migration trends, and changes in housing and building
attributes (e.g., size and insulation).
Emissions from natural gas consumption represent over
70 percent of the direct (not including electricity) fossil fuel
emissions from the residential and commercial sectors. In
2002, these emissions increased by 3 percent in each of these
sectors. Slightly cooler winter conditions in the United States
(see Figure 3-13) and the decrease in natural gas prices (28
percent) led to higher demand for natural gas.
Electricity sales to the residential and commercial
end-use sectors in 2002 increased by 5 and 2 percent,
respectively. This trend can be attributed to the hot summer
of 2002, which led to increased air-conditioning related
electricity consumption (see Figure 3-14), and to reduced
electricity prices (3 and 2 percent lower to the residential
and commercial sectors, respectively). Despite an increase
in electricity consumption from both sectors, electricity-
related emissions fell in the commercial sector as the decline
in carbon intensity of electricity generation outweighed
the slight increase in electricity demand. Emissions from
the residential sector increased by 2.8 percent in 2002, as
the increase in energy demand was more robust than in
the commercial sector. Consumption of electricity in the
residential sector is more price-sensitive than the commercial
sector, as individual consumers have more choices than
120
§ 110
'M
I S
| 1M-
| 90-
80
Cooling Degree Days1
Normal
(1,215 Cooling Degree Days)
^lOtOt1— OOOJ
T— CM
CNJ CM
Figure 3-15
Electricity Generation Retail Sales by End-Use Sector
1,400
1,200-
| 1,000
I 800-
600
400 J
1972 1976
Industrial
1988 1992 1996 2000
businesses and institutions. Therefore, the declining price of
electricity in 2002 further increased the electricity demanded
by residences.
Electricity Generation
The process of generating electricity is the single largest
source of CO2 emissions in the United States (39 percent).
Electricity was consumed primarily in the residential,
commercial, and industrial end-use sectors for lighting,
heating, electric motors, appliances, electronics, and air
conditioning (see Figure 3-15). Electricity generation also
accounted for the largest share of CO2 emissions from fossil
fuel combustion, approximately 40 percent in 2002.
The electric power industry includes all power producers,
consisting of both regulated utilities and nonutilities (e.g.
independent power producers, qualifying cogenerators, and
'' Degree days are relative measurements of outdoor air temperature. Heating degree days are deviations of the mean daily temperature below 65° F.
Excludes Alaska and Hawaii. Normals are based on data from 1971 through 2000.
Degree days are relative measurements of outdoor air temperature. Cooling degree days are deviations of the mean daily temperature above 65° F.
Excludes Alaska and Hawaii. Normals are based on data from 1971 through 2000.
Energy 3-11
-------
other small power producers). While utilities primarily generate
power for the U.S. electric grid for sale to retail customers,
nonutilities produce electricity for their own use, to sell to large
consumers, or to sell on the wholesale electricity market (e.g.,
to utilities for distribution and resale to customers). However,
the electric power industry in the United States has undergone
significant changes as both federal and state government
agencies have modified regulations to create a more competitive
market for electricity generation. These changes have led to
the growth of nonutility power producers, including the sale
of generating capacity by electric utilities to nonutilities. As a
result, the Department of Energy no longer categorizes electric
power generation into these ownership groups, and is instead
using two new functional categories: electricity-only and
combined-heat-and-power. Electricity-only plants are those that
solely produce electricity, whereas combined-heat-and-power
plants produce both electricity and heat.
In 2002, the amount of electricity generated increased
by 3 percent due to the growing economy and hotter summer
weather. However, CO2 emissions increased by only 1
percent, as a larger share of electricity was generated from
renewable resources. In fact, overall carbon intensity from
energy consumption for electricity generation decreased in
2002 (see Table 3-9). One of the main reasons for the increase
in renewable energy was a 22 percent growth in output from
hydroelectric dams.
Coal is consumed primarily by the electric power sector
in the United States, which accounted for 93 percent of total
coal consumption for energy purposes in 2002. Consequently,
changes in electricity demand have a significant impact on
coal consumption and associated U.S. CO2 emissions. Coal
consumption for electricity generation increased by 2.2
percent in 2002, due to the increase in electricity demand.
However, natural gas consumption for electricity generation
grew at a higher rate of 3.4 percent, partially attributed to
fuel-switching from coal to natural gas.
•
Methodology
The methodology used by the United States for
estimating CO2 emissions from fossil fuel combustion is
conceptually similar to the approach recommended by the
IPCC for countries that intend to develop detailed, sectoral-
based emission estimates (IPCC/UNEP/OECD/IEA 1997). A
detailed description of the U.S. methodology is presented in
Annex 2.1, and is characterized by the following steps:
1. Determine fuel consumption by fuel type and sector.
Total fossil fuel consumption for each year is estimated
by aggregating consumption data by end-use sector
(e.g., commercial, industrial, etc.), primary fuel type
(e.g., coal, petroleum, gas), and secondary fuel cat-
egory (e.g., motor gasoline, distillate fuel oil, etc.). Fuel
consumption data for the United States were obtained
directly from the Energy Information Administration
(EIA) of the U.S. Department of Energy (DOE), primar-
ily from the Monthly Energy Review and unpublished
supplemental tables on petroleum product detail (EIA
2003a). The United States does not include territories in
its national energy statistics, so fuel consumption data
for territories were collected separately from the EIA.22
Portions of the fuel consumption data for three fuel
categories—coking coal, petroleum coke, and natural
gas—were reallocated to the industrial processes chap-
ter, as they were actually consumed during non-energy
related industrial activity. To make these adjustments,
additional data were collected from EFMA (1995),
U.S. Census Bureau (1991 through 1994), U.S. Census
Bureau (1998 through 2003), EIA (2000 through 2003),
EIA (200 Ib), USGS (2003), USGS (1998 through 2002),
USGS (1995), USGS (1995 through 2003), USGS (1991
through 1994), USGS (1991 through 2003), and Onder
andBagdoyan(1993).23
For consistency of reporting, the IPCC has recom-
mended that countries report energy data using the
International Energy Agency (IEA) reporting convention
and/or IEA data. Data in the IEA format are presented
"top down" that is, energy consumption for fuel types
and categories are estimated from energy production
data (accounting for imports, exports, stock changes,
and losses). The resulting quantities are referred to
as "apparent consumption." The data collected in the
United States by EIA, and used in this inventory, are,
instead, "bottom up" in nature. In other words, they are
Fuel consumption by U.S. territories (i.e. American Samoa, Guam, Puerto Rico, U.S. Virgin Islands, Wake Island, and other U.S. Pacific Islands) is
included in this report and contributed emissions of 46 Tg CO2 Eq. in 2002.
See sections on Iron and Steel Production, Ammonia Manufacture, Titanium Dioxide Production, Ferroalloy Production, and Aluminum Production
in the Industrial Processes chapter.
3-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Box 3-2: Carbon Intensity of U.S. Energy Consumption
are ttedonteant source of snergy in the United States, and C02 Is emitted as a product from tnelr combusBon. Useful
«an^
Energy-related C02 emissions can be reduced by not only lowering total energy consumption (e.g., through conservation measures)
but
economy. Tr»time series tncoiporales arty fte
Small quantities of CO2, however, are released from some geologic formations tapped for geothermal energy. These emissions are included with fossil
fuel combustion emissions from the electricity generation. Carbon dioxide emissions may also be generated from upstream activities (e.g., manufacture
of the equipment) associated with fossil fuel and renewable energy activities, but are not accounted for here.
' Generally, more than 97 percent of the carbon in fossil fuel is oxidized to CO, with most carbon combustion technologies used in the United States.
19 One exajoule (EJ) is equal to 1018 joules or 0.9478 QBtu.
Net carbon fluxes from changes in biogenic carbon reservoirs in wooded or croplands are accounted for in the estimates for Land-Use Change and Forestry.
Energy 3-13
-------
In contrast to Table 3-8, Table 3-9 presents carbon Intensity values that incorporate energy consumed from all sources (i.e., fossil
fuels, renewables, and nuclear)/ In addition, Vie emissions related to the generation of electricity have been attributed to both electricity
generation and the end-use sectors in which that electricity was eventually consumed.21 This table, therefore, provides a more complete
picture of the actual carbon intensify of each end-use sector per unit of energy consumed. The transportation end-use sector in Table
3-9 emerges as fte most carbon pensive when all sources of energy are fnetodad,
-------
collected through surveys at the point of delivery or use
and aggregated to determine national totals.24
It is also important to note that U.S. fossil fuel energy
statistics are generally presented using gross calorific
values (GCV) (i.e., higher heating values). Fuel con-
sumption activity data presented here have not been
adjusted to correspond to international standard, which
are to report energy statistics in terms of net calorific
values (NCV) (i.e., lower heating values).25
2. Determine the total carbon content of fuels consumed.
Total carbon was estimated by multiplying the amount
of fuel consumed by the amount of carbon in each fuel.
This total carbon estimate defines the maximum amount
of carbon that could potentially be released to the atmo-
sphere if all of the carbon in each fuel was converted to
CO2. The carbon content coefficients used by the United
States were obtained from EIA's Emissions of Greenhouse
Gases in the United States 2002 (EIA 2003b) and EIA's
Monthly Energy Review and unpublished supplemental
tables on petroleum product detail EIA (EIA 2003a). They
are presented in Annexes 2.1 and 2.2.
3. Subtract the amount of carbon stored in products. Non-
energy uses of fossil fuels can result in storage of some
or all of the carbon contained in the fuel for some period
of time, depending on the end-use. For example, asphalt
made from petroleum can sequester up to 100 percent
of the carbon for extended periods of time, while other
fossil fuel products, such as lubricants or plastics, lose
or emit some carbon when they are used and/or burned
as waste. Because U.S. aggregate energy statistics in-
clude consumption of fossil fuels for non-energy uses,
the portion of carbon that remains in products after they
are manufactured was subtracted from potential carbon
emission estimates.26 The amount of carbon remaining
in products was based on the best available data on
the end-uses and fossil fuel products. These non-en-
ergy uses occurred in the industrial and transportation
end-use sectors and U.S. territories. Emissions of CO2
associated with the disposal of these fossil fuel-based
products are not accounted for here, but are instead
accounted for under the Waste Combustion section in
this chapter. Estimates of carbon stored in products are
further discussed in the section entitled Carbon Stored
in Products from Non-fuel Uses of Fossil Fuels.
4. Subtract the amount of carbon exported as CO2. Since
2000, the Dakota Gasification Plant in North Dakota has
been exporting CO2 to Canada, which was originally
generated as a byproduct from the production of syn-
thetic natural gas from coal gasification. Since this CO2
is not emitted to the atmosphere in the United States, it
is subtracted from the potential carbon emissions from
industrial other coal. The composition of the exported
gas was obtained from the Dakota Gasification Company
(2003), and data on the pipeline flow rate was obtained
from Fitzpatrick (2002) and Erickson (2003).
5. Subtract the amount of carbon from international
bunker fuels. According to the UNFCCC reporting
guidelines emissions from international transport ac-
tivities, or bunker fuels, should not be included in na-
tional totals. U.S. energy consumption statistics include
these bunker fuels (e.g., distillate fuel oil, residual
fuel oil, and jet fuel) as part of consumption by the
transportation end-use sector, however, so emissions
from international transport activities were calculated
separately following the same procedures used for
emissions from consumption of all fossil fuels (i.e.,
estimation of consumption, determination of carbon
content, and adjustment for the fraction of carbon not
oxidized).27 The Office of the Under Secretary of De-
fense (Installations and Environment) and the Defense
Energy Support Center (Defense Logistics Agency) of
the U.S. Department of Defense (DoD) (DESC 2003)
supplied data on military jet fuel use. Commercial jet
fuel use was obtained from BEA (1991 through 2003)
and DOT (1991 through 2003); residual and distillate
fuel use for civilian marine bunkers was obtained from
DOC (1991 through 2003). The carbon content of these
fuels was subtracted from the carbon contents of the
corresponding fuels in the transportation end-use sec-
tor. Estimates of international bunker fuel emissions are
24 See IPCC Reference Approach for estimating CO2 emissions from fossil fuel combustion in Annex 4 for a comparison of U.S. estimates using
top-down and bottom-up approaches.
A crude convention to convert between gross and net calorific values is to multiply the heat content of solid and liquid fossil fuels by 0.95 and gaseous fuels by
0.9 to account for the water content of the fuels. Biomass-based fuels in U.S. energy statistics, however, are generally presented using net calorific values.
2" See Carbon Stored in Products from Non-Energy Uses of Fossil Fuels section in this chapter for a more detailed discussion.
97
See International Bunker Fuels section in this chapter for a more detailed discussion.
Energy 3-15
-------
discussed further in the section entitled International
Bunker Fuels.
6. Adjust for carbon that does not oxidize during combus-
tion. Because combustion processes are not 100 percent
efficient, some of the carbon contained in fuels is not
emitted to the atmosphere. Rather, it remains behind
as soot and ash. The estimated amount of carbon not
oxidized due to inefficiencies during the combustion
process was assumed to be 1 percent for petroleum and
coal and 0.5 percent for natural gas (see Annex 2.1).
Unoxidized or partially oxidized organic (i.e., carbon
containing) combustion products were assumed to have
eventually oxidized to CO2 in the atmosphere.28 IPCC
provided fraction oxidized values for petroleum and
natural gas (IPCC/UNEP/OECD/IEA 1997). Bechtel
(1993) provided the fraction oxidation value for coal.
Carbon intensity estimates were developed using
nuclear and renewable energy data from EIA (2003 a)
and fossil fuel consumption data as discussed above and
presented in Annex 2.1.
7. Allocate transportation emissions by vehicle type. This
report provides a more detailed accounting of emissions
from transportation because it was such a large consumer
of fossil fuels in the United States.29 For fuel types other
than jet fuel, fuel consumption data by vehicle type and
transportation mode were used to allocate emissions by fuel
type calculated for the transportation end-use sector. These
fuel consumption data were obtained from AAR (2003),
Benson (2002), BEA (1991 through 2003), DESC (2003),
DOC (1991 through 2003), DOE (1993 through 2003),
DOT (1991 through 2003), EIA (2003a), EIA (2003c),
EIA (1991 through 2003), FAA (1995 through 2003), and
FHWA (1996 through 2003), and heat contents and densi-
ties were obtained from EIA (2003a) and USAF (1998).30
The difference between total U.S. jet fuel consumption (as
reported by EIA) and civilian air carrier consumption for
both domestic and international flights (as reported by DOT
and BEA) plus military jet fuel consumption is reported as
"other" under the jet fuel category in Table 3-7, and includes
such fuel uses as blending with heating oils and fuel used
for chartered aircraft flights.
Uncertainty
For estimates of CO2 from fossil fuel combustion, the
amount of CO2 emitted is directly related to the amount of
fuel consumed, the fraction of the fuel that is oxidized, and
the carbon content of the fuel. Therefore, a careful accounting
of fossil fuel consumption by fuel type, average carbon
contents of fossil fuels consumed, and production of fossil
fuel-based products with long-term carbon storage should
yield an accurate estimate of CO2 emissions.
Nevertheless, there are uncertainties in the consumption
data, carbon content of fuels and products, and carbon
oxidation efficiencies. For example, given the same primary
fuel type (e.g., coal, petroleum, or natural gas), the amount
of carbon contained in the fuel per unit of useful energy can
vary. For the United States, however, the impact of these
uncertainties on overall CO2 emission estimates is believed
to be relatively small. See, for example, Marland and Pippin
(1990).
The uncertainty analysis was performed by primary fuel
type for each end-use sector, using the IPCC-recommended
Tier 2 uncertainty estimation methodology, Monte Carlo
Stochastic Simulation technique, with @RISK software. For
this uncertainty estimation, the inventory estimation model
for CO2 from fossil fuel combustion was integrated with the
relevant inventory variables from the inventory estimation
model for International Bunker Fuels, to realistically
characterize the interaction (or endogenous correlation)
between the variables of these two models. A total of 163
input variables were modeled (141 for CO2 from Fossil Fuel
Combustion and 22 for International Bunker Fuels).
In developing the uncertainty estimation model,
uniform distribution was assumed for all activity-related
input variables and emission factors, based on the SAIC/
EIA (2001) report.31 Triangular distribution was assigned
for the oxidization factors (or combustion efficiency). The
9R
See Indirect CO2 from CH4 Oxidation section in this chapter for a more detailed discussion.
Electricity generation is not considered a final end-use sector, because energy is consumed primarily to provide electricity to the other sectors.
-^ For a more detailed description of the data sources used for the analysis of the transportation end use sector see the Mobile Combustion (excluding
CO2) and International Bunker Fuels sections of the Energy chapter, Annex 3.2, and Annex 3.7.
SAIC/EIA (2001) characterizes the underlying probability density function for the input variables as a combination of uniform and normal distributions
(the former to represent the bias component and the latter to represent the random component). However, for purposes of the current uncertainty analysis,
it was determined that uniform distribution was more appropriate to characterize the probability density function underlying each of these variables.
3-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-10: Uncertainty Estimates for C02 from Fossil Fuel Combustion by Fuel Type and Sector
2002 Emission Estimate
Uncertainty Range Relative to Emission Estimate3
Fuel/Sector
ptffsteteft,
Coal*
ResWentW
Commercial
WusWaf
Transparfafon
SeetrfE% generation
U.S. Territories
Natural Gas"
Residential
Commercial
Industrial
Transportaion
Ele<*rtcly Generation
U.S. Territories
Petroleum"
Residential
Commerctal
WusWal
Transportation
UectfcOBI»8
U.S. Territories
Total (excluding Geothermal)11
Geothermal '••;. '/.••':'••/
Total (including Geothermal)bc
2,085.6
1.1
1.2
121.9
' -.. m
1,868.4
OJ
1,195 J
267.2
189.4
423.7
•• ,35.2 "
299.1
1.2
2,499.4
104.7
'•'•• &?•*"••'•*
4BS.1
1>72&2
72.2
44.4
;. • 5,110,8; .'^
• . •• . 83-.. ;.
S.611J
Lower Bound
1,954.7
1,1
8.7
123.1
NE
1,808.3
0.8
1,181.3
260.6
165.2
412.1
34.3
291.5
1.1
2,284.9
. m§
•••-'"• -: sas
352.5
1,624.7
70.4
41.4
$.528.3
HI
1,128.8
Upper Bound
2,209.6
1.3
10.6
147.8
NE
2,061.8
1.1
1,258.1
286.9
181,8
455.2
37.7
315.3
1.4
2,547.0
110.5
55.4
454.1
1,855.7
75.4
49.3
5,912.2
NE
5,912,1
Lower Bound
-3%
• .• -5% ,
-5%-
• ^»-. •'.-
NA
.-a% ' -. •
%12%V '.'.' "v
• • -1% •'•'•*•
-2%
•2%
-3%
-2%
-3%
-12%
-5%
-5%
4%
-13%
-6%
-2%
-7%
•1%
: m
.'• -t% . ",„•:
Upper Bound
• f10%:',. "'
••fISll.-..' '• •
- • *lS%-
•''-4*iH%>-': '
' '/;••:'! HP^.; '.". '
-4'lM -' .'• '
-• ;' >&$fflb ,•
• •• -*!%'
4-7%
. •' ' 4-7% •/ : •
- . +7%
••'• 4-7%-
-f5%
+17%
-1-6%
4-6%
+5%
+12%
.4-7%
+4%
+11%
*l^ •.,;.
,;' ,'':.;-:li;:- •
: ..;--*l^ '•'•:"'
', hence, the tow and high emission estimates for the
, but an uncertainty analysis was not performed for C02 emissions from geothermal production.
uncertainty ranges were assigned to the input variables
based on the data reported in SAIC/EIA (2001) and on
conversations with various agency-personnel.32
The uncertainty ranges for the activity-related input
variables were typically asymmetric around their inventory
estimates; the uncertainty ranges for the emissions factors
were symmetric. Bias (or systematic uncertainties) associated
with these variables accounted for much of the uncertainties
associated with these variables (SAIC/EIA 2001 ).33 For
purposes of this uncertainty analysis, each input variable was
simulated 10,000 times through Monte Carlo Sampling.
The preliminary results of the quantitative uncertainty
analysis (see Table 3-10) indicate that, on average, in 19 out of 20
times (i.e., there is a 95 percent probability), the total greenhouse
gas emissions estimate from this source is within the range of
approximately 5,528.6 to 5,912.2 Tg CO2 Eq. (indicating that
the actual CO2 emissions are likely to fall within the range of
approximately 1 percent below and 5 percent above the emission
estimate of 5,611.0 Tg CO2 Eq.).
32 In the SAIC/EIA (2001) report, the quantitative uncertainty estimates were developed for each of the three major fossil fuels used within each end-use
sector; the variations within the sub-fuel types within each end-use sector were not modeled. However, for purposes of assigning uncertainty estimates
to the sub-fuel type categories within each end-use sector in the current uncertainty analysis, SAIC/EIA (2001)-reported uncertainty estimates were
extrapolated.
Although, in general, random uncertainties are the main focus of statistical uncertainty analysis, when the uncertainty estimates are elicited from experts,
their estimates include both random and systematic uncertainties. Hence, both these types of uncertainties are represented in this uncertainty analysis.
Energy 3-17
-------
Although statistics of total fossil fuel and other energy
consumption are relatively accurate, the allocation of this
consumption to individual end-use sectors (i.e., residential,
commercial, industrial, and transportation) is less certain.
For example, for some fuels the sectoral allocations
are based on price rates (i.e., tariffs), but a commercial
establishment may be able to negotiate an industrial rate
or a small industrial establishment may end up paying an
industrial rate, leading to a misallocation of emissions.
Also, the deregulation of the natural gas industry and the
more recent deregulation of the electric power industry have
likely led to some minor problems in collecting accurate
energy statistics as firms in these industries have undergone
significant restructuring.
Non-energy uses of fuel can add complexity because
the carbon might not be emitted to the atmosphere (e.g.,
plastics, asphalt, etc.) or might be emitted at a delayed
rate. This report makes assumptions about the proportions
of fuels used in these non-energy production processes
that result in the sequestration of carbon. Additionally,
inefficiencies in the combustion process, which can result
in ash or soot remaining unoxidized for long periods, were
also assumed. These factors all contribute to the uncertainty
in the CO2 estimates. More detailed discussions on the
uncertainties associated with Carbon Stored in Products
from Non-Energy Uses of Fossil Fuels can be found within
that section of this chapter.
Various uncertainties surround the estimation of
emissions from international bunker fuels, which are
subtracted from U.S. totals (see the detailed discussions
on these uncertainties provided in the International Bunker
Fuels section of this chapter). Another source of uncertainty
is fuel consumption by U.S. territories. The United States
does not collect energy statistics for its territories at the
same level of detail as for the fifty states and the District of
Columbia. Therefore, estimating both emissions and bunker
fuel consumption by these territories is difficult.
For Table 3-7, uncertainties also exist as to the data used
to allocate CO2 emissions from the transportation end-use
sector to individual vehicle types and transport modes. In
many cases, bottom-up estimates of fuel consumption by
vehicle type do not match aggregate fuel-type estimates from
EIA. Further research is planned to improve the allocation
into detailed transportation end-use sector emissions. In
particular, residual fuel consumption data for marine vessels
are highly uncertain, as shown by the large fluctuations in
emissions.
QA/QC and Verification
A source-specific QA/QC plan for CO2 from fossil fuel
combustion was developed and implemented. This effort
included a Tier 1 analysis, as well as portions of a Tier 2
analysis. The Tier 2 procedures that were implemented
involved checks specifically focusing on the activity data
and methodology used for estimating CO2 emissions from
fossil fuel combustion in the United States. Emission
totals for the different sectors and fuels were compared
and trends were investigated to determine whether any
corrective actions were needed. Minor corrective actions
were taken.
Recalculations Discussion
In previous inventories, a single annually variable
carbon content coefficient for LPG was used. This factor
was comprised of the carbon content of each type of LPG,
weighted by the proportion that each was consumed. For the
current inventory, two series of weighted-average carbon
content for LPG are used: one for fuel use only, and one for
non-fuel use in the industrial sector.
Emissions from industrial coal are now adjusted to
account for carbon exported as CO2 to Canada. This CO2 is
a byproduct of synthetic natural gas production through the
gasification of industrial coal.
The previously static feedstock storage factor is
now annually variable, based on a revised methodology
that is described in the Recalculations discussion of the
"Carbon Stored in Products from Non-Energy Uses of
Fossil Fuels."
The Energy Information Administration (EIA 2003a)
updated energy consumption data for all years. The
major changes include: (1) revisions to U.S. territories'
petroleum use data for 1995 through 2001; (2) inclusion of
an additional fuel category—commercial petroleum coke;
and (3) revisions to historical data per extensive review
and resolution of anomalies by EIA (e.g., distillate fuel
use in all sectors). These revisions specifically impacted
the residential, commercial, and industrial petroleum
estimates.
3-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
The combination of the methodological and histori-
cal data changes, as well as changes in the estimates of
Carbon Stored in Products from Non-Energy Uses of
Fossil Fuels and International Bunker Fuels (which affect
emissions from this source), resulted in an average annual
decrease of 12.3 Tg CO2 Eq. (0.2 percent) in CO2 emis-
sions for the period 1990 through 2001.
Planned Improvements
Several items are being evaluated to improve the
estimates of CO2 emissions from fossil fuel combustion and
to reduce uncertainty:
• Currently in the emission calculation spreadsheets,
carbon from bunker fuels and carbon stored by fuels is
subtracted from energy-fuel-use carbon. This calculation
will be revised in order to subtract out bunker and non-
energy fuel use at the consumption step, allowing for
clearer and more transparent emission calculations.
• Currently, the IPCC guidelines recommend a default
factor of 0.99 to represent the fraction of carbon in
fossil fuels that is oxidized to CO2 during the fuel
combustion of petroleum, though national experts are
encouraged to improve upon this assumption if better
data is available. As a result, carbon mass balances for
light-duty gasoline cars and trucks have been analyzed
to assess what would be the most appropriate carbon
oxidation fraction for these vehicles. The analysis,
currently under peer review, suggests that the amount
of unoxidized carbon is insignificant compared to the
gaseous carbon fraction, and that 1.00 should be used
to represent the oxidized carbon fraction in future in-
ventories for gasoline fueled light-duty vehicles. Upon
further peer review, the revised factor is expected to be
used in future inventories. A further examination into
diesel fueled vehicles is also planned.
• The 0.99 oxidation factor for coal will be further inves-
tigated in order to verify or revise this value.
• Efforts will be taken to work with EIA and other agen-
cies to improve the quality of the U.S. territories data.
These improvements are not all-inclusive, but are part
of an ongoing analysis and efforts to continually improve
the CO2 from fossil fuel combustion estimates.
3.2. Carbon Stored in Products from
Non-Energy Uses of Fossil Fuels
(IPCC Source Category 1A)
In addition to being combusted for energy, fossil fuels are
also consumed for non-energy uses (NEU). The types of fuels
consumed in non-energy uses are listed in Table 3-11. These
fuels are used in the industrial and transportation end-use sectors
and are quite diverse, including natural gas, liquid petroleum
gases (LPG), asphalt (a viscous liquid mixture of heavy crude
oil distillates), petroleum coke (manufactured from heavy oil),
and coal coke (manufactured from coking coal.) The non-energy
fuel uses are equally diverse, and include application as solvents,
lubricants, and waxes, or as raw materials in the manufacture of
plastics, rubber, synthetic fibers, and fertilizers.
Carbon dioxide emissions arise from non-energy uses via
several pathways. Emissions may occur during the manufacture
of a product, as is the case in producing plastics or rubber from
fuel-derived feedstocks. Additionally, emissions may occur
during the product's lifetime, such as during solvent use.
Overall, throughout the time series, more than 64 percent of
the total carbon consumed for non-energy purposes is stored in
products, and not released to the atmosphere. However, some
of the products release CO2 at the end of their commercial
life when they are disposed. These emissions are covered
separately in this chapter in the Waste Combustion section.
There is some overlap between fossil fuels consumed
for non-energy uses and the fossil-derived CO2 emissions
accounted for in the Industrial Processes chapter. To avoid
double-counting, the "raw" non-energy fuel consumption data
reported by EIA are adjusted to account for these overlaps,
as shown in Table 3-11. In 2002, fossil fuel consumption for
non-energy uses constituted 7 percent (5,629 TBtu) of overall
fossil fuel consumption, approximately the same proportion
as in 1990. There are also net exports of petrochemicals that
are not completely accounted for in the EIA data, and these
affect the total carbon content of non-energy fuels; the effects
of these adjustments are also shown in the table. In 2002, the
adjusted carbon content of fuels consumed for non-energy
uses was approximately 103.4 Tg C, an increase of 24 percent
since 1990. About 71.1 Tg of this carbon was stored, while the
remaining 34.9 Tg C was emitted. The proportion of carbon
emitted has remained the same since 1990, at about 31 to 35
percent of total non-energy consumption (see Table 3-12).
Energy 3-19
-------
Table 3-11: 2002 Non-Energy Use (NEU) Fossil Fuel Consumption, Storage, and Emissions
Sector/Fuel Type
Industry
Industrial Coking Coal
Natural Gas to Chemical Plants
Asphalt & Road Oil
LPG
Lubricants
Pentanes Ptas
Petrochemical Feedstocks
Naphtha (<401 deft F)
Other Oil (>401d«sg.F)
Still Gas
Petroleum Coke
Special Naphtha
Distillate Fuel Oil
Residual Fuel
Waxes
Miscellaneous Products
Transportation
Lubricants
U.S. Territories
Lubricants
Other Petroleum p§c. Prod.)
Total
103.4
Note: Totals may not sum due to independent rounding.
derived from these nafe.
Methodology
The first step in estimating carbon stored in products was
to determine the aggregate quantity of fossil fuels consumed
for non-energy uses. The carbon content of these feedstock
fuels is equivalent to potential emissions, or the product of
consumption and the fuel-specific carbon content values. Both
the non-energy fuel consumption and carbon content data were
supplied by the EIA (2003) (see Annex 2.1). Consumption of
natural gas, LPG, pentanes plus, naphthas, and other oils were
adjusted to account for net exports of these products that are
not reflected in the raw data from EIA. Consumption values
for industrial coking coal, petroleum coke, and natural gas in
Table 3-11 were adjusted to subtract non-energy uses that are
addressed in the Industrial Process chapter.34
For the remaining non-energy uses, the amount of
carbon stored was estimated by multiplying the potential
emissions by a storage factor. For several fuel types — such as
petrochemical feedstocks, LPG, pentanes plus, natural gas for
non-fertilizer uses, asphalt and road oil, and lubricants—U.S.
data on carbon stocks and flows were used to develop carbon
storage factors, calculated as the ratio of (a) the carbon stored
by the fuel's non-energy products to (b) the total carbon
content of the fuel consumed. A lifecycle approach was used
in the development of these factors in order to account for
losses in the production process and during use. Because
losses associated with municipal solid waste management are
handled separately in this chapter under Waste Combustion,
the storage factors do not account for losses at the disposal
end of the life cycle. For the other fuel types, the storage
factors were taken directly from the IPCC Guidelines for
National Greenhouse Gas Inventories, which in turn draws
from Marland and Rotty (1984).
Lastly, emissions were estimated by subtracting the
carbon stored from the potential emissions. More detail on
34 These source categories include Iron and Steel Production, Ammonia Manufacture, Titanium Dioxide Production, Ferroalloy Production, and Aluminum
Production.
3-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-12: Storage and Emissions from NEU Fossil Fuel Consumption (Tg C02 Eq.)
Potential Emissions
Carbon Stored
Emissions
tut
2000
2002
308.0 387.8 403J 379.8
2484 mt 271,2 258.0
114.0 12?;7 t32J 120.8
374,4 379.2
257,1 260.6
117 J 128.1
the methodology for calculating storage and emissions from
each of these sources is provided in Annex 2.3.
Where storage factors were calculated specifically for
the United States, data were obtained on fuel products such as
asphalt, plastics, synthetic rubber, synthetic fibers, carbon black,
personal cleansers, pesticides, and solvents, and industrial releases
including VOC, solvent, and non-combustion CO emissions,
TRI releases, refinery wastewater, hazardous waste incineration,
and energy recovery. Data were taken from a variety of industry
sources, government reports, and expert communications.
Sources include EPA's compilations of air emission factors (EPA
1995,2001), National Air Quality and Emissions Trends Report
data (EPA 2002a), Toxics Release Inventory, 1998 (2000b),
Biennial Reporting System data (EPA 2000a), pesticide sales
and use estimates (EPA 1998, 1999, 2002b) and hazardous
waste data (EPA 2000a); the El A Manufacturer's Energy
Consumption Survey (MECS) (EIA 1994, 1997, 2001b); the
National Petrochemical & Refiners Association (NPRA 2001);
the National Asphalt Pavement Association (Connolly 2000);
the Emissions Inventory Improvement Program (EIIP 1998,
1999); the U.S. Bureau of the Census (1999,2003); the American
Plastics Council (APC 2000, 2001, 2003; Eldredge-Roebuck
2000); the Society of the Plastics Industry (SPI 2000); the
Rubber Manufacturers'Association (RMA 2002; STMC 2003);
the International Institute of Synthetic Rubber Products (IISRP
2000); the Fiber Economics Bureau (FEE 2001); the American
Chemistry Council (ACC 2002, 2003); Material Safety Data
Sheets (Miller 1999); the Chemical Manufacturer's Association
(CMA 1999); and the International Carbon Black Association
(ICBA) (Johnson 2003). Specific data sources are listed in full
detail in Annex 2.3.
Uncertainty
A Tier 2 Monte Carlo analysis was performed using @ RISK
software to determine the level of uncertainty surrounding the
estimates of the feedstocks carbon storage factor and the quantity
of carbon stored in feedstocks in 2002. The Tier 2 analysis was
performed to allow the specification of probability density
functions for key variables, within a computational structure
that mirrors the calculation of the inventory estimate.
As noted above, the non-energy use analysis is based on
national storage factors for (1) feedstock materials (natural gas,
LPG, pentanes plus, naphthas, and other oils), (2) asphalt, and
(3) lubricants. For the remaining fuel types, the storage factors
were taken directly from the IPCC Guidelines for National
Greenhouse Gas Inventories. To characterize uncertainty, four
separate analyses were conducted, corresponding to each of
the four categories. In all cases, statistical analyses or expert
judgments of uncertainty were not available directly from the
information sources for the activity variables; thus, uncertainty
estimates were determined using assumptions based on source
category knowledge. The uncertainty analyses reported
here represent an initial attempt to define and structure the
uncertainty analysis.
The preliminary results of the uncertainty analyses are
summarized in Table 3-13. For both carbon storage and
storage factor, across the four non-energy use components
the greatest uncertainty (in terms of the largest standard
deviation) is associated with the "other" category (i.e., those
fuels for which default IPCC storage factors are used). The
lubricants storage factor also exhibits high uncertainty, but
as the total carbon in this use category is small relative to
the other categories, the standard deviation of carbon stored
is relatively small (0.2 Tg C).
The feedstocks category—the largest use category in
terms of total carbon flows—appears to have tight confidence
limits. This is due, in part, to the way the analysis was
structured. As discussed in Annex 2.3, the storage factor
for feedstocks is based on an analysis of six fates that result
in long-term storage (e.g., plastics production), and nine
that result in emissions (e.g., volatile organic compound
emissions). Rather than modeling the total uncertainty
around all 15 of these fate processes, the current analysis
addresses only the storage fates, and assumes that all carbon
that is not stored is emitted. As the production statistics that
drive the storage values are relatively well-characterized,
Energy 3-21
-------
Table 3-13: Quantitative Uncertainty Estimates for Carbon Stored in Products (Tg C) and Carbon Storage Factor (Percent)
Source
Carbon Stored (Tg)
Feedstocks
Asphalt
Lubricants
Other /
Storage Factor (%)
Feedstocks
Aspnalt
lubricants
Other
2002 Estimate
71.2
38.1
25.6
0.6
6.9
67%
100%
9%
48%
f|n«.
UnCfciiaimy noiiye nciauvc tu ciiiiadiuii cauiiidic-
(TSCJ •'(%)•-.-.
Lower Bound
66,2
36.9
24.2
0.4
4.5
66%
98%
5%
31%
Upper Bound
mi
40.6
27.2
1.2
10.1
69%
100%
17%
68%
Lower Bound
••" ' " • *1% " •
4%
-5%
-40%
-34%
-2%
-2%
-44%
-35%
Upper Bound
+1t%
+6%
+6%
+83%
+46%
+3%
-0.4%
+89%
+42%
"Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
this approach yields a result that is probably biased toward
understating uncertainty.
As is the case with the other uncertainty analyses
discussed throughout this document, the uncertainty
results above address only those factors that can be readily
quantified. More details on the uncertainty analysis are
provided in Annex 2.3.
QA/QC and Verification
A source-specific QA/QC plan for non-energy uses of
fossil fuels was developed and implemented. This effort
included a Tier 1 analysis, as well as portions of a Tier
2 analysis for non-energy uses involving petrochemical
feedstocks. The Tier 2 procedures that were implemented
involved checks specifically focusing on the activity data
and methodology for estimating the fate of carbon (in terms
of storage and emissions) across the various end-uses of
fossil carbon. Emission and storage totals for the different
subcategories were compared, and trends across the time
series were carefully analyzed to determine whether any
corrective actions were needed. Corrective actions were taken
to rectify minor errors and to improve the transparency of
the calculations, facilitating future QA/QC.
Recalculations Discussion
The methodology for calculating petrochemical
feedstock storage factors has been revised in several ways.
First, the calculations have been updated to estimate an
annual storage factor, rather than the single factor estimated
for 1998 and applied to all years in the time series. This
modification involved the addition or revision of historical
data in the sub-categories of plastics, synthetic rubber,
synthetic fibers, carbon black, non-combustion CO, VOCs,
solvents, pesticides, energy recovery, and hazardous waste
incineration. Additionally, the net import/export adjustment
factors have been updated to be more comprehensive and
include more petrochemical-based commodities. Together
these methodological and data changes resulted in an average
annual storage factor that is 0.03 higher than the previous
factor; this represents a 5 percent increase in value.
Planned Improvements
The storage of carbon in products from non-energy uses
of fossil fuels has been thoroughly studied, but there are still
several improvements planned for the future:
• Collecting additional information on energy recovery from
Manufacturing Energy Consumption Surveys. An effort is
planned to carefully examine the "microdata" from these
surveys to determine the nature and quantity of materials
initially identified as being destined for "non-energy use"
that are actually combusted for energy recovery.
• Modifying the calculations for rubber consumption. The
current analysis includes only annual rubber disposed in
the form of scrap tires. A future analysis would consider
and quantify: (1) the quantity of rubber (comprising
about 0.5 Tg C annually) consumed in durable and non-
durable goods other than tires, (2) the rubber consumed
to produce tires which wears off by the time the tire is
disposed, and (3) the quantities of organic components
of the tire (fillers, antiozonant) not currently included
in the mass balance.
3-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
• Improving the estimate of domestic plastic consumption.
The consumption data for some of the plastic resins in
the dataset include consumption in Canada and Mexico.
This is likely to be one of the primary reasons that
carbon outputs (storage plus emissions) exceed inputs
(feedstock consumption) for most years in the feedstocks
mass balance (see Annex 2.3 for details). Improved data
on U.S. (rather than North American) consumption for
those resins would help to improve the accuracy of this
estimate.
• Better characterize flows of fossil carbon. Additional
"fates" may be researched, including: the fossil carbon
load in organic chemical wastewaters; an expanded
import and export analysis (i.e., evaluating additional
commodities); and improving the characterization
of cleansers (to exclude any potential biogenic
carbon sources).
Finally, although U.S.-specific storage factors have been
developed for feedstocks, asphalt, and lubricants, default
values from IPCC are still used for many of the non-energy
fuel types (e.g., industrial coking coal, distillate oil, residual
oil). Over the long term, there are plans to improve these
storage factors by conducting analyses of carbon fate similar
to those described in Annex 2.3.
3.3. Stationary Combustion
(excluding C02) (IPCC Source
Category 1 A)
Stationary combustion encompasses all fuel combustion
activities except those related to transportation (i.e., mobile
combustion). Other than CO2, which was addressed in
the previous section, gases from stationary combustion
include the greenhouse gases CH4 and N2O and the ambient
air pollutants NOX, CO, and NMVOCs.35 Emissions of
these gases from stationary combustion sources depend
upon fuel characteristics, size and vintage, along with
combustion technology, pollution control equipment, and
ambient environmental conditions. Emissions also vary with
operation and maintenance practices.
Nitrous oxide and NOX emissions from stationary
combustion are closely related to air-fuel mixes and
combustion temperatures, as well as the characteristics
of any pollution control equipment that is employed.
Carbon monoxide emissions from stationary combustion
are generally a function of the efficiency of combustion;
they are highest when less oxygen is present in the air-fuel
mixture than is necessary for complete combustion. These
conditions are most likely to occur during start-up, shutdown
and during fuel switching (e.g., the switching of coal grades
at a coal-burning electric utility plant). Methane and NMVOC
emissions from stationary combustion are primarily a
function of the CH4 and NMVOC content of the fuel and
combustion efficiency.
Emissions of CH4 decreased 16 percent overall from
8.2 Tg CO2 Eq. (391 Gg) in 1990 to 6.9 Tg CO2 Eq. (328
Gg) in 2002. This decrease in CH4 emissions was primarily
due to lower wood consumption in the residential sector.
Conversely, N2O emissions rose 11 percent since 1990 to
14.0 Tg CO2 Eq. (45 Gg) in 2002. The largest source of N2O
emissions was coal combustion by electricity generators,
which alone accounted for 62 percent of total N2O emissions
from stationary combustion in 2002. Overall, however,
stationary combustion is a small source of CH4 and N2O in
the United States.
In contrast, stationary combustion was a significant
source of NOX emissions, but a smaller source of CO and
NMVOCs. In 2002, emissions of NOX from stationary
combustion represented 38 percent of national NOX
emissions, while CO and NMVOC emissions from stationary
combustion contributed approximately 4 and 8 percent,
respectively, to the national totals. From 1990 to 2002,
emissions of NOX and CO from stationary combustion
decreased by 24 and 21 percent, respectively, and emissions
of NMVOCs increased by 26 percent.
The decrease in NOX emissions from 1990 to 2002
are mainly due to decreased emissions from electricity
generation. The decrease in CO and increase in NMVOC
emissions over this time period can largely be attributed
to apparent changes in residential wood use, which is the
most significant source of these pollutants from stationary
combustion. Table 3-14 through Table 3-17 provide CH4
and N2O emission estimates from stationary combustion by
sector and fuel type. Estimates of NOX, CO, and NMVOC
emissions in 2002 are given in Table 3-18.36
" Sulfur dioxide (SO2) emissions from stationary combustion are addressed in Annex 6.3.
See Annex 3.1 for a complete time series of ambient air pollutant emission estimates for 1990 through 2002.
Energy 3-23
-------
Table 3-14: CH4 Emissions from Stationary Combustion (Tg C02 Eq.)
Sector/Fuel Type
Electricity Generation
CoaJ
Fuel Oil
Natural gas
Wood
Industrial
Coal
Fuel Oil
Natural gas
Wood
Commercial
Coal
Fuel Oil
Natural gas
Wood
Residential
Coal
Fuel Oil
Natural Gas
Wood
U.S. Territories
Coal
Fuel Oil
Natural Gas
Wood
Total
1918
0.6
o>;
•' W
. •: «
. :03v
'It;
Q£
02
0.8
0,9
8.8
. ' *• :.
0.2
0,3
0.2
4.6
0.2
0.3
0.5
3;7
+ "
• ' +.
+ •
• +'
+ .
8.2
| 1966
K 8.6
: ' 0.4
E.:* 0.1 '
:.- - 0.1
0.1
: • 2.5
0.3
0.2
1.0
1.1
0.8
I +
0.2
0.3
0.3
4.7
0.1
0.3
0.6
3.8
0.1
0.1
1887
0.6
0.4
0.1
0.1
0.1
2.6
0.3
0.2
1.0
1.1
0.8
4
0.1
0.3
0.3
3.7
0.1
0.3
0.5
2.7
0.1
+
0.1
1698
• e.7
0.4
0.1
0.1
0.1
2.4
0.3
0,2
0.9
1.0
0.8
4
0.1
0.3
0.3
3.3
0.1
0.3
0.5
2.4
0.1
4.
0.1
1899
: 8.7 ':
0.4
; 0.1
'-. 0.1 • ' •
>0.l:"-v
-' 2,4 '••:
0.3
0.2
o.§
1.0
6.8
4'
0,1
0.3
0.3
3.1
0.1
0.3
0,5
2.6
8.1
-t- '
0.1
2fB6
8,7
0.4
0.1
0.1
0.1
2.4
0.3
0.2
0.9
1.0
0.9
4
0.2
0.3
0.3
3.7
0.1
0.3
0,5
2.7
0.1
4
4
VlWttvYv
: 6.? '.
0,4
0.1
0.1
0.1
• , tr - •
OJ
0.2
0.9
0.9
8.8
-f
0.2
0.3
0.3
3.5
0.1
0.3
0.5
2.6
4
-f
4
2002
8.7
0.4
0.1
0.1
0.1
2.2
0.3
0.2
0.8
1.0
8.8
4-
0.2
0.3
0.3
3.1
0.1
0.3
0.5
2.2
0.1
4-
0.1
8.8
7.8
7.2
7.7
+ Does not exceed 0.05 Tg C02 Eq.
Note: Totals may not sum due to independent rounding.
Table 3-15: N20 Emissions from Stationary Combustion (Tg C02 Eq.)
Sector/Fuel Type 1888
Electricity Generation
Coal
Fuel Oil
Natural Gas
Wood
Industrial
Coal
Fuel Oil
Natural Gas
Wood
Commercial
Coal
Fuel Oil
Natural Gas
Wood
Residential
Coal
Fuel Oil
Natural Gas
Wood
U.S. Territories
Coal
Fuel Oil
Natural Gas
Wood
Total
U
7,1
0.2
0.1
0.2
3.5
0.7
0.7
0.2
1.8
8.4
0.1
0,2
0.1
' +
1.1
'+
0.3
0.1
0.7
0.1
+
0.1
+
+
12.6
13.9
14.0
13.8
13.9
14.4
7.2
13.9
6.9
1996
8.5
8.0
0.2
0.1
0.2
3.8
0.7
0.8
0.3
2.1
6.4
0.1
0.1
0.1
0.1
1.2
4
0.3
0.2
0.7
6.1
+
0.1
1997
8.7
8.2
0.2
0.1
0.2
3.9
0.7
0.8
0.3
2.2
0.4
0.1
0.1
0.1
0.1
1.8
4
0.3
0.2
0.5
8.1
4
0.1
1998
8.9
8.4
0.2
0.1
0.2
3.6
0.6
0.7
0.3
2.0
6.3
4
0.1
0.1
0.1
8.9
+
0.2
0.1
0.5
6.1
4
0.1
1998
8.9
8.4
0.2
0.2
0.2
3.6
0.6
0.7
0.3
2.0
8.3
4
0.1
0.1
0.1
8.9
,4
0.3
0,2
0.5
6.1
4
0.1
2866
9.3
8.8
0.2
0.2
0.2
3.6
0.6
0.7
0.3
2.0
0.3
4
0.1
0,1
0.1
1.8
• 4
0.3
0.2
0.5
0.1
4
0.1
2881
9.1
8.5
0.2
0.2
0.2
3.4
0.6
0.8
0.3
1.8
0.3
4 .
0.1
0.1
0.1
1.8
. '4
0.3
0.2
0.5
6,1
' • 4
0.1
2862
9.2
8.7
0.2
0.2
0.2
3.5
0.6
0.8
0.2
1.9
0.3
4
0.1
0.1
0.1
0.9
4
0.3
0.2
0.4
0.1
4
0.1
14.8
+ Does not exceed 0.05 Tg C02 Eq.
Note: Totals may not sum due to independent rounding.
3-24 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-16: CH4 Emissions from Stationary Combustion (Gg)
Sector/Fuel Type
Electricity Generation
Coal
Fuel Oil
Natural Gas
Wood
Industrial
Coal
Fuel Oil
Natural Gas
Wood
Commercial
Coal
Fuel Oil
Natural Gas
Wood
Residential
Coal
Fuel Oil
Natural Gas
Wood
U.S. Territories
Coal
Fuel Oil
Natural Gas
Wood
Total
1990
27
16
4
3
4
107
16
8
39
43
36
1
10
14
12
219
8
14
23
175
2
+
2
+
+
391
1996
418
+ Does nol exceed 0.5 Gg
Note: Totals may not sum due to independent rounding.
Table 3-17: N20 Emissions from Stationary Combustion (Gg)
Sector/Fuel Type
Electricity Generation
Coal
Fuel Oil
Natural Gas
Wood
Industrial
Coal
Fuel Oil
Natural Gas
Wood
Commercial
Coal
Fuel Oil
Natural Gas
Wood
Residential
Coal
Fuel Oil
Natural Gas
Wood
U.S. Territories
Coal
Fuel Oil
Natural Gas
Wood
Total
1990
24
23
1
+
1
11
2
2
1
6
1
+
1
+
+
4
+
1
+
2
+
+
+
+
+
41
45
+ Does not exceed 0.5 Gg
Note: Totals may not sum due to independent rounding.
1997
1998
1999
2000
369
344
355
367
1
H-
2
45
45
45
47
2001
344
3
1
2
+
45
2002
29
18
2
4
4
121
15
8
46
51
40
1
8
16
15
226
5
15
27
179
2
30
19
3
4
4
122
16
8
46
52
40
1
7
17
15
175
5
14
26
130
2
32
19
4
5
4
115
15
8
45
48
38
1
7
16
14
157
4
13
23
116
2
32
19
4
5
4
114
14
8
43
49
39
1
7
16
16,
168
4
15
24
124
2
33
20
3
5
4
115
14
8
44
49
41
1
8
17
16
175
4
16
26
130
2
33
20
4
5
4
106
14
9
41
43
36
1
7
16
12
166
4
15
25
122
2
32
20
3
6
4
107
14
8
40
45
37
1
7
16
12
149
4
15
25
105
2
2
-f
328
1996
27
26
+
+
1
12
2
2
1
7
1
1997
28
27
1
+
1
13
2
2
1
7
1
1998
29
27
1
+
1
12
2
2
1
6
1
1999
29
27
1
+
1
12
2
2
1
6
1
2000
30
28
1
1
1
12
2
2
1
7
1
2001
29
27
1
1
1
11
2
3
1
6
1
2002
30
28
1
1
1
11
2
3
1
6
1
1
1
1
•f
-f
45
Energy 3-25
-------
Table 3-18: NOX, CO, and NMVOC Emissions from
Stationary Combustion in 2002 (Gg)
Sector/Fuel Type
Electric Generation
Coal
Fuel Oil
Natural gas
Wood
Other Fuels3
Internal Combustion
Industrial
Coal
Fuel Oil
Natural gas
Wood
Other Fuels3
Internal Combustion
Commercial/Institutional
Coal
Fuel Oil
Natural gas
Wood
Other Fuels3
Residential
Coal"
Fuel Oil"
Natural Gas"
Wood
Other Fuels
Total
NOX
4,091
3,480
136
304
34
NA
137
2,491
516
153
911
NA
115
795
371
27
69
218
NA
56
589
NA
NA
NA
29
560
7,542
CO
486
244
31
102
NA
36
74
1,107
122
44
356
NA
313
272
133
11
15
71
NA
36
2,235
NA
NA
NA
2,046
189
3,961
NMVOC
57
27
5
13
NA
2
11
152
10
8
52
NA
28
54
40
1
4
16
NA
19
898
NA
NA
NA
869
29
1,147
NA (Not Available)
Note: Totals may not sum due to independent rounding. See Annex 3.1
for emissions in 1990 through 2002.
a Includes LPG, waste oil, coke oven gas, and coke (EPA 2003).
b Coal, fuel oil, and natural gas emissions are included in "Other Fuels"
(EPA 2003).
Methodology
Methane and N2O emissions were estimated by
multiplying fossil fuel and wood consumption data by
emission factors (by sector and fuel type). National coal,
natural gas, fuel oil, and wood consumption data were
grouped by sector: industrial, commercial, residential,
electricity generation, and U.S. territories. For the CH4
and N2O estimates, fuel consumption data for the United
States were obtained from EIA's Monthly Energy Review
and unpublished supplemental tables on petroleum product
detail (EIA 2003). Because the United States does not
include territories in its national energy statistics, fuel
consumption data for territories were provided separately
by the EIA.37 Estimates for wood biomass consumption
for fuel combustion do not include wood wastes, liquors,
municipal solid waste, tires, etc. that are reported as biomass
by EIA. Emission factors for the four end-use sectors were
provided by the Revised 1996IPCC Guidelines for National
Greenhouse Gas Inventories (IPCC/UNEP/OECD/IEA
1997). U.S. territories' emission factors were estimated using
the U.S. emission factors for the primary sector in which
each fuel was combusted.
Emissions estimates for NOX, CO, and NMVOCs in this
section were obtained from preliminary data (EPA 2003),
which, in its final iteration, will be published on the National
Emission Inventory (NEI) Air Pollutant Emission Trends web
site. The major categories included in this section are those
used in EPA (2003): coal, fuel oil, natural gas, wood, other
fuels (including LPG, coke, coke oven gas, and others), and
stationary internal combustion. The EPA estimates emissions
of NOX, CO, and NMVOCs by sector and fuel source using a
"bottom-up" estimating procedure. In other words, emissions
were calculated either for individual sources (e.g., industrial
boilers) or for multiple sources combined, using basic
activity data as indicators of emissions. Depending on the
source category, these basic activity data may include fuel
consumption, fuel deliveries, tons of refuse burned, raw
material processed, etc.
The overall emission control efficiency of a source
category was derived from published reports, the 1985
National Acid Precipitation and Assessment Program
(NAPAP) emissions inventory, and other EPA databases.
The U.S. approach for estimating emissions of NOX, CO,
and NMVOCs from stationary combustion, as described
above, is consistent with the methodology recommended by
the IPCC (IPCC/UNEP/OECD/IEA 1997).
More detailed information on the methodology for
calculating emissions from stationary combustion, including
emission factors and activity data, is provided in Annex 3.1.
Uncertainty
Methane emission estimates from stationary sources
exhibit high uncertainty, primarily due to difficulties in
calculating emissions from wood combustion (i.e., fireplaces
and wood stoves). The estimates of CH4 and N2O emissions
presented are based on broad indicators of emissions (i.e., fuel
use multiplied by an aggregate emission factor for different
37 U.S. territories data also include combustion from mobile activities because data to allocate territories' energy use were unavailable. For this reason,
CH4 and N2O emissions from combustion by U.S. territories are only included in the stationary combustion totals.
3-26 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-19: Quantitative Uncertainty Estimates for CH4 and N20 Emissions from Stationary Combustion, Including Biomass
(Tg C02 Eq. and Percent)
Source
Gas
2002 Emission Estimate
(TflC02Eq.)
Uncertainty Range Relative to Emission Estimate3
(To,C02Eq.) (%)
Stationary Combustion
Stationary Combustion
CH4
N20
6.9
14.0
Lower Bound
4.3
10.3
Upper Bound
11.7
39.4
Lower Bound
-38%
-26%
Upper Bound
+70%
+181%
1 Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
sectors), rather than specific emission processes (i.e., by
combustion technology and type of emission control).
An uncertainty analysis was performed by primary fuel
type for each end-use sector, using the IPCC-recommended
Tier 2 uncertainty estimation methodology, Monte Carlo
Stochastic Simulation technique, with @RISK software.
The uncertainty estimation model for this source
category was developed by integrating the CH4 and N2O
stationary source inventory estimation models with the
model for CO2 from fossil fuel combustion to realistically
characterize the interaction (or endogenous correlation)
between the variables of these three models. A total of 83
input variables were simulated for the uncertainty analysis of
this source category (58 from the CO2 emissions from fossil
fuel combustion inventory estimation model and 25 from the
stationary source inventory models).
In developing the uncertainty estimation model, uniform
distribution was assumed for all activity-related input variables
and N2O emission factors, based on the SAIC/EIA (2001)
report.38 For these variables, the uncertainty ranges were
assigned to the input variables based on the data reported in
SAIC/EIA (2001).39 However, the CH4 emission factors differ
from those used by EIA. Since these factors were obtained
from IPCC/UNEP/OECD/IEA (1997), uncertainty ranges
were assigned based on IPCC default uncertainty estimates
(IPCC Good Practice Guidance 2000).
The uncertainty ranges for the activity-related input
variables and N2O emission factors were typically
asymmetric around their inventory estimates. The uncertainty
ranges for the non-biomass-related CH4 emission factors
were symmetric around their inventory estimates; for
biomass, they were asymmetric around their emission factor
estimates. Bias (or systematic uncertainties) associated
with these variables accounted for much of the uncertainty
associated with the activity data and N2O emission factor
variables.40 For purposes of this uncertainty analysis, each
input variable was simulated 10,000 times through Monte
Carlo sampling.
The preliminary results of the quantitative uncertainty
analysis (see Table 3-19) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the CH4
emissions estimate from stationary combustion (including
biomass) is within the range of approximately 4.3 to 11.7
Tg CO2 Eq. (or the actual CH4 emissions from stationary
sources are likely to fall within the range of approximately
38 percent below and 70 percent above the emission estimate
of 6.9 Tg CO2 Eq.).41 However, the actual estimate of CH4
emissions from stationary combustion (excluding biomass)
on
J SA1C/EIA(2001) characterizes the underlying probability density function for the input variables as a combination of uniform and normal distributions
(the former distribution to represent the bias component and the latter to represent the random component). However, for purposes of the current uncertainty
analysis, it was determined that uniform distribution was more appropriate to characterize the probability density function underlying each of these
variables.
In the SAIC/EIA (2001) report, the quantitative uncertainty estimates were developed for each of the three major fossil fuels used within each end-use
sector; the variations within the sub-fuel types within each end-use sector were not modeled. However, for purposes of assigning uncertainty estimates
to the sub-fuel type categories within each end-use sector in the current uncertainty analysis, SAIC/EIA (2001 )-reported uncertainty estimates were
extrapolated.
Although, in general, random uncertainties are the main focus of statistical uncertainty analysis, when the uncertainty estimates are elicited from experts,
their estimates include both random and systematic uncertainties. Hence, both these types of uncertainties are represented in this uncertainty analysis.
The low emission estimates reported in this section have been rounded down to the nearest integer values and the high emission estimates have been
rounded up to the nearest integer values.
Energy 3-27
-------
is likely to be within the range of approximately 2.0 to 4.8
Tg CO2 Eq. (i.e., approximately 39 percent below and 44
percent above the 2002 inventory emission estimate for
this source category). For N2O emissions from stationary
combustion, there is 95 percent probability that the actual
emissions estimate (including biomass) is likely to be within
the range of approximately 10.3 to 39.4 Tg CO2 Eq. (i.e.,
approximately 26 percent below and 181 percent above the
2002 inventory emission estimate for this source category).
The actual estimate of N2O emissions from stationary
combustion (excluding biomass) is likely to be within the
range of approximately 6.7 to 34.2 Gg (i.e., approximately
41 percent below and 201 percent above the 2002 inventory
emission estimate for this source category).
The uncertainties associated with the emission
estimates of CH4 and N2O are greater than those associated
with estimates of CO2 from fossil fuel combustion, which
mainly rely on the carbon content of the fuel combusted.
Uncertainties in both CH4 and N2O estimates are due to the
fact that emissions are estimated based on emission factors
representing only a limited subset of combustion conditions.
For the ambient air pollutants, uncertainties are partly due
to assumptions concerning combustion technology types,
age of equipment, emission factors used, and activity data
projections.
QA/QC and Verification
A source-specific QA/QC plan for stationary combustion
was developed and implemented. This effort included a
Tier 1 analysis, as well as portions of a Tier 2 analysis. The
Tier 2 procedures that were implemented involved checks
specifically focusing on the activity data and emission factor
sources and methodology used for estimating CH4, N2O,
and the ambient air pollutants from stationary combustion
in the United States. Emission totals for the different sectors
and fuels were compared and trends were investigated. No
corrective actions were necessary.
Recalculations Discussion
Historical CH4 and N2O emissions from stationary
sources (excluding CO2) were revised due to two changes.
First, emissions from fuel use in the U.S. territories is now
included. Second, slight changes to emission estimates for
the other sectors are due to revised data from EIA (2003).
This latter revision is explained in greater detail in the
sections on CO2 Emissions from Fossil Fuel Combustion
and Carbon Stored in Products from Non-Energy Uses of
Fossil Fuels within this chapter. The combination of the
methodological and historical data changes resulted in an
average annual increase of 0.07 Tg CO2 Eq. (0.9 percent) in
CH4 emissions and an average annual increase of 0.12 Tg
CO2 Eq. (0.9 percent) in N2O emissions for the period 1990
through 2001.
Planned Improvements
Several items are being evaluated to improve the
CH4 and N2O emission estimates from stationary source
combustion and to reduce uncertainty. Efforts will be taken
to work with EIA and other agencies to improve the quality
of the U.S. territories data. Because these data are not broken
out by stationary and mobile uses, further research will
be aimed at trying to allocate consumption appropriately.
In addition, the uncertainty of biomass emissions will be
further investigated. Currently, the exclusion of biomass
increases the uncertainty, although it was expected to reduce
the uncertainty. These improvements are not all-inclusive,
but are part of an ongoing analysis and efforts to continually
improve these stationary estimates.
3.4. Mobile Combustion (excluding
C02) (IPCC Source Category 1A)
Mobile combustion emits greenhouse gases other than
CO2, including CH4, N2O, and the ambient air pollutants
NOX, CO, and NMVOCs. While air conditioners and
refrigerated units in vehicles also emit hydrofluorocarbons
(HFCs), these gases are covered in Chapter 3, Industrial
Processes, under the section entitled Substitution of Ozone
Depleting Substances. As with stationary combustion, N2O
and NOX emissions are closely related to fuel characteristics,
air-fuel mixes, combustion temperatures, as well as usage
of pollution control equipment. Nitrous oxide, in particular,
can be formed by the catalytic processes used to control
NOX, CO, and hydrocarbon emissions. Carbon monoxide
emissions from mobile combustion are significantly
affected by combustion efficiency and the presence of post-
combustion emission controls. Carbon monoxide emissions
are highest when air-fuel mixtures have less oxygen than
required for complete combustion. These emissions occur
especially in idle, low speed, and cold start conditions.
3-28 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Methane and NMVOC emissions from motor vehicles are
a function of the CH4 content of the motor fuel, the amount
of hydrocarbons passing uncombusted through the engine,
and any post-combustion control of hydrocarbon emissions,
such as catalytic converters.
Emissions from mobile combustion were estimated by
transport mode (e.g., highway, air, rail), fuel type (e.g. motor
gasoline, diesel fuel, jet fuel), and vehicle type (e.g. passenger
cars, light-duty trucks). Road transport accounted for the
majority of mobile source fuel consumption, and hence, the
majority of mobile combustion emissions. Table 3-20 and
Table 3-21 provide CH4 and N2O emission estimates in Tg
CO2 Eq., respectively; Table 3-22 and Table 3-23 present
these estimates in Gg of each gas. Estimates of NOX, CO,
and NMVOC emissions are given in Table 3-24 through
Table 3-26.42
Mobile combustion was responsible for a small portion
(0.7 percent) of national CH4 emissions but was the second
largest source of N2O (13 percent) in the United States. From
1990 to 2002, CH4 emissions declined by 15 percent, to 4.2
Tg CO2 Eq. (201 Gg), due largely to control technologies
employed on highway vehicles in the United States that
reduce CO, NOX, NMVOC, and CH4 emissions. The same
Figure 3-17
70 -
60 -
50 -
40 -
30 -
20 -
10
0
Mobile Source CH4 and N20 Emissions
N20
CH4
i I i
technologies, however, resulted in higher N2O emissions,
resulting in a 20 percent increase in N2O emissions from
mobile sources between 1990 and 1995. Nitrous oxide
emissions have subsequently declined 13 percent as
improvements in the emission control technologies installed
on new vehicles have reduced emission rates of both NOX and
N2O per vehicle mile traveled. As a result, N2O emissions
in 2002 were only 4 percent higher than in 1990, at 52.9
Tg CO2 Eq. (171 Gg) (see Figure 3-17). Overall, CH4 and
Table 3-20: CH4 Emissions from Mobile Combustion (Tg C02 Eq.)
1W|
Gasoline Highway
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Ught-Duty Trucks
Heavy-Duty Vehicles
Alternative Fuel Highway
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft
Other6
4J
2.4
1,6.
0,2
0.1
0,2
0.1
P.2
Total
1996
4 J
2.0
1.8
0.1
0.1
0.3
0.3
+
0.5
0.1
0.1
0.1
+
0.1
4.8
1SI?
ft*
2,0
1.7
0.1
0,1
0.3
0.3
0.1
0.4
0.1
0.1
0.1
+
0,2
4.7
1998
3.8
2,0
1.6
0.1
0.1
0.3
0.3
0.1
0.4
•f ;
0.1
0.1
+
0.1
4.5
19S9
3.7
1J
1.6
0.1
0.1
0.3
0.3
0.1
0.4
0.1
0.1
0,1
4-
0.2
4.5
2000
3.6
1.0
1.5
0.1
0.1
0.3
0.3
0.1
0.5
0,1
0.1
0.1
+
0.2
4.4
2001
3.4
1.8
1,5
' 0.1
+
0.3
0.3
0.1
0.5
0,1
0.1
0.1
-t-
0.1
4.3
. 2002
3.3
1.8
1.4
0.1
-f
0.3
0.3
0.1
0.5
0.1
0.1
0.1
+
0.1
4.2
+ Does not exceed 0.05 Tg COj Efl.
Note: Totals may not sum to tfi InieperKtent rounding.
4 See Annex 3.2 for definitions of Wghway »eWcle ^rpes.
6 "Other" Includes snowmeMes, small psolfcw pwered u8ll^ equipment, heavy-duty gasoline powered utility equipment, and heavy-duty diesel powered
utility equipment.
42 See Annex 3.2 for a complete time series of emission estimates for 1990 through 2002.
Energy 3-29
-------
Table 3-21: N20 Emissions from Mobile Combustion (Tg C02 Eq.)
Fuel Type/Vehicle Type
Gasoline Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Alternative Fuel Highway
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft
Other*
Total
1990
45.6
30.9
13.9
0.7
+
2.0
0.1
0.2
1.8
4
3.0
0.4
0.3
0.3
0.1
1.7
0.2
50.7
199S
54.9
33.0
20.8
1.0
+
2.6
0.1
0.2
2.4
0.1
3.1
0.4
0.3
0.3
0.1
1.8
0.1
60.7
1997
54.5
32.5
20.9
1.1
4
2.8
0.1
0.2
2.5
0.1
3.0
0.3
0.3
0.3
0.2
1.7
0.1
60.3
1998
53.7
32.2
20.4
1.1
4
2.9
0.1
0.2
2.6
0.1
2.9
0.2
0.3
0.3
0.2
1.8
0.1
59.6
1999
52.5
31.2
20.2
1.1
4
3.0
4
0.3
2.7
0.1
3.0
0.3
0.3
0.3
0.1
1.8
0.1
58.6
2000
51.0
30.2
19.7
1.1
+
3.0
4
0.3
2.7
0.1
3.3
0.5
0.3
0.3
0.2
1.9
0.1
57.4
2001
48.6
28,8
18.8
1.1
4
3.1
4
0.3
2.8
fl.1
3.1
0.3
0.3
0.3
0.2
1.8
0.2
55.0
2002
46.4
27.4
17.9
1.1
4
3.2
4
0,3
2.9
0.1
3.2
0.4
0.3
0.3
0.2
1.7
0.2
52.9
+ Does not exceed 0.05 Tg C02 Eq.
Note: Totals may not sum due to independent rounding.
* "Other" includes snowmobiles, small gasoline powered utility equipment, heavy-duty gasoline powered utility equipment, and heavy-duty diesel powered
utility equipment.
Table 3-22: CH4 Emissions from Mobile Combustion (Gg)
Fuel Type/Vehicle Type
Gasoline Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Alternative Fuel Highway
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft
Other*
Total
1990
203
116
75
9
4
11
+
4
10
1
22
4
3
6
1
7
1
236
1996
190
95
85
6
4
13
+
+
13
2
22
4
3
6
1
7
1
227
1997
185
93
82
6
3
14
+
+
13
3
21
3
3
6
1
7
1
222
1998
180
93
78
5
3
14
4
+
13
3
20
2
3
5
1
7
1
217
1999
174
91
76
5
3
14
4
4
13
4
21
3
3
5
1
7
1
213
2000
169
89
73
5
3
14
4
+
13
4
23
5
3
5
1
7
1
218
2001
164
88
69
4
2
14
+
•4
13
5
22
3
3
6
1
7
1
205
2002
159
86
67
4
2
14
4
4
13
5
23
4
3
6
1
7
1
201
+ Does not exceed 0.5 Gg
Note: Totals may not sum due to independent rounding.
* "Other* includes snowmobiles, small gasoline powered utility equipment, heavy-duty gasoline powered utility equipment, and heavy-duty diesel
powered utility equipment.
3-30 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-23: N20 Emissions from Mobile Combustion (Gg)
Fuel Type/Vehicle Type
Gasoline Highway
Passertf er Cars
Light-Duty Trucks
Heavy-Dirty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Alternative Fuel Highway
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft
Other*
Total
1990
147
100
45
2
+
7
+
+
6
+
10
1
1
1
+
6
1
163
1996
1
8
10
196
1997
177 176
106 105
67 67
3 3
9
1
8
10
194
1998
1999
2000
173
104
66
4
9
1
8
169
101
65
4
10
1
9
10
164
97
63
4
10
1
9
11
192
189
185
2001
10
1
9
10
177
2002
157 150
93 88
61 58
4 3
+ Does not exceed 0.5 Gg
Note: Totals may not sum due to Independent rounding.
* "Other" includes snowmobiles, small gasoline powered utility equipment, heavy-duty gasoline powered utility equipment, and heavy-duty diesel
powered utility equipment.
Table 3-24: NOX Emissions from Mobile Combustion (Gg)
10
1
9
10
1
1
1
+
6
+
1
1
1
+
6
+
1
1
1
+
6
+
1
1
1
+
6
+
2
1
1
1
6
+
1
1
1
1
6
1
1
1
1
1
6
1
171
Fuel Type/Vehicle Type
Gasoline Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Alternative Fuel Highway3
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft11
Other0
Total
1990
5,746
3,847
1,364
515
20
2,956
39
20
2,897
1E
3,432
953
857
437
641
63
480
12,134
1996
4,322
2,533
1,318
459
13
3,600
15
11
3,575
IE
3,791
1,008
951
486
708
67
572
1997
4,268
2,447
1,334
475
13
3,708
13
10
3,685
IE
3,792
963
962
487
708
75
597
1998
4,090
2,316
1,294
467
13
3,729
11
9
3,709
IE
3,772
919
973
487
706
83
604
1999
3,913
2,152
1,264
484
13
3,660
10
8
3,643
IE
4,009
885
984
538
827
91
683
2000
3,812
2,084
1,303
411
13
3,803
7
6
3,791
IE
3,780
966
908
484
697
80
645
2001
3,942
2,150
1,363
414
14
3,542
6
6
3,530
IE
3,770
971
907
480
690
73
650
2002
3,934
2,146
1,360
413
14
3,535
6
6
3,523
IE
3,883
1,000
934
494
710
76
669
11,714 11,768 11.S92 11,582 11,395 11,254 11,352
IE (Included Elsewhere)
Note: Totals may not sum due to Independent rounding.
a NO* emissions from alternative fuel highway vehicles are Included under gasoline and diesel highway vehicles.
b Aircraft estimates include only emissions related to landing and take-off (LTD) cycles, and therefore do not include cruise attitude emissions.
c "Other" includes gasoline powered recreational, industrial, lawn and garden, light commercial, logging, airport service, other equipment; and diesel
powered recreational, industrial, lawn and garden, light construction, airport service.
Energy 3-31
-------
Table 3-25: CO Emissions from Mobile Combustion (Gg)
Fuel Type/Vehicle Type 1990
Gasoline Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Alternative Fuel Highway"
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft
Other8
Total
98,328
60,75?
29,237
8,093
240
1,696
35
': ••:-22--
1,839
IE
19,459
1,679
8§
582
1,090
217
15,807
119,482
1996
69,941
38,327
26,610
4,867
138
1,370
15
14
:-• 1,341
IE
22,098
1,951
94
638
1,140
225
18,049
93,409
1997
67,589
36,825
25,748
4,787
150
1,301
13
13
1,276
IE
21,474
1,948
89
636
1,098
250
17,453
90,284
1998
8i,248
35,686
24,754
4,642
163
1,202
10
12
1,179
IE
21,493
1,943
83
633
1,081
274
17,478
87,940
1989
80*727
32,661
23,159
4,744
163
1,113
10
9
1,094
IE
22,738
2,280
105
677
1,154
307
18,210
84,574
2000
80,617
32,867
24,532
3,104
154
1,088
7
6
1,075
IE
21,935
1,94§
90
626
1,047
245
17,981
83,680
2001
«8;8S?
37,250
26,811
2,842
155
1,B2§
•• •: 7
6
1,011
IE
22,38?
1,952
90
621
1,041
233
18,449
90,268
2002
58,653
32^679
23,345
2,493
136
899
6
5
887
IE
22,511
1,963
90
625
1,047
235
18,551
82,063
Efncludedllsewhere):
Mote: Totals may not sum due to Independent rounding.
* CO emissions from alternative fuel highway vehicles are included under gasoline and diesel highway vehicles,
b Aircraft estimates include only emissions related tolanding and take-off (LTO) cycles, and therefore do not include cruise altitude emissions.
c "Other'' includes gasoline powered recreational, industrial, lawn and garden, fight commercial, logging, airport service, other equipment; and diesel
powered recreatiohal, Industrial, lawn and garden, light construction, airport service.
Table 3-26: NMVOC Emissions from Mobile Combustion (Gg)
Fuel Type/Vehicle Type
Gasoline Highway
Passenger Cars
, tight-Duty Trucks
,Htavy-Quty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-DuV Vehicles
Alternative Fuel Highway8
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft"
Other4
Total
1990
8,110
5,120
2,374
575
42
406
16
14
377
IE
2,416
608
33
85
149
28
1,513
10,933
1996
5,360
3,049
1,947
343
21
283
7
9
268
IE
2,663
765
37
86
153
28
1,593
8,306
1997
5,167
2,928
1,882
336
22
263
6
8
249
IE
2,498
766
35
83
142
32
1,441
7,928
1998
5,067
2,895
1,812
335
25
249
5
7
237
IE
2,427
763
33
81
137
35
1,378
7,742
1999
4,865
2,777
1,713
347
27
227
5
6
216
IE
2,567
811
40
86
14S
40
1,442
7,658
2000
4,615
2,610
1,750
232
23
216
3
4
209
IE
2,398
744
35
76
130
24
1,390
i,m
2001
4,217
2,355
1,638
203
22
204
-. 3
4
198
IE .
2,379
730
35
72
125
19
1,387
8,88ft
2002
4,132
2,308
1,605
199
21
200
3
4
194
IE
2,439
748
36
74
128
: 20
1,432
8,771
IE (Included Elsewhere) ,
NclKToilterra/nttisuwd^ •• . . ;
a NMVOC errtsslonslrorflatternittvefciel highway vehicles are Wuded:under gasoline and diesel highway vehicles. ,:
6 Aircraft 8sttaattssir*lude only emissions related to landing and take-of (LTO) cycles, and ttieretore do not include cruise aitude frtteste*, \
c *f^r" tocludef gasolW"flow«red recreational, industrial, lawn arid garden, light commercial, togging, airport service, otter equipment and oTeset
powered recreationaMndustrtal, lawn and garden, light construction, airport service.
3-32 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
N2O emissions were predominantly from gasoline-fueled
passenger cars and light-duty gasoline trucks.
Mobile sources comprise the single largest source cat-
egory of CO, NOX, and NMVOC emissions in the United
States. In 2002, mobile combustion contributed 89 percent
of CO emissions, 57 percent of NOX emissions, and 45
percent of NMVOC emissions. Since 1990, emissions of
NMVOCs from mobile combustion decreased by 38 per-
cent, CO emissions decreased 31 percent, and emissions
of NOX decreased by 6 percent.
Methodology
Estimates of CH4 and N2O emissions from mobile
combustion were calculated by multiplying emission factors
by measures of activity for each fuel and vehicle type (e.g.,
light-duty gasoline trucks). Depending upon the category,
activity data included such information as fuel consumption,
fuel deliveries, and vehicle miles traveled (VMT). The
activity data and emission factors used are described in
the subsections that follow. A complete discussion of the
methodology used to estimate emissions from mobile
combustion and the emission factors used in the calculations
is provided in Annex 3.2.
EPA (2003c) provided emissions estimates of NOX, CO,
and NMVOCs for eight categories of highway vehicles,43
aircraft, and seven categories of non-highway vehicles.44 These
emission estimates were provided from preliminary EPA data,
which, in its final iteration, will be published on the National
Emission Inventory (NEI) Air Pollutant Emission Trends web
site. The methodology used to develop these estimates can
be found on EPA's Air Pollutant Emission Trends website, at
.
Highway Vehicles
Emission estimates for gasoline and diesel highway
vehicles were based on VMT and emission factors by
vehicle type, fuel type, model year, and control technology.
Emissions from alternative fuel vehicles (AFVs)45 were
based on VMT by vehicle and fuel type.
The Revised 1996 IPCC Guidelines (IPCC/UNEP/
OECD/IEA 1997) provided most of the emission factors for
CH4, and were developed using MOBILE5a, a model used by
the EPA to estimate exhaust and running loss emissions from
highway vehicles. The MOBILESa model uses information
on ambient temperature, vehicle speeds, national vehicle
registration distributions, gasoline volatility, and other
variables in order to produce these factors (EPA 1997).
Emission factors for CH4 for Tier 1 and LEV46 heavy-duty
gasoline vehicles were determined using emission factors
from the California Air Resources Board mobile source
emissions factor model for 2002 (CARB 2000).
Emission factors for N2O from gasoline passenger cars
were obtained from EPA (1998) instead of IPCC default
values because the U.S. default values in the Revised 1996
IPCC Guidelines were based on three studies that tested
a total of five cars using European rather than U.S. test
protocols. EPA (1998), meanwhile, reports emission factors
for older passenger cars (roughly pre-1992 in California and
pre-1994 in the rest of the United States) from published
references, and for newer cars from a recent testing program
at EPA's National Vehicle and Fuel Emissions Laboratory
(NVFEL). These emission factors for gasoline highway
vehicles are lower than the U.S. default values in theRevised
1996 IPCC Guidelines, but are higher than the European
default values, both of which were published before the more
recent tests and literature review conducted by the NVFEL.
Other references used in developing these factors include
Smith and Carey (1982), Urban and Garbe (1980), Prigent
and de Soete (1989), and Dash (1992). More details may be
found in EPA (1998). Some of these factors were revised
slightly by ICF Consulting (2001).
Nitrous oxide emission factors for most gasoline
vehicles other than passenger cars (i.e., light-duty gasoline
trucks, heavy-duty gasoline vehicles, and motorcycles) were
scaled from N2O factors from passenger cars with the same
These categories included: gasoline passenger cars, diesel passenger cars, light-duty gasoline trucks less than 6,000 pounds in weight, light-duty
gasoline trucks between 6,000 and 8,500 pounds in weight, light-duty diesel trucks, heavy-duty gasoline trucks and buses, heavy-duty diesel trucks and
buses, and motorcycles.
These categories included: gasoline and diesel farm tractors, other gasoline and diesel farm machinery, gasoline and diesel construction equipment,
snowmobiles, small gasoline utility engines, and heavy-duty gasoline and diesel general utility engines.
45 Alternative fuel and advanced technology vehicles are those that can operate using a motor fuel other than gasoline or diesel. This includes electric or
other bifuel or dual fuel vehicles that may be partially powered by gasoline or diesel.
See Annex 3.2 for definitions of control technology levels.
Energy 3-33
-------
control technology, based on their relative fuel economy.
Fuel economy for each vehicle category was derived from
data in DOE (1993 through 2003), FHWA (1996 through
2003), EPA/DOE (2001), and Census (2000). This scaling
was supported by limited data showing that light-duty trucks
emit more N2O than passenger cars with equivalent control
technology. The method of using fuel consumption ratios
to determine emission factors will be replaced as additional
testing data become available. Emission factors for N2O for
Tier 1 and LEV heavy-duty gasoline vehicles were estimated
from the ratio of NOX emissions to N2O emissions for Tier 0
heavy-duty gasoline trucks.
Because of limited data on N2O emissions from U.S.
diesel vehicles, N2O emission factors for diesel highway
vehicles were taken from the European default values found
in the Revised 1996 IF>CC Guidelines (IPCC/UNEP/OECD/
IEA 1997).
Emission factors for AFVs were developed after
consulting a number of sources, including Argonne National
Laboratory's GREET 1.5-Transportation Fuel Cycle Model
(Wang 1999), Lipman and Delucchi (2002), the Auto/Oil
Air Quality Improvement Research Program (CRC 1997),
the California Air Resources Board (Brasil and McMahon
1999), and the University of California Riverside (Norbeck,
et al., 1998). The primary approach taken was to calculate
CH4 emissions from actual test data and determine N2O
emissions from NOX emissions from the same tests. While
the formation of N2O is highly dependent on the type of
catalyst used and the catalyst temperature, tailpipe N2O is
likely to increase as engine out NOX emissions increase.
Thus as a first approximation, for a given emission control
group, the NOX to N2O emission ratio will likely be constant.
A complete discussion of the data source and methodology
used to determine emission factors from AFVs is provided
in Annex 3.2.
Annual VMT data for 1990 through 2002 were obtained
from the Federal Highway Administration's (FHWA)
Highway Performance Monitoring System database as
reported in Highway Statistics (FHWA 1996 through
2003). A methodology was developed to allocate the VMT
from FHWA's vehicle categories to EPA's fuel-specific
vehicle categories, relying on VMT, fuel economy, and fuel
consumption estimates from Census (2000), EPA/DOE
(2001), and FHWA (1996 through 2003). VMT for AFVs
were taken from Browning (2003). The temporally fixed age
distribution of the U.S. vehicle fleet and the average annual
age-specific vehicle mileage accumulation of U.S. vehicles
were obtained from EPA (2000).
Control technology and standards data for highway
vehicles were obtained from the EPA's Office of Trans-
portation and Air Quality (EPA 2003a, 2002b, 2000, 1998,
and 1997). These technologies and standards are defined
in Annex 3.2, and were compiled from EPA (1993), EPA
(1994a), EPA (1994b), EPA (1998), EPA (1999), and IPCC/
UNEP/OECD/IEA (1997).
Non-Highway
Fuel consumption data were employed as a measure
of activity for non-highway vehicles, and then fuel-specific
emission factors were applied.47 Activity data were obtained
from AAR (2003), BEA (1991 through 2003), Benson
(2002), DOE (2003), DESC (2002), DOC (1991 through
2003), DOT (1991 through 2003), EIA (2002a), EIA (2002b),
EIA (2003a), EIA (2003b), EIA (2003c), and EIA (1991
through 2003). Emission factors for non-highway modes
were taken from IPCC/UNEP/OECD/IEA (1997).
Uncertainty
This section discusses the uncertainty of the emissions
estimates for CH4 and N2O. Uncertainty was analyzed
separately for highway vehicles and non-highway vehicles,
due to differences in their characteristics and their
contributions to total mobile source emissions.
Uncertainty analysis was not conducted for CO, NOX,
and NMVOC emissions. Emission factors for these gases
have been extensively researched, since these gases are
regulated emissions from motor vehicles in the United States,
and the uncertainty of these emissions estimates is believed
to be relatively low. A much higher level of uncertainty
is associated with CH4 and N2O emission factors, since
emissions of these gases are not regulated in the United
States, and unlike CO2 emissions, the emission pathways
of CH4 and N2O are also highly complex.
47 The consumption of international bunker fuels is not included in these activity data, but is estimated separately under the International Bunker Fuels
source category.
3-34 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Highway Vehicles
An uncertainty analysis was conducted for the highway
portion of the mobile source sector using the IPCC-
recommended Tier 2 uncertainty estimation methodology,
Monte Carlo Stochastic Simulation technique, using ©RISK
software. The uncertainty analysis was performed on 2002
estimates of CH4and N2O emissions, incorporating probability
distribution functions associated with certain inputs. Two types
of uncertainty inputs were modeled: (1) vehicle mile traveled
(VMT) data, by vehicle and fuel type and (2) emission factor
data, by vehicle, fuel, and control technology type.
Mobile combustion emissions of CH4 and N2O per
vehicle mile traveled vary significantly due to fuel type
and composition, technology type, operating speeds and
conditions, type of emission control equipment, equipment
age, and operating and maintenance practices. The primary
activity data, VMT, are collected and analyzed each year by
government agencies.
To determine the uncertainty associated with the
activity data and emission factors used to calculate CH4 and
N2O, the agencies and experts that supply the data were
contacted. Because few of these sources were able to provide
quantitative estimates of uncertainty, expert judgment was
used to assess the uncertainty associated with activity data
and emission factors.
Although CH4 is not a regulated air pollutant in the
United States, CH4 emissions are normally measured in
vehicle emission tests to determine the non-methane portion
of the hydrocarbon emissions, which is more reactive in
producing ozone. The CH4 emission factors for highway
vehicles used in the inventory were obtained from IPCC/
UNEP/OECD/IEA (1997), and were originally from EPA's
emission factor model, MOBILES. These factors only reflect
limited data on newer vehicles and control technologies and
do not reflect improvements in emission control technology
in the last several years. New data were subsequently used
to develop emission factors for light-duty gasoline cars and
trucks in the MOBILE6 model, including Tier 0 and earlier
vehicles, but are not reflected in the emission factors used in
the inventory. Current vehicles in the U.S. fleet are therefore
not well represented by the CH4 emission factors used in
the inventory. Moreover, Tier 1 and LEV vehicle emission
factors were estimated for the inventory based upon the
differences in emission standards for hydrocarbons from
Tier 0 vehicles, not actual measurements. Thus, a higher
uncertainty was placed on those emission factors. Since
very limited data were used to estimate CH4 emissions from
diesel vehicles, a high level of uncertainty was assigned to
these factors as well.
The N2O emission factors for gasoline highway vehicles
were provided or derived from EPA (1998), and are based
on limited data (since N2O is not a regulated air pollutant,
measurements of it in automobile exhaust have not been
routinely collected). The emission factors used for Tier 0 and
older cars were based on tests of 28 vehicles; those for newer
vehicles were based on tests of 22 vehicles. This sample is
small considering that it is being used to characterize the
entire U.S. fleet, and the associated uncertainty is therefore
large. Moreover, the data represent older technology than is
currently in the marketplace. Research data have shown that
N2O emissions from vehicles with catalytic converters are
greater than those without emission controls, and vehicles
with aged catalysts emit more than new vehicles. In addition,
newer three-way catalyst systems produce fewer N2O
emissions. Since the publication of EPA (1998), new and
improved emission control technologies have been used on
both Tier 1 and LEV vehicles, and more LEVs and ULEVs
have been introduced into the fleet. Additional sources of
uncertainty include the following: 1) emissions from ULEVs
are estimated using the same emission factors for LEVs, 2)
light-and heavy-duty gasoline truck N2O emission factors
were extrapolated from passenger car data based upon
fuel economy differences, and 3) Tier 1 and LEV emission
factors for heavy-duty gasoline vehicles were estimated using
the ratio of N2O to NOX produced by heavy-duty gasoline
vehicles meeting Tier 0 standards.
Emission factors for diesel vehicles were based
upon European default values in the Revised 1996 IPCC
Guidelines (IPCC/UNEP/OECD/IEA 1997), since little
data on N2O emissions from U.S. diesel-fueled vehicles
existed. As these emission factors do not reflect variations
by control technology and are based on European studies, a
high uncertainty is associated with these estimates.
The emission factors for CH4 and N2O are in the process
of being revised based on new data from vehicle emission
tests. Information recently compiled includes CH4 emissions
data taken from 1982 through 2000 from 13,277 tests on
6,950 vehicles of various classes and control technologies,
and N2O data taken from 1998 through 2001 from 95 tests on
64 vehicles of various classes and control technologies. These
Energy 3-35
-------
data are currently being analyzed and reviewed to develop
emission factors for use in EPA's new emissions model,
MOVES. Upon final EPA and peer review, these factors
will be used in future inventories. To assess emission factor
uncertainty for the current inventory, the newly available CH4
and N2O emissions data was compared to the emission factors
used in the inventory to determine uncertainties associated
with the current emission factors.
Initial analyses of these data indicate that the current
emission factors for passenger cars are high. As N2O
emission factors for other gasoline vehicle types (light-duty
trucks, heavy duty trucks, and motorcycles) were based on
the N2O emission factors for passenger cars, the resulting
emission factors for these vehicle types are also believed to be
high. Using the newly available data, probability distribution
functions for N2O and CH4 emission factors were developed
for the uncertainty analysis that reflect these beliefs. The CH4
and N2O emission factors will be revised in future inventories
based on this continuing research.
Estimates of VMT for highway vehicles by vehicle
type in the United States were provided by FHWA (1996
through 2002), and were generated though the cooperation
of FHWA and state and local governments. These estimates
are subject to several possible sources of error, such as
unregistered vehicles, unreported fuel sales to avoid fuel
taxes, differences in achieved versus estimated fuel economy,
and measurement and estimation errors. These VMT were
apportioned by fuel type, and then allocated to individual
model years using temporal profiles of both the vehicle fleet
by age and vehicle usage by model year in the United States
provided by EPA (2000). While the uncertainty associated
with total U.S. VMT is believed to be low, the uncertainty
within individual source categories was assumed to be higher
given uncertainties associated with apportioning total VMT
into individual vehicle categories, by technology type, and
equipment age. The uncertainty of individual estimates
was assumed to relate to the magnitude of estimated VMT
(i.e., it was assumed smaller sources had greater percentage
uncertainty). A further source of uncertainty occurs since
FHWA and EPA use different definitions of vehicle type and
estimates of VMT by vehicle type (provided by FHWA) are
broken down by fuel type using EPA vehicle categories.
A total of 94 highway data input variables (i.e., VMT
and emission factors for individual vehicle categories and
technologies) were simulated through Monte Carlo Stochastic
Simulation technique using @RISK software. In developing
the uncertainty estimation model, a normal distribution
was assumed for all activity-related input variables (e.g.,
VMT). To the extent possible, the dependencies and other
correlations among the activity data were incorporated into
the model to ensure consistency in the model specification
and simulation. Emission factors were assigned triangular
distributions, with upper and lower bounds assigned to
input variables based on expert judgment, incorporating
information available from the most recent vehicle test
data set. The bounds for the emission factor-related input
variables were typically asymmetric around their inventory
estimates. Bias (or systematic uncertainties) accounted
for much of the uncertainty associated with the emission
factors.48 An analysis of new preliminary data for emission
factors indicates the actual emission factors might be much
lower than the currently used inventory estimates. The results
of this analysis are reported in the section below, entitled
Quantitative Estimates of Uncertainty.
Non-Highway
Emissions from non-highway vehicles are a small
portion of total emissions from mobiles sources, representing
11 percent of CH4 emissions from mobile sources and 6
percent of N2O emissions from mobile sources in 2002.
Given that they comprise a small share of mobile source
emissions, even large uncertainties in these estimates will
have a relatively small impact on the total emission estimate
for mobile sources. As a result, a quantitative analysis of
uncertainty of emissions from non-highway vehicles has
not been performed. However, sources of uncertainty for
non-highway vehicles are being investigated by examining
the underlying uncertainty of emission factors and fuel
consumption data.
Overall, a significant amount of uncertainty is associated
with the emission estimates for non-road sources. A primary
cause is a large degree of uncertainty surrounding emission
factors. The IPCC Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories reports
that CH4 emissions from aviation and marine sources may
48 Although, in general, random uncertainties are the main focus of statistical uncertainty analysis, when the uncertainty estimates are elicited from experts,
their estimates include both random and systematic uncertainties. Hence, both these types of uncertainties are represented in this uncertainty analysis.
3-36 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
be uncertain by a factor of two, while N2O emissions may
be uncertain by an order of magnitude for marine sources
and several orders of magnitude for aviation. No information
is provided on the uncertainty of emission factors for other
non-highway sources.
Fuel consumption data have a lower uncertainty
than emission factors, though large uncertainties do exist
for individual sources. Motor gasoline consumption for
recreational boating, farm equipment, construction, and heavy-
duty equipment was obtained from FHWA (1996 though
2003). FHWA collects data on fuel use from the department
of revenue in each U.S. state, based on tax receipts, and then
attributes motor gasoline consumption to end uses. The total
fuel use estimate adds to uncertainty due to the different
ways in which states collect taxes, and how states account
for special fuels such as gasohol (which consists of a mixture
of gasoline and ethyl alcohol). The methods that FHWA
uses to estimate consumption by end use sector have higher
uncertainties. FHWA is able to discern what is the use of
gasoline, in some instances, based on whether it is taxed at
different rates. However, FHWA uses a complex methodology
to attribute gasoline to highway and non-highway uses, using
inputs from the Census Bureau's Vehicle Inventory and Use
Survey (VIUS) and other sources. These models are currently
being revised by FHWA, as they believe the current models
overestimate fuel use for certain categories in 2001 and 2002
(e.g., construction equipment).
Gasoline consumption for small utility equipment and
snowmobiles add to total uncertainty, as estimates for these
sources are not available annually from published data
sources; instead, estimates were held constant or extrapolated
for missing years. Additional data are needed to improve
these estimates.
Distillate consumption for ships and boats, farm
equipment, construction, and heavy-duty utility equipment
was obtained from sales estimates from EIA's Fuel Oil and
Kerosene Sales (EIA 1991 through 2003). The estimates for
distillate consumption for non-road sources have associated
uncertainty, as EIA's estimates are based on sales to economic
sectors, and it can be difficult to determine how much
of the fuel sold in each sector is used by off-highway or
stationary sources and to further attribute this consumption
to specific final users. For example, some fuel purchased
by the construction sector may be used for operating heavy
construction equipment, while some may be used for
operating equipment such as stationary electric generators.
This distinction between off-highway and stationary fuel
users is not made by EIA.
EIA does provide coefficients of variation to estimate
sampling error, which occur due to the fact that these
estimates are based on a sample set. However, as EIA points
out, these coefficients do not take into account all the sources
of potential bias, which includes incomplete information,
misinterpretation of survey questions, and other factors that
may cause estimates of fuel sales to be different from actual
sales. In addition, diesel for ships and boats is adjusted for
bunker fuel consumption, which introduces an additional
(and much higher) level of uncertainty.
Domestic consumption for residual fuel consumption
by ships and boats is obtained from EIA (2003a). These
estimates fluctuate widely from year to year; the fluctuations
are unexplained and the estimates are believed to be highly
uncertain. The estimate of domestic consumption is then
adjusted downward to account for international bunker fuels,
which represents the primary use of residual fuel by ships and
boats. As the international bunker fuel data are considered to
have a moderate level of uncertainty,49 the overall uncertainty
of the domestic ships and boats estimate for residual fuel
consumption is considered high.
Domestic jet fuel and aviation gasoline consumption
data are obtained from EIA (2003a). Like diesel and residual
marine fuel consumption, jet fuel consumption for aviation
is adjusted downward to account for international bunker
fuels. The international bunker fuel estimates introduce a
significant amount of uncertainty. Additionally, all jet fuel
consumption in the transportation sector is assumed to be
consumed by aircraft. Some fuel purchased by airlines is
not necessarily used in aircraft, but instead used to power
auxiliary power units, in ground equipment, and to test
engines. Some jet fuel may also be used for other purposes
such as blending with diesel fuel or heating oil.
In calculating CH4 emissions from aircraft, an average
emission factor is applied to total jet fuel consumption. This
average emission factor takes into account the fact that CH4
emissions occur only during the landing and take-off (LTO)
cycles, with no CH4 being emitted during the cruise cycle.
" This is discussed in the section on International Bunker Fuels.
Energy 3-37
-------
Table 3-27: Quantitative Uncertainty Estimates for CH4 and N20 Emissions from Highway Vehicles (Tg C02 Eq. and Percent)
Source
2002 Emission Estimate
Gas (TgC02Eq.)
Uncertainty Range Relative to Emission Estimate*
J {%)
Lower Bound Upper Bound Lower Bound Upper Bound
Mobile Sources
Mobile Sources
CH4
N20
4.2
52.9
3.8
43.3
4.6
61.7
-9%
-18%
-1-9%
+17%
a Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
However, a better approach would be to apply emission
factors based on the number of LTO cycles. Using LTO data
to estimate CH4 emissions is currently being investigated for
future inventories.
Lastly, in EPA (2003), U.S. aircraft emission estimates
for CO, NOX, and NMVOCs are based upon LTO cycles and,
consequently, only estimate near ground-level emissions,
which are more relevant for air quality evaluations. These
estimates also include both domestic and international
flights. Therefore, estimates presented here may overestimate
IPCC-defined domestic CO, NOX, and NMVOC emissions
by including LTO cycles by aircraft on international flights
but underestimate total emissions because they exclude
emissions from aircraft on domestic flight segments at
cruising altitudes.
The uncertainty associated with the emission estimates
for non-highway vehicles is being investigated and
quantitatively analysis of the uncertainty of these sources
will be included in future inventories.
Quantitative Estimates of Uncertainty
The preliminary results of the quantitative uncertainty
analysis (see Table 3-27) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions from this source is within the
range of approximately 3.8 to 4.6 Tg CO2 Eq. (or the actual
CH4 emissions from mobile sources are likely to fall within
the range of approximately 9 percent below and 9 percent
above the emission estimate of 4.2 Tg CO2 Eq.). Under the
same 95 percent confidence interval, the actual estimate
of N2O emissions in 2002 is likely to be within the range
of approximately 43.3 and 61.7 Tg CO2 Eq. (indicating
that the actual N2O emissions from mobile sources are
likely to fall within the range of approximately 18 percent
below and 17 percent above the emission estimate of 52.9
Tg C02 Eq.).50
This uncertainty analysis is only the beginning of a
multi-year process for developing credible quantitative
uncertainty estimates for this source category using the IPCC
Tier 2 approach to Uncertainty Analysis. In the upcoming
years, the type and the characteristics of the actual probability
density functions underlying the input variables will be
identified and more credibly characterized. Moreover, there
are plans to revise the emission factors next year, which will
alter the uncertainty results. Accordingly, the quantitative
uncertainty estimates reported in this section should be
considered as preliminary and illustrative.
QA/QC and Verification
A source-specific QA/QC plan for mobile combustion
was developed and implemented. This effort included a Tier
1 analysis, as well as portions of a Tier 2 analysis. The Tier 2
procedures focused on the emission factor and activity data
sources and the methodology used for estimating emissions.
These procedures included a qualitative assessment of the
emission factors to determine whether they appear consistent
with the most recent emissions data available; and, where
a complete time series of activity data were unavailable,
alternative ways to estimate missing years were investigated
to ensure that the estimates were as representative of national
trends as possible.
These results include emission estimates for non-highway sources, in order to express uncertainty for mobile sources as a whole. However, quantitative
uncertainty estimates for non-highway vehicles have not yet been included in this analysis, but will be included in future inventories.
3-38 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Recalculations Discussion
In order to ensure the highest quality estimates possible,
the methodology is continuously revised based on comments
from internal and external reviewers. This year, adjustments
were made to emission factors and activity data to more
accurately reflect the characteristics of mobile sources. These
changes, detailed below, together resulted in the following
changes in estimates compared to the previous inventory:
between 1990 and 2001, the yearly change in CH4 estimates
ranged from a decrease of 0.03 Tg CO2 Eq. to an increase
of 0.01 Tg CO2 Eq., and averaged to a yearly decrease
of 0.01 Tg CO2 Eq. (0.2 percent). During the same time
period, the yearly change in N2O estimates ranged from a
decrease of 0.13 Tg CO2 Eq. to an increase of 0.26 Tg CO2
Eq., and averaged to a yearly decrease of 0.01 Tg CO2 Eq.
(0.2 percent).
The N2O and CH4 emission factors for light-duty LPG
vehicles were revised. Previously, these estimates were
calculated as the average of the emission factors associated
with light-duty original equipment manufacturer (OEM)
vehicles and retrofit vehicles. However, most of the vehicles in
the current fleet represent OEM vehicles, as the older retrofit
vehicles are either phased out of the fleet or are currently
running on gasoline. To better represent the light-duty fleet
of LPG vehicles, the light-duty LPG emission factors are set
equal to the OEM emission factors for LPG vehicles.
The VMT for light-duty AFVs were revised, due to a
more refined analysis of the fleet penetration of each type
of vehicle. With more comprehensive information on AFV
sales, an improved estimation of the breakdown of VMT by
type of light-duty AFV was developed. A summary of this
data can be found in Browning (2003).
The emission estimate for locomotive residual consumption
was removed based upon conversations with experts in the
field. Previously, it was estimated that a small portion of EIA's
"other" residual fuel oil consumption was rail.
Emissions from diesel consumption by commuter
and intercity rail were included in the inventory in the
locomotives category. These emissions were not previously
estimated. Consumption data for these sources were obtained
from DOE (2003).
Finally, the source of data on residual fuel oil consumption
by ships and boats was changed from EIA's Fuel Oil and
Kerosene Sales (EIA 1991 through 2003) to EIA's Monthly
Energy Review and unpublished supplemental tables on
petroleum product detail (EIA 2003a). Since residual fuel
is no longer assumed to be consumed by any transportation
mode other than ships and boats, total transportation residual
fuel consumption from EIA (2003a) is now viewed as the
best estimate for this source category.
Planned Improvements
While the data used for this report represent the most
accurate information available, two areas have been identified
that could potentially be improved in the short term given
available resources: 1) N2O and CH4 emission factors, and
2) fuel consumption estimates for small utility equipment
and snowmobiles. Potential improvements to these areas
will be investigated and included (if appropriate) in future
inventories. In addition, EPA is currently in the process of
developing a new emission estimation model called MOVES,
which is designed to estimate emissions produced by on-road
and non-road mobile sources. EPA will be examining how to
use MOVES to improve emission estimation methodologies
in the future.
3.5. Coal Mining
(IPCC Source Category 1B1 a)
All underground and surface coal mining liberates
CH4 as part of the normal mining operations. The amount
of CH4 liberated depends on the amount that remains in the
coal ("in situ") and surrounding strata when mining occurs.
The in-situ CH4 content depends upon the amount of CH4
created during the coal formation (i.e., coalification) process,
and the geologic characteristics of the coal seams. During
coalification, deeper deposits tend to generate more CH4
and retain more of the gas afterwards. Accordingly, deep
underground coal seams generally have higher CH4 contents
than shallow coal seams or surface deposits.
Three types of coal mining related activities release CH4
to the atmosphere: underground mining, surface mining, and
post-mining (i.e., coal-handling) activities. Underground coal
mines contribute the largest share of CH4 emissions. All 96 gassy
underground coal mines employ ventilation systems to ensure
that CH4 levels remain within safe concentrations. These systems
can exhaust significant amounts of CH4 to the atmosphere in
low concentrations. Additionally, twenty-one U.S. coal mines
supplement ventilation systems with degasification systems.
Energy 3-39
-------
Table 3-28: CH4 Emissions from Coal Mining (Tg C02 Eq.)
Activity
1988
Underground Mining
Liberated
Recovered & Used
Surface Mining
Post-Mining (Underground)
Post-Mining (Surface)
Total
81.9
Note: Totals may not sum due to Independent rounding.
Table 3-29: CH4 Emissions from Coal Mining (Gg)
1 1996
45.3
59.8
(14.5)
9.2
7.2
1.5
I 63.2
1997
44.3
55.7
(11.4)
9.3
7.4
1.5
62.6
19S8
44,4
58.6
(14.2)
9.4
7.4
1.5
62.8
1199
41.6
54.4
(12.7)
§.0
6.8
1.5
S8.9
2000
39.4
54.0
8.8
6.7
1.4
56.2
2001
38.1
542
(16.0)
9,2
6.8
1.5
55.6
2002
35.6
53.3
(17.7)
8.8
6.4
1.4
52.2
Activity
1990
Underground Mining
Liberated
Recovered & Used
Surface Mining
Post-Mining (Underground)
Post-Mining (Surface)
Total
3,900
Note: Totals may not sum due to independent rounding.
1996
2,158
2,850
(692)
438
341
71
3,008
1997
2,111
2,654
(543)
445
354
72
2,983
1998
2,117
2,791
(674)
448
352
73
2,989
1999
1,982
2,589
(807)
428
325
69
2.805
2000
1,876
2,573
(697)
417
317
68
2,677
2001
1,816
2,580
(764)
438
323
71
2,648
2002
1,695
2,538
(843)
420
304
68
2,487
Degasification systems are wells drilled from the surface or
boreholes drilled inside the mine that remove large volumes of
CH4 before, during, or after mining. In 2002, ten coal mines
collected CH4 from degasification systems and sold this gas to
a pipeline, thus reducing emissions to the atmosphere. Surface
coal mines also release CH4 as the overburden is removed and
the coal is exposed, but the level of emissions is much lower
than from underground mines. Finally, some of the CH4 retained
in the coal after mining is released during processing, storage,
and transport of the coal.
Total CH4 emissions in 2002 were estimated to be 52.2 Tg
CO2 Eq. (2,487 Gg), declining 36 percent since 1990 (see Table
3-28 and Table 3-29). Of this amount, underground mines
accounted for 68 percent, surface mines accounted for 17
percent, and post-mining emissions accounted for 15 percent.
With the exception of 1994 and 1995, total CH4 emissions
declined in each successive year during this period. In 1993,
CH4 generated from underground mining dropped, primarily
due to labor strikes at many large underground mines. In 1994
and 1995, CH4 emissions increased due to resumed production
at high emitting mines after the labor strike. The decline in
CH4 emissions from underground mines in 2002 is the result
of the reduction of overall coal production, the mining of less
gassy coal, and an increase in CH4 recovered and used. Surface
mine emissions and post-mining emissions remained relatively
constant from 1990 to 2002.
The methodology for estimating CH4 emissions from
coal mining consists of two parts. The first part involves
estimating CH4 emissions from underground mines. Because
of the availability of ventilation system measurements,
underground mine emissions can be estimated on a mine-by-
mine basis and then summed to determine total emissions.
The second step involves estimating emissions from surface
mines and post-mining activities by multiplying basin-
specific coal production by basin-specific emission factors.
Underground mines. Total CH4 emitted from underground
mines was estimated as the sum of CH4 liberated from
ventilation systems and CH4 liberated by means of
degasification systems, minus CH4 recovered and used. The
Mine Safety and Heath Administration (MSHA) samples
CH4 emissions from ventilation systems for all mines with
detectable51 CH4 concentrations. These mine-by-mine
51 MSHA records coal mine methane readings with concentrations of greater than 50 ppm (parts per million) methane. Readings below this threshold
are considered non-detectable.
3-40 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
measurements are used to estimate CH4 emissions from
ventilation systems.
Some of the higher-emitting underground mines also
use degasification systems (e.g., wells or boreholes) that
remove CH4 before, during, or after mining. This CH4 can
then be collected for use or vented to the atmosphere. Various
approaches were employed to estimate the quantity of CH4
collected by each of the twenty-one mines using these systems,
depending on available data. For example, some mines report
to EPA the amount of CH4 liberated from their degasification
systems. For mines that sell recovered CH4 to a pipeline,
pipeline sales data published by state petroleum and natural
gas agencies were used to estimate degasification emissions.
For those mines for which no other data are available, default
recovery efficiency values were developed, depending on the
type of degasification system employed.
Finally, the amount of CH4 recovered by degasification
systems and then used (i.e., not vented) was estimated. This
calculation was complicated by the fact that most CH4 is
not recovered and used during the same year in which the
particular coal seam is mined. In 2002, ten active coal mines
sold recovered CH4 into the local gas pipeline networks.
Emissions avoided for these projects were estimated using
gas sales data reported by various state agencies. For most
mines with recovery systems, companies and state agencies
provided individual well production information, which
was used to assign gas sales to a particular year. For the few
remaining mines, coal mine operators supplied information
regarding the number of years in advance of mining that gas
recovery occurs.
Surface Mines and Post-Mining Emissions. Surface
mining and post-mining CH4 emissions were estimated by
multiplying basin-specific coal production, obtained from the
Energy Information Administration's Coal Industry Annual
(see Table 3-30) (EIA 2002), by basin-specific emission
factors. Surface mining emission factors were developed by
assuming that surface mines emit two times as much CH4
as the average in situ CH4 content of the coal. Revised data
on in situ CH4 content and emissions factors are taken from
EPA (1996) and AAPG (1984). This calculation accounts for
CH4 released from the strata surrounding the coal seam. For
post-mining emissions, the emission factor was assumed to
be 32.5 percent of the average in situ CH4 content of coals
mined in the basin.
Table 3-30: Coal Production (Thousand Metric Tons)
1890,
1,991
1992
1993;
1984
368*627
'.siagtit-
312,065
532,816
534,290
§34214
; 931,068
maw
paw
807,602
1988
1997
371.81S
381,82$ ,
378,964
2000
2001
2002
•338,173
345,305
324,218
676,142
667J19
973,765
1,021,446
,991,838
Uncertainty
The emission estimates from underground ventilation
systems were based on actual measurement data, which
are believed to have relatively low uncertainty. A degree
of imprecision was introduced because tne measurements
were not continuous but rather an average of quarterly
instantaneous readings. Additionally, tne measurement
equipment used possibly resulted in an average of 10 percent
overestimation of annual CH4 emissions (Mutmansky and
Wang 2000). Estimates of CH4 liberated and recovered by
degasification systems are also relatively certain because
many coal mine operators provided information on individual
well gas sales and mined through dates. Many of the recovery
estimates use data on wells within 100 feet of a mined area.
A level of uncertainty currently exists concerning the radius
of influence of each well. The number of wells counted, and
thus the avoided emissions, may increase if the drainage area
is found to be larger than currently estimated.
Compared to underground mines, there is considerably
more uncertainty associated with surface mining and post-
mining emissions because of the difficulty in developing
accurate emission factors from field measurements. However,
since underground emissions comprise the majority of total
coal mining emissions, the uncertainty associated with
underground emissions is the primary factor that determines
overall uncertainty. The preliminary results of the quantitative
uncertainty analysis (see Table 3-31) indicate that, on
average, in 19 out of 20 times (i.e., there is a 95 percent
probability), the total greenhouse gas emissions estimate
from this source is within the range of approximately 44.4
to 60.1 Tg CO2 Eq. (indicating that the actual CH4 emissions
Energy 3-41
-------
Table 3-31: Quantitative Uncertainty Estimates for CH4 Emissions from Coal Mining (Tg C02 Eq. and Percent)
Source
2002 Emission Estimate
Gas (TgC02Eq.)
Uncertainty Range Relative to Emission Estimate3
Lower Bound Upper Bound Lower Bound Upper Bound
Coal Mining
CH4
52.2
44,4
0.1
4-15%
aRange of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
are likely to fall within the range of approximately 15 percent
below and 15 percent above the emission estimate of 52.2
Tg C02 Eq.).
Recalculations Discussion
In-situ gas content is the principal variable used to
determine post-mining methane emissions of mined coal.
Previously, in-situ values used were based on average CH4
content values summarized in Exhibit 3-4 of the U.S. EPA
publication, EPA/400/9-90/008; Methane Emissions From
Coal Mining, Issues and Opportunities, September 1990.
The original source of information is derived from three
primary sources: 1986 USBM Circular 9067, Results of the
Direct Method Determination of the Gas Contents of U.S.
Coal Basins, 1983 U.S. DOE Report (DOE/METC/83-76),
Methane Recovery from Coalbeds: A Potential Energy
Source, and a series of 1986-88 Gas Research Institute
Topical Reports called A Geologic Assessment of Natural
Gas from Coal Seams. No data was available for eight of the
coal mining states and therefore default values from other
coal basins were assigned to those states.
Since Circular 9067 contained only a portion of the
gas content data compiled by USBM, the complete dataset,
published in 1996 Evaluation and Analysis of Gas Content and
Coal Properties of Major Coal Bearing Regions of the United
States, EPA/600/R-96-065, is now the basis of new in-situ gas
content value. In addition, gas content data from the U.S. DOE
Methane Recovery from Coalbed Projects (MRCP), which
was the original source of data for the GRI Topical Reports
noted above, was utilized. (Condensed versions of the original
MRCP reports for 13 U.S. coal basins are compiled in Coalbed
Methane Resources of the United States, AAPG Studies in
Geology Series #77, published in 1984).
The compiled gas content data for each of the coal
basins was sorted by depth to determine in-situ values for
surface and underground mines, separately. Overburden
depths of surface mines were analyzed using Keystone Coal
Industry Manuals from 1991 through 2003 and found that the
maximum depth was 250 feet. Therefore, gas content data
from samples taken less than 250 feet deep were assigned to
surface mines and the samples collected from deeper depths
to underground mines. The combination of these changes
and the historical data revisions described here resulted in
an average annual decrease of 5.0 Tg CO2 Eq. (7 percent) in
CH4 emissions for the period 1990 through 2001.
Planned Improvements
To reduce the uncertainty associated with the radius of
influence of each well, the appropriate drainage radius will
be investigated for future inventories. Since the number of
wells counted may increase if the drainage area is found to
be larger than currently estimated, additional mines may be
included in future estimates of recovery.
3.6. Abandoned Underground Coal
Mines (IPCC Source Category 1B1 a)
All underground and surface coal mining liberates
CH4 as part of the normal mining operations. The amount
of CH4 liberated depends on the amount that resides in the
coal ("in situ") and surrounding strata when mining occurs.
The in-situ CH4 content depends upon the amount of CH4
created during the coal formation (i.e., coalification) process,
and the geologic characteristics of the coal seams. During
coalification, more deeply buried deposits tend to generate
more CH4 and retain more of the gas after uplift to minable
depths. Deep underground coal seams generally have higher
CH4 contents than shallow coal seams or surface deposits.
Underground coal mines contribute the largest share of
CH4 emissions, with active underground mines the leading
source of underground emissions. However, mines also
continue to release CH4 after closure. As mines mature
and coal seams are mined through, mines close and are
abandoned. Many are sealed and some flood through
3-42 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
intrusion of groundwater or surface water into the void. Shafts
or portals are generally filled with gravel and capped with
a concrete seal, while vent pipes and boreholes are plugged
in a manner similar to oil and gas wells. Some abandoned
mines are vented to the atmosphere to prevent the buildup
of CH4 that may find its way to surface structures through
overburden fractures. As work stops within the mines, the
CH4 liberation decreases but it does not stop completely.
Following an initial decline, abandoned mines can liberate
CH4 at a near-steady rate over an extended period of time,
or, if flooded, produce gas for only a few years. The gas
can migrate to the surface through the conduits described
above, particularly if they have not been sealed adequately. In
addition, diffuse emissions can occur when CH4 migrates to
the surface through cracks and fissures in the strata overlying
the coal mine. The following factors influence abandoned
mine emissions:
• Time since abandonment;
• Gas content and adsorption characteristics of coal;
• Methane flow capacity of the mine;
• Mine flooding;
• Presence of vent holes; and
• Mine seals.
Methane emissions from U.S. abandoned coal mines in
1990 were 3.4 Tg CO2Eq. Gross abandoned mine emissions
ranged from 3.4 to 6.8 Tg CO2 Eq. from 1990 through
2002, varying as much as 1.0 Tg CO2 Eq. from year-to-year.
Fluctuations were due mainly to the number of mines closed
during a given year as well as the magnitude of the emissions
from those mines when active. Abandoned mine emissions
peaked in 1996 due to the large number of mine closures from
1994 to 1996 (76 gassy mines closed during the three-year
period). In spite of this rapid rise, abandoned mine emissions
have been on the decline since 1996. There were fewer than
ten gassy mine closures during each of the years from 1998
through 2000. By 2002, abandoned mine emissions were
reduced to 4.1 Tg CO2Eq. (see Table 3-32 and Table 3-33).
Methodology
Estimating CH4 emissions from an abandoned coal
mine requires predicting the emissions of a mine from the
time of abandonment through the inventory year of interest.
The flow of CH4 from the coal to the mine void is primarily
dependent on mine's emissions when active and the extent to
which the mine is flooded or sealed. The CH4 emission rate
before abandonment reflects the gas content of the coal, rate
of coal mining, and the flow capacity of the mine in much
the same way as the initial rate of a water-free conventional
gas well reflects the gas content of the producing formation
and the flow capacity of the well. Existing data on abandoned
mine emissions through time, although sparse, appear to
fit the hyperbolic type of decline curve used in forecasting
production from natural gas wells.
In order to estimate CH4 emissions over time for a
given mine, it is necessary to apply a decline function,
initiated upon abandonment, to that mine. In the analysis,
Table 3-32: CH4 Emissions from Abandoned Coal Mines (Tg C02 Eq.)
Activity
Abandoned Underground Mines
Recovered & Used
Total
Note: Totals may not sum due to independent rounding.
1998 1997
6.4
0.5
6.0
1998
1999
2000
6.8
1.2
5.6
6.1
1.3
5.6
1.2
4.8
4.4
5.5
1.0
4.4
2001
5.2
1.0
4.2
2802
5.2
1,1
4.1
Table 3-33: CH4 Emissions from Abandoned Coal Mines (Gg)
Activity
Abandoned Underground Mines
Recovered & Used
Total
Note: Totals may not sum due to independent rounding.
1196
307
23
283
1997
1998
1999
2009
321
56
266
290
62
268
57
261
50
228
211
211
2001
248
48
200
2002
247
50
196
Energy 3-43
-------
mines were grouped by coal basin with the assumption
that they will generally have the same initial pressures,
permeability and isotherm. As CH4 leaves the system, the
reservoir pressure, Pp declines as described by the isotherm.
The emission rate declines because the mine pressure (Pw)
is essentially constant at atmospheric pressure, for a vented
mine, and the PI term is essentially constant at the pressures
of interest (atmospheric to 30 psia). A rate-time equation can
be generated that can be used to predict future emissions.
This decline through time is hyperbolic in nature and can be
empirically expressed as:
Where:
q = the gas rate at time t in mcf/d
Qi = the initial gas rate at time zero (t0) in million cubic
feet per day (mcfd)
b = the hyperbolic exponent, dimensionless
Dj = the initial decline rate, 1/yr
t = elapsed time from to in years
This equation is applied to mines of various initial
emission rates that have similar initial pressures, permeability
and adsorption isotherms (EPA 2003).
The decline curves are also affected by both sealing
and flooding. Based on field measurement data, it was
assumed that most U.S. mines prone to flooding will
become completely flooded within 8 years and therefore no
longer have any measurable CH4 emissions. Based on this
assumption, an average decline rate for flooding mines was
established oy fitting a decline curve to emissions from field
measurements. An exponential equation was developed from
emissions data measured at eight abandoned mines known to
be filling with water located in two of the five basins. Using
a least squaies, curve-fitting algorithm, emissions data were
matched to the exponential equation shown below. There was
not enough data to establish basin-specific equations as was
done with the vented, non-flooding mines (EPA 2003).
q = qieW
Where:
q = the gas flow rate at time t in mcf/d
q; = the initial gas flow rate at time zero (t0) in mcfd
D = the decline rate, 1/yr
t = elapsed time from t0 in years
Seals have an inhibiting effect on the rate of flow of
CH4 into the atmosphere compared to the rate that would
be emitted if the mine had an open vent. The total volume
emitted will be the same, but will occur over a longer
period. The methodology, therefore, treats the emissions
prediction from a sealed mine similar to emissions from
a vented mine, but uses a lower initial rate depending on
the degree of sealing. The computational fluid dynamics
simulator was again used with the conceptual abandoned
mine model to predict the decline curve for inhibited flow.
The percent sealed is defined as 100 x (1 - initial emissions
from sealed mine / emission rate at abandonment prior to
sealing). Significant differences are seen between 50 percent,
80 percent and 95 percent closure. These decline curves
were therefore used as the high, middle, and low values for
emissions from sealed mines (EPA 2003).
For active coal mines, those mines producing over 100
mcfd account for 98 percent of all CH4 emissions. This
same relationsnip is assumed for abandoned mines. It was
determined that 374 abandoned mines closing after 1972
produced emissions greater than 100 mcfd when active.
Further, the status of 240 of the 374 mines (or 64 percent) is
known to be either 1) vented to the atmosphere, 2) sealed to
some degree (either earthen or concrete seals), or 3) flooded
(enough to inhibit methane flow to the atmosphere). The
remaining 36 percent of the mines were placed in one of
the three categories by applying a probability distribution
analysis based on the known status of other mines located
in the same coal basin (EPA 2003).
Inputs to the decline equation require the average
emission rate and the date of abandonment. Generally this
data is available for mines abandoned after 1972; however,
such data are largely unknown for mines closed before 1972.
Information that is readily available such as coal production
by state and county are helpful, but do not provide enough
data to directly employ the methodology used to calculate
emissions from mines abandoned after 1971. It is assumed
that pre-1972 mines are governed by the same physical,
geologic and hydrologic constraints that apply to post-1972
mines, thus their emissions may be characterized by the
same decline curves.
During the 1970s, 78 percent of CH4 emissions from
coal mining came from seventeen counties in seven states.
In addition, mine closure dates were obtained for two states,
Colorado and Illinois, throughout the 20th century. The data
3-44 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-34: Range of Uncertainty Estimates for CH4 Emissions from Abandoned Underground Coal Mining
(Tg C02 Eq. and Percent)
2002 Emission Estimate
Gas (TflC02Eq.)
Uncertainty Range Relative to Emission Estimate8
Lower Bound Upper Bound Lower Bound Upper Bound
Abandoned Coal Mines
Ctj:
4,1
4.8
was used to establish a frequency of mine closure histogram
(by decade) and applied to the other five states with gassy
mine closures. As a result, basin-specific decline curve
equations were applied to 145 gassy coal mines estimated
to have closed between 1920 and 1971 in the United States,
representing 78 percent of the emissions. State-specific,
initial emission rates were used based on average coal mine
methane emissions rates during the 1970s (EPA 2003).
Abandoned mines emission estimates are based on all
closed mines known to have active mine CH4 ventilation
emission rates greater than 100 mcfd at the time of
abandonment. For example, for 1990 the analysis included
145 mines closed before 1972 and 230 mines closed
between 1972 and 1990. Initial emission rates based on
MSHA reports, time of abandonment, and basin-specific
decline curves influenced by a number of factors were
used to calculate annual emissions for each mine in the
database. Coal mine degasification data are not available
for years prior to 1990, thus the initial emission rates used
reflect ventilation emissions only for pre-1990 closures.
Methane degasification amounts were added to ventilation
data for the total CH4 liberation rate for fourteen mines that
closed between 1992 and 2002. Since the sample of gassy
mines (with active mine emissions greater than 100 mcfd)
is assumed to account for 78 percent of the pre-1971 and
98 percent of the post-1971 abandoned mine emissions, the
modeled results were multiplied by 1.22 and 1.02 to account
for all U.S. abandoned mine emissions. Once the 1991
through 2002 totals were calculated, they were downwardly
adjusted to reflect abandoned mine CH4 emissions avoided
from those mines. The inventory totals were not adjusted for
abandoned mine reductions in 1990 through 1992, because
no data was reported for abandoned coal mining methane
recovery projects during that time.
Uncertainty
The parameters for which values must be estimated for
each mine in order to predict its decline curve are: 1) the coal's
adsorption isotherm; 2) CH4 flow capacity as expressed by
permeability; and 3) pressure at abandonment. Because these
parameters are not available for each mine, an approach was used
that generates a probability distribution of potential outcomes
based on the most likely value and the probable range of values
for each parameter. The range of values is not meant to capture
the extreme values, but values that represent the highest and
lowest quartile of the cumulative probability density function of
the parameter. Once the low, mid, and high values are selected,
they are applied to a probability density function.
The emission estimates from underground ventilation
systems were based on actual measurement data, which
are believed to have relatively low uncertainty. A degree
of imprecision was introduced because the measurements
were not continuous, but rather an average of quarterly
instantaneous readings. Additionally, the measurement
equipment used possibly resulted in an average of 10 percent
overestimation of annual CH4 emissions (Mutmansky and
Wang 2000). Estimates of CH4 liberated and recovered by
degasification systems are also relatively certain because
many coal mine operators provided information on individual
well gas sales and mined through dates.
The preliminary results of the quantitative uncertainty
analysis (see Table 3-34) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions from this source is within the range
of approximately 3.5 to 4.8 Tg CO2 Eq. (indicating that the
actual CO2 emissions are likely to fall within the range of
approximately 15 percent below and 17 percent above the
emission estimate of 4.1 Tg CO2 Eq.). One of the reasons for
the relatively narrow range is that mine-specific data is used in
the methodology. The largest degree of uncertainty is associated
Energy 3-45
-------
with the unknown status mines (which account for 36 percent
of the mines), with a ±60 percent uncertainty.
QA/QC and Verification
As part of a Tier 2 analysis, the United States undertook
an effort to verify the model results used in the U.S. Inventory
with field measurements. Field measurements were used
to test the accuracy of the mathematical decline curves to
be used for basin-specific emissions estimates. A series of
field measurements were conducted at abandoned mine vent
locations across the United States. Between November 1998
and February 2000, EPA recorded measurements at five mines
that were not flooded. Measurements were recorded at two
abandoned mines located in Ohio and Virginia continuously
for 6 to 12 hours. As the methodology was finalized, EPA
measured emissions from three additional mines located in
Illinois and Colorado. These measurements were recorded
hourly for 3 to 4 days and were normalized to average
barometric pressures. Prior to these measurements, EPA's
Office of Research and Development initiated a field research
program in the early 1990s. Data for 21 abandoned mines
located throughout the Northern and Central Appalachian,
Black Warrior, and Illinois Basins were collected using
similar techniques.
Measurements for all field data recorded were plotted
against predicted emissions as part of the two studies from
1991 through 2000. Emission rates from nine of the ten
mines that were measured fall very close to the predicted
mid-case decline rate for their respective basins. For the
exponential decline curve fit to the flooding mines, six of nine
measurements fall within a 95 percent predictive confidence
interval of the mean.
Of the abandoned mines in the database, only about
14 percent of the mines maintain vents to the atmosphere.
Therefore, it is difficult to obtain field data. Additional field
measurements, however, would be beneficial to further
calibrate the equations defined above. Furthermore, it would
be useful to extend measurements of diffuse emissions from
sealed mines, since they comprise 41 percent of total mines.
Recalculations Discussion
Methane emissions from abandoned coal mines are
being reported for the first time in this report.
3.7. Petroleum Systems
(IPCC Source Category 1 B2a)
Methane emissions from petroleum systems are primarily
associated with crude oil production, transportation, and
refining operations. During each of these activities, CH4
is released to the atmosphere as fugitive emissions, vented
emissions, emissions from operational upsets, and emissions
from fuel combustion. Total CH4 emissions from petroleum
systems in 2002 were 23.2 Tg CO2 Eq. (1,104 Gg). Since
1990, emissions declined due to a decline in domestic oil
production and industry efforts to make emissions reductions
(see Table 3-35 and Table 3-36). The various sources of
emissions are detailed below.
Production Field Operations. Production field operations
account for over 97 percent of total CH4 emissions from
petroleum systems. Vented CH4 from field operations
account for approximately 87 percent of the emissions from
the production sector, fugitive emissions account for five
percent, combustion emissions seven percent, and process
Table 3-35: CH4 Emissions from Petroleum Systems (Tg C02 Eq.)
Activity
Crude Oil Transportation
twr
0.5 0.6
1998 2000
Z*;3
,§ 1t.T 11:5
ms toj me ms*
tor « O.S 0.5 ft
t.1 2.0, 1.9 * 12
1J 1.t, 1.3 1,3 1,:
*:-i$:y.-i& •.--<•.'
0J
See Table 3-44 of Annex 3 to this report.
22.5
•M-v.-vlW'
.14<-;-,-**-
;iy5:;%^
H.f ^.t
>**
3-46 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-36: CH4 Emissions from Petroleum Systems (Gg)
Activity
1990
Production Field Operations3
Tank venting
Pneumatic device venting
Wellhead fugitives
Combustion & process upsets
Misc. venting & fugitives
Crude Oil Transportation
Refining
Total estimated emissions
1,375
1996 1997 1998 1999 2000 2001 2002
1,187 1,182 1,157 1,097 1,086 1,086 1,072
547 557 549 520 523 523 513
516 515 504 488 478 475 474
25
98
63
6
26
1,218
25
98
63
6
27
1,215
25
96
62
6
27
1,190
24
92
61
6
27
1,129
22
91
60
5
28
1,119
22
91
60
5
27
1,118
22
91
60
5
27
1,104
' Including CH4 emissions reductions achieved by the Natural Gas STAR Program. See Table 3-38 of Annex 3 to this report.
upset emissions barely one percent. The most dominant
sources of vented emissions are field storage tanks, natural-
gas-powered pneumatic devices (low and high bleed), and
chemical injection. These four sources alone emit 84 percent
of the production field operations emissions. Emissions
from storage tanks occur when the CH4 entrained in crude
oil under pressure volatilizes once the crude oil is put into
storage tanks at atmospheric pressure. Two additional large
sources, oil well heads and gas engines, categorized under
fugitives and combustion emissions, together account for
nine percent of the production sector. The remaining seven
percent of the emissions are distributed among 33 additional
activities within these four categories. Total emissions from
the production sector account for CH4 emissions reductions
achieved by the EPA Natural STAR Program.
Crude Oil Transportation. Crude transportation
activities account for less than one half percent of total CH4
emissions from the oil industry. Venting from tanks and
marine vessel loading operations accounts for 64 percent
of CH4 emissions from crude oil transportation. Fugitive
emissions, almost entirely from floating roof tanks, account
18 percent. The remaining 17 percent is distributed among
4 additional sources within these two categories.
Crude Oil Refining. Crude oil refining processes and
systems account for only two and a half percent of total CH4
emissions from the oil industry because most of the CH4 in
crude oil is removed or escapes before the crude oil is delivered
to the refineries. Within refineries, vented emissions account
for about 87 percent of the emissions, while fugitive and
combustion emissions account for approximately 6 percent
each. Refinery system blowdowns for maintenance and
the process of asphalt blowing with air to harden it are the
primary venting contributors. Most of the fugitive emissions
from refineries are from leaks in the fuel gas system. Refinery
combustion emissions accumulate from small amounts of
unburned CH4 in process heater stack emissions and from
unburned CH4 in engine exhausts and flares.
Methodology
The methodology for estimating CH4 emissions from
petroleum systems is based on a comprehensive study of
CH4 emissions from U.S. petroleum systems, Estimates of
Methane Emissions from the U.S. Oil Industry (Draft Report)
(EPA 1999) and Methane Emissions from the U.S. Petroleum
Industry (Radian 1996a-d). These studies combined emission
estimates from 70 activities occurring in petroleum systems
from the oil wellhead through crude oil refining, including 39
activities for crude oil production field operations, 11 for crude
oil transportation activities, and 20 for refining operations.
Annex 3.5 provides greater detail on the emission estimates
for these 70 activities. The estimates of CH4 emissions from
petroleum systems do not include emissions downstream from
oil refineries because these emissions are very small compared
to CH4 emissions upstream from oil refineries.
The methodology for estimating CH4 emissions from the
70 oil industry activities employs emission factors initially
developed by EPA (1999) and activity factors that are
based on EPA (1999) and Radian (1996a-d). Emissions are
estimated for each activity by multiplying emission factors
(e.g., emission rate per equipment item or per activity) by
their corresponding activity factor (e.g., equipment count or
frequency of activity). The report provides emission factors
and activity factors for all activities except those related
to offshore oil production. For offshore oil production, an
emission factor was calculated by dividing an emission
Energy 3-47
-------
Table 3-37: Range of Uncertainty Estimates for CH4 Emissions from Petroleum Systems (Tg C02 Eq. and Percent)
estimate from the Minerals Management Service (MMS) by
the number of platforms. Emission factors were held constant
for the period 1990 through 2002.
Activity factors for 1990 through 2002 were collected
from a wide variety of statistical resources. For some years,
complete activity factor data were not available. In such cases,
one of three approaches was employed. Where appropriate,
the activity factor was calculated from related statistics using
ratios developed for Radian (1996a-d). For example, Radian
(1996a-d) found that the number of heater treaters (a source of
CH4 emissions) is related to both number of producing wells
and annual production. To estimate the activity factor for heater
treaters, reported statistics for wells and production were used,
along with the ratios developed for Radian (1996a-d). In other
cases, the activity factor was held constant from 1990 through
2002 based on EPA (1999). Lastly, the previous year's data
were used when data for the current year were unavailable.
See Annex 3.5 for additional detail.
Nearly all emission factors were taken from Radian
(1996e). The remaining emission factors were taken from
the following sources: the American Petroleum Institute
(API 1996), EPA default values, MMS reports (MMS 1995
and 1999), the Exploration and Production (E&P) Tank
model (API and GRI), reports by the Canadian Association
of Petroleum Producers (CAPP 1992 and 1993), and the
consensus of industry peer review panels.
Among the more important references used to obtain
activity factors are the Energy Information Administration
annual and monthly reports (EIA 1995-2003), the API Basic
Petroleum Data Book (API 2002), Methane Emissions from
the Natural Gas Industry prepared for the Gas Research
Institute (GRI) and EPA (Radian 1996a-d), consensus of
industry peer review panels, MMS reports (MMS 1995 and
1999), and the Oil & Gas Journal (OGJ 1990 through 2002).
Annex 3.5 provides a complete list of references.
Uncertainty
The detailed, bottom-up analysis used to evaluate
U.S. petroleum systems reduces the uncertainty related
to the CH4 emission estimates in comparison with a
top-down approach. However, a number of uncertainties
remain. Emission factors and activity factors are based on
a combination of measurements, equipment design data,
engineering calculations and studies, surveys of selected
facilities and statistical reporting. Statistical uncertainties
arise from natural variation in measurements, equipment
types, operational variability and survey and statistical
methodologies. Published activity factors are not available
every year for all 70 activities analyzed for petroleum
systems; therefore, some are estimated. Because of the
dominance of six major sources, which account for 90
percent of the total emissions, the uncertainty surrounding
the six sources has been estimated and serves as the basis
for determining the uncertainty surrounding petroleum
systems emissions estimates. The preliminary results of the
quantitative uncertainty analysis (see Table 3-37) indicate
that, on average, in 19 out of 20 times (i.e., there is a 95
percent probability), the total greenhouse gas emissions
from this source is within the range of approximately 20.2
to 32.7 Tg CO2 Eq. (or that the actual CO2 emissions are
likely to fall within the range of approximately 13 percent
below and 41 percent above the emission estimate of 23.2
Tg C02 Eq.).
3-48 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Recalculations Discussion
Estimates of CH4 from petroleum systems contain three
changes with respect to previous inventories. First, the activity
factor for CH4 emissions from oil tanks in the production sector
was modified to avoid double counting vapor recovery unit
reductions. The previous methodology included an assumption
that 29 percent of crude oil production was flared, stored in
tanks with vapor recovery units, or in floating roof tanks. The
new calculation assumes venting emissions from crude oil
tanks is based on the crude oil production from the lower 48
states only. The adjustment has been made to prevent double
counting vapor recovery units emissions from the Natural Gas
STAR Program and to correct for Alaskan crude production
which has been using vapor recovery units since pre-1990.
Natural Gas STAR does not include any reductions from
Alaskan production at this time. The second change was the
use of a new data source for the fuel gas systems in the refinery
sector. Previously, the activity factor for fuel gas systems was
the number of total refineries in the United States. However, the
number of operating petroleum refineries is now available on
an annual basis. The model has been changed to reflect a more
accurate activity factor based on operating refineries as the
emissions sources. The final change is the revision of the high
and low bleed pneumatic devices emission factors. Emission
factors for pneumatic devices in the production sector were
recalculated using emission data published in the EPA/GRI
1996 study, averaging the high bleed data for those devices
that were judged to be in the production sector, and averaging
low bleed data for those devices in the production sector. The
combination of these changes resulted in an average annual
increase of 1.4 Tg CO2 Eq. (7 percent) in CH4 emissions for
the period 1990 through 2001.
Planned Improvements
Several improvements to the emission estimates are
being evaluated that fine-tune and better track changes
in emissions. These include, but are not limited to, some
activity factors that are also accounted for in the Natural Gas
STAR Program emission reductions, some emission factors
for consistency between CH4 emissions from petroleum
systems and natural gas systems and some source listings
for consistency between these two sources.
3.8. Natural Gas Systems (IPCC
Source Category 1B2b)
The U.S. natural gas system encompasses hundreds of
thousands of wells, hundreds of processing facilities, and over
a million miles of transmission and distribution pipelines.
Overall, natural gas systems emitted 121.8 Tg CO2 Eq. (5,801
Gg) of CH4 in 2002, a slight decrease over 1990 emissions
(see Table 3-38 and Table 3-39). Improvements in management
Table 3-38: CH4 Emissions from Natural Gas Systems (Tg C02 Eq.)
Stage
HeldProduction
Proofsplng / ,
Transmissionand Storage
Total
ttote: Tottls may not sum due to independant Minding.
Table 3-39: CH4 Emissions from Natural Gas Systems (Gg)
»=v:y19l6 ;
^.U32a- '
I 14.8
'••••: 46.7
f\ 33.6
127.4
1997
33.2
14.8
46.0
32,1
126.1
1998
33.7
14.7
45.1
30.9
124.1
1999
30.8
14,6
43.9
31.6
120.9
2000
35.0
14.8
43.3
32.5
125.7
2001
38.5
15.1
39.4
31.9
124.9
2002
38.1
14.6
39.7
29.4
121.8
Stage
1996
field Production
Processing
Transmission and Storage
Distribution
1,445
702
2,223
Total
5,811
Note; Ttitals may not sumtte to, independent rounding,
1997
1998
1999
2000
2001
2002
: 1,538
705
, 2,223
: 1.599*
1,579
705 -
2,191
1,530
1,806
700
2,150
1,473
1,467
694
2,090
1,506
1,668
705
2,062
1.549
1,833
718
1,876
1,520
1,817
697
1,890
1,398
6,065 6,005 5,929 5,757 5,985 5,946 5,801
Energy 3-49
-------
practices and technology, along with the replacement of older
equipment, have helped to stabilize emissions (EPA 2002).
Methane emissions from natural gas systems are
generally process related, with normal operations, routine
maintenance, and system upsets being the primary
contributors. Emissions from normal operations include:
natural gas combusting engines and turbine exhaust, bleed
and discharge emissions from pneumatic devices, and fugitive
emissions from system components. Routine maintenance
emissions originate from pipelines, equipment, and wells
during repair and maintenance activities. Pressure surge relief
systems and accidents can lead to system upset emissions.
Below is a characterization of the four major stages of the
natural gas system. Each of the stages is described and the
different factors affecting CH4 emissions are discussed.
Field Production. In this initial stage, wells are used to
withdraw raw gas from underground formations. Emissions
arise from the wells themselves, gathering pipelines, and well-
site gas treatment facilities such as dehydrators and separators.
Fugitive emissions and emissions from pneumatic devices
account for the majority of emissions. Emissions from field
production accounted for approximately 26.5 percent of CH4
emissions from natural gas systems between 1990 and 2002.
Processing. In this stage, natural gas liquids and various
other constituents from the raw gas are removed, resulting in
"pipeline quality" gas, which is injected into the transmission
system. Fugitive emissions from compressors, including
compressor seals, are the primary emission source from this
stage. Processing plants account for about 11.8 percent of
CH4 emissions from natural gas systems.
Transmission and Storage. Natural gas transmission
involves high pressure, large diameter pipelines that transport
gas long distances from field production and processing
areas to distribution systems or large volume customers
such as power plants or chemical plants. Compressor station
facilities, which contain large reciprocating and turbine
compressors, are used to move the gas throughout the
United States transmission system. Fugitive emissions from
these compressor stations and from metering and regulating
stations account for the majority of the emissions from
this stage. Pneumatic devices and engine exhaust are also
sources of emissions from transmission facilities. Methane
emissions from transmission have historically accounted
for approximately a third of the emissions from natural gas
systems.
Natural gas is also injected and stored in underground
formations during periods of low demand (e.g., summer),
and withdrawn, processed, and distributed during periods
of high demand (e.g., winter). Compressors and dehydrators
are the primary contributors to emissions from these storage
facilities. Approximately one percent of total emissions from
natural gas systems can be attributed to storage facilities.
Distribution. Distribution pipelines take the high-
pressure gas from the transmission system at "city gate"
stations, reduce the pressure and distribute the gas through
mains and service lines to individual end users. There
were over 1,141,759 miles of distribution mains in 2002,
an increase from just over 837,300 miles in 1990 (OPS
2002a). Distribution system emissions, which account
for approximately 25.6 percent of emissions from natural
gas systems, result mainly from fugitive emissions from
gate stations and non-plastic piping (cast iron, steel).52 An
increased use of plastic piping, which has lower emissions
than other pipe materials, has reduced the growth in emissions
from this stage. Distribution system emissions in 2002 were
slightly lower than 1990 leveis.
Methodology
The basis for estimates of CH4 emissions from the
U.S. natural gas industry is a detailed study by the Gas
Research Institute and EPA (EPA/GRI1996). The EPA/GRI
study developed over 100 emission and activity factors to
characterize emissions from the various components within
the operating stages of the U.S. natural gas system. The
study was based on a combination of process engineering
studies and measurements at representative gas facilities.
From this analysis, a 1992 emission estimate was developed
using the emission and activity factors. For other years,
a set of industry activity factor drivers was developed
that can be used to update activity factors. These drivers
include statistics on gas production, number of wells,
system throughput, miles of various kinds of pipe, and other
statistics that characterize the changes in the U.S. natural
gas system infrastructure and operations.
The percentages of total emissions from each stage may not add to 100 because of independent rounding.
3-50 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-40: Range of Uncertainty Estimates for CH4 Emissions from Natural Gas Systems (Tg C02 Eq. and Percent)
Source
Gas
Lower Bound Upper Bound Lower Bound Upper Bound
Natural Gas Systems CH4
121,8
73.1
170,5
-40%
4-40%
See Annex 3.4 for more detailed information on the
methodology and data used to calculate CH4 emissions from
natural gas systems.
Activity factor data were taken from the following
sources: American Gas Association (AGA 1991-1998);
American Petroleum Institute (API 2002); Minerals and
Management Service (DOI1998-2003); Natural Gas Annual
(EIA 1993, 1996, 1997, 1998a, 2003d, 2003f, 1998g);
Natural Gas Monthly (EIA 2003b, 2001, 2003c, 2001,
2003e); Office of Pipeline Safety (OPS 2003 a,b); Oil and
Gas Journal (OGJ 1999 through 2002). The Gas Systems
Analysis model was used to aid in collecting data for non-
associated and associated wells (GSAM 1997). All emissions
factors were taken from EPA/GRI (1996). Coalbed CH4 well
activity factors were taken from the Wyoming Oil and Gas
Conservation Commission and the Alabama State Oil and
Gas Board.
Uncertainty
The heterogeneous nature of the natural gas industry
makes it difficult to sample facilities that are completely
representative of the entire industry. Because of this, scaling
up from model facilities introduces a degree of uncertainty.
Additionally, highly variable emission rates were measured
among many system components, making the calculated
average emission rates uncertain. The preliminary results
of the quantitative uncertainty analysis (see Table 3-40)
indicate that, on average, in 19 out of 20 times (i.e., there is
a 95 percent probability), the total greenhouse gas emissions
from this source is within the range of approximately
73.1 to 170.5 Tg CO2 Eq. (or that the actual CO2 emissions
are likely to fall within the range of approximately 40 percent
below and 40 percent above the emission estimate of 121.8
TgC02Eq.).
Recalculations Discussion
Emissions with Natural Gas STAR reductions were
updated using new Gas STAR emissions reduction data.
New sources for water production activity factors were used
for the entire time series for coalbed CH4 emissions. These
historical data changes resulted in an average annual increase
of 1.1 Tg CO2 Eq. (0.9 percent) in CH4 emissions for the
period 1990 through 2001.
Planned Improvements
Several improvements to the emission estimates are
being evaluated that fine-tune and better track changes in
emissions. These include, but are not limited to, some activity
factors that are also accounted for in the Natural Gas STAR
Program emission reductions, some emission factors for
consistency between emission estimates from Petroleum
Systems and Natural Gas Systems, and some source listings
for consistency between these two sources.
3.9. Municipal Solid Waste
Combustion (IPCC Source
Category 1A5)
Combustion is used to manage about 7 to 17 percent of the
municipal solid wastes generated in the United States, depending
on the source of the estimate and the scope of materials included
in the definition of solid waste (EPA 2000c, Goldstein and
Matdes 2001). Almost all combustion of municipal solid
wastes in the United States occurs at waste-to-energy facilities
where energy is recovered, and thus emissions from waste
combustion are accounted for in the Energy chapter. Combustion
of municipal solid wastes results in conversion of the organic
inputs to CO2. According to the IPCC Guidelines, when the CO2
emitted is of fossil origin, it is counted as a net anthropogenic
emission of CO2 to the atmosphere. Thus, the emissions from
Energy 3-51
-------
Box 3-3: Biogenic Emissions and Sinks of Carbon
For many countries, C02 emissions from the combustion or degradation of biogenic materials are important because of the significa^^
amount of energy they derive from biomass (e.g., burning fuelwood). The fate of biogenic materials is also important when evaluating
waste management emissions (e.g., the decomposition of paper). The carbon contained in paper was originally stored in trees during
photosynthesis. Under natural conditions, this material would eventually degrade and cycle back to the atmosphere as C02. The quantity
of carbon that these degradation processes cycle through the Earth's atmosphere, waters, soils, and biota is much greater than the
quantity added by anthropogenic greenhouse gas sources, tot the focus of tie UNFCCC Is on emissions resulting from human activities
and subject to human control, because it is these emissions that have the potential to alter the climate by disrupting fie natural balances
in carbon's biogeochemical cycle, and enhancing the atmosphere's natural greenhouse effect.
Carbon dioxide emissions front biogenic materials (e.g., paper, wood products, and yard trimmings) grown on a sustainable basis
are considered to mimic the closed loop of ttw natural carbon cycle that is, tJieyretumto^afiTOphereC02Wwasc^a^rerrioved
by photosynthesis. However, CH4 emissions from landfilled waste occur due to the man-made anaerobic conditions conducive to CH4
formation that exist in landfills, and are consequently included in this inventory.
The removal of carton from the natural cycling of carbon between the atmosphere and biogenic materials which occurs when wastes
of biogenic origin are deposited in landfills sequesters carbon. When wastes of sustainable, biogenic origin are lanolilied, and do not
completely decompose, the carbon that remains is effectively removed from the global carbon cycle. LandfiHing of forest products, yard
trimmings, and food scraps resulted in long-term storage of 165.4 Tg C02 Eq. in 2002. Carbon storage that results from forest products,
yard trimmings, and food scraps disposed in landfills is accounted for in the Land-Use Change and Forestry chapter,
waste combustion are calculated by estimating the quantity of hazardous" waste and are included in the municipal solid waste
waste combusted and the fraction of the waste that is carbon
derived from fossil sources.
Most of the organic materials in municipal solid wastes
are of biogenic origin (e.g., paper, yard trimmings), and
have their net carbon flows accounted for under the Land-
Use Change and Forestry chapter (see Box 3-3). However,
some components— plastics, synthetic rubber, and synthetic
fibers — are of fossil origin. Plastics in the U.S. waste stream
are primarily in the form of containers, packaging, and durable
goods. Rubber is found in durable goods, such as carpets, and
in non-durable goods, such as clothing and footwear. Fibers
in municipal solid wastes are predominantly from clothing
and home furnishings. Tires are also considered a "non-
combustion estimate, though waste disposal practices for tires
differ from the rest of municipal solid waste.
Approximately 24 million metric tons of municipal solid
wastes were combusted in the United States in 2002. Carbon
dioxide emissions from combustion of municipal solid wastes
rose 72 percent since 1990, to an estimated 1 8.8 Tg CO2 Eq.
( 1 8,78 1 Gg) in 2002, as the volume of plastics and other fossil
carbon-containing materials in MSW increased (see Table
3-41 and Table 3-42). Waste combustion is also a source of
N2O emissions (De Soete 1993). Nitrous oxide emissions
from municipal solid waste combustion were estimated to
be 0.4 Tg CO2 Eq. (1 Gg) in 2002, and have not changed
significantly since 1990.
Table 3-41: C02 and N20 Emissions from Municipal Solid Waste Combustion (Tg C02 Eq.)
Gas/Waste Product
Plastics
Synthetic Rubber in Tires
Carbon Black in Tires
Synthetic Rubber in MSW
Synthetic Fibers
1990
Total
1996
17.2
11.4
0.9
1.2
1.7
2$
8.4
T7.S
tW7
17.8
11.9
0.9
1.2
1.7
2.1
0.4
18.1
1998
17.1
11.4
0.9
1.2
1.6
2.0
0.3
17.4
1999
17J
12.0
0,9
15
1.S
2.0
0.3
18.0
2000
18.0
12.1
0.9
1.2
• 17
2.1
0.4
18J
toot
18J
12J
0.9
1,2
1,8
2.2
«.*
10
2002
18.8
12.7
0.9
1.2
1.8
2.2
0.4
11,1
3-52 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-42: C02 and N20 Emissions from Municipal Solid Waste Combustion (Gg)
Gas/Waste Product
Carbon Black in Tires
Synthetic Rubber in MSW
SyiMe F8«s
' '
1996
17,183
11,377
895
1,170
1,725
2,026
1
1997
17>7I1
11,914
-89i
1,165
1,725
2,085
1
1998
17,894
11,427
887
1,160
1,627
1,992
1
1999
17,632
t1,950
890
1,164
1,612
2,016
1
2008
17,979
12,145
893
1,167
1,689
2,086
1
2001
18,781
12,718
895
1,170
1,810
2,187
• - ' - 1 .
2002
18,7*1
12,718
895
1,170
1,810
2,187
- ' ' •' 1
Table 3-43: NO., CO, and NMVOC Emissions from Municipal Solid Waste Combustion (Gg)
Gas/Source
Waste Incineration
Open Burning
CO
Waste Incineration
Open Burning
NMVOCS
Waste Incineration
Open Burning
Note: Totals may not sum due to independent rounding.
1996
135
46
89
2428
66
2,562
384
23
281
1997
140
48
92
2,668
68
2,600
313
23
290
1998
145
49
96
2,826
69
2,757
326
23
303
1999
142
48
94
2,833
69
2,764
326
20
306
2800
149
50
99
2,914
70
2,844
332
20
312
2001
149
50
99
2,916
72
2,844
333
21
312
2002
149
50
99
3,294
81
3,213
333
21
313
Ambient air poiiutants are also emitted during waste
incineration ana open burning, as shown in Table 3-43. These
emissions are a relatively small portion of the overall ambient
air pollutant emissions, comprising less than 5 percent for
each gas over trie entire time series.
Methodology
Emissions of CO2 from MSW combustion include CO2
generated by the combustion of plastics, synthetic fibers, and
synthetic rubber, as well as the combustion of synthetic rubber
and carbon black in tires. These emissions were calculated
by multiplying the amount of each material combusted by
the carbon content of the material and the fraction oxidized
(98 percent). Plastics combusted in municipal solid wastes
were categorized into seven plastic resin types, each material
having a discrete carbon content. Similarly, synthetic rubber is
categorized into three product types, and synthetic fibers were
categorized into four product types, each having a discrete
carbon content. Scrap tires contain several types of synthetic
rubber, as well as carbon black. Each type of synthetic rubber
has a discrete carbon content, and carbon black is 100 percent
carbon. Emissions of CO2 were calculated based on the
number of scrap tires used for fuel and the synthetic rubber
and carbon black content of the tires.
More detail on the methodology for calculating
emissions from each of these waste combustion sources is
provided in Annex 3.6.
For each of the methods used to calculate CO2 emissions
from municipal solid waste combustion, data on the quantity
of product combusted and the carbon content of the product
are needed. It was estimated that approximately 24 million
metric tons of municipal solid wastes were combusted in the
United States in 2002. Waste generation was approximated
using a population-based linear regression model, and the
percentage of generation managed by incineration was
assumed to be the same as for 2000 (Goldstein and Madtes
2001). For plastics, synthetic rubber, and synthetic fibers,
the amount of material in municipal solid wastes and its
portion combusted were taken from the Characterization
of Municipal Solid Waste in the United States (EPA 2000c,
2002a, 2003). For synthetic rubber and carbon black in
scrap tires, this information was provided by the U.S. Scrap
Tire Markets 2001 (RMA 2002) and Scrap Tires, Facts and
Figures (STMC 2000, 2001, 2002, 2003).
Average carbon contents for the "Other" plastics
category, synthetic rubber in municipal solid wastes, and
synthetic fibers were calculated from 1998 production
statistics, which divide their respective markets by chemical
Energy 3-53
-------
Table 3-44: Municipal Solid Waste Generation (Metric Tons)
and Percent Combusted
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Waste Generation
268,365,714
254,628,360
264,668,342
278,388,835
292,915,829
296,390,405
297,071,712
308,870,755
339,865,243
347,089,277
371,071,109
369,801 ,530*
380,268,726a
Combusted (%)
11.5
10.0
11.0
10.0
10.0
10.0
10.0
9.0
7.5
7,0
7.0
7,0"
7.0"
* Waste generation derived from linear regression model as 2001 and
2002 data is not yet available.
b 2000 data used as a surrogate since 2001 and 2002 data are not yet
available.
compound. For synthetic rubber in scrap tires information
about scrap tire composition was taken from the Scrap Tire
Management Council's Internet web site (STMC 2003).
The assumption that 98 percent of organic carbon
is oxidized (which applies to all municipal solid waste
combustion categories for CO2 emissions) was reported in
the EPA's life cycle analysis of greenhouse gas emissions and
sinks from management of solid waste (EPA 2002b).
Combustion of municipal solid waste also results in
emissions of N2O. These emissions were calculated as a
function of the total estimated mass of municipal solid
waste combusted and an emission factor. The N2O emission
estimates are based on different data sources. As noted above,
N2O emissions are a function of total waste combusted in each
year; for 1990 through 2000, these data were derived from
the December 2001 issue ofBioCycle (Goldstein and Matdes
2001). For 2001 and 2002, the estimates are extrapolated,
using a linear regression model of waste generation based on
historical data of U.S. population and waste generation from
1990 through 2000. Table 3-44 provides data on municipal
solid waste generation and percentage combustion for the
total waste stream. The emission factor of N2O emissions per
quantity of municipal solid waste combusted is an average of
values from IPCC's Good Practice Guidance (2000).
EPA (2003) provided emission estimates for NOx, CO,
and NMVOCs from waste incineration and open burning,
which were determined using industry published production
data and applying average emission factors.
Uncertainty
A Tier 2 Monte Carlo analysis was performed to
determine the level of uncertainty surrounding the estimates
of CO2 emissions from municipal solid waste combustion.
A Tier 2 analysis was performed to allow the specification
of probability density functions for key variables, within a
computational stru cture that mirrors the calculation of the
inventory estimate. Uncertainty estimates and distributions
for waste generation variables (i.e., plastics, synthetic rubber,
and textiles generation) were obtained from the authors
of the Municipal Solid Waste in the United States reports.
Statistical analyses or expert judgments of uncertainty
were not available directly from the information sources
for the other variables; thus, uncertainty estimates for
these variables were determined using assumptions based
on source category knowledge and the known uncertainty
estimates for the waste generation variables. The highest
levels of uncertainty surround the variables that are based
on assumptions (e.g., percent of clothing and foot wear
that is composed of synthetic rubber); the lowest levels of
uncertainty surround variables that were determined by
quantitative measurements (e.g., combustion efficiency,
carbon content of carbon black).
The preliminary results of the quantitative uncertainty
analysis (Table 3-45) indicate that, on average, in 19 out of
Table 3-45: Range of Uncertainty Estimates for C02 from Municipal Solid Waste Combustion (Tg C02 Eq. and Percent)
Source
2002 Emission Estimate Uncertainty Range Relative to Emission Estimate3
Gas (TgC02Eq.) (TgC02Eq.) (%)
Lower Bound Upper Bound Lower Bound Upper Bound
Municipal Solid Waste Combustion C02
18.8
15.6
22,1
-t7%
a Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
3-54 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions from this source is within the
range of approximately 15.6 to 22.1 Tg CO2 Eq. (or that the
actual CO2 emissions are likely to fall within the range of
approximately 17 percent below and 17 percent above the
emission estimate of 18.8 Tg CO2 Eq.).
The uncertainties in the waste combustion emission
estimates arise from both the assumptions applied to the data
and from the quality of the data.
• MSW Combustion Rate. A source of uncertainty affect-
ing both fossil CO2 and N2O emissions is the estimate
of the MSW combustion rate. The EPA (2000c, 2002a,
2003) estimates of materials generated, discarded, and
combusted carry considerable uncertainty associated
with the material flows methodology used to generate
them. Similarly, the BioCycle (Glenn 1999, Goldstein
and Matdes 2000, Goldstein and Matdes 2001) estimate
of total waste combustion used for the N2O emissions
estimate is based on a survey of state officials, who
use differing definitions of solid waste and who draw
from a variety of sources of varying reliability and ac-
curacy. Despite the differences in methodology and data
sources, the two references the EPA's Office of Solid
Waste (EPA 2000a, 2002b, 2003) and BioCycle (Glenn
1999, Goldstein and Matdes 2000, Goldstein and Matdes
2001) provide estimates of total solid waste combusted
that are relatively consistent (see Table 3-46).
• Fraction Oxidized. Another source of uncertainty for the
CO2 emissions estimate is fraction oxidized. Municipal
waste combustors vary considerably in their efficiency as
a function of waste type, moisture content, combustion
conditions, and other factors. Despite this variability in
oxidation rates, a value of 98 percent was assumed for
this analysis.
• Missing Data on Municipal Solid Waste Composition.
Disposal rates have been interpolated when there is an
incomplete interval within a time series. Where data are
not available for years at the end of a time series (1990,
2001, 2002), they are set equal to the most recent years
for which estimates are available.
• Average Carbon Contents. Average carbon contents
were applied to the mass of "Other" plastics combusted,
synthetic rubber in tires and municipal solid waste, and
Table 3-46: U.S. Municipal Solid Waste Combusted, as
Reported by EPA and BioCycle (Metric Tons)
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
EPA
28,855,809
27,773,783
29,568,442
28,696,188
29,532,844
32,182,194
32,831,450
33,597,844
31,205,358
30,859,134
30,512,946
30,569,746
NA
BioCycle
30,632,057
25,462,836
29,113,518
27,838,884
29,291,583
29,639,040
29,707,171
27,798,368
25,489,893
24,296,249
25,974,978
23,483,876*
24,148,585a
NA (Not Available)
a Used linear regression model to estimate generation for 2001 and
2002 as data were not yet available.
synthetic fibers. These average values were estimated
from the average carbon content of the known products
recently produced. The true carbon content of the com-
busted waste may differ from this estimate depending
on differences in the chemical formulation between the
known and unspecified materials, and differences be-
tween the composition of the material disposed and that
produced. For rubber, this uncertainty is probably small
since the major elastomers' carbon contents range from
77 to 91 percent; for plastics, where carbon contents
range from 29 to 92 percent, it may be more significant.
Overall, this is a small source of uncertainty.
Synthetic/Biogenic Assumptions. A portion of the fiber
and rubber in municipal solid waste is biogenic in origin.
Assumptions have been made concerning the allocation
between synthetic and biogenic materials based primar-
ily on expert judgment.
Combustion Conditions Affecting N2O Emissions. Be-
cause insufficient data exist to provide detailed estimates
of N2O emissions for individual combustion facilities,
the estimates presented exhibit high uncertainty. The
emission factor for N2O from municipal solid waste
combustion facilities used in the analysis is an average
of default values used to estimate N2O emissions from
facilities worldwide (Johnke 1999, UK: Environment
Agency 1999, Yasuda 1993). These factors span an order
Energy 3-55
-------
of magnitude, reflecting considerable variability in the
processes from site to site. Due to a lack of information
on the control of N2O emissions from MSW combus-
tion facilities in the United States, the estimate of zero
percent for N2O emissions control removal efficiency
also exhibits uncertainty.
Development of a full quantitative uncertainty analysis
for total emissions from municipal solid waste combustion
is expected to be a multi-year process. Subsequent Inventory
reports will build on the analysis above, adding an analysis
of the uncertainty of N2O emissions and incorporating
more precise estimates of uncertainty for more activity
variables.
Recalculations Discussion
The method for calculating N2O emissions from municipal
solid waste combustion has been revised to use a new emission
factor. This updated factor is the average of several emission
factors reported in the IPCC Good Practice Guidance (2000)
for the type of combustors used in the United States, and is
thus more representative of U.S. emissions. Additionally, the
method for filling in a time series where data are unavailable
has been modified in this year's inventory. Data at the ends
of time series are held constant at the level of the closest year
with reported data;53 data for years within the time series are
linearly interpolated between the bracketing data points.
This inventory section also includes updated data for
several sub-categories within the municipal solid waste
combustion sector. The percentage of discards in the overall
waste stream that is combusted (which is used in calculations
for plastics, synthetic rubber in municipal solid wastes, and
synthetic fibers) was revised; rather than using a single data
point (for 1998) this year's calculations use an annually
variable time series of data. Activity data on generation and
recovery of plastics, synthetic rubber in municipal solid
wastes, and synthetic fibers have been updated using the
draft report Municipal SolidWaste in the United States: 2001
Facts and Figures (EPA 2003) and Municipal Solid Waste
in the United States: 1999 Facts and Figures (EPA 2001).
Tire usage data have been updated based on the most current
scrap tire report, U.S. Scrap Tire Markets 2001 (RMA 2002).
Together, these methodological and historical data changes
result in an average annual decrease of 4.4 Tg CO2 Eq. (22
percent) of CO2 emissions and an average annual increase of
0.1 Tg CO2 Eq. (46 percent) in N2O emissions for the period
1990 through 2001.
3.10. Natural Gas Flaring and
Ambient Air Pollutant Emissions from
Oil and Gas Activities (IPCC Source
Category 1B2)
The flaring of natural gas from on- and off-shore oil wells
is a small source of CO2. In addition, oil and gas activities also
release small amounts of NOX, CO, and NMVOCs. This source
accounts for only a smaii proportion of overall emissions of
each of these gases. Emissions of NOX, and CO from petroleum
and natural gas production activities were Doth less than 1
percent of national totals, while NMVOC and SO2 emissions
were roughly 2 percent of national totals.
The flaring (i.e. comoustiori) and venting of natural
gas during petroleum production result in trie release of
CO2 and CH4 emissions, respectively. Barns arid Edmonds
(1990) noted that of total reported U.S. venting and flaring,
approximately 20 percent may be vented, with the remaining
80 percent flared, but it is now believed that flaring accounts
for an even greater proportion. Studies indicate that the
percentage of natural gas that is flared from off-shore
U.S. production is consideraoiy lower (approximately 30
percent in 2002), due in part to differences in the legislation
governing on- and off-shore natural gas production. Methane
emissions from venting are accounted for under Petroleum
Systems. For 2002, total CO2 emissions from flaring
activities were estimated to be 5.3 Tg CO2 Eq. (5,299 Gg),
a decrease of 9 percent from 1990 levels. On-shore flaring
activities accounted for 5.1 Tg CO2 Eq. (5,066 Gg), or 96
percent, of the total flaring emissions, while off-shore flaring
constituted 0.2 Tg CO2 Eq. (233 Gg), or 4 percent, of the
total (see Table 3-47).
In addition, oil and gas activities, including production,
transportation, and storage, result in the release of small
amounts of NOX, CO, and NMVOCs. Ambient air pollutant
emissions from this source from 1990 to 2002 are presented
below (see Table 3-49).
53
linear regression model so as to be consistent with the input data used in the landfill methane section of the Inventory.
An exception to this methodology exists for the MSW generation activity data for 2001 and 2002. These data are generated using a population-based
3-56 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-47: C02 Emissions from On-Shore and Off-Shore Natural Gas Flaring (Tg C02 Eq.)
Table 3-48: C02 Emissions from On-Shore and Off-Shore Natural Gas Flaring (Gg)
_ ', " _; ^ it r j ;t ..-.Li^iA. .Jj.i
Location
On-Short Waitifi,
Off-Shore Baijh|
1W?
7,565 6,250 " '. '
7,874 *,§«
Methodology
Estimates of CO2 emissions from on- and off-shore
natural gas flaring were prepared using an emission factor of
54.71 Tg CO2 EqVQBtu of flared gas, and an assumed flaring
efficiency of 100 percent. Ambient air pollutant emission
estimates for NOX, CO, and NMVOCs were determined using
industry-published production data and applying average
emission factors.
Total on-shore natural gas vented and flared was taken
from EIA's Natural Gas Annual (EIA 2003). It was assumed
that all reported vented and flared gas was flared. This
assumption is consistent with that used by EIA in preparing
their emission estimates, under the assumption that many
states require flaring of natural gas (EIA 2000b). The total
off-shore natural gas vented and flared was obtained from
the Minerals Management Service's OGOR-B reports (MMS
2003). The percentage of natural gas flared was estimated
using data from a 1993 air quality study and emissions
inventory of the Gulf of Mexico (MOADS) and a 2000
emissions inventory conducted for the Breton National
Wilderness Area Management Plan (BOADS).
Table 3-49: NOX. NMVOCs, and CO Emissions from Oil and
Gas Activities (Gg)
Yter
HO*
eft
NMVOCs
1997
1998
19f9
2000
2001
2002
130
130
113
115
117
118
333; :>• -.•
" 832 V,:,-.
• "152; -•'•:v:-
-182 -:;'..•'
153
153
• '>''^& '":
440 .,V,
% ':^3f8.- '. '
348
357
348
There is a discrepancy in the time series for on-shore
natural gas vented and flared as reported in EIA (2003). One
facility in Wyoming had been incorrectly reporting CO2
vented as CH4. EIA corrected these data in the Natural Gas
Annual 2000 (EIA 2001) for the years 1998 and 1999 only.
Data for 1990 through 1997 were adjusted by assuming a
proportionate share of CO2 in the flare gas for those years as
for 1998 and 1999. The adjusted values are provided in Table
Table 3-50: Volume Flqred Offshore (MMcf) and Fraction Vented and Flared (Percent)
Natural Gas Flaring
Total Guff of Mexteo (SOW) VWaif & fttfe$ ptef):..r13MW:'"
Estimated Flaring ftacttofl gf Sj[»l%^&|i[^i>
T«tal / •- " ••'•- •.'-'. •>• ••
fj^v^.-.ftg.;
mm mt im
15,440 ftm 14,057 12,985 ' 12,823 12,823
-;'J33%.' 3^% Bf% '; 31% 30% 30%
Energy 3-57
-------
Table 3-51: Total Natural Gas Reported Vented and Flared
(Million Ft3) and Thermal Conversion Factor (Btu/Ft3)
Vented and
Year Flared (original)
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
150,415
169,909
167,519
226,743
228,336
283,739
272,117
256,351
103,019
110,285
91,232
85,678
83,803
Vented and
Flared (revised)*
91,130
92,207
83,363
108,238
109,493
144,265
135,709
124,918
103,019
110,285
91,232
85,678
83,803
Tnermal
Conversion Factor
1,106
1,108
1,110
1,106
1,105
1,106
1,109
1,107
1,109
1,107
1,107
1,105
1,105
* Wyoming venting and flaring estimates were revised. See text for
further emanation.
3-51. The emission and thermal conversion factors were also
provided by EIA (2003) and are included in Table 3-51.
Emission estimates for NOX, CO, and NMVOCs from
petroleum refining, petroleum product storage and transfer,
and petroleum marketing operations were obtained from
preliminary data (EPA 2003), which, in its final iteration, will
be published on the National Emission Inventory (NEI) Air
Pollutant Emission Trends web site. Included are gasoline,
crude oil and distillate fuel oil storage and transfer operations,
gasoline bulk terminal and bulk plants operations, and retail
gasoline service stations operations.
Uncertainty
Uncertainties in CO2 emission estimates primarily arise
from assumptions concerning the flaring efficiency and the
correction factor applied to 1990 through 1997 venting and
flaring data. Uncertainties in ambient air pollutant emission
estimates are partly due to the accuracy of the emission
factors used and projections of growth.
Recalculations Discussion
The methodology for estimating emissions from natural
gas flaring, which had previously focused solely on on-shore
activity, was revised to include emissions from off-shore
flaring. The activity data and emission factor used to calculate
the emissions from on-shore flaring remained constant, so
the addition of the off-shore flaring calculation was solely
responsible for the relatively small change in total CO2
emissions from natural gas flaring. The change resulted in
an average annual increase in CO2 emissions of 0.27 Tg CO2
Eq. (4 percent) for the period 1990 through 2001.
3.11. International Bunker
Fuels (IPCC Source Category 1:
Memo Items)
Emissions resulting from the combustion of fuels used
for international transport activities, termed international
bunker fuels under the UNFCCC, are currently not included
in national emission totals, but are reported separately
based upon location of fuel sales. The decision to report
emissions from international bunker fuels separately, instead
of allocating them to a particular country, was made by the
Intergovernmental Negotiating Committee in establishing
the Framework Convention on Climate Change.54 These
decisions are reflected in the Revised 1996 IPCC Guidelines,
in which countries are requested to report emissions from
ships or aircraft that depart from their ports with fuel
purchased within national boundaries and are engaged in
international transport separately from national totals (IPCC/
UNEP/OECD/IEA 1997).55
Greenhouse gases emitted from the combustion of
international bunker fuels, like other fossil fuels, include
CO2, CH4, N2O, CO, NOX, NMVOCs, paniculate matter, and
sulfur dioxide (SO2).56 Two transport modes are addressed
under the IPCC definition of international bunker fuels:
See report of the Intergovernmental Negotiating Committee for a Framework Convention on Climate Change on the work of its ninth session, held at
Geneva from 7 to 18 February 1994 (A/AC.237/55, annex I, para. Ic).
55 Note that the definition of international bunker fuels used by the UNFCCC differs from that used by the International Civil Aviation Organization.
-*6 Sulfur dioxide emissions from jet aircraft and marine vessels, although not estimated here, are mainly determined by the sulfur content of the fuel. In
the United States, jet fuel, distillate diesel fuel, and residual fuel oil average sulfur contents of 0.05, 0.3, and 2.3 percent, respectively. These percentages
are generally lower than global averages.
3-58 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
aviation and marine.57 Emissions from ground transport
activities by road vehicles and trains even when crossing
international borders are allocated to the country where
the fuel was loaded into the vehicle and, therefore, are not
counted as bunker fuel emissions.
The IPCC Guidelines distinguish between different
modes of air traffic. Civil aviation comprises aircraft used for
the commercial transport of passengers and freight, military
aviation comprises aircraft under the control of national
armed forces, and general aviation applies to recreational and
small corporate aircraft. The IPCC Guidelines further define
international bunker fuel use from civil aviation as the fuel
combusted for civil (e.g., commercial) aviation purposes by
aircraft arriving or departing on international flight segments.
However, as mentioned above, and in keeping with the IPCC
Guidelines, only the fuel purchased in the United States and
used by aircraft taking-off (i.e., departing) from the United
States are reported here. The standard fuel used for civil
aviation is kerosene-type jet fuel, while the typical fuel used
for general aviation is aviation gasoline.58
Emissions of CO2 from aircraft are essentially a function
of fuel use. Methane, N2O, CO, NOX, and NMVOC emissions
also depend upon engine characteristics, flight conditions,
and flight phase (i.e., take-off, climb, cruise, decent, and
landing). Methane, CO, and NMVOCs are the product
of incomplete combustion and occur mainly during the
landing and take-off phases. In jet engines, N2O and NOX
are primarily produced by the oxidation of atmospheric
nitrogen, and the majority of emissions occur during the
cruise phase. The impact of NOX on atmospheric chemistry
depends on the altitude of the actual emission. The cruising
altitude of supersonic aircraft, near or in the ozone layer, is
higher than that of subsonic aircraft. At this higher altitude,
NOX emissions contribute to stratospheric ozone depletion.59
At the cruising altitudes of subsonic aircraft, however, NOX
emissions contribute to the formation of tropospheric ozone.
At these lower altitudes, the positive radiative forcing effect
of ozone has enhanced the anthropogenic greenhouse gas
forcing.60 The vast majority of aircraft NOX emissions occur
at these lower cruising altitudes of commercial subsonic
aircraft (NASA 1996).61
International marine bunkers comprise emissions
from fuels burned by ocean-going ships of all flags that are
engaged in international transport. Ocean-going ships are
generally classified as cargo and passenger carrying, military
(i.e., Navy), fishing, and miscellaneous support ships (e.g.,
tugboats). For the purpose of estimating greenhouse gas
emissions, international bunker fuels are solely related to
cargo and passenger carrying vessels, which is the largest of
the four categories, and military vessels. Two main types of
fuels are used on sea-going vessels: distillate diesel fuel and
residual fuel oil. Carbon dioxide is the primary greenhouse
gas emitted from marine shipping. In comparison to aviation,
the atmospheric impacts of NOX from shipping are relatively
minor, as the emissions occur at ground level.
Overall, aggregate greenhouse gas emissions in 2002 from
the combustion of international bunker fuels from both aviation
and marine activities were 87.7 Tg CO2 Eq., or 24 percent
below emissions in 1990 (see Table 3-52). Although emissions
from international flights departing from the United States
have increased significantly (59 percent), emissions from
international shipping voyages departing the United States
have decreased by 60 percent since 1990. Increased military
activity during the Persian Gulf War resulted in an increased
level of military marine emissions in 1990 and again in 1998
with further U.S. military activity in Iraq; civilian marine
emissions during this period exhibited a similar trend.62 The
majority of these emissions were in the form of CO2; however,
small amounts of CH4 and N2O were also emitted. Emissions
of NOX by aircraft during idle, take-off, landing and at cruising
altitudes are of primary concern because of their effects on
ground-level ozone formation (see Table 3-53).
5 Most emission related international aviation and marine regulations are under the rubric of the International Civil Aviation Organization (ICAO) or the
International Maritime Organization (IMO), which develop international codes, recommendations, and conventions, such as the International Convention
of the Prevention of Pollution from Ships (MARPOL).
CO
Naphtha-type jet fuel was used in the past by the military in turbojet and turboprop aircraft engines.
5" Currently there are only around a dozen civilian supersonic aircraft in service around the world that fly at these altitudes, however.
" However, at this lower altitude, ozone does little to shield the earth from ultraviolet radiation.
°' Cruise altitudes for civilian subsonic aircraft generally range from 8.2 to 12.5 km (27,000 to 41,000 feet).
See Uncertainty section for a discussion of data quality issues.
Energy 3-59
-------
Table 3-52: Emissions from International Bunker Fuels (Tg C02 Eq.)
Gas/Mode
Aviation
Marine
CH4
Aviation
Marine
N20
Aviation
Marine
Total
+ Does not exceed 0.05 To. C02 Eq,
Note: Totals may not sum due to i
1997
-'till'
109.9
55.9
54.0
0.1
+
0.1
1.0
0.5
0.4
115.1
57.2
57,9
0.2
+
0.1
1.8
0.6
0.4
tJ1.D
116.3
emissions.
Table 3-53: Emissions from International Bunker Fuels (Gg)
Gas/Mode
C02
Aviation
Marine
CH4
Aviation
Marine
NzO
Aviation
Marine
CO
Aviation
Marine
NO,
Aviation
Marine
NMVOC
Aviation
Marine
1990
113,866
46,594
67,272
8
1
7
' j;
1
2
11«
77
39
iM
184-
1,803
59
11
e
1997
109,889 115.094
4»
52,188
; > 50,1:09 .
6
.•-• " -1
>:,'• • 5
' "-• • 3
... 2
.'-'„'. ' ' 1
*115
: '•.•-: as
29
1,550
, 207
1,343
48
13
36
55,929
53,960
7
2
5
3
2
1
124
92
32
1,668
222
1,446
52
14
38
57,194
57,900
7
2
6
3
2
1
128
94
34
1,780
227
1,554
55
14
41
58,868.
46,429
6
• 2 •
5
3
2
t
124
97
27
1,478
233
1,245
48
15
33
/: w,iM$/'':">;'.
';• 40,859 •'"'"'/•'
'.-""-.'' '>f %:... •;
' ' " ' '2V
. X -4 •''".."
,;. '' 'vl| -: •••
2,. :':
'.'•
• ; . r .
•-v-i«-.vr'
;ljj$ ' .',
'"- ,.• ,' 2^,'.,-
'»^334 :
, -"'.aw.'-;;
1,095
• -.'. 'MI ;'
' - . ,15" . : '
"' " '' '29-' .-
M^,i\!"''
;«li^w-'.''.:b ':'
,'•*' ;'-'''.;'S ''.
•••'•' ':2 •'•'•''
•. '• 4 '.''•:
...-• ••: 3 ; .- .:-
" • ,\ ;gl ; ''•;
;, '..I/'''
,".'.1l8|--:"'
98
;:,-a. /
'1,2i6 '••'
"'235' ' •
: 1,031,
.;{ -42 ";. •
'.".-•.15. ; "
:27-' "
$1,143
t?J01
:'. '".' 4
2
/• 3
3
- - '2
1
114
97
,16
978
234
743
34
15
20
Note: Totals may not sum due to independent rounding. Includes aircraft cruise attitude emissions.
Methodology
Emissions of CO2 were estimated through the application
of carbon content and fraction oxidized factors to fuel
consumption activity data. This approach is analogous to that
described under CO2 from Fossil Fuel Combustion. Carbon
content and fraction oxidized factors for jet fuel, distillate fuel
oil, and residual fuel oil were taken directly from the EIA and
are presented in Annex 2.1, Annex 2.2, and Annex 3.7. Heat
content and density conversions were taken from EIA (2003)
and USAF (1998). A complete description of the methodology
and a listing of the various factors employed can be found in
Annex 2.1. See Annex 3.7 for a specific discussion on the
methodology used for estimating emissions from international
bunker fuel use by the U.S. military.
Emission estimates for CH4, N2O, CO, NOX, and
NMVOCs were calculated by multiplying emission factors
by measures of fuel consumption by fuel type and mode.
Emission factors used in the calculations of CH4, N2O, CO,
NOX, and NMVOC emissions were obtained from the Revised
1996IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997). For
aircraft emissions, the following values, in units of grams
of pollutant per kilogram of fuel consumed (g/kg), were
employed: 0.09 for CH4, 0.1 for N2O, 5.2 for CO, 12.5 for
NOX, and 0.78 for NMVOCs. For marine vessels consuming
either distillate diesel or residual fuel oil the following values,
in the same units, except where noted, were employed: 0.32
for CH4, 0.08 for N2O, 1.9 for CO, 87 for NQX, and 0.052
g/MJ for NMVOCs. Activity data for aviation included
3-60 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 3-54: Aviation Jet Fuel Consumption for International Transport (Million Gallons)
2,482 2,583 •'. 2,1
Table 3-55: Marine Fuel Consumption for International Transport (Million Gallons)
1997
^3J74
621
518
3,272'
318
.. 511
• aa'i-i
1,§37
264 158
,318 348
2,443
solely jet fuel consumption statistics, while the marine mode
included both distillate diesel and residual fuel oil.
Activity data on aircraft fuel consumption were collected
from three government agencies. Jet fuel consumed by U.S.
flag air carriers for international flight segments was supplied
by the Bureau of Transportation Statistics (DOT 1991 through
2003). It was assumed that 50 percent of the fuel used by U.S.
flagged carriers for international flights—both departing and
arriving in the United States—was purchased domestically
for flights departing from the United States. In other words,
only one-half of the total annual fuel consumption estimate
was used in the calculations. Data on jet fuel expenditures
by foreign flagged carriers departing U.S. airports was taken
from unpublished data collected by the Bureau of Economic
Analysis (BEA) under the U.S. Department of Commerce
(BEA 1991 through 2003). Approximate average fuel prices
paid by air carriers for aircraft on international flights was
taken from DOT (1991 through 2003) and used to convert
the BEA expenditure data to gallons of fuel consumed. Data
on U.S. Department of Defense (DoD) aviation bunker fuels
and total jet fuel consumed by the U.S. military was supplied
by the Office of the Under Secretary of Defense (Installations
and Environment), DoD. Estimates of the percentage of
each Services' total operations that were international
operations were developed by DoD. Military aviation bunkers
included international operations, operations conducted
from naval vessels at sea, and operations conducted from
U.S. installations principally over international water in
direct support of military operations at sea. Military aviation
bunker fuel emissions were estimated using military fuel
and operations data synthesized from unpublished data by
the Defense Energy Support Center, under DoD's Defense
Logistics Agency (DESC 2003). Together, the data allow the
quantity of fuel used in military international operations to
be estimated. Densities for each jet fuel type were obtained
from a report from the U.S. Air Force (USAF 1998). Final jet
fuel consumption estimates are presented in Table 3-54. See
Annex 3.7 for additional discussion of military data.
Activity data on distillate diesel and residual fuel oil
consumption by cargo or passenger carrying marine vessels
departing from U.S. ports were taken from unpublished
data collected by the Foreign Trade Division of the U.S.
Department of Commerce's Bureau of the Census (DOC 1991
through 2003). Activity data on distillate diesel consumption
by military vessels departing from U.S. ports were provided
by DESC (2003). The total amount of fuel provided to naval
vessels was reduced by 13 percent to account for fuel used
while the vessels were not-underway (i.e., in port). Data on the
percentage of steaming hours underway versus not-underway
were provided by the U.S. Navy. These fuel consumption
estimates are presented in Table 3-55.
Energy 3-61
-------
Uncertainty
Emission estimates related to the consumption
of international bunker fuels are subject to the same
uncertainties as those from domestic aviation and marine
mobile combustion emissions; however, additional
uncertainties result from the difficulty in collecting accurate
fuel consumption activity data for international transport
activities separate from domestic transport activities.63
For example, smaller aircraft on shorter routes often carry
sufficient fuel to complete several flight segments without
refueling in order to minimize time spent at the airport gate or
take advantage of lower fuel prices at particular airports. This
practice, called tankering, when done on international flights,
complicates the use of fuel sales data for estimating bunker
fuel emissions. Tankering is less common with the type of
large, long-range aircraft that make many international flights
from the United States, however. Similar practices occur in
the marine shipping industry where fuel costs represent a
significant portion of overall operating costs and fuel prices
vary from port to port, leading to some tankering from ports
with low fuel costs.
Particularly for aviation, the DOT (1991 through
2003) international flight segment fuel data used for U.S.
flagged carriers does not include smaller air carriers and
unfortunately defines flights departing to Canada and some
flights to Mexico as domestic instead of international. As
for the BE A (1991 through 2003) data on foreign flagged
carriers, there is some uncertainty as to the average fuel price,
and to the completeness of the data. It was also not possible
to determine what portion of fuel purchased by foreign
carriers at U.S. airports was actually used on domestic flight
segments; this error, however, is believed to be small.64
Uncertainties exist with regard to the total fuel used by
military aircraft and ships, and in the activity data on military
operations and training that were used to estimate percentages
of total fuel use reported as bunker fuel emissions. Total
aircraft and ship fuel use estimates were developed from
DoD records, which document fuel sold to the Navy and
Air Force from the Defense Logistics Agency. These data
may slightly over or under estimate actual total fuel use in
aircraft and ships because each Service may have procured
fuel from, and/or may have sold to, traded with, and/or given
fuel to other ships, aircraft, governments, or other entities.
There are uncertainties in aircraft operations and training
activity data. Estimates for the quantity of fuel actually used
in Navy and Air Force flying activities reported as bunker
fuel emissions had to be estimated based on a combination
of available data and expert judgment. Estimates of marine
bunker fuel emissions were based on Navy vessel steaming
hour data, which reports fuel used while underway and fuel
used while not underway. This approach does not capture
some voyages that would be classified as domestic for a
commercial vessel. Conversely, emissions from fuel used
while not underway preceding an international voyage are
reported as domestic rather than international as would be
done for a commercial vessel. There is uncertainty associated
with ground fuel estimates for 1997 through 2001. Small fuel
quantities may have been used in vehicles or equipment other
than that which was assumed for each fuel type.
There are also uncertainties in fuel end-uses by fuel-
type, emissions factors, fuel densities, diesel fuel sulfur
content, aircraft and vessel engine characteristics and fuel
efficiencies, and the methodology used to back-calculate
the data set to 1990 using the original set from 1995. The
data were adjusted for trends in fuel use based on a closely
correlating, but not matching, data set. All assumptions used
to develop the estimate were based on process knowledge,
Department and Component data, and expert judgments.
The magnitude of the potential errors related to the various
uncertainties has not been calculated, but is believed to be
small. The uncertainties associated with future military
bunker fuel emission estimates could be reduced through
additional data collection.
Although aggregate fuel consumption data have been
used to estimate emissions from aviation, the recommended
method for estimating emissions of gases other than CO2 in
the Revised 1996IPCC Guidelines is to use data by specific
aircraft type (IPCCAJNEP/OECD/IEA 1997). The IPCC
also recommends that cruise altitude emissions be estimated
separately using fuel consumption data, while landing and
See uncertainty discussions under Carbon Dioxide Emissions from Fossil Fuel Combustion.
" Although foreign flagged air carriers are prevented from providing domestic flight services in the United States, passengers may be collected from
multiple airports before an aircraft actually departs on its international flight segment. Emissions from these earlier domestic flight segments should be
classified as domestic, not international, according to the IPCC.
3-62 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
take-off (LTO) cycle data be used to estimate near-ground
level emissions of gases other than CO2.65
There is also concern as to the reliability of the existing
DOC (1991 through 2003) data on marine vessel fuel
consumption reported at U.S. customs stations due to the
significant degree of inter-annual variation.
QA/QC and Verification
A source-specific QA/QC plan for international bunker
fuels was developed and implemented. This effort included a
Tier 1 analysis, as well as portions of a Tier 2 analysis. The
Tier 2 procedures that were implemented involved checks
specifically focusing on the activity data and emission factor
sources and methodology used for estimating CO2, CH4, and
N2O from international bunker fuels in the United States.
Emission totals for the different sectors and fuels were
compared and trends were investigated. Minor corrective
actions were necessary.
Recalculations Discussion
Historical activity data for aviation was slightly revised
for both U.S. and foreign carriers. These changes were due
to revisions to international fuel cost for foreign carriers and
international jet fuel consumption for U.S. carriers, provided
by DOT (1991 through 2003). These historical data changes
resulted in minimal changes to the emission estimates for
1990 through 2001, averaging an annual increase of 0.4 Tg
CO2 Eq. (0.4 percent) in CO2 emissions, less than 0.01 Tg
CO2 Eq. (0.2 percent) in CH4 emissions, and less than 0.01
Tg CO2 Eq. (0.4 percent) in N2O emissions.
3.12. Wood Biomass and
Ethanol Consumption (IPCC
Source Category 1 A)
The combustion of biomass fuels such as wood, charcoal,
and wood waste and biomass-based fuels such as ethanol
from corn and woody crops generates CO2. However, in the
long run the CO2 emitted from biomass consumption does
not increase atmospheric CO2 concentrations, assuming the
biogenic carbon emitted is offset by the uptake of CO2 resulting
from the growth of new biomass. As a result, CO2 emissions
from biomass combustion have been estimated separately
from fossil fuel-based emissions and are not included in the
U.S. totals. Net carbon fluxes from changes in biogenic carbon
reservoirs in wooded or crop lands are accounted for in the
Land-Use Change and Forestry chapter.
In 2002, total CO2 emissions from the burning of
woody biomass in the industrial, residential, commercial,
and electricity generation sectors were approximately 195.6
Tg CO2 Eq. (195,624 Gg) (see Table 3-56 and Table 3-57).
As the largest consumer of woody biomass, the industrial
sector was responsible for 72 percent of the CO2 emissions
from this source. The residential sector was the second
largest emitter, constituting 18 percent of the total, while
the commercial and electricity generation sectors accounted
for the remainder.
Biomass-derived fuel consumption in the United States
consisted primarily of ethanol use in the transportation
sector. Ethanol is primarily produced from corn grown
in the Midwest, and was used mostly in the Midwest and
Table 3-56: C02 Emissions from Wood Consumption by End-Use Sector (Tg C02 Eq.)
End-Use Sector
1990
Industrial
Commercial
Electricity Generation
135.3
59,9
4,0
13 J
Total
212J
Note: Totals may not sum due to independent rounding.
1998
158.0
61.4
5.2
14.2
238.8
199?
162.4
44.6
5.0
14.1
226.3
1998
150.5
39.9
5.0
14.1
209.5
1999
152.0
42.7
5.4
14.2
ftt.3
2000
mt
44.F
«.§
t$fi.-.
2f?J
2BB1
131,4
42J
4.3
13,0
194.1
2002
141.3
36.1
4: J
13.9
195.6
65 It should be noted that in the EPA (2003), U.S. aviation emission estimates for CO, NOx, and NMVOCs are based solely upon LTO cycles and
consequently only capture near ground-level emissions, which are more relevant for air quality evaluations. These estimates also include both domestic
and international flights. Therefore, estimates given under Mobile Source Fossil Fuel Combustion overestimate IPCC-defined domestic CO, NOX, and
NMVOC emissions by including landing and take-off (LTO) cycles by aircraft on international flights but underestimate because they do not include
emissions from aircraft on domestic flight segments at cruising altitudes. EPA (2003) is also likely to include emissions from ocean-going vessels departing
from U.S. ports on international voyages.
Energy 3-63
-------
Table 3-57: C02 Emissions from Wood Consumption by End-Use Sector (Gg)
Table 3-58: C02 Emissions from Ethanol Consumption
South. Pure ethanol can be combusted, or it can be mixed
with gasoline as a supplement or octane-enhancing agent.
The most common mixture is a 90 percent gasoline, 10
percent ethanol blend known as gasohol. Ethanol and ethanol
blends are often used to fuel public transport vehicles such
as buses, or centrally fueled fleet vehicles. These fuels burn
cleaner than gasoline (i.e., lower in NOX and hydrocarbon
emissions), and have been employed in urban areas with poor
air quality. However, because ethanol is a hydrocarbon fuel,
its combustion emits CO2.
In 2002, the United States consumed an estimated
174 trillion Btus of ethanol, and as a result, produced
approximately 11.5 Tg CO2 Eq. (11,473 Gg) (see Table 3-58)
of CO2 emissions. Ethanol production and consumption has
grown steadily every year since 1990 with the exception of
1996. Ethanol production dropped sharply in the middle of
1996 because of short corn supplies and high prices. Plant
output began to increase toward the end of the growing
season and approached normal levels by the end of the year.
However, total 1996 ethanol production fell far short of the
1995 level (EIA 1997). Since the low in 1996, production
has returned to its normal growth pattern.
Methodology
Woody biomass emissions were estimated by taking
U.S. consumption data (EIA 2003) (see Table 3-59), provided
in energy units for the industrial, residential, commercial,
and electric generation sectors, and applying two EIA
gross heat contents (Lindstrom 2003). One heat content
(16.953114 MMBtu/MT Wood & Wood Waste) was applied
to the industrial sector's consumption, while the other heat
content (15.432359 MMBtu/MT Wood & Wood Waste) was
applied to the consumption data for the other sectors. An EIA
emission factor of 0.434 MT C/MT Wood (Lindstrom 2003)
was then applied to the resulting quantities of woody biomass
Table 3-59: Woody Biomass Consumption by Sector (Trillion Btu)
3-64 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Box 3-4: Formation of C02 through Atmospheric CH4 Oxidation
'
:;^™^;M:. -2,888
^%*^*;.:V.-I
rf*?*/;?.'--; j-^-1^
^g-,-c.jvv' ?; , y:,,g.,£:C-
:i:4"
^^®^^Si:Xi Si; ^sB
- -%*^**f** ^.; » Jtrnn** «r,««-j«t . »f»«ifvr ^ . , T^^TW;T:f ^^-.;V"1KHQ? SS^SSJ^WT* *
*•/ |,pt-.;";^5,;.-- 1,190 ^ 1,1?$ :-
It is assumed that 100 percent of the CH4 emissions from combustion sources are accounted for in the overall carbon emissions calculated as CO2for sources using
emission factors and carbon mass balances. However, it may be the case for some types of combustion sources that the oxidation factors used for calculating CO2
emissions do not accurately account for the full mass of carbon emitted in gaseous form (i.e., partially oxidized or still in hydrocarbon form).
See Annex 2.3 for a more detailed discussion on accounting for indirect emissions from CO and NMVOCs.
Energy 3-65
-------
Table 3-60: Ethanol Consumption
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Trillion Btu
• 63
73
83
97
109
117
84
106
117
122
439
147
174
to obtain CO2 emissions estimates. It was assumed that the
woody biomass contains black liquor and other wood wastes,
has a moisture content of 12 percent, and is converted into
carbon dioxide with 100 percent efficiency. The emissions
from ethanol consumption were calculated by applying an
EIA emission factor of 17.99 Million Metric Tons of Carbon
Equivalent (Tg C)/QBtu (Lindstrom 2003) to U.S. ethanol
consumption data that were provided in energy units (EIA
2003) (see Table 3-60).
Uncertainty
It is assumed that the combustion efficiency for
woody biomass is 100 percent, which is believed to be an
overestimate of the efficiency of wood combustion processes
in the United States. Decreasing the combustion efficiency
would increase emission estimates. Additionally, the heat
content applied to the consumption of woody biomass in
the residential, commercial, and electric power sectors is
unlikely to be a completely accurate representation of the
heat content for all the different types of woody biomass
consumed within these sectors. Emission estimates from
ethanol production are more certain than estimates from
woody biomass consumption due to better activity data
collection methods and uniform combustion techniques.
Recalculations Discussion
The methodology for calculating emissions from wood
biomass and ethanol consumption was modified to improve
transparency, and include more recent emission factors and
heat contents. Over the 1990 through 2001 time period, the
changes resulted in an average annual increase in emissions
from wood biomass consumption of 38.0 Tg CO2 Eq. (21
percent) and an average annual decrease in emissions from
ethanol consumption of 0.4 Tg CO2 Eq. (5 percent).
3-66 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
4. Industrial Processes
Greenhouse gas emissions are produced as a by-product of various non-energy-related industrial activities.
That is, these emissions are produced from an industrial process itself and are not directly a result of energy
consumed during the process. For example, raw materials can be chemically transformed from one state to another. This
transformation can result in the release of greenhouse gases such as carbon dioxide (CO2), methane (CH4), or nitrous oxide
(N2O). The processes addressed in this chapter include iron and steel production, cement production, ammonia manufacture
and urea application, lime manufacture, limestone and dolomite use (e.g., flux stone, flue gas desulfurization, and glass
manufacturing), soda ash production and use, titanium dioxide production, phosphoric acid production, ferroalloy production,
CO2 consumption, aluminum production, petrochemical production, silicon carbide production, nitric acid production, and
adipic acid production (see Figure 4-1).
In addition to the three greenhouse gases listed above, there are also industrial sources of several classes of man-made
fluorinated compounds called hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). The present
contribution of these gases to the radiative forcing effect of all anthropogenic greenhouse gases is small; however, because of their
extremely long lifetimes, many of them will continue to accumulate in the atmosphere as long as emissions continue. In addition,
many of these gases have high global wanning potentials, and sulfur hexafluoride is the most potent greenhouse gas the IPCC has
evaluated. Usage of HFCs for the substitution of ozone depleting substances is growing rapidly, as they are the primary substitutes
for ozone depleting substances (ODSs), which are being phased-out under the Montreal Protocol on Substances that Deplete
the Ozone Layer. In addition to ODS
substitutes, HFCs, PFCs, SF6, and other
fluorinated compounds are employed and
emitted by a number of other industrial
sources in the United States. These
industries include aluminum production,
HCFC-22 production, semiconductor
manufacture, electric power transmission
and distribution, and magnesium metal
production and processing.
In 2002, industrial processes
generated emissions of 310.7 Tg CO2 Eq.,
or 4.5 percent of total U.S. greenhouse
gas emissions. Carbon dioxide emissions
from all industrial processes were 147.3
Tg CO2 Eq. (147,308 Gg) in 2002. This
amount accounted for only 2.5 percent
of national CO2 emissions. Methane
emissions from petrochemical, silicon
Figure 4-1
2002 Industrial Processes Chapter Greenhouse Gas Sources
Substitution ol Ozone Depleting Substances
Iron and Steel Production
Cement Manufacture
HCFC-22 Production
Ammonia Production and Urea Application
Nitric Acid Production
Electrical Transmission and Distribution
Lime Manufacture
Aluminum Production
Adipic Acid Production
Limestone and Dolomite Use
Semiconductor Manufacture
Soda Ash Manufacture and Consumption
Magnesium Production and Processing
Titanium Dioxide Production
Petrochemical Production
Carbon Dioxide Consumption
Ferroalloy Production
Phosphoric Acid Production
Silicon Carbide Production <0.05
Industrial Processes as a
Portion of all Emissions
4.5%
10 20 30 40
50 60 70
Tg CO, Eq
90 100
Industrial Processes 4-1
-------
carbide, and iron and steel production resulted in emissions of
approximately 2.5 Tg CO2 Eq. (120 Gg) in 2002, which was
0.4 percent of U.S. CH4 emissions. Nitrous oxide emissions
from adipic acid and nitric acid production were 22.6 Tg
CO2 Eq. (73 Gg) in 2002, or 5.4 percent of total U.S. N2O
emissions. In 2002, combined emissions of HFCs, PFCs
and SF6 totaled 138.2 Tg CO2 Eq. Overall, emissions from
industrial processes increased by 4.5 percent from 1990 to
2002 despite decreases in emissions from several industrial
processes, such as iron and steel, electrical transmission
and distribution, HCFC-22 production, and aluminum
production. The increase in overall emissions was driven by
a rise in the emissions originating from cement manufacture
and, primarily, the emissions from the use of substitutes for
ozone depleting substances.
Table 4-1 summarizes emissions for the Industrial
Processes chapter in units of teragrams of CO2 equivalent
(Tg CO2 Eq.), while unweighted native gas emissions in
gigagrams (Gg) are provided in Table 4-2.
Table 4-1: Emissions from Industrial Processes (Tg C02 Eq.)
In order to ensure the quality of the emission estimates
from industrial processes, the IPCC QA/QC procedures were
implemented by means of the Quality Assurance/Quality
Control and Uncertainty Management Plan for the U.S.
Greenhouse Gas Inventory: Procedures Manual for QA/
QC and Uncertainty Analysis ("QA/QC plan"). This plan
encompasses Tier 1 and Tier 2 procedures, and recommends
that all Tier 1 procedures be performed annually, while Tier
2 procedures are performed when there are major shifts in
the methodology. Tier 1 addresses annual procedures and
checks to be used when gathering, maintaining, handling,
documenting, checking and archiving the data, supporting
documents, and files associated with the Industrial Processes
section of the U.S. Inventory. Tier 2 procedures and checks
specifically focus on the emission factor and activity data
sources and methodology used for estimating emissions from
Industrial Processes for the U.S. Inventory. Tier 1 procedures
and checks have been performed on all industrial process
sources; where Tier 2 procedures or checks were performed
for a source, they will be described within the QA/QC
and Verification Discussion of that source description. In
4-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-2: Emissions from Industrial Processes (Gg)
Gas/Source
Silicon Carbide Production
•"••' •"•
Semiconductor Manufacture
M (Mixture of gases)
35,414
33,278
19,306'
11,236;
: 5*533-
«?,42S
13,914
.,7,448
4)325
948
2,02?
57
t
87
67
19
M
M
3
1
M
M
4-
,OJ
8.0S?
••S898-
4,217
81
56
1,
83
65
18
M
M
3
1
,M
M
4-
'w:
3
I'-
ll •
M
4-''
147,308
. 54v4f 1
-1,3
17,652
t&t2l 12,304
&?33; .5,836
\,:-/i223
: 1,338
1,272
1,237
120
72
47
4-
73
54
19
M
M
2
1
M
its
68
§1
+ .
51
16
M
'•2.
1
M
Note: Totals may not sum due to independent rounding.
addition to the national QA/QC plan, a more detailed plan
was developed specifically for the CO2 and CH4 industrial
processes sources. This plan was based on the U.S. strategy,
but was tailored to include specific procedures recommended
for these sources.
The general method employed to estimate emissions for
industrial processes, as recommended by the Intergovernmental
Panel on Climate Change (IPCC), involves multiplying
production data (or activity data) for each process by an
emission factor per unit of production. The uncertainty of
the emission estimates is therefore generally a function of a
combination of the uncertainties surrounding the production
and emission factor variables. Uncertainty of activity data
and the associated probability density functions for industrial
processes CO2 sources were estimated based on expert
assessment of available qualitative information. Uncertainty
estimates and probability density functions for the emission
factors used to calculate emissions from this source were
devised based on IPCC recommendations.
The uncertainty of activity data, which is obtained through
a survey of manufacturers conducted by various organizations
(specified within each source), is a function of the reliability
of plant-level production data and is influenced by the
completeness of the survey response. The emission factors
used were either derived using calculations that assume precise
and efficient chemical reactions, or were based upon empirical
data in published references. As a result, uncertainties in
the emission coefficients can be attributed to, among other
things, inefficiencies in the chemical reactions associated
with each production process or to the use of empirically-
derived emission factors that are biased; therefore, they may
not represent U.S. national averages. Additional assumptions
are described within each source.
The uncertainty analysis performed to quantify
uncertainties associated with the 2002 inventory estimates
from industrial processes is only the beginning of a multi-
year process for developing credible quantitative uncertainty
estimates for these source categories using the IPCC Tier 2
Industrial Processes 4-3
-------
approach. It is expected that in subsequent years, the type and
the characteristics of the actual probability density functions
underlying the input variables will be identified and better
characterized (resulting in development of more reliable
inputs for the model, including accurate characterization of
correlation between variables), based on expert elicitations
obtained through implementation of elicitation protocols.
Accordingly, the quantitative uncertainty estimates reported
in this section should be considered as preliminary and
illustrative. The interconnectivity among data used for
estimating emissions for different sources can influence the
uncertainty analysis of each individual source. While this
preliminary uncertainty analysis recognizes very significant
connections among sources, a more comprehensive approach
that accounts for all linkages will be identified as the
uncertainty analysis moves forward.
4.1. Iron and Steel Production
(IPCC Source Category 2C1)
In addition to being an energy intensive process, the
production of iron and steel also generates process-related
emissions of CO2 and CH4. Iron is produced by first
reducing iron oxide (iron ore) with metallurgical coke in
a blast furnace to produce pig iron (impure iron containing
about 3 to 5 percent carbon by weight). Metallurgical coke
is manufactured in a coke plant using coking coal as a raw
material. Iron may be introduced into the blast furnace in the
form of raw iron ore, pellets, briquettes, or sinter. Pig iron is
used as a raw material in the production of steel (containing
about 0.4 percent carbon by weight). Pig iron is also used as
a raw material in the production of iron products in foundries.
The pig iron production process produces CO2 emissions and
fugitive CH4 emissions.
The production of metallurgical coke from coking coal
and the consumption of the metallurgical coke used as a
reducing agent in the blast furnace are considered in the
inventory to be non-energy (industrial) processes, not energy
(combustion) processes. Coal coke is produced by heating
coking coal in a coke oven in a low-oxygen environment.
The process drives off the volatile components of the coking
coal and produces coal coke. Coke oven gas and coal tar
are carbon by-products of the coke manufacturing process.
Coke oven gas is generally burned as a fuel within the steel
mill. Coal tar is used as a raw material to produce anodes
used for primary aluminum production and other electrolytic
processes, and also used in the production of other coal tar
products. The coke production process produces CO2
emissions and fugitive CH4 emissions.
Sintering is a thermal process by which fine iron-bearing
particles, such as air emission control system dust, are baked,
which causes the material to agglomerate into roughly one-
inch pellets that are then recharged into the blast furnace for
pig iron production. Iron ore particles may also be formed
into larger pellets or briquettes by mechanical means, and
then agglomerated by heating prior to being charged into the
blast furnace. The sintering process produces CO2 emissions
and fugitive CH4 emissions.
The metallurgical coke is a reducing agent in the blast
furnace. Carbon dioxide is produced as the metallurgical coke
used in the blast furnace process is oxidized. Steel (containing
less than 2 percent carbon by weight) is produced from pig
iron in a variety of specialized steel making furnaces. The
majority of CO2 emissions from the iron and steel process
come from the use of coke in the production of pig iron, with
smaller amounts evolving from the removal of carbon from
pig iron used to produce steel. Some carbon is also stored
in the finished iron and steel products.
Emissions of CO2 and CH4 from iron and steel
production in 2002 were 54.4 Tg CO2 Eq. (54,411 Gg) and
1.0 Tg CO2 Eq. (47.4 Gg), respectively (see Table 4-3 and
Table 4-4). Emissions have fluctuated significantly from 1990
to 2002 due to changes in domestic economic conditions
and changes in product imports and exports. For the past
several years, domestic production of pig iron, sinter, and coal
coke has declined. Despite recovering somewhat in 2000,
Table 4-3: C02 and CH4 Emissions from Iron and Steel Production (Tg C02 Eq.)
Year
1990
C02
CH4
Total
1996
68.3
1.3
69.6
1997
71.9
1.3
73.1
1998
67.4
1.2
68.6
1999
64.4
1.2
65.5
2000
65.7
1.2
66.9
2001
59.1
1.1
60.1
2002
54.4
1.0
55.4
4-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-4: C02 and CH4 Emissions from Iron and Steel Production (Gg)
1998
68,324
60.4
1997
71,864
59.6
1998
§7,429
57.2
1999
64,376
55.8
2808
65,693
57.5
2081
59,074
50.8
2002
54,411
47.4
domestic pig iron production, coke, and sinter production fell
in 2001 and again in 2002. Pig iron production in 2002 was
16 percent lower than in 2000 and 21 percent below 1995
levels. Coke production in 2002 was 15 percent lower than
in 2001 and 42 percent below 1990 levels. A slowdown in
the domestic and worldwide economy and the availability
of low-priced imports limit growth in domestic production
(USGS 2002).
Methodology
Since coke is consumed as a reducing agent during the
manufacture of pig iron, the corresponding quantity of coal
consumed during coking operations was identified. This
quantity of coal is considered a non-energy use. Data were
also collected on the amount of imported coke consumed in
the blast furnace process. These data were converted to their
energy equivalents. The carbon content of the combusted
coal and imported coke was estimated by multiplying their
energy consumption by material specific carbon-content
coefficients. The carbon-content coefficients used are
presented in Annex 6.4.
Emissions from the re-use of scrap steel and imported
pig iron in the steel production process were calculated by
assuming that all the associated carbon-content of these
materials are released on combustion. Steel has an associated
carbon-content of approximately 0.4 percent, while pig iron
is assumed to contain 4 percent carbon by weight.
Emissions from carbon anodes, used during the
production of steel in electric arc furnaces (EAF), were also
estimated. Emissions of CO2 were calculated by multiplying
the annual production of steel in electric arc furnaces by an
emission factor (4.4 kg CO2/ton steelEAF). It was assumed
that the carbon anodes used in the production of steel in
electric arc furnaces are composed of 80 percent petroleum
coke and 20 percent coal tar pitch (DOE 1997). Since coal
tar pitch is a by-product of the coking process and its carbon-
related emissions have already been accounted for earlier in
the iron and steel emissions calculation as part of the coking
process, the emission factor was reduced by 20 percent to
Table 4-5: CH4 Emission Factors for Coal Coke, Sinter, and
Pig Iron Production
Material Produced
9 Ctyicg produced
Cpai Coke
Pig Iron
Sinter
0.5
0.9
0.5
Source: IPCC/UNEP/OECD/1EA1995
avoid double counting. Additionally, emissions from the
coal tar pitch component of carbon anodes consumed
during the production of aluminum, which are accounted
for in the aluminum production section of this chapter, have
been subtracted from the total coal tar emissions that were
calculated above.
Carbon storage was accounted for by assuming that all
domestically manufactured steel had a carbon content of 0.4
percent. Furthermore, any pig iron that was not consumed
during steel production, but fabricated into finished iron
products, was assumed to have a by-weight carbon content
of 4 percent.
The production processes for coal coke, sinter, and pig
iron result in fugitive emissions of CH4, which are emitted
via leaks in the production equipment rather than through the
emission stacks or vents of the production plants. The fugitive
emissions were calculated by applying emission factors taken
from the 7995IPCC Guidelines (IPCC/UNEP/OECD/IEA
1995) (see Table 4-5) to annual domestic production data for
coal coke, sinter, and pig iron.
Data relating to the amount of coal consumed at coke
plants, for the production of coke for domestic consumption
in blast furnaces, as well as the quantity of coke imported
for iron production were taken from the Energy Information
Administration (EIA), Quarterly Coal Report January-Dec
2002 (EIA 2003); U.S. Coal Domestic and International Issues
(EIA 2001); Mineral Yearbook: Iron and Steel (USGS 2002a,
2001a, 2000a, 1999, 1997, 1995a, 1993) and the American
Iron and Steel Institute (AISI), Annual Statistical Report (AISI
2002, 2000). Scrap steel and imported pig iron consumption
data for 1990 through 2002 were obtained from Annual
Industrial Processes 4-5
-------
Table 4-6: Production and Consumption Data for the Calculation of C02 and CH4 Emissions from Iron and Steel Production
(Thousand Metric Tons)
Coke Corwurnptsn for P^fcaB-
Domestic Pig Iron Producte for Steel:
Baste Oxygen Rirnaw Steel PpWucBoH
Electffc Arc Furnace Steel Pratefr
CH4 " -
Coke Production :,
Iron Ore Consumption for SWflr '•'. '
Domestic Pig Iron Production feSSrt
..
. 35,881' -•
."JH^NJ .--•
4§,OB1
5J.22?
: 33,§1?
27,400 >25,5?3
22,180- itooo
48,918 48,«78 47,470 45,071' 47,318, 741,7;* '3t,6M
54,824 55,386 54,146 52,364 53,864 :4tg»\ 45,463
40,71! 43,088 44,513 45,063 47,850 42,743 40,124
20,933 20,083 18,181 18,240 18,877 17,130 44,601
11,778 1t,426 10,791 11,072 10,78* , 9;it4 18;876
48,858 48,678 47,470 45,67? 47,3j9f 41,740:
Statistical Reports (AISI 2002, 2001, 1995). Crude steel
production, as well as pig iron use for purposes other than steel
production, was also obtained from Annual Statistical Reports
(AISI 2002,2001,1996). Carbon content percentages for pig
iron and crude steel and the CO2 emission factor for carbon
anode emissions from steel production were obtained from
1PCC Good Practice Guidance and Uncertainty Management
(IPCC 2000). Aluminum production data for 1990 through
2002 were obtained from Mineral Industry Surveys: Aluminum
Annual Report (USGS 2002, 200 Ib, 2000b, 1998, 1995b).
Annual consumption of iron ore used in sinter production for
1990 through 2002 were obtained from the USGS Iron Ore
yearbook (USGS 2002b,2001b,2000b, 1999b, 1998b, 1997b,
1996b, 1995b, 1994b). The CO2 emission factor for carbon
anode emissions from aluminum production was taken from
the Revised 1996 IPCC Guidelines (IPCC/VNEP/OECD/IEA
1997). Estimates for the composition of carbon anodes used
during steel and aluminum production were obtained from
Energy and Environmental Profile of the U.S. Aluminum
Industry (DOE 1997).
Uncertainty
The time series data for production of coal coke, sinter,
pig iron, steel, and aluminum and import and export data
upon which the calculations are based are considered to be
consistent for the entire time series. The estimates of CO2
emissions from production and utilization of coke are based
on energy consumption data, average carbon contents, and the
fraction of carbon oxidized. These data and factors produce
a relatively accurate estimate of CO2 emissions. However,
there are uncertainties associated with each of these factors.
For example, carbon oxidation factors may vary depending
on inefficiencies in the combustion process, where varying
degrees of ash or soot can remain unoxidized.
Simplifying assumptions were made concerning the
composition of carbon anodes (80 percent petroleum coke
and 20 percent coal tar). For example, within the aluminum
industry, the coal tar pitch content of anodes can vary from 15
percent in prebaked anodes to 24 to 28 percent in Soderberg
anode pastes (DOE 1997). An average value was assumed
and applied to all carbon anodes utilized during aluminum
and steel production. The assumption is also made that all
coal tar used during anode production originates as a by-
product of the domestic coking process. Similarly, it was
assumed that all pig iron and crude steel have carbon contents
of 4 percent and 0.4 percent, respectively. The carbon content
of pig iron can vary between 3 and 5 percent, while crude
steel can have a carbon content of up to 2 percent, although
it is typically less than 1 percent (IPCC 2000).
There is uncertainty in the most accurate CO2 emission
factor for carbon anode consumption in aluminum production.
Emissions vary depending on the specific technology used by
each plant (Prebake or Soderberg). The Revised 1996 IPCC
Guidelines (IPCC/UNEP/OECD/IEA 1997) provide CO2
emission factors for each technology type. Consistent with
the assumptions used in the Aluminum Production source,
it was assumed that production was split 80 percent prebake
and 20 percent Soderberg for the whole time series. Similarly,
the carbon anode emission factor for steel production can vary
between 3.7 and 5.5 kg CO2/ton steel (IPCC 2000). For this
analysis, the upper bound value was used.
For the purposes of the CH4 calculation it is assumed
that none of the CH4 is captured in stacks or vents and that
all of the CH4 escapes as fugitive emissions. Additionally,
the CO2 emissions calculation is not corrected by subtracting
the carbon content of the CH4, which means there may be a
slight double counting of carbon as both CO2 and CH4.
4-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-7: Quantitative Uncertainty Estimates for C02 and CH4 Emissions from Iron and Steel Production (Tg. C02 Eq. and Percent)
2002 Emission Estimate
Source
Gas
Iron and Steel Production
Iron and Steel Production
CH4
54.4
1.0
Lower Bound
22.7
,0.6
Upper Bound
97.1
1.4
Lower Bound
-58%
-39%
Upper Bound
+78%
4-39%
a Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 99% confidence interval.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-7) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions from this source is within the
range of approximately 22.7 to 97.1 Tg CO2 Eq. (or that the
actual CO2 emissions are likely to fall within the range of
approximately 58 percent below and 78 percent above the
emission estimate of 54.4 Tg CO2 Eq.).
For CH4 emissions from iron and steel, the preliminary
results of the quantitative uncertainty analysis (see Table
4-7) indicate that 19 out of 20 times (i.e., there is 95 percent
probability), the actual estimate in 2002 is likely to be within
the range of 0.6 Tg CO2 Eq. to 1.4 Tg CO2 Eq. (or that the
actual CH4 emissions are likely to fall within the range of
approximately 39 percent below and 39 percent above the
emission estimate of 1.0 Tg CO2 Eq.).
Recalculations Discussion
Methane emissions from iron and steel production have
been added to this source for the entire time series. These
calculations are based on the methodology and emission
factors in the 1995 IPCC Guidelines. Methane emission
factors for pig iron production and sinter production
do not appear in the 1996 IPCC Guidelines, therefore
these emissions have not previously been included in the
inventory calculations. They were added this year based on
a recommendation from the UNFCCC upon review of the
2001 U.S. Inventory.
4.2. Cement Manufacture (IPCC
Source Category 2A1)
Cement manufacture is an energy and raw material
intensive process that results in the generation of CO2 from
both the energy consumed in making the cement and the
chemical process itself.1 Cement production has accounted
for about 2.4 percent of total global industrial and energy-
related CO2 emissions, and the United States is the world's
third largest cement producer (IPCC 1996). Cement is
manufactured in almost every U.S. state. Carbon dioxide
emitted from the chemical process of cement production
represents one of the largest sources of industrial CO2
emissions in the United States.
During the cement production process, calcium
carbonate (CaCO3) is heated in a cement kiln at a temperature
of about 1,300°C (2,400°F) to form lime (i.e., calcium oxide
or CaO) and CO2. This process is known as calcination or
calcining. Next, the lime is combined with silica-containing
materials to produce clinker (an intermediate product), with
the earlier by-product CO2 being released to the atmosphere.
The clinker is then allowed to cool, mixed with a small
amount of gypsum, and used to make portland cement. The
production of masonry cement from portland cement requires
additional lime and, thus, results in additional CO2 emissions.
However, this additional lime is already accounted for in the
Lime Manufacture source category in this chapter; therefore,
the additional emissions from making masonry cement from
clinker are not counted in this source category's total. They
are presented here for informational purposes only.
In 2002, U.S. clinker production—including Puerto
Rico—totaled 81,294 thousand metric tons, and U.S.
masonry cement production was estimated to be 4,400
thousand metric tons (USGS 2002). The resulting emissions
of CO2 from 2002 cement production were estimated to be
42.9 Tg CO2 Eq. (42,898 Gg) (see Table 4-8). Emissions
from masonry production from clinker raw material were
estimated to be 0.1 Tg CO2 Eq. (99 Gg) in 2002, but again
are accounted for under Lime Manufacture.
The CO2 emissions related to the consumption of energy for cement manufacture are accounted for under CO2 from Fossil Fuel Combustion in the
Energy chapter.
Industrial Processes 4-7
-------
Table 4-8: CO, Emissions from Cement Production*
Year
TgC02Eq.
Gg
1990^
1996
1997
1998
1999
2000
2001
2002
33,3
38.3
39.2
40,0
41.2
41.4
42.9
31278
37,079
38,323
39,218
39,991
41,190
41,357
42,898
* Totals exclude C02 emissions from making masonry cement from
clinker, which are accounted (or under Lime Manufacture.
After falling in 1991 by 2 percent from 1990 levels,
cement production emissions have grown every year since.
Overall, from 1990 to 2002, emissions increased by 29
percent. Cement is a critical component of the construction
industry; therefore, the availability of public construction
funding, as well as overall economic growth, have had
considerable influence on cement production.
Methodology
Carbon dioxide emissions from cement manufacture
are created by the chemical reaction of carbon-containing
minerals (i.e., calcining limestone). While in the kiln,
limestone is broken down into CO2 and lime with the CO2
released to the atmosphere. The quantity of the CO2 emitted
during cement production is directly proportional to the
lime content of the clinker. During calcination, each mole
of CaCO3 (i.e., limestone) heated in the clinker kiln forms
one mole of lime (CaO) and one mole of CO2:
CaCO3 + heat -> CaO + CO2
Carbon dioxide emissions were estimated by applying
an emission factor, in tons of CO2 released per ton of clinker
produced, to the total amount of clinker produced. The emission
factor used in this analysis is the product of the average lime
fraction for clinker of 64.6 percent (IPCC 2000) and a constant
reflecting the mass of CO2 released per unit of lime. This
calculation yields an emission factor of 0.507 tons of CO2 per
ton of clinker produced, which was determined as follows:
EFclinker = 0.646 CaO x
44.01 g/mole CO2
56.08 g/mole CaO
= 0.507 tons CO2/ton clinker
During clinker production, some of the clinker
precursor materials remain in the kiln as non-calcinated,
partially calcinated, or fully calcinated cement kiln dust.
The emissions attributable to the calcinated portion of the
cement kiln dust are not accounted for by the clinker emission
factor. The IPCC recommends that these additional cement
kiln dust CO2 emissions should be estimated as 2 percent of
the CO2 emissions calculated from clinker production. Total
cement production emissions were calculated by adding the
emissions from clinker production to the emissions assigned
to cement kiln dust (IPCC 2000).
Masonry cement requires additional lime over and
above the lime used in clinker production. In particular, non-
plasticizer additives such as lime, slag, and shale are added to
the cement, increasing its weight by approximately 5 percent.
Lime accounts for approximately 60 percent of this added
weight. Thus, the additional lime is equivalent to roughly
2.86 percent of the starting amount of the product, since:
0.6 x 0.057(1 + 0.05) = 2.86%
An emission factor for this added lime can then be
calculated by multiplying this 2.86 percent by the molecular
weight ratio of CO2 to CaO (0.785) to yield 0.0224 metric
tons of additional CO2 emitted for every metric ton of
masonry cement produced.
As previously mentioned, the CO2 emissions from the
additional lime added during masonry cement production
are accounted for in the section on CO2 emissions from
Lime Manufacture. Thus, the activity data for masonry cement
production are shown in this chapter for informational purposes
only, and are not included in the cement emission totals.
The activity data for clinker and masonry cement
production (see Table 4-9) were obtained from U.S.
Geological Survey (USGS 1992, 1995a, 1995b, 1996,
Table 4-9: Cement Production (Gg)
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Clinker
64,355
62,918
63,415
66,957
69,786
71,257
71,706
74,112
75,842
77,337
79,656
79,979
81,294
Masonry
3,209
2,856
3,093
2,975
3,283
3,603
3,469
3,634
3,989
4,375
4,332
4,450
4,400
4-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-10: Quantitative Uncertainty Estimates for C02 Emissions from Cement Manufacture (Tg C02 Eq. and Percent)
Gas
f2NH3
Not all of the CO2 produced in the production of
ammonia is emitted directly to the atmosphere. Both
ammonia and carbon dioxide are used as raw materials in
the production of urea [CO(NH2)2], which is another type of
nitrogenous fertilizer that contains carbon as well as nitrogen.
The chemical reaction that produces urea is:
2 NH3 + CO2 -» NH2COONH4 -> CO(NH2)2 + H2O
The carbon in the urea that is produced and assumed to
be subsequently applied to agricultural land as a nitrogenous
Industrial Processes 4-9
-------
fertilizer is ultimately released into the environment as CO2;
therefore, the CO2 produced by ammonia production and
subsequently used in the production of urea does not change
overall CO2 emissions. However, the CO2 emissions are
allocated to the ammonia and urea production processes in
accordance to the amount of ammonia and urea produced.
Net emissions of CO2 from ammonia production in 2002
were 9.6 Tg CO2 Eq. (9,642 Gg). Carbon dioxide emissions
from this source are summarized in Table 4-11. Emissions
of CO2 from urea application in 2002 totaled 8.0 Tg CO2
Eq. (8,010 Gg). Carbon dioxide emissions from this source
are summarized in Table 4-12.
Methodology
The calculation methodology for non-combustion CO2
emissions from production of nitrogenous fertilizers is based
on a CO2 emission factor published by the European Fertilizer
Manufacturers Association (EFMA). The CO2 emission
factor (1.2 tons CO2/ton NH3) is applied to the total annual
domestic ammonia production. Emissions of CO2 from
ammonia production are then adjusted to account for the
use of some of the CO2 produced from ammonia production
as a raw material in the production of urea. For each ton of
urea produced, 8.8 of every 12 tons of CO2 are consumed
and 6.8 of every 12 tons of ammonia are consumed. The CO2
emissions reported for ammonia production are therefore
reduced by a factor of 0.73 multiplied by total annual
domestic urea production, and that amount of CO2 emissions
is allocated to urea fertilizer application. Total CO2 emissions
resulting from nitrogenous fertilizer production do not
change as a result of this calculation, but some of the CO2
emissions are attributed to ammonia production and some of
the CO2 emissions are attributed to urea application.
The calculation of the total non-combustion CO2 emissions
from nitrogenous fertilizers accounts for CO2 emissions from
Table 4-11: C02 Emissions from Ammonia Manufacture
Year
TQ COZ Eq.
1990
12.6
12,553
1996
1997
1998
1999
2000
2001
2002
13.8
14.0
14.2
12.9
12.1
8.9
9.6
13,825
14,028
14,215
12,948
12,100
8,852
9,642
the application of imported and domestically produced urea.
For each ton of imported urea applied, 0.73 tons of CO2 are
emitted to the atmosphere. The amount of imported urea applied
is calculated based on the net of urea imports and exports.
All ammonia production and subsequent urea production
was assumed to be from the same process—conventional catalytic
reforming of natural gas feedstock. Further, ammonia and urea are
assumed to be manufactured in the same manufacturing complex,
as both the raw materials needed for urea production are produced
by the ammonia production process.
The emission factor of 1.2 ton CO2/ton NH3 was taken
from the European Fertilizer Manufacturers Association Best
Available Techniques publication, Production of Ammonia
(EFMA 1995). The EFMA reported an emission factor range
of 1.15 to 1.30 ton CO2/ton NH3, with 1.2 ton CO2/ton NH3 as
a typical value. The EFMA reference also indicates that more
than 99 percent of the CH4 feedstock to the catalytic reforming
process is ultimately converted to CO2. Ammonia and urea
production data (see Table 4-13 and Table 4-14, respectively)
were obtained from the Census Bureau of the U.S. Department
of Commerce (U.S. Census Bureau 1991, 1992, 1993, 1994,
1998,1999,2000, 2001a, 2001b, 2002a, 2002b, 2002c, 2003)
as reported in Current Industrial Reports Fertilizer Materials
and Related Products annual and quarterly reports. Import and
export data were obtained from the U.S. Census Bureau Current
Industrial Reports Fertilizer Materials and Related Products
annual reports (U.S. Census Bureau) for 1997 through 2002, The
Fertilizer Institute (TFI2002) for 1993 through 1996, and the
United States International Trade Commission Interactive Tariff
and Trade DataWeb (U.S. FTC 2002) for 1990 through 1992.
Uncertainty
A factor of the uncertainty in this calculation is how
accurately the emission factor used represents an average across
all ammonia plants. The EFMA reported an emission factor
Table 4-12: C02 Emissions from Urea Application
Year
Tg C02 Eg.
1990
6.8
1996
1997
1998
1999
2000
2001
2002
">•-'• &5 '•
6.6
7.7
7.7
7.5
7.4
8.0
'' '•.••'.'< :$$&• -.":.' •'• •
6,622
7,719
7,667
7,488
7,398
8,010
4-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-13: Ammonia Production
Table 4-14: Urea Production
YSrar
1990
1991
1992
1993
1994
1995
1996
199?
1998
1999
2000
2001
2002
Thousand Metric Tons
'"'' ^ ''•'":"': 15,425 :
15,576
: - 16,261
15,599
16,211
15,788
16,260
16,231
16,761
15,728
14,342
11,012
12,336
Yfear
Thousand Metric Tons
1990
1991
1992
1993
1994
1995
8,124
7,373
8rl42
1997
1998
1999
2000
2001
2002
8,042
1,969
range of 1.15 to 1.30 ton CO2/ton NH3, with 1.2 ton CO2/ton
NH3 reported as a typical value. The actual emission factor
depends upon the amount of air used in the ammonia production
process, with 1.15 ton CO2/ton NH3 being the approximate
stoichiometric minimum that is achievable for the conventional
reforming process. By using natural gas consumption data for
each ammonia plant, more accurate estimates of CO2 emissions
from ammonia production could be calculated. However, these
consumption data are often considered confidential. Also,
natural gas is consumed at ammonia plants both as a feedstock
to the reforming process and for generating process heat and
steam. Natural gas consumption data, if available, would need
to be divided into feedstock use (non-energy) and process heat
and steam (fuel) use, as CO2 emissions from fuel use and non-
energy use are calculated separately.2
Natural gas feedstock consumption data for the U.S.
ammonia industry as a whole is available from the Energy
Information Administration (EIA) Manufacturers Energy
Consumption Survey (MECS) for the years 1985, 1988,
1991,1994 and 1998 (EIA 1994; EIA 1998). These feedstock
consumption data collectively correspond to an effective average
emission factor of 1.0 ton CO2/ton NH3, which appears to be
below the stoichiometric minimum that is achievable for the
Table 4-15: Urea Net Imports
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Thousand Metric Tons
1,086
648
656
2,305
2,249
2,055
1,051
1,600
2,483
2;374
3,241
4,008
3,885
conventional steam reforming process. The EIA data for natural
gas consumption for the years 1994 and 1998 correspond
more closely to the CO2 emissions calculated using the EFMA
emission factor than do data for previous years. The 1994 and
1998 data alone yield an effective emission factor of 1.1 ton
CO2/ton NH3, corresponding to CO2emissions estimates that are
approximately 1.5 Tg CO2 Eq. below the estimates calculated
using the EFMA emission factor of 1.2 ton CO2/ton NH3.
Natural gas feedstock consumption data are not available from
It appears that the IPCC emission factor for ammonia production of 1.5 ton CO2 per ton ammonia may include both CO2 emissions from the natural
gas feedstock to the process and some CO2 emissions from the natural gas used to generate process heat and steam for the process. Table 2-5, Ammonia
Production Emission Factors, in Volume 3 of the Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories Reference Manual (IPCC 1997)
includes two emission factors, one reported for Norway and one reported for Canada. The footnotes to the table indicate that the factor for Norway does
not include natural gas used as fuel but that it is unclear whether the factor for Canada includes natural gas used as fuel. However, the factors for Norway
and Canada are nearly identical (1.5 and 1.6 tons CO2 per ton ammonia, respectively) and it is likely that if one value does not include fuel use, the other
value also does not. For the conventional steam reforming process, however, the EFMA reports an emission factor range for feedstock CO2 of 1.15 to
1.30 ton per ton (with a typical value of 1.2 ton per ton) and an emission factor for fuel CO2 of 0.5 tons per ton. This corresponds to a total CO2 emission
factor for the ammonia production process, including both feedstock CO2 and process heat CO2, of 1.7 ton per ton, which is closer to the emission factors
reported in the IPCC 1996 Reference Guidelines than to the feedstock-only CO2 emission factor of 1.2 ton CO2 per ton ammonia reported by the EFMA.
Because it appears that the emission factors cited in the IPCC Guidelines may actually include natural gas used as fuel, we use the 1.2 tons/ton emission
factor developed by the EFMA.
Industrial Processes 4-11
-------
Table 4-16: Quantitative Uncertainty Estimates for C02 Emissions from Ammonia Manufacture and Urea Application
(Tg C02 Eq. and Percent)
. A.-it •• - - **
EIA for other years, and data for 1991 and previous years may
underestimate feedstock natural gas consumption, and therefore
the emission factor was used to estimate CO2 emissions from
ammonia production, rather than EIA data.
All ammonia production and subsequent urea production
was assumed to be from the same process—conventional
catalytic reforming of natural gas feedstock. However, actual
emissions may differ because processes other than catalytic
steam reformation and feedstocks other than natural gas may
have been used for ammonia production. Urea is also used for
other purposes than as a nitrogenous fertilizer. It was assumed
that 100 percent of the urea production and net imports are
used as fertilizer or in otherwise emissive uses. It is also
assumed that ammonia and urea are produced at collocated
plants from the same natural gas raw material.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-16) indicate that, on average, in 19
out of 20 times (i.e., there is a 95 percent probability), the
total greenhouse gas emissions estimate from Ammonia
Manufacture is within the range of approximately 8.0 to 11.3
Tg CO2 Eq. (or that the actual CO2 emissions are likely to
fall within the range of approximately 17 percent below and
17 percent above the emission estimate of 9.6 Tg CO2 Eq.).
For Urea Application, the total greenhouse gas emissions
estimate is within the range of approximately 7.4 to 8.7 Tg
CO2 Eq. (or that the actual CO2 emissions are likely to fall
within the range of approximately 8 percent below and 8
percent above the emission estimate of 8.0 Tg CO2 Eq.).
Recalculations Discussion
Ammonia and urea emissions for 2001 were adjusted to
reflect revised production information from the U.S. Census
Bureau (U.S. Census Bureau 2003). Revised 2001 ammonia
and urea production data both decreased by two percent.
These changes resulted in a two percent decrease in CO2
emissions from ammonia manufacture and a one percent
decrease in CO2 emissions from urea application.
4.4. Lime Manufacture
(IPCC Source Category 2A2)
Lime is an important manufactured product with many
industrial, chemical, and environmental applications. Its major
uses are in steel making, flue gas desulfurization (FGD) systems
at coal-fired electric power plants, construction, and water
purification. Lime has historically ranked fifth in total production
of all chemicals in the United States. For U.S. operations, the
term "lime" actually refers to a variety of chemical compounds.
These include calcium oxide (CaO), or high-calcium
quicklime; calcium hydroxide (Ca(OH)2), or hydrated lime;
dolomitic quicklime ([CaOMgO]); and dolomitic hydrate
([Ca(OH)2'MgO] or [Ca(OH)2.Mg(OH)2]).
Lime production involves three main processes: stone
preparation, calcination, and hydration. Carbon dioxide is
generated during the calcination stage, when limestone—
mostly calcium carbonate (CaCO3)—is roasted at high
temperatures in a kiln to produce CaO and CO2. The CO2 is
given off as a gas and is normally emitted to the atmosphere.
Some of the CO2 generated during the production process,
however, is recovered at some facilities for use in sugar refining
and precipitated calcium carbonate (PCC)3 production. It
is also important to note that, for certain applications, lime
reabsorbs CO2 during use (see Uncertainty, below).
Lime production in the United States—including Puerto
Rico—was reported to be 17,951 thousand metric tons in 2002
(USGS 2003). This resulted in estimated CO2 emissions of 12.3
Tg CO2 Eq. (12,304 Gg) (see Table 4-17 and Table 4-18).
Precipitated calcium carbonate is a specialty filler used in premium-quality coated and uncoated papers.
4-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
At the turn of the 20th Century, over 80 percent of lime
consumed in the United States went for construction uses.
The contemporary quicklime market is distributed across four
end-use categories as follows: metallurgical uses, 35 percent;
environmental uses, 28 percent; chemical and industrial uses,
24 percent, construction uses, 12 percent; and refractory
dolomite, one percent. In the construction sector, hydrated
lime is still used to improve durability in plaster, stucco, and
mortars. The use of hydrated lime for traditional building
decreased by about 5 percent in 2002 (USGS 2003).
Lime production in 2002 declined five percent from 2001,
the fourth consecutive drop in annual production. Overall, from
1990 to 2002, lime production has increased by 13 percent. The
increase in production is attributed in part to growth in demand for
environmental applications, especially flue gas desulfurization
technologies. In 1993, EPA completed regulations under the
Clean Air Act capping sulfur dioxide (SO2) emissions from
electric utilities. Lime scrubbers' high efficiencies and increasing
affordability have allowed the flue gas desulfurization end-use
to expand significantly over the years. Phase II of the Clean Air
Act Amendments, which went into effect on January 1, 2000,
remains the driving force behind the growth in the flue gas
desulfurization market (USGS 2003).
Methodology
During the calcination stage of lime manufacture, CO2
is given off as a gas and normally exits the system with
the stack gas. To calculate emissions, the amounts of high-
calcium and dolomitic lime produced were multiplied by
their respective emission factors. The emission factor is the
product of a constant reflecting the mass of CO2 released per
unit of lime and the average calcium plus magnesium oxide
(CaO + MgO) content for lime (95 percent for both types of
lime). The emission factors were calculated as follows:
For high-calcium lime: [(44.01 g/mole CO2) -=- (56.08
g/mole CaO)] x (0.95 CaO/lime) = 0.75 g CO2/g lime
For dolomitic lime: [(88.02 g/mole CO2) 4- (96.39 g/mole
CaO)] x (0.95 CaO/lime) = 0.87 g CO2/g lime
Production is adjusted to remove the mass of chemically
combined water found in hydrated lime, using the midpoint
of default ranges provided by the IPCC Good Practice
Guidance (IPCC 2000). These factors set the chemically
combined water content to 27 percent for high-calcium
hydrated lime, and 24 percent for dolomitic hydrated lime.
Table 4-17: Net CO? Emissions from Lime Manufacture
Year
Tg CQ2 Eg.
1990
mm
1996
1997
1998
1999
2000
2001
2002
11-2
13,5
13.7
13.9
13.5
13,3
12.8
12.3
Table 4-18: CO, Emissions from Lime Manufacture (Gg)
Year
Potential Recovered* Net Emissions
1990
11,730
(493)
11,238
1996
1997
1998
1999
2000
2001
2002
14,347
14,649
14,975
14,655
14,548
13,941
13,355
(S52)
(964)
(1,061)
CM 88)
(1,233)
(1,118)
(1,051)
13,495
13,685
13,914
13,466
13,315
12,823
12,304
* For sugar refining and precipitated calcium carbonate pradueBon.
Note: Totals may not sum due to independent rounding,
Lime production in the United States was 17,951
thousand metric tons in 2002 (USGS 2003), resulting in
potential CO2 emissions of 13.4 Tg CO2 Eq. Some of the
CO2 generated during the production process, however, was
recovered for use in sugar refining and precipitated calcium
carbonate (PCC) production. Combined lime manufacture
by these producers was 1,762 thousand metric tons in 2002.
It was assumed that approximately 80 percent of the CO2
involved in sugar refining and PCC was recovered, resulting
in actual CO2 emissions of 12.3 Tg CO2 Eq.
The activity data for lime manufacture and lime consumption
by sugar refining and PCC production for 1990 through 2002
(see Table 4-19) were obtained from USGS (1992,1994,1995,
1996,1997,1998,1999,2000,2001,2002,2003). Hydrated lime
production is reported separately in Table 4-20. The CaO and
CaO'MgO contents of lime were obtained from the IPCC Good
Practice Guidance (IPCC 2000). Since data for the individual
lime types (high-calcium and dolomitic) was not provided
prior to 1997, total lime production for 1990 through 1996 was
allocated according to the 1997 distribution. For sugar refining
and PCC, it was assumed that 100 percent of lime manufacture
Industrial Processes 4-13
-------
Table 4-19: Lime Production and Lime Use for Sugar Refining and PCC (Thousand Metric Tons)
Year
ite
ction**
Use for Sugar Refining and PCC
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2,895
2,838,
2;925
3,024-
3.30S
3,434
3,552
3,423
3,598
3,621
3,227-
3,051
826
964
1,023
1,279
1,374
i;sos
1,429:
1,616
1,779
1,992
2,067
1,874
1,762
Table 4-20: Hydrated Lime Production (Thousand Metric Tons)
Ytew
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
High-Calcium Hy
1,781 v
1,841
1,892
1,908;
i942
2,027
1,858
1,820
1,950
2,010
1,550
2,830;
1,500
drate Dolomitlc Hydrate
•"-•;•-- v '•: 31§ --
' :'-• "' '. 329 . ..
.'.'.,-:•-. ; :338 '
342
, .348
•- •'<>.•-• -.•'-ate-.
•->•'";•*•:• ;r 382 .
• :i -vfaK
• ,' , --" ' 383
-,. ,.-.: 298
421
447
. /:- 431
and consumption was high-calcium, based on communication
with the National Lime Association (Males 2003).
Uncertainty
Uncertainties in the emission estimate can be attributed
to slight differences in the chemical composition of these
products. Although the methodology accounts for various
formulations of lime, it does not account for the trace impurities
found in lime, such as iron oxide, alumina, and silica. Due to
differences in the limestone used as a raw material, a rigid
specification of lime material is impossible. As a result, few
plants manufacture lime with exactly the same properties.
In addition, a portion of the CO2 emitted during lime
manufacture will actually be reabsorbed when the lime is
consumed. As noted above, lime has many different chemical,
industrial, environmental, and construction applications. In
many processes, CO2 reacts with the lime to create calcium
carbonate (e.g., water softening). Carbon dioxide reabsorption
rates vary, however, depending on the application. For example,
100 percent of the lime used to produce precipitated calcium
carbonate reacts with CO2; whereas most of the lime used in
steel making reacts with impurities such as silica, sulfur, and
aluminum compounds. A detailed accounting of lime use
in the United States and further research into the associated
processes are required to quantify the amount of CO2 that is
reabsorbed.4 As more information becomes available, this
emission estimate will be adjusted accordingly.
In some cases, lime is generated from calcium carbonate
by-products at pulp mills and water treatment plants.5
The lime generated by these processes is not included in
the USGS data for commercial lime consumption. In the
pulping industry, mostly using the Kraft (sulfate) pulping
process, lime is consumed in order to causticize a process
liquor (green liquor) composed of sodium carbonate and
sodium sulfide. The green liquor results from the dilution
of the smelt created by combustion of the black liquor
where biogenic carbon is present from the wood. Kraft mills
recover the calcium carbonate "mud" after the causticizing
4 Representatives of the National Lime Association estimate that CO2 reabsorption that occurs from the use of lime may offset as much as a quarter of
the CO2 emissions from calcination (Males 2003).
5 Some carbide producers may also regenerate lime from their calcium hydroxide by-products, which does not result in emissions of CO2. In making
calcium carbide, quicklime is mixed with coke and heated in electric furnaces. The regeneration of lime in this process is done using a waste calcium
hydroxide (hydrated lime) [CaC2 + 2H2O ® C2H2 + Ca(OH)2], not calcium carbonate [CaCO3]. Thus, the calcium hydroxide is heated in the kiln to simply
expel the water [Ca(OH)2 + heat ® CaO + H2O] and no CO2 is released.
4-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-21: Quantitative Uncertainty Estimates for C02 Emissions from Lime Manufacture (Tg C02 Eq. and Percent)
Source
2002 Emission Estimate
Gas (TgC02Eq.)
Uncertainty Range Relative to Emission Estimate8
(?BC02le|.) (%)
Lower Bound Upper Bound Lower Bound Upper Bound
Lime Manufacture CD2
13,3
-9%
4-8%
operation and most sulfate mills recover the waste calcium
carbonate after the causticizing operation and calcine it
back into lime—thereby generating CO2—for reuse in the
pulping process. Although this re-generation of lime could
be considered a lime manufacturing process, the CO2 emitted
during this process is mostly biogenic in origin, and therefore
would not be included in Inventory totals.
In the case of water treatment plants, lime is used in the
softening process. Some large water treatment plants may
recover their waste calcium carbonate and calcine it into
quicklime for reuse in the softening process. Further research
is necessary to determine the degree to which lime recycling
is practiced by water treatment plants in the United States.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-21) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
the range of approximately 11.2 to 13.3 Tg CO2 Eq. (or that
the actual CO2 emissions are likely to fall within the range
of approximately 9 percent below and 8 percent above the
emission estimate of 12.3 Tg CO2 Eq.).
Recalculations Discussion
The 2001 production data of high calcium quicklime and
the 2001 CO2 recovery from sugar refining were revised in
the 2002 Minerals Yearbook (USGS 2003). These changes
resulted in a 0.3 percent decrease in 2001 net CO2 emissions
from lime manufacture.
4.5. Limestone and Dolomite Use
(IPCC Source Category 2A3)
Limestone (CaCO3) and dolomite (CaCO3MgCO3)6
are basic raw materials used by a wide variety of industries,
including construction, agriculture, chemical, metallurgy, glass
manufacture, and environmental pollution control. Limestone
is widely distributed throughout the world in deposits of
varying sizes and degrees of purity. Large deposits of limestone
occur in nearly every state in the United States, and significant
quantities are extracted for industrial applications. For some of
these applications, limestone is sufficiently heated during the
process to generate CO2 as a by-product. Examples of such
applications include limestone used as a flux or purifier in
metallurgical furnaces, as a sorbent in flue gas desulfurization
systems for utility and industrial plants, or as a raw material
in glass manufacturing and magnesium production.
In 2002, approximately 10,820 thousand metric tons of
limestone and 2,252 thousand metric tons of dolomite were
consumed for these applications. Overall, usage of limestone
and dolomite resulted in aggregate CO2 emissions of 5.8 Tg
CO2 Eq. (5,836 Gg) (see Table 4-22 and Table 4-23). Emissions
in 2002 increased 2 percent from the previous year and have
increased 5 percent overall from 1990 through 2002.
Methodology
Carbon dioxide emissions were calculated by multiplying
the quantity of limestone or dolomite consumed by the average
carbon content, approximately 12.0 percent for limestone
and 13.2 percent for dolomite (based on stoichiometry).
This assumes that all carbon is oxidized and released. This
methodology was used for flux stone, glass manufacturing,
flue gas desulfurization systems, chemical stone, mine dusting
or acid water treatment, acid neutralization, and sugar refining
and then converting to CO2 using a molecular weight ratio.
Traditionally, the production of magnesium metal was the
only other use of limestone and dolomite that produced CO2
emissions. At the start of 2001, there were two magnesium
production plants operating in the United States and they used
different production methods. One plant produced magnesium
metal using a dolomitic process that resulted in the release of
CO2 emissions, while the other plant produced magnesium
from magnesium chloride using a CO2-emissions-free process
' Limestone and dolomite are collectively referred to as limestone by the industry, and intermediate varieties are seldom distinguished.
Industrial Processes 4-15
-------
Table 4-22: C02 Emissions from Limestone & Dolomite Use (Tg C02 Eq.)
Activity
1996
4.2
0.4
2.0
0.1
1.1
7.8
1917
5.0
0.3
1.4
0.1
0.4
7.2
1998
5.1
0.2
1.2
0.1
0;9
7.4
1999
6.0
0
1.2
0.1
0.7
8.1
2000
2.8
0.4
1.8
0.1
0.9
6.0
2001
2.5
0.1
2.6
0.1
0;5
8J
2082
2.4
0.1
2.8
0.6
5.8
Flux Stone
Glass Making
F6D
Magnesium Production
Ofter Miscellaneous Uses
Total ~
Notes: Totals may not sum due to Independent founding. Other miscellaneous uses Include cnemical stone, mine dusting or acid watertreatment, acid
neutralization, and sugar refining.
Table 4-23: C02 Emissions from Limestone & Dolomite Use (Gg)
Activity
Flux Stone
Limestone
Dolomite
Glass Making
Limestone •
Dolomite
FGD
Magnesium Production
Other Miscellaneous Uses
Total
Notes: Totals may not sum due to
neutralization, and sugar refining.
1996
4,236
3,328
908
415
294
121
1,991
73
1,101
7,817
1997
5,023
3,963
1,060
319
319
0
1,426
73
401
7,242
1998
5,132
4,297
835
157
65
91
1,230
73
858
7,449
1999
6,030
4,265
1,765
0
0
0
1,240
73
713
8,057
2000
2,829
1,810
1,020
368
368
0
1,773
73
915
5,959
2001
2,514
1,640
874
113
113
0
2,551
53
501
5,733
2002
2,405
1,330
1,075
110
110
0
2,766
0
555
5,836
• miscellaneous uses include chemical stone, mine dusting or acid watertreatment, acid
called electrolytic reduction. However, the plant utilizing the
dolomitic process ceased its operations prior to the end of
2001, so the 2002 emissions from limestone and dolomite use
contain zero emissions from this particular sub-use.
Consumption data for 1990 through 2002 of limestone
and dolomite used for flux stone, glass manufacturing, flue
gas desulfurization systems, chemical stone, mine dusting or
acid water treatment, acid neutralization, and sugar refining
(see Table 4-24) were obtained from personal communication
with Valentine Tepordei of the USGS regarding data in the
Minerals Yearbook: Crushed Stone Annual Report (Tepordei
2002 and USGS 1993, 1995a, 1995b, 1996a, 1997a, 1998a,
1999a, 2000a, 200la, 2002). The production capacity data for
1990 through 2002 of dolomitic magnesium metal (see Table
4-25) also came from the USGS (1995c, 1996b, 1997b, 1998b,
1999b, 2000b, 2001b, 2002). During 1990 and 1992, the USGS
did not conduct a detailed survey of limestone and dolomite
consumption by end-use. Consumption figures for 1990 were
Table 4-24: Limestone and Dolomite Consumption (Thousand Metric Tons)
Activity
Flux Stone
Limestone
Dolomite
Glass Making
Limestone
Dolomite
FGD
Other Miscellaneous Uses
Total
1990
6,738
5,804
933
489
430
59
3,258
1,835
12,319
;996
466
564
902
922
669
253
523
481
392
1997
11,226
9,007
2,219
725
725
0
3,242
898
16,091
1998
11,514
9,767
1,748
340
149
191
2,795
1,933
16,582
1999
13,390
9,694
3,696
0
0.
0
2,819
1,620
17,830
2000
6,24*
4,113
2,t35
836
836
0
4,030
2,080
13,194
2001
iw
1,83!
258
258
0
5,798
1,138
12,751
2002
5,275
3,023
2,252
250
250
0
6,286
1,261
13J72
Note: "Other miscellaneous uses' includes chemical stone, mine dustfng or acid water treatment, acid neutralizaflon, and sugar refining.
4-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
estimated by applying the 1991 percentages of total limestone
and dolomite use constituted by the individual limestone
and dolomite uses to the 1990 total use figure. Similarly, the
1992 consumption figures were approximated by applying an
average of the 1991 and 1993 percentages of total limestone
and dolomite use constituted by the individual limestone and
dolomite uses to the 1992 total figure.
Additionally, each year the USGS withholds certain
limestone and dolomite end-uses due to confidentiality
agreements regarding company proprietary data. For the
purposes of this analysis, emissive end-uses that contained
withheld data were estimated using one of the following
techniques: (1) the value for all the withheld data points
for limestone or dolomite use was distributed evenly to all
withheld end-uses; (2) the average percent of total limestone
or dolomite for the withheld end-use in the preceding and
succeeding years; or (3) the average fraction of total limestone
or dolomite for the end-use over the entire time period.
Finally, there is a large quantity of crushed stone
reported to the USGS under the category "unspecified uses."
A portion of this consumption is believed to be limestone
or dolomite used for emissive end uses. The quantity listed
for "unspecified uses" was, therefore, allocated to each
reported end-use according to each end uses fraction of total
consumption in that year.7
Table 4-25: Dolomitic Magnesium Metal Production
Capacity (Metric Tons)
Uncertainty
Uncertainties in this estimate are due, in part, to
variations in the chemical composition of limestone. In
addition to calcium carbonate, limestone may contain
smaller amounts of magnesia, silica, and sulfur. The exact
specifications for limestone or dolomite used as flux stone
vary with the pyrometallurgical process, the kind of ore
processed, and the final use of the slag. Similarly, the quality
of the limestone used for glass manufacturing will depend
on the type of glass being manufactured.
Yfear
1990
1991
-1992
1993
1994
1995
•t f\n&
1996
1997
1QQfi
ibao
1999
2000
2001
2002 ,
Production Capacity
35,000
35,000
14,901
12,964
21,1tt
"• 22,212.;". .
jtn mm
40JTO
Jofii
4offi
- 40,000
29,167
: .'".** .,> ,-.••?:"•-;>.. "
Note: Production capacity for 2002 amounts to 2
U.S. production plant employing the dotonnitic |
mid-2001 (USGS 2002).
ttdown
Uncertainties also exist in the activity data. Much of the
limestone consumed in the United States is reported as "other
unspecified uses;" therefore, it is difficult to accurately allocate
this unspecified quantity to the correct end-uses. Also, some of
the limestone reported as "limestone" is believed to actually be
dolomite, which has a higher carbon content. Additionally, there
is significant inherent uncertainty associated with estimating
withheld data points for specific end uses of limestone and
dolomite. Lastly, the uncertainty of the estimates for limestone
used in glass making is especially high. Large fluctuations in
reported consumption exist, reflecting year-to-year changes in
the number of survey responders. The uncertainty resulting
from a shifting survey population is exacerbated by the gaps
in the time series of reports. However, since glass making
accounts for a small percent of consumption, its contribution
to the overall emissions estimate is low.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-26) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
Table 4-26: Quantitative Uncertainty Estimates for C02 Emissions from Limestone and Dolomite Use (Tg C02 Eq. and Percent)
Source
Lower Bound Upper Bound lower Bound Upper Bound
,419
6J
•17%
+18%
This approach was recommended by USGS.
Industrial Processes 4-17
-------
the range of approximately 4.9 to 6.9 Tg CO2 Eq. (or that
the actual CO2 emissions are likely to fall within the range
of approximately 17 percent below and 18 percent above the
emission estimate of 5.8 Tg CO2 Eq.).
Recalculations Discussion
The recalculation of limestone and dolomite consisted
of a correction in the way unspecified data, both reported and
estimated, was apportioned to the various emissive uses. This
change resulted in an average annual increase of 0.2 Tg CO2
Eq. (3 percent) in CO2 emissions from 1990 through 2001.
4.6. Soda Ash Manufacture
and Consumption (IPCC
Source Category 2A4)
Soda ash (sodium carbonate, Na2CO3) is a white
crystalline solid that is readily soluble in water and strongly
Table 4-27: C02 Emissions from Soda Ash Manufacture and
Consumption
Year
Tg C02 Eq.
1990
4.1
1996
1997
1998
1999
2000
2001
2002
4.2
4.4
4.3
4.2
4.2
4.1
4.1
Table 4-28: C02 Emissions from Soda Ash Manufacture and
Consumption (Gg)
Year Manufacture Consumption
Total
1990
1,431
2,710
4,141
1996
1997
1998
1999
2000
2001
2002
1,587
1,665
1,607
1,548
1,529
1,500
1,470
2,652
2,689
2,718
2,668
2,652
2,648
2,668
4,239
4,354
4,325
4,217
4,181
4,147
4,139
Note: Totals may not sum due to independent rounding.
alkaline. Commercial soda ash is used as a raw material
in a variety of industrial processes and in many familiar
consumer products such as glass, soap and detergents,
paper, textiles, and food. It is used primarily as an alkali,
either in glass manufacturing or simply as a material that
reacts with and neutralizes acids or acidic substances.
Internationally, two types of soda ash are produced—natural
and synthetic. The United States produces only natural
soda ash and is the largest soda ash-producing country in
the world. Trona is the principal ore from which natural
soda ash is made.
Only three states produce natural soda ash: Wyoming,
California, and Colorado. Of these three states, only
net emissions of CO2 from Wyoming were calculated.
This difference is a result of the production processes
employed in each state.8 During the production process
used in Wyoming, trona ore is treated to produce soda
ash. Carbon dioxide is generated as a by-product of this
reaction, and is eventually emitted into the atmosphere. The
one Colorado facility produces soda ash using nahcolite,
a different production process than is used in Wyoming,
and emissions from this process will be included in future
inventories. In addition, CO2 may also be released when
soda ash is consumed.
In 2002, CO2 emissions from the manufacture of soda
ash from trona were approximately 1.5 Tg CO2 Eq. (1,470
Gg). Soda ash consumption in the United States generated
2.7 Tg CO2 Eq. (2,668 Gg) in 2002. Total emissions from
soda ash in 2002 were 4.1 Tg CO2 Eq. (4,139 Gg) (see Table
4-27 and Table 4-28). Emissions have fluctuated since 1990.
These fluctuations were strongly related to the behavior of
the export market and the U.S. economy. Emissions in 2002
decreased by less than 1 percent from the previous year, and
have increased overall by less than 1 percent since 1990.
The United States has the world's largest deposits of
trona and represents about one-third of total world soda
ash output. The distribution of soda ash by end-use in
2002 was glass making, 48 percent; chemical production,
26 percent; soap and detergent manufacturing, 11 percent;
distributors, five percent; flue gas desulfurization, pulp and
paper production, water treatment, two percent each; and
miscellaneous, four percent (USGS 2003).
Q
In California, soda ash is manufactured using sodium carbonate-bearing brines instead of trona ore. To extract the sodium carbonate, the complex brines
are first treated with CO2 in carbonation towers to convert the sodium carbonate into sodium bicarbonate, which then precipitates from the brine solution.
The precipitated sodium bicarbonate is then calcined back into sodium carbonate. Although CO2 is generated as a by-product, the CO2 is recovered and
recycled for use in the carbonation stage and is not emitted.
4-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
The domestic 2002 market for soda ash was nearly
identical to that of 2001: a decline in the first period partially
offset by an increase in exports. Although the United States
continues to be the major supplier of world soda ash, China's
soda ash manufacturing capacity is rapidly increasing. This
will likely cause greater competition in Asian markets in the
future. The world market for soda ash is expected to grow
1.5 to 2 percent annually (USGS 2003).
Methodology
During the production process, trona ore is calcined in
a rotary kiln and chemically transformed into a crude soda
ash that requires further processing. Carbon dioxide and
water are generated as by-products of the calcination process.
Carbon dioxide emissions from the calcination of trona can
be estimated based on the following chemical reaction:
2(Na3H(CO3)2 x2H2O) -* 3Na2CO3 + 5H2O + CO2
[trona] [soda ash]
Based on this formula, approximately 10.27 metric tons
of trona are required to generate one metric ton of CO2. Thus,
the 15.1 million metric tons of trona mined in 2002 for soda
ash production (USGS 2003) resulted in CO2 emissions of
approximately 1.5 Tg CO2 Eq. (1,470 Gg).
Once manufactured, most soda ash is consumed in
glass and chemical production, with minor amounts in soap
and detergents, pulp and paper, flue gas desulfurization and
water treatment. As soda ash is consumed for these purposes,
additional CO2 is usually emitted. In these applications, it is
assumed that one mole of carbon is released for every mole
of soda ash used. Thus, approximately 0.113 metric tons of
carbon (or 0.415 metric tons of CO2) are released for every
metric ton of soda ash consumed.
The activity data for trona production and soda ash
consumption (see Table 4-29) were taken from USGS (1994,
1995,1996,1997,1998,1999,2000,2001,2002,2003). Soda
Table 4-29: Soda Ash Manufacture and Consumption
(Thousand Metric Tons)
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Manufacture*
14,700
14,700
14,900
14,500
14,600
16,500
16,300
17;100
16,500
15,900
15,700
15,400
15,100
Consumption
6,530
6,280
6,320
6,280
6,260
6,500
6,390
i,480
;8,S50
6,430
6,390
6,380
6,430
* Soda ash manufactured from trona ore only.
ash manufacture and consumption data were collected by the
USGS from voluntary surveys of the U.S. soda ash industry.
All six of the soda ash manufacturing operations in the United
States completed surveys to provide data to the USGS.
Uncertainty
Emissions from soda ash manufacture are considered
to have low associated uncertainty. Both the emission
factor and activity data are reliable. However, emissions
from soda ash consumption are dependent upon the type of
processing employed by each end-use. Specific information
characterizing the emissions from each end-use is limited.
Therefore, there is uncertainty surrounding the emission
factors from the consumption of soda ash.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-30) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
the range of approximately 3.8 to 4.4 Tg CO2 Eq. (or that
the actual CO2 emissions are likely to fall within the range
Table 4-30: Quantitative Uncertainty Estimates for C02 Emissions from Soda Ash Manufacture and Consumption
(Tg C02 Eq. and Percent)
2002 Emissio* Estimate
Uncertainty Range Relative to Emission Estimate8
Source
Lower Bound Upper Bound Lower Bound Upper Bound
Soda Ash Manufacture and
Consumption
CO,
4.1
3.8
4.4
-7%
+7%
a Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
Industrial Processes 4-19
-------
of approximately 7 percent below and 7 percent above the
emission estimate of 4.1 Tg CO2 Eq.).
Planned Improvements
Emissions from soda ash production in Colorado, which
is produced using the nahcolite production process, will be
investigated for inclusion in future inventories.
4.7. Titanium Dioxide Production
(IPCC Source Category 2B5)
Titanium dioxide (TiO2) is a metal oxide manufactured
from titanium ore, and is principally used as a pigment.
Titanium dioxide is a principal ingredient in white paint, and
TiO2 is also used as a pigment in the manufacture of white
paper, foods, and other products. There are two processes for
making TiO2, the chloride process and the sulfate process.
Carbon dioxide is emitted from the chloride process, which
uses petroleum coke and chlorine as raw materials and
emits process-related CO2. The sulfate process does not use
petroleum coke or other forms of carbon as a raw material
and does not emit CO2. In 2002, approximately 97 percent
of the titanium dioxide production capacity was chloride
process and the remainder was sulfate process.
The chloride process is based on the following chemical
reactions:
2 FeTiO3 + 7 C12 + 3 C -> 2 TiCl4 + 2 FeCl3 + 3 CO2
2 TiCl4 + 2 02 -> 2 Ti02 + 4 C12
The carbon in the first chemical reaction is provided
by petroleum coke, which is oxidized in the presence of
the chlorine and FeTiO3 (the Ti-containing ore) to form
CO2. The majority of U.S. TiO2 was produced in the United
States through the chloride process, and a special grade of
Table 4-31: CO? Emissions from Titanium Dioxide
Year
Tg C02 Eq.
Gg
1990
1,308
199i
1997
1998
1999
2000
2001
2002
1.7
1.8
1.8
1.9
1.9
1.9
2.0
1,836
1,819
1,853
1,918
1,857
1,997
petroleum coke is manufactured specifically for this purpose.
Emissions of CO2 from titanium dioxide production in 2002
were 2.0 Tg CO2 Eq. (1,997 Gg), an increase of 8 percent
from the previous year and 53 percent from 1990 due to
increasing production within the industry (see Table 4-31).
Methodology
Emissions of CO2 from titanium dioxide production
were calculated by multiplying annual titanium dioxide
production by chlorine process-specific emission factors.
Data were obtained for the total amount of titanium dioxide
produced each year, and it was assumed that 97 percent of
the total production in 2002 was produced using the chloride
process. An emission factor of 0.4 metric tons C/metric ton TiO2
was applied to the estimated chloride process production. It was
assumed that all titanium dioxide produced using the chloride
process was produced using petroleum coke, although some
titanium dioxide may have been produced with graphite or
other carbon inputs. The amount of petroleum coke consumed
annually in titanium dioxide production was calculated based
on the assumption that petroleum coke used in the process is
90 percent carbon and 10 percent inert materials.
The emission factor for the titanium dioxide chloride
process was taken from the report Everything You've Always
Wanted to Know about Petroleum Coke (Onder and Bagdoyan
1993). Titanium dioxide production data for 1990 through
2002 (see Table 4-32) were obtained from the U.S. Geological
Survey's (USGS) Minerals Yearbook: Titanium Annual Report
(USGS 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
1999, 2000, 2001, 2002, 2003). Data for the percentage of
the total titanium dioxide production capacity that is chloride
Table 4-32: Titanium Dioxide Production
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Metric Tons i
979,000
992,000
t ,140,000
1,180,000
1,210,000
1,2S0,0«
1,230,000
fj4Wie ;.; ',;,. /
'. . . t,3S0,i06\" ••„'. ' '.
• • - • i$S(MlB&: , . '• '"
IjfJ^rt'ifift^Y'
*v'"rvMrtJ!Jw- '*" •' ' • ' ' ' '
• t,3$&J3§fr'..:V'v,\
. _ ";!&Q^}jrV
4-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-33: Quantitative Uncertainty Estimates for C02 Emissions from Titanium Dioxide Production (Tg C02 Eq. and Percent)
Source
2002 Emission Estimate
Gas (TgC02Eq.)
Uncertainty Range Relative to Emission Estimate*
(%)
Lower Bound Upper Bound Lower Bound Upper Bound
Titanium DioxMe Production
CO,
2.0
1.6
2.4
-21%
-1-21%
9 Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
process for 1994 through 2002 were also taken from the
USGS Minerals Yearbook. Percentage chloride process data
were not available for 1990 through 1993, and data from the
1994 USGS Minerals Yearbook were used for these years.
Because a sulfate-process plant closed in September 2001,
the chloride process percentage for 2001 was estimated based
on a discussion with Joseph Gambogi, USGS Commodity
Specialist (2002). By 2002, only one sulfate plant remained
online in the United States. The composition data for petroleum
coke were obtained from Onder and Bagdoyan (1993).
Uncertainty
Although some titanium dioxide may be produced using
graphite or other carbon inputs, information and data regarding
these practices were not available. Titanium dioxide produced
using graphite inputs may generate differing amounts of CO2
per unit of titanium dioxide produced compared to the use of
petroleum coke. The most accurate method for these estimates
would be basing calculations on the amount of reducing agent
used in the process, rather than the amount of titanium dioxide
produced. These data were not available, however.
Also, annual titanium production is not reported by
USGS by the type of production process used (chloride or
sulfate). Only the percentage of total production capacity is
reported. It was assumed that titanium dioxide was produced
using the chloride process and the sulfate process in the
same ratio as the ratio of the total U.S. production capacity
for each process. This assumes that the chloride process
plants and sulfate process plants operate at the same level of
utilization. Finally, the emission factor was applied uniformly
to all chloride process production, and no data were
available to account for differences in production efficiency
among chloride process plants. In calculating the amount
of petroleum coke consumed in chloride process titanium
dioxide production, literature data were used for petroleum
coke composition. Certain grades of petroleum coke are
manufactured specifically for use in the titanium dioxide
chloride process, however this composition information was
not available.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-33) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
the range of approximately 1.6 to 2.4 Tg CO2 Eq. (or that
the actual CO2 emissions are likely to fall within the range
of approximately 21 percent below and 21 percent above the
emission estimate of 2.0 Tg CO2 Eq.).
4.8. Phosphoric Acid Production
(IPCC Source Category 2A7)
Phosphoric acid [H3PO4] is a basic raw material in the
production of phosphate-based fertilizers. Phosphate rock
is mined in Florida, North Carolina, Idaho, Utah, and other
areas of the United States and is used primarily as a raw
material for phosphoric acid production. The production of
phosphoric acid from phosphate rock produces byproduct
gypsum [CaSO4-2H2O], referred to as phosphogypsum.
The composition of natural phosphate rock varies
depending upon the location where it is mined. Natural
phosphate rock mined in the United States generally contains
inorganic carbon in the form of calcium carbonate (limestone)
and also may contain organic carbon. The chemical composition
of phosphate rock (francolite) mined in Florida is:
Ca10.x.y Na, Mgy (PO4)6.X(CO3)XF2+0 4x
The calcium carbonate component of the phosphate rock
is integral to the phosphate rock chemistry. Phosphate rock can
also contain organic carbon that is physically incorporated into
the mined rock but is not an integral component of the phosphate
rock chemistry. Phosphoric acid production from natural
phosphate rock is a source of CO2 emissions. The source of the
CO2 emissions is the chemical reaction of the inorganic carbon
(calcium carbonate) component of the phosphate rock.
Industrial Processes 4-21
-------
The phosphoric acid production process involves
chemical reaction of the calcium phosphate (Ca3(PO4)2)
component of the phosphate rock with sulfuric acid (H2SO4)
and recirculated phosphoric acid (H3PO4) (EFMA 1997). The
primary chemical reactions for the production of phosphoric
acid from phosphate rock are:
Ca3(P04)2 + 4H3P04 -» 3Ca(H2P04)2
3Ca(H2PO4)2 + 3H2SO4 + 6H2O ->
3CaS04 6H20 + 6H3PO4
The limestone (CaCO3) component of the phosphate rock
reacts with the sulfuric acid in the phosphoric acid production
process to produce calcium sulfate (phosphogypsum) and
carbon dioxide. The chemical reaction for the limestone-
sulfuric acid reaction is:
CaC03 + H2S04 + H20 -> CaSO4 2H2O + CO2
Total marketable phosphate rock production in 2002
was 37.4 million metric tons. Approximately 86 percent of
domestic phosphate rock production was mined in Florida and
North Carolina, with the remaining 14 percent of production
being mined in Idaho and Utah. Florida alone represented
more than 75 percent of domestic production. In addition, 2.7
million metric tons of crude phosphate rock was imported for
consumption in 2002. Marketable phosphate rock production,
including domestic production and imports for consumption,
increased by approximately 6 percent between 2001 and 2002.
However, over the 1990 to 2002 period, production decreased
by 15 percent. The 35.3 million metric tons produced in 2001
was the lowest production level recorded since 1965 and was
driven by a worldwide decrease in demand for phosphate
fertilizers. Domestic consumption is anticipated to increase
over the next several years as planted acreage and associated
phosphate fertilizer application increase (USGS, 2002). Total
CO2 emissions from phosphoric acid production were 1.3 Tg
CO2 Eq. (1,339 Gg) in 2002 (see Table 4-34).
Table 4-34: C02 Emissions from Phosphoric Acid Production
Year
Tg C02 Eq.
Gg
1990
1.5
1,529
1996
1997
1998
1999
2000
2001
2002
1.6
1.5
1.6
1.5
1.4
1.3
1.3
1,551
1,544
1,593
1,539
1,382
1,264
1,339
Methodology
Carbon dioxide emissions from production of phosphoric
acid from phosphate rock is calculated by multiplying the
average amount of calcium carbonate contained in the natural
phosphate rock by the amount of phosphate rock that is used
annually to produce phosphoric acid, accounting for domestic
production and net imports for consumption.
The USGS reports in the Minerals Yearbook, Phosphate
Rock, the aggregate amount of phosphate rock mined
annually in Florida and North Carolina and the aggregate
amount of phosphate rock mined annually in Idaho and Utah,
and reports the annual amounts of phosphate rock exported
and imported for consumption (see Table 4-35). Data for
domestic production of phosphate rock, exports of phosphate
rock, and imports of phosphate rock for consumption for
1990 through 2002 were obtained from USGS Mineral
Yearbook, Phosphate Rock (USGS 1994,1995,1996,1997,
1998, 1999, 2000, 2001, 2002, 2003).
The carbonate content of phosphate rock varies
depending upon where the material is mined. Composition
data for domestically mined and imported phosphate
rock were provided by the Florida Institute of Phosphate
Research (FIPR 2003). Phosphate rock mined in Florida
contains approximately 3.5 percent inorganic carbon (as
CO2), and phosphate rock imported from Morocco contains
approximately 5 percent inorganic carbon (as CO2). Calcined
phosphate rock mined in North Carolina and Idaho contains
approximately 1.5 percent and 1.0 percent inorganic carbon
(as CO2), respectively (see Table 4-36).
Carbonate content data for phosphate rock mined in Florida
are used to calculate the CO2 emissions from consumption
of phosphate rock mined in Florida and North Carolina (85
percent of domestic production) and carbonate content data for
phosphate rock mined in Morocco are used to calculate CO2
emissions from consumption of imported phosphate rock. The
CO2 emissions calculation is based on the assumption that all of
the domestic production of phosphate rock is used in uncalcined
form. The USGS reported that one phosphate rock producer
in Idaho is producing calcined phosphate rock, however, no
production data were available for this single producer (USGS
2003). Carbonate content data for uncalcined phosphate rock
mined in Idaho and Utah (14 percent of domestic production in
2002) were not available, and carbonate content was therefore
estimated from the carbonate content data for calcined phosphate
rock mined in Idaho.
4-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-35: Phosphate Rock Domestic Production, Exports, and Imports (Thousand Metric Tons)
Location/Year
U.3,ft«i«*w >:;:
IDSOT
Exports -FL&NC
Imports • Morocco
Tola 1 U.S. Consu mption
"" '= ,42,494 V1
: f ,3« 1
6,240 J
451 :
44,011
1996
38,100
5,480
1,570
1,800
43,790
ttW
3&6G4
5T496
335
1,830
43,595
im
38,000
5,840
378
1,760
45,022
f«8
. 35,900
5,540
272
2,170
43,338
2000
31,900
• 5,470
299
1,930
39,001
mi
28,100
4,jm
r
2,500
35,321
2002
2f,800
4,920
39
2,700
37,381
Source: US6S, 2003,2002,2001,2000,1999,1998,1997,1996,1995.
Table 4-36: Chemical Composition of Phosphate Rock (percent by weight)
Composition
Total Carton fas C)
Inorganic Carbon (as C)
Organic Carbon (as C)
Inorganic Carbon (as C02)
Central Florida
1:60
1,0
0,60
3.67
North Florida
1.76:
0.93
0.83
3.43
North Carolina
(calcined)
0.78
0.41
0.35
1.50
Idaho (calcined)
0.60
0.27
to
Morocco
1,56
1.46
0.1.
5.0
Source: RPR 2003
-None
The CO2 emissions calculation methodology is based
on the assumption that all of the inorganic carbon (calcium
carbonate) content of the phosphate rock reacts to CO2 in the
phosphoric acid production process and is emitted with the
stack gas. The methodology also assumes that none of the
organic carbon content of the phosphate rock is converted
to CO2 and that all of the organic carbon content remains in
the phosphoric acid product.
Uncertainty
Phosphate rock production data used in the emission
calculations are developed by the USGS through monthly and
semiannual voluntary surveys of the eleven companies that
owned phosphate rock mines during 2002. The phosphate rock
production data are not considered to be a significant source
of uncertainty, because all eleven of the domestic phosphate
rock producers are reporting their annual production to the
USGS. Data for imports for consumption and exports of
phosphate rock used in the emission calculation are based on
international trade data collected by the U.S. Census Bureau.
These U.S. government economic data are not considered to
be a significant source of uncertainty.
In addition, the carbonate composition of domestic
phosphate rock could potentially vary by ±1 percent (i.e., from
2.5 percent to 4.5 percent) based on the carbonate content data
provided by the FIPR. An assumed increase of one percent in
the carbonate content (i.e., from 3.5 percent to 4.5 percent)
translates into an approximately 20 percent increase in the
calculated CO2 emissions from phosphoric acid production.
One source of potentially significant uncertainty in the
calculation of CO2 emissions from phosphoric acid production
is the data for the carbonate composition of phosphate rock.
The composition of phosphate rock varies depending upon
where the material is mined, and may also vary over time. Only
one set of data from the Florida Institute of Phosphate Research
was available for the composition of phosphate rock mined
domestically and imported, and data for uncalcined phosphate
rock mined in North Carolina and Idaho were unavailable.
Inorganic carbon content (as CO2) of phosphate rock could
vary ± 1 percent from the data included in Table 4-36, resulting
in a variation in CO2 emissions of ±20 percent. Another source
of uncertainty is the disposition of the organic carbon content
of the phosphate rock. A representative of the FIPR indicated
that in the phosphoric acid production process the organic
carbon content of the mined phosphate rock generally remains
in the phosphoric acid product, which is what produces the
color of the phosphoric acid product (FIPR 2003a). Organic
carbon is therefore not included in the calculation of CO2
emissions from phosphoric acid production. However, if,
for example, 50 percent of the organic carbon content of the
phosphate rock were to be emitted as CO2 in the phosphoric
acid production process, the CO2 emission estimate would
increase by on the order of 50 percent.
Industrial Processes 4-23
-------
Table 4-37: Quantitative Uncertainty Estimates for C02 Emissions from Phosphoric Acid Production (Tg C02 Eq. and Percent)
Source
2002 Emission Estimate
(Tp.C02Eq.)
Uncertainty flange Relative to Emission Estimate8
Lower Bound Upper Bound Lower Bound Upper Bound
Phosphoric Acid Production C02
- 1.3
1.0
1.7
-26%
«*-28%
3 Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence Interval.
A third source of uncertainty is the assumption that all
domestically produced phosphate rock is used in phosphoric acid
production and used without first being calcined. Calcination
of the phosphate rock would result in conversion of some of
the organic carbon in the phosphate rock into CO2. However,
according to the USGS, only one producer in Idaho is currently
calcining phosphate rock, and no data were available concerning
the annual production of this single producer (USGS 2003).
Total production of phosphate rock in Utah and Idaho combined
amounts to approximately 14 percent of total domestic production
in 2002. If it is assumed that 100 percent of the reported domestic
production of phosphate rock for Idaho and Utah was first
calcined, and it is assumed that 50 percent of the organic carbon
content of the total production for Idaho and Utah was converted
to CO2 in the calcination process, the CO2 emission estimate
would increase by on the order of 10 percent.
Finally, USGS indicated that 5 percent of domestically
produced phosphate rock is used to manufacture elemental
phosphorus and other phosphorus-based chemicals, rather
than phosphoric acid (USGS 2003a). According to USGS,
there is only one domestic producer of elemental phosphorus,
in Idaho, and no data were available concerning the annual
production of this single producer. Elemental phosphorus is
produced by reducing phosphate rock with coal coke, and
it therefore is anticipated that 100 percent of the carbonate
content of the phosphate rock will be converted to CO2 in
the elemental phosphorus production process. The CO2
emissions calculation also is based on the assumption that
phosphate rock consumption other than for phosphoric acid
production (approximately 5 percent of total phosphate rock
consumption) also results in emission of 100 percent of the
inorganic carbon content of the phosphate rock but none of
the organic carbon content, as CO2. If none of the inorganic
carbon were to be emitted from these other processes, the
CO2 emissions estimate could decrease by on the order of 5
percent. If all of the organic carbon and inorganic carbon were
to be emitted from these other processes the CO2 emissions
estimate could increase by on the order of 5 percent.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-37) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
the range of approximately 1.0 to 1.7 Tg CO2 Eq. (or that
the actual CO2 emissions are likely to fall within the range
of approximately 26 percent below and 28 percent above the
emission estimate of 1.3 Tg CO2 Eq.).
Recalculations Discussion
Carbon dioxide emissions from phosphoric acid
production from phosphate rock are being reported for the
first time in this report. Phosphoric acid production is being
added as a result of ongoing research into sources of carbon
dioxide emissions from mineral processing industries.
Planned Improvements
The estimate of CO2 emissions from phosphoric
acid production could be improved through collection of
additional data. Additional data is being collected concerning
the carbonate content of uncalcined phosphate rock mined
in various locations in the United States and imported to
improve the CO2 emissions estimate. Additional research will
also be conducted concerning the disposition of the organic
carbon content of the phosphate rock in the phosphoric acid
production process. Only a single producer of phosphate
rock is calcining the product, and only a single producer is
manufacturing elemental phosphorus. Annual production data
for these single producers will probably remain unavailable.
4.9. Ferroalloy Production (IPCC
Source Category 2C2)
Carbon dioxide is emitted from the production of several
ferroalloys. Ferroalloys are composites of iron and other
elements such as silicon, manganese, and chromium. When
incorporated in alloy steels, ferroalloys are used to alter the
4-24 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
material properties of the steel. Estimates from two types of
ferrosilicon (25 to 55 percent and 56 to 95 percent silicon),
silicon metal (about 98 percent silicon), and miscellaneous
alloys (36 to 65 percent silicon) have been calculated.
Emissions from the production of ferrochromium and
ferromanganese are not included here because of the small
number of manufacturers of these materials in the United
States. Subsequently, government information disclosure
rules prevent the publication of production data for these
production facilities. Similar to emissions from the production
of iron and steel, CO2 is emitted when metallurgical coke is
oxidized during a high-temperature reaction with iron and
the selected alloying element. Due to the strong reducing
environment, CO is initially produced. The CO is eventually
oxidized to CO2. A representative reaction equation for the
production of 50 percent ferrosilicon is given below:
Fe2O3 + SiO2 + 7C -> 2FeSi + 7CO
Emissions of CO2 from ferroalloy production in 2002
were 1.2 Tg CO2 Eq. (1,237 Gg) (see Table 4-38), a 7 percent
reduction from the previous year and a 38 percent reduction
since 1990.
Methodology
Emissions of CO2 from ferroalloy production were
calculated by multiplying annual ferroalloy production by
material-specific emission factors. Emission factors taken
from the Revised 1996 IPCC Guidelines (IPCC/UNEP/
OECD/IEA 1997) were applied to ferroalloy production.
For ferrosilicon alloys containing 25 to 55 percent silicon
and miscellaneous alloys (including primarily magnesium-
ferrosilicon, but also including other silicon alloys)
containing 32 to 65 percent silicon, an emission factor for
50 percent silicon ferrosilicon (2.35 tons CO2/ton of alloy
Table 4-39: Production of Ferroalloys (Metric Tons)
Table 4-38: C02 Emissions from Ferroalloy Production
Year
TgC02Eq.
fit
1990
1996 ^
1997
1998
1999
2000
2001 :
2002
2.0
2.0
2.6
2.0
1.7
1!3
1.2
/, " ' - „ -Jt 'Y '
••• HM* '• '
2,038
z,m
1i99i;
t.Jftt ,
•• - ..!#*>.• -
1,23?
produced) was applied. Additionally, for ferrosilicon alloys
containing 56 to 95 percent silicon, an emission factor for
75 percent silicon ferrosilicon (3.9 tons CO2 per ton alloy
produced) was applied. The emission factor for silicon
metal was assumed to be 4.3 tons CO2/ton metal produced.
It was assumed that 100 percent of the ferroalloy production
was produced using petroleum coke using an electric arc
furnace process (IPCC/UNEP/OECD/IEA 1997), although
some ferroalloys may have been produced with coking coal,
wood, other biomass, or graphite carbon inputs. The amount
of petroleum coke consumed in ferroalloy production was
calculated assuming that the petroleum coke used is 90
percent carbon and 10 percent inert material.
Ferroalloy production data for 1990 through 2002 (see
Table 4-39) were obtained from the U.S. Geological Survey's
(USGS) Minerals Yearbook: Silicon Annual Report (USGS
1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2000, 2001, 2002, 2003). Until 1999, the USGS reported
production of ferrosilicon containing 25 to 55 percent
silicon separately from production of miscellaneous alloys
containing 32 to 65 percent silicon; beginning in 1999, the
USGS reported these as a single category (see Table 4-39).
Ferrosilicon 25%-55% Ferrosilicon 56%-95%
Misc. Alloys (32-65%)
1190
.''.';'ttS96:' '•""•"'
1997
1918
1999
2000
2001
2002
>"' ;T7'--'^g£J|jg'- "'jr.':'-*'-;"
175,000
162,000
252,000
229,000
167,000
156,000
• 132,080 :
147,000
147,000
145,000
100,000
89,000
98,600
^••••'^ '•"^ys^a^:^"".'.'-"--
187,086
115,000
195,000
184,000
137,600
113$08
•-•••'•••''' 'J'":^tfiUQBft-'"' '-•"-" •
108,OM
99,800
NA
NA
NA
NA
NA (Not Available)
Industrial Processes 4-25
-------
Table 4-40: Quantitative Uncertainty Estimates for C02 Emissions from Ferroalloy Production (Tg C02 Eq. and Percent)
Source
Gas
Lower Bound Upper Bound Lower Bound Upper Bound
Ferroalloy Production C02
t,2
1.1
1.4
-9%
1 Range of emissions estimates predicted by Monte Carto Stochastic Simulation for a 95% confidence Interval.
The composition data for petroleum coke was obtained from
Onder and Bagdoyan (1993).
Uncertainty
Although some ferroalloys may be produced using wood
or other biomass as a carbon source, information and data
regarding these practices were not available. Emissions from
ferroalloys produced with wood or other biomass would not
be counted under this source because wood-based carbon is of
biogenic origin.9 Emissions from ferroalloys produced with
coking coal or graphite inputs would be counted in national
trends, but may generate differing amounts of CO2 per unit
of ferroalloy produced compared to the use of petroleum
coke. The most accurate method for these estimates would be
basing calculations on the amount of reducing agent used in
the process, rather than the amount of ferroalloys produced.
These data were not available, however.
Also, annual ferroalloy production is now reported by
the USGS in three broad categories: ferroalloys containing
25 to 55 percent silicon (including miscellaneous alloys),
ferroalloys containing 56 to 95 percent silicon, and silicon
metal. It was assumed that the IPCC emission factors apply
to all of the ferroalloy production processes, including
miscellaneous alloys. Finally, production data for silvery
pig iron (alloys containing less than 25 percent silicon) are
not reported by the USGS to avoid disclosing company
proprietary data. Emissions from this production category,
therefore, were not estimated.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-40) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
the range of approximately 1.1 to 1.4 Tg CO2 Eq. (or that
the actual CO2 emissions are likely to fall within the range
of approximately 9 percent below and 9 percent above the
emission estimate of 1.2 Tg CO2 Eq.).
4.10. Carbon Dioxide Consumption
(IPCC Source Category 2B5)
Carbon dioxide (CO2) is used for a variety of applications,
including food processing, chemical production, carbonated
beverages, refrigeration, and enhanced oil recovery (EOR).
Carbon dioxide used for EOR is injected into the ground to
increase reservoir pressure, and is considered for the purposes
of this analysis to remain sequestered in the underground
formations.10 For the most part, however, CO2 used in
non-EOR applications will eventually be released to the
atmosphere.
Carbon dioxide is produced from a small number of
natural wells, as a by-product from the production of chemicals
(e.g., ammonia), or separated from crude oil and natural gas.
Depending on the raw materials that are used, the byproduct
CO2 generated during production processes may already be
accounted for in the CO2 emission estimates from fossil fuel
consumption (either during combustion or from non-energy
uses). For example, ammonia is primarily manufactured
using natural gas as both a feedstock and energy source.
Carbon dioxide emissions from natural gas combustion
for ammonia production are accounted for in the Energy
chapter under Fossil Fuel Combustion and, therefore, are not
included here. Carbon dioxide emissions from natural gas
used as feedstock for ammonia production are accounted for
in this chapter under Ammonia Manufacture and, therefore,
are also not included under Carbon Dioxide Consumption.
Carbon dioxide is also produced as a byproduct of crude oil
9 Emissions and sinks of biogenic carbon are accounted for in the Land-Use Change and Forestry chapter.
10 It is unclear to what extent the CO, used for EOR will be re-released. For example, the CO2 used for EOR may show up at the wellhead after a few
years of injection (Hangebrauk et al. 1992). This CO,, however, is typically recovered and re-injected into the well. More research is required to determine
the amount of CO2 that in fact escapes from EOR operations. For the purposes of this analysis, it is assumed that all of the CO2 used in EOR remains
sequestered.
4-26 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
and natural gas production. This CO2 may be emitted directly
to the atmosphere, reinjected into underground formations,
used for EOR, or sold for other commercial uses. Carbon
dioxide separated from crude oil and natural gas has not been
estimated.'' Therefore, the only CO2 consumption that is
accounted for here is CO2 produced from natural wells other
than crude oil and natural gas wells.
There are two such facilities currently in operation,
one in Mississippi and one in New Mexico, both of which
produce CO2 for use in EOR and for use in other commercial
applications (e.g., chemical manufacturing). In 2002,
CO2 emissions from these two facilities not accounted
for elsewhere were 1.3 Tg CO2Eq. (1,272 Gg) (see Table
4-41). This amount represents an increase of 50 percent
from the previous year and an increase of 43 percent from
emissions in 1990. This increase was due to an increase in
the reported production for use in industrial applications
from one facility.
Methodology
Carbon dioxide emission estimates for 2001 and
2002 were based on production data for the two facilities
currently producing CO2 from natural wells. Some of the
CO2 produced by these facilities is used for EOR and some is
used for other applications (e.g., chemical manufacturing).
Carbon dioxide production from these two facilities that
was used for EOR is assumed to remain sequestered and
is not included in the CO2 emissions totals. It is assumed
that 100 percent of the CO2 production used for end-use
applications other than EOR is eventually released into
the atmosphere.
Carbon dioxide production data for the fourth quarter
of 2001 and fourth quarter of 2002 for the Jackson Dome,
Mississippi facility, and the percentage of total production
that was used in EOR and non-EOR applications, were
obtained from the Annual Reports for Denbury Resources,
the operator of the facility (Denbury Resources 2001;
Denbury Resources 2002). Fourth quarter production data
were annualized for the entire calendar years for 2001 and
2002. Carbon dioxide production data for the Bravo Dome,
New Mexico facility were obtained from the New Mexico
Bureau of Geology and Mineral Resources for the years
Table 4-41: C02 Emissions from Carbon Dioxide Consumption
Year
TgC02Eq.
SSI
1
1987
1998
1990
2m
2001
2002
.-• 1492-'.
1990 through 2000 (Broadhead 2003). According to the New
Mexico Bureau, the amount of carbon dioxide produced from
Bravo Dome for use in non-EOR applications is less than
one percent of total production. Production data for 2001
and 2002 were not available for Bravo Dome. Production for
2001 and 2002 for Bravo Dome is assumed to be the same
as the production for the year 2000.
Denbury Resources acquired the Jackson Dome facility
in 2001, and CO2 production data for the facility are not
available for years prior to 2001. Therefore for 1990 through
2000, CO2 emissions from CO2 consumption are estimated
based on the total annual domestic commercial consumption
of CO2, as reported by the U.S. Census Bureau, multiplied by
the percentage of the total domestic non-EOR consumption
that was provided by the Jackson Dome and Bravo Dome
facilities; the two facilities that were producing CO2 from
natural wells in 2001. The total domestic consumption of
CO2 as reported by the U.S. Census Bureau was about
11,414 thousand metric tons in 2001. The total non-EOR CO2
produced from natural wells in 2001 was about 850 thousand
metric tons, corresponding to 7.4 percent of the total domestic
CO2 consumption. This 7.4 percent factor was applied to the
annual CO2 consumption data for the years 1990 through
2000 as reported by the U.S. Census Bureau to estimate
annual CO2 emissions from consumption of CO2 produced
from natural wells. The remaining 92.6 percent of the total
annual CO2 consumption is assumed either to be accounted
for in the CO2 emission estimates from other categories
(the most important being Fossil Fuel Combustion) or to be
produced from biogenic sources (e.g., grain fermentation)
that are not accounted for here.
The United States is in the process of developing a methodology to account for CO2 emissions from Natural Gas Systems and Petroleum Systems for
inclusion in future Inventory submissions. For more information please see Annex 5.
Industrial Processes 4-27
-------
Table 4-42: Carbon Dioxide Consumption
1997
1998
1999
2000
2W1
2982
11,8*3,388-
13,354*282
Carbon dioxide consumption data (see Table 4-42) for
years 1991 and 1992 were obtained from Industry Report 1992,
provided by the U.S. Census Bureau. Consumption data are
not available for 1990, and therefore CO2 consumption data for
1990 is assumed to be equal to that for 1991. Consumption data
for 1993 and 1994 were obtained from U.S. Census Bureau
Manufacturing Profile, 1994. Consumption data for 1996
through 2002 were obtained from the U.S. Census Bureau's
Industry Report, 1996, 1998, 2000, 2002.
Uncertainty
Uncertainty exists in the assumed allocation of CO2
produced from fossil fuel by-products and biogenic sources
(92.6 percent) and CO2 produced from natural wells (7.4
percent) for the years 1990 through 2000. The allocation
for these years is assumed to be the same allocation as for
2001, the last year for which data are available to calculate
the allocation. Uncertainty also exists with respect to the
number of facilities that are currently producing CO2 from
natural wells and for which CO2 emissions are not accounted
for elsewhere. Research indicates that there are only two
such facilities, however, additional facilities may exist that
have not been identified. In addition, it is possible that CO2
recovery exists in particular production and end-use sectors
that are not accounted for elsewhere. Such recovery may or
may not affect the overall estimate of CO2 emissions from
CO2 is applied. For example, research has identified one
ammonia production facility that is recovering CO2 for use in
EOR. Such CO2 is assumed to remain sequestered. Recovery
of CO2 from ammonia production facilities for use in EOR
is discussed in this chapter under Ammonia Production.
Further research is required to determine whether CO2 is
being recovered from other facilities for application to end
uses that are not accounted for elsewhere.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-43) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
the range of approximately 1.1 to 1.4 Tg CO2 Eq. (or that
the actual CO2 emissions are likely to fall within the range
of approximately 10 percent below and 10 percent above the
emission estimate of 1.3 Tg CO2 Eq.).
Recalculations Discussion
The methodology used to calculate CO2 consumption
was revised because the underlying assumption upon which
the previous methodology was based, that 20 percent of the
CO2 produced for domestic consumption was from "natural
sources" is more than ten years out of date and conflicts with
more recently available data. Research conducted indicates
that there are only two facilities producing CO2 from natural
sources for domestic non-EOR consumption. The estimate
of CO2 emissions from CO2 Consumption for the years
2001 and 2002 has been revised and is now based on actual
production data for these two facilities.
For years prior to 2001, estimates have been updated
and are now based on total annual domestic commercial
consumption of CO2, as reported by the U.S. Census Bureau,
multiplied by the percentage of the total domestic non-
EOR consumption that was provided by the two facilities
producing CO2 from natural wells in 2001 (7.4 percent.)
The CO2 consumption published by the U.S. Census
Bureau is being used for the current methodology because
that sector depending upon the end use to which the recovered
Table 4-43: Quantitative Uncertainty Estimates for C02 Emissions from Carbon Dioxide Consumption (Tg C02 Eq. and Percent)
Source
Gas
Uncertainty Range Relative
lower Bound Upper Bound
Carbon Dioxide Consumption C02
1.3
-,•••• ,,114; ••: ..:.V.VJQ%'-V. v
4-28 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
the U.S. Census Bureau data are public, contain actual CO2
consumption collected from CO2 producers and consumers,
and cover all years except 1990. Additionally, the Census
Bureau provides documentation that can be used as a basis
for uncertainty analysis.
These changes in the methodology and data sources used
to calculate CO2 emissions from CO2 consumption resulted
in an average annual decrease of 0.2 Tg CO2 Eq. (19 percent)
from previous estimates.
A 2001 industry publication (Sim 2001) provides data
to indicate that the assumption that 20 percent of domestic
CO2 consumption is derived from natural sources does not
reflect current industry conditions. This reference provides
a breakdown of both CO2 production and consumption by
industry sector for the year 2000. Sim (2001) indicates that
9.9 million short tons of CO2 were produced in 2000 for
industrial consumption. For the year 2000, 35 percent of the
reported domestic production sold in industry was produced
by the recovery of CO2 from ammonia production. Carbon
dioxide produced from refineries and from oil and gas wells
each accounted for 21 percent of domestic CO2 production.
Carbon dioxide recovered from ethanol production accounted
for 14 percent of domestic production, and CO2 produced
from cogeneration and other sources accounted for the
remaining 9 percent of domestic production. Neither the CO2
production data reported in Sim (2001) nor the production
data published by the Census Bureau include all of the CO2
produced from natural wells for use for EOR, which in 2000
was more than 22 million metric tons. Sim (2001) also
indicates that for the year 2000, 70 percent of domestic CO2
reported consumed in commerce (a total of 7.5 million short
tons) was used for refrigeration or food production, including
dry ice and beverage carbonation. Of the remaining reported
consumption, 10 percent was used in manufacturing processes,
7 percent was used for oil recovery, and 13 percent was used
in other applications. Neither the CO2 consumption data
reported by Sim (2001) nor the Census Bureau consumption
data include all of the CO2 used for enhanced oil recovery.
4.11. Petrochemical Production
(IPCC Source Category 2B5)
Methane is released, in small amounts, during the
production of some petrochemicals. Petrochemicals are
chemicals isolated or derived from petroleum or natural
gas. Emissions are presented here from the production of
five chemicals: carbon black, ethylene, ethylene dichloride,
styrene, and methanol.
Carbon black is an intensely black powder generated
by the incomplete combustion of an aromatic petroleum
feedstock. Most carbon black produced in the United States
is added to rubber to impart strength and abrasion resistance,
and the tire industry is by far the largest consumer. Ethylene is
consumed in the production processes of the plastics industry
including polymers such as high, low, and linear low density
polyethylene (HOPE, LDPE, LLDPE), polyvinyl chloride
(PVC), ethylene dichloride, ethylene oxide, and ethylbenzene.
Ethylene dichloride is one of the first manufactured chlorinated
hydrocarbons with reported production as early as 1795. In
addition to being an important intermediate in the synthesis
of chlorinated hydrocarbons, ethylene dichloride is used as an
industrial solvent and as a fuel additive. Styrene is a common
precursor for many plastics, rubber, and resins. It can be found
in many construction products, such as foam insulation, vinyl
flooring, and epoxy adhesives. Methanol is an alternative
transportation fuel as well as a principle ingredient in windshield
wiper fluid, paints, solvents, refrigerants, and disinfectants. In
addition, methanol-based acetic acid is used in making PET
plastics and polyester fibers. The United States produces close
to one quarter of the world's supply of methanol.
Aggregate emissions of CH4 from petrochemical
production in 2002 were 1.5 Tg CO2 Eq. (72 Gg) (see Table
4-44), an increase of 6 percent from the previous year and
30 percent from 1990.
Methodology
Emissions of CH4 were calculated by multiplying annual
estimates of chemical production by an emission factor. The
following factors were used: 11 kg CH4/metric ton carbon
Table 4-44: CH4 Emissions from Petrochemical Production
Year
TgC02Eq.
1990
. tsie —
1997
1998
1999
2000
2001
2002
••••• 1.6 - > :
1.6
1.7
1,7
1.7
1.4
1.5
/ n
78
80
81
80
68
72
Industrial Processes 4-29
-------
Table 4-45: Production of Selected Petrochemicals (Thousand Metric Tons)
Chemical
Carfjotfilaek
-•
Ethylene Dichloride
Serene
Methane!
1997
1998
5,280
1,588
28,088
W.324
5,t71
5,743
t,6J0
23,474"
ti,«
3,183
5JW
, > 23,623
"4288.
v 4,874
-3,289
Table 4-46: Quantitative Uncertainty Estimates for CH4 Emissions from Petrochemical Production (Tg C02 Eq. and Percent)
Source
Uncertainty Range Relative to Emission Estimate8
Lower Bound Upper Bound
1,5
1.4
tft
4-8%
1 Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
black, 1 kg CH4/metric ton ethylene, 0.4 kg CH4/metric ton
ethylene dichloride,'2 4 kg CH4/metric ton styrene, and 2 kg
CH4/metric ton methanol. These emission factors were based
upon measured material balances. Although the production
of other chemicals may also result in CH4 emissions, there
were not sufficient data to estimate their emissions.
Emission factors were taken from the Revised 1996
IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997). Annual
production data for 1990 (see Table 4-45) were obtained
from the Chemical Manufacturer's Association Statistical
Handbook (CMA 1999). Production data for 1991 through
2002 were obtained from the American Chemistry Council's
Guide to the Business of Chemistry (2003).
Uncertainty
The emission factors used here were based on a limited
number of studies. Using plant-specific factors instead of
average factors could increase the accuracy of the emission
estimates, however, such data were not available. There
may also be other significant sources of CH4 arising from
petrochemical production activities that have not been
included in these estimates.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-46) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
the range of approximately 1.4 to 1.6 Tg CO2 Eq. (or that
the actual CH4 emissions are likely to fall within the range
of approximately 7 percent below and 8 percent above the
emission estimate of 1.5 Tg CO2 Eq.).
Recalculations Discussion
The estimates of petrochemical emissions for 2000
and 2001 have been revised due to methanol production
modifications in the Guide to the Business of Chemistry
2002. Historical data for methanol production in 2000
decreased from 5,221 thousand metric tons to 4,876;
methanol production for 2001 also decreased from 5,053
to 3,402 thousand metric tons. These changes resulted in a
decrease of less than one percent and four percent of total
petrochemical emissions for 2000 and 2001, respectively.
4.12. Silicon Carbide Production
(IPCC Source Category 2B4)
Methane is emitted from the production of silicon carbide,
a material used as an industrial abrasive. To make silicon
carbide (SiC), quartz (SiO2) is reacted with carbon in the form
of petroleum coke. Methane is produced during this reaction
from volatile compounds in the petroleum coke. Although CO2
is also emitted from this production process, the requisite data
were unavailable for these calculations. However, emissions
associated with the utilization of petroleum coke in this process
are accounted for under the Non-Energy Uses of Fossil Fuel
' 2 The emission factor obtained from 1PCC/UNEP/OECD/IEA (1997), page 2.23, is assumed to have a misprint; the chemical identified should be ethylene
dichloride (C2H4C12) rather than dichloroethylene (C2H2C12).
4-30 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-47: CH, Emissions from Silicon Carbide Production
Year
1897
1988
1899
2000
2001
2002
4
4-
Does not exceed 0.05 Tg C0Z iq. or 0.5 6g
Table 4-48: Production of Silicon Carbide
Year
1890
1991
1992
1993
19»4
1995
1996
1997
1998
1999
2000
2001
2002
Metric Tons
105,000
78,900
84,300
74,900
84,700
75,400
73,600
68,200
69,800
65,000
45,000
40,000
30,000
section of the Energy chapter. Emissions of CH4 from silicon
carbide production in 2002 were 0.3 Gg CH4 (0.01 Tg CO2
Eq.) (see Table 4-47).
Methodology
Emissions of CH4 were calculated by multiplying annual
silicon carbide production by an emission factor (11.6 kg
CH4/metric ton silicon carbide). This emission factor was
derived empirically from measurements taken at Norwegian
silicon carbide plants (IPCC/UNEP/OECD/IEA 1997).
The emission factor was taken from the Revised 1996
IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997). Production
data for 1990 through 2002 (see Table 4-48) were obtained
from the Minerals Yearbook: Volume I-Metals and Minerals,
Manufactured Abrasives (USGS 1991, 1992, 1993, 1994,
1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003).
Uncertainty
The emission factor used here was based on one study
of Norwegian plants. The applicability of this factor to
average U.S. practices at silicon carbide plants is uncertain.
A better alternative would be to calculate emissions based on
the quantity of petroleum coke used during the production
process rather than on the amount of silicon carbide produced.
These data were not available, however.
4.13. Nitric Acid Production (IPCC
Source Category 2B2)
Nitric acid (HNO3) is an inorganic compound used
primarily to make synthetic commercial fertilizers. It is
also a major component in the production of adipic acid—a
feedstock for nylon—and explosives. Virtually all of the
nitric acid produced in the United States is manufactured
by the catalytic oxidation of ammonia (EPA 1997). During
this reaction, N2O is formed as a by-product and is released
from reactor vents into the atmosphere.
Currently, the nitric acid industry controls for NO and NO2
(i.e., NOX). As such, the industry uses a combination of non-
selective catalytic reduction (NSCR) and selective catalytic
reduction (SCR) technologies. In the process of destroying
NOX, NSCR systems are also very effective at destroying N2O.
However, NSCR units are generally not preferred in modern
plants because of high energy costs and associated high gas
temperatures. NSCRs were widely installed in nitric plants
built between 1971 and 1977. Approximately 20 percent of
nitric acid plants use NSCR (Choe et al. 1993). The remaining
80 percent use SCR or extended absorption, neither of which
is known to reduce N2O emissions.
Nitrous oxide emissions from this source were estimated
at 16.7 Tg CO2 Eq. (54.0 Gg) in 2002 (see Table 4-49).
Emissions from nitric acid production have decreased 6.2
percent since 1990, with the trend in the time series closely
tracking the changes in production.
Table 4-49: N-,0 Emissions from Nitric Acid Production
Year
T9C02Eq.
1990
17.8
57,6
1986
1997
1998
1999
2000
2001
2002
20.7
21.2
20,9
20.1
19.6
15.9
16.7
66.8
68.4
67.4
64,9
63.2
51.3
54.0
Industrial Processes 4-31
-------
Table 4-50: Nitric Acid Production
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Thousand Metric Tons
7,196
7,191
7,379
7,486
-7,904
8,018
8,349
8,556
8,421
8j113
7,898
6,416
8,752
Methodology
Nitrous oxide emissions were calculated by multiplying
nitric acid production by the amount of N2O emitted per unit
of nitric acid produced. The emissions factor was determined
as a weighted average of 2 kg N2O / metric ton HNO3 for
plants using non-selective catalytic reduction (NSCR)
systems and 9.5 kg N2O / metric ton HNO3 for plants not
equipped with NSCR (Choe et al. 1993). In the process of
destroying NOX, NSCR systems destroy 80 to 90 percent of
the N2O, which is accounted for in the emission factor of 2
kg N2O / metric ton HNO3. An estimated 20 percent of HNO3
plants in the United States are equipped with NSCR (Choe et
al. 1993). Hence, the emission factor is equal to (9.5 x 0.80)
+ (2 x 0.20) = 8 kg N2O per metric ton HNO3.
Nitric acid production data for 1990 (see Table 4-50) was
obtained from Chemical and Engineering News, "Facts and
Figures" (C&EN 2001). Nitric acid production data for 1991
through 1999 (see Table 4-50) were obtained from Chemical
and Engineering News, "Facts and Figures" (C&EN 2002).
Nitric acid production data for 2000 through 2002 were
obtained from Chemical and Engineering News, "Facts and
Figures" (C&EN 2003). The emission factor range was taken
from Choe et al. (1993).
Uncertainty
In general, the nitric acid industry is not well-categorized.
A significant degree of uncertainty exists in nitric acid
production figures because nitric acid plants are often part
of larger production facilities, such as fertilizer or explosives
manufacturing. As a result, only a small quantity of nitric acid
is sold on the market, making production quantities difficult
to track. Emission factors are also difficult to determine
because of the large number of plants using many different
technologies. The uncertainty for nitric acid production was
assumed to be ±10 percent. The emissions factor accounts for
emissions from plants with and without NSCR. Assuming
a ±10 percent uncertainty for both the percentage of NSCR
and non-NSCR plants and a ±10 percent uncertainty for the
associated emissions from each type of plant, results in an
overall ±13 percent uncertainty in the emissions factor. Using
these uncertainty estimates and a Tier 1 analysis results in
an uncertainty of 17 percent for emissions from nitric acid
production (see Table 4-51).
QA/QC and Verification
An IPCC Tier 1 level QA/QC verification was performed.
This process resulted in the creation of a mechanism to track
production and emissions values from past reporting years.
Recalculations Discussion
The nitric acid production values for 2000 to 2001 were
updated. These changes resulted in a 3 percent increase in
2000 production and emissions and a 10 percent decrease
in 2001 production and emissions.
Planned Improvements
Planned improvements are focused on assessing
the plant-by-plant implementation of NOX abatement
technologies to more accurately match plant production
capacities to appropriate emission factors, instead of using
a national profiling of abatement implementation. Also, any
Table 4-51: Quantitative Uncertainty Estimates for N20 Emissions from Nitric Acid Production (Tg C02 Eq. and Percent)
Year 2002 Emissions
Estimate (TgC02Eq.)
Lower Bound
Nitric Acid Production
JML
16.7
17%
13.9
19.6
4-32 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
large scale updates to abatement configurations would be
useful in revising the national profile.
4.14. Adipic Acid Production (IPCC
Source Category 2B3)
Adipic acid production is an anthropogenic source
of N2O emissions. Worldwide, few adipic acid plants
exist. The United States is the major producer with three
companies in four locations accounting for approximately
one-third of world production. Adipic acid is a white
crystalline solid used in the manufacture of synthetic fibers,
coatings, plastics, urethane foams, elastomers, and synthetic
lubricants. Commercially, it is the most important of the
aliphatic dicarboxylic acids, which are used to manufacture
polyesters. Food grade adipic acid is also used to provide
some foods with a "tangy" flavor (Thiemems and Trogler
1991). Approximately 90 percent of all adipic acid produced
in the United States is used in the production of nylon 6,6
(CMR 2001).
Adipic acid is produced through a two-stage process
during which N2O is generated in the second stage. The first
stage of manufacturing usually involves the oxidation of
cyclohexane to form a cyclohexanone/cyclohexanol mixture.
The second stage involves oxidizing this mixture with nitric
acid to produce adipic acid. Nitrous oxide is generated as a
by-product of the nitric acid oxidation stage and is emitted in
the waste gas stream (Thiemens and Trogler 1991). Process
emissions from the production of adipic acid vary with
the types of technologies and level of emissions controls
employed by a facility. In 1990, two of the three major adipic
acid producing plants had N2O abatement technologies in
place and as of 1998, the three major adipic acid production
facilities had control systems in place.13 Only one small
plant, representing approximately two percent of production,
does not control for N2O (Reimer 1999).
Nitrous oxide emissions from this source were estimated
to be 5.9 Tg CO2 Eq. (19.0 Gg) in 2002 (see Table 4-52).
National adipic acid production has increased by
approximately 25 percent over the period of 1990 through
2002, to approximately 0.9 million metric tons. At the same
time, emissions have been significantly reduced due to the
widespread installation of pollution control measures.
Table 4-52: N20 Emissions from Adipic Acid Production
Wear
1§9$
1997
1998
1999
2000
2001
2002
•'"" 'f£6'': '"•'"•':'•"
10.3 ..
S,0
5J
i.O
4.9
5J •.. . ;.
" :5fcd-'
ms
19J ;
,. 'tffj;. '..-.
tis
-'ISJ'1
19,0
Methodology
For two production plants, 1990 to 2002 emission
estimates were obtained directly from the plant engineer
and account for reductions due to control systems in place at
these plants during the time series. For the other two plants,
N2O emissions were calculated by multiplying adipic acid
production by the ratio of N2O emitted per unit of adipic
acid produced and adjusting for the actual percentage of
N2O released as a result of plant-specific emission controls.
On the basis of experiments (Thiemens and Trogler 1991),
the overall reaction stoichiometry for N2O production in the
preparation of adipic acid was estimated at approximately 0.3
mt of N2O per metric ton of product. Emissions are estimated
using the following equation:
N2O emissions = [production of adipic acid (mt of adipic acid)]
x [0.3 mt N2O / mt adipic acid] x [1 - (N2O destruction factor
x abatement system utility factor) ]
The "N20 destruction factor" represents the percentage
of N2O emissions that are destroyed by the installed abatement
technology. The "abatement system utility factor" represents
the percentage of time that the abatement equipment operates
during the annual production period. Overall, in the United
States, two of the plants employ catalytic destruction, one
plant employs thermal destruction, and the smallest plant uses
no N2O abatement equipment. The N2O abatement system
destruction factor is assumed to be 95 percent for catalytic
abatement and 98 percent for thermal abatement (Reimer et
al. 1999, Reimer 1999).
National adipic acid production data (see Table 4-53) for
1990 through 2002 were obtained from the American Chemistry
Council (ACC 2002). Plant capacity data for 1990 through 1994
13
During 1997, the N2O emission controls installed by the third plant operated for approximately a quarter of the year.
Industrial Processes 4-33
-------
Table 4-53: Adipic Acid Production
Year
Thousand Metric Tons
1992 /
1993
1994 . ;
,1995
199& - •
1997
1998
1999
2000
2001
2002
' . "".".'T24...'- -
' f&
• •- '-824 • " "
'880
:83S
871;.
3/B2.
'„'• 907
" - • ' 825
835
921
were obtained from Chemical and Engineering News, "Facts
and Figures" and "Production of Top 50 Chemicals" (C&EN
1992,1993,1994,1995). Plant capacity data for 1995 and 1996
were kept the same as 1994 data. The 1997 plant capacity data
were taken from Chemical Market Reporter "Chemical Profile:
Adipic Acid" (CMR 1998). The 1998 plant capacity data for all
four plants and 1999 plant capacity data for three of the plants
were obtained from Chemical Week, Product focus: adipic acid/
adiponitrile (CW 1999). Plant capacity data for 2000 for three
of the plants were updated using Chemical Market Reporter,
"Chemical Profile: Adipic Acid" (CMR 2001). For 2001 and
2002, the plant capacity for these three plants were kept the same
as the year 2000 capacity. Plant capacity data for 1999 to 2002
for the one remaining plant was kept the same as 1998. The
emission factor was based on Thiemens and Trogler (1991). The
national production and plant capacities were utilized for two of
the four plants. Information for the other two plants was obtained
directly from the plant engineer (Childs 2002, 2003).
Uncertainty
To calculate emissions for the two plants where emissions
were not provided by the plant engineer, production data on a
plant-specific basis was needed. However, these production
data are considered confidential and were not available from
the plants. As a result, plant-specific production figures
for the two plants were calculated by allocating national
adipic acid production using existing plant capacities. This
allocation creates a degree of uncertainty in the adipic acid
production data as all plants are assumed to operate at
equivalent utilization levels as represented by their capacities.
Also, plant capacity reference data is inconsistently available
from year to year, which can affect the uncertainty of the
allocated production through the time series.
The emission factor was based on experiments (Thiemens
and Trogler 1991) that attempt to replicate the industrial
process and, thereby, measure the reaction stoichiometry for
N2O production in the preparation of adipic acid. However,
the extent to which the lab results are representative of actual
industrial emission rates is not known.
A 5 percent uncertainty was assumed for the two plants
with directly reported emissions. For the remaining two
plants, a 20 percent uncertainty was assumed for production.
Abatement factor uncertainty for these two plants was based
on a 5 percent IPCC estimate for the N2O destruction factor
and an assumed 5 percent uncertainty in the abatement
system utility factor (IPCC 2000). These estimates result in
an overall abatement uncertainty of 7 percent. Combining this
abatement uncertainty with the 10 percent IPCC emissions
factor uncertainty results in an overall 12 percent emissions/
abatement uncertainty. Combining the 5 percent plant-specific
emissions uncertainty and the 20 percent activity and 12
percent emissions/abatement uncertainty for the remaining two
plants yields an overall uncertainty for the inventory estimate
of 10 percent (see Table 4-54).
QA/QC and Verification
An IPCC Tier 1 level QA/QC verification was performed.
This process resulted in the creation of a mechanism to track
production and emissions values from past reporting years.
National production values were compared to previous
estimates based on alternative data sources, which resulted in
order of magnitude verification on the total national levels.
Table 4-54: Quantitative Uncertainty Estimates for N20 Emissions from Adipic Acid Production (Tg C02 Eq. and Percent)
Source
Year 2002 Emissions
Gas (Tg C02 Eq.)
Uncertainty Range Relative to 2002 Emission
Uncertainty (%) Estimate (Tg C02 Eq.)
Lower Bound
Adipic Acid Production N20
5.9
10%
5.3
6.5
4-34 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Planned Improvements
Improvement efforts are focused on obtaining direct
measurement data from the remaining two plants when and
if they become available. If they become available, cross
verification with top-down approaches will provide a useful
Tier 2 level QA check. Also, additional information on the
actual performance of the latest catalytic and thermal abatement
equipment at plants with continuous emission monitoring may
support the re-evaluation of current default abatement values.
4.15. Substitution of Ozone Depleting
Substances (IPCC Source Category 2F)
Hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs)
are used as alternatives to several classes of ozone-depleting
substances (ODSs) that are being phased out under the terms
of the Montreal Protocol and the Clean Air Act Amendments
of 1990.14 Ozone depleting substances—chlorofluorocarbons
(CFCs), halons, carbon tetrachloride, methyl chloroform, and
hydrochlorofluorocarbons (HCFCs)—are used in a variety
of industrial applications including refrigeration and air
conditioning equipment, solvent cleaning, foam production,
sterilization, fire extinguishing, and aerosols. Although HFCs
and PFCs, unlike ODSs, are not harmful to the stratospheric
ozone layer, they are potent greenhouse gases. Emission
estimates for HFCs and PFCs used as substitutes for ODSs
are provided in Table 4-55 and Table 4-56.
In 1990 and 1991, the only significant emissions of HFCs
and PFCs as substitutes to ODSs were relatively small amounts
of HFC-152a—a component of the refrigerant blend R-500 used
in chillers—and HFC-134a in refrigeration end-uses. Beginning
in 1992, HFC-134a was used in growing amounts as a refrigerant
in motor vehicle air conditioners and in refrigerant blends such
as R-404A.'5 In 1993, the use of HFCs in foam production and
Table 4-55: Emissions of HFCs and PFCs from ODS Substitution (Tg C02 Eq.)
Gas
HFC-23
HFC-32
HFG-125
HFC-134a
HFC-143a
HFC-236fa
CF4
Others*
Total
1990 |
0.3
0.3 1
1998
• • 4
0.1
5.2
24.5
2.0
4-
+
3.1
35.0
1997
4
0.2
7.0
31.4
3.5
0.1
4-
4.2
46.4
1998
+
0.3
8.8
36.7
5.2
0.4
4
5.2
56.5
1999
0.1
0.3
10.0
42.2
6.6
0.9
+
5.7
65.8
2000
0,1
0.3
11.2
48.0
8.2
1.4
4
6.0
75.1
2001
0.1
0.3
12.3
52.7
10.1
1.8
4
6.2
83.4
2002
0.1
0.3
13.4
56.9
12.2
2.1
4
6.6
91.7
+ Does not exceed 0.05 Tg C02 Eq.
* Others include HFC-152a, HFC-227ea, HFC-245fa, HFC-4310mee, and PFC/PFPEs, the latter being a proxy for a diverse collection of PFCs and
perfueropoiyethers (PFPEs) employed for solvent applications. For estimating purposes, the SWP value used for PFC/PFPEs was based upon C6F14.
Note: Totals may not sum due to Independent rounding.
Table 4-56: Emissions of HFCs and PFCs from ODS Substitution (Mg)
Gas
HFC-23
HFC-32
HFC-125
HFC-134a
HFC-143a
HFC-236fa
CF4
Others*
1990
4-
4
4
4^
4
4
4-
M
1996
2
139
1,868
18,870
531
+
4
M
1997
3
289
2,516
24,136
926
9
4
M
1998
4
430
3,134
28,202
1,369
64
1
M
1999
5
439
3,571
32,491
1,738
142
1
M
2000
6
441
4,004
36,888
2,162
214
1
M
2001
7
459
4,385
40,512
2,647
281
1
M
2002
8
492
4,777
43,798
3,203
341
2
M
y (Mixture of Gases)
+ Does not exceed 0.5 Mg
* Others include HFC-152a, HFC-227ea, HFC-245fa, HFC-4310mee and PFC/PFPEs, the latter being a proxy for a diverse collection of PFCs and
perfluoropolyethers (PFPEs) employed for solvent applications.
14 [42 U.S.C § 7671, CAA § 6011
15 R.404A contains HFC-125, HFC-143a, and HFC-134a.
Industrial Processes 4-35
-------
as an aerosol propellant began, and in 1994 these compounds
also found applications as solvents and sterilants. In 1995, ODS
substitutes for halons entered widespread use in the United
States as halon production was phased out.
The use and subsequent emissions of HFCs and PFCs as
ODS substitutes has been increasing from small amounts in
1990 to 91.7 Tg CO2 Eq. in 2002. This increase was in large
part the result of efforts to phase out CFCs and other ODSs
in the United States. In the short term, this trend is expected
to continue, and will likely accelerate in the next decade as
HCFCs, which are interim substitutes in many applications, are
themselves phased-out under the provisions of the Copenhagen
Amendments to the Montreal Protocol. Improvements in the
technologies associated with the use of these gases and the
introduction of alternative gases and technologies, however,
may help to offset this anticipated increase in emissions.
Methodology
A detailed vintaging model of ODS-containing equipment
and products was used to estimate the actual—versus
potential—emissions of various ODS substitutes, including
HFCs and PFCs. The name of the model refers to the fact that
the model tracks the use and emissions of various compounds
for the annual "vintages" of new equipment that enter service
in each end-use. This vintaging model predicts ODS and
ODS substitute use in the United States based on modeled
estimates of the quantity of equipment or products sold
each year containing these chemicals and the amount of the
chemical required to manufacture and/or maintain equipment
and products over time. Emissions for each end-use were
estimated by applying annual leak rates and release profiles,
which account for the lag in emissions from equipment as
they leak over time. By aggregating the data for more than
40 different end-uses, the model produces estimates of annual
use and emissions of each compound. Further information on
the Vintaging Model is contained in Annex 3.8.
Uncertainty
Given that emissions of ODS substitutes occur from
thousands of different kinds of equipment and from millions
of point and mobile sources throughout the United States,
emission estimates must be made using analytical tools
such as the Vintaging Model or the methods outlined in
IPCC/UNEP/OECD/IEA (1997). Though the model is
more comprehensive than the IPCC default methodology,
significant uncertainties still exist with regard to the levels
of equipment sales, equipment characteristics, and end-
use emissions profiles that were used to estimate annual
emissions for the various compounds.
The Vintaging Model estimates emissions from over 40
end-uses, but the uncertainty estimation was performed on
only the top 14 end-uses, which account for 95 percent of
emissions from this source category. In order to calculate
uncertainty, functional forms were developed to simplify
some of the complex "vintaging" aspects of some end-use
sectors, especially with respect to refrigeration and air-
conditioning, and to a lesser degree, fire extinguishing.
These sectors calculate emissions based on the entire
lifetime of equipment, not just equipment put into
commission in the current year, which necessitated these
simplifying equations. The functional forms used variables
that included growth rates, emission factors, transition from
ODSs, change in charge size as a result of the transition,
disposal quantities, disposal emission rates, and either
stock for the current year or original ODS consumption.
Uncertainty was estimated around each variable within the
functional forms based on expert judgment, and a Monte
Carlo analysis was performed.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-57) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
Table 4-57: Quantitative Uncertainty Estimates for HFC and PFC Emissions from ODS Substitution (Tg C02 Eq. and Percent)
2002 Emission Estimate
Source
Lower Bound Upper Bound Lower Bound Upper Bound
Substitution of Ozone
Depleting Substances
HFC and PFC
91.7
90.7
116.5
-1%
+27%
1 Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
4-36 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
the range of approximately 90.7 to 116.5 Tg CO2 Eq. (or that
the actual HFC and PFC emissions are likely to fall within
the range of approximately 1 percent below and 27 percent
above the emission estimate of 91.7 Tg CO2 Eq.).
Recalculations Discussion
An extensive review of the chemical substitution trends,
market sizes, growth rates, and charge sizes, together with
input from industry representatives, resulted in updated
assumptions for the Vintaging Model. Additionally, a new
version of the Vintaging Model was developed for this
Inventory year. This model incorporated improvements
to the emission estimating methodologies, differences in
charge sizes between original chemicals and substitutes,
and improvements to the way retrofits and recovery and
recycling are accounted for. These changes resulted in an
average annual increase of 6.7 Tg CO2 Eq. (9.1 percent) in
HFC and PFC emissions for the period 1990 through 2001.
4.16. HCFC-22 Production
(IPCC Source Category 2E1)
Trifluoromethane (HFC-23 or CHF3) is generated as a
by-product during the manufacture of chlorodifluoromethane
(HCFC-22), which is primarily employed in refrigeration
and air conditioning systems and as a chemical feedstock for
manufacturing synthetic polymers. Since 1990, production
and use of HCFC-22 has increased significantly as it has
replaced chlorofluorocarbons (CFCs) in many applications.
Because HCFC-22 depletes stratospheric ozone, its
production for non-feedstock uses is scheduled to be phased
out by 2020 under the U.S. Clean Air Act.16 Feedstock
production, however, is permitted to continue indefinitely.
HCFC-22 is produced by the reaction of chloroform
(CHC13) and hydrogen fluoride (HF) in the presence of a
catalyst, SbCl5. The reaction of the catalyst and HF produces
SbClxFy, (where x + y = 5), which reacts with chlorinated
hydrocarbons to replace chlorine atoms with fluorine. The
HF and chloroform are introduced by submerged piping
into a continuous-flow reactor that contains the catalyst in a
hydrocarbon mixture of chloroform and partially fluorinated
intermediates. The vapors leaving the reactor contain HCFC-
21 (CHC12F), HCFC-22 (CHC1F2), HFC-23 (CHF3), HC1,
chloroform, and HF. The under-fluorinated intermediates
(HCFC-21) and chloroform are then condensed and returned
to the reactor, along with residual catalyst, to undergo further
fluorination. The final vapors leaving the condenser are
primarily HCFC-22, HFC-23, HC1 and residual HF. The HC1
is recovered as a useful byproduct, and the HF is removed.
Once separated from HCFC-22, the HFC-23 is generally
vented to the atmosphere as an unwanted by-product, or may
be captured for use in a limited number of applications.
Emissions of HFC-23 in 2002 were estimated to be
19.8 Tg CO2 Eq. (1.7 Gg). This quantity is the same as the
quantity of emissions in 2001, and represents a 43 percent
decrease from emissions in 1990 (see Table 4-58). Although
HCFC-22 production has increased by 4 percent since 1990,
the intensity of HFC-23 emissions (i.e., the amount of
HFC-23 emitted per kilogram of HCFC-22 manufactured)
has declined by 46 percent over the same period, lowering
emissions. Three HCFC-22 production plants operated in the
United States in 2002, two of which used thermal oxidation
to significantly lower (and in at least one case, virtually
eliminate) their HFC-23 emissions.
In the future, production of HCFC-22 in the United States
is expected to decline as non-feedstock HCFC production is
phased-out. Feedstock production is anticipated to continue
growing, mainly for manufacturing fluorinated polymers.
Methodology
The methodology employed for estimating emissions is
based upon measurements at individual HCFC-22 production
plants. Plants using thermal oxidation to abate their HFC-23
emissions monitor the performance of their oxidizers to verify
that the HFC-23 is almost completely destroyed. The other
Table 4-58: HFC-23 Emissions from HCFC-22 Production
• 1990
TgC02Eq.
3S.O
3.0
1996
1997
1998
1999
2000
2001
2002
• 31.1
30.0
40.2
30.4
29.8
19.8
19.8
2.7
2.6
3.4
2.6
2.5
1.7
1.7
As construed, interpreted, and applied in the terms and conditions of the Montreal Protocol on Substances that Deplete the Ozone Layer.
[42 U.S.C. §7671m(b), CAA §614]
Industrial Processes 4-37
-------
Table 4-59: HCFC-22 Production
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
69
138,9
142.7
149.6
132.4
146.8
154.7
166.1
164.5
182.8
165.5
186.9
152,4
144.2
plants periodically measure HFC-23 concentrations in the output
stream using gas chromatography. This information is combined
with information on quantities of critical feed components (e.g.,
HF) and/or products (HCFC-22) to estimate HFC-23 emissions
using a material balance approach. HFC-23 concentrations are
determined at the point the gas leaves the chemical reactor;
therefore, estimates also include fugitive emissions.
Production data and emission estimates were prepared in
cooperation with the U.S. manufacturers of HCFC-22 (ARAP
2003). Annual estimates of U.S. HCFC-22 production are
presented in Table 4-59.
Uncertainty
A high level of confidence has been attributed to the
HFC-23 concentration data employed because measurements
were conducted frequently and accounted for day-to-day and
process variability. Reported emissions are roughly within 10
percent of the true value (see Table .4-60). This methodology
accounted for the declining intensity of HFC-23 emissions
over time. The use of a constant emission factor would not
have allowed for such accounting. More simplistic emission
estimates generally assume that HFC-23 emissions are
between 2 and 4 percent of HCFC-22 production on a mass
ratio basis.
4.17. Electrical Transmission
and Distribution (IPCC Source
Category 2F7)
Sulfur hexafluoride's largest use, both domestically and
internationally, is as an electrical insulator and interrupter in
equipment that transmits and distributes electricity (RAND
2002). The gas has been employed by the electric power
industry in the United States since the 1950s because of its
dielectric strength and arc-quenching characteristics. It is
used in gas-insulated substations, circuit breakers, and other
switchgear. Sulfur hexafluoride has replaced flammable
insulating oils in many applications and allows for more
compact substations in dense urban areas.
Fugitive emissions of SF6 can escape from gas-insulated
substations and switch gear through seals, especially from
older equipment. The gas can also be released during
equipment installation, servicing, and disposal. In the past,
some electric utilities vented SF6 to the atmosphere during
servicing and disposal; however, increased awareness and the
relatively high cost of the gas have reduced this practice.
Emissions of SF6 from electrical transmission and
distribution systems were estimated to be 14.8 Tg CO2
Eq. (0.6 Gg) in 2002. This quantity represents a 49
percent decrease below the estimate for 1990 (see Table
4-61 and Table 4-62). This decrease, which is reflected
in the atmospheric record, is believed to be a response to
increases in the price of SF6 and to growing awareness of
the environmental impact of SF6 emissions.
Methodology
The 2002 estimate of SF6 emissions from electrical
equipment (14.8 Tg CO2 Eq.) is comprised of (1) estimated
emissions of approximately 14.1 Tg CO2 Eq. from U.S. electric
power systems, and (2) estimated emissions of approximately
0.7 Tg CO2 Eq. from U.S. electrical equipment manufacturers
(original equipment manufacturers, or OEMs). The 2002 estimate
Table 4-60: Quantitative Uncertainty Estimates for HFC-23 Emissions from HCFC-22 Production (Tg C02 Eq. and Percent)
Source
Year 2002 Emissions
Gas (Tg C02 Eq.)
Uncertainty Range Relative to 2002 Emission
Uncertainty (%) Estimate (Tg C02 Eq.)
Lower Bound
Upper Bound
HCFC-22 Production
HFC-23
19.8
10%
17.8
21.8
4-38 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 4-61: SF6 Emissions from Electric Power Systems
and Original Equipment Manufactures (Tg C02 Eq.)
Table 4-62: SF6 Emissions from Electric Power Systems
and Original Equipment Manufactures (Gg)
Year
Electric Power
Systems
Original Equipment
Manufactures
Year
Total
Total
1990
28.9
0.3
29.2
1996
1997
1998
1999
2000
2001
2002
23.8
21.3
16.7
15.8
15.2
14.9
14.1
0.4
0.3
0.4
0.6
0.7
0.7
0.7
24.3
21.7
17.1
16.4
15.9
15.6
14.8
of emissions from electric power systems is based on the reported
2002 emissions (5.2 Tg CO2 Eq.) of participating utilities in
EPA's SF6 Emissions Reduction Partnership for Electric Power
Systems, which began in 1999. These emissions were scaled up
to the national level using the results of a regression analysis that
indicated that utilities' emissions are strongly correlated with
their transmission miles. The analysis further showed that the
relationship between emissions and transmission miles differed
for facilities with less or more than 10,000 miles. Therefore two
regression equations were developed for small plants (with less
than 10,000 miles of transmission lines) and large facilities (with
10,000 miles or more of transmission lines).
For 1999, the following regression equations were
developed based on SF6 emissions reported by 49 partner
utilities (representing approximately 45 percent of U.S. net
generation):
Small utilities (less than 10,000 transmission miles,
1999, in kilograms):
Emissions = 0.874 x Transmission Miles
Large utilities (more than 10,000 transmission miles,
1999, in kilograms):
Emissions = 0.558 x Transmission Miles
These regression equations were used to determine 1999
SF6 emissions from both the non-reporting partner utilities
and the non-partner utilities. Extrapolating the equations
above, SF6 emissions were estimated for the non-reporting
partner utilities and the non-partner utilities. The results of the
extrapolation were added to the emissions reported by partner
utilities to estimate that U.S. electric power systems emitted
a total of 660,000 kg of SF6 (15.8 Tg CO2 Eq.) in 1999.
The estimate of 2000 emissions was developed similarly.
Fifty partners reported emissions totaling 264,600 kg of SF6,
1990
1996
1997
1998
1999
2000
2001
2002
1.2
1.0
0.9
0.7
0.7
0.7
0.7
0.6
or 6.3 Tg CO2 Eq. Because it appeared that partners had
significantly reduced their emission rate from the previous year,
a statistical analysis of the trend in emissions between 1999 and
2000 was performed. This analysis showed that the downward
trend was statistically significant (at a 95 percent confidence
level), and new regression equations were developed to
extrapolate 2000 partner-reported emissions to non-reporting
partners. This approach was selected because it was assumed
that the emission trends of the non-reporting partners would
be similar to those of the reporting partners, because all
partners commit to reducing SF6 emissions through technically
and economically feasible means. However, non-partners were
assumed to have implemented no changes that would have
reduced emissions over the previous year. Hence, the 1999
regression equation was used to determine SF6 emissions from
non-partners. Total 2000 emissions were then determined by
summing the partner-reported emissions, the non-reporting
partner emissions (determined with the 2000 regression
equation) and the non-partner emissions (determined using
the 1999 regression equation). Using this approach, total 2000
emissions from electric power systems were estimated to be
635,300 kg of SF6 (15.2 Tg CO2 Eq.).
The approach used to determine the 2000 emissions was
applied in subsequent years (i.e., new regression equations
were developed using partner-reported emissions and miles
and extrapolated to non-reporting partners; and the 1999
regression equations are applied to the non-partners). The
2002 regression equations used to estimate non-reporting
partner emissions were:
Small utilities (less than 10,000 transmission
miles, 2002, in kilograms):
Emissions = 0.598 x Transmission Miles
Industrial Processes 4-39
-------
Large utilities (more than 10,000 transmission
miles, 2002, in kilograms):
Emissions = 0.40 x Transmission Miles
Using this approach, total 2002 emissions from electric
power systems were estimated to be 588,900 kg of SF6
(14.1TgC02Eq.).
The 2002 emissions estimate for OEMs (0.7 Tg CO2 Eq.)
was derived by assuming that manufacturing emissions equal
10 percent of the quantity of SF6 charged into new equipment.
The quantity of SF6 charged into new equipment was estimated
based on statistics compiled by the National Electrical
Manufacturers Association (NEMA). The 10 percent emission
rate is the average of the "ideal" and "realistic" manufacturing
emission rates (4 percent and 17 percent, respectively)
identified in a paper prepared under the auspices of the
International Council on Large Electric Systems (CIGRE) in
February 2002 (O'Connell, et al., 2002). Emissions for 1999
through 2001 were estimated similarly.
Because most participating utilities reported emissions
only for 1999 through 2002, it was necessary to model SF6
emissions from electric power systems for the years 1990
through 1998. To do so, it was assumed that during this period,
U.S. emissions from this source followed the same trajectory
as global emissions from this source. To estimate global
emissions, the RAND survey of global SF6 sales to electric
utilities was used, together with the following equation, which
is derived from the equation for emissions in the IPCC report,
Good Practice Guidance and Uncertainty Management in
National Greenhouse Gas Inventories (IPCC 2000):
Emissions = SF6 purchased to refill existing equipment +
nameplate capacity of retiring equipment
Note that the above equation holds whether the gas from
retiring equipment is released or recaptured; if the gas is
recaptured, it is used to refill existing equipment, lowering
the amount of SF6 purchased by utilities for this purpose.
It was assumed that the SF6 used to refill existing equipment
in a given year approximately equaled the SF6 purchased by
utilities in that year. Nameplate capacity of retiring equipment
in a given year was assumed to equal 77.5 percent of the amount
of gas purchased by electrical equipment manufacturers 30 years
previous. The remaining 22.5 percent was assumed to have
been emitted at the time of manufacture. These results were
then summed to yield estimates of global SF6 emissions from
1990 through 1998. Gas purchases by utilities and equipment
manufacturers from 1961 through 2001 are available from the
RAND (2002) survey. It was assumed that SF6 purchases were
strongly related to emissions. The 22.5 percent emission rate
is an average of IPCC SF6 emission rates for Europe and Japan
for years before 1996 (IPCC 2000). The 30-year lifetime for
electrical equipment is also drawn from IPCC (2000).
To estimate U.S. emissions for 1990 through 1998,
estimated global emissions for each year from 1990 through
1998 were divided by the estimated global emissions from
1999. The result was a time series that gave each year's sales
as a multiple of 1999 sales. Each year's normalized sales
were then multiplied by the estimated U.S. emissions of SF6
from electric power systems in 1999 (estimated to be 15.8 Tg
CO2 Eq.) to estimate U.S. emissions of SF6 from electrical
equipment in that year. This yielded a time series that was
related to statistics for both SF6 emissions and SF6 sales.
Emissions from OEMs were estimated for 1990 through
1998 using OEM statistics for this period.
Uncertainty
Using IPCC Good Practice Guidance Tier 1 methodology,
the overall uncertainty associated with the 1999 through
2002 SF6 emission estimates from the electric transmission
and distribution is estimated to be ±13 percent (see Table
4-63). This estimate incorporates uncertainties associated
with SF6 emissions from electric power systems of ±13
percent, and SF6 emissions from OEMs of ±66 percent. For
Table 4-63: Quantitative Uncertainty Estimates for SF6 Emissions from Electrical Transmission and Distribution
(Tg C02 Eq. and Percent)
Source
Year 2002 Emissions
Gas (Tg C02 Eq.) Uncertainty (%)
Uncertainty Range Relative to 2002 Emission
Estimate (Tg C02 Eq.)
Lower Bound
Upper Bound
Electrical Transmission
and Distribution SFe
14.8
13%
12.8
16.7
4-40 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
electric power systems, the regression equations used to
extrapolate U.S. emissions from participant reports have a
variance (at the 95 percent confidence level) of ±2 Tg CO2
Eq. for 1999 through 2002. In addition, emission rates for
utilities that were not participants, which accounted for
approximately 65 percent of U.S. transmission miles, may
differ from those that were participants. There is uncertainty
in using global sales data to extrapolate 1990 through 1998
emissions from 1999 emissions; however, global sales of
SF6 appear to closely reflect global emissions. That is, global
sales declined by 24 percent between 1995 and 1998, while
atmospheric measurements indicate that world emissions of
SF6 declined by 27 percent during the same period. However,
U.S. emission patterns may differ from global emission
patterns. For OEMs, uncertainty estimates are based on the
assumption that SF6 statistics obtained from NEMA have
an uncertainty of 10 percent. Additionally, the OEMs SF6
emissions rate has an uncertainty bounded by the proposed
"actual" and "ideal" emission rates defined in O'Connell,
et al. (2002). That is, the uncertainty in the emission rate is
approximately 65 percent.
Recalculations Discussion
The methodology and activity data used for estimating
1990 through 1998 emissions have been updated relative
to the previous inventory. As in previous inventories, U.S.
SF6 emissions from utilities are assumed to have followed
the trend of global SF6 emissions from utilities during this
period. However, the method for estimating global emissions
now accounts for SF6 that is recaptured and/or released from
retiring equipment, rather than assuming that global emissions
are equal to global sales of SF6 to electric utilities. With this
new methodology, global emissions are estimated to equal
the sum of global sales to electric utilities and 77.5 percent
of the global sales to manufacturers of electrical equipment
30 years previous. The remaining 22.5 percent is assumed to
have been emitted at the time of equipment manufacture. In
addition to this methodological change, the revised estimates
reflect a more recent (2002) version of the RAND survey
of SF6 manufacturers. For 1990, emission estimates from
electric power systems have decreased from 32.1 Tg CO2
Eq. to 29.2 Tg CO2 Eq., while for 1998, estimates decreased
from 20.9 Tg CO2 Eq. to 17.1 Tg CO2 Eq.
Additionally, electric power system emission estimates
for 2000 and 2001 were recalculated using additional data that
partners submitted subsequent to the publication of the previous
inventory. Using these additional submissions, the regression
equations were updated and new extrapolations to non-reporting
partners were made. Following this recalculation, 2000 and
2001 SF6 emissions from electric power systems increased
slightly from 15.4 Tg CO2 Eq. to 15.6 Tg CO2 Eq., and 15.3
Tg CO2 Eq. to 14.8 Tg CO2 Eq., respectively.
Planned Improvements
Currently, there are over 70 companies in EPA's SF6
Emissions Reduction Partnership for Electric Power Systems;
however, not all of these report every year. As companies
report emissions data to fill in their historical data gaps,
regression equations will need to be revised to reflect
the new information. This will result in a change to prior
reported emission estimates, but will lead to a reduction in
the uncertainty of the value.
4.18. Aluminum Production (IPCC
Source Category 2C3)
Aluminum is a light-weight, malleable, and corrosion
resistant metal that is used in many manufactured products
including aircraft, automobiles, bicycles, and kitchen
utensils. In 2002, the United States was the third largest
producer of primary aluminum, with 11 percent of the world
total (USGS 2003). The United States was also a major
importer of primary aluminum. The production of primary
aluminum—in addition to consuming large quantities of
electricity—results in process-related emissions of CO2 and
two perfluorocarbons (PFCs): perfluoromethane (CF4) and
perfluoroethane (C2F6).
Carbon dioxide is emitted during the aluminum
smelting process when alumina (aluminum oxide, A12O3)
is reduced to aluminum using the Hall-Heroult reduction
process. The reduction of the alumina occurs through
electrolysis in a molten bath of natural or synthetic cryolite
(Na3AlF6). The reduction cells contain a carbon lining that
serves as the cathode. Carbon is also contained in the anode,
which can be a carbon mass of paste, coke briquettes, or
prebaked carbon blocks from petroleum coke. During
reduction, some of this carbon is oxidized and released to
the atmosphere as CO2.
Process emissions of CO2 from aluminum production
were estimated at 4.2 Tg CO2 Eq. (4,223 Gg) in 2002 (see
Industrial Processes 4-41
-------
Table 4-64: CO, Emissions from Aluminum Production
Year
1990
6,315
19&
1997
1998
1999
2000
2001
2002
5.8
5.8
5.9
5,7
4.1
4.2
5,821
5,792
5,895
5,723
4,1.14
4,223
Table 4-65: PFC Emissions from Aluminum Production
(TgC02Eq.)
Year
EF,
Total
1990
15.8
2.3
18,1
1996
1997
1998
1999
2000
2001
2002
11,1
9.8
8.1
8.0
8.0
3.5
4.5
1.4
1.2
1.0
0.9
0.9
0.5
0.7
12.5
11.0
9.0
8.9
8.9
4.0
5.2
Note: Totals may not sum due to independent rounding.
Table 4-66: PFC Emissions from Aluminum Production (Gg)
Year
CF,
1990
2.4
0.2
1i96
1997
1998
1999
2000
2001
2002
1.7
1.5
1.2
1.2
1.2
0.5
0.7
0.1
0.1
0.1
0.1
0.1
0.1
0.1
Table 4-64). The carbon anodes consumed during aluminum
production consist of petroleum coke and, to a minor extent,
coal tar pitch. The petroleum coke portion of the total CO2
process emissions from aluminum production is considered
to be a non-energy use of petroleum coke, and is accounted
for here and not with Fossil Fuel Combustion emissions in
the Energy chapter. Similarly, the coal tar pitch portion of
these CO2 process emissions is accounted for here rather
than in the Iron and Steel section, where it would otherwise
be counted.
In addition to CO2 emissions, the aluminum production
industry is also a source of PFC emissions. During the
smelting process, when the alumina ore content of the
electrolytic bath falls below critical levels required for
electrolysis, rapid voltage increases occur, termed "anode
effects." These anode effects cause carbon from the anode
and fluorine from the dissociated molten cryolite bath to
combine, thereby producing fugitive emissions of CF4 and
C2F6. In general, the magnitude of emissions for a given level
of production depends on the frequency and duration of these
anode effects. As the anode effects become longer and more
frequent, a corresponding rise in emission levels occurs.
Primary aluminum production-related emissions of
PFCs are estimated to have declined 71 percent since 1990.
Since 1990, emissions of CF4 and C2F6 have each declined
71 percent to 4.5 Tg CO2 Eq. of CF4 (0.7 Gg) and 0.7 Tg
CO2 Eq. of C2F6 (0.1 Gg) in 2002, as shown in Table 4-65
and Table 4-66. This decline was due to both reductions
in domestic aluminum production and actions taken by
aluminum smelting companies to reduce the frequency and
duration of anode effects.
U.S. primary aluminum production for 2002—totaling
2,700 thousand metric tons—increased by 3 percent from
2001. Due to high electric power costs in various regions
of the country, aluminum production has been curtailed
at several U.S. smelters resulting in current production
levels being nearly 26 percent lower than 2000 levels.
The transportation industry remained the largest domestic
consumer of aluminum, accounting for about 34 percent
(USGS 2003).
Methodology
Carbon dioxide is generated during alumina reduction
to aluminum metal following the reaction below:
2A12O3 + 3C -» 4A1 + 3CO2
The CO2 emission factor employed was estimated from
the production of primary aluminum metal and the carbon
consumed by the process. Emissions vary depending on
the specific technology used by each plant (e.g., Prebake
or Soderberg). The Revised 1996IPCC Guidelines (IPCC/
UNEP/OECD/IEA 1997) provide CO2 emission factors
for each technology type. During alumina reduction in a
prebake anode cell process, approximately 1.5 metric tons of
CO2 are emitted for each metric ton of aluminum produced
(IPCC/UNEP/OECD/IEA 1997). Similarly, during alumina
4-42 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
reduction in a Soderberg cell process, approximately 1.8
metric tons of CO2 are emitted per metric ton of aluminum
produced (IPCC/UNEP/OECD/IEA 1997). Based on
information gathered by EPA's Voluntary Aluminum
Industrial Partnership (VAIP) program, production was
assumed to be split 80 percent prebake and 20 percent
Soderberg for the whole time series.
PFC emissions from aluminum production were
estimated using a per unit production emission factor that
is expressed as a function of operating parameters (anode
effect frequency and duration), as follows:
PFC (CF4 or C2F6) kg/metric ton Al = S x
Anode Effect Minutes/Cell-Day
where,
S = Slope coefficient
Anode Effect Minutes/Cell-Day = Anode Effect Frequency
x Anode Effect Duration
For 9 out of the 23 U.S. smelters, smelter-specific slope
coefficients based on field measurements have been used to
develop PFC estimates. In 2002, only 3 out of the 16 operating
smelters use smelter-specific slope coefficients. For the
remaining smelters, technology-specific slope coefficients
from Good Practice Guidance and Uncertainty Management
in National Greenhouse Gas Inventories (IPCC 2000) were
applied. The slope coefficients were combined with smelter-
specific anode effect data, collected by aluminum companies
and reported to the VAIP, to estimate emission factors over
time. Where smelter-specific anode effect data were not
available between 1990 and 2001 (2 out of 23 smelters),
industry averages were used. Emission factors were multiplied
by annual production to estimate annual emissions at the
smelter level. In 2002, smelter-specific production data was
available for 14 of the 16 operating smelters; production at
one of the remaining smelters was estimated based on national
aluminum production and capacity data (USGS), and the
other one was held constant at 2001 levels. Between 1990
and 2001, production data has been provided by 21 of the 23
U.S. smelters; however, the specific number has varied by
year based on smelter-specific data availability or production
curtailment. Emissions were then aggregated across smelters to
estimate national emissions. The methodology used to estimate
emissions is consistent with the methodologies recommended
by the Good Practice Guidance and Uncertainty Management
in National Greenhouse Gas Inventories (IPCC 2000).
Table 4-67: Production of Primary Aluminum
•' .'• '..*».-' V"'
1899
1981
-• -'•&£' ::,-. :
• 1i§3i '"-•'
19l4
1995
1916
1981
1998
1999
2000
2001
2002
Thousand Metric Tons
4,048
4,121
' .'-••' 4,042
, ..- ,'-SJt5;
' . .' :'tJif :
• • . •."•• ''•''"&$&'•-
• ' •' '$j$xi .•'.
' : :-.';-:'-:8^8^'i;'
•' •' '. . : '••; ":^$F\$f:
•' ' " ' " ^3,l?t":
''•.'• 3,fllS>:'
• • . '• •-. .".'; 2,&7
' ; .'..' :. ' :=' ' ;r 471*7 •''
' ' ' ' .-* '•
National primary aluminum production data for 1990
through 1999 and 2001 (see Table 4-67) were obtained
from USGS, Mineral Industry Surveys: Aluminum Annual
Report (USGS 1995, 1998, 2000, 2001, 2002). The USGS
requested data from the 11 domestic producers, all of whom
responded. Primary aluminum production data for 2000
were obtained by using information from VAIP program
submittals and from USGS, Mineral Industry Surveys:
Aluminum Annual Report (USGS 2001). Comparing a subset
of smelter specific production data from VAIP submittals
and the USGS Mineral Industry Surveys: Aluminum Annual
Report (USGS 2001), it was observed that in 2000, the VAIP
program data was approximately 200 thousand metric tons
less than the USGS production total. The data from VAIP
were believed to provide a more accurate estimate of U.S.
aluminum production and therefore were used to calculate
emissions for 2000. This shortfall is again observed for 2002,
and again the VAIP data were used.
The CO2 emission factors were taken from the Revised
1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997).
PFC emission estimates were provided by aluminum
smelters participating in the VAIP program. Where smelter-
specific operational data were not available (i.e., aluminum
production, slope coefficients, and anode effect data),
estimates were drawn from other sources. For aluminum
production data, estimates were developed based on smelter-
specific production capacities, as reported by USGS. Default
technology-specific coefficients were drawn from the IPCC's
Good Practice Guidance (IPCC 2000). Information on the
average frequency and duration of anode effects was taken
from the International Aluminum Institute's anode effect
survey (IAI2000).
Industrial Processes 4-43
-------
Uncertainty
Carbon dioxide emissions vary depending on the
specific technology used by each plant. A more accurate
method would be to calculate CO2 emissions based upon
the amount of carbon—in the form of petroleum coke or
tar pitch—consumed by the process; however, this type of
information was not available.
The preliminary results of the quantitative uncertainty
analysis (see Table 4-68) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
the range of approximately 3.3 to 5.1 Tg CO2 Eq. (or that
the actual CO2 emissions are likely to fall within the range
of approximately 23 percent below and 21 percent above the
emission estimate of 4.2 Tg CO2 Eq.).
Using IPCC Good Practice Guidance Tier 1 methodology,
the overall uncertainty associated with the 2002 CF4 and
C2F6 emission estimates is ±12 and ±19 percent, respectively
(see Table 4-69). For the 2001 estimates,.the uncertainty was
estimated to be ± 16 percent ±18 percent, respectively; and for
1990, the corresponding uncertainties are ±8 percent and ±10
percent, respectively. For each smelter, uncertainty associated
with the quantity of aluminum produced, the frequency and
duration of anode effects, and the slope factor was estimated.
Error propagation analysis was then applied to estimate the
overall uncertainty of the emissions estimate for each smelter
and for the U.S. aluminum industry as a whole. The uncertainty
of aluminum production estimates ranged between 1 percent
and 25 percent, depending on whether a smelter's production
was reported or estimated. The uncertainty of the frequency
and duration of anode effects ranged between 2 percent and 78
percent, depending on whether these parameters were reported
or were estimated using industry-wide averages. Given the
limited uncertainty data on site-specific slope coefficients
(i.e., those developed using IPCC Tier 3b methodology),.
it was assumed that the overall uncertainty associated with
the slope coefficients would be similar to that given by the
IPCC guidance for technology-specific slope coefficients.
Consequently, the uncertainty assigned to the slope coefficients
ranged between 7 percent and 35 percent, depending upon the
gas and the smelter technology type. In general, where precise
quantitative information was not available on the uncertainty of
a parameter, a conservative (upper-bound) value was used.
Occasionally, SF6 is also used by the aluminum
industry as a cover gas or a fluxing and degassing agent
in experimental and specialized casting operations. In its
application as a cover gas, SF6 is mixed with nitrogen or
CO2 and injected above the surface of molten aluminum;
as a fluxing and degassing agent, SF6 is mixed with argon,
nitrogen, and/or chlorine and blown through molten
aluminum. These practices are not employed extensively by
primary aluminum producers and are believed to be isolated
to secondary casting firms. The aluminum industry in the
United States and Canada was estimated to use 230 metric
tons of SF6 per year (Maiss and Brenninkmeijer 1998);
however, this estimate is highly uncertain.
Table 4-68: Quantitative Uncertainty Estimates for C02 Emissions from Aluminum Production (Tg C02 Eq.)
Source
42
f>:-;
Table 4-69: Quantitative Uncertainty Estimates for PFC Emissions from Aluminum Production (Tg C02 Eq. and Percent)
Gas
Aluminum
4-44 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Historically, SF6 from aluminum activities has been
omitted from estimates of global SF6 emissions, with the
caveat that any emissions would be insignificant (Ko et al.
1993, Victor and MacDonald 1998). Emissions are believed
to be insignificant, given that the concentration of SF6 in the
mixtures is small and a portion of the SF6 is decomposed in
the process (MacNeal et al. 1990, Gariepy and Dube 1992,
Ko et al. 1993, Ten Eyck and Lukens 1996, Zurecki 1996).
Emissions of SF6 from aluminum fluxing and degassing
have not been estimated. Uncertainties exist as to the
quantity of SF6 used by the aluminum industry and its rate
of destruction in its uses as a degassing agent or cover gas.
Recalculations Discussion
The smelter-specific emission factors used for estimating
PFC emissions, as well as aluminum production levels, were
revised to reflect recently reported data concerning smelter
operating parameters. These data were provided in cooperation
with participants in the VAIP program. These revisions resulted
in a reduction of total PFC emissions of approximately 1
percent for the years 1990 through 1994, as well as an increase
in total PFC emissions by 12 percent for 2000, and a decrease
in total PFC emissions by 4 percent 2001.
Planned Improvements
A measurement study is currently taking place at three
U.S. aluminum smelters to develop facility-specific slope
coefficients. Consequently, use of these coefficients, instead
of IPCC defaults, will enable the calculation of more accurate
PFC emission estimates from these facilities.
4.19. Semiconductor Manufacture
(IPCC Source Category 2F6)
The semiconductor industry uses multiple long-lived
fluorinated gases in plasma etching and chemical vapor
deposition (CVD) processes. The gases most commonly
employed are trifluoromethane (HFC-23), perfluoromethane
(CF4), perfluoroethane (C2F6), nitrogen trifluoride (NF3), and
sulfur hexafluoride (SF6), although other compounds such
as perfluoropropane (C3F8) and perfluorocyclobutane (c-
C4F8) are also used. The exact combination of compounds
is specific to the process employed.
Plasma etching is performed to provide pathways for
conducting material to connect individual circuit components
in silicon wafers, using HFCs, PFCs, SF6, and other gases
in plasma form. The etching process uses plasma-generated
fluorine atoms that react at the semiconductor surface
according to prescribed patterns to selectively remove substrate
material. A single semiconductor wafer may require as many
as 100 distinct process steps that use these gases. Chemical
vapor deposition chambers, used for depositing materials that
will act as insulators and wires, are cleaned periodically using
PFCs and other gases. During the cleaning cycle the gas is
converted to fluorine atoms in plasma, which etches away
residual material from chamber walls, electrodes, and chamber
hardware. However, due to the low destruction efficiency (i.e.,
high dissociation energy) of PFCs, a portion of the gas flowing
into the chamber flows unreacted through the chamber and,
unless emission abatement technologies are used, this portion
is emitted into the atmosphere. In addition to emissions of
unreacted gases, these compounds can also be transformed in
the plasma processes into a different HFC or PFC compound,
which is then exhausted into the atmosphere. For example,
when either CHF3 or C2F6 is used in cleaning or etching, CF4
is generated and emitted as a process by-product.
For 2002, total weighted emissions of all fluorinated
greenhouse gases by the U.S. semiconductor industry were
estimated to be 4.4 Tg CO2 Eq. Combined emissions of all
fluorinated greenhouse gases are presented in Table 4-70 and
Table 4-71 below. The rapid growth of this industry and the
increasing complexity of semiconductor products which use
more PFCs in the production process have led to an increase in
emissions of 52 percent since 1990. However, the growth rate
in emissions began to slow in 1997, and emissions declined
by 40 percent between 1999 and 2002. This decline is due
both to a drop in production (with a continuing decline in
silicon consumption) and to the initial implementation of PFC
emission reduction methods, such as process optimization.
Methodology
Emissions from semiconductor manufacturing were
estimated using two sets of data. For 1990 through 1994,
emission estimates were based on the historical consumption
of silicon (i.e., square centimeters), the estimated average
number of interconnecting layers in the chips produced, and
an estimated per-layer emission factor. (The number of layers
per chip, and hence the PFC emissions per square centimeter
of silicon, increases as the line-width of the chip decreases.)
The average number of layers per chip was based on industry
Industrial Processes 4-45
-------
Table 4-70: PFC, HFC, and SF6 Emissions from Semiconductor Manufacture (Tg C02 Eq.)
1996
1.4
2,8
0,0
-.- 0,0
. 0.3
1.0
6,1
5.5
198?
1.6
3,2
0.0
;Q.O
0,4
1.1
0.1
6.3
1998
1.8
3.6
0.0
0.0
0.4
1.3
O.t
7.1
1999
1.8
3.7
0,0
0.0
0.4
1.3
0.1
7.2
2000
18
3.0
O.t
-0.0
/Q.3
11
0.1
6,3
2001
1.3
2.1
0.1
0.0
0.2
0,8
0.1
4.S
2002
11
22
0.1
0.0
» 0.2
0.7
0.3
4.4
Does not 0xcee
-------
specific emissions. During this period, the emissions of each
gas represents the sum of the portion reported by partners and
the portion from non-partners, which is obtained by assuming
the distribution for earlier years is applicable.
Participants estimate their emissions using a range of
methods. For 2002, most participants cited a method at
least as accurate as the IPCC's method 2c, recommended
in Good Practice Guidance and Uncertainty Management
in National Greenhouse Gas Inventories (IPCC 2000).
The partners with relatively high emissions typically use
the more accurate IPCC 2b or 2a methods, multiplying
estimates of their PFC consumption by process-specific
emission factors that they have either measured or obtained
from tool suppliers.
Data used to develop emission estimates were
prepared in cooperation with the Partnership. Estimates
of the capacities and characteristics of plants operated by
participants and non-participants were derived from the
Semiconductor Equipment and Materials International
(SEMI) World Fab Watch (formerly International Fabs
on Disk) database (1996 to 2003). Estimates of silicon
consumed by line-width from 1990 through 1994 were
derived from information from VLSI Research (2003),
and the number of layers per line-width was obtained from
International SEMATECH's International Technology
Roadmap: 2000 Update.
Uncertainty
Using IPCC Good Practice Guidance Tier 1 methodology,
the overall uncertainty associated with the 2002 emissions
estimates is estimated to be ±10 percent (see Table 4-72)
For partnership participants, an uncertainty of 15
percent was assigned to PFC emissions data that they
supplied to the partnership. This value accounts for
uncertainty in partners' estimates of gas-volume usage.
Based on this assumption, the relative error associated with
partnership emissions in 2002 is ±7 percent (or ±0.2 Tg CO2
Eq. of 3.4 Tg CO2 Eq.). Non-partner emission estimates
incorporate uncertainties associated with PEVM emission
factors (±30 percent), U.S. silicon consumption estimates
(±13 percent), and estimates of non-partner shares of U.S.
manufacturing capacity (±5 percent). Using these data,
the relative error associated with non-partner emissions
estimates in 2002 is estimated to be ±32 percent (or ±0.4
Tg CO2 Eq. of 1.2 Tg CO2 Eq.).
Recalculations Discussion
Emissions estimates reported above reflect several
revisions to those figures previously reported. Changes
have resulted from updates to EPA's PEVM—the model
responsible for estimating non-partner emissions—that
incorporate more current reference data (i.e., plant capacities
and silicon consumption by line-width), as well as updates
to the historical data supplied by several partnership
participants. These updates have resulted in an average
reduction in emission estimates on the order of 9 percent for
the period 1995 through 2001. Additionally, the methodology
used to estimate the distribution of historical emissions by
gas type has changed. The current estimates use market and
confidential gas sales survey information and IPCC emission
factors to calculate emissions by gas type.
Planned Improvements
The method by which non-partner related emissions
are estimated (i.e., PEVM) is not expected to change (with
the exception of possible future updates to emission factors
and added technology nodes). Future improvements to the
national emissions estimates will primarily be associated
with determining the portion of national emissions to
attribute to partner report totals (currently about 80 percent)
and, as the nature of the reports change through time and
Table 4-72: Quantitative Uncertainty Estimates for HFC, PFC, and SF6 Emissions from Semiconductor Manufacture
(Tg C02 Eq. and Percent)
Year 2002 Emissions Uncertainty Range Relative to 2002 Emission
Source Gas (TgC02Eq.) Uncertainty (%) Estimate (Tg COZ Eq.)
Semiconductor Manufacture
MFC, PFC,
incfSFg 44
Lower Bound
tW , 3.9
Upper Bound
4.8
Industrial Processes 4-47
-------
reduction efforts increase, determining what emission
reduction efforts—if any—are assumed to be occurring at
non-partner facilities (currently none).
4.20. Magnesium Production
and Processing (IPCC Source
Category 2C4)
The magnesium metal production and casting industry
uses SF6 as a cover gas to prevent the violent oxidation of
molten magnesium in the presence of air. A dilute gaseous
mixture of SF6 with dry air and/or CO2 is blown over molten
magnesium metal to induce and stabilize the formation of
a protective crust. A minute portion of the SF6 reacts with
the magnesium to form a thin molecular film of mostly
magnesium oxide and magnesium fluoride. It is currently
assumed that the amount of SF6 reacting in magnesium
production and processing is negligible and thus all SF6 used
is emitted into the atmosphere. Sulfur hexafluoride has been
used in this application around the world for the last twenty
years. It has largely replaced salt fluxes and SO2, which are
more toxic and corrosive than SF6.
The magnesium industry emitted 2.4 Tg CO2 Eq. (0.1 Gg)
of SF6 in 2002 (see Table 4-73). This represents a significant
decline from previous years. The decline is attributable to
decreased production and casting levels, as well as reductions in
SF6 usage via process optimizations by industry participants in
EPA's SF6 Emission Reduction Partnership for the Magnesium
Industry. One of the two remaining U.S. primary producers
closed in October 2001. There are no significant plans for
expansion of primary magnesium production in the United
States, but demand for magnesium metal by U.S. casting
companies has grown as auto manufacturers design more
Table 4-73: SF6 Emissions from Magnesium Production
and Processing
Year
Gg
1990
5.4
1999
2000
2001
2902
lightweight magnesium parts into vehicle models. Foreign
magnesium producers are expected to meet the growing U.S.
demand for primary magnesium.
Methodology
Emission estimates for the magnesium industry
incorporate information provided by industry participants
in EPA's SF6 Emission Reduction Partnership for the
Magnesium Industry. The partnership started in 1999, and
currently participating companies represent 100 percent
of U.S. primary production and over 80 percent of the
casting sector (i.e., die, gravity, wrought and anode casting).
Emissions for 1999 through 2002 from primary production,
some secondary production, and a large fraction of die
casting were reported by participants. The 1999 through
2002 emissions from the remaining secondary production
and casting were estimated by multiplying industry emission
factors (kg SF6per metric ton of Mg produced or processed)
by the amount of metal produced or consumed in the five
major processes (other than primary production) that require
SF6 melt protection: 1) secondary production; 2) die casting;
3) gravity casting; 4) wrought products; and 5) anodes. The
emission factors are provided below in Table 4-74. Because
there was only one primary producer in the United States in
2002, the emission factor for primary production is withheld
to protect production information. However, the emission
factor has not risen above the 1995 value of 1.1 kg SF6 per
metric ton.
Die casting emissions for 1999 through 2002, which is
believed to account for about 40 percent of all SF6 emissions
from U.S. casting and recycling processes, were estimated
using emission factors derived from information supplied
by industry partners. The weighted average 2002 emission
factor for die casting was estimated to be 0.71 kg SF6 per
metric ton of magnesium processed. In 2002, it was assumed
Table 4-74: SF6 Emission Factors (kg SF6 per Metric Ton of
Magnesium)
Year Secondary Die
1993
2000
2001
2002
1
1
1
1
iCastinga Gravity Wrought Anodes
2.14
OJ1
0.7S
0.71
, , 2
2
2
2
1
1
1
1
1
1
1
1
non-partners, an emission factor of 5.2 kg SF6 per metric ton of
4-48 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
that partnership participants accounted for a significant
proportion of all U.S. die casting. In prior years, when this
was not the case, it was assumed that non-participant die
casters, were similar to participants who cast small parts.
Due to process requirements, it is understood that these
casters consume larger quantities of SF6 per metric ton of
processed magnesium compared to those that cast large parts.
Consequently, emissions estimates from this group of die
casters were developed using an average emission factor of
5.2 kg SF6 per metric ton of magnesium. The emission factors
for the other industry sectors were based on discussions with
industry representatives.
Data used to develop these emission estimates were
provided in cooperation with the partnership participants
and the U.S. Geological Survey (USGS). U.S. magnesium
metal production (primary and secondary) and consumption
(casting) data from 1990 through 2002 are available from the
USGS (USGS 2003). Emission factors from 1990 through
1998 were based on a number of sources. Emission factors
for primary production were available from U.S. primary
producers for 1994 and 1995, and an emission factor for die
casting was available for the mid-1990s from an international
survey (Gjestland & Magers 1996).
To estimate emissions for 1990 through 1998, industry
emission factors were multiplied by the corresponding
metal production and consumption statistics from USGS.
The primary production emission factors were 1.1 kg per
metric ton in both 1994 and 1995, and the die casting
factor was 4.1 kg per metric ton. It was assumed that these
emission factors have remained constant throughout the
early 1990s. However, it was assumed that after 1996, the
emission factors for primary production and die casting
declined linearly to the level estimated based on partner
reports. This assumption is consistent with the trend
in sales to the magnesium sector that is reported in the
RAND survey of major SF6 manufacturers, which shows
a decline of 70 percent from 1996 to 1999 (RAND 2002).
The emission factors for the other processes (i.e., secondary
production, and gravity, wrought, and anode casting), about
which less is known, were assumed to remain constant.
Uncertainty
Using IPCC Good Practice Guidance Tier 1 methodology,
the overall uncertainty associated with the 2002 and 2001
SF6 emissions estimates is estimated to be ±16 percent (see
Table 4-75)
For partnership participants, an uncertainty of 5 percent
was assigned to SF6 emissions data that they supplied to
the partnership. These data have low uncertainty since
they are prepared through facility-specific tracking of SF6
cylinder purchases, usage and returns. If partners did not
report emissions data during the current reporting year, SF6
emissions data were estimated using available emission
factor and production information reported in prior years,
1999,2000 or 2001. For example, to estimate 2002 emission
factors, the average change in emission factor from 2001 to
2002 for reporting partners was applied to the 2001 emission
factor of the non-reporting partner. It was assumed that
the uncertainty associated with this extrapolated emission
factor is 25 percent. For production data, if estimates were
unavailable for the current reporting year, data from the last
reported year was applied. The uncertainty associated with
this approach ranged from 30 to 50 percent depending on
whether the production data was obtained from the previous
or an earlier year's partner report.
For those industry processes, such as gravity, anode,
wrought casting that are not represented in EPA's partnership,
SF6 emissions were estimated using production and
consumption statistics reported by USGS and an estimated
process-specific emission factor (see Table 4-75). The
uncertainty associated with USGS-reported statistics and
Table 4-75: Quantitative Uncertainty Estimates for SF6 Emissions from Magnesium Production and Processing (Tg C02 Eq.
and Percent)
Source
Year 2002 Emissions
Uncertainty Range Relative to 2002 Emission
Uncertainty (%) Estimate (Tg C02 Eq.)
2.4
16%
2.0
2.8
Industrial Processes 4-49
-------
emission factors were assumed to be 25 percent and 75
percent, respectively. In general, where precise quantitative
information was not available on the uncertainty of a
parameter, a conservative (upper-bound) value was used.
There are additional uncertainties in these estimates,
such as the basic assumption that SF6 neither reacts nor
decomposes during use. It is possible that the melt surface
reactions and high temperatures associated with molten
magnesium cause some gas degradation. Recent measurement
studies have identified SF6 cover gas degradation at hot-
chambered die casting machines on the order of 10 percent
(Bartos et al. 2003). As is the case for other sources of
SF6 emissions, total SF6 consumption data for magnesium
production and processing in the United States were not
available. Sulfur hexafluoride may also be used as a cover
gas for the casting of molten aluminum with high magnesium
content; however, it is unknown to what extent this technique
is used in the United States.
Recalculations Discussion
The emission estimate for 2001 was adjusted downward
slightly from that previously reported. This revision
reflects an update to historical data supplied by partnership
participants. This change has resulted in a decrease of 0.014
Tg CO2 Eq. (0.5 percent) in SF6 emissions in 2001.
Planned Improvements
A study is currently taking place to measure the
degree of destruction of cover gas compounds, such as
SF6 and HFC-134a, at magnesium die casting facilities.
Results from this work, which have so far indicated SF6
degradation on the order of 10 percent in a hot-chambered
die casting process (Bartos et al. 2003), could be applied
to the inventory methodology to account for cover gas
decomposition.
Additionally, as more companies join the partnership,
in particular those from sectors not currently represented,
such as gravity and anode casting, emission factors will be
refined to incorporate these additional data.
4.21. Industrial Sources of Ambient
Air Pollutants
In addition to the main greenhouse gases addressed
above, many industrial processes generate emissions of
ambient air pollutants. Total emissions of nitrogen oxides
(NOX), carbon monoxide (CO), and nonmethane volatile
organic compounds (NMVOCs) from non-energy industrial
processes from 1990 to 2002 are reported in Table 4-77.
Table 4-77: NOX, CO, and NMVOC Emissions from Industrial Processes (Gg)
Gas/Source
NO,
Chemical & Allied Product Manufacturing
Metals Processing
Storage and Transport
Other Industrial Processes
Miscellaneous*
CO
Chemical & Allied Product Manufacturing
Metals Processing
Storage and Transport
Other Industrial Processes
Miscellaneous*
NMVOCs
Chemical & AIM Product Manufacturing
Metals Processing
Storage and Transport
Other Industrial Processes
1998 1999 2000 2001 2002
888
113
75
14
m
1
629
115
81
15
417
1
637
117
81
15
424
-.1
605
102
79
9
415
1
.*rt;
1(W
82
•"".9
- 481 :
•.'~'-;";t>
662
IfJi
87
". »
458 i
•'A T.-.-'
649
98
84
9
457
. , 1
2,145
S81 -320
1,544 1,118
145
^ 517
4-50 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Box 4-1: Potential Emission Estimates of HFCs, PFCs, and SF6
Emissions of HFCs, PFCs and SF6 from" industrial processes can be estimated In two ways,.either as potential emissions or as actual
emissions, fmission estimates in thischapter are "actual emissions," wWebare deified by the Revised 1996 IPCC Guidelines for National
Greenhouse 6as Inventories {IPCC/UNEP/KCttlEA 199?) as estimates that take into account the time tag between consumption and
emissions. In contrast, "potential emissions" are defined to be equal to the amount of at chemical consumed in a country, minus the amount
of a chemical recovered for destruction or export in the year of consideration. Potential emissions will generally be greater for a given
year than actual emissions, since some amount of chemical consumed will be stored In products or equipment and will not be emitted
to the atmosphere until a later date, rf ever. Because all chemicals consumed wi eventually be emitted Into the atmosphere, in the long
term the cumulative, emission estimates using the two approaches should be equivalent unless the chemical is captured and destroyed.
Although actual emissions are considered to be the more accurate estimation approach for a single year, estimates of potential emissions
are provided for informational purposes.
Separate estimates of potential emissions were not made for industrial processes that fall into the following categories:
• By-productemissions. Some emissions do not resuttfromthe consumption or use of a chemical, but are the unintended by-products
of another process. For such emissions, which include emissions of GF4 and £fs from aluminum production and of HFC-23 from
HCFC-22 production, the distinction between potential and actual emissions is not relevant.
* Mentlalearissions that equal actual emissions. For some sources, such as magnesium production and processing, it is assumed
that there is no delay between consumption and emission and that no destruction of the chemical takes place. In this case, actual
emissions equal potential emissions.
Table 4-76 presents potential emission estimates for HFCs and PFCs from the substitution of ozone depleting substances, HFCs,
PFCs, and SF6 torn semiconductor manufacture, and SF6 from magnesium production and processing, and electrical transmission and
distribution.17 Potential emissions associated with the substitution for ozone depleting substances were calculated through a combination
of the EPA's Virrtaging Model and information provided by U.S. chemical manufacturers. Estimates of HFCs, PFCs, and SF6 consumed by
semiconductor manufacture were developed by dividing chemlcal-by-chemicalemissions by the appropriate chemical-specific emission
factors from the IPCC Good Practice Guidance {Tier 2c). Estimates of CF4 consumption were adjusted to account for the conversion of
other chemicals Into CF4 during the semiconductor manufacturing process, again using the default factors from the IPCC Good Practice
Guidance, U.S. utility purchases of SF6 for electrical equipment from 1998 through 2002 were estimated based on reports by participants
in EPA's SF6 Emission Reduction Program for Electric Power Systems. U.S. utility purchases of SF6 for electrical equipment from 1990
through 1998 were backcasted based on world sales of SF6 to utilities. Purchases of SF6 by utilities were added to SF8 purchases by
electrical equipment manufacturers to obtain total SF6 purchases by the electrical equipment sector.
Table 4-76:2002 Potential and Actual Emissions of HFCs, PFCs, and SF6 from Selected Sources (Tg C02 Eq.)
Source
Substitution of Ozone Depleting Substances
Aluminum Production
HCFC-22 Production
Semiconductor Manufacture
Magnesium Production and Processing
Electrical Transmission and Distribution
Potential
169.7
-
-
6.6
2.4
16.3
Actual
91.7
5.2
19.8
4.4
2.4
14.8
Methodology
These emission estimates were obtained from preliminary
data (EPA 2003), which, in its final iteration, will be published
on the National Emission Inventory (NEI) Air Pollutant
Emission Trends web site. Emissions were calculated either
for individual categories or for many categories combined,
using basic activity data (e.g., the amount of raw material
processed) as an indicator of emissions. National activity
data were collected for individual categories from various
agencies. Depending on the category, these basic activity
data may include data on production, fuel deliveries, raw
material processed, etc.
See Annex 5 for a discussion of sources of SF6 emissions excluded from the actual emissions estimates in this report.
Industrial Processes 4-51
-------
Activity data were used in conjunction with emission factors, reports, the 1985 National Acid Precipitation and Assessment
which together relate the quantity of emissions to the activity. Program emissions inventory, and other EPA databases.
Emission factors are generally available from the EPA's Compilation
of Air Pollutant Emission Factors, AP-42 (EPA 1997). The EPA Uncertainty
currently derives the overall emission control efficiency of a source Uncertainties in these estimates are partly due to the
category from a variety of information sources, including published accuracy of the emission factors used and accurate estimates
of activity data.
4-52 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
5. Solvent and Other Product Use
Greenhouse gas emissions are produced as a by-product of various solvent and other product uses. In the United
States, solvent-related activities were a minor source of U.S. anthropogenic greenhouse gas emissions, accounting
for less than 0.1 percent of total emissions on a carbon equivalent basis in 2002 (see Table 5-1).
Table 5-1: N70 Emissions from Solvent and Other Product Use
G§
1986
;.? - 4.5 •
14,4
f8tt
4,8
15.4
1t8t
4.8
15.4
t«9t
4.8
15.4
2000
4.8
15.4
2001
4.8
15,4
2002
4.8
15.4
5.1. Nitrous Oxide Product Usage (IPCC Source Category 3D)
Nitrous oxide is a clear, colorless, oxidizing liquefied gas, with a slightly sweet odor. Nitrous oxide is produced
by thermally decomposing ammonium nitrate (NH4NO3), a chemical commonly used in fertilizers and explosives. The
decomposition creates steam (H2O) and N2O by a low pressure, low-temperature (500°F) reaction. Once the steam is
condensed out, the N2O is purified, compressed, dried, and liquefied for storage and distribution. Two manufacturers of
N2O exist in the United States (CGA 2002).
Nitrous oxide is primarily used in carrier gases with oxygen to administer more potent inhalation anesthetics for general
anesthesia and as an anesthetic in various dental and veterinary applications. As such, it is used to treat short-term pain, for sedation
Table 5-2: N20 Emissions from Nitrous Oxide
Product Usage
Year
TgCO,Eq.
SfltM)
1190
13,9
in minor elective surgeries and as an induction anesthetic. The second main
use of N2O is as a propellant in pressure and aerosol products, the largest
application being pressure-packaged whipped cream. Small quantities of
N2O are also used in the following applications:
• Oxidizing agent and etchant used in semiconductor manufacturing;
• Oxidizing agent used, with acetylene, in atomic
absorption spectrometry;
• Production of sodium azide, which is used to inflate airbags;
• Fuel oxidant in auto racing; and
• Oxidizing agent in blowtorches used by jewelers and others
(Heydorn 1997).
Production of N2O in 2002 was approximately 17.0 thousand metric tons. Nitrous oxide emissions were 4.8 Tg CO2
Eq. (15.4 Gg) in 2002 (see Table 5-2). Production of N2O has stabilized over the past decade because medical markets
have found other substitutes for anesthetics, and more medical procedures are being performed on an outpatient basis using
local anesthetics that do not require N2O. The use of N2O as a propellant for whipped cream has also stabilized due to the
increased popularity of cream products packaged in reusable plastic tubs (Heydorn 1997).
1996
1997
1998
1999
2000
2001
2002
4.5
4.8
4.8
4.8
4.8
4.8
4.8
14.4
15.4
15.4
15.4
15.4
15.4
15.4
Solvent and Other Product Use 5-1
-------
Methodology
Emissions from N2O product usage were calculated by
first multiplying the total amount of N2O produced in the
United States by the share of the total quantity of N2O that
is used by each sector. This value was then multiplied by the
associated emissions rate for each sector. After the emissions
were calculated for each sector, they were added together
to obtain a total estimate of N2O product usage emissions.
Emissions were determined using the following equation:
Nitrous Oxide Product Usage Emissions =
Zj [Total U.S. Production of Nitrous Oxide] x
[Share of Total Quantity of N2O Usage by Sector i] x
[Emissions Rate for Sector i], where i = sector.
The share of total quantity of N2O usage by sector
represents the share of national N2O produced that is used by the
specific sector (i.e., anesthesia, food processing, etc.). In 2002,
the medical/dental industry used an estimated 86 percent of total
N2O produced, followed by food processing propellants at 6.5
percent. All other categories combined used the remainder of
the N2O produced (Tupman 2002). This sector breakdown has
changed only slightly over the past decade. For instance, the
small share of N2O usage in the production of sodium azide has
declined significantly during the decade of the 1990s. Due to
the lack of information on the specific time period of the phase-
out in this market sector, most of the N2O usage for sodium
azide production is assumed to have ceased after 1996, with the
majority of its small share of the market assigned to the larger
medical/dental consumption sector. Once the N2O is allocated
across these sectors, a usage emissions rate is then applied for
each sector to estimate the amount of N2O emitted.
Only the medical/dental and food propellant sectors are
estimated to release emissions into the atmosphere, and therefore
Table 5-3: N20 Production (Thousand Metric Tons)
these sectors are the only usage sectors with emission rates. For
the medical/dental sector, due to the poor solubility of N2O in
blood and other tissues, approximately 97.5 percent of the N2O
is not metabolized during anesthesia and quickly leaves the
body in exhaled breath. Therefore, an emission factor of 97.5
percent is used for this sector (Tupman 2002). For N2O used as
a propellant in pressurized and aerosol food products, none of the
N2O is reacted during the process and all of the N2O is emitted to
the atmosphere resulting in an emissions factor of 100 percent for
this sector (Heydorn 1997). For the remaining sectors, all of the
N2O is consumed/reacted during the process, and therefore the
emissions rate is considered to be zero percent (Tupman 2002).
The 1990 through 1992 and 1996 N2O production data
were obtained from SRI Consulting's Nitrous Oxide, North
America report (Heydorn 1997). These data were provided as
a range. For example, in 1996, Heydorn (1997) estimates N2O
production to range between 13.6and 18.1 thousand metric tons.
Tupman (2003) was able to provide a narrower range for 1996
that falls within the production bounds described by Heydorn
(1997). These data are considered more industry specific and
current. The midpoint of the narrower production range (15.9 to
18.1 thousand metric tons) was used to estimate N2O emissions
for years 1993 through 2002 (Tupman 2003).
The 1996 share of the total quantity of N2O used by each
sector was obtained from SRI Consulting's Nitrous Oxide, North
America report (Heydorn 1997). The 1990 through 1995 share
of total quantity of N2O used by each sector was kept the same
as the 1996 number provided by SRI Consulting. The 1997
through 2002 share of total quantity of N2O usage by sector
was obtained from communication with a N2O industry expert
(Tupman 2003). The emissions rate for the food processing
propellant industry was obtained from SRI Consulting's Nitrous
Oxide, North America report (Heydorn 1997), and confirmed
by a N2O industry expert (Tupman 2002). The emissions rate
for all other sectors was obtained from communication with a
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Thousand Metric Tons
16.3
15.9
15.0
17.0
17.0
. 17.0
17.0
17.0
17.0
17.0
17.0
17.0
17.0
N2O industry expert (Tupman 2002). The emissions rate for the
medical/dental sector was substantiated by the Encyclopedia of
Chemical Technology (Othmer 1990).
Uncertainty
Since plant-specific N2O production data is confidential,
emissions are based on national production statistics acquired
as ranges through reports and interviews with industry experts
Heydorn (1997) and Tupman (2002). Based on these ranges,
the uncertainty associated with the production estimate that
5-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 5-4: Quantitative Uncertainty Estimates for N20 Emissions from Nitrous Oxide Product Usage (Tg C02 Eq. and Percent)
Source
2002 Emissions
Gas (TgC02Eq.) Uncertainty (%)
Uncertainty Range Relative to 2002 Emission
Estimate (TgC02Eq.)
Lower Bound
NtttousCMdeProAtctUsap
4.8
.7%
4.4
B.1
was used to develop industry emissions in 2002 was calculated
at 1 percent. Information regarding the industry specific use of
N2O is also confidential. Thus, the predicted share of the total
quantities of N2O used by each sector are somewhat uncertain
because they are also based on industry expert opinion. While
the level of certainty differs by industry, the market shares only
vary within a range of 2 to 3 percentage points. The emissions
rate for the medical/dental industry, an estimate also based
on industry opinion, carries an uncertainty level of 3 percent.
Unqualified areas of uncertainty include the schedule of the
market decline of sodium azide production.
An uncertainty analysis, based on the Tier 1 methods
found in IPCC's Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories, was
conducted for all inputs to the N2O Product Usage sector
analysis, including activity data, source category shares of
N2O consumption, and emission factors. The combined
uncertainty of this source was calculated to be 7.2 percent.
Recalculations Discussion
A change was made to the shares of total N2O usage
apportioned to each sector. The emissions previously reported
were based on a value, the midpoint of an industry-reported
range, as the sectoral share for each sector. These midpoints
however, summed across the sectors, resulted in a total
appropriation above 100 percent. In order to avoid over-
estimation of emissions, these midpoints were normalized
so that, while their relative shares remain the same, the total
equals 100 percent of total N2O usage. This change resulted
in a 0.5 percent decrease in estimated emissions for years 1997
to 2001 when compared to last year's published estimates.
Planned Improvements
Planned improvements include a continued evaluation
of alternative production statistics for cross verification and
a reassessment of sector usage to accurately represent the
latest trends in the product usage.
5.2. Ambient Air Pollutants from
Solvent Use
The use of solvents and other chemical products can
result in emissions of various ozone precursors (i.e., ambient
air pollutants).1 Nonmethane volatile organic compounds
(NMVOCs), commonly referred to as "hydrocarbons," are the
primary gases emitted from most processes employing organic
or petroleum based solvents. Surface coatings accounted for
just under a majority of NMVOC emissions from solvent
use—41 percent in 2002—while "non-industrial"2 uses
accounted for about 38 percent and degreasing applications for
7 percent. Overall, solvent use accounted for approximately
22 percent of total U.S. emissions of NMVOCs in 2002, and
has decreased 15 percent since 1990.
Although NMVOCs are not considered direct greenhouse
gases, their role as precursors to the formation of ozone—which
is a greenhouse gas—results in their inclusion in a greenhouse
gas inventory. Emissions from solvent use have been reported
separately by the United States to be consistent with the
inventory reporting guidelines recommended by the IPCC.
These guidelines identify solvent use as one of the major
source categories for which countries should report emissions.
In the United States, emissions from solvents are primarily the
result of solvent evaporation, whereby the lighter hydrocarbon
molecules in the solvents escape into the atmosphere. The
evaporation process varies depending on different solvent uses
and solvent types. The major categories of solvent uses include:
degreasing, graphic arts, surface coating, other industrial uses of
solvents (i.e., electronics, etc.), dry cleaning, and non-industrial
uses (i.e., uses of paint thinner, etc.). Because some of these
Solvent usage in the United States also results in the emission of small amounts of hydrofluorocarbons (HFCs) and hydrofluoroethers (HFEs), which
1
are included under Substitution of Ozone Depleting Substances in the Industrial Processes chapter.
••}
^ "Non-industrial" uses include cutback asphalt, pesticide application adhesives, consumer solvents, and other miscellaneous applications.
Solvent and Other Product Use 5-3
-------
Table 5-5: Emissions of NOX, CO, and NMVOC from Solvent Use (Gg)
«e* • -.'.•• •. •
Degreasing
Graphic Arts
Dry Cleaning
Surface Coating
Other Industrial Processes*
Non-Industrial Processes'"
Other
CO
Degreasing
Graphic Arts
Dry Cleaning
Surface Coating
Otter Industrial Processes9
Non-Industrial Processes'"
Other
NMVOCs
Oegreasing
Graphic Arts
Dry Cleaning
Surface Coating
Other IndusWal Processes*
Non-lndusWal Processes6
Other
1
MA
8,217
671
249
2,289
85
1,724
;: IMS
•::;*> • 8
+
1
+
•-. ' 2
+
+
4
1
4
4
:: 4
; 1
'. , +
+
4
4,969
: 546
261
140
2,155
96
1,768
3
.if&.v.
-.'» '
4-
1
4
2
4
+
4 -
1
4
4
4
1
4-
4
4
5,100
566
266
148
2,228
100
1,790
3
/ 1t9${-^
': v ' Iv '
"4- '
1
- + •'-
1 2, '
4
4
4-' '
1
4
4
4- -
1
4
4
4- >
4,871
337
272
151
1,989
101
1,818
3
,,,;t88i;,;
;; (t-'iy.
' * rlii
, ; ~ ,4-1 , '
. ', ' -4 •'
-: - 3 -
'4
4
•• 4
41
, 4 ,
, -• 4-
, • +~
4&
4
:" 4
4
4,533
360
222
205
1851
04
1,701
40
;••***.
V-'t •
+'•
'-,:.-- *"
• '. *
3
'4-
+
4,
41
, 4-
4'
'4-
45
4
4
. 4
4,422
318
224
268
1,782
99
1,690
41
•' >^W'
.'••'••' -.* ,'
4- ••
.' t
4.-
3
•4-
4
4-
44
4
4
4.
44
4- -
4
4
4,584
334
230
274
1,878
104
1,721
43
2002
3
•" 4
4
4
3
4
4
4
44
• +
4-
4
44
4
4-
4
4,420
322
222
264
1,811
101
1,659
41
3 Includes rubber and plastics manufacturing, ana other miscellaneous applications.
6 Includes cutback asphalt, pesticide application adhesives, consumer solvents, and other miscellaneous applications.
Note: Totals may not sum due to independent rounding.
4 Does not exceed 0.5 Gg.
industrial applications also employ thermal incineration as a
control technology, combustion by-products (CO and NOx)
are also reported with this source category.
Total emissions of nitrogen oxides (NOX), nonmethane
volatile organic compounds (NMVOCs), and carbon monoxide
(CO) from 1990 to 2002 are reported in Table 5-5.
Methodology
Emissions were calculated by aggregating solvent use data
based on information relating to solvent uses from different
applications such as degreasing, graphic arts, etc. Emission
factors for each consumption category were then applied to
the data to estimate emissions. For example, emissions from
surface coatings were mostly due to solvent evaporation as the
coatings solidify. By applying the appropriate solvent-specific
emission factors to the amount of solvents used for surface
coatings, an estimate of emissions was obtained. Emissions
of CO and NOX result primarily from thermal and catalytic
incineration of solvent laden gas streams from painting booths,
printing operations, and oven exhaust.
These emission estimates were obtained from preliminary
data (EPA 2003), which, in its final iteration, will be published
on the National Emission Inventory (NEI) Air Pollutant
Emission Trends web site. Emissions were calculated
either for individual categories or for many categories
combined, using basic activity data (e.g., the amount of
solvent purchased) as an indicator of emissions. National
activity data were collected for individual applications from
various agencies.
Activity data were used in conjunction with emission
factors, which together relate the quantity of emissions to the
activity. Emission factors are generally available from the
EPA's Compilation of Air Pollutant Emission Factors, AP-42
(EPA 1997). The EPA currently derives the overall emission
control efficiency of a source category from a variety of
information sources, including published reports, the 1985
National Acid Precipitation and Assessment Program
emissions inventory, and other EPA databases.
Uncertainty
Uncertainties in these estimates are partly due to the
accuracy of the emission factors used and the reliability of
correlations between activity data and actual emissions.
5-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
6. Agriculture
Figure 6-1
Agricultural activities contribute directly to emissions of greenhouse gases through a variety of processes. This
chapter provides an assessment of non-carbon dioxide emissions from the following source categories: enteric
fermentation in domestic livestock, livestock manure management, rice cultivation, agricultural soil management, and field
burning of agricultural residues (see Figure 6-1). Carbon dioxide (CO2) emissions and removals from agriculture-related
land-use activities, such as conversion of grassland to cultivated land, are discussed in the Land-Use Change and Forestry
chapter. Carbon dioxide emissions from on-farm energy use are accounted in the Energy chapter.
In 2002, agricultural activities were responsible for emissions of 467.1 Tg CO2 Eq., or 6.7 percent of total U.S. greenhouse
gas emissions. Methane (CH4) and nitrous oxide (N2O) were the primary greenhouse gases emitted by agricultural activities.
Methane emissions from enteric fermentation and manure
management represent about 19 percent and 7 percent of total
CH4 emissions from anthropogenic activities, respectively. Of
all domestic animal types, beef and dairy cattle were by far
the largest emitters of CH4. Rice cultivation and agricultural
crop residue burning were minor sources of CH4. Agricultural
soil management activities such as fertilizer application and
other cropping practices were the largest source of U.S. N2O
emissions, accounting for 69 percent. Manure management
and field burning of agricultural residues were also small
sources of N2O emissions.
Table 6-1 and Table 6-2 present emission estimates
for the Agriculture chapter. Between 1990 and 2002, CH4
emissions from agricultural activities increased by 3.0 percent
while N2O emissions increased by 9.4 percent. In addition to
Table 6-1: Emissions from Agriculture (Tg C02 Eq.)
2002 Agriculture Chapter Greenhouse Gas Sources
Agricultural Soil Management
Enteric Fermentation
Manure Management
Rice Cultivation
Field Burning of Agricultural Residues 1.1
0 50 100 150 200 250 300
Tg CO, Eq
Gas/Source
CH4
Enteric Fermentation
Manure Management
Rice Cultivation
Field Burning of Agricultural Residues
N20
Agricultural Soil Management
Manure Management
Field Burning of Agricultural Residues
Total
1990 •
156.7 •
117.9 •
31.0 •
7.1 •
0.7 •
279.3 •
262.8 •
16.2 •
0.4 •
436.0 |
1 1996
162.8
120.5
34.6
7.0
0.8
305.5
288.1
17.0
0.4
I 468.3
1997
162.9
118.3
36.3
7.5
0.8
310.9
293.2
17.3
0.4
473.8
1998
164.1
116.7
38.8
7.9
0.8
312.0
294.2
17.3
0.5
476.2
1999
164.3
116.6
'38.6
8.3
0.8
309.9
292.1
17.4
0.4
474.2
2800
161.9
115.7
38.0
7.5
0.8
308.0
289.7
17.7
0.5
469.9
2001
161.5
114.3
38.8
7.6
0.8
307.0
288.6
18.0
0.5
468.6
2002
161.4
114.4
39.5
6.8
0.7
305.6
287.3
17.8
0.4
467.1
Note: Totals may not sum due to Independent rounding.
Agriculture 6-1
-------
Table 6-2: Emissions from Agriculture (Gg)
Gas/Source
1990
CH4
Enteric Fermentation
Manure Management
Rice Cultivation
Field Burning of Agricultural Residues
N20
Agricultural Soil Management
Manure Management
Reid Burning of Agricultural Residues
Note: Totals may not sum due to independent rounding.
CH4 and N2O, field burning of agricultural residues was also
a minor source of the ambient air pollutants carbon monoxide
(CO) and nitrogen oxides (NOX).
6.1. Enteric Fermentation (IPCC
Source Category 4A)
Methane is produced as part of normal digestive
processes in animals. During digestion, microbes resident in
an animal's digestive system ferment food consumed by the
animal. This microbial fermentation process, referred to as
enteric fermentation, produces CH4 as a by-product, which
can be exhaled or eructated by the animal. The amount of
CH4 produced and excreted by an individual animal depends
primarily upon the animal's digestive system, and the amount
and type of feed it consumes.
Among domesticated animal types, ruminant animals
(e.g., cattle, buffalo, sheep, goats, and camels) are the major
emitters of CH4 because of their unique digestive system.
Ruminants possess a rumen, or large "fore-stomach,"
in which microbial fermentation breaks down the feed
they consume into products that can be metabolized. The
microbial fermentation that occurs in the rumen enables them
1996
7,752
5,737
1,648
332
36
985
929
55
1
1997
7,756
5,635
1,728
356
37
1,003
946
56
1
1998
7,816
5,557
1,846
376
38
1,007
949
56
1
1999
7,823
5,551
1,840
395
37
1,000
942
56
1
2000
7,711
5,509
1,807
357
38
993
• : 93S
57
1
2001
7,693
5,443
1,849
364
37
990
931
5&
1
2002
7,688
5,450
1,879
325
34
986
927
58
1
to digest coarse plant material that non-ruminant animals
cannot. Ruminant animals, consequently, have the highest
CH4 emissions among all animal types.
Non-ruminant domesticated animals (e.g., swine, horses,
and mules) also produce CH4 emissions through enteric
fermentation, although this microbial fermentation occurs in
the large intestine. These non-ruminants emit significantly
less CH4 on a per-animal basis than ruminants because the
capacity of the large intestine to produce CH4 is lower.
In addition to the type of digestive system, an animal's
feed quality and feed intake also affects CH4 emissions. In
general, a lower feed quality and a higher feed intake leads
to higher CH4 emissions. Feed intake is positively related
to animal size, growth rate, and production (e.g., milk
production, wool growth, pregnancy, or work). Therefore, feed
intake varies among animal types as well as among different
management practices for individual animal types.
Methane emission estimates from enteric fermentation
are provided in Table 6-3 and Table 6-4. Total livestock
CH4 emissions in 2002 were 114.4 Tg CO2 Eq. (5,450 Gg),
increasing very slightly since 2001 due to minor increases
in some animal populations and dairy cow milk production.
Beef cattle remain the largest contributor of CH4 emissions
Table 6-3: CH4 Emissions from Enteric Fermentation (Tg C02 Eq.)
Livestock Type
Beef Cattle
Dairy Cattle
ttJrsss
Shetp
Swine
Goats
1990
83,2
28,8
Isi^
1.8
1,7
0.3
ToW 117,9
1996
88.8
26.3
1.9
1.4
1.8
0.2
120.5
1997
86.6
26.4
2.0
1.3
1.8
0.2
118.3
1998
85:0
26.3
2.0
1.3
2,0
0.2
116.7
1999
84,7
26.6
2.0
1,2
1.9
0.2
116J
2000
83.5
27,0
2,0
1.2
1J
0,2
115.7
2001
82,1
16.9
2,0
1.2
1J
0,2
114 j
2002
82.1
27.1
2.0
1.1
1.9
0.2
114.4
: Totals may not sum due to independent rounding.
6-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 6-4: CH4 Emissions from Enteric Fermentation (Gg)
Livestock Type
Beef Cattle
Dairy Cattle
Horses
Stieep
Swine
Goats
Total
1990 1
3,961 1
1,375 I
91 i
91-1
W-!
' 13,1
5,812
1996
4,227
1,254
93
68
84
10,
5,737
1997
4,124
1,255
93
64
88
10
5,635
1998
4,046
1,251
94
63
93
10
5,557
1999
4,035
1,266
93
58
90
10
5,551
2000
3,976 ,
1,284
94
56
88
10 ,
5,509
2001
3,911
1,283
95
56
80
.to
5,443
2002
3,912
1,289
95
53
'. 90
10
MIT
Note: Totals may not sum due to independent rounding.
from enteric fermentation, accounting for 72 percent in
2002. Emissions from dairy cattle in 2002 accounted for
24 percent, and the remaining emissions were from horses,
sheep, swine, and goats.
From 1990 to 2002, emissions from enteric fermentation
have decreased by 3 percent. Generally, emissions have been
decreasing since 1995, mainly due to decreasing populations
of both beef and dairy cattle and improved feed quality for
feedlot cattle. During this timeframe, populations of sheep
and goats have also decreased, while horse populations
increased and the populations of swine fluctuated.
Methodology
Livestock emission estimates fall into two categories:
cattle and other domesticated animals. Cattle, due to
their large population, large size, and particular digestive
characteristics, account for the majority of CH4 emissions
from livestock in the United States. Cattle production systems
in the United States are better characterized in comparison
with other livestock production systems. A more detailed
methodology (i.e., IPCC Tier 2) was therefore applied to
estimating emissions for cattle. Emission estimates for other
domesticated animals were handled using a less detailed
approach (i.e., IPCC Tier 1).
While the large diversity of animal management
practices cannot be precisely characterized and evaluated,
significant scientific literature exists that describes the
quantity of CH4 produced by individual ruminant animals,
particularly cattle. A detailed model that incorporates this
information and other analyses of livestock population,
feeding practices and production characteristics was used
to estimate emissions from cattle populations.
National cattle population statistics were disaggregated
into the following cattle sub-populations:
Dairy Cattle
• Calves
• Heifer Replacements
• Cows
Beef Cattle
• Calves
• Heifer Replacements
• Heifer and Steer Stockers
• Animals in Feedlots
• Cows
• Bulls
Calf birth estimates, end of year population statistics,
detailed feedlot placement information, and slaughter weight
data were used in the model to initiate and track cohorts of
individual animal types having distinct emissions profiles.
The key variables tracked for each of the cattle population
categories are described in Annex 3.9. These variables include
performance factors such as pregnancy and lactation as well
as average weights and weight gain. Annual cattle population
data were obtained from the U.S. Department of Agriculture's
National Agricultural Statistics Service (1995 a,b, 1999 a,c,d,f,
2000 a,c,d,f, 2001 a,c,d,f, 2002 a,c,d,f, 2003 a,c,d,f).
Diet characteristics were estimated by region for U.S.
dairy, beef, and feedlot cattle. These estimates were used to
calculate Digestible Energy (DE) values and CH4 conversion
rates (Ym) for each population category. The IPCC recommends
Ym values of 3.5 to 4.5 percent for feedlot cattle and 5.5 to 6.5
percent for all other cattle. Given the availability of detailed
diet information for different regions and animal types in
the United States, DE and Ym values unique to the United
States were developed, rather than using the recommended
IPCC values. The diet characterizations and estimation of DE
and Ym values were based on contact with state agricultural
Agriculture 6-3
-------
extension specialists, a review of published forage quality
studies, expert opinion, and modeling of animal physiology.
The diet characteristics for dairy cattle were from Donovan
(1999), while beef cattle were derived from NRC (2000). DE
and Ym for dairy cows were calculated from diet characteristics
using a model simulating ruminant digestion in growing
and/or lactating cattle (Donovan and Baldwin 1999). For
feedlot animals, DE and Ym values recommended by Johnson
(1999) were used. Values from EPA (1993) were used for
dairy replacement heifers. For grazing beef cattle, DE values
were based on diet information in NRC (2000) and Ym values
were based on Johnson (2002). Weight data were estimated
from Feedstuffs (1998), Western Dairyman (1998), and expert
opinion. See Annex 3.9 for more details on the method used
to characterize cattle diets in the United States.
In order to estimate CH4 emissions from cattle, the
population was divided into region, age, sub-type (e.g.,
calves, heifer replacements, cows, etc.), and production (i.e.,
pregnant, lactating, etc.) groupings to more fully capture
differences in CH4 emissions from these animal types.
Cattle diet characteristics were used to develop regional
emission factors for each sub-category. Tier 2 equations
from IPCC (2000) were used to produce CH4 emission
factors for the following cattle types: dairy cows, beef cows,
dairy replacements, beef replacements, steer stackers, heifer
stackers, steer feedlot animals, and heifer feedlot animals.
To estimate emissions from cattle, population data were
multiplied by the emission factor for each cattle type. More
details are provided in Annex 3.9.
Emission estimates for other animal types were
based on average emission factors representative of entire
populations of each animal type. Methane emissions from
these animals accounted for a minor portion of total CH4
emissions from livestock in the United States from 1990
through 2002. Also, the variability in emission factors for
each of these other animal types (e.g. variability by age,
production system, and feeding practice within each animal
type) is less than that for cattle. Annual livestock population
data for these other livestock types, except horses, as well
as feedlot placement information were obtained from the
U.S. Department of Agriculture's National Agricultural
Statistics Service (USDA 1994 a-b, 1998, 1999 b,e,
2000 b,e, 2001 b,e, 2002 b,e, 2003 b,e). Horse data were
obtained from the Food and Agriculture Organization (FAO)
statistical database (FAO 2002), because USDA does not
estimate U.S. horse populations. Methane emissions from
sheep, goats, swine, and horses were estimated by using
emission factors utilized in Crutzen et al. (1986, cited in
IPCC/UNEP/OECD/IEA 1997). These emission factors are
representative of typical animal sizes, feed intakes, and feed
characteristics in developed countries. The methodology
is the same as that recommended by IPCC (IPCC/UNEP/
OECD/IEA 1997, IPCC 2000).
See Annex 3.9 for more detailed information on the
methodology and data used to calculate CH4 emissions from
enteric fermentation.
Uncertainty
Quantitative uncertainty of this source category
was performed through the IPCC-recommended Tier 2
uncertainty estimation methodology, Monte Carlo Stochastic
Simulation technique. These estimates were developed
for the 2001 inventory estimates. No significant changes
occurred in the method of data collection, data estimation
methodology, or other factors that influence the uncertainty
ranges around the 2002 activity data and emission factor
input variables. Consequently, these uncertainty estimates
were directly applied to the 2002 emission estimates.
A total of 185 primary input variables (178 for cattle and
8 for non-cattle) were identified as key input variables for
uncertainty analysis. The normal distribution was assumed
for almost all activity- and emission factor-related input
variables. The triangular distribution was assigned for three
input variables (specifically, for cow-birth ratios for the current
and the past two years). For some key input variables, the
uncertainty ranges around their estimates (used for inventory
estimation) were collected from published documents and other
public sources. In addition, both endogenous and exogenous
correlations between selected primary input variables were
modeled. The exogenous correlation coefficients between the
probability distributions of selected activity-related variables
were developed as educated estimates.
The uncertainty ranges associated with the activity-
related input variables were plus or minus 10 percent or lower.
However, for many emission factor-related input variables,
the lower- and/or the upper-bound uncertainty estimates were
over 20 percent. The preliminary results of the quantitative
uncertainty analysis (Table 6-5) indicate that, on average, in 19
out of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
6-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 6-5: Quantitative Uncertainty Estimates for CH4 Emissions from Enteric Fermentation (Tg C02 Eq. and Percent)
Source
2002 Emission Estimate Uncertainty Range Relative to Emission Estimate'
Gas (TgC02Eq.) (T9C02Eq.) (%)
Lower Bound Upper Bound Lower Bound Upper Bound
Enteric Fermentation
CH4
114.4 : 101,9
135.0
+18%
a Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval
the range of approximately 101.9 to 135.0 Tg CO2 Eq. (or that
the actual CH4 emissions are likely to fall within the range
of approximately 11 percent below and 18 percent above the
emission estimate of 144.4 Tg CO2 Eq.). Among the individual
sub-source categories, beef cattle accounts for the largest amount
of methane emissions as well as the largest degree of uncertainty
in the inventory emission estimates. Consequently, the cattle
sub-source categories together contribute to the largest degree
of uncertainty in the inventory estimates of methane emissions
from livestock enteric fermentation. Among non-cattle, horses
account for the largest degree of uncertainty in the inventory
emission estimates.
QA/QC and Verification
In order to ensure the quality of the emission estimates
from enteric fermentation, the IPCC Tier 1 and Tier 2
Quality Assurance/Quality Control (QA/QC) procedures
were implemented that were consistent with the U.S. QA/QC
plan. Tier 2 QA procedures included independent peer review
of the emission estimates and input parameters by national
agricultural experts. Particular emphasis was placed this year
on review of the feed characteristic inputs and the output
of volatile solids excretion from the cattle model. Energy
consumption and waste output (as represented by the volatile
solids production) were verified against published nutritional
balances and the waste excretion rates. During the next
inventory cycle, an improvement workshop is planned which
will focus on specific aspects of uncertainty in the enteric
model and bring together national experts for discussion on
ways to improve aspects of the modeling.
Recalculations Discussion
While there were no changes in the methodologies used
for estimating CH4 emissions from enteric fermentation,
emissions were revised slightly due to changes in historical
data. The USDA has revised population estimates for some
cattle statistics, such as population, livestock placements, and
slaughter statistics for 2000 and 2001. Emission estimates
changed for these years for both beef and dairy cattle because
inputs were revised to reflect updated USDA estimates. In
2000, both beef and dairy cattle emissions changed less
than one Gg. In 2001, beef cattle CH4 emissions decreased
25 Gg while dairy cattle emissions increased one Gg. For
other livestock types, there was a slight increase in swine
population for 2001, which resulted in an increase in CH4
emissions of less than one Gg in that year.
Planned Improvements
In addition to the peer review workshop planned for the
next year's inventory, revisions to the cattle enteric model are
currently underway to produce nitrogen excretion rates for
the different cattle groups modeled. Similar to the volatile
solids excretion rates, this would allow the nitrogen output
data to be used directly as input to the manure management
inventory, which would improve consistency between the
two categories. Additional review and possible updates to the
feed characteristics will be considered as more peer review
feedback is obtained on these values. The objective of these
improvements will be to produce more representative feed
regimes for different regions of the country, and for the
different sub-groups of cattle.
6.2. Manure Management (IPCC
Source Category 4B)
The management of livestock manure can produce
anthropogenic CH4 and N2O emissions. Methane is produced
by the anaerobic decomposition of manure. Nitrous oxide is
produced as part of the nitrogen cycle through the nitrification
and denitrification of the organic nitrogen in livestock manure
and urine.
Agriculture 6-5
-------
When livestock or poultry manure are stored or treated in
systems that promote anaerobic conditions (e.g., as a liquid/
slurry in lagoons, ponds, tanks, or pits), the decomposition of
materials in the manure tends to produce CH4. When manure
is handled as a solid (e.g., in stacks or pits) or deposited
on pasture, range, or paddock lands, it tends to decompose
aerobically and produce little or no CH4. A number of other
factors related to how the manure is handled also affect the
amount of CH4 produced. Ambient temperature, moisture, and
manure storage or residency time affect the amount of CH4
produced because they influence the growth of the bacteria
responsible for CH4 formation. For example, CH4 production
generally increases with rising temperature and residency time.
Also, for non-liquid based manure systems, moist conditions
(which are a function of rainfall and humidity) favor CH4
production. Although the majority of manure is handled as
a solid, producing little CH4, the general trend in manure
management, particularly for large dairy and swine producers,
is one of increasing use of liquid systems. In addition, use of
daily spread systems at smaller dairies is decreasing, due to
new regulations limiting the application of manure nutrients,
which has resulted in an increase of manure managed and
stored on site at these smaller dairies.
The composition of the manure also affects the amount
of CH4 produced. Manure composition varies by animal
type, including the animal's digestive system and diet. In
general, the greater the energy content of the feed, the greater
the potential for CH4 emissions. For example, feedlot cattle
fed a high-energy grain diet generate manure with a high
CH4-producing capacity. Range cattle fed a low energy diet
of forage material produce manure with about 50 percent
of the CH4-producing potential of feedlot cattle manure.
However, some higher energy feeds also are more digestible
than lower quality forages, which can result in less overall
waste excreted from the animal. Ultimately, a combination of
diet types and the growth rate of the animals will affect the
quantity and characteristics of the manure produced.
A very small portion of the total nitrogen excreted
is expected to convert to N2O in the waste management
system. The production of N2O from livestock manure
depends on the composition of the manure and urine, the
type of bacteria involved in the process, and the amount of
oxygen and liquid in the manure system. For N2O emissions
to occur, the manure must first be handled aerobically where
ammonia or organic nitrogen is converted to nitrates and
nitrites (nitrification), and then handled anaerobically where
the nitrates and nitrites are reduced to nitrogen gas (N2),
with intermediate production of N2O and nitric oxide (NO)
(denitrification) (Groffman, et al. 2000). These emissions
are most likely to occur in dry manure handling systems
that have aerobic conditions, but that also contain pockets of
anaerobic conditions due to saturation. For example, manure
at cattle drylots is deposited on soil, oxidized to nitrite and
nitrate, and has the potential to encounter saturated conditions
following rain events.
Certain N2O emissions are accounted for and discussed
under Agricultural Soil Management. These are emissions
from livestock manure and urine deposited on pasture, range,
or paddock lands, as well as emissions from manure and urine
that is spread onto fields either directly as "daily spread" or
after it is removed from manure management systems (e.g.,
lagoon, pit, etc.).
Table 6-6 and Table 6-7 provide estimates of CH4 and
N2O emissions from manure management by animal category.
Estimates for CH4 emissions in 2002 were 39.5 Tg CO2 Eq.
(1,879 Gg), 27 percent higher than in 1990. The majority of
this increase was from swine and dairy cow manure, where
emissions increased 35 percent, and is attributed to shifts
by the swine and dairy industries towards larger facilities.
Larger swine and dairy farms tend to use liquid systems to
manage (flush or scrape) and store manure. Thus the shift
toward larger facilities is translated into an increasing use
of liquid manure management systems, which have higher
potential methane emissions than dry systems. This shift
was accounted for by incorporating state-specific weighted
CH4 conversion factor (MCF) values in combination with
the 1992 and 1997 farm-size distribution data reported in the
Census of Agriculture (USDA 1999e). From 2001 to 2002,
there was a 1.6 percent increase in CH4 emissions, due to
minor shifts in the animal populations.
As stated previously, smaller dairies are moving away
from daily spread systems. Therefore, more manure is
managed and stored on site, contributing to additional CH4
emissions over the time series. A description of the emission
estimation methodology is provided in Annex 3.10.
Total N2O emissions from manure management systems
in 2002 were estimated to be 17.8 Tg CO2 Eq. (58 Gg). The
10 percent increase in N2O emissions from 1990 to 2002 can
be partially attributed to a shift in the poultry industry away
from the use of liquid manure management systems, in favor
6-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 6-6: CH4 and N20 Emissions from Manure Management (Tg C02 Eq.)
Gas/Animal Type
199B
Dairy Cattle
Beef Cattle
Swfrw
SMep ,
Goate
Poultry
Horses
N20
tteiryCaie
ieefeiiir
SwWe ;
Sf»e«p
Goats *
•"Hwisisr / :*'"' '•
11,4
3.1
13.1
0.1
• • 4*~;
• ; ' 2.7 :
0.6
16.2
' "' 4J
4:0
0.4
• . • 4
• • • 4- '
••; : ' w-
"•#•*
1996
34.fi
12.8
3.2
15.3
4- '
2.6
0,6
17.0
4,0
5.1
0,4
-f
7.2
0.2
51J
1997
36.3
13,4
3.1
16.4
4
2J
0.6
17.3
4.0
5.4
0.4
+
7.2
0.2
53.6
1998
38.8
13.9
3.1
18.4
. 4
2.7
0.6
17.3
3.9
5.5
0,4
4.
7.2
0.2
56.1
1999
38.6
14.7
3,1
17,6
+
2.6
0.6
17.4
4.0
5.5
0.4
+
7.2
0.2
56.0
2000
38.0
14.6
3.0
17.1
+
2.6
0.6
17.7
4.0
5,9
0.4
+
7,2
0.2
55.7
2001
38.8
15.1
3.0
17.4
4
2.7
0.6
18.0
3.9
6.1
0.4
• , +
7.3
0.2
56.8
2002
39.5
15.4
3.0
17.7
+
2.6
0.6
17.8
3.9
5.9
0.4
+
7.4
0.2
57.3
Note 'fcfiftm^not mm doe to independent rounding.
Table 6-7: CH4 and N20 Emissions from Manure Management (Gg)
Peuff
1,471
§45
14S
623
3
1
128
29
52
14
16
1
.. *•••.
" -f
20
1;
1996
1,848
611
152
729
2
1
124
29
55
13
16
1
+
+
23
1
1997
1,728
639
149
781
2
1
127
29
56
13
17
1
+
-f.
23
1
1998
1,846
661
146
876
2
1
130
30
56
13
18
1
•f .
+
23
1
1999
1,840
700
146
839
2
1
123
29
56
13
18
1
+
+
23
1
2000
1.8OT
6§4
145
813
2
1.
124
30
57
13'
19
1
•¥
4'
23
1
1001
1,849
719
144
826
2
1
127
30
58
13
20
1
,4
• 4'
23
1
2002
1,879
735
143
844
2
1
124
30
58
13
19
1
4
' +
24
1
Note: Totals {My not sum due to independent rounding.
of litter-based systems and high-rise houses. In addition,
there was an overall increase in the population of poultry
and swine from 1990 to 2002, although swine populations
declined slightly in 1993,1995, 1996,1999, and 2000 from
previous years. Nitrous oxide emissions showed a 0.7 percent
decrease from 2001 to 2002, due to minor shifts in animal
population.
The population of beef cattle in feedlots increased
over the period of 1990 to 2002, resulting in increased N2O
emissions from this sub-category of cattle. Although dairy
cow populations decreased overall for the period 1990 to
2002, the population of dairies managing and storing manure
on site—as opposed to using pasture, range, or paddock or
daily spread systems—increased. Over the same period,
dairies also experienced a shift to more liquid manure
management systems at large operations, which result in
lower N2O emissions then dry systems. The net result is
a slight decrease in dairy cattle N2O emissions over the
period 1990 to 2002. As stated previously, N2O emissions
from livestock manure deposited on pasture, range, or
Agriculture 6-7
-------
paddock land and manure immediately applied to land in
daily spread systems are accounted for under Agricultural
Soil Management.
Methodology
The methodologies presented in Good Practice Guidance
and Uncertainty Management in National Greenhouse Gas
Inventories (IPCC 2000) form the basis of the CH4 and N2O
emissions estimates for each animal type. The calculation of
emissions requires the following information:
• Animal population data (by animal type and state)
• Amount of nitrogen produced (amount per 1000 pound
animal times average weight times number of head)
• Amount of volatile solids produced (amount per 1000
pound animal times average weight times number of
head)
• Methane producing potential of the volatile solids (by
animal type)
• Extent to which the CH4 producing potential is realized
for each type of manure management system (by state
and manure management system)
• Portion of manure managed in each manure management
system (by state and animal type)
• Portion of manure deposited on pasture, range, or pad-
dock or used in daily spread systems
Following is a summary of the methodologies used to
estimate CH4 and N2O emissions from manure management
for this inventory. See Annex 3.10 for more detailed
information on the methodology and data used to calculate
CH4 and N2O emissions from manure management.
Both CH4 and N2O emissions were estimated by first
determining activity data, including animal population, waste
characteristics, and manure management system usage. For
swine and dairy cattle, manure management system usage
was determined for different farm size categories using data
from USDA (USDA 1996b, 1998d, 2000h) and EPA (ERG
2000a, EPA 2001a, 2001b). For beef cattle and poultry,
manure management system usage data was not tied to farm
size (ERG 2000a, USDA 2000i). For other animal types,
manure management system usage was based on previous
estimates (EPA 1992).
Next, MCFs and N2O emission factors were determined
for all manure management systems. MCFs for dry systems
and N2O emission factors for all systems were set equal to
default IPCC factors for temperate climates (IPCC 2000).
MCFs for liquid/slurry, anaerobic lagoon, and deep pit
systems were calculated based on the forecast performance
of biological systems relative to temperature changes as
predicted in the van't Hoff-Arrhenius equation (see Annex
3.10 for detailed information on MCF derivations for liquid
systems). The MCF calculations model the average monthly
ambient temperature, a minimum system temperature, the
carryover of volatile solids in the system from month to
month due to long storage times exhibited by anaerobic
lagoon systems, and a factor to account for management
and design practices that result in the loss of volatile solids
from lagoon systems.
For each animal group the base emission factors were
then weighted to incorporate the distribution of management
systems used within each state and thereby to create an
overall state-specific weighted emission factor. To calculate
this weighted factor, the percent of manure for each animal
group managed in a particular system in a state was
multiplied by the emission factor for that system and state,
and then summed for all manure management systems in
the state.
Methane emissions were estimated using the volatile
solids (VS) production for all livestock. For poultry and
swine animal groups, for example, VS production was
calculated using a national average VS production rate from
the Agricultural Waste Management Field Handbook (USDA
1996a), which was then multiplied by the average weight of
the animal and the state-specific animal population. For most
cattle groups, regional animal-specific VS production rates
that are related to the diet of the animal for each year of the
inventory were used (Peterson et al., 2003). The resulting VS
for each animal group was then multiplied by the maximum
CH4 producing capacity of the waste (B0) and the state-
specific CH4 conversion factors.
Nitrous oxide emissions were estimated by determining
total Kjeldahl nitrogen (TKN)1 production for all livestock
wastes using livestock population data and nitrogen
excretion rates based on measurements of excreted manure.
For each animal group, TKN production was calculated
Total Kjeldahl nitrogen is a measure of organically bound nitrogen and ammonia nitrogen.
6-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
using a national average nitrogen excretion rate from the
Agricultural Waste Management Field Handbook (USDA
1996a), which was then multiplied by the average weight of
the animal and the state-specific animal population. State-
specific weighted N2O emission factors specific to the type
of manure management system were then applied to total
nitrogen production to estimate N2O emissions.
The data used to calculate the inventory estimates were
based on a variety of sources. Animal population data for all
livestock types, except horses and goats, were obtained from
the U.S. Department of Agriculture's National Agricultural
Statistics Service (USDA 1994a-b, 1995a-b, 1998a-b, 1999a-
c, 2000a-g, 2001a-f, 2002a-f, 2003a-f). Horse population data
were obtained from the FAOSTAT database (FAO 2003),
because USDA does not estimate U.S. horse populations.
Goat population data were obtained from the Census of
Agriculture (USDA 1999d). Information regarding poultry
turnover (i.e., slaughter) rate was obtained from state Natural
Resource Conservation Service (NRCS) personnel (Lange
2000). Dairy cow and swine population data by farm size for
each state, used for the weighted MCF and emission factor
calculations, were obtained from the Census of Agriculture,
which is conducted every five years (USDA 1999e).
Manure management system usage data for dairy and
swine operations were obtained from USDA's Centers
for Epidemiology and Animal Health (USDA 1996b,
1998d, 2000h) for small operations and from preliminary
estimates for EPA's Office of Water regulatory effort for
large operations (ERG 2000a; EPA 2001a, 200Ib). Data for
layers were obtained from a voluntary United Egg Producers'
survey (UEP 1999), previous EPA estimates (EPA 1992),
and USDA's Animal Plant Health Inspection Service (USDA
2000i). Data for beef feedlots were also obtained from EPA's
Office of Water (ERG 2000a; EPA 2001a, 2001 b). Manure
management system usage data for other livestock were taken
from previous estimates (EPA 1992). Data regarding the use
of daily spread and pasture, range, or paddock systems for
dairy cattle were obtained from personal communications
with personnel from several organizations, and data provided
by those personnel (Poe et al. 1999). These organizations
include state NRCS offices, state extension services, state
universities, USDA National Agriculture Statistics Service
(NASS), and other experts (Deal 2000, Johnson 2000, Miller
2000, Stettler 2000, Sweeten 2000, and Wright 2000).
Additional information regarding the percent of beef steer
and heifers on feedlots was obtained from contacts with the
national USDA office (Milton 2000).
Methane conversion factors for liquid systems were
calculated based on average ambient temperatures of the
counties in which animal populations were located. The
average county and state temperature data were obtained
from the National Climate Data Center (NOAA 2001,2002,
2003), and the county population data were calculated
from state-level population data from NASS and county-
state distribution data from the 1992 and 1997 Census
data (USDA 1999e). County population distribution data
for 1990 and 1991 were assumed to be the same as 1992;
county population distribution data for 1998 through 2002
were assumed to be the same as 1997; and county population
distribution data for 1993 through 1996 were extrapolated
based on 1992 and 1997 data.
The maximum CH4 producing capacity of the volatile
solids, or B0, was determined based on data collected in a
literature review (ERG 2000b). B0 data were collected for
each animal type for which emissions were estimated.
Nitrogen excretion rate data from the USDA Agricultural
Waste Management Field Handbook (USDA 1996a) were
used for all livestock except sheep, goats, and horses.
Data from the American Society of Agricultural Engineers
(ASAE 1999) were used for these animal types. Volatile
solids excretion rate data from the USDA Agricultural
Waste Management Field Handbook (USDA 1996a) were
used for swine, poultry, bulls, and calves not on feed. In
addition, volatile solids production rates from Peterson et
al. (2003) were used for dairy and beef cows, heifers, and
steer for each year of the inventory. Nitrous oxide emission
factors and MCFs for dry systems were taken from Good
Practice Guidance and Uncertainty Management in National
Greenhouse Gas Inventories (IPCC 2000).
Uncertainty
An analysis was conducted on the 2001 manure
management inventory to determine the uncertainty
associated with estimating nitrous oxide and methane
emissions from livestock manure management. Because
no substantial modifications were made to the inventory
methodology since the development of these estimates, it is
expected that this analysis is applicable to the uncertainty
associated with the 2002 manure management inventory. The
Agriculture 6-9
-------
Table 6-8: Quantitative Uncertainty Estimates for CH4 and N20 Emissions from Manure Management (Tg C02 Eq. and percent)
Source
Manure Management
Manure Management
2002 Emission Estimate Uncertainty Range Relative to Emission Estimate3
Gas (To-COzis.) (fiC%6|.) ; <%)
CH4
N20
39.5
17,8
Lower Bound
32.4
15.0
Upper Bound
47.3
m
Lower Bound
•18%
-16%;
Upper Bound
4-20%
•4-24%
"Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval
analysis used the Tier 2 uncertainty methodology as outlined
in the IPCC Good Practice Guidance (IPCC 2000).
Quantitative uncertainty of this source category
was performed through the IPCC-recommended Tier
2 uncertainty estimation methodology, Monte Carlo
Stochastic Simulation technique. The uncertainty analysis
was developed on the methods used to estimate nitrous
oxide and methane emissions from manure management
systems. The series of equations used in the inventory were
condensed into a single equation for each animal type and
state. The equations for each animal group contained four
to five variables around which the uncertainty analysis was
performed for each state.
The preliminary results of the quantitative uncertainty
analysis (see Table 6-8) indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the CH4
greenhouse gas emissions estimate from this source is within
the range of approximately 32.4 to 47.3 Tg CO2 Eq. (or that
the actual CH4 emissions are likely to fall within the range
of approximately 18 percent below and 20 percent above
the emission estimate of 39.5 Tg CO2 Eq.). For N2O, the
emissions estimate is within the range of approximately 15.0
to 22.1 Tg CO2 Eq. (or that the actual N2O emissions are
likely to fall within the range of approximately 16 percent
below and 24 percent above the emission estimate of 17.8
Tg CO2 Eq.) (ERG 2003).
The primary factors contributing to the uncertainty in
emission estimates are a lack of information on the usage
of various manure management systems in each regional
location and the exact CH4 generating characteristics of
each type of manure management system. Because of
significant shifts in the swine and dairy sectors toward larger
farms, it is believed that increasing amounts of manure are
being managed in liquid manure management systems. The
existing estimates reflect these shifts in the weighted MCFs
based on the 1992 and 1997 farm-size data. However, the
assumption of a direct relationship between farm size and
liquid system usage may not apply in all cases and may vary
based on geographic location. In addition, the CH4 generating
characteristics of each manure management system type are
based on relatively few laboratory and field measurements,
and may not match the diversity of conditions under which
manure is managed nationally.
Good Practice Guidance and Uncertainty Management in
National Greenhouse Gas Inventories (IPCC 2000) published
a default range of MCFs for anaerobic lagoon systems of 0
to 100 percent, which reflects the wide range in performance
that may be achieved with these systems. There exist relatively
few data points on which to determine country-specific MCFs
for these systems. In the United States, many livestock waste
treatment systems classified as anaerobic lagoons are actually
holding ponds that are substantially organically overloaded
and therefore not producing CH4 at the same rate as a properly
designed lagoon. In addition, these systems may not be well
operated, contributing to higher loading rates when sludge is
allowed to enter the treatment portion of the lagoon or the lagoon
volume is pumped too low to allow treatment to occur. Rather
than setting the MCF for all anaerobic lagoon systems in the
United States based on data available from optimized lagoon
systems, an MCF methodology was developed that more closely
matches observed system performance and accounts for the
affect of temperature on system performance.
However, there is uncertainty related to this methodology.
The MCF methodology used in the inventory includes a
factor to account for management and design practices that
result in the loss of volatile solids from the management
system. This factor is currently estimated based on data
from anaerobic lagoons in temperate climates, and from only
three systems. However, this methodology is intended to
account for systems across a range of management practices.
Future work in gathering measurement data from animal
6-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
waste lagoon systems across the country will contribute
to the verification and refinement of this methodology. It
will also be evaluated whether lagoon temperatures differ
substantially from ambient temperatures and whether the
lower bound estimate of temperature established for lagoons
and other liquid systems should be revised for use with this
methodology.
The IPCC provides a suggested MCF for poultry waste
management operations of 1.5 percent. Additional study
is needed in this area to determine if poultry high-rise
houses promote sufficient aerobic conditions to warrant
a lower MCF.
The default N2O emission factors published in Good
Practice Guidance and Uncertainty Management in National
Greenhouse Gas Inventories (IPCC 2000) were derived using
limited information. The IPCC factors are global averages;
U.S.-specific emission factors may be significantly different.
Manure and urine in anaerobic lagoons and liquid/slurry
management systems produce CH4 at different rates, and
would in all likelihood produce N2O at different rates, although
a single N2O emission factor was used for both system types.
In addition, there are little data available to determine the
extent to which nitrification-denitrification occurs in animal
waste management systems. Ammonia concentrations that
are present in poultry and swine systems suggest that N2O
emissions from these systems may be lower than predicted
by the IPCC default factors. At this time, there are insufficient
data available to develop U.S.-specific N2O emission factors;
however, this is an area of on-going research, and warrants
further study as more data become available.
Uncertainty also exists with the maximum CH4 producing
potential of volatile solids excreted by different animal groups
(i.e., B0). The B0 values used in the CH4 calculations are
published values for U.S. animal waste. However, there are
several studies that provide a range of B0 values for certain
animals, including dairy and swine. The B0 values chosen for
dairy assign separate values for dairy cows and dairy heifers to
better represent the feeding regimens of these animal groups.
For example, dairy heifers do not receive an abundance of
high energy feed and consequently, dairy heifer manure will
not produce as much CH4 as manure from a milking cow.
However, the data available for B0 values are sparse, and do
not necessarily reflect the rapid changes that have occurred in
this industry with respect to feed regimens.
QA/QC and Verification
Tier 1 and Tier 2 QA/QC activities were conducted
consistent with the U.S. QA/QC plan. As part of its Tier 2
level independent peer review, national experts in manure
management, excretion, and related issues attended a
workshop in July, 2003 for the purpose of discussing and
reviewing specific activity data used to develop the manure
management estimates. Input was solicited from these
experts on the following specific items:
• Volatile Solids Excretion Rates
• Nitrogen Excretion Rates
• Methane Producing Capacity (Bo)
• Temperature Dependence
• Retention Time
• Management and Design Practices
• Methane Conversion Factor
• Methane Production Methodology
Comments were received from the panel on these topics
and suggestions for future investigation. These suggestions and
comments are being considered for future improvements.
Recalculations Discussion
No changes have been incorporated into the methodology
for the manure management emission estimates; however,
changes were made to correct errors and updates in the
population data from previous inventory submittals. Also, the
typical animal mass for two animal groups was adjusted to
reflect recent analyses, and the distribution of animals at sheep
operations was adjusted to reflect a refined methodology. Each
of these changes is described in detail below.
• Population. Two errors in the population data were iden-
tified: the value for Hens, Vermont, 1998 was corrected
from 12,000 to 30,000; the value for Broilers, Alabama,
1995 was corrected from 16,363,636 to 163,636,363.
Additionally, all USDA data from 1998 through the
present year underwent review pursuant to USDA NASS
annual review procedures. The population data in these
years reflects some adjustments due to this review.
• Typical animal mass. The typical animal mass for beef
cows and beef calves were reevaluated and adjusted.
Typical animal mass of beef cows was adjusted from
590 kilograms to 533 kilograms, and typical animal
mass for beef calves was adjusted from 159 kilograms
to 118 kilograms (ERG 2003b).
Agriculture 6-11
-------
• Sheep distribution. The 1990 through 2001 U.S. Inven-
tory contained estimates of the percentage of sheep on
feed based on the 1993 USDA Census of Agriculture
estimates of the number of lambs on feed on feedlots.
These data only contained data for sixteen states, and
the data source indicates this list is not comprehensive.
The previous inventory estimates presented data for
sheep on feed for those 13 states indicated in the 1993
lambs on feedlots table; however, the data describing the
states with sheep on feed contains 28 states. Therefore,
the methodology was changed in the current inventory
to account for sheep on feedlots from all 28 states using
the percent on-feed at feedlots from the average of the
13 states data from lambs on feed at feedlots.
• Implied emission factors. In the previously-submitted
Common Reporting Format (CRF) tables, implied
emission factors for N2O were above the emission
factors that the IPCC recommends. The implied N2O
factors from specific waste management systems were
incorrectly calculated using the product of the total
national nitrous oxide emitted and the percent waste
management system distribution, without consideration
of the emission factor specific to that system. For the
current inventory, this methodology has been changed
so that the CRF reports implied nitrous oxide factors
from specific waste management systems according to
both percent distribution and the emission factor for
that specific component.
Planned Improvements
Currently, temperate zone MCFs are used for non-
liquid waste management systems, including pasture/range/
paddock, daily spread, solid storage, and drylot operations.
However, there are some states that have an annual average
temperature that would fall below 15°C (i.e., "cool").
Therefore, CH4 emissions from certain non-liquid waste
management systems may be overestimated; however, the
difference is expected to be relatively small due to the low
MCFs for all "dry" management systems. The use of both
cool and temperate MCFs for non-liquid waste management
systems will be investigated for future inventories.
Although an effort was made to introduce the variability
in volatile solids production due to differences in diet for beef
and dairy cows, heifers, and steer, further research is needed
to confirm and track diet changes over time. A methodology
to assess variability in swine volatile solids production would
be useful in future inventory estimates.
The American Society of Agricultural Engineers
is publishing new standards for manure production
characteristics in 2004. These data will be investigated and
evaluated for incorporation into future estimates.
The development of the National Ammonia Emissions
Inventory for the United States used similar data sources to
the current estimates of emissions from manure management,
and through the course of development of the Ammonia
Inventory, updated waste management distribution data
were identified. Future estimates will attempt to reflect these
updated data.
The methodology to calculate MCFs for liquid systems
will be examined to determine how to account for a maximum
temperature in the liquid systems. Additionally, available
research will be investigated to develop a relationship
between ambient air temperature and temperature in
liquid waste management systems in order to improve that
relationship in the MCF methodology.
Research will be initiated into the estimation and
validation of the maximum CH4-producing capacity of
animal manure (B0), for the purpose of obtaining more
accurate data to develop emission estimates.
The 2002 Census of Agriculture is expected to be
available in mid-2004. These data will be used to update
assumptions that previously relied on the 1992 and 1997
Census of Agriculture.
6.3. Rice Cultivation (IPCC Source
Category 4C)
Most of the world's rice, and all rice in the United States,
is grown on flooded fields. When fields are flooded, aerobic
decomposition of organic material gradually depletes the
oxygen present in the soil and floodwater, causing anaerobic
conditions in the soil to develop. Once the environment
becomes anaerobic, CH4 is produced through anaerobic
decomposition of soil organic matter by methanogenic
bacteria. As much as 60 to 90 percent of the CH4 produced
is oxidized by aerobic methanotrophic bacteria in the soil
(Holzapfel-Pschornetal. 1985,Sassetal. 1990). Some of the
CH4 is also leached away as dissolved CH4 in floodwater that
percolates from the field. The remaining un-oxidized CH4
6-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
is transported from the submerged soil to the atmosphere
primarily by diffusive transport through the rice plants. Minor
amounts of CH4 also escape from the soil via diffusion and
bubbling through floodwaters.
The water management system under which rice is
grown is one of the most important factors affecting CH4
emissions. Upland rice fields are not flooded, and therefore
are not believed to produce CH4. In deepwater rice fields (i.e.,
fields with flooding depths greater than one meter), the lower
stems and roots of the rice plants are dead so the primary
CH4 transport pathway to the atmosphere is blocked. The
quantities of CH4 released from deepwater fields, therefore,
are believed to be significantly less than the quantities released
from areas with more shallow flooding depths. Some flooded
fields are drained periodically during the growing season,
either intentionally or accidentally. If water is drained and
soils are allowed to dry sufficiently, CH4 emissions decrease
or stop entirely. This is due to soil aeration, which not only
causes existing soil CH4 to oxidize but also inhibits further
CH4 production in soils. All rice in the United States is grown
under continuously flooded conditions; none is grown under
deepwater conditions. Mid-season drainage does not occur
except by accident (e.g., due to levee breach).
Other factors that influence CH4 emissions from flooded
rice fields include fertilization practices (especially the use of
organic fertilizers), soil temperature, soil type, rice variety,
and cultivation practices (e.g., tillage, seeding and weeding
practices). The factors that determine the amount of organic
material that is available to decompose (i.e., organic fertilizer
use, soil type, rice variety,2 and cultivation practices) are the
most important variables influencing the amount of CH4
emitted over an entire growing season because the total
amount of CH4 released depends primarily on the amount of
organic substrate available. Soil temperature is known to be
an important factor regulating the activity of methanogenic
bacteria, and therefore the rate of CH4 production. However,
although temperature controls the amount of time it takes
to convert a given amount of organic material to CH4, that
time is short relative to a growing season, so the dependence
of total emissions over an entire growing season on soil
temperature is weak. The application of synthetic fertilizers
has also been found to influence CH4 emissions; in particular,
both nitrate and sulfate fertilizers (e.g., ammonium nitrate,
and ammonium sulfate) appear to inhibit CH4 formation.
Rice is cultivated in eight states: Arkansas, California,
Florida, Louisiana, Mississippi, Missouri, Oklahoma, and
Texas. Soil types, rice varieties, and cultivation practices for
rice vary from state to state, and even from farm to farm.
However, most rice farmers utilize organic fertilizers in the
form of rice residue from the previous crop, which is left
standing, disked, or rolled into the fields. Most farmers also
apply synthetic fertilizer to their fields, usually urea. Nitrate
and sulfate fertilizers are not commonly used in rice cultivation
in the United States. In addition, the climatic conditions of
Arkansas, southwest Louisiana, Texas, and Florida allow for
a second, or ratoon, rice crop. Methane emissions from ratoon
crops have been found to be considerably higher than those
from the primary crop. This second rice crop is produced from
regrowth of the stubble after the first crop has been harvested.
Because the first crop's stubble is left behind in ratooned
fields, and there is no time delay between cropping seasons
(which would allow for the stubble to decay aerobically), the
amount of organic material that is available for decomposition
is considerably higher than with the first (i.e., primary) crop.
Rice cultivation is a small source of CH4 in the United
States (Table 6-9 and Table 6-10). In 2002, CH4 emissions
from rice cultivation were 6.8 Tg CO2 Eq. (325 Gg). Although
annual emissions fluctuated unevenly between the years 1990
and 2002, ranging from an annual decrease of 11 percent to
an annual increase of 17 percent, there was an overall decrease
of 4 percent over the twelve-year period, due to an overall
decrease in ratoon crop area.3 The factors that affect the rice
acreage in any year vary from state to state, although the price
of rice relative to competing crops is the primary controlling
variable in most states. Price is the primary factor affecting rice
area in Arkansas, as farmers will plant more of what is most
lucrative amongst soybeans, rice, and cotton. Government
support programs have also been influential in so much as
they affect the price received for a rice crop (Slaton 2001b,
Mayhew 1997). California rice area is primarily influenced
by price and government programs, but is also affected by
water availability (Mutters 2001). In Florida, rice acreage is
largely a function of the price of rice relative to sugarcane
and corn. Most rice in Florida is rotated with sugarcane, but
2 The roots of rice plants shed organic material, which is referred to as "root exudate." The amount of root exudate produced by a rice plant over a growing
season varies among rice varieties.
The 11 percent decrease occurred between 1992 and 1993; the 17 percent increase happened between 1993 and 1994.
Agriculture 6-13
-------
Table 6-9: CH4 Emissions from Rice Cultivation (Tg C02 Eq.)
State
Primary
Arkansas
California
Florida
Louisiana
Mississippi
Missouri
Oklahoma
Texas
Ratoon
Arkansas
Florida
Louisiana
Texas
Total
1990
5.1
2.1
0.7
1.0
0.4
0.1
0.6
2.1
0.0
1.1
0.9
7.1
1996
5.0
2.1
0.9
+
1.0
0.4
0.2
+
0.5
1.9
0.0
0.1
1.1
0.8
7.0
1997
5.6
2.5
0.9
+
1.0
0.4
0.2
+
0.5
1.9
0.0
0.1
1.2
0.7
7.5
1998
5.8
2.7
0.8
•f
1.1
0.5
0.3
4
0.5
2.1
+
0.1
1.2
0.8
7.9
1999
6.3
2.9
0.9
+
1.1
0.6
0.3
4-
0.5
2.0
+ •
0.1
1.2
0.7
8.3
208ft
iJ
2.5
1.0
•4
0.9
0.4
0.3
NA
0.4
2.0
0.0
0.1
1.3
0.7
7.5
• -'..airJV-"-
x: §j V:
2.9
0.8
4-
1.0
0.5
0.4
• 4- •
0.4
1.7
0.0
• 4-
1.1
0.6
. 7.6 ;
2802
5.7
2.7
0,9
•4-
1.0
0.5
0.3
+
0.4
1.1
0.0
4
0.5
0.5
6.8
+ Does not exceed 0.05 Tg C02 Eq.
NA (Not Available)
Note: Totals may not sum due to independent rounding.
Table 6-10: CH4 Emissions from Rice Cultivation (Gg CH4)
State
1990
Primary
Arkansas
California
Florida
Louisiana
Mississippi
Missouri
Oklahoma
Texas
Ratoon
Arkansas
Florida
Louisiana
Texas
241
102
34
1
46
21
7
4
30
98
0
2
52
45
Total
339
+ Does not exceed 0.5 Gg
NA (Not Available)
Note: Totals may not sum due to independent rounding.
sometimes it is more profitable for farmers to follow their
sugarcane crop with sweet corn or more sugarcane instead
of rice (Schueneman 1997, 2001b). In Louisiana, rice area
is influenced by government support programs, the price of
rice relative to cotton, soybeans, and corn, and in some years,
weather (Saichuk 1997, Linscombe 2001b). For example, a
drought in 2000 caused extensive saltwater intrusion along
the Gulf Coast, making over 32,000 hectares unplantable.
The dramatic decrease in ratooned area in Louisiana in 2002
was the result of hurricane damage to that state's rice-cropped
area. In Mississippi, rice is usually rotated with soybeans, but if
soybean prices increase relative to rice prices, then some of the
1996
240
99
43
2
45
18
8
4
25
92
0
3
50
38
332
1997
265
118
44
2
50
20
10
4
22
91
0
3
55
33
356
1998
279
126
39
2
53
23
12
4
24
98
+
3
59
36
376
1999
300
138
43
2
52
27
16
4
22
95
+
4
58
33
395
2000
260
120
47
2
41
19
14
NA
18
97
0
2
61
34
357
2801
283
138
40
1
46
22
18
+ '
18
81
0
2
52
27
364
2002
274
128
45
1
45
22
15
4
18
52
0
2
25
24
325
acreage that would have been planted in rice, is instead planted
in soybeans (Street 1997, 2001). In Missouri, rice acreage is
affected by weather (e.g., rain during the planting season may
prevent the planting of rice), the price differential between rice
and soybeans or cotton, and government support programs
(Stevens 1997, Guethle 2001). In Oklahoma, the state having
the smallest harvested rice area, rice acreage is limited to the
areas in the state with the right type of land for rice cultivation.
Acreage is limited to growers who can afford the equipment,
labor, and land for this intensive crop (Lee 2003). Texas rice
area is affected mainly by the price of rice, government support
programs, and water availability (Klosterboer 1997, 2001b).
6-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Methodology
The Revised 1996 IPCC Guidelines (IPCC/UNEP/
OECD/IEA 1997) recommends utilizing harvested rice
areas and area-based seasonally integrated emission factors
(i.e., amount of CH4 emitted over a growing season per
unit harvested area) to estimate annual CH4 emissions from
rice cultivation. This methodology is followed with the use
of U.S.-specific emission factors derived from rice field
measurements. Seasonal emissions have been found to be
much higher for ratooned crops than for primary crops, so
emissions from ratooned and primary areas are estimated
separately using emission factors that are representative of
the particular growing season. This is consistent with IPCC
Good Practice Guidance and Uncertainty Management in
National Greenhouse Gas Inventories (IPCC 2000).
The harvested rice areas for the primary and ratoon crops
in each state are presented in Table 6-11. Primary crop areas for
1990 through 2002 for all states except Florida and Oklahoma
were taken from U.S. Department of Agriculture's Field Crops
Final Estimates 1987-1992 (USDA 1994), Field Crops Final
Estimates 1992-1997 (USDA 1998), Crop Production 2000
Summary (USDA 2001), Crop Production 2001 Summary
(USDA 2002), and Crop Production 2002 Summary (USDA
2003). Harvested rice areas in Florida, which are not reported by
USDA, were obtained from Tom Schueneman (1999b, 1999c,
2000,200la) and Arthur Kirstein (2003), Florida agricultural
extension agents, and Dr. Chris Deren (2002) of the Everglades
Research and Education Centre at the University of Florida.
Harvested rice areas for Oklahoma, which also are not reported
by USDA, were obtained from Danny Lee of the Oklahoma
Farm Services Agency (Lee 2003). Acreages for the ratoon
crops were derived from conversations with the agricultural
extension agents in each state. In Arkansas, ratooning occurred
only in 1998 and 1999, when the ratooned area was less than
1 percent of the primary area (Slaton 1999, 2000, 200la). In
Florida, the ratooned area was 50 percent of the primary area
from 1990 to 1998 (Schueneman 1999a), about 65 percent
of the primary area in 1999 (Schueneman 2000), around 41
percent of the primary area in 2000 (Schueneman 200la),
about 60 percent of the primary area in 2001 (Deren 2002),
and about 54 percent of the primary area in 2002 (Kirstein
2003). In Louisiana, the percentage of the primary area that
was ratooned was constant at 30 percent over the 1990 to
1999 period, but increased to approximately 40 percent in
Table 6-11: Rice Areas Harvested (Hectares)
State/Crop
Arkansas
Primary
Ratoon*
California
Florida
Primary
Ratoon
Louisiana
Primary
Ratoon
Mississippi
Missouri
Oklahoma
Texas
Primary
Ratoon
Total Primary
Total Ratoon
Total
1998
485,633
NO
159,854
4,978
2,489
220,558
66,168
181,174
32,376
617
142,857
1,148,047
125,788
1,273,847
| 1996
I 473,493
NO
282,347
;- 8.S03
4,452
:;, 215,702
. -84,711
84,178
38,446
: 19
120,599
48,240
1,143,885
,;; 117,482
[ f #61,887
1187
562,525
NO
288,822
7,089
3,845
235,937
70,781
88,817
41,349
12
104,816
41,926
1,263,468
118,552
1,388,828
1888
60QȤ71
202
185,350
8,094
4,047
250811
75,273
188,418
17,871
18
114,529
45,811
1,326,203
125,334
1,451,536
1988
202
284,371
7,229
4,673
249,282
74,?88
138,7m
74,184
228
104,816
41J26.
1,428,736
121,888
1,550,325
2888
570,619
V NO,
221,773
7,801
3,193
194,253
.77,701
mm
68,393
MA
86,605
43,302
1,287,888
124,197
1J81.884
2881
856,010
NO
198,811
4,562
2,752
220,963
66,289
102,388
83,772
285
87,414
34,966
1,345,984
104,006
1,449,991
2802
608,256
NO
213,879
5,077
: 2,734
216,512
32,477
182,388
73,654
274
83,367
30,846
1,383,286
66,856
1,369,262
* Arkansas ratooning occurred only in 1998 and 1999.
NO (Not Occurring)
NA (Not Available)
Note: Totals may not sum due to independent rounding.
Agriculture 6-15
-------
2000, before returning to 30 percent in 2001 and dropping to
15 percent in 2002 (Linscombe 1999a, 2001 a, 2002,2003 and
Bollich 2000). In Texas, the percentage of the primary area
that was ratooned was constant at 40 percent over the entire
1990 to 1999 period and in 2001, but increased to 50 percent
in 2000 due to an early primary crop; it then decreased to 40
percent in 2001 and 37 percent in 2002 (Klosterboer 1999,
2000, 2001a, 2002, 2003).
To determine what seasonal CH4 emission factors should
be used for the primary and ratoon crops, CH4 flux information
from rice field measurements in the United States was collected.
Experiments which involved atypical or nonrepresenative
management practices (e.g., the application of nitrate or
sulfate fertilizers, or other substances believed to suppress CH4
formation), as well as experiments in which measurements
were not made over an entire flooding season or floodwaters
were drained mid-season, were excluded from the analysis. The
remaining experimental results4 were then sorted by season
(i.e., primary and ratoon) and type of fertilizer amendment (i.e.,
no fertilizer added, organic fertilizer added, and synthetic and
organic fertilizer added). The experimental results from primary
crops with synthetic and organic fertilizer added (Bossio et al.
1999, Cicerone et al. 1992, Sass et al. 199la and 1991 b) were
averaged to derive an emission factor for the primary crop,
and the experimental results from ratoon crops with synthetic
fertilizer added (Lindau and Bollich 1993, Lindau et al. 1995)
were averaged to derive an emission factor for the ratoon crop.
The resultant emission factor for the primary crop is 210 kg
CH4/hectare-season, and the resultant emission factor for the
ratoon crop is 780 kg CH4/hectare-season.
Uncertainty
The largest uncertainty in the calculation of CH4 emissions
from rice cultivation is associated with the emission factors.
Seasonal emissions, derived from field measurements in the
United States, vary by more than one order of magnitude. This
inherent variability is due to differences in cultivation practices,
in particular, fertilizer type, amount, and mode of application;
differences in cultivar type; and differences in soil and climatic
conditions. A portion of this variability is accounted for by
separating primary from ratooned areas. However, even within
a cropping season or a given management regime, measured
emissions may vary significantly. Of the experiments used to
derive the emission factors applied here, primary emissions
ranged from 22 to 479 kg CH4/hectare-season and ratoon
emissions ranged from 481 to 1,490 kg CH4/hectare-season.
From these ranges, an uncertainty for the emission factors of
109 percent for primary crops and 65 percent for ratoon was
calculated. In order to perform a Tier 2-level Monte Carlo type
uncertainty analysis, some information regarding the statistical
distribution of the uncertainty is required. Variability about
the rice emission factor means were not normally distributed
for either primary or ratooned crops, but rather skewed,
with a tail trailing to the right of the mean, and a lognormal-
type statistical distribution was applied. The bounds of the
distribution were set at 0 (indicating that CH4 absorption was
unlikely given this management system) and three times the
emission factor itself.
Uncertainty regarding primary cropping area is an
additional consideration. Uncertainty associated with
primary rice-cropped area for each state was obtained from
expert judgment, and ranged from 4 percent to 10 percent of
the mean area. A triangular distribution of uncertainty was
assumed about the mean for areas, which was bounded at
half and one and a half times the estimated area.
Another source of uncertainty lies in the ratooned areas,
which are not compiled regularly. Ratooning accounts for
less than 5 percent of the total rice-cropped area, though it is
responsible for a proportionately larger portion of emissions.
Expert judgment estimated the uncertainty associated with
ratooned areas at between 0 percent and 7.5 percent. A
triangular distribution of uncertainty was assumed, and bound
at half and one and a half times the estimated proportion of
ratooned area.
To account for each of these uncertainties, a Tier 2-level
uncertainty analysis was performed using the information
provided above. The preliminary results of the quantitative
uncertainty analysis (see Table 6-12) indicate that, on average,
in 19 out of 20 times (i.e., there is a 95 percent probability),
the total greenhouse gas emissions estimate from this source
is within the range of approximately 2.8 to 14.7 Tg CO2 Eq.
(or that the actual CH4 emissions are likely to fall within the
range of approximately 58 percent below and 116 percent
above the emission estimate of 6.8 Tg CO2 Eq.).
4 In some of these remaining experiments, measurements from individual plots were excluded from the analysis because of the reasons just mentioned.
In addition, one measurement from the ratooned fields (i.e., the flux of 2.041 g/m2/day in Lindau and Bollich 1993) was excluded since this emission rate
is unusually high compared to other flux measurements in the United States, as well as in Europe and Asia (IPCC/UNEP/OECD/IEA 1997).
6-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 6-12: Quantitative Uncertainty Estimates for CH4 Emissions from Rice Cultivation (Tg C02 Eq. and Percent)
A final source of uncertainty is in the practice of flooding
outside of the normal rice season. According to agricultural
extension agents, all of the rice-growing states practice this on
some part of their rice acreage. Estimates of these areas range
from 5 to 68 percent of the rice acreage. Fields are flooded
for a variety of reasons: to provide habitat for waterfowl, to
provide ponds for crawfish production, and to aid in rice straw
decomposition. To date, however, CH4 flux measurements
have not been undertaken over a sufficient geographic range or
under representative conditions to account for this source or its
associated uncertainty adequate for inclusion in the emission
estimates or uncertainty evaluations presented here.
Recalculations Discussion
In researching another component of this Inventory,
it was determined that a previously unaccounted for state
(Oklahoma) produces rice on relatively small areas. Methane
emissions from rice cultivation have therefore been revised
to include harvested rice areas in the state of Oklahoma. This
addition caused an average annual increase of 0.01 percent
in emissions from 1990 through 2002.
6.4. Agricultural Soil Management
(IPCC Source Category 4D)
Nitrous oxide is produced naturally in soils through the
microbial processes of nitrification and denitrification.5 A
number of agricultural activities add nitrogen to soils, thereby
increasing the amount of nitrogen available for nitrification and
denitrification, and ultimately the amount of N2O emitted. These
activities may add nitrogen to soils either directly or indirectly
(see Figure 6-2). Direct additions occur through various soil
Figure 6-2
Direct and Indirect N?0 Emissions from Agricultural Soils
Volatilization
This graphic illustrates the sources and pathways of nitrogen that
result in direct and indirect N20 emissions from agricultural soils in the
United States. Sources of nitrogen applied to, or deposited on, soils are
represented with arrows on the left-hand side of the graphic. Emission
pathways are also shown with arrows. On the lower right-hand side is
a cut-away view of a representative section of a managed soil; histosol
cultivation is represented here.
management practices and from the deposition of manure on
soils by animals on pasture, range, and paddock (i.e., by animals
whose manure is not managed). Soil management practices
that add nitrogen to soils include fertilizer use, application of
managed livestock manure and sewage sludge, production of
nitrogen-fixing crops and forages, retention of crop residues,
and cultivation of histosols (i.e., soils with a high organic
Nitrification and denitrification are two processes within the nitrogen cycle that are brought about by certain microorganisms in soils. Nitrification is the
aerobic microbial oxidation of ammonium (NH4) to nitrate (NO3), and denitrification is the anaerobic microbial reduction of nitrate to nitrogen gas (N2).
Nitrous oxide is a gaseous intermediate product in the reaction sequence of denitrification, which leaks from microbial cells into the soil and then into the
atmosphere. Nitrous oxide is also produced during nitrification, although by a less well understood mechanism (Nevison 2000).
Cultivation of histosols does not, per se, "add" nitrogen to soils. Instead, the process of cultivation enhances mineralization of nitrogen-rich organic
matter that is present in histosols, thereby enhancing N2O emissions from histosols.
Agriculture 6-17
-------
Table 6-13: N20 Emissions from Agricultural Soil Management (Tg C02 Eq.)
ltt.1 ^j^-VjBJJt ' ' ^-'"^* """^ ""
Note: Totals my not sum
Table 6-14: N20 Emissions from Agricultural Soil Management (Gg N20)
Activity
Direct
Managed Soils
Pasture, Range, & Paddock Livestock
1997 1998 , 1899 2808 2881 2082
§77
559
us
250
573 •'••
«». •
2S4
588 «
940 Itt «4t
«8f
S27
Note: Totals may not sum t
Table 6-15: Direct N20 Emissions from Managed Soils (Tg C02 Eq.)
Activity
Commercial fertilizers*
Applied Livestock Manure
Sewage Sludge
N Fixation
Crop Residue
t-Bstpsot CuMvatien
Total
Mote:
* Excludes sewage sludge and livestock manure used as commercial fertilizers.
[ 1996
61.2
k- 13.7
0.6
I 63.9
26.8
• 2.8
[ 169.1
1987
61.3
14.0
0.7
68.2
28.7
2.9
175.6
I9lt
61.4
14.2
0.7
69:2
29.3
2.9
177J
1199
61.7
68A
W.3
: 2J
17SJ
2088
59:9
68.8
29.0
2,9 ,
tlfj
2881
58.1
•34.4.
0.7
70.6
29.3
19
178,1
2882
60.3
14,4
0.8
67.7
27.2
2.9
173.3
matter content, otherwise known as organic soils).6 Indirect
additions of nitrogen to soils occur through two mechanisms:
1) volatilization and subsequent atmospheric deposition of
applied nitrogen;7 and 2) surface runoff and leaching of applied
nitrogen into groundwater and surface water. Other agricultural
soil management activities, such as irrigation, drainage, tillage
practices, and fallowing of land, can affect fluxes of N2O, as well
as other greenhouse gases, to and from soils. However, because
there are significant uncertainties associated with these other
fluxes, their contributions have not been estimated.
Agricultural soil management is the largest source of N2O in
the United States.8 Estimated emissions from this source in 2002
were 287.3 Tg CO2 Eq. (927 Gg N2O) (see Table 6-13 and Table
6-14). Although annual agricultural soil management emissions
fluctuated between 1990 and 2002, there was a general increase
in emissions over the thirteen-year period of approximately 9
percent (see Annex 3.11 for a complete time series of emission
estimates). This general increase was due primarily to an increase
in synthetic fertilizer use, manure production, and crop and forage
production over the period. Year-to-year fluctuations are largely a
reflection of annual variations in synthetic fertilizer consumption
and crop production.
Estimated direct and indirect N2O emissions, by subsource,
are provided in Table 6-15, Table 6-17, and Table 6-19.
These processes entail volatilization of applied nitrogen as ammonia (NH3) and oxides of nitrogen (NOX), transformations of these gases within the
atmosphere (or upon deposition), and deposition of the nitrogen primarily in the form of paniculate ammonium (NH4), nitric acid (HNO3), and oxides
of nitrogen.
Q
Note that the emission estimates for this source category include applications of nitrogen to all soils (e.g., forest soils, urban areas, golf courses, etc.),
but the term "Agricultural Soil Management" is kept for consistency with the reporting structure of the Revised 1996 IPCC Guidelines (IPCC/UNEP/
OECD/IEA 1997).
6-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 6-16: Direct N20 Emissions from Pasture, Range, and Paddock Livestock Manure (Tg C02 Eq.)
Animal Type
1990
Beef Cattle
Dairy Cows
Swine
Sheep
Goats
Poultry
Horses
Total
37.2
Note: Totals may not sum due to independent rounding.
Table 6-17: Indirect N20 Emissions (Tg C02 Eq.)
1996
35.6
1.4
0,3
0.3
0.2
0.1
2,3
40.0
1997
34.5
1.3
0.2
0.3
0.2
0.1
2.3
38.8
1998
33.7
1.3
0.2
0.3
0.2
0.1
2.3
38.0
1999
33.4
1.2
0.2
0.3
0.2
0.1
2.3
37.6
2000
32.8
1.2
0.2
0.3
0.2
0.1
2.3
37.0
2001
32.5
1.2
0.2
0.3
0,2
0.1
2.3
36.7
2002
32.4
1.1
0.2
0.2
0.2
0.1
2.3
36.6
Activity
1990
Volatilization & Aim. Deposition
Commercial Fertilizers*
Total Livestock Manure
Sewage Sludge
Surface Leaching & Runoff
Commercial Fertilizers*
Applied and PRP Livestock Manure
Sewage Sludge
Total
72.3
1996
12.4
5.4
6,8
0.1
66.6
40.8
25.3
0.5
79.0
1997
12.3
5.5
6.7
0.1
66.4
40.9
25,1
0.5
78.7
1998
12.3
5.5
6.7
0.1
66.3
41.0
24.9
0.5
78.6
1999
12.3
5.5
6.6
0.1
66.3
41.1
24.7
0.5
78.6
2000
12.1
5.3
6.6
0.1
65.1
39.9
24.6
0.5
77.2
2001
11.9
5.2
6.6
0.1
63,9
38.7
24.6
0.6
75.8
2002
12.1
5.4
6.6
0.2
65.3
40.2
24.6
0.6
77.4
Note: lo&ls may not sum due to independent rounding.
* Excludes sewage sludge and livestock manure used as commercial fertilizers.
Methodology
The methodology used to estimate emissions from
agricultural soil management is consistent with the Revised
1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997), as
amended by the IPCC Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories (IPCC
2000). The Revised 1996 IPCC Guidelines divide this N2O
source category into three components: (1) direct emissions
from managed soils due to applied nitrogen and cultivation of
histosols; (2) direct emissions from soils due to the deposition
of manure by livestock on pasture, range, and paddock; and
(3) indirect emissions from soils induced by applied fertilizers,
sewage sludge and total livestock manure nitrogen.
Annex 3.11 provides more detailed information on the
methodologies and data used to calculate N2O emissions
from each of these three components.
Direct N20 Emissions from Managed Soils
Direct N2O emissions from managed soils are composed
of two parts, which are estimated separately and then
summed. These parts are 1) emissions due to nitrogen
applications, and 2) emissions from histosol cultivation.
Estimates of direct N2O emissions from nitrogen
applications were based on the total amount of nitrogen
applied to soils annually through the following practices:
(a) the application of synthetic and organic commercial
fertilizers, (b) the application of livestock manure through
both daily spread operations and through the eventual
application of manure that had been stored in manure
management systems, (c) the application of sewage sludge,
(d) the production of nitrogen-fixing crops and forages, and
(e) the retention of crop residues (i.e., leaving residues in the
field after harvest). For each of these practices, the annual
amounts of nitrogen applied were estimated as follows:
a) Synthetic and organic commercial fertilizer nitrogen ap-
plications were derived from annual fertilizer consump-
tion data and the nitrogen content of the fertilizers.
b) Livestock manure nitrogen applications were based
on the assumption that all livestock manure is applied
to soils except for two components: 1) a small por-
Agriculture 6-19
-------
tion of poultry manure that is used as a livestock feed
supplement, and 2) the manure from pasture, range, and
paddock livestock. The manure nitrogen data were derived
from animal population and weight statistics, information
on manure management system usage, annual nitrogen
excretion rates for each animal type, and information on
the fraction of poultry litter that is used as a livestock
feed supplement.
c) Sewage sludge nitrogen applications were derived from
estimates of annual U.S. sludge production, the nitrogen
content of the sludge, and periodic surveys of sludge
disposal methods.
d) The amounts of nitrogen made available to soils through
the cultivation of nitrogen-fixing crops and forages
were based on estimates of the amount of nitrogen in
aboveground plant biomass, which were derived from
annual crop production statistics, mass ratios of aboveg-
round residue to crop product, dry matter fractions, and
nitrogen contents of the plant biomass.
e) Crop residue nitrogen retention data were derived from
information about which residues are typically left on
the field, the fractions of residues left on the field, annual
crop production statistics, mass ratios of aboveground
residue to crop product, and dry matter fractions and
nitrogen contents of the residues.
After the annual amounts of nitrogen applied were
estimated for each practice, the amounts of nitrogen for
commercial fertilizers, sewage sludge, and livestock manure
were reduced by the fraction that is assumed to volatilize
according to the Revised 1996 IPCC Guidelines and the IPCC
Good Practice Guidance and Uncertainty Management in
National Greenhouse Gas Inventories. The net amounts
left on the soil from each practice were then summed and
added to the applied nitrogen from N-fixing crops and crop
residues to yield total unvolatilized applied nitrogen, which
was multiplied by the IPCC default emission factor for
nitrogen applications.
Estimates of annual N2O emissions from histosol
cultivation were based on estimates of the total U.S. acreage
of histosols cultivated annually for each of two climatic zones:
1) temperate, and 2) sub-tropical. To estimate annual
emissions, the total temperate area was multiplied by the IPCC
default emission factor for temperate regions, and the total sub-
tropical area was multiplied by the average of the IPCC default
emission factors for temperate and tropical regions.9
Total annual emissions from nitrogen applications, and
annual emissions from histosol cultivation, were then summed
to estimate total direct emissions from managed soils.
Direct N20 Emissions from Pasture, Range, and Paddock
Livestock Manure
Estimates of N2O emissions from this component
are based on the amount of nitrogen in the manure that is
deposited annually on soils by livestock on pasture, range,
and paddock (PRP). Estimates of annual manure nitrogen
from these livestock were derived from animal population
and weight statistics; information on the fraction of the total
population of each animal type that is on pasture, range, or
paddock; and annual nitrogen excretion rates for each animal
type. The annual amount of manure nitrogen from each
animal type were summed over all animal types to yield total
pasture, range, and paddock manure nitrogen, which was then
multiplied by the IPCC default emission factor for pasture,
range, and paddock nitrogen to estimate N2O emissions.
Indirect N20 Emissions from Soils
Indirect emissions of N2O are composed of two parts,
which are estimated separately and then summed. These
parts are 1) emissions resulting from volatilization and
subsequent deposition of the nitrogen in applied fertilizers,
applied sewage sludge, and all livestock manure, 1" and 2)
leaching and runoff of nitrogen in applied fertilizers, applied
sewage sludge, and applied plus deposited livestock manure.
The activity data (i.e., nitrogen in applied fertilizers, applied
sewage sludge, all livestock manure, and applied plus
deposited livestock manure) were estimated in the same way
as for the direct emission estimates.
To estimate the annual amount of applied nitrogen
that volatilizes, the annual amounts of applied synthetic
fertilizer nitrogen, applied sewage sludge nitrogen, and
all livestock manure nitrogen were each multiplied by the
appropriate IPCC default volatilization fraction. The three
amounts of volatilized nitrogen were then summed, and the
" Note that the IPCC default emission factors for histosols have been revised in the IPCC Good Practice Guidance and Uncertainty Management in
National Greenhouse Gas Inventories (IPCC 2000). These revised default emission factors (IPCC 2000) were used in these calculations.
Total livestock manure nitrogen is used in the calculation of indirect N2O emissions from volatilization because all manure nitrogen, regardless of how
the manure is managed or used, is assumed to be subject to volatilization.
6-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
sum was multiplied by the IPCC default emission factor for
volatilized/deposited nitrogen.
To estimate the annual amount of nitrogen that leaches
or runs off, the annual amounts of applied synthetic fertilizer
nitrogen, applied sewage sludge nitrogen, and applied plus
deposited livestock manure nitrogen were each multiplied by
the IPCC default leached/runoff fraction. The three amounts
of leached/runoff nitrogen were then summed, and the sum
was multiplied by the IPCC default emission factor for
leached/runoff nitrogen.
Total annual indirect emissions from volatilization, and
annual indirect emissions from leaching and runoff, were
then summed to estimate total indirect emissions of N2O
from managed soils.
The activity data used in these calculations were
obtained from numerous sources. Annual synthetic and
organic fertilizer consumption data for the United States were
obtained from annual publications on commercial fertilizer
statistics (TVA 1991, 1992a, 1993, 1994; AAPFCO 1995,
1996, 1997, 1998, 1999, 2000b, 2002, 2003). Fertilizer
nitrogen contents were taken from these same publications
and AAPFCO (2000a). Livestock population data were
obtained from USDA publications (USDA 1994b,c; 1995a,b;
1998a,c; 1999a-e; 2000a-g; 2001b-g; 2002b-g; 2003b-g),
the FAOSTAT database (FAO 2003), and Lange (2000).
Manure management information was obtained from Poe et
al. (1999), Safley et al. (1992), and personal communications
with agricultural experts (Anderson 2000, Deal 2000,
Johnson 2000, Miller 2000, Milton 2000, Stettler 2000,
Sweeten 2000, Wright 2000). Livestock weight data were
obtained from Safley (2000), USDA (1996, 1998d), and
ASAE (1999); daily rates of nitrogen excretion from ASAE
(1999) and USDA (1996); and information about the fraction
of poultry litter used as a feed supplement from Carpenter
(1992). Data collected by the EPA were used to derive annual
estimates of land application of sewage sludge (EPA 1993,
1999). The nitrogen content of sewage sludge was taken
from Metcalf and Eddy, Inc. (1991). Annual production
statistics for nitrogen-fixing crops were obtained from USDA
reports (USDA 1994a, 1998b, 2000i, 2001a, 2002a, 2003a),
a book on forage crops (Taylor and Smith 1995, Pederson
1995, Beuselinck and Grant 1995, Hoveland and Evers
1995), and personal communications with forage experts
(Cropper 2000, Gerrish 2000, Hoveland 2000, Evers 2000,
and Pederson 2000). Mass ratios of aboveground residue
to crop product, dry matter fractions, and nitrogen contents
for nitrogen-fixing crops were obtained from Strehler and
Stutzle (1987), Barnard and Kristoferson (1985), Karkosh
(2000), Ketzis (1999), and IPCC/UNEP/OECD/IEA (1997).
Annual production statistics for crops whose residues are
left on the field, except for rice in Florida and Oklahoma,
were obtained from USDA reports (USDA 1994a, 1998b,
20001,2001a, 2002a, 2003a). Production statistics for rice in
Florida and Oklahoma are not recorded by USDA, so these
were derived from Schueneman (1999,2001), Deren (2002),
and Schueneman and Deren (2002) for Florida and from Lee
(2003) and Schueneman and Deren (2002) for Oklahoma.
Aboveground residue to crop mass ratios, residue dry matter
fractions, and residue nitrogen contents were obtained
from Strehler and Stutzle (1987), Turn et al. (1997), Ketzis
(1999), and Barnard and Kristoferson (1985). Estimates
of the fractions of residues left on the field were based on
information provided by Karkosh (2000), and on information
about rice residue burning (see the Agricultural Residue
Burning section). The annual areas of cultivated histosols
were estimated from 1982, 1992, and 1997 statistics in
USDA's 1997 National Resources Inventory (USDA 2000h,
as extracted by Eve 2001, and revised by Ogle 2002).
All emission factors,11 volatilization fractions, and
the leaching/runoff fraction were taken from the Revised
1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997),
as amended by the IPCC Good Practice Guidance and
Uncertainty Management in National Greenhouse Gas
Inventories (IPCC 2000).
Uncertainty
The amount of N2O emitted from managed soils
depends not only on N inputs, but also on a large number of
variables, including organic carbon availability, O2 partial
pressure, soil moisture content, pH, soil temperature, and
soil amendment management practices. However, the effect
of the combined interaction of these variables on N2O
flux is complex and highly uncertain. The IPCC default
methodology, which is used here, is based only on N inputs
Note that the emission factor used for cultivated histosols in the sub-tropics is the average of the tropical and temperate default IPCC emission
factors.
Agriculture 6-21
-------
and does not incorporate other variables. As noted in the
Revised 1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA
1997), this is a generalized approach that treats all soils
equivalently, with the exception of cultivated histosols.
IPCC default emission factors do not have associated
uncertainties in either the Guidelines or Good Practice
Guidance documents (IPCC/UNEP/OECD/IEA 1997, IPCC
2000). In quantifying the uncertainty in N2O emissions
from agricultural soils, we have assumed an uncertainty
for these factors as follows.
Uncertainties exist in both the activity data and
emission factors used to derive emission estimates.
Even when data were derived from published reports,
few uncertainty estimates are provided or made available
upon request. Where such information is lacking, it was
necessary to apply expert judgment in surmising the
uncertainty associated with each factor in developing these
emission estimates.
Fertilizer statistics include only those fertilizers
that enter the commercial market, so non-commercial
fertilizers (organics, in particular, excluding manure and
crop residues) have not been captured. For the purposes of
quantitative uncertainty analysis, the uncertainty in synthetic
fertilizer applications was assumed to range from half to
one and a half times the estimated value, and uncertainty
in organic fertilizers (including manure) was assumed to
range from zero to twice the estimated application rate,
with a triangular statistical distribution. Managed and daily
spread manure N varied from half to one and a half times
their estimated values.
The N content of applied fertilizers varied from half
to one and a half times the estimated value in a triangular
distribution.
Statistics on sewage sludge applied to soils were
not available on an annual basis; annual production and
application estimates were based on figures and projections
that were calculated from surveys that yielded uncertainty
levels as high as 14 percent (Bastian 1999). Annual data were
obtained by interpolating and extrapolating at constant rates
from these uncertain figures, though change between the
years was unlikely to be constant (Bastian 2001). Uncertainty
in the land application of sewage sludge for the quantitative
analysis was assumed to range from half to one and a half
times the estimated value for both sludge production and
land applications, in a triangular distribution.
Production statistics for nitrogen-fixing crops that are
forage legumes are uncertain because statistics are not compiled
for any of these crops except alfalfa, and the alfalfa statistics
include alfalfa mixtures with other types of forage (e.g., clover).
Conversion factors for the nitrogen-fixing crops were based on
a limited number of studies, and may not be representative of
all conditions in the United States. Uncertainty with this input
was assumed to range from half to one and a half times the
estimated value in a triangular distribution.
Data on crop residues left on the field are not available,
so expert judgment was used to estimate the amount of
residues left on soils, with an associated uncertainty ranging
from half to one and a half times the estimated value, in a
triangular distribution.
Finally, estimates of cultivated histosol areas are
uncertain because they are from a natural resource inventory
that was not explicitly designed as a soil survey, and
contains data for only three years (1982, 1992, and 1997).
Annual histosol areas were estimated by linear interpolation
and extrapolation, and uncertainty was assumed to range
from half to one and a half times the estimated values for
both temperate and subtropical histosols, in a triangular
distribution.
Livestock excretion values, while based on detailed
population and weight statistics, were derived using
simplifying assumptions concerning the types of management
systems employed. Uncertainties in PRP N, which are
derivative activity data, were assumed to range from one half
to one and a half times the estimated value, in a triangular
distribution.
Uncertainty in the volatilization rates for synthetic and
organic fertilizers, manure, and sludge, were triangularly
distributed and ranged from half to one and a half times
their estimated values. The proportion of N leached or runoff
varied from zero to twice the estimated value, distributed in
a triangular statistical distribution.
All emission factors (e.g., emission factors for applied
N, temperate and subtropical histosols, PRP manure,
volatilization, and leaching and runoff) were assumed to
have a lognormal statistical distribution ranging from zero
to three times their estimated value.
The preliminary results of the quantitative uncertainty
analysis Table 6-18 indicate that, on average, in 19 out of
20 times (i.e., there is a 95 percent probability), the total
6-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 6-18: Quantitative Uncertainty Estimates of N20 Emissions from Agricultural Soil Management (Tg C02 Eq. and Percent)
Source
2002 Emission Estimate
Gas (Tg C02 Eq.)
Uncertainty Range Relative to Emission Estimate3
(TgC02Eq.) (%)
Agricultural Soil Management
Agricultural Soil Management
Agricultural Soil Management
Direct N20
Indirect N20
Total N20
209.9
77.4
287.3
Lower Bound
63.2
12.7
100.3
Upper Bound
596.5
298.8
736.5
Lower Bound
-70%
-84%
-65%
Upper Bound
+184%
+286%
+156%
'Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
greenhouse gas emissions estimate from this source is within
the range of approximately 100.3 to 736.5 Tg CO2 Eq. (or
that the actual emissions are likely to fall within the range
of approximately 65 percent below and 156 percent above
the emission estimate of 287.3 Tg CO2 Eq.).
Recalculations Discussion
Estimates of N2O emissions from agricultural soil
management have been revised due to methodological and
historical data changes in the calculations of nitrogen from
livestock that is applied to soils. These changes include
corrections to: the typical animal mass value for beef
cows and calves; the accounting of sheep in New England
states; state broiler populations; and updated NASS animal
population estimates for the years 1998 through 2001.
Additionally, the factor for converting short tons to metric
tons was revised to include another significant digit, and
the percent residue applied for rice in the year 2001 was
corrected. In combination, these changes resulted in an
average annual decrease of 4.9 Tg CO2 Eq. (2 percent) in
N2O emissions over the 1990 through 2001 period.
Planned Improvements
EPA is currently working in collaboration with the
Agricultural Research Service and the Natural Resource
Ecology Lab at Colorado State University to use the
DAYCENT ecosystem process model (Del Grosso et al.
2001, Parton et al. 1998) to estimate N2O emissions from
agricultural soil management in next year's Inventory. In
countries like the United States, which cover large land
areas and have a diversity of climate, soils, land use and
management systems, the use of an ecosystem process model
such as DAYCENT can have great advantages over the single
emission factor approach as specified in the IPCC Guidelines
for estimating N2O emissions. Potential advantages of a
dynamic simulation-based approach include the use of
actual observed weather, observed annual crop yields, and
detailed soil and management information for estimating
N2O emissions. One of the greatest challenges involved in
this effort will be obtaining the activity data (e.g., synthetic
fertilizer and manure nitrogen inputs) at the appropriate
spatial scale for use in the DAYCENT model. This effort
will develop county-level estimates of N2O emissions from
agricultural soils that can be summed to produce a national-
level estimate.
6.5. Field Burning of Agricultural
Residues (IPCC Source Category 4F)
Large quantities of agricultural crop residues are
produced by farming activities. There are a variety of ways
to dispose of these residues. For example, agricultural
residues can be left on or plowed back into the field,
composted and then applied to soils, landfilled, or burned
in the field. Alternatively, they can be collected and used as
fuel, animal bedding material, or supplemental animal feed.
Field burning of crop residues is not considered a net source
of CO2 because the carbon released to the atmosphere as
CO2 during burning is assumed to be reabsorbed during the
next growing season. Crop residue burning is, however, a
net source of CH4, N2O, CO, and NOX, which are released
during combustion.
Field burning is not a common method of agricultural
residue disposal in the United States; therefore, emissions
from this source are minor. The primary crop types whose
residues are typically burned in the United States are wheat,
rice, sugarcane, corn, barley, soybeans, and peanuts. Of these
residues, less than 5 percent is burned each year, except for
Agriculture 6-23
-------
Table 6-19: Emissions from Field Burning of Agricultural Residues (Tg C02 Eq.)
CH4
Sugarcane
Corn
Barley
Wheat
Wee
Sugarcane
Corn
Soybeans
-i- Does not exceed 0.05 Tg CO? Eq.
0,1
ftl
4
M;
4
4-
4
0.3
•f
U
- ,*, V1'
•«*'£.:;
.-•4 >:-vi
•*•,"
fct
4 .•
<3J
4
tj
M
At
'4-
*'
4-
, 4;,_
-.41.
2002
0,1
0.1
,<.+
0,2
0.4
. ' 4-
4
4
04
4
t).3
4-
1.1
rice.12 Annual emissions from this source over the period
1990 through 2002 have remained relatively constant,
averaging approximately 0.7 Tg CO2 Eq. (35 Gg) of CH4,
0.4 Tg CO2 Eq. (1 Gg) of N2O, 706 Gg of CO, and 33 Gg
of NOX (see Table 6-19 and Table 6-20).
Methodology
The methodology for estimating greenhouse gas
emissions from field burning of agricultural residues is
consistent with the Revised 1996IPCC Guidelines (IPCC/
UNEP/OECD/IEA 1997). In order to estimate the amounts
of carbon and nitrogen released during burning, the following
equations were used:13
Carbon Released = (Annual Crop Production) x
(Residue/Crop Product Ratio)
x (Fraction of Residues Burned in situ) x (Dry Matter
Content of the Residue)
x (Burning Efficiency) x (Carbon Content of the Residue)
x (Combustion Efficiency)14
Nitrogen Released = (Annual Crop Production) x
(Residue/Crop Product Ratio)
x (Fraction of Residues Burned in situ) x (Dry Matter
Content of the Residue)
x (Burning Efficiency) x (Nitrogen Content of the
Residue) x (Combustion Efficiency)
Emissions of CH4 and CO were calculated by multiplying
the amount of carbon released by the appropriate IPCC
default emission ratio (i.e., CH4-C/C or CO-C/C). Similarly,
N2O and NOX emissions were calculated by multiplying the
amount of nitrogen released by the appropriate IPCC default
emission ratio (i.e., N2O-N/N or NOX-N/N).
The crop residues that are burned in the United States
were determined from various state-level greenhouse gas
emission inventories (ILENR 1993, Oregon Department of
Energy 1995, Wisconsin Department of Natural Resources
1993) and publications on agricultural burning in the United
States (Jenkins et al. 1992, Turn et al. 1997, EPA 1992).
The fraction of rice straw burned each year is significantly higher than that for other crops (see "Methodology" discussion below).
Note: As is explained later in this section, the fraction of rice residues burned varies among states, so these equations were applied at the state level for
rice. These equations were applied at the national level for all other crop types.
Burning Efficiency is defined as the fraction of dry biomass exposed to burning that actually burns. Combustion Efficiency is defined as the fraction
of carbon in the fire that is oxidized completely to CO2. In the methodology recommended by the IPCC, the "burning efficiency" is assumed to be
contained in the "fraction of residues burned" factor. However, the number used here to estimate the "fraction of residues burned" does not account for
the fraction of exposed residue that does not burn. Therefore, a "burning efficiency factor" was added to the calculations.
6-24 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 6-20: Emissions from Field Burning of Agricultural Residues (Gg)*
Gas/Crop Type 1990
CH4
Wheat
Rice
Sugarcane
Corn
Barley
Soybeans
Peanuts
N20
Wheat
Rice
Sugarcane
Corn
Barley
Soybeans
Peanuts
CO
Wheat
Rice
Sugarcane
Corn
Barley
Soybeans
Peanuts
HO,
Wheat
Rice
Sugarcane
Corn
iarley
Soybeans
Peanuts
33
7
4
1
13
1
7
+
1
+
+
+
+
+
1
+
689
137
86
18
282
16
148
2
28
4
3
+
7
1
14
4-
1996
36
5
4
1
i 16
' 9
1
+
1997
37
6
3
1
16
1
10
-f-
1
+
1998
38
6
3
1
17
1
10
+
1
*
1999
37
5
4
1
16
+
10
+
1
• *
2000
38
5
4
1
17
1
10
+
1
+
2001
37
5
4
1
16
-f
11
+
1
+
2002
34
4
3
1
15
+
10
-t-
1
+
1
+
753
114
91
19
328
15
183
2
32
3
3
+
8
17
1
-f
767
124
72
21
328
13
207
2
34
3
3
4
8
20
1
+
788
128
64
22
347
13
211
2
35
3
2
+
8
20
1
+
767
115
76
23
336
10
204
2
34
3
3
+
8
19
1
+
790
112
76
24
353
12
212
2
35
3
3
+
8
20
1
+
770
98
77
23
338
9
222
3
35
3
3
+
8
21
1
+
706
81
60
24
320
8
210
2
33
2
2
+
8
20
* Mi molecular weight basis.
+ Does not exceed 0.5 Gg
Note: Totals may not sum due to independent rounding.
Crop production data for all crops except rice in Florida
and Oklahoma were taken from the USDA's Field Crops, Final
Estimates 1987-1992, 1992-1997 (USDA 1994, 1998), Crop
Production 1999 Summary (USDA 2000), Crop Production
2000 Summary (USDA 2001), Crop Production 2001 Summary
(USDA 2002), and Crop Production 2002 Summary (USDA
2003). Rice production data for Florida and Oklahoma, which
are not collected by USDA, were estimated by applying average
primary and ratoon crop yields for Florida (Schueneman and
Deren 2002) to Florida acreages (Schueneman 1999b, 2001;
Deren 2002; Kirstein 2003) and Oklahoma acreages15 (Lee
2003). The production data for the crop types whose residues
are burned are presented in Table 6-21.
The percentage of crop residue burned was assumed
to be 3 percent for all crops in all years, except rice, based
on state inventory data (ILENR 1993, Oregon Department
of Energy 1995, Noller 1996, Wisconsin Department of
Natural Resources 1993, and Cibrowski 1996).16 Estimates
of the percentage of rice residue burned were derived from
state-level estimates of the percentage of rice area burned
each year, which were multiplied by state-level, annual rice
production statistics. The annual percentages of rice area
burned in each state were obtained from the agricultural
extension agents in each state and reports of the California
Air Resources Board (CARB) (Bollich 2000; Deren
2002; Guethle 1999, 2000, 2001, 2002, 2003; Fife 1999;
^ Rice production yield data are not available for Oklahoma so the Florida values are used as a proxy.
!° Rice cultivated in Oklahoma is an exception. As no percent burned data are known, it was assumed that 3 percent (the general crop burning default)
of rice residue in Oklahoma is burned annually.
Agriculture 6-25
-------
Table 6-21: Agricultural Crop Production (Thousand Metric Tons of Product)
Crop
Wheat
Rice
Sugarcane
Com*
Barley
Soybeans
Peanuts
*Corn for grain (i.e., excludes corn for sRage).
Table 6-22: Percentage of Rice Area Burned by State
State
Percent Burned
'Values provided in Table 6-23,
b Burning of crop residues is illegal in Florida.
Arkansas
California
Florida6
Louisiana
Mississippi
Missouri
Oklahoma0
Texas
13
variable*
0
& :
10
5
3
1
,13
27 ~
0
0
40
S
3
• 2.
13
27
0:
5
40
8
3 . •
0
• ' /;-'%il^%l^v":-'V:l:,:
'" ^"iljSiSM'-r^:^^"':' •'/:'
• 3M«4p&*3sk.>v -. •' ••'- .•-- '- '•• j- =
. -•-•^•^ir--1^?.c> •-:-.:,•?••
:ff:J;-, |3^i2^f -*; ij '"''I1 ^ '•' : ', ''. '-'-• 'i "
• -'%H%^w'-?.?,?"V-7 ••::-;:;:,, •' ."•" •
H^'Sjlfti, •'•""•' '.::'!' ""'-'A'''' ..:.-"
"mf.$v>&~-- -V;.'V;:
;-'iiit^;-A^.;.;';-"--
v;4fcl: ;>:-
^IS;:::^-''/
••?O.W-r---
•;i:$:::;:r>." '
'-^::';-ji.1..
.. ;"3r: ;•:>" ',."
•: ^ •:•>-!'. V
California Air Resources Board 1999, 2001; Klosterboer
1999a, 1999b, 2000, 2001, 2002, 2003; Lindberg 2002,
2003; Linscombe 1999a, 1999b, 2001,2002,2003; Mutters
2002,2003; Najita2000,2001; Schueneman 1999a, 1999b,
2001; Slaton 1999a, 1999b, 2000; Street 1999a, 1999b,
2000, 2001, 2002, 2003; Wilson 2001, 2002, 2003) (see
Table 6-22 and Table 6-23). The estimates provided for
Arkansas and Florida remained constant over the entire
1990 through 2002 period, while the estimates for all other
states varied over the time series. For California, it was
assumed that the annual percents of rice area burned in
Table 6-23: Percentage of Rice Area Burned in California
Year
1990
1996
1997
1998
1999
2000
2001
2002
34
33
27
27
23
13
the Sacramento Valley are representative of burning in the
entire state, because the Sacramento Valley accounts for
over 95 percent of the rice acreage in California (Fife 1999).
These values declined between 1990 and 2002 because of a
legislated reduction in rice straw burning (Lindberg 2002)
(see Table 6-23).
All residue/crop product mass ratios except sugarcane
were obtained from Strehler and Stutzle (1987). The datum
for sugarcane is from University of California (1977).
Residue dry matter contents for all crops except soybeans
and peanuts were obtained from Turn et al. (1997). Soybean
dry matter content was obtained from Strehler and Stiitzle
(1987). Peanut dry matter content was obtained through
personal communications with Jen Ketzis (1999), who
accessed Cornell University's Department of Animal
Science's computer model, Cornell Net Carbohydrate and
Protein System. The residue carbon contents and nitrogen
contents for all crops except soybeans and peanuts are from
Turn et al. (1997). The residue carbon content for soybeans
and peanuts is the IPCC default (IPCC/UNEP/OECD/IEA
1997). The nitrogen content of soybeans is from Barnard
and Kristoferson (1985). The nitrogen content of peanuts
6-26 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 6-24: Key Assumptions for Estimating Emissions from Agricultural Residue Burning
Efficiency Efficiency
Wheat
Rice
Sugarcane
Com
Bariey
Soybeans
Peanuts
• . '._:":- Y>;>'i£-':f."'
' ••'.'">'•'•& ' ".'
0,8
1.0
1,2
2.1
1,0
.-.FC'^
-------
Table 6-26: Quantitative Uncertainty Estimates for CH4 and N20 Emissions from Field Burning of Agricultural Residues
(Tg C02 Eq. and Percent)
Field Barring of Agricultural ResMoes".
0,7
0.4
Recalculations Discussion
This year, it was determined that Oklahoma was a
rice-growing state. As a consequence, the activity data used
to estimate greenhouse gas emissions from field burning
of agricultural residues have been revised to include rice
residues from that state. Additionally, Florida rice production
is now estimated using current, state-specific yield figures
from the published literature, rather than industry estimates.
These changes together caused less than a 1 percent average
annual increase in emissions. These changes resulted an
average annual increase of less than 0.01 Tg CO2 Eq. (0.8
percent) in CH4 emissions and an average annual increase
of less than 0.01 Tg CO2 Eq. (0.7 percent) in N2O emissions
for the period 1990 through 2001.
6-28 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
7. Land-Use Change and Forestry
This chapter provides an assessment of the net carbon dioxide (CO2) flux1 caused by 1) changes in forest carbon
stocks, 2) changes in carbon stocks in urban trees, 3) changes in agricultural soil carbon stocks, and 4) changes
in carbon stocks in landfilled yard trimmings and food scraps. Seven components of forest carbon stocks are analyzed:
trees, understory vegetation, forest floor, down dead wood, soils, wood products in use, and landfilled wood products. The
estimated CO2 flux from each of these forest components was derived from U.S. forest inventory data, using methodologies
that are consistent with the Revised 1996IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997). Changes in carbon stocks in
urban trees were estimated based on field measurements in ten U.S. cities and data on national urban tree cover, using a
methodology consistent with the Revised 1996 IPCC Guidelines. Changes in agricultural soil carbon stocks include mineral
and organic soil carbon stock changes due to use and management of cropland and grazing land, and emissions of CO2 due
to the application of crushed limestone and dolomite to agricultural soils (i.e., soil liming). The methods used to estimate
all three components of changes in agricultural soil carbon stocks are consistent with the Revised 1996 IPCC Guidelines.
Changes in yard trimming and food scrap carbon stocks in landfills were estimated using analysis of life-cycle greenhouse
gas emissions and sinks associated with solid waste management (EPA 1998). Note that the chapter title "Land-Use Change
and Forestry" has been used here to maintain consistency with the IPCC reporting structure for national greenhouse gas
inventories; however, the chapter covers land-use activities, in addition to land-use change and forestry activities. Therefore,
except in table titles, the term "land use, land-use change, and forestry" will be used in the remainder of this chapter.
Unlike the assessments in other chapters, which are generally based on annual activity data, the flux estimates in this
chapter, with the exception of those from wood products, urban trees, and liming, are based on periodic activity data in the
form of forest, land use, and municipal solid waste surveys, which are tabulated on a less frequent basis. Carbon dioxide fluxes
from forest carbon stocks (except the wood product components) and from agricultural soils (except the liming component) are
calculated on an average annual basis over five or ten year periods. The resulting annual averages are applied to years between
surveys. Because each state is surveyed separately and at different times, using this data structure, the estimated CO2 fluxes
from forest carbon stocks differ at the national level from year to year. The exception is forest soils, which are considered only
at the regional scale and therefore have constant fluxes over multi-year intervals, with large discontinuities between intervals.
Agricultural soils show a pattern similar to that of forest soils. In addition, because the most recent national forest and land-use
surveys were completed for the year 1999, the estimates of CO2 flux from forests and agricultural soils are based in part on
modeled projections. Carbon dioxide flux from urban trees is based on neither annual data nor periodic survey data, but instead
on data collected through the 1990s. The annual average flux for this period has been extrapolated to the entire time series.
Land use, land-use change, and forestry activities in 2002 resulted in a net sequestration of 690.7 Tg CO2 Eq. (188
Tg C) (Table 7-1 and Table 7-2). This represents an offset of approximately 12 percent of total U.S. CO2 emissions. Total
land use, land-use change, and forestry net sequestration declined by approximately 28 percent between 1990 and 2002.
This decline was primarily due to a decline in the rate of net carbon accumulation in forest carbon stocks. Annual carbon
accumulation in landfilled yard trimmings and food scraps also slowed over this period, as did annual carbon accumulation
1 The term "flux" is used here to encompass both emissions of greenhouse gases to the atmosphere, and removal of carbon from the atmosphere. Removal
of carbon from the atmosphere is also referred to as "carbon sequestration."
Land-Use Change and Forestry 7-1
-------
Table 7-1: Net C02 Flux from Land-Use Change and Forestry (Tg C02 Eq.)
Sink Category
1990
Forests
Urban Trees
Agricultural Soils
Landfilled Yard Trimmings and food Scraps
Total
(846.6)
(58.7)
(26.0;
(957.9)
(7BS.8) (W5.8) (WB.2) (S89.7) (B9B.7)
Note: Parentheses indicate net sequestration. Totals nay not sum due to independent rounding
partially on projections. '
Table 7-2: Net C02 Flux from Land-Use Change and Forestry (Tg C)
Sink Category '
Forests
Urban Trees
Agricultural Soils
LandflHed Yard Trimmings and Food Scraps
Total
(261)
Note: 1 Tg C = 1 teragram cartxm = 1 miion metric tons carbon. Parentheses indicate net sequestration. Totals may not sum due to independent
rounding. Gray shading identifies estimates that rely at least partially on projections.
in agricultural soils. The constant rate of carbon accumulation
in urban trees is a reflection of limited underlying data (i.e.,
this rate represents an average for 1990 through 1999), as
described above.
The methodology, results, and uncertainty associated
with each of the four carbon stock categories are discussed
in the chapter sections below. Where relevant, the sections
also include a discussion of significant recalculations with
respect to previous inventory documents, and plans for
improvements in the methodology.
7.1. Changes in Forest Carbon
Stocks (IPCC Source Category 5A)
For estimating carbon flux, carbon in forest ecosystems
can be divided into the following seven storage pools.
• Trees, including the coarse roots, stems, branches, and
foliage of living trees and standing dead trees.
• Understory vegetation, including shrubs and bushes,
including the roots, stems, branches, and foliage.
• Forest floor, including fine woody debris, tree litter, and
humus.
• Down dead wood, including logging residue and other
coarse dead wood on the ground, and stumps and roots
of stumps.
• Soil, including all organic material in soil except coarse
roots.
• Harvested wood products in use.
• Harvested wood products in landfills.
Carbon is continuously cycled among these storage
pools and between forest ecosystems and the atmosphere
as a result of biological processes in forests (e.g.,
photosynthesis, growth, mortality, and decomposition)
and anthropogenic activities (e.g., harvesting, thinning,
clearing, and replanting). As trees photosynthesize and
grow, carbon is removed from the atmosphere and stored
in living tree biomass. As trees age, they continue to
accumulate carbon until they reach maturity, at which
point they store a relatively constant amount of carbon.
As trees die and otherwise deposit litter and debris on the
forest floor, soil organisms consume much of the biomass.
Consequently, carbon is released to the atmosphere due to
respiration or is added to the soil.
The net change in forest carbon is not equivalent to
the net flux between forests and the atmosphere because
timber harvests do not cause an immediate flux of carbon
to the atmosphere. Instead, harvesting transfers carbon to
a "product pool." Once in a product pool, most carbon is
emitted over time as CO2 when the wood product combusts
7-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
or decays. The rate of emission varies considerably among
different product pools. For example, if timber is harvested
to produce energy, combustion releases carbon immediately.
Conversely, if timber is harvested and used as lumber in a
house, it may be many decades or even centuries before the
lumber decays and carbon is released to the atmosphere.
If wood products are disposed of in landfills, the carbon
contained in the wood may be released many years
or decades later, or may be stored almost permanently in
the landfill.
This section of the Land-Use Change and Forestry
chapter quantifies the net changes in carbon stocks in five
forest carbon pools and two harvested wood pools. The net
change in stocks for each pool is estimated, and then the
changes in stocks are summed over all pools to estimate
total net flux.
Forest carbon storage pools, and the flows between
them via emissions, sequestration, and transfers, are shown
in Figure 7-1. In this figure, forest carbon storage pools
are represented by boxes, while flows between storage
pools, and between storage pools and the atmosphere, are
represented by arrows. Note that the boxes are not identical
to the storage pools identified in this chapter. The storage
pools identified in this chapter are defined differently
in this graphic to better illustrate the processes that result
in transfers of carbon from one pool to another, and that
result in emissions to the atmosphere as well as uptake
from the atmosphere.
Approximately 33 percent (747 million acres) of
the U.S. land area is forested (Smith et al. 2001). From
the early 1970s to the early 1980s, forest land declined
by approximately 5.9 million acres. During the 1980s
and 1990s, forest area increased by about 9.2 million
acres. These net changes in forest area represent average
annual fluctuations of only about 0.1 percent. Given the
low rate of change in U.S. forest land area, the major
influences on the current net carbon flux from forest land
are management activities and the ongoing impacts of
previous land-use changes. These activities affect the net
flux of carbon by altering the amount of carbon stored in
forest ecosystems. For example, intensified management of
forests can increase both the rate of growth and the eventual
Figure 7-1
Forest Sector Carbon Pools and Flows
Legend
fj] Carbon Pool
—> Carbon transfer or flux
Combustion
Source: Adapted from Heath and Birdsey (1997)
Land-Use Change and Forestry 7-3
-------
Table 7-3: Net Changes in Carbon Stocks in Forest and Harvested Wood Pools, and Total Net Forest Carbon Flux (Tg C02 Eq.)
Carbon Pool
Forest
Trees
Understory
Forest Floor
Down Dead Wood
Forest Soils
Harvested Wood
Wood Products
Landfilled Wood
Total Net Flux
1990
(83fc8f
(354.2)
0.8
(38.1)
(32J)
(212.7)
(218,1)
(47.6)
(182.4!
(846J)
1996
(756.5)
(464.6)
(3.1)
(12.7)
(63.5)
(212.7)
(287.6)
(56.1)
(151.5)
(964.1)
1997
(517.4)
(401.0)
(1.7)
2.7
(62.4)
(55.0)
(212.7)
(57.7)
(155.0)
(738.1)
1998
(411,7)
(307.5)
(0.5)
11.0
(59.7)
(55.0)
(206.1)
(51.9)
(154.2)
(617.8)
1999
(373.8)
(275.0)
2.2
16.2
(62.2)
(55.0)
(214.7)
(61>5)
(153.1)
(588.4)
2W8
(391.5)
(289.9)
2.5
17.2
(66,3)
(55.0)
(210.8)
(58.7)
(152.1)
(602.3)
2801
(386.4)
(285.5)
2.2
16.5
(64.6)
(55.0)
(213.8)
(59.0)
(154.8)
(600.2)
2802
(388.4)
(285.5)
2.2
16.5
(64.6)
(55.0)
(214.4)
(59.2)
(155.3)
(600.8)
+ Does not exceed 0.5 Tg C02 Eq.
Note: Parentheses indicate net cation sequestration (f.e., a net removal of carbon from the atmosphere). Total net flux is an estimate of the actual net flux
between the total forest cartoon pool and the atmosphere. Estimates are based on a combination of historical data and projections as described in the text
and in Annex 3.12. Forest estimates are based on interpolations between periodic measurements; harvested wood estimates are based on results from
annual surveys and models. The sum of estimates in a column may not equal estimated totals due to independent rounding.
biomass density2 of the forest, thereby increasing the
uptake of carbon. Harvesting forests removes much of the
aboveground carbon, but trees can grow on this area again
and sequester carbon. The reversion of cropland to forest
land increases carbon storage in biomass, forest floor, and
soils. The net effect of both forest management and land-
use change involving forests is captured in the estimates of
carbon stocks and fluxes presented in this chapter.
In the United States, improved forest management
practices, the regeneration of previously cleared forest
areas, as well as timber harvesting and use have resulted
in net uptake (i.e., net sequestration) of carbon each
year from 1990 through 2002. Due to improvements in
U.S. agricultural productivity, the rate of forest clearing
for crop cultivation and pasture slowed in the late 19th
century, and by 1920 this practice had all but ceased. As
farming expanded in the Midwest and West, large areas of
previously cultivated land in the East were taken out of crop
production, primarily between 1920 and 1950, and were
allowed to revert to forests or were actively reforested. The
impacts of these land-use changes still affect carbon fluxes
from forests in the East. In addition, carbon fluxes from
Eastern forests have been affected by a trend toward active
management on private land. Collectively, these changes
have nearly doubled the biomass density in Eastern forests
since the early 1950s. More recently, the 1970s and 1980s
saw a resurgence of federally-sponsored forest management
programs (e.g., the Forestry Incentive Program) and soil
conservation programs (e.g., the Conservation Reserve
Program), which have focused on tree planting, improving
timber management activities, combating soil erosion,
and converting marginal cropland to forests. In addition to
forest regeneration and management, forest harvests have
also affected net carbon fluxes. Because most of the timber
harvested from U.S. forests is used in wood products, and
many discarded wood products are disposed of in landfills
rather than by incineration, significant quantities of carbon
in harvested wood are transferred to long-term storage pools
rather than being released rapidly to the atmosphere. The
size of these long-term carbon storage pools has increased
during the last century.
Changes in carbon stocks in U.S. forests and harvested
wood were estimated to account for an average annual net
sequestration of 736 Tg CO2 Eq. (201 Tg C) over the period
1990 through 2002 (Table 7-3, Table 7-4, and Figure 7-2).
Net sequestration is a reflection of net forest growth and
increasing forest area over this period, particularly before
1997, as well as net accumulation of carbon in harvested
wood pools. The variation among years in total forest
carbon stocks is due primarily to variation in tree carbon
stocks. Surveys are periodic, and estimates in non-survey
years are interpolated. The national estimates reflect the
combination of these individual patterns of variation among
survey years that vary for each state. Total land use, land-
use change, and forestry net sequestration declined by
approximately 28 percent between 1990 and 2002. This
2 The term "biomass density" refers to the mass of vegetation per unit area. It is usually measured on a dry-weight basis. Dry biomass is about 50 percent
carbon by weight.
7-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 7-4: Net Changes in Carbon Stocks in Forest and Harvested Wood Pools, and Total Net Forest Carbon Flux (Tg C)
Carbon Pool
Forest
Trees
Understory
.Forest Floor
Down Dead Wood
Forest Sols
Harvested Wood
Wood Products
Landfilled Wood
Total Net Flux
rtw
(1?4|
. (97)
'(10)
(9)
(58)
(57)
(13)
(44)
(231)
1996 188?
1999 2080
2001
2002
(209)
; (127);
(3)
(17)
(58)
(57)
(*5)-
•.- .jam
(141)
>"•$*)•••
','/'•''• j
I17)
(15)
(88)
(16)
(42)
(112)
.'. (84);
3
(16)
(15)
(56)
(14)
(42)
(102)
(?§!
4
(17)
(15)
(58)
(17)
(42)
(187)
1
. •&.
(18)
(15)
(57)
(18),
(41)
(105)
(78)
4
(18)
(15)
(58)
(16)
(42)
(185)
, (78)
4
(18)
(15)
(58)
16)
(42)
(283) (188) (168) (168) (184) (164) (164)
+ Does not exceed 0.5 Tg C.
Note: Parentheses indicate net carbon sequestration (i.e., a net removal of carbon from the atmosphere). Total net flux is an estimate of the actual net flux
and in Annex 3.12. Forest estimates are based on interpolations between periodic measurements; harvested wood estimates are based on results from
annual surveys and models. The sum of estimates in a column may not equal estimated totals due to Independent rounding.
Table 7-5: Carbon Stocks in Forest and Harvested Wood Pools (Tg C)
Carton Pool
1880
1880
1887
1888 1888
2000
2001
1,217
1,033
2,307
1,232
1,074
2,365
1,248
1,117
2,421
1,262
1,159
1,279
1,200
1,295:
1,242
2882
1 24,587
18,122
652
4,574
1,239
24,735
18,248
653
4,577
1,256
24,861
18,358
654
4,576
1,273
24,818
18,442
654
4,573
1,290
25,845
18,517
653
4,560
1,307
25,137
18,596
652
4,564
1,325
25,227
18,674
652
4,560
. 1,342
Forest
Trees
Understory
Forest Floor
Down Dead Wood
Forest Soils {see Table 7-6)
Harvested Wood
Wood Products
Landfilled Wood
Total Carbon Stock' i IIVI _____| Mill 27,842 27,226 27,379 27,525 27,674 27.823
Note: Forest carbon stocks do not include forest stocks in Alaska, Hawaii, or U.S. territories, or trees on non-forest tog (e.§., urban frees). Wood product
stocks include exports, even If the logs are processed in other countries, and exclude imports. Estimates are based on a combination of historical date and
projections as discussed in Annex 3.12. Forest values are based on periodic measurements; harvested wood estimates are based on annual surveys, forest
soils are based on estimates of stoctcs in 1987,1997, and 2002 only. Values for other years are extrapolated from the most recent measurement year. Hie
sum of estimates in a column may not equal estimated totals due to independent rounding.
* Total Carbon Stock values do not include Forest Soils.
1,311
1,284
decline was primarily due to a decline in the estimated rate
of sequestration in forest soils. Estimates of soil carbon
stocks depend solely on forest area and type. Thus, any
estimated changes in soil carbon stocks over time were
due to changes in total forest area and/or changes in forest
type. Because the rate of increase in forest area slowed
after 1997, a concomitant decrease in the rate of carbon
sequestration by forest soils resulted.
The pattern of change in soil carbon stocks reflects the
assumption that changes in soil carbon occur instantaneously
as a function of changes in net forest area and changes
among forest types and the use of survey data only from
three nominal reporting years. An improved methodology
is being developed to account for the ongoing effects of
Table 7-6: Carbon Stocks in Forest Soils (Tg C)
1887
1887
2802
Forest Soils
25,681
26,262
26,337
Note: Estimates are based on a combination of periodic historical data
and projections as described In the text and in Annex 3.12.
changes in land use and forest management, as discussed in
the "Planned Improvements" section below.
Methodology
The methodology described herein is consistent with the
Revised 1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA
1997). For developing estimates of net carbon flux from
Land-Use Change and Forestry, including all pools except
Land-Use Change and Forestry 7-5
-------
for harvested wood, carbon stock estimates were derived
from periodic inventories of forest stocks, and net changes
in carbon stocks were interpolated between survey years.
Figure 7-2
Estimates of Forest Carbon Flux in Major Pools
Figure 7-3
Carbon emissions from harvested wood were determined
by accounting for the variable rate of decay of harvested
wood according to its disposition (e.g., product pool, landfill,
combustion).3 Different data sources were used to estimate
the carbon stocks and stock change in (1) forests (live and
dead trees, understory, forest floor, and down dead wqod),
(2) forest soils, and (3) harvested wood products. Therefore,
these pools are described separately below.
Tree, Understory, Forest Floor and Down Dead Wood Carbon
The overall approach for determining non-soil forest
carbon stock change was to estimate non-soil forest carbon
stocks, based on data from two forest surveys conducted
several years apart, and then to subtract the estimates
developed for two consecutive years to calculate the net
change in carbon stocks. Forest survey data were obtained
from the USDA Forest Service, Forest Inventory and Analysis
program (Prayer and Furnival 1999, Smith et al. 2001).
Historically, the Forest Inventory and Analysis program did
not conduct detailed surveys of all forest land, but instead
focused on land capable of supporting timber production
Average Carbon Density in the Forest Tree Pool in the Conterminous U.S. During 2003
-50
-100-
I -150-
I
3 -200 -
Note: Estimates for harvested wood and forest soils are based on the
same methodology and data as the previous U.S. Inventory (USEPA,
2003). Estimates for all pools are based on measured forest inventory
data and modeled projections as described in the text.
Total Net includes all forest pools: trees, understory, forest floor, down
dead wood, forest soils, wood products, and landfilled wood.
Total Forest Tree
Pool Carbon
(Vha)
151-200
201-250
251-300
Note: Estimates are based on forest inventory data and modeled projections as described in the text.
3 The product estimates in this study use the "production approach" meaning that they do not account for carbon stored in imported wood products, but
do include carbon stored in exports, even if the logs are processed in other countries (Heath et al. 1996).
7-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
(timberland4). In addition, some reserved forest land and
some other forest land were surveyed. To include all forest
lands, estimates were made for timberlands and then were
extrapolated for non-timberland forests. Growth, harvests,
land-use change, and other estimates of temporal change
were derived from repeated surveys conducted every 5 to 14
years, depending on the state. Because each state has been
surveyed periodically, the most recent data for most states are
generally several years old. Therefore, forest areas, volumes,
growth, land-use changes, and other forest characteristics,
as of January 1, 2003, were extrapolated with a modeling
system that represents the U.S. forest sector (see Annex 3.12
and Haynes 2003).
For each periodic inventory in each state, each carbon pool
was estimated using coefficients from the FORCARB2 model
(Birdsey and Heath 1995, Birdsey and Heath 2001, Heath et
al. 2003), which is part of the forest sector modeling system
described in Annex 3.12. Tree biomass and carbon stocks
were based on the growing stock volume from survey data
or model projections. Calculations were made using volume-
to-biomass conversion factors for different types of forests
as presented in Smith et al. (2003). Biomass estimates were
divided by two to obtain estimates of carbon in living trees
(i.e., it was assumed that dry biomass is 50 percent carbon).
Understory carbon was estimated from inventory data using
equations presented in Birdsey (1996). Forest floor carbon was
estimated from inventory data using the equations presented
in Smith and Heath (2002). Down dead wood was estimated
using a procedure similar to that used for estimating carbon in
understory vegetation, as described in Annex 3.12.
Carbon stocks were calculated separately for each state
between 1991 and 2002, and for the most recent inventory
prior to 1991. For each pool in each state in each year, from
1990 through 2002, carbon stocks were estimated by linear
interpolation between survey years. Carbon stock estimates
for each pool were summed over all states to form estimates
for the conterminous United States. Annual stock changes
were estimated by subtracting national carbon stocks as of
January 1 of the inventory year from that of the subsequent
year (i.e., 2002 fluxes represent the January 1, 2003 stock
minus the January 1,2002 stock). Data sources and methods
for estimating individual carbon pools are described more
fully in Annex 3.12.
Forest Soil Carbon
Soil carbon stock estimates are based solely on forest
area and on average carbon density for each broad forest
type group. Thus, any changes in soil carbon stocks are due
to changes in total forest area or changes in the areas of
forest types. Unlike other pools, estimates were not made
for individual states, but instead for each of 10 regions in
the conterminous United States. Data on the carbon content
of soils were obtained from the national STATSGO spatial
database (USDA 1991). These data were combined with
Forest Inventory and Analysis survey data to estimate soil
carbon in all forest lands by broad forest type group (see
Annex 3.12 for list of forest type groups). Estimates were
made for 1987 and 1997 based on compilations of forest
inventory data made for these reporting years (Waddell et al.
1989, Smith et al. 2001). For 2002, estimates were projected
using the FORCARB2 model as described in Annex 3.12.
The average annual soil stock change for 1990 through
1996 was derived by subtracting the January 1, 1997 stock
from the 1987 stock, and dividing by the number of years
between estimates (10). The net annual stock changes for
1997 through 2001 were derived in the same way using the
1997 and 2002 stocks. The net annual stock change for 2002
was extrapolated from 2001 (i.e., the same estimate was used
for 2002 as for 2001). In principal, estimates of soil carbon
stocks could be made by interpolation, as described above
for other forest carbon pools. However, this approach has not
been used because an improved methodology for estimating
soil carbon is currently under development (see "Planned
Improvements" below). Further information on soil carbon
estimates is presented in Annex 3.12 and by Heath et al.
(2003), and Johnson and Kern (2003).
Harvested Wood Carbon
Estimates of carbon stock changes in wood products
and wood discarded in landfills were based on the methods
described by Skog and Nicholson (1998). Carbon stocks in
4 Forest land in the United States includes all land that is at least 10 percent stocked with trees of any size. Timberland is the most productive type of forest
land, growing at a rate of 20 cubic feet per acre per year or more. In 1997, there were about 503 million acres of timberland, which represented 67 percent
of all forest lands (Smith and Sheffield 2000). Forest land classified as timberland is unreserved forest land that is producing or is capable of producing
crops of industrial wood. The remaining 33 percent of forest land is classified as reserved forest land, which is forest land withdrawn from timber use by
statute or regulation, or other forest land, which includes forests on which timber is growing at a rate less than 20 cubic feet per acre per year.
Land-Use Change and Forestry 7-7
-------
wood products in use and wood products stored in landfills
were estimated from 1910 onward based on historical data
from the USDA Forest Service (USDA 1964, Ulrich 1989,
Howard 2001), and historical data as implemented in the
framework underlying the North American Pulp and Paper
(NAPAP, Ince 1994) and the Timber Assessment Market
and the Aggregate Timberland Assessment System Timber
Inventory models (TAMM/ATLAS, Haynes 2003, Mills and
Kincaid 1992) that are part of the forest sector modeling system
described in Annex 3.12. Beginning with data on annual wood
and paper production, the fate of carbon in harvested wood was
tracked for each year from 1910 through 2002, and included
the change in carbon stocks in wood products, the change in
carbon in landfills, and the amount of carbon emitted to the
atmosphere (CO2 and CH4) both with and without energy
recovery. To account for imports and exports, the production
approach was used, meaning that carbon in exported wood
was counted as if it remained in the United States, and carbon
in imported wood was not counted.
Uncertainty
The forest survey data that underlie the forest carbon
estimates are based on a statistical sample designed to
represent the wide variety of growth conditions present
over large territories. However, forest survey data that are
currently available generally exclude timber stocks on
most forest land in Alaska, Hawaii, and U.S. territories.
For this reason, estimates have been developed only for
the conterminous United States. Within the conterminous
United States, the USDA Forest Service mandates that
forest area data are accurate within 3 percent at the 67
percent confidence level (one standard error) per 405,000
ha of forest land (Miles et al. 2001). For larger areas, the
uncertainty in area is concomitantly smaller. For volume data,
the accuracy is targeted to be 5 percent for each 28,300 m3
at the same confidence level. An analysis of uncertainty in
growing stock volume data for timber-producing lands was
undertaken for five states: Florida, Georgia, North Carolina,
South Carolina, and Virginia (Phillips et al. 2000). Nearly
all of the uncertainty was found to be due to sampling rather
than the regression equations used to estimate volume from
tree height and diameter. Standard errors for growing stock
volume ranged from 1 to 2 percent for individual states and
less than 1 percent for the 5-state region. However, the total
standard error for the change in growing stock volume was
estimated to be 12 to 139 percent for individual states, and 20
percent for the 5-state region. The high relative uncertainty
for growing stock volume change in some states was due
to small net changes in growing stock volume. However,
the uncertainty in volume change may be smaller than was
found in this study because estimates from samples taken
at different times on permanent survey plots are correlated,
and such correlation reduces the uncertainty in estimates of
changes in volume or carbon over time (Smith and Heath
2000). Based on these accuracy guidelines and these results
for the Southeastern United States, forest area and volume
data for the conterminous United States are expected to be
reasonably accurate, although estimates of small changes in
growing stock volume may have substantial uncertainty.
In addition to uncertainty in growing stock volume,
there is uncertainty associated with the estimates of carbon
stocks in other ecosystem pools. Estimates for these pools
are derived from extrapolations of site-specific studies
to all forest land since survey data on these pools are
not generally available. Such extrapolation introduces
uncertainty because available studies may not adequately
represent regional or national averages. Uncertainty may
also arise due to (1) modeling errors, for example relying
on coefficients or relationships that are not well known, and
(2) errors in converting estimates from one reporting unit to
another (Birdsey and Heath 1995). An important source of
uncertainty is that there is little consensus from available data
sets on the effect of land use change and forest management
activities (such as harvest) on soil carbon stocks. For
example, while Johnson and Curtis (2001) found little or
no net change in soil carbon following harvest, on average,
across a number of studies, many of the individual studies
did exhibit differences. Heath and Smith (2000b) noted that
the experimental design in a number of soil studies limited
their usefulness for determining effects of harvesting on soil
carbon. Because soil carbon stocks are large, estimates need
to be very precise, since even small relative changes in soil
carbon sum to large differences when integrated over large
areas. The soil carbon stock and stock change estimates
presented herein are based on the assumption that soil carbon
density for each broad forest type group stays constant over
time. As more information becomes available, the effects of
land use and of changes in land use and forest management
will be better accounted for in estimates of soil carbon (see
"Planned Improvements").
7-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Another source of uncertainty is the use of projected
(modeled) estimates of current forest area, forest type, rate
of harvest, effect of forest management, and growing stock
volume. These projections are used within the forest sector
modeling system described in Annex 3.12 to produce current
carbon stock estimates. As discussed above, forest survey data
for some individual states are many years old, and current
estimates thus depend on the use of the forest sector modeling
system. Although this modeling system has been used
repeatedly for national assessments, there are uncertainties
associated with each of the models in this system.
Recent studies have begun to quantify the uncertainty
in national-level forest carbon budgets based on the methods
adopted here. Smith and Heath (2000) and Heath and Smith
(2000a) report on an uncertainty analysis they conducted
on carbon sequestration in privately owned timberlands
throughout the conterminous United States. These studies
are not exactly comparable to the estimates in this chapter
because they used an older version of the FORCARB
model and are based on older data. However, the relative
magnitudes of the uncertainties are informative. For the
period 1990 through 1999, the true mean carbon flux was
estimated to be within 15 percent of the reported mean at the
80 percent confidence level. The corresponding true mean
carbon stock estimate for 2000 was within approximately
5 percent of the reported mean value at the 80 percent
confidence level. The relatively greater uncertainty in flux
estimates compared to stock estimates is roughly similar to
that found for estimates of growing stock volume discussed
above (Phillips et al. 2000). In both analyses, there are greater
uncertainties associated with smaller estimates of flux than
larger ones. Uncertainty in the estimates presented in this
inventory may be greater than those presented by Heath
and Smith (2000a) for several reasons. Most importantly,
their analysis did not include uncertainty in growing stock
volume data or uncertainties in stocks and fluxes of carbon
from harvested wood.
QA/QC and Verification
As discussed above and in Annex 3.12, the USDA
Forest Service Forest Inventory and Analysis program has
conducted consistent forest surveys based on extensive
statistically-based sampling of most of the forest land in the
conterminous United States since 1952. The main purpose
of the Forest Inventory and Analysis program has been to
estimate areas, volume of growing stock, and timber products
output and utilization factors. The Forest Inventory and
Analysis program includes numerous quality assurance and
quality control procedures, including calibration among
field crews, duplicate surveys of some plots, and systematic
checking of recorded data. Because of the statistically-based
sampling, the large number of survey plots, and the quality
of the data, the survey databases developed by the Forest
Inventory and Analysis program form a strong foundation for
carbon stock estimates. Field sampling protocols, summary
data, and detailed inventory databases are archived and are
publicly available on the Internet ().
Many key calculations for estimating current forest
carbon stocks based on FIA data are based on the forest sector
modeling system that is used to project forest area, harvests,
tree volumes, and carbon stocks. This modeling system is
described briefly in Annex 3.12 and more fully in the citations
presented therein. These models have been used for many
years—and in some cases decades—to produce national
assessments of forest condition, timber products output, and
forest carbon stocks and stock changes. This forest sector
modeling system has been reviewed and published in the
refereed scientific literature as cited in Annex 3.12.
General quality control procedures were used in
performing calculations to estimate carbon stocks based on
historical FIA data or model projections. Forest Inventory and
Analysis data and some model projections are given in English
units, but carbon stock estimates were developed using metric
units. To avoid unit conversion errors, a standard conversion
table in electronic form was used (Appendix B of Smith et
al. 2001). Additionally, calculations of total forest area were
checked against published Forest Inventory and Analysis data
(for example, Smith et al. 2001) to assure that no areas of forest
were being counted twice or not counted at all. Finally, carbon
stock estimates were compared with previous inventory report
estimates to assure that any differences could be explained
by either new data or revised calculation methods (see the
"Recalculations" discussion below).
Recalculations Discussion
The forest inventory data used to estimate soil carbon
flux and harvested wood flux are the same as in the previous
inventory. However, estimates of non-soil forest carbon
stocks and fluxes in other pools are now based on forest
inventory data from individual states. This methodological
Land-Use Change and Forestry 7-9
-------
Figure 7-4
Estimates of Forest Carbon Flux in Major
Pools: Comparison of New Estimates with
those in Previous Inventory
1992 1994 1996 1998 2000 2002
0
-50
t -100 -
I
I -150 -
Forest Soils (Current and Previous)
Trees
Trees (Previous)
Total Net
Total Net (Previous)
Note: Estimates for harvested wood and forest soils based on the same
methodology and data as the previous inventory (EPA 2003).
Total Net includes all forest pools: trees, understory, forest floor, down
dead wood, forest soils, wood products, and landfilled wood.
change from regionally-based to state-based assessment
has resulted in a significant decrease, relative to previous
Inventories, in forest stock estimates for recent years. Average
survey years for each state are presented in Annex 3.12.
Estimating carbon stocks and fluxes for individual states
allows greater precision in assigning the survey year for each
state. For example, in the previous Inventory (EPA 2003),
1997 was given as the measurement year (Smith et al. 2001)
for the 1997 national Resource Planning Act assessment
data, although the average survey date was 1990. Because
the actual survey year was several years prior to the nominal
Resource Planning Act reporting year for most states, using
the average survey date for each state has removed a source of
bias in estimates of the survey year. Since there is a trend of
increasing carbon stocks in forests over time, removing this
bias has tended to reduce estimates of recent forest carbon
sequestration because the previously reported increase in
carbon stocks now occurs at earlier dates. The same amount
of carbon stock change is now spread over a longer time
period, removing part of the stock change from the time
interval considered by this Inventory. This methodology also
results in more variation in the non-soil forest carbon fluxes,
because average flux values are calculated between different
years in different states. Thus current national estimates
of non-soil forest carbon fluxes vary substantially among
years, whereas previous estimates varied only among years
in which Resource Planning Act assessments were reported,
such as 1997. These effects can be seen in Figure 7-4, which
shows the difference between current and previous estimates
of tree and forest carbon flux. Figure 7-4 also demonstrates
the consistency in the methodology for reporting soil carbon
fluxes relative to last year's inventory, represented by the
single line labeled "Forest Soils."
Planned Improvements
The Forest Inventory and Analysis program has
adopted a new annualized design, such that a portion of
each state will be surveyed each year (Gillespie 1999). The
annualized survey also includes a plan to measure attributes
that are needed to estimate carbon in various pools, such
as soil carbon and forest floor carbon. Currently, carbon
in pools other than trees must be estimated based on other
measured characteristics or other less comprehensive data
sets. The annualized survey will also improve coverage of
non-timberland forests, which have not been surveyed as
thoroughly as timberland forests. However, annual data are
not yet available for most states. During the next several
years, the use of annual data, including new data on soil and
forest floor carbon stocks, and new data on non-timberlands,
will improve the precision and accuracy of estimates of forest
carbon stocks and fluxes.
As more information becomes available about historical
land use, the ongoing effects of changes in land use and forest
management will be better accounted for in estimates of soil
carbon (Birdsey and Lewis 2003). Currently, soil carbon
estimates are based on the assumption that soil C density
depends only on broad forest type group, not on land use
history. However, many forests in the Eastern United States
are re-growing on abandoned agricultural land. During
such regrowth, soil and forest floor carbon stocks often
increase substantially over many years or even decades,
especially on highly eroded agricultural land. In addition,
with deforestation, soil carbon stocks often decrease over
many years. A new methodology is being developed to
account for these changes in soil carbon over time. This
methodology includes estimates of area changes among land
uses (especially forest and agriculture), estimates of the rate
of soil carbon stock gain with afforestation, and estimates of
the rate of soil carbon stock loss with deforestation over time.
This topic is important because soil carbon stocks are large,
and soil carbon flux estimates contribute substantially to total
forest carbon flux, as shown in Table 7-6 and Figure 7-4.
The estimates of carbon stored in harvested wood
products are currently being revised using more detailed
7-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
wood products production and use data and improved
and more detailed parameters on disposition and decay of
products. In addition, more validation steps will be taken as
suggested by the IPCC Good Practice Guidance for Land
Use, Land-Use Change and Forestry (LULUCF). Preliminary
results suggest that the estimated additions of carbon stored
in harvested wood products may be somewhat lower than
the estimates shown in this report.
7.2. Changes in Carbon
Stocks in Urban Trees (IPCC
Source Category 5A5)
Urban forests constitute a significant portion of the total
U.S. tree canopy cover (Dwyer et al. 2000). It is estimated
that urban areas (cities, towns, and villages), which cover
3.5 percent of the continental United States, contain about
3.8 billion trees. With an average tree canopy cover of 27.1
percent, urban areas account for approximately 3 percent of
total tree cover in the continental United States (Nowak et al.
2001). Trees in urban areas of the continental United States
were estimated by Nowak and Crane (2002) to account for an
average annual net sequestration of 58.7 Tg CO2 Eq. (16 Tg C).
These data were collected throughout the 1990s, and have been
applied to the entire time series in this report (see Table 7-7).
Annual estimates of CO2 flux have not been developed, but
are believed to be relatively constant from 1990 through 2002.
Net carbon flux from urban trees is proportionately greater on
an area basis than that of forests. This is primarily the result of
different net growth rates in urban areas versus forests—urban
trees often grow faster than forest trees because of the relatively
open structure of the urban forest (Nowak and Crane 2002).
Also, areas in each case are accounted for differently. Because
urban areas contain less tree coverage than forest areas, the
carbon storage per hectare of land is in fact smaller for urban
areas. However, urban tree reporting occurs on a per unit tree
cover basis (tree canopy area), rather than total land area.
Urban trees therefore appear to have a greater carbon density
than forested areas (Nowak and Crane 2002).
Methodology
The methodology used by Nowak and Crane (2002) is
based on average annual estimates of urban tree growth and
Table 7-7: Net Flux from Urban Trees (Tg C02 Eq. and Tg C)
TgC02Eq.
TgC
1
1997
19S8
199S
2000
2001
2002
(58.7)
(58.7)
(58.7)
.(58J)
(58.7)
(§8.7)
(58.7)
(16)
(16)
(18)
(18)
(16)
(1.6)
Me: Parentheses indicate net sequestrate.
decomposition, which were derived from field measurements
and data from the scientific literature, urban area estimates
from U.S. Census data, and urban tree cover estimates from
remote sensing data. This approach is consistent with, but more
robust than, the default IPCC methodology in the Revised 1996
IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997).5
Nowak and Crane (2002) developed estimates of annual
gross carbon sequestration from tree growth and annual gross
carbon emissions from decomposition for ten U.S. cities:
Atlanta, GA; Baltimore, MD; Boston, MA; Chicago, IL;
Jersey City, NJ; New York, NY; Oakland, CA; Philadelphia,
PA; Sacramento, CA; and Syracuse, NY. The gross carbon
sequestration estimates were derived from field data that
were collected in these ten cities during the period from
1989 through 1999, including tree measurements of stem
diameter, tree height, crown height, and crown width, and
information on location, species, and canopy condition.
The field data were converted to annual gross carbon
sequestration rates for each species (or genus), diameter
class, and land-use condition (forested, park-like, and open
growth) by applying allometric equations, a root-to-shoot
ratio, moisture contents, a carbon content of 50 percent (dry
weight basis), an adjustment factor to account for smaller
aboveground biomass volumes (given a particular diameter)
in urban conditions compared to forests, an adjustment factor
to account for tree condition (fair to excellent, poor, critical,
dying, or dead), and annual diameter and height growth
rates. The annual gross carbon sequestration rates for each
species (or genus), diameter class, and land-use condition
were then scaled up to city estimates using tree population
information. The field data from the 10 cities, some of which
It is more robust in that both growth and decomposition are accounted for, and data from individual trees are scaled up to state and then national estimates
based on data on urban area and urban tree canopy cover.
Land-Use Change and Forestry 7-11
-------
Table 7-8: Carbon Stocks (Metric Tons C), Annual Carbon Sequestration (Metric Tons C/yr), Tree Cover (Percent), and
Annual Carbon Sequestration per Area of Tree Cover (kg C/m2 cover-yr) for Ten U.S. Cities
City
New York, NY
Atlanta, GA
Sacramento, CA
Chicago, IL
Baltimore, MD
Philadelphia, PA
Boston, MA
Syracuse, NY
Oakland, CA
Jersey City, NJ
Carbon
Stocks
1,225,20)
1,220,200
1,107,300
854,800
528,700
481 ,000
289,800
148,300
145,800
19,300
Gross Annual
Sequestration
38,400
42,100
20,200
40,100
14,800
14,600
9,500
4,700
NA
800
Net Annual
Sequestration
20,800
32,200
NA
NA
10,800
10,700
6,900
3,500
NA
600
Tree Cover
20.9
36.7
13.0
11.0
25.2
15.7
22.3
24.4
21.0
11.5
Gross Annual ,
Sequestration per
Area of Tree Cover
0.23
0.34
0.66
0.61
0,28
0.27
0.30
0.30
NA
0.18
Net Annual
Sequestration per
Area of Tree Cover
0.12
0,26
" NA
m.
0,20
0:20
, 0,22
0.22
NA
0.13
NA = not analyzed
are unpublished, are described in Nowak and Crane (2002)
and references cited therein. The allometric equations were
taken from the scientific literature (see Nowak 1994, Nowak
et al. 2002), and the adjustments to account for smaller
volumes in urban conditions were based on information
in Nowak (1994). A root-to-shoot ratio of 0.26 was taken
from Cairns et al. (1997), and species- or genus-specific
moisture contents were taken from various literature sources
(see Nowak 1994). Adjustment factors to account for tree
condition were based on percent crown dieback (Nowak
and Crane 2002). Tree growth rates were also taken from
existing literature. Average diameter growth was based on the
following sources: estimates for trees in forest stands came
from Smith and Shirley (1984); estimates for trees on land
uses with a park-like structure came from deVries (1987);
and estimates for more open-grown trees came from Nowak
(1994). Formulas from Reining (1988) formed the basis for
average height growth calculations.
The annual gross carbon emission estimates were
derived by applying to carbon stock estimates, which were
derived as an intermediate step in the gross sequestration
calculations, estimates of annual mortality by tree diameter
and condition class, assumptions about whether dead trees
would be removed from the site—since removed trees were
assumed to decay faster than those left on the site—and
assumed decomposition rates for dead trees left standing
and dead trees that are removed. The annual gross carbon
emission rates for each species (or genus), diameter class,
and condition class were then scaled up to city estimates
using tree population information. Estimates of annual
mortality rates by diameter class and condition class were
derived from a study of street-tree mortality (Nowak 1986).
Assumptions about whether dead trees would be removed
from the site were based on expert judgment of the authors.
Decomposition rates were based on literature estimates
(Nowak and Crane 2002).
Annual net carbon sequestration estimates were derived
for seven of the ten cities by subtracting the annual gross
emission estimates from the annual gross sequestration
estimates.6
National annual net carbon sequestration by urban
trees was estimated from the city estimates of gross and net
sequestration, and urban area and urban tree cover data for
the contiguous United States. Note that the urban areas are
based on U.S. Census data, which define "urban" as having
a population density greater than 1,000 people per square
mile or population total greater than 2,500. Therefore,
urban encompasses most cities, towns, and villages (i.e., it
includes both urban and suburban areas). The gross and net
carbon sequestration values for each city were divided by
each city's area of tree cover to determine the average annual
sequestration rates per unit of tree area for each city. The
median value for gross sequestration (0.30 kg C/m2-year)
was then multiplied by an estimate of national urban tree
cover area (76,151 km2) to estimate national annual gross
sequestration. To estimate national annual net sequestration,
6 Three cities did not have net estimates.
7-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 7-9: Quantitative Uncertainty Estimates for C02 Emissions from Changes in Carbon Stocks in Urban Trees
(Tg C02 Eq. and Percent)
IPCC Source Category
Year 2002 Emissions
fias CflCOiM «*6ertahtty(%)
Emission Estimate
Lower Bound
30%
(81.4)
Nate: Parentheses indicate net sequestration.
the estimate of national annual gross sequestration was
multiplied by the average of the ratios of net to gross
sequestration for those cities that had both estimates. The
average of these ratios is 0.70. The urban tree cover area
estimates for each of the 10 cities and the contiguous United
States were obtained from Dwyer et al. (2000) and Nowak
et al. (2001).
Uncertainty
Only the uncertainty associated with sampling was
quantifiable, as reported by Nowak and Crane (2002). The
average standard deviation for urban tree carbon storage
was 27 percent of the mean carbon storage on an area basis.
Additionally, a 5 percent uncertainty was associated with
national urban tree covered area. These estimates are based
on field data collected in ten U.S. cities, and uncertainty
in these estimates increases as they are scaled up to the
national level.
There is additional uncertainty associated with the
biomass equations, conversion factors, and decomposition
assumptions used to calculate carbon sequestration and
emission estimates (Nowak et al. 2002). These results also
exclude changes in soil carbon stocks, and there may be
some overlap between the urban tree carbon estimates and
the forest tree carbon estimates. However, both the omission
of urban soil carbon flux and the potential overlap with forest
carbon are believed to be relatively minor (Nowak 2002).
Because these are inestimable, they are not quantified as
part of this analysis.
These values and considerations were assembled under
a Tier 1 level uncertainty analysis to yield an uncertainty
estimate for the net flux associated with urban trees in the
United States for 2002 of 39 percent. The results are shown
in Table 7-9.
QA/QC and Verification
The net carbon flux resulting from urban trees
was calculated using estimates of gross and net carbon
sequestration estimates for urban trees and urban tree
coverage area found in literature. The validity of these data
for their use in this section of the Inventory was evaluated
through correspondence established with an author of the
papers. Through the correspondence, the methods used
to collect the urban tree sequestration and area data were
further clarified and the use of these data in the Inventory
was reviewed and validated (Nowak 2002).
7.3. Changes in Agricultural
Soil Carbon Stocks
(IPCC Source Category 5D)
The amount of organic carbon contained in soils depends
on the balance between inputs of organic material (e.g.,
decayed plant matter, roots, and organic amendments such
as manure and crop residues) and loss of carbon through
decomposition. The quantity and quality of organic matter
inputs and their rate of decomposition are determined by the
combined interaction of climate, soil properties, and land
use. Agricultural practices such as clearing, drainage, tillage,
planting, grazing, crop residue management, fertilization,
and flooding, can modify both organic matter inputs and
decomposition, and thereby result in a net flux of carbon to or
from soils. In addition, the application of carbonate minerals
to soils through liming operations results in emissions of
CO2. The IPCC methodology for estimation of net CO2 flux
from agricultural soils (IPCC/UNEP/OECD/IEA 1997) is
divided into three categories of land-use/land-management
activities: 1) agricultural land-use and land-management
activities on mineral soils; 2) agricultural land-use and land-
Land-Use Change and Forestry 7-13
-------
management activities on organic soils; and 3) liming of soils.
Mineral soils and organic soils are treated separately because
they respond differently to land-use practices.
Mineral soils contain comparatively low amounts of
organic carbon (usually less than 20 percent by weight),
much of which is concentrated near the soil surface. Typical
well-drained mineral surface soils contain from 1 to 6 percent
organic carbon (by weight), although some mineral soils can
be saturated for 30 or more days during normal years and
contain as much as 18 percent organic carbon, depending
on the clay content (NRCS 1999). Mineral subsoils contain
even lower amounts of organic carbon (NRCS 1999, Brady
and Weil 1999). When mineral soils undergo conversion from
their native state to agricultural use, as much as half the soil
organic carbon can be lost to the atmosphere. The rate and
ultimate magnitude of carbon loss will depend on native
vegetation, conversion method and subsequent management
practices, climate, and soil type. In the tropics, 40 to 60
percent of the carbon loss generally occurs within the first 10
years following conversion; after that, carbon stocks continue
to decline but at a much slower rate. In temperate regions,
carbon loss can continue for several decades. Eventually,
the soil will reach a new equilibrium that reflects a balance
between carbon accumulation from plant biomass and
carbon loss through oxidation. Any changes in land-use or
management practices that result in increased organic inputs
or decreased oxidation of organic carbon (e.g., improved crop
rotations, cover crops, application of organic amendments
and manure, and reduction or elimination of tillage) will
result in a net accumulation of soil organic carbon until a
new equilibrium is achieved.
Organic soils, also referred to as histosols, include
all soils with more than 12 to 20 percent organic carbon
by weight, depending on clay content (NRCS 1999,
Brady and Weil 1999). The organic layer of these soils is
also typically extremely deep. Organic soils form under
waterlogged conditions, in which decomposition of plant
residues is retarded. When organic soils are cultivated, they
are first drained which, together with tilling or mixing of
the soil, aerates the soil, and thereby accelerates the rate of
decomposition and CO2 generation. Because of the depth and
richness of the organic layers, carbon loss from cultivated
organic soils can continue over long periods of time. When
organic soils are disturbed, through cultivation and/or
drainage, the rate at which organic matter decomposes, and
therefore the rate at which CO2 emissions are generated,
is determined primarily by climate, composition (i.e.,
decomposability) of the organic matter, and the specific
land-use practices undertaken. The use of organic soils for
annual crops results in greater carbon loss than conversion to
pasture or forests, due to deeper drainage and more intensive
management practices (Armentano and Verhoeven 1990, as
cited in IPCC/UNEP/OECD/IEA 1997).
Lime in the form of crushed limestone (CaCO3) and
dolomite (CaMg(CO3)2) is commonly added to agricultural
soils to ameliorate acidification. When these compounds
come in contact with acid soils they degrade, thereby
generating CO2. Complete degradation of applied limestone
and dolomite could take several years, but it could also take
significantly less time, depending on the soil conditions and
the type of mineral applied.
Of the three activities, use and management of mineral
soils was the most important component of total flux during
the 1990 through 2002 period. Carbon sequestration in
mineral soils in 2002 was estimated at approximately 64.7
Tg CO2 Eq. (18 Tg C), while emissions from organic soils
were estimated at 34.7 Tg CO2 Eq. (10 Tg C) and emissions
from liming were estimated at 8.8 Tg CO2 Eq. (2 Tg C).
Together, the three activities accounted for net sequestration
of approximately 21.2 Tg CO2 Eq. (6 Tg C) in 2002. Total
annual net CO2 flux was negative (i.e., net sequestration
occurred) each year over the 1990 to 2002 period. Between
1990 and 2002, total net carbon sequestration in agricultural
soils decreased by close to 20 percent. Net sequestration
across the inventory period is largely due to annual cropland
converted to permanent pastures and hay production, a
reduction in the frequency of summer-fallow use in semi-
arid areas, and some increase in the adoption of conservation
tillage (i.e. reduced and no till practices). The relatively large
shift in annual net sequestration from 1990 to 1995 is the
result of calculating average annual mineral and organic soil
fluxes from periodic, rather than annual, activity data.7
The spatial variability in annual, per hectare CO2 flux for
mineral and organic soils is displayed in Figure 7-5 through
Figure 7-8. The highest rates of sequestration occur in the
southern Great Plains, the corn-belt states of the Midwest,
the lower Mississippi River Valley, and the wheat-dominated
cropping region of the Pacific Northwest. Sequestration
Mineral and organic soil results for the entire time series are presented in Annex 3.13.
7-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Figure 7-5
Net Annual C02 Flux, per Hectare, From Mineral Soils Under Agricultural Management, 1990-1992
Note: Positives represent emissions,
and negatives represent sequestration.
Map does not include soil organic carbon
change resulting from manure and
sewage sludge additions.
This map shows the spatial variability in net annual carbon dioxide flux from mineral soils for the year 1990 through 1992.
The color assigned to each polygon represents the average annual flux per hectare for the area of managed mineral soils in that polygon.
metric ton C02/ha
I I < -0.3
|B-0.2 to-0.1
m -0.1 to 0
OtoO.1
Figure 7-6
Net Annual C02 Flux, per Hectare, From Mineral Soils Under Agricultural Management, 1993-2002
Note: Positives represent emissions,
and negatives represent sequestration.
Map does not include soil organic carbon
change resulting from manure and
sewage sludge additions or enrollment in
CRP after 1997.
This map shows the spatial variability in net annual carbon dioxide flux from mineral soils for the year 1993 through 2002.
The color assigned to each polygon represents the average annual flux per hectare for the area of managed mineral soils in that polygon.
metric ton C02/ha
II < -0.3
^^ -0.2 to -0.1
^^ -0.1 to 0
^B °to °-1
•I >0.1
Land-Use Change and Forestry 7-15
-------
Figure 7-7
Net Annual C02 Flux, per Hectare. From Organic Soils Under Agricultural Management. 1990-1992
metric ton C02/ha
H >40
^^ 30 to 40
20 to 30
| | no organic soils
This map shows the spatial variability in net annual carbon dioxide flux from organic soils for the year 1990 through 1992.
The color assigned to each polygon represents the average annual flux per hectare for the area of managed organic soils in that polygon.
Figure 7-8
Net Annual C02 Flux, per Hectare, From Organic Soils Under Agricultural Management. 1993-2002
metric ton C02/ha
H > 40
m 30 to 40
|B 20 to 30
m 10 to 20
| | no organic soils
This map shows the spatial variability in net annual carbon dioxide flux from organic soils for the year 1993 through 2002.
The color assigned to each polygon represents the average annual flux per hectare for the area of managed organic soils in that polygon.
7-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 7-10: Net C02 Flux from Agricultural Soils (Tg C02 Eq.)
Soil Type
Mineral Soils
Organic Soils
Liming of Soils
Total Net Flux
1999 2000 2081
Note: Parentheses indicate
based on historical data only.
Table 7-11: Net Carbon Flux from Agricultural Soils (Tg C)
Soil Type
Mineral Soils
Organic Soils
liming of Soils
Total Net Flux
1999 2000 2001
Note: ParenBieses indicate
based on historical data only.
rates are also relatively high in the southeastern United
States. Those regions either have high Conservation Reserve
Program enrollment, (particularly the Great Plains region),
and/or have adopted conservation tillage at a higher rate. The
greatest mineral soil sequestration rates are in the south and
east central United States and in a small area of the Pacific
Northwest, while the greatest organic soil emission rates
are along the southeast coast, in the northeast central United
States, and along the central west coast.
The flux estimates presented here are restricted to CO2
fluxes associated with the use and management of agricultural
soils. Agricultural soils are also important sources of other
greenhouse gases, particularly nitrous oxide (N2O) from
application of fertilizers, manure, and crop residues and
from cultivation of legumes, as well as methane (CH4) from
flooded rice cultivation. These emissions are accounted for
in the Agriculture chapter.8 It should be noted that other
land-use and land-use change activities result in fluxes of
non-CO2 greenhouse gases to and from soils that are not
comprehensively accounted for currently. These include
emissions of CH4 and N2O from managed forest soils (above
what would occur if the forest soils were undisturbed), as well
as CH4 emissions from artificially flooded lands, resulting
from activities such as dam construction. Aerobic (i.e., non-
flooded) soils are a sink for CH4, so soil drainage can result
in soils changing from a CH4 source to a CH4 sink, but if
the drained soils are used for agriculture, fertilization, and
tillage, disturbance can reduce the ability of soils to oxidize
CH4. The non-CO2 emissions and sinks from these other land
use and land-use change activities were not assessed due to
scientific uncertainties about the greenhouse gas fluxes that
result from these activities.
Methodology
The methodologies used to calculate net CO2 flux from
use and management of mineral and organic soils and from
liming follow the Revised 1996 IPCC Guidelines (IPCC/
UNEP/OECD/IEA 1997, Ogle et al. 2002, Ogle et al. in
press), except where noted below. (Additional details on the
methodology and data used to estimate flux from mineral
and organic soils are described in Annex 3.13). Mineral
soil organic carbon stocks were estimated for 1982, 1992,
and 1997 for the conterminous United States and Hawaii
using U.S. data on climate, soil types, land use and land
management activity data, reference carbon stocks (for
agricultural soils rather than native soils) and field studies
addressing management effects on soil organic carbon
storage. National-scale data on land-use and management
changes over time were obtained from the 7997 National
8 Nitrous oxide emissions from agricultural soils and methane emissions from rice fields are addressed under the Agricultural Soil Management and Rice
Cultivation sections, respectively, of the Agriculture chapter.
Land-Use Change and Forestry 7-17
-------
Resources Inventory (USDA-NRCS 2000). The 7997
National Resources Inventory provides land use/management
data and soils information for more than 400,000 locations
in U.S. agricultural lands. Two other sources were used
to supplement the land-use information from the 7997
National Resources Inventory. The Conservation Technology
Information Center (CTIC 1998) provided data on tillage
activity, with adjustments for long-term adoption of no-till
agriculture (Towery 2001), and Euliss and Gleason (2002)
provided activity data on wetland restoration of Conservation
Reserve Program Lands.
Major Land Resource Areas (MLRAs) were used as
the base spatial unit for mapping climate regions in the
United States. Each MLRA represents a geographic unit
with relatively similar soils, climate, water resources, and
land uses (NRCS 1981 ).9 Major Land Resource Areas were
classified into climate zones according to the IPCC categories
using the Parameter-Evaluation Regressions on Independent
Slopes Model (PRISM) climate-mapping program of Daly
et al. (1994). Reference carbon stocks were estimated
using the National Soil Survey Characterization Database
(NRCS 1997) and cultivated cropland as the reference
condition, rather than native vegetation as used in the Revised
1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997).
Changing the reference condition was necessary because soil
measurements under agricultural management are much more
common and easily identified in the National Soil Survey
Characterization Database (NRCS 1997). Management
factors were derived from published literature to determine
the impact of management practices on soil organic carbon
storage, including changes in tillage, cropping rotations and
intensification, as well as land-use change between cultivated
and uncultivated conditions (Ogle et al. in press). Euliss and
Gleason (2002) provided the data for computing the change
in soil organic carbon storage resulting from restoration of
Conservation Reserve Program Lands (Olness et al. in press,
Euliss et al. in prep). Combining information from these
data sources, carbon stocks were estimated 50,000 times
for 1982, 1992, and 1997, using a Monte Carlo simulation
approach and the probability density functions for U.S.-
specific management factors, reference carbon stocks, and
land-use activity data (Ogle et al. in press, Ogle et al. 2002).
The annual carbon flux for 1990 through 1992 was estimated
by calculating the annual change in stocks between 1982
and 1992; annual carbon flux for 1993 through 2002 was
estimated by calculating the annual change in stocks between
1992 and 1997.
Annual carbon emission estimates from organic soils
used for agriculture between 1990 and 2002 were derived
using Revised 1996 IPCC Guidelines (IPCC/UNEP/OECD/
IEA 1997), except that U.S.-specific carbon loss rates were
used in the calculations rather than default IPCC rates (Ogle
et al. 2002). Similar to mineral soils, the final estimates
include a measure of uncertainty as determined from the
Monte Carlo simulation. Data from published literature
were used to derive probability density functions for carbon
loss rates (Ogle et al. in press), which were used in turn to
compute emissions based on the 1992 and 1997 land areas
in each climate/land-use category defined in the Revised
1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997). The
area estimates were derived from the same climate, soil, and
land-use/management databases that were used for mineral
soil calculations (Daly et al. 1994, USDA-NRCS 2000). The
annual flux estimated for 1992 was applied to 1990 through
1992, and the annual flux estimated for 1997 was applied to
1993 through 2002.
Annual carbon flux estimates for mineral soils between
1990 and 2002 were adjusted to account for additional carbon
sequestration from manure and sewage sludge applications,
as well as gains or losses in carbon sequestration due to
changes in Conservation Reserve Program enrollment after
1997. The amount of land receiving manure and sewage
sludge was estimated from nitrogen application data from
the Agricultural Soil Management section of the Agriculture
chapter of this volume, and an assumed application rate
derived from Kellogg et al. (2000). The total land area was
subdivided between cropland and grazing land based on
supplemental information collected by the USDA (ERS
2000, NASS 2002). Carbon storage rate was estimated at
0.10 metric tons C per hectare per year for cropland and
0.33 metric tons C per hectare per year for grazing land.
To estimate the impact of enrollment in the Conservation
Reserve Program after 1997, the change in enrollment
acreage relative to 1997 were derived based on Barbarika
(2002), and the differences in mineral soil areas were
multiplied by 0.5 metric tons C per hectare per year.
Carbon dioxide emissions from degradation of limestone
and dolomite applied to agricultural soils were calculated
The polygons displayed in Figure 6-5 through Figure 6-8 are the Major Land Resource Areas.
7-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 7-12: Quantities of Applied Minerals (Thousand Metric Tons)
Mineral
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2080 2001 2002
Limestone 19,012 20,312 17,984 15,609 16,686 17,297 17,479 16,539 14,882 16,894 15,863 16,09? 15,799
Dolomite 2,360 2,618 2,232 1,740 2,264 2,769 2,499 2,989 6,389 3,420 3,812 3,951 3,878
by multiplying the annual amounts of limestone and
dolomite applied (see Table 7-12) by CO2 emission factors
(0.120 metric ton C/metric ton limestone, 0.130 metric ton
C/metric ton dolomite).10 These emission factors are based
on the assumption that all of the carbon in these materials
evolves as CO2 in the same year in which the minerals
are applied. The annual application ;ates of limestone and
dolomite were derived from estimates and industry statistics
provided in the Minerals Yearbook and Mineral Industry
Surveys (Tepordei 1993, 1994, 1995, 1996, 1997, 1998,
1999, 2000, 2001, 2002, 2003; USGS 2002, 2003). To
develop these data, USGS (U.S. Bureau of Mines prior to
1997) obtained production and use information by surveying
crushed stone manufacturers. Because some manufacturers
were reluctant to provide information, the estimates of total
crushed limestone and dolomite production and use were
divided into three components: 1) production by end-use,
as reported by manufacturers (i.e., "specified" production);
2) production reported by manufacturers without end-uses
specified (i.e., "unspecified" production); and 3) estimated
additional production by manufacturers who did not respond
to the survey (i.e., "estimated" production).
To estimate the "unspecified" and "estimated" amounts
of crushed limestone and dolomite applied to agricultural
soils, it was assumed that the fractions of "unspecified" and
"estimated" production that were applied to agricultural
soils in a specific year were equal to the fraction of
"specified" production that was applied to agricultural
soils in that same year. In addition, data were not available
for 1990, 1992, and 2002 on the fractions of total crushed
stone production that were limestone and dolomite, and
on the fractions of limestone and dolomite production
that were applied to soils. To estimate the 1990 and 1992
data, a set of average fractions were calculated using the
1991 and 1993 data. These average fractions were applied
to the quantity of "total crushed stone produced or used"
reported for 1990 and 1992 in the 1994 Minerals Yearbook
(Tepordei 1996). To estimate 2002 data, the previous year's
fractions were applied to a 2002 estimate of total crushed
stone presented in the USGS Mineral Industry Surveys:
Crushed Stone and Sand and Gravel in the First Quarter
of2002 (USGS 2002).
The primary source for limestone and dolomite activity
data is the Minerals Yearbook, published by the Bureau of
Mines through 1994 and by the U.S. Geological Survey from
1995 to the present. In 1994, the "Crushed Stone" chapter in
Minerals Yearbook began rounding (to the nearest thousand)
quantities for total crushed stone produced or used. It then
reported revised (rounded) quantities for each of the years
from 1990 to 1993. In order to minimize the inconsistencies
in the activity data, these revised production numbers have
been used in all of the subsequent calculations.
Uncertainty
Uncertainties for mineral and organic soils were
quantified using a Monte Carlo Approach by constructing
probability distribution functions (PDF) for inputs to the IPCC
equations, including management factors, carbon emission
rates for organic soils, and land use and management activity
data, and then simulating a range of values based on 50,000
iterations (Ogle et al. in press, Annex 3.13). Uncertainty
estimates do not include manure, sludge, or Conservation
Reserve Program contributions to C storage. Uncertainty
results based on the Monte Carlo simulation are shown in
Table 7-13. PDFs for management factors were derived
from a synthesis of 91 published studies, which addressed
the impact of management on soil organic carbon storage.
Uncertainties in land use and management activity data
were also derived from a statistical analysis. The National
Resources Inventory (NRI) has a two-stage sampling design
that allowed PDFs to be constructed assuming a multivariate
normal distribution accounting for dependencies in activity
data. PDFs for the tillage activity data, as provided by the
Conservation Technology and Information Center, were
10 The default emission factor for dolomite provided in the Workbook volume of the Revised 1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997) is
incorrect. The value provided is 0.122 metric ton carbon/metric ton of dolomite; the correct value is 0.130 metric ton carbon/metric ton of dolomite.
Land-Use Change and Forestry 7-19
-------
Table 7-13: Quantitative Uncertainty Estimates for C02 Flux from Agricultural Soil Carbon Stocks (Tg C02 Eq. and Percent)
Source
(1993-2002) (TgC02 Eg.)
Lower Bound Upper Bound Lower Bound Upper Bound
Mineral Soils C02
Organic Soils C02
(40,8)
34.7
(59.0)
23.5
(23.8)
49,1
-42%
-32%
-1-42%
a Includes mineral and organic soils only; estimates do not include the change in carbon storage resulting from ttie annual application of manure and sewage
sludge, or the change in Conservation Reserve Program enrollment after 1997; the emissions value represents the average of years 1993-2002.
b Range of emissions estimates predicted by Monte Carlo Stochastic Simulation for a 95% confidence interval.
constructed on a bivariate normal distribution with a log-
ratio scale, accounting for the negative dependence among
the proportions of land under conventional and conservation
tillage practices. Lastly, enrollment in wetland restoration
programs was estimated from contract agreements, but due
to a lack of information, PDFs were constructed assuming
a nominal ±50 percent uncertainty range.
The time-series calculations were consistent for each
reporting year of the inventory in terms of methodology, with
the only difference in reported values stemming from the
changes in land use and management activities across U.S.
agricultural lands. In addition, the same management factors
(i.e., emission factors) were used each year for calculating
the impact of land use and management on soil C stocks.
There is no evidence that changing management practices
has a quantitatively different impact on soil C stocks over the
inventory period. For example, changing from conventional
to no-till management in 1990 or at a later date such as the
year 2000 is assumed to have the same cumulative impact
on soil C stocks over a 20 year period.
Although the mineral and organic soil estimates have
been improved during the last two years using a Monte Carlo
approach with the incorporation of U.S.-specific reference
carbon stocks and management factor values, several
limitations remain in the analysis. First, minimal data exist
on where and how much manure and sewage sludge has been
applied to U.S. agricultural lands. Consequently, uncertainties
have not been estimated for the change in soil organic carbon
storage resulting from these applications. Second, due to the
IPCC requirement that inventories include all land areas that
are potentially subject to land-use change, the 1997 National
Resources Inventory dataset includes some points designated
as non-agricultural land-uses if this designation changed
during the period from 1992 to 1997. The non-agricultural
land uses are urban, water, and miscellaneous non-cropland
(e.g., roads and barren areas). The impact on carbon storage
resulting from converting cropland to non-agricultural uses
is not well understood, and therefore, those points were
not included in the calculations. Third, this inventory may
underestimate losses of carbon from organic soils because the
1997 National Resources Inventory was not designed as a soil
survey and organic soils frequently occur as relatively small
inclusions within major soil types. Lastly, this methodology
does not take into account changes in carbon stocks due to
pre-1982 land use and land-use change.
Uncertainties in the estimates of emissions from liming
result from both the methodology and the activity data. The
IPCC method assumes that all the inorganic carbon in the
applied minerals evolves to CO2, and that this degradation
occurs in the same year that the minerals are applied. However,
recent research has shown that liming can either be a carbon
source or a sink, depending upon weathering reactions, which
are pH dependent (Hamilton et al. 2002). Moreover, it can take
several years for agriculturally applied limestone and dolomite
to degrade completely. However, application rates are fairly
constant over the entire time series, so this latter assumption
may not contribute significantly to overall uncertainty.
There are several sources of uncertainty in the limestone
and dolomite activity data. When reporting data to the
USGS (or U.S. Bureau of Mines), some producers do not
distinguish between limestone and dolomite. In these
cases, data are reported as limestone, so this could lead to
an overestimation of limestone and an underestimation of
dolomite. In addition, the total quantity of crushed stone
listed each year in the Minerals Yearbook excludes American
Samoa, Guam, Puerto Rico, and the U.S. Virgin Islands.
The Mineral Industry Surveys further excludes Alaska and
Hawaii from its totals.
7-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Recalculations Discussion
The estimates of changes in agricultural soil C stocks
have been modified in several ways relative to the previous
inventory. First, management factors have been rescaled
to provide a better approximation of impacts in different
climatic regions of the United States, instead of using a single
management factor for the entire country (Ogle et al., in
prep). These changes only affected mineral soil calculations,
and served to provide better regional estimates of land use
and management impacts. New factors were derived if there
were a sufficient number of studies to evaluate climate trends
and if management effects differed significantly across
thermal and moisture regimes based on the IPCC climate
types. These revisions alter the mineral soil calculations by
removing statistical bias that can result from the application
of a single management factor value for all agricultural lands.
For example, tillage factors were derived for moist and dry
climates because field experiments have shown that the
impact of tillage differs due to the prevailing moisture regime
(i.e., changing tillage management alters the amount of soil
organic carbon more in a moist climate than it does in a dry
climates). The second change in this year's inventory involved
incorporation of the latest soils information, based on a new
version of the soil database that accompanies the National
Resources Inventory (USDA-NRCS 2000). Those data were
incorporated into the analysis and the total areas in various
soil categories were adjusted based on the revisions.
Estimates of CO2 emissions from agricultural soil
management have been revised due to methodological and
historical data changes in the calculations of nitrogen from
livestock that is applied to soils. These changes include
corrections to: the typical animal mass value for beef
cows and calves; the accounting of sheep in New England
states; state broiler populations; and updated NASS animal
population estimates for the years 1998 through 2001.
Additionally, the factor for converting short tons to metric
tons was revised to include another significant digit, and
the percent residue applied for rice in the year 2001 was
corrected. In combination, these changes resulted in a minor
effect on the agricultural soil C estimates with a reduction
in the CO2 sink by less than 1 percent.
Emissions from organic soils have changed slightly from
those reported in the previous inventory for the years 1993 to
2001, as a result of altering the number of significant digits
used for converting the mass of carbon to CO2.
The quantity of applied minerals reported in the previous
inventory for 2001 has been revised. Consequently, the
reported emissions resulting from liming in 2001 have also
changed. In the previous inventory, to estimate 2001 data, the
previous year's fractions were applied to a 2001 estimate of
total crushed stone presented in the USGS Mineral Industry
Surveys: Crushed Stone and Sand and Gravel in the First
Quarter of 2002 (USGS 2002). Since publication of the
previous inventory, the Minerals Yearbook has published
actual quantities of crushed stone sold or used by producers
in the United States in 2001. These values have replaced those
used in the previous inventory to calculate the quantity of
minerals applied to soil and the emissions from liming.
Planned Improvements
Three planned improvements are currently underway
that will enhance reporting of changes in agricultural soil
carbon stocks. First, uncertainty will be estimated for the
change in carbon storage due to manure additions to crop and
grazing lands. Through this revision, the impact of manure
management will be fully integrated into the uncertainty
analysis, instead of estimating its impact in a separate set of
calculations (see Annex 3.13).
Second, losses from organic soils will be re-calculated in
future inventories to include area which has been converted
between agricultural uses and urban, miscellaneous non-
cropland or open water. This inventory does not estimate
the impacts of non-agricultural uses on soil C stocks (nor
will this be included in future estimates), but does need to
estimate the impacts of the agricultural uses during the time
periods when organic soils are managed with drainage for
cropping and grazing purposes. Consequently, emissions
have been underestimated, leading to lower implied emission
factors in the Common Reporting Format (CRF) tables. This
problem will be corrected and there will be a slight increase
in estimated emissions from those soils.
The third improvement deals with an alternative
inventory approach to better represent between-year
variability in annual fluxes. This new annual activity-based
inventory will use the Century ecosystem simulation model,
which relies on actual climate, soil, and land use/management
databases to estimate variation in fluxes. This inventory will
provide a more robust accounting of carbon stock changes in
U.S. agricultural lands than the more simplistic IPCC soil C
accounting approach. This approach is likely to be used in the
Land-Use Change and Forestry 7-21
-------
future for reporting of land use and management impacts on
agricultural soil C stocks, and therefore a short description of
this method compared to the IPCC approach is provided.
The Century ecosystem model has been widely tested
and found to be successful in simulating those processes
affecting soil organic carbon storage (Metherell et al. 1993,
Parton et al. 1994). Simulation modeling differs from
the IPCC approach in that annual changes are computed
dynamically as a function of inputs of carbon and nitrogen
to soil (e.g., crop residues, manure) and carbon emissions
from organic matter decomposition, which are governed by
climate and soil factors as well as management practices. The
model distinguishes between all major field crops (maize,
wheat and other small grains, soybean, sorghum, cotton) as
well as hay and pasture (grass, alfalfa, clover). Management
variables include tillage, fertilization, irrigation, drainage,
and manure addition.
Input data are largely derived from the same sources as
the IPCC-based method (i.e., climate variables come from the
PRISM database; crop rotation, irrigation and soil characteristics
from the National Resources Inventory (NRI); and tillage data
from the Conservation Technology Information Center (CTIC).
In addition, the Century analysis uses detailed information
on crop rotation-specific fertilization and tillage implements
obtained from USDA's Economic Research Service. The main
difference between the methods is that the climate, soil, and
management data serve as driving variables in the Century
simulation, whereas in the IPCC approach these data are more
highly aggregated and are used for classification purposes. In
the Century-based analysis, land areas having less than 5 percent
of total area in crop production are excluded and several less-
dominant crops (e.g., vegetables, sugar beets and sugar cane,
potatoes, tobacco, orchards, and vineyards), for which the model
has not yet been parameterized, are not included. Thus, the total
area included in the Century analysis (149 million hectares) will
be smaller than the corresponding area of cropland (165 million
hectares) included in the IPCC estimates.
Preliminary results using the Century model suggest
(as with the IPCC model) that U.S. cropland mineral soils
(excluding organic soils) are currently acting as a carbon
sink. The Century model estimates are that U.S. cropland
soils sequestered an average of approximately 77 Tg CO2
Eq. annually (21 Tg C/year) for 1992 through 1997. Organic
soils (which contribute large C losses) have not yet been
simulated by Century.
As with the IPCC method, increases in mineral soil C
stocks in the Century analysis are associated with reduced
tillage, Conservation Reserve Program lands, reduced bare
fallow and some increase in hay area. However, the Century
analysis also includes the effect of a long-term trend in
increasing residue inputs due to higher productivity on
cropland in general, contributing to increasing soil carbon
stocks. Work is underway to refine model input data and to
estimate uncertainty for the dynamic model approach.
Potential advantages of a dynamic simulation-based
approach include the ability to use actual observed weather,
observed annual crop yields, and more detailed soils and
management information to drive the estimates of soil carbon
change. This would facilitate annual estimates of carbon
stock changes and CO2 emissions from soils that would
better reflect interannual variability in cropland production
and weather influences on carbon cycle processes.
7.4. Changes in Yard Trimming
and Food Scrap Carbon Stocks in
Landfills (IPCC Source Category 5E)
As is the case with carbon in landfilled forest products,
carbon contained in landfilled yard trimmings and food
scraps can be stored indefinitely. In the United States, yard
trimmings (i.e., grass clippings, leaves, and branches) and
food scraps comprise a significant portion of the municipal
waste stream, and a large fraction of the collected yard
trimmings and food scraps are discarded in landfills.
However, both the amount of yard trimmings and food scraps
collected annually and the fraction that is landfilled have
declined over the last decade. In 1990, nearly 51 million
metric tons (wet weight) of yard trimmings and food scraps
were generated (i.e., put at the curb for collection or taken
to disposal or composting facilities) (EPA 2003). Since then,
programs banning or discouraging disposal have led to an
increase in backyard composting and the use of mulching
mowers, and a consequent 20 percent decrease in the amount
of yard trimmings collected. At the same time, a dramatic
increase in the number of municipal composting facilities has
reduced the proportion of collected yard trimmings that are
discarded in landfills—from 72 percent in 1990 to 34 percent
in 2002. There is considerably less centralized composting
of food scraps; generation has grown by 26 percent since
1990, though the proportion of food scraps discarded in
7-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 7-14: Net Changes in Yard Trimming and Food Scrap Stocks (Tg C02 Eq.)
Carbon Pool
Yard Trimmings
Grass
Leaves
Branetjes
Food Scraps
Total Net Flux
1996
1197
1998
2000
(11.3)
(1.0)
(5.9)
(4.4)
42.%
(104)
(OJ)
(5.4)
(4,0)
(8.8)
(0.8)
(5,1)
(3.7)
(2.1)
(8.4)
(0.7)
(4,5)
(7.2)
(0.6)
(4.0)
(2;6)
128.0)
f«9) (t2.4)
Note: Totals my not sum due to independent rounding.
Table 7-15: Net Changes in Yard Trimming and Food Scrap Stocks (Tg C)
Carbon Pool
1990
Yard Trimmings
Grass
Leaves
Branches
Food Scraps
Total Net Flux
Note: Totals may not sum due to independent rounding.
2001
2002
(7.4) (7.4)
(0.7) (0.7)
(4.0) (4.0)
(2J) ; (2.7)
(2.7)
WD
1996
(3.1)
(0-3)
(1.6)
(1.2)
(0.6)
(3.7)
1997
(2.8)
(0.2)
(1-5)
(1.1)
(0.7)
(3.5)
1998
(2J)
(0.2)
(1.4)
(1.0)
(0.8)
(3.4)
1999
(2.3)
(0.2)
(1.2)
(0.9)
(8.8)
(3-D
2600
(2.0)
(0,2)
(1.1)
(0-7)
(0.8)
(2.8)
2001
(2.0)
(0.2)
(1.1)
(0.7)
(0.8)
(2.8)
2002
(2.0)
(0.2)
(1.1)
(0.7)
(0.7)
(2.8)
landfills has decreased slightly from 81 percent in 1990 to
77 percent in 2002. Overall, there has been a decrease in the
yard trimmings and food scrap landfill disposal rate, which
has resulted in a decrease in the rate of landfill carbon storage
from 26.0 Tg CO2 Eq. in 1990 to 10.1 Tg CO2 Eq. in 2002
(Table 7-15 and Table 7-14).
Methodology
Estimates of net carbon flux resulting from landfilled
yard trimmings and food scraps were developed by
estimating the change in landfilled carbon stocks between
inventory years. Carbon stock estimates were calculated by
determining the mass of landfilled carbon resulting from yard
trimmings or food scraps discarded in a given year; adding
the accumulated landfilled carbon from previous years; and
subtracting the portion of carbon landfilled in previous years
that decomposed.
To determine the total landfilled carbon stocks for a
given year, the following were estimated: 1) the composition
of the yard trimmings, 2) the mass of yard trimmings and
food scraps discarded in landfills, 3) the carbon storage
factor of the landfilled yard trimmings and food scraps, and
4) the rate of decomposition of the degradable carbon. The
composition of yard trimmings was assumed to be 30 percent
grass clippings, 40 percent leaves, and 30 percent branches
on a wet weight basis (Oshins and Block 2000). The yard
trimmings were subdivided because each component has its
own unique carbon storage factor and rate of decomposition.
The mass of yard trimmings and food scraps disposed of in
landfills was estimated by multiplying the quantity of yard
trimmings and food scraps discarded by the proportion of
discards managed in landfills. Data on discards (i.e., the
amount generated minus the amount diverted to centralized
composting facilities) for both yard trimmings and food
scraps were taken primarily from Municipal Solid Waste in
the United States: 2001 Facts and Figures (EPA 2003). That
report provides data for 1960, 1970, 1980, 1990, 1995, and
1999 through 2001. To provide data for some of the missing
years in the 1990 through 1999 period, two earlier reports
were used (Characterization of Municipal Solid Waste in the
United States: 1998 Update (EPA 1999), and Municipal Solid
Waste in the United States: 2000 Facts and Figures (EPA
2002)). Remaining years in the time series for which data
were not provided were estimated using linear interpolation,
except for 2002, which was assumed to have the same
discards as 2001. These reports do not subdivide discards of
individual materials into volumes landfilled and combusted,
although they provide an estimate of the proportion of overall
wastestream discards managed in landfills and combustors
(i.e., ranging from 81 percent and 19 percent respectively in
1990, to 79 percent and 21 percent in 2001).
Land-Use Change and Forestry 7-23
-------
Table 7-16: Moisture Content (%), Carbon Storage Factor (CSF), Initial Carbon Content (%), Proportion of Initial Carbon
Sequestered (%), and Half-Life (years) for Landfilled Yard Trimmings and Food Scraps
Variable
Grass
Leaves
Branches
Food Scraps
Moisture Content (% H20)
CSF {kg C sequestered /dry to
Mai Carbon Content (%)
70
0.32
45
71
5
4t-
84"
10
0.38
49
77
20
70
0,08
51
16
5
'Adjusted using meffianeyleUs in flstaref at (JttT).
The amount of carbon disposed of in landfills each year,
starting in 1960, was estimated by converting the discarded
landfilled yard trimmings and food scraps from a wet weight
to a dry weight basis, and then multiplying by the initial
(i.e., pre-decomposition) carbon content (as a fraction of dry
weight). The dry weight of landfilled material was calculated
using dry weight to wet weight ratios (Tchobanoglous, et al.
1993 cited by Barlaz 1998) and the initial carbon contents
were determined by Barlaz (1998) (Table 7-16).
The amount of carbon remaining in the landfill for each
subsequent year was tracked based on a simple model of carbon
fate. According to Barlaz (1998), a portion of the initial carbon
resists decomposition and is essentially persistent in the landfill
environment; the modeling approach applied here builds on
his findings. Barlaz (1998) conducted a series of experiments
designed to measure biodegradation of yard trimmings, food
scraps, and other materials, in conditions designed to promote
decomposition (i.e., by providing ample moisture and nutrients).
After measuring the initial carbon content, the materials were
placed in sealed containers along with a "seed" containing
methanogenic microbes from a landfill. Once decomposition
was complete, the yard trimmings and food scraps were re-
analyzed for carbon content. The mass of carbon remaining,
divided by the original dry weight of the material, was reported
as the carbon storage factor (Table 7-16).
For purposes of simulating U.S. landfill carbon flows,
the carbon storage factors are divided by the initial carbon
content to determine the proportion of initial carbon that does
not decompose. The remaining portion is assumed to degrade
(and results in emissions of CH4 and CO2). For example, for
branches Barlaz (1998) reported the carbon storage factor
as 38 percent (of dry weight), and the initial carbon content
as 49 percent (of dry weight). Thus, the proportion of initial
carbon that does not decompose is 77 percent (i.e., 0.38/0.49).
The remaining 23 percent degrades.
The degradable portion of the carbon is assumed to
decay according to first order kinetics. Grass and food scraps
are assumed to have a half-life of 5 years; leaves and branches
are assumed to have a half-life of 20 years.
For each of the four materials (grass, leaves, branches,
food scraps), the stock of carbon in landfills for any given
year is calculated according to the following formula:
MQ
ICC
LFC ; t = Wj ,n * (1 - MQ) * ICCi * { [CSF; / ICQ]
+ [(1 - (CSFj / ICC; )) * e-k*« - n> ] }
where,
t = the year for which carbon stocks are being estimated,
LFC it = the stock of carbon in landfills in year t, for waste
i (grass, leaves, branches, food scraps)
Wj n = the mass of waste i disposed in landfills in year n,
in units of wet weight
n = the year in which the waste was disposed, where
1960 < n < t
= the moisture content of waste i,
= the initial carbon content of waste i,
CSF; = the carbon storage factor of waste i,
e = the natural logarithm,
k = the first order rate constant for waste i, and is equal to
0.693 divided by the half-life for decomposition.
For a given year t, the total stock of carbon in landfills
(TLFCt) is the sum of stocks across all four materials. The
annual flux of carbon in landfills (Ft) for year t is calculated
as the change in stock compared to the preceding year:
Ft = TLFCt-TLFCt_!
Thus, the carbon placed in a landfill in year n is tracked
for each year t through the end of the inventory period (2002).
For example, disposal of food scraps in 1960 resulted in
depositing about 1,140,000 metric tons of carbon. Of this
7-24 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 7-17: Carbon Stocks in Yard Trimmings and Food Scraps (Tg of C)
Carbon Pool
1990
Grass
Leaves
Branches
Total Carbon Stocks
f«*.1
Note: Totals may not sum due to independent rounding.
1996
197.1
21.8
93.1
82.2
242
2211,3
1997
199.9
22,0
94.6
83.3
24.9
f24»
1998
202.5
22.2
96.0
84.3
2IJ
228.2
1999
204.8
22.4
972
85.1
26.4
231.3
2808
28S.8
22.6
98.3
85.8
27.2
234.0
2881
208.8
22.8
99.4
88.6
2*J
2S|&
2802
210.8
23.0
100.5
87.4
28.7
239.6
amount, 16 percent (180,000 metric tons) is persistent; the
remaining 84 percent (960,000 metric tons) is degradable. By
1965, half of the degradable portion (480,000 metric tons)
decomposes, leaving a total of 660,000 tonnes (the persistent
portion, plus the remaining half of the degradable portion).
Continuing the example, by 2002, the total food scraps
carbon originally disposed in 1960 had declined to 182,000
metric tons (i.e., virtually all of the degradable carbon had
decomposed). By summing the carbon remaining from 1960
with the carbon remaining from food scraps disposed in
subsequent years (1961 through 2002), the total landfill carbon
from food scraps in 2002 was 28.7 million metric tons. This
value is then added to the carbon stock from grass, leaves, and
branches to calculate the total landfill carbon stock in 2002,
yielding a value of 239.6 million metric tons (as shown in Table
7-17). In exactly the same way total net flux is calculated for
forest carbon and harvested wood products, the total net flux
of landfill carbon for yard trimmings and food scraps for a
given year (Table 7-15) is the difference in the landfill carbon
stock for a given year minus the stock in the preceding year.
For example, the net change in 2002 shown in Table 7-15 (2.8
Tg C) is equal to the stock in 2002 (239.6 Tg C) minus the
stock in 2001 (236.8 Tg C).
When applying the carbon storage factor data reported by
Barlaz (1998), an adjustment was made to the reported value
for leaves, because the carbon storage factor was higher than
the initial carbon content. This anomalous result, probably
due to errors in the laboratory measurements, was addressed
by applying a mass balance calculation, and assuming
that (a) the initial carbon content was correctly measured,
and (b) the carbon storage factor was incorrect. The same
experiment measured not only the persistence of carbon (i.e.,
the carbon storage factor), but also the yield of methane for
each of the individual waste materials (Eleazer et al. 1997).
The anaerobic decomposition process results in release of
equal molar volumes of CH4 and CO2. Thus, to derive a more
realistic estimate of the carbon storage factor for leaves, the
carbon released in the form of methane during decomposition
was multiplied by two (to include the loss of carbon through
CO2), and then subtracted from the initial carbon content of
the leaves. This estimate of carbon remaining was used to
derive the carbon storage factor (0.46).
Uncertainty
Uncertainty in the landfilled carbon storage estimates
results from a small carbon storage factor data set. Very few
experiments have measured the amount of carbon persisting
in conditions promoting decomposition. Furthermore, since
these experiments have only used conditions conducive to
decomposition, they may underestimate carbon storage.
Additionally, the method used to calculate carbon storage in
landfills does not account for varying landfill moisture contents
resulting from different climates and degrees of landfill cover.
Landfills still receiving waste receive a thin, loose soil cover at
the end of the day, while landfills which have been filled and
permanently removed from operation are covered to prevent
infiltration and leaching. Accounting for the amount of moisture
and infiltration in a landfill could greatly increase or decrease
the estimated rate of decomposition in landfills.
Recalculations Discussion
The methods used in the current inventory to estimate
landfilled carbon storage vary from previous years'
inventories in the following three ways.
• The current inventory accounts for the landfilling of
food scraps for the first time; this increases the landfilled
carbon flux by 10 to 29 percent over the period with
respect to the flux for yard trimmings.
• The current inventory uses carbon storage factors for
grass clippings and branches, which were measured
Land-Use Change and Forestry 7-25
-------
experimentally. The previous inventory used carbon
storage factors for grass clippings and branches derived
by subtracting the carbon emitted as CH4 and CO2,
during decomposition, from the carbon in the original
dried yard trimmings, i.e., the same approach as used
for leaves in the current inventory.
The approach used to express the timing of carbon stor-
age in previous inventories differed from the approach
used for the current inventory. Unlike the approach
used currently, in which the stocks of landfill carbon
were computed, and net flux was calculated as the dif-
ference in stocks from year to year, a "static" approach
was used previously. Specifically, in the static method,
the "ultimate" carbon storage—i.e., the amount stored
after all degradation is complete—was attributed in the
year of disposal. There was no tracking of the degradable
portion of carbon, and no simulation of the dynamics
of decomposition and their effect of net landfill carbon
stocks. As an example of the static approach, in 2000,
disposal of branches resulted in deposition of 1,140,000
metric tons of carbon. Of that mass, 77 percent, or
874,000 metric tons is stored indefinitely. The previous
inventory would have calculated carbon storage from
branches as 874,000 metric tons, i.e., it did not track
storage and decomposition from preceding years in
the time series, as is done in the current inventory. The
stocks approach adopted this year reflects the physical
conditions in landfills more accurately, and it is con-
ceptually consistent with the approach used to estimate
landfill carbon storage for harvested wood products.
Planned Improvements
As noted above, the estimates presented in this section
are driven by a small carbon storage factor data set, and some
of these measurements (especially for leaves) deserve close
scrutiny. There are ongoing efforts to conduct additional
measurements of some of the samples from Dr. Mort Barlaz's
original experiments, with the objective of improving the
mass balance for several materials. There are also efforts to
assure consistency between the estimates of carbon storage
described in this chapter and the estimates of landfill CH4
emissions described in the Waste chapter.
7-26 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
8. Waste
Waste management and treatment activities are sources of greenhouse gas emissions (see Figure 8-1). Landfills were
the largest source of anthropogenic methane (CH4) emissions, accounting for 32 percent of total U.S. CH4 emissions.1
Smaller amounts of CH4 are emitted from wastewater systems by bacteria used in various treatment processes. Wastewater
treatment systems are also a potentially significant source of
nitrous oxide (N2O) emissions; however, methodologies are not
currently available to develop a complete estimate. Nitrous oxide
emissions from the treatment of the human sewage component
of wastewater were estimated, however, using a simplified
methodology. Nitrogen oxide (NOX), carbon monoxide (CO), and
non-methane volatile organic compounds (NMVOCs) are emitted
by waste activities, and are addressed separately at the end of this
chapter. A summary of greenhouse gas emissions from the Waste
chapter is presented in Table 8-1 and Table 8-2.
Overall, in 2002, waste activities generated emissions
of 237.2 Tg CO2 Eq., or 3.4 percent of total U.S. greenhouse
gas emissions.
Table 8-1: Emissions from Waste (Tg C02 Eq.)
Figure 8-1
2002 Waste Chapter Greenhouse Gas Sources
Landfills
Wastewater
Treatment
Human Sewage
50
100
Tg CO,Eq
150
Gas/Source
1990
CH4
Landfills
Wastewater Treatment
N20
Human Sewage
Total
246.9
Note: Totals may not sum due to independent rounding.
Table 8-2: Emissions from Waste (Gg)
Gas/Source
CH4
Landfills
Wastewater Treatment
N20
Human Sewage
1990
11,147
9,998
1,149
41
41
Note: Totals may not sum due to independent rounding.
200
1996
235.7
208.8
26.9
14.2
14.2
249.9
1997
230.8
203.4
27.4
14.4
14.4
245.2
1998
224.3
196.6
27.7
14.7
14.7
239.0
1999
226.0
197.8
28.2
15.2
15.2
241.2
2000
227.7
199.3
28.4
15.3
15.3
243.0
2001
221.4
193.2
28.1
15.4
15.4
236.8
2002
221.7
193.0
28.7
15.6
15.6
237.2
1996
11,224
9,942
1,281
46
46
1997
10,990
9,685
1,305
47
47
1998
10,679
9,360
1,320
47
47
1999
10,763
9,419
1,343
49
49
2000
10,841
9,491
1,350
49
49
2001
10,541
9,202
1,339
50
50
2002
10,557
9,192
1,365
50
50
Landfills also store carbon, due to incomplete degradation of organic materials such as wood products and yard trimmings, as described in the Land-Use
Change and Forestry chapter.
Waste 8-1
-------
8.1. Landfills (IPCC Source
Category 6A1)
Landfills are the largest anthropogenic source of
CH4 emissions in the United States. In 2002, landfill CH4
emissions were approximately 193 Tg CO2 Eq. (9,192 Gg).
Emissions from municipal solid waste (MSW) landfills, which
received about 61 percent of the total solid waste generated
in the United States, accounted for about 94 percent of total
landfill emissions, while industrial landfills accounted for the
remainder. Over 2,100 operational landfills exist in the United
States (BioCycle 2001), with the largest landfills receiving
most of the waste and generating the majority of the CH4.
After being placed in a landfill, biogenic waste (such
as paper, food scraps, and yard trimmings) is initially
digested by aerobic bacteria. After the oxygen has been
depleted, the remaining waste is available for consumption
by anaerobic bacteria, which can break down organic
matter into substances such as cellulose, amino acids,
and sugars. These substances are further broken down
through fermentation into gases, and short-chain organic
compounds that form the substrates for the growth of
methanogenic bacteria. Methane-producing anaerobic
bacteria convert these fermentation products into stabilized
organic materials and biogas consisting of approximately
50 percent carbon dioxide (CO2) and 50 percent CH4, by
volume.2 Significant CH4 production typically begins one
or two years after waste disposal in a landfill and may last
from 10 to 60 years.
From 1990 to 2002, net CH4 emissions from landfills
decreased by approximately 8 percent (see Table 8-3 and
Table 8-4), with small increases occurring in some interim
Table 8-3: CH4 Emissions from Landfills (Tg C02 Eq.)
years. This slightly downward trend in overall emissions is
the result of increases in the amount of landfill gas collected
and combusted by landfill operators, which has more than
offset the additional CH4 emissions resulting from an increase
in the amount of municipal solid waste landfilled.
Methane emissions from landfills are a function of several
factors, including: (1) the total amount of municipal solid waste
in landfills, which is related to total municipal solid waste
landfilled annually for the last 30 years; (2) the characteristics
of landfills receiving waste (i.e., composition of waste-in-place;
size, climate); (3) the amount of CH4 that is recovered and
either flared or used for energy purposes; and (4) the amount
of CH4 oxidized in landfills instead of being released into the
atmosphere. The estimated total quantity of waste-in-place
contributing to emissions increased from about 4,926 Tg in 1990
to 6,385 Tg in 2002, an increase of 30 percent (see Annex 3.14).
During this period, the estimated CH4 recovered and flared from
landfills increased as well. In 1990, for example, approximately
1,302 Gg of CH4 were recovered and combusted (i.e., used for
energy or flared) from landfills. In 2002, the estimated quantity
of CH4 recovered and combusted increased to 6,073 Gg.
Over the next several years, the total amount of
municipal solid waste generated is expected to increase
slightly. The percentage of waste landfilled, however, may
decline due to increased recycling and composting practices.
In addition, the quantity of CH4 that is recovered and either
flared or used for energy purposes is expected to increase,
as a result of a 1996 regulation that requires large municipal
solid waste landfills to collect and combust landfill gas (see
40 CFR Part 60, Subparts Cc 2002), and an EPA program
that encourages voluntary CH4 recovery and use at landfills
not affected by the regulation.
Activity
1990
MSW Landfills
Industrial Landfills
Recovered
Gas-to-Energy
Flared
Oxidized1
243.6
17,1
Total
218.0
Note: Totals may not sum due to Independent rounding.
11ncludes oxidation at both municipal and industrial landfills.
1996
283,9
19.9
(28.6)
(43.2)
(23,2)
208.8
1997
289.8
20.3
(34,0)
(50.2)
(22.6)
203.4
1998
295.0
20.6
(40.7)
(56.5)
(21,85
196.fi
1999
302,1
21.1
(45.7)
(57.7)
(22J)
197J
2009
307.8
21,5
(49.9)
(58.0)
(22;1)
199.3
2001
314.0
22.0
$5,2)
(66.1)
(21,5)
193.2
2002
319.6
22,4
(57.7)
(69,8)
(21.4)
193 M
2 The percentage of CO2 in biogas released from a landfill may be smaller because some CO2 dissolves in landfill water (Bingemer and Crutzen 1987).
Additionally, less than 1 percent of landfill gas is composed of non-methane volatile organic compounds (NMVOCs).
8-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Table 8-4: CH4 Emissions from Landfills (Gg)
ActMy
MSWlandife
IndusfrW Lsrtis
Recovered
Sas-to-Energy
Rarsd
Oxidized*
Tatal ....*•
Note: Totals may not sum duet} independent rounding.
4 Includes oxidation at municipal and industrial landfills.
1181
1918
1989
2800 2001
2002
13,520
946
13,802
966
14,fl4?
S83
14,385
1,007
14,659
1,026
14,954
1,047
15,221
1,065
(2J92)
(1,S4Q)
(2,177) (2,376) (2,630) (2,748)
(2,750) (2,784) (3,146) (3,325)
(1.047) (1.iif) 11.021) (1.021)
9JW 8,418 9,491
9,192
Methodology
Methane emissions from landfills were estimated to
equal the CH4 produced from municipal landfills, minus
the CH4 recovered and combusted, plus the CH4 produced
by industrial landfills, minus the CH4 oxidized before being
released into the atmosphere.
The methodology for estimating CH4 emissions from
municipal landfills is based on a model that updates the
population of U.S. landfills each year. This model is based
on the pattern of actual waste disposal, as evidenced in an
extensive landfill survey by the EPA's Office of Solid Waste
in 1986. A second model was employed to estimate emissions
from the landfill population (EPA 1993). For each landfill
in the data set, the amount of waste-in-place contributing to
CH4 generation was estimated using its year of opening, its
waste acceptance rate, year of closure, and design capacity.
Data on national municipal waste landfilled each year was
apportioned by landfill. Emissions from municipal landfills
were then estimated by multiplying the quantity of waste
contributing to emissions by emission factors (EPA 1993).
For further information see Annex 3.14.
The landfill population model, including actual waste
disposal data from individual landfills, was developed from
a survey performed by the EPA's Office of Solid Waste (EPA
1988). National landfill waste generation and disposal data
for 1991 through 2002 were obtained from BioCycle (2001).
Because BioCycle does not account for waste generated
in U.S. territories, waste generation for the territories was
estimated using population data obtained from the U.S.
Census Bureau (2000) and per capita municipal solid waste
generation from EPA's Municipal Solid Waste Disposal in the
United States report (2002a). Documentation on the landfill
CH4 emissions methodology employed is available in EPA's
Anthropogenic Methane Emissions in the United States,
Estimates for 1990: Report to Congress (EPA 1993).
The estimated landfill gas recovered per year was based on
updated data collected from vendors of flaring equipment and a
database of landfill gas-to-energy (LFGTE) projects compiled
by EPA's Landfill Methane Outreach Program (LMOP). Based
on the information provided by vendors, the CH4 combusted by
112 flares in operation from 1990 to 2002 was estimated. This
quantity likely underestimates flaring, because EPA does not
have information on all flares in operation. Additionally, the
LFGTE database provided data on landfill gas flow and energy
generation for 382 LFGTE projects. If both flare data and
LFGTE recovery data for a particular landfill were available,
then the emissions recovery was based on the LFGTE data,
which provides actual landfill-specific data on gas flow for
direct use projects and project capacity (i.e., megawatts) for
electricity projects. The flare data, on the other hand, only
provided a range of landfill gas flow for a given flare size.
Given that each LFGTE project was likely to also have had
a flare, double counting reductions from flares and LFGTE
projects was avoided by subtracting emissions reductions
associated with LFGTE projects for which a flare had not
been identified from the emissions reductions associated with
flares.3 Information on flares was obtained from vendors (ICF
2002, RTI 2003), and information on landfill gas-to-energy
projects was obtained from the EPA's Landfill Methane
Outreach Program database (EPA 2003).
Due to the differences in referencing landfills and incomplete data on the national population of flares, matching flare vendor data with the LFGTE data
was problematic and a flare could not be identified for each of the LFGTE projects. Because each LFGTE project likely has a flare, the aggregate estimate
of emission reductions through flaring was reduced by the LFGTE projects for which a specific flare could not be identified. This approach eliminated the
potential for double counting emissions reductions at landfills with both flares and a LFGTE project.
Waste 8-3
-------
Emissions from industrial landfills were assumed
to be equal to seven percent of the total CH4 emissions
from municipal landfills (EPA 1993). The amount of
CH4 oxidized by the landfill cover at both municipal and
industrial landfills was assumed to be ten percent of the
CH4 generated that is not recovered (Liptay et al. 1998). To
calculate net CH4 emissions, both CH4 recovered and CH4
oxidized were subtracted from CH4 generated at municipal
and industrial landfills.
Uncertainty
Several types of uncertainty are associated with the
estimates of CH4 emissions from landfills. The primary
uncertainty concerns the characterization of landfills.
Information is not available for waste in place for every
landfill—a fundamental factor that affects CH4 production.
The heterogeneity of waste disposed in landfills is uncertain
as well. The approach used here assumes that the landfill
set is representative of waste composition and reflects
this heterogeneity. Also, the approach used to estimate the
contribution of industrial non-hazardous wastes to total
CH4 generation employs introduces uncertainty. Aside
from uncertainty in estimating CH4 generation potential,
uncertainty exists in the estimates of oxidation efficiency.
The preliminary results of the quantitative uncertainty
analysis (see Table 8-5), indicate that, on average, in 19 out
of 20 times (i.e., there is a 95 percent probability), the total
greenhouse gas emissions estimate from this source is within
the range of approximately 135.1 to 250.9 Tg CO2 Eq. (or that
the actual CH4 emissions are likely to fall within the range
of approximately 30 percent below and 30 percent above the
emissions estimate of 193.0 Tg CO2 Eq.).
The N2O emissions from application of sewage sludge
on landfills are not explicitly modeled as part of greenhouse
gas emissions from landfills. Nitrous oxide emissions from
sewage sludge applied to landfills would be relatively
small because the microbial environment in landfills is
not very conducive to the nitrification and denitrification
processes that result in N2O emissions. The total nitrogen
(N) in sewage sludge increased from 189 to 247 Gg total
N between 1990 and 2002. The quantity of sewage sludge
applied to landfills decreased from 28 to 11 percent from
1990 to 2001 (EPA 1993).
Recalculations Discussion
The estimates for the current inventory are based on the
same basic methodology as the estimates for the previous
inventory; however, a few minor improvements were
made. For the previous inventory estimates, the nationwide
emissions avoided by LFGTE projects for which flares
could not be identified in the flare database were subtracted
from the nationwide estimate of emissions avoided by
flaring. This conservative approach was used to avoid
double counting of emissions avoided by LFGTE projects
and flaring. For the current estimates, this correction was
made on a state-by-state basis rather than a nationwide
basis. This approach is still conservative and avoids double
counting; however, it resulted in slightly higher estimates
of emissions avoided by flaring. The emissions avoided by
flaring increased by about 1.6 percent over the time series
as a result of this change.
Another change to the estimates for flaring resulted
from additional vendors supplying information for flares
that were installed from 1994 to 2002. As a result of
identifying more landfills with flares, the emissions avoided
by flaring increased by about 3 percent over the period
from 1994 to 2001.
The procedure used to estimate emissions avoided
by LFGTE projects that generate electricity were revised
to improve the estimates and to develop a uniform set
of calculation procedures. Adjustments were made to
the availability factor (the fraction of the time a system
Table 8-5: Quantitative Uncertainty Estimates for CH4 Emissions from Landfills (Tg C02 Eq. and Percent)
Source
2002 Emission Estimate
Gas
Lower Bound Upper Bound Lower Bound Upper Bound
Landfills CH4
193,0
-38%
1 Range of emissions estoates predicted by Monte Carlo Stochastic Simulation for a 95% Cofffldenee interval.
8-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
is available for producing power), the heat rate, and the
methane heating value. The new approach increased
emissions avoided by LFGTE projects by 12 to 14 percent
and reduced net methane emissions by 1 to 3 percent over
the time series.
Changes were also made to the LFGTE database used to
estimate emissions avoided by these projects. The changes
included corrections to megawatt capacity and gas flow rates,
adding new projects that started in 2002, and accounting for
projects that shut down. These changes decreased emissions
avoided by LFGTE projects by an average of about 2 percent
and increased net methane emissions by about 0.3 percent
over the time series.
Planned Improvements
For the future inventories, the regression equations used
for methane generation will be re-evaluated using a database
of several hundred landfills provided by the Landfill Methane
Outreach Program. The database contains information on landfill
gas collection rates and waste in place for LFTGE projects. This
analysis will allow for an update of emission factors due to
changing wastestream and waste management characteristics.
Additional information will be obtained on landfills in the
United States to develop a representative sample and improve
the landfill population database used for the inventory.
8.2. Wastewater Treatment
(IPCC Source Category 6B)
Wastewater from domestic (municipal sewage) and
industrial sources is treated to remove soluble organic matter,
suspended solids, pathogenic organisms, and chemical
contaminants. Treatment may either occur off-site or on-
site. For example, in the United States, approximately 25
percent of domestic wastewater is treated in septic systems
or other on-site systems. Soluble organic matter is generally
removed using biological processes in which microorganisms
consume the organic matter for maintenance and growth.
The resulting biomass (sludge) is removed from the effluent
prior to discharge to the receiving stream. Microorganisms
can biodegrade soluble organic material in wastewater under
aerobic or anaerobic conditions, where the latter condition
produces methane. During collection and treatment,
wastewater may be accidentally or deliberately managed
under anaerobic conditions. In addition, the sludge may be
further biodegraded under aerobic or anaerobic conditions.
Untreated wastewater may also produce methane if contained
under anaerobic conditions.
The organic content, expressed in terms of either
biochemical oxygen demand (BOD) or chemical oxygen
demand (COD), determines the methane producing potential
of wastewater. BOD represents the amount of oxygen that
would be required to completely consume the organic matter
contained in the wastewater through aerobic decomposition
processes. COD refers to the amount of oxygen consumed
under specified conditions in the oxidation of the organic
and oxidizable inorganic matter and is a parameter typically
used to characterize industrial wastewater.
In 2002, methane emissions from domestic wastewater
treatment were 14.0 Tg CO2 Eq. (668 Gg). Emissions have
increased since 1990 in response to the increase in the U.S.
human population. Industrial emission sources include
wastewater from the pulp and paper, meat and poultry
processing, and the vegetables, fruits and juices processing
industry.4 In 2002, CH4 emissions from industrial wastewater
treatment were estimated to be 14.6 Tg CO2 Eq. (697 Gg).
The increase compared to the 2001 estimates is due to
increases in production outputs in all three sectors. Table 8-6
and Table 8-7 provide emission estimates from domestic and
industrial wastewater treatment.
Table 8-6: CH4 Emissions from Domestic and Industrial Wastewater Treatment (Tg C02 Eq.)
Activity
1990
Domestic
Industrial*
12.1
12.0
Total
24.1
I
1996
13.1
13,8
26,9
1887
13.3
14.2
27.4
1988
13.4
14.3
27.7
1999
13,6
14.6
28.2
2000
13.7
14.6
28.4
2001
13.9
14.3
28.1
2002
14.0
14.6
28.7
* Industrial activity includes the pulp and paper, meat and poultry, and the vegetables, fruits and juices processing industry.
Note: Totals may not sum due to independent rounding.
4 Industrial wastewater emissions from petroleum systems are included in the petroleum systems section in the Energy chapter.
Waste 8-5
-------
Table 8-7: CH4 Emissions from Domestic and Industrial Wastewater Treatment (Gg)
Activity
1990
Domestic
Industrial*
578
571
Total
1,149
I
1996
1997
1998
1999
2000
2001
2002
624
658
631
674
639
681
646
65S
697
660
679
697
1,281
1,305
1,320
1,341
1,380 1,33?
1,365
* Industrial activity includes the pulp and paper, meat and poultry, and the vegetables, fruits and juices processing industry.
Note: Totals may not sum due to independent rounding.
Table 8-8: U.S. Population (Millions) and Wastewater
BOD Produced (Gg)
Year
1990
1995
1996
1997
1998
1999
2000
2001
2002
Population
250
266
269
273
276
279
282
285
288
BOD5
5,926
6,322
6,396
6,473
6,549
6,625
6,700
6,774
6,846
Methodology
Domestic wastewater CH4 emissions were estimated
using the default IPCC methodology. National population
data for 1990 to 2002, used in the domestic wastewater
emissions estimates, were based on data from the U.S.
Census Bureau (2002). Per-capita production of BOD55
for domestic wastewater was obtained from EPA (1997b).
The emission factor (0.6 kg CH4/kg BOD5) was taken from
IPCC Good Practice Guidance (IPCC 2000). The percent
of wastewater BOD5 that was anaerobically digested was
assumed to be 16.25 percent. This value also accounts for
U.S. septic systems and is based on expert judgment and on
septic system usage data from EPA (1996).
Methane emissions estimates from industrial wastewater
were developed according to the methodology described in
the IPCC (2000). Industry categories that are likely to have
significant CH4 emissions from their wastewater treatment
were identified. High volumes of wastewater generated and
a high organic COD wastewater load were the main criteria.
The top three industries that met these criteria included pulp
and paper manufacturing, meat and poultry packing, and
vegetables, fruits and juices processing.6
Methane emissions from these categories were estimated
by multiplying the annual product output (metric tons/year)
by the average outflow (m3/ton of output), the organics
loading in the outflow (grams of organic COD/m3), the
emission factor (grams CH4/grams COD), and the percentage
of organic COD assumed to degrade anaerobically. In
developing estimates for the pulp and paper category, BOD
was used instead of COD, because more accurate BOD
numbers were available. The emission factor used for pulp
and paper wastewater was 0.6 kg CH4/kg BOD5, whereas the
emission factor for meat and poultry, and vegetables, fruits
and juices category is 0.25 kg CH4/kg COD (IPCC 2000). The
pertinent industry-specific parameters are specified below.
Wastewater treatment for the pulp and paper industry
typically includes neutralization, screening, sedimentation,
and flotation/hydrocycloning to remove solids (World
Bank 1999, Nemerow and Dasgupta 1991). The most
important step is lagooning for storage, settling, and
biological treatment (secondary treatment). In determining
the percent that degraded anaerobically, both primary and
secondary treatment were considered. Primary treatment
lagoons are aerated to reduce anaerobic activity. However,
the lagoons are large and zones of anaerobic activity may
occur. Approximately 42 percent of the BOD passes on to
secondary treatment, which are less likely to be aerated
(EPA 1993). It was assumed that 25 percent of the BOD
in secondary treatment lagoons degrades anaerobically,
while 10 percent passes through to be discharged with the
effluent (EPA 1997a). Overall, the percentage of wastewater
organics that degrade anaerobically was determined to be
10.3 percent. A time series of CH4 emissions for post-1990
years was developed based on production figures reported in
the Lockwood-Post Directory (Lockwood-Post, 2002). The
overall wastewater outflow was estimated to be 85 m3/ton and
5 The 5-day biochemical oxygen demand (BOD) measurement (Metcalf and Eddy 1991).
6 Industrial wastewater emissions from petroleum systems are included in the petroleum systems section in the Energy chapter.
8-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
the average BOD loading entering the secondary treatment
lagoons was estimated to be 0.4 gram BOD/liter. Both values
are based on information from multiple handbooks.
The meat and poultry processing industry makes extensive
use of anaerobic lagoons in sequence to screening, fat traps
and dissolved air flotation. An estimated 77 percent of all
wastewater organics from this industry degrades anaerobically
(EPA 1997b). Production data for the meat and poultry industry
were obtained from the U.S. Census (2002). EPA (1997b)
provides wastewater outflows of 13 (out of a range of 8 to 18)
mVmetric ton and an average COD value of 4.1 (out of a range
of 2 to 7) g/liter. These parameters are currently undergoing
review, based on a recent comprehensive survey conducted
by EPA's Office of Water (EPA 2002).
Treatment of wastewater from fruits, vegetables, and
juices processing includes screening, coagulation/settling and
biological treatment (lagooning). The flows are frequently
seasonal, and robust treatment systems are preferred for
on-site treatment. Effluent is suitable for discharge to the
sewer. This industry is likely to use lagoons intended for
aerobic operation, but the large seasonal loadings may
develop limited anaerobic zones. In addition, some anaerobic
lagoons may also be used (Nemerow and Dasgupta, 1991).
Consequently, it was estimated that 5 percent of these
wastewater organics degrade anaerobically. The USDA
National Agricultural Statistics Service (USDA 2002)
provided production data for the fruits, vegetables, and
juices processing sector. Outflow data for various subsectors
(canned fruit, canned vegetables, frozen vegetables, fruit
juices, jams, baby food) were obtained from World Bank
(1999) and an average wastewater outflow of 5.6 m3/metric
ton was used. For the organics loading, a COD value of 5
g/liter was used (EPA 1997b).
Table 8-9: U.S. Pulp and Paper, Meat and Poultry, and
Vegetables, Fruits and Juices Production (Million Metric Tons)
Uncertainty
The uncertainty associated with the emission factor
for CH4 emissions from wastewater is estimated to be 30
percent (IPCC 2000). For domestic wastewater, uncertainty
Year
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Pulp and paper
128.9
129.2
134.5
134.1
139.3
140.9
140.3
145.6
144.0
145.1
142.8
134.3
137.5
Meat and Poultry
28.2
29.0
30.0
31.0
32.0
33.6
34.2
34.6
35.7
37.0
37.4
37.5
38.6
Vegetables,
Fruits and Juices
30.2
31.2
33.5
34.1
37.3
36.8
36.4
37.7
36.5
37.4
38.9
35.0
36.9
associated with the occurrence of anaerobic conditions in
treatment systems was estimated to be 25 percent, based on
septic tank usage data from EPA (1996) and expert judgment.
Also, the per-capita BOD uncertainty is 30 percent (IPCC
2000). The combined uncertainty for domestic wastewater
was estimated to be 49 percent.
Large uncertainties are associated with the industrial
wastewater emission estimates. Wastewater outflows and
organics loadings vary considerably for different plants
and different sub-sectors (e.g., paper vs. board, poultry vs.
beef, or baby food vs. juices). Uncertainties for outflows
are between 38 and 55 percent for the different source
categories and are based on expert judgment and the
literature (Nemerow and Dasgupta, 1991; World Bank,
1999). Uncertainties for organic loadings are based on similar
references and are estimated at 25, 51, and 60 percent for
pulp and paper, meat and poultry, and fruits, vegetables and
juices, respectively. The uncertainty associated with the
degree in which anaerobic degradation occurs in treatment
systems is estimated at 50 percent for all three industrial
categories. The composite uncertainty for the industrial
wastewater subcategory is approximately 59 percent. The
Table 8-10: Quantitative Uncertainty Estimates for CH4 Emissions from Wastewater Treatment (Tg C02 Eq. and Percent)
Year 2802 Emissions Uncertainty Range Relative to Emission Estimate
Source Gas (TgC02Eq.) Uncertainty (%) (TgC02Eq.)
Lower Bound
Upper Bound
Wastewater Treatment CH,
28.7
39%
17.5
39.8
Waste 8-7
-------
overall uncertainty for the wastewater category is estimated
to be 39 percent (see Table 4-51).
Recalculations Discussion
The time series for domestic wastewater has been updated
relative to the previous inventory due to an increase in the per
capita protein intake. The time series for industrial wastewater
also changed due to updated production estimates for the red
meat, poultry, and fruit and vegetable industries.
Planned Improvements Discussion
EPA's Office of Water is finalizing the Effluent
Limitations Guidelines and New Source Performance
Standards for the Meat and Poultry Products Point Source
Category. It is anticipated that research data from this effort
can be used to improve the methodology for estimating CH4
emissions from this category.
8.3. Human Sewage
(Domestic Wastewater)
(IPCC Source Category 6B)
Domestic human sewage is usually mixed with other
household wastewater, which includes shower drains, sink
drains, washing machine effluent, etc. and transported by a
collection system to either a direct discharge, an on-site or
decentralized wastewater treatment system, or a centralized
wastewater treatment system. Decentralized wastewater
treatment systems are septic systems and package plants.
Centralized wastewater treatment systems may include a
variety of processes, ranging from lagooning to advanced
tertiary treatment technology for removing nutrients. Often,
centralized wastewater treatment systems also treat certain
flows of industrial, commercial, and institutional wastewater.
Table 8-11: N20 Emissions from Human Sewage
Year
Tg CO, Eq.
1990
12.8
41
1996
1997
1998
1999
2000
2001
2002
14.1
14.4
14.6
15.1
15.1
15.4
15.6
46
47
47
49
49
50
50
After processing, treated effluent is discharged to a receiving
water environment (e.g., river, lake, estuary, etc.), or applied
to soils, or disposed of below the surface.
Nitrous oxide may be generated during both nitrification
and denitrification of the nitrogen present, usually in the
form of urea, ammonia, and proteins. These are converted
to nitrate via nitrification, an aerobic process converting
ammonia-nitrogen into nitrate (NO3"). Denitrification occurs
under anoxic conditions (without free oxygen), and involves
the biological conversion of nitrate into dinitrogen gas (N2).
Nitrous oxide can be an intermediate product of both processes,
but is more often associated with denitrification.
The United States identifies two distinct sources for
N2O emissions from domestic wastewater: emissions from
wastewater treatment processes; and emissions from effluent
that has been discharged into aquatic environments. The 2002
emissions of N2O from wastewater treatment processes and
from effluent were estimated to be 0.3 Tg CO2 Eq. (0.9 Gg) and
15.3 Tg CO2 Eq. (49 Gg), respectively. Total N2O emissions
from domestic wastewater were estimated to be 15.6 Tg CO2
Eq. (50 Gg) (see Table 8-11). Emissions from wastewater
treatment processes have gradually increased as a result of
increasing U.S. population and protein consumption.
Methodology
The IPCC default methodology (IPCC/UNEP/OECD/
IEA 1997) assumes that nitrogen disposal, and thus N2O
emissions associated with land disposal, subsurface disposal,
and domestic wastewater treatment are negligible and all
nitrogen is discharged directly into aquatic environments. For
the United States, N2O emissions from domestic wastewater
(human sewage) were estimated using the IPCC methodology
with three modifications:
• In the United States, a certain amount of nitrogen is
removed with the sewage sludge, which is land applied,
incinerated or landfilled (Nsludge). The nitrogen disposal
into aquatic environments is reduced to account for the
sewage sludge application.
• The IPCC methodology uses annual, per capita protein
consumption (kg/year). This number is likely to under-
estimate the amount of protein entering the sewer or
septic system. Food (waste) that is not consumed is often
washed down the drain, as a result of the use of garbage
disposals. Also, bath and laundry water can be expected
to contribute to nitrogen loadings. A factor of 1.4 is intro-
8-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
duced to account for this nitrogen. Furthermore, industrial
wastewater co-discharged with domestic wastewater is not
accounted for in the existing methodology. To correct for
this, a factor of 1 .25 is used. The fraction of non-consump-
tion protein in domestic wastewater (combined value of
1 .75) is based on expert judgment and on Metcalf & Eddy
(1991) and Mullick (1987).
• Process emissions from wastewater treatment plants are
not accounted for in the current IPCC methodology. To
estimate N2O emissions from U.S. wastewater treatment
plants, an overall emission factor (4 g N2O/person.year)
was introduced. This emission factor is based on a factor
of 3.2 g N2O/person.year (Czepiel 1995) multiplied
by a factor of the 1 .25 factor mentioned above, which
adjusts for co-discharged industrial nitrogen and which
is based on expert judgment. The nitrogen quantity
associated with these emissions (N^^j) is calculated
by multiplying the N2O emitted by (2 x I4)l^ and it is
subtracted from the total quantity of nitrogen that is
ultimately disposed into the aquatic environment.
With the modifications described above, N2O emissions
from domestic wastewater were estimated using the IPCC
default methodology (IPCC/UNEP/OECD/IEA 1997). This
methodology is illustrated below:
N2O(s) = (USpop x 0.75 x EFj x 10'3) +
Table 8-12: U.S. Population (Millions) and Average Protein
Intake (kg/Person/Year)
{ [(Protein x 1 .75 x FracNPR x USTOp) -
- N
] x
siudge
where,
N2O(s) = N2O emissions from domestic wastewater
("human sewage") [kg/year]
USpop = U.S. population
0.75 = Fraction of population using wastewater treatment
plants (as opposed to septic systems)
EFj = Emission factor (4g N2O/person-year) expressing
emissions from the wastewater treatment plants
Protein = Annual, per capita protein consumption
1.75 = Fraction of non-consumption protein in domestic
wastewater
FracNPR = Fraction of nitrogen in protein
= Quantity of wastewater nitrogen removed by
wastewater treatment processes [(USpQP x 0.75
x EFjX 10-3) x 28/44]
- Quantity of sewage sludge N not entering aquatic
environments
Year
'"J%teJt'iJ»la» -
j .rump,-,
ISP?
1998
1999
2000
2001
2002
m
273
278
279
282,
285
288
40J
41J
;42J
,41J
4t8
41.8
EF2 = Emission factor (kg N2O-N/kg sewage-N produced)
C44/^) = The molecular weight ratio of N2O to N2.
U.S. population data were taken from the U.S. Census
Bureau (2002). The fraction of the U.S. population using
wastewater treatment plants is from the NEEDS Survey (EPA
1996). The emission factor (E[) to estimate emissions from
wastewater treatment is based on Czepiel, et al. (1995). Data
on annual per capita protein consumption were provided by
the United Nations Food and Agriculture Organization (FAO
2001). See Table 8-12.
Because data on protein intake were unavailable for
2002, the value of per capita protein consumption for the
previous year was used. An emission factor to estimate
emissions from effluent (EF2) has not been specifically
estimated for the United States, thus the default IPCC value
(0.01 kg N2O-N/kg sewage-N produced) was applied. The
fraction of nitrogen in protein (0.16 kg N/kg protein) was
also obtained from IPCC/UNEP/OECD/IEA (1997).
Uncertainty
Nitrous oxide emissions from wastewater treatment are
estimated to be substantially less than emissions from effluent-
surface water. Thus, this wastewater treatment subcategory was
not considered in the uncertainty analysis. The U.S. population,
per capita protein intake data (Protein), and fraction of nitrogen
in protein (FracNPR) are believed to be fairly accurate. The
uncertainty in activity data was estimated to be 26 percent. The
fraction that expresses the ratio of non-consumption nitrogen was
estimated to have an uncertainty of 25 percent, based on expert
judgment. The emission factor for effluent (EF2) is the default
emission factor from IPCC (1996) where it is expressed as 0.01
based on a range of 0.002 to 0.02 kg N2O per kg N-sewage.
Consequently, EF2 was allocated an uncertainty of 80 percent.
Waste 8-9
-------
Table 8-13: Quantitative Uncertainty Estimates for N20 Emissions from Human Sewage (Tg C02 Eq. and Percent)
Source
Year 2002 Emissions
Gas (TgC02Eq.) Uncertainly (%)
Lower Bound
Upper Bound
Human Sewage
tSJ
2.5
28.6
The combined uncertainty for N2O emissions from human sewage
was estimated to be 84 percent (see Table 8-13).
Recalculations Discussion
The time series for domestic wastewater has changed
slightly relative to that reported in the previous inventory
due to an increase in per capita protein intake.
8.4. Waste Sources of
Ambient Air Pollutants
In addition to the main greenhouse gases addressed
above, waste generating and handling processes are also
sources of ambient air pollutant emissions. Total emissions
of NOX, CO, and NMVOCs from waste sources for the years
1990 through 2002 are provided in Table 8-14.
Methodology and Data Sources
These emission estimates were obtained from preliminary
data (EPA 2003), which, in its final iteration, will be published
on the National Emission Inventory (NEI) Air Pollutant
Emission Trends web site. Emission estimates of these gases
Table 8-14: Emissions of NOX. CO, and NMVOC from Waste (Gg)
were provided by sector, using a "top down" estimating
procedure—emissions were calculated either for individual
sources or for many sources combined, using basic activity data
(e.g., the amount of raw material processed) as an indicator of
emissions. National activity data were collected for individual
source categories from various agencies. Depending on the
source category, these basic activity data may include data on
production, fuel deliveries, raw material processed, etc.
Activity data were used in conjunction with emission
factors, which relate the quantity of emissions to the activity.
Emission factors are generally available from the EPA's
Compilation of Air Pollutant Emission Factors, AP-42 (EPA
1997). The EPA currently derives the overall emission control
efficiency of a source category from a variety of information
sources, including published reports, the 1985 National Acid
Precipitation and Assessment Program emissions inventory,
and other EPA data bases.
Uncertainty
Uncertainties in these estimates are primarily due to the
accuracy of the emission factors used and accurate estimates
of activity data.
Gas/Source
NO,
Landfills
Wastewater Treatment
Miscellaneous*
CO
Landfills
Wastewater Treatment
Miscellaneous*
NMVOCs
Landfills
Wastewater Treatment
Miscellaneous3
1990
1
1
673
58
57
558
1996
3
2
1
5
5
158
32
61
65
1997
3
2
1
5
5
+
+
157
32
62
64
1998
3
2
1
5
5
+
•f
161
33
63
65
1999
3
3
+
14
13
1
+
151
29
64
58
2000
3
3
+
14
13
1
+
153
29
65
59
2001
3
3
t
14
13
1
•f
158
30
68
60
2002
3
3
+
15
14
1
+
158
30
68
60
a Miscellaneous includes TSDFs (Treatment, Starap, and Disposal Facilities under the Resource Conservation and Recovery Act [42 y .S.C. § 6924,
SWDA § 30G4]) and otter waste categories.
Note: Totals may not sum due to independent rounding.
+ Does not exceed 0.5 6g
8-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
9. Other
The United States does not report any greenhouse gas emissions under the "other" IPCC sector.
Other 9-1
-------
9-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
10. Recalculations and
Improvements
Each year, emission and sink estimates are recalculated and revised for all years in the Inventory of U.S. Greenhouse
Gas Emissions and Sinks, and attempts to improve both the analyses themselves, through the use of better methods
or data, and the overall usefulness of the report. In this effort, the United States follows the IPCC Good Practice Guidance,
which states, regarding recalculations of the time series, "It is good practice to recalculate historic emissions when methods
are changed or refined, when new source categories are included in the national inventory, or when errors in the estimates
are identified and corrected (IPCC 2000)."
The results of all methodology changes and historical data updates are presented in this section; detailed descriptions of
each recalculation are contained within the source descriptions contained elsewhere in this report. Table 10-1 summarizes
the quantitative effect of these changes on U.S. greenhouse gas emissions and Table 10-2 summarizes the quantitative
effect on U.S. sinks, both relative to the previously published U.S. Inventory (i.e., 1990-2001 report). These tables present
the magnitude of these changes in units of teragrams of carbon dioxide (CO2) equivalent (Tg CO2 Eq.). In addition to the
changes summarized by the tables below, three new sources—CO2 emissions from phosphoric acid production and CH4
emissions from abandoned coal mines and iron and steel production—have been added to the current Inventory.
The Recalculations Discussion section of each source presents the details of each recalculation. In general, when
methodological changes have been implemented, the entire time series (i.e., 1990 through 2001) has been recalculated to
reflect the change. Changes in historical data are generally the result of changes in statistical data supplied by other agencies.
References for the data are provided for additional information.
The following emission sources, which are listed in descending order of absolute average annual change in emissions
from 1990 through 2001, underwent some of the most important methodological and historical data changes. A brief summary
of the recalculation and/or improvement undertaken is provided for each emission source.
• Land-Use Change and Forestry. The most influential of the changes in the calculation of CO2 sequestration from
land-use change and forestry was a switch in basing the estimates of non-soil forest carbon stocks and fluxes in other
pools on state-based assessment rather than regionally-based assessment. Overall, this change, along with several other
alterations, resulted in an average annual decrease in the net CO2 sequestration of 126.8 Tg CO2 Eq. (13.2 percent) for
the period 1990 through 2001.
• CO'2 from Fossil Fuel Combustion. The emissions calculation was revised to incorporate a new carbon content coef-
ficient for LPG, industrial coal emissions that now account for carbon exported as CO2 to Canada, an annually variable
(rather than static) feedstock storage factor, and updated energy consumption data for all years. Overall, these changes
and revisions to "Carbon Stored in Products from Non-Energy Uses of Fossil Fuels" and "International Bunker Fuels"
(which affect emissions from this source) resulted in an average annual decrease in CO2 emissions from fossil fuel
combustion of 12.3 Tg CO2 Eq. (0.2 percent) for the period 1990 through 2001.
Recalculations and Improvements 10-1
-------
Table 10-1: Revisions to U.S. Greenhouse Gas Emissions (Tg C02 Eq.)
Gas/Source
C02
Fossil Fuel Combustion
Natural Gas Flaring
Cement Manufacture
Lime Manufacture ? , ;
Limestone and DotomSte Use f
Soda Ash Manufacture and Consumption
Carbon Dioxide Consumption
Waste Combustion
Titanium Dioxide Production
Aluminum Production
Iron and Steel Production
Ferroalloys
Ammonia Manufacture & Urea Application
PhosphoricAcWProdi»tta^ : -• •
Land-Use Change and Forestry (Sink),
International Bunker Fuels
Biomass Combustion
Stationary Sources
Mobile Sources
Natural Gas Systems
Petroleum Systems
Petrochemical Production
Silicon Carbide Production
Iron and Steel Production*
Enteric Fermentation
Manure Management
Rice Cultivation
Field Burning of Agricultural Residues
Landfills
Waste water Treatment
International Bunker Fuels
N20
Stationary Sources
Mobile Sources
AdipicAcid
Nitric Acid
Manure Management
Human Sewage
N20 Product Usage
Waste Combustion
Aluminum Production
Semiconductor Manufacture
Magnesium Production and Processino
Net Change in Total Emissions"
Percent Change
(0.1)
0.3
NC
••*••
we
1986
(18J)
(15.7)
0.3
NC
NC
02
HC
(0.4)
(2.2)
NC
NC
NC
NC
NC
1.6
5.8
4-
244.3
0.2
0.1
4-
(5.2)
6.0
(0.1)
1.7
4-
NC
1,3
4-
0.3)
4- -
4-
(3.3)
0.1
4
(4.8)
0.1
4-
NC
4-
4-
(5.1)
4-
4-
NC
0.1
4-
12
4.6
NC
NC
0.1
§.4)
Np
-------
Table 10-2: Revisions to Net C02 Sequestration from Land-Use Change and Forestry (Tg C02 Eq.)
Forests
Urban Trees
Agricultural Soils
Net Change in Total Flux
Percent Change
1996
14.9
NC
(5:4)
0.7)-.
8J
0.5%
1987
28.9
m
(5:4)
(3,8)
18.7
13%
1998
133.9
NC
(S.4)
(3,8)
124.7
15.0%
1888
174.2
NO
(5.4)
(3.S)
165.3
18.7%
mo
153.0
NC
(5.3)
(3.3),
144.5
17.3%
2001
158.8
NC
(5.6)
(4,9)
148.4
17;7%
NC:(NoChanp) • • . • . , '•',.-
Note: Numbers in parentheses indicate an increase In estimated net sequestration, or a decrease in net flux of C02 to the atmosphere. In ttie "percent
change* row, negative raid :
increased. Totals may not sum due to independent rounding.
Substitution of Ozone Depleting Substances. The calcula-
tion of emissions was adjusted to incorporate the use of both
a new Vintaging Model and a set of updated assumptions
for the model. Overall, changes resulted in an average an-
nual increase in HFC, PFC, and SF6 emissions from the
substitution of ozone depleting substances of 6.7 Tg CO2
Eq. (9.1 percent) for the period 1990 through 2001.
Coal Mining. The major change in the calculation of
emissions was the incorporation of new in-situ gas content
values. Overall, changes resulted in an average annual de-
crease in CH4 emissions from coal mining of 5.0 Tg CO2
Eq. (7.1 percent) for the period 1990 through 2001.
Agricultural Soil Management. The emissions calcula-
tion changed to incorporate a corrected percent residue
applied for rice in the year 2001, an additional significant
digit in the conversion between short tons and metric
tons, and a number of methodological and historical data
revisions in the calculations of nitrogen from livestock
that is applied to soils. Overall, changes resulted in an
average annual decrease in N2O emissions from agricul-
tural soil management of 4.9 Tg CO2 Eq. (1.7 percent)
for the period 1990 through 2001.
Waste Combustion. The calculation of emissions has
been revised to incorporate a new emission factor, a
new method for filling in a time series where data are
unavailable, and updated data for several sub-categories
within the municipal solid waste combustion sector.
Overall, changes resulted in an average annual decrease
in CO2 emissions from waste combustion of 4.4 Tg CO2
Eq. (21.8 percent) for the period 1990 through 2001.
Landfills. Revisions to the emissions calculation incor-
porated an improvement in the estimation of emissions
avoided by landfill gas to energy projects for which flares
could not be identified in the flare database, additional
data on flares that were installed from 1994 to 2002,
changes to the landfill gas to energy database, and revi-
sions to the procedure used to estimate emissions avoided
by landfill gas to energy projects that generate electricity.
Overall, changes resulted in an average annual decrease
in CH4 emissions from landfills of 4.0 Tg CO2 Eq. (1.9
percent) for the period 1990 through 2001.
Petroleum Systems. The calculation of emissions was
revised to incorporate a modified activity factor for
methane emissions from oil tanks in the production
sector, a new data source for fuel gas systems in the
refinery sector, and a revision of the emission factors for
high and low bleed pneumatic devices. Overall, changes
resulted in an average annual increase in CH4 emissions
from petroleum of 1.7 Tg CO2 Eq. (7.4 percent) for the
period 1990 through 2001.
Natural Gas Systems. The emissions calculation was
revised to incorporate new Gas STAR emissions reduc-
tion data and new sources of water production activity
factors for coalbed methane emissions. Overall, changes
resulted in an average annual increase in CH4 emissions
from natural gas systems of 1.1 Tg CO2 Eq. (0.9 percent)
for the period 1990 through 2001.
Semiconductor Manufacture. The emissions calculation
was changed to incorporate an updated version of EPA's
PEVM model with more current reference data, updated
historical data for several participants in the PFC Reduc-
tion/Climate Partnership for the Semiconductor Industry,
and an alteration in the methodology for estimating the
distribution of historical emissions by gas type. Overall,
changes resulted in an average annual decrease in HFC,
PFC, and SF6 emissions from semiconductor manufac-
ture of 0.3 Tg CO2 Eq. (4.3 percent) for the period 1990
through 2001.
Recalculations and Improvements 10-3
-------
Natural Gas Flaring. The methodology for estimating
emissions, which had previously focused solely on on-
shore natural gas flaring, was revised to include emis-
sions from offshore flaring. Overall, changes resulted
in an average annual increase in CO2 emissions from
natural gas flaring of 0.3 Tg CO2 Eq. (4.3 percent) for
the period 1990 through 2001.
Carbon Dioxide Consumption. The methodology used to
calculate emissions was revised to adjust an outdated un-
derlying assumption that 20 percent of the CO2 produced
for domestic consumption was from "natural sources."
Overall, changes resulted in an average annual decrease
in CO2 emissions from CO2 consumption of 0.2 Tg CO2
Eq. (19.2 percent) for the period 1990 through 2001.
10-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
11. References
Executive Summary
BEA (2004) 2003 Comprehensive Revision of the National
Income and Product Accounts: Current-dollar and "real"
GDP, 1929-2003. Bureau of Economic Analysis (BEA),
U.S. Department of Commerce, Washington, DC. Updated
January 30, 2003, accessed February 25, 2004. .
EIA (2003) Monthly Energy Review, July 2003 and
Unpublished Supplemental Tables on Petroleum
Product detail. Energy Information Administration, U.S.
Department of Energy, Washington, DC, DOE/EIA-
0035(2003/07).
EPA (2003) E-mail correspondence containing preliminary
ambient air pollutant data between EPA OAP and EPA
OAQPS. December 22, 2003.
EPA (1997) National Air Pollutant Emissions Trends
Report, 1900-1996. U.S. Environmental Protection
Agency, Office of Air Quality Planning and Standards,
Research Triangle Park, NC.
IPCC (2001) Climate Change 2001: A Scientific Basis,
Intergovernmental Panel on Climate Change; J.T.
Houghton, Y. Ding, D.J. Griggs, M. Noguer, P.J. van
der Linden, X. Dai, C.A. Johnson, and K. Maskell, eds.;
Cambridge University Press. Cambridge, U.K.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Gas Inventories Programme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
IPCC (1996) Climate Change 1995: The Science of
Climate Change. Intergovernmental Panel on Climate
Change; J.T. Houghton, L.G. Meira Filho, B.A. Callander,
N. Harris, A. Kattenberg, and K. Maskell, eds.; Cambridge
University Press. Cambridge, U.K.
IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories.
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
Keeling, C.D. and T.P. Whorf (2003) Atmospheric CO2
records from sites in the SIO air sampling network. In
Trends: A Compendium of Data on Global Change.
Carbon Dioxide Information Analysis Center, Oak Ridge
National Laboratory. Oak Ridge, TN.
U.S. Census Bureau (2003) U.S. Census Bureau,
Population Division. Table NA-EST2002-01 - National
Population Estimates: April 1, 2000 to July 1, 2002.
Release Date: December 31, 2002.
WMO (1999) Scientific Assessment of Ozone Depletion,
Global Ozone Research and Monitoring Project-Report
No. 44, World Meteorological Organization, Geneva,
Switzerland.
Introduction
Biasing and Jones (2003). Current Greenhouse Gas
Concentrations. In Trends: A Compendium of Data on
Global Change. Carbon Dioxide Information Analysis
Center, Oak Ridge National Laboratory. Oak Ridge, TN.
Duffield, J. (2004) Telephone and email conversation
between Caren Mintz of ICF Consulting and Jim Duffield,
Office of Energy Policy and New Uses, USDA, January.
EIA (2003) Monthly Energy Review, July 2003 and
Unpublished Supplemental Tables on Petroleum
Product detail. Energy Information Administration, U.S.
Department of Energy, Washington, DC, DOE/EIA-
0035(2003/07).
References 11-1
-------
EIA (1991 through 2003) Fuel Oil and Kerosene Sales.
Energy Information Administration, U.S. Department of
Energy, Washington, DC, DOE/EIA-0535-annual.
UNFCCC (2003) National Communications: Greenhouse
Gas Inventories from Parties included in Annex I to the
Convention, UNFCCC Guidelines on Reporting and
Review. Conference of the Parties, Eigth Session, New
Delhi. (FCCC/CP/2002/8) March 28, 2003
IPCC (2001) Climate Change 2001: A Scientific Basis,
Intergovernmental Panel on Climate Change; J.T.
Houghton, Y. Ding, D.J. Griggs, M. Noguer, PJ. van
der Linden, X. Dai, C.A. Johnson, and K. Maskell, eds.;
Cambridge University Press. Cambridge, U.K.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Gas Inventories Programme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
IPCC (1999) Aviation and the Global Atmosphere.
Intergovernmental Panel on Climate Change; Penner, J.E.,
et al., eds.; Cambridge University Press. Cambridge, U.K.
IPCC (1996) Climate Change 1995: The Science of
Climate Change. Intergovernmental Panel on Climate
Change; J.T. Houghton, L.G. Meira Filho, B.A. Callander,
N. Harris, A. Kattenberg, and K. Maskell, eds.; Cambridge
University Press. Cambridge, U.K.
IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories.
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
NRC (2001) Climate Change Science: An Analysis
of Some Key Questions. Committee of the Science
of Climate Change, National Research Council
(available on the internet at .)
WMO (1999) Scientific Assessment of Ozone Depletion,
Global Ozone Research and Monitoring Project-Report
No. 44, World Meteorological Organization, Geneva,
Switzerland.
Trends in Greenhouse Gas Emissions
BE A (2004) 2003 Comprehensive Revision of the National
Income and Product Accounts: Current-dollar and "real"
GDP, 1929-2003. Bureau of Economic Analysis (BEA),
U.S. Department of Commerce, Washington, DC. Updated
January 30, 2003, accessed February 25, 2004. .
Duffield, J. (2004) Telephone and email conversation
between Caren Mintz of ICF Consulting and Jim Duffield,
Office of Energy Policy and New Uses, USDA, January.
EIA (2003a) Monthly Energy Review, July 2003 and
Unpublished Supplemental Tables on Petroleum
Product detail. Energy Information Administration, U.S.
Department of Energy, Washington, DC, DOE/EIA-
0035(2003/07).
EIA (2003b) Short-Term Energy Outlook. Energy
Information Administration, U.S. Department of Energy,
Washington, DC, December.
Keeling, C.D. and T.P. Whorf (2003) Atmospheric CO2
records from sites in the SIO air sampling network. In
Trends: A Compendium of Data on Global Change.
Carbon Dioxide Information Analysis Center, Oak Ridge
National Laboratory. Oak Ridge, TN.
U.S. Census Bureau (2003) U.S. Census Bureau,
Population Division. Table NA-EST2002-01 - National
Population Estimates: April 1, 2000 to July 1, 2002.
Release Date: December 31, 2002.
Energy
Marland, G., T.A. Boden, and R. J. Andres. 2003. "Global,
Regional, and National Fossil Fuel CO2 Emissions."
Trends: A Compendium of Data on Global Change.
Carbon Dioxide Information Analysis Center, Oak Ridge
National Laboratory, U.S. Department of Energy, Oak
Ridge, TN.
Carbon Dioxide Emissions from Fossil
Fuel Combustion
AAR (2003) Railroad Facts, 2002 Ed. Policy and
Economics Department, Association of American
Railroads, Washington, DC.
BEA (2004) 2003 Comprehensive Revision of the National
Income and Product Accounts: Current-dollar and "real"
GDP, 1929-2003. Bureau of Economic Analysis (BEA),
U.S. Department of Commerce, Washington, DC. Updated
January 30, 2003, accessed February 25, 2004.
-------
Dakota Gasification Company (2003), Carbon Dioxide
Gas Specification Sheet, Bismarck, ND, .
DESC (2003) Unpublished data from the Defense Fuels
Automated Management System (DFAMS). Defense
Energy Support Center, Defense Logistics Agency, U.S.
Department of Defense, Washington, DC.
DOC (1991 through 2003) Unpublished "Report of Bunker
Fuel Oil Laden on Vessels Cleared for Foreign Countries."
Foreign Trade Division, Bureau of the Census, U.S.
Department of Commerce, Washington, DC. Form-563.
DOE (1993 through 2003) Transportation Energy Data
Book. Office of Transportation Technologies, Center for
Transportation Analysis, Energy Division, Oak Ridge
National Laboratory, ORNL-6959.
DOT (1991 through 2003) Fuel Cost and Consumption.
Airline Information, Bureau of Transportation Statistics,
U.S. Department of Transportation, Washington, DC.
EFMA (1995). Production of Ammonia. European
Fertilizer Manufacturers Association. March 1.
EIA (2003a) Monthly Energy Review, July 2003 and
Unpublished Supplemental Tables on Petroleum
Product detail. Energy Information Administration, U.S.
Department of Energy, Washington, DC, DOE/EIA-
0035(2003/07).
EIA (2003b) Emissions of Greenhouse Gases in the
United States 2002. Office of Integrated Analysis and
Forecasting, Energy Information Administration, U.S.
Department of Energy, Washington, DC. DOE-EIA-
0573(2002). February.
EIA (2003c) International Energy Annual 2001, Energy
Information Administration, U.S. Department of Energy,
Washington, DC. DOE/EIA-0219(01)-annual. March.
EIA (2003d) Natural Gas Annual 2001. Energy
Information Administration, U.S. Department of Energy,
Washington, DC, DOE/EIA-0131(01)-annual. February.
EIA (2003e) Short-Term Energy Outlook. Energy
Information Administration, U.S. Department of Energy,
Washington, DC, December.
EIA (200 la) Manufacturing Consumption of Energy 1998.
Energy Information Administration, U.S. Department of
Energy, Washington, DC.
EIA (2001b) U.S. Coal, Domestic and International Issues,
Energy Information Administration, U.S. Department of
Energy, Washington, DC, March.
EIA (2000 through 2003) Quarterly Coal Report, Energy
Information Administration, U.S. Department of Energy,
Washington, DC. DOE/EIA-0121
EIA (1991 through 2003) Fuel Oil and Kerosene Sales.
Energy Information Administration, U.S. Department of
Energy, Washington, DC, DOE/EIA-0535-annual.
Erickson, T. (2003) Plains CO2 Reduction (PCOR)
Partnership, Presented at the Regional Carbon
Sequestration Partnership Meeting Pittsburgh,
Pennsylvania, November 3, 2003, Energy and
Environmental Research Center, University of North
Dakota, .
FAA (1995 through 2003) "General Aviation Aircraft
Fuel Consumption." FAA Aerospace Forecasts, Fiscal
Years 2002-2013. Federal Aviation Administration, U.S.
Department of Transportation, Washington, DC. Table 32.
Fitzpatrick, E. (2002) The Weybum Project: A Model for
International Collaboration, .
FHWA (1996 through 2003, draft version) Highway
Statistics. Federal Highway Administration, U.S.
Department of Transportation. Washington, DC, report
FHWA-PL-96-023-annual.
FRB (2003) "Industrial Production and Capacity
Utilization." Federal Reserve Board, Federal Reserve
Statistical Release, G.17, Accessed 16 December 2003.
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories.
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
Marland, G., and A. Pippin (1990) "United States
Emissions of Carbon Dioxide to the Earth's Atmosphere
by Economic Activity." Energy Systems and Policy,
14(4):323.
NOAA (2002a) "State, Regional, and National Monthly
Heating Degree Days, 1971-2000," United States
Climate Normals, Historical Climatography Series No.
5-1. National Climatic Data Center, National Oceanic
and Atmospheric Administration, U.S. Department of
Commerce. August 15.
NOAA (2002b) "State, Regional, and National Monthly
Cooling Degree Days, 1971-2000," United States
Climate Normals, Historical Climatography Series No.
5-2. National Climatic Data Center, National Oceanic
and Atmospheric Administration, U.S. Department of
Commerce. August 15.
Onder, H., and E.A. Bagdoyan (1993) Everything You've
Always Wanted to Know about Petroleum Coke. Allis
Mineral Systems.
References 11-3
-------
SAIC/EIA (2001). "Monte Carlo Simulations of
Uncertainty in U.S. Greenhouse Gas Emission Estimates."
Final Report. Prepared by Science Applications
International Corporation (SAIC) for Energy Information
Administration (EIA), Office of Integrated Analysis and
Forecasting, U.S. Department of Energy, Washington,
D.C. 22 June.
USAF (1998) Fuel Logistics Planning. U.S. Air Force
document AFPAM23-221, 1 May.
U.S. Census Bureau (2003a) Annual Population Estimates
by State, Department of Commerce, Washington DC. 9
July. .
U.S. Census Bureau (2003b) U.S. International Trade
Commission (USITC) Trade Dataweb, . Accessed fall 2002 - spring 2003.
U.S. Census Bureau (2002) National Intercensal Estimates
(1990-2000), Department of Commerce, Washington
DC. 13 September, .
U.S. Census Bureau (1998 through 2003) Current
Industrial Reports Fertilizer Materials and Related
Products:Annual Report, .
U.S. Census Bureau (1991 through 1994) Current
Industrial Reports Fertilizer Materials Annual Report,
Report No. MQ28B.
USGS (2003) Mineral Commodity Summaries. U.S.
Geological Survey, Reston, VA. January.
USGS (1998 through 2002) Mineral Yearbook: Aluminum
Annual Report. U.S. Geological Survey, Reston, VA.
USGS (1995 through 2003) Mineral Yearbook: Silicon
Annual Report 2002. U.S. Geological Survey, Reston, VA.
USGS (1995) Mineral Industry Surveys: Aluminum
Annual Review 1994. U.S. Geological Survey, U.S.
Department of the Interior, formerly Bureau of Mines.
Washington, DC. May.
USGS (1991 through 1994) Silicon: Annual Report.
U.S. Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC.
USGS (1991 through 2003) Mineral Yearbook: Titanium
Annual Report. U.S. Geological Survey, Reston, VA.
Carbon Stored in Products from
Non-Energy Uses of Fossil Fuels
Adler, B. (2001) Personal communication between Robert
Lanza of ICF Consulting and Bob Adler of the U.S. Energy
Information Administration (EIA). September 14, 2001.
ACC (2003) Guide to the Business of Chemistry.
American Chemistry Council. Arlington, VA.
ACC (2002) Guide to the Business of Chemistry.
American Chemistry Council. Arlington, VA.
APC (2003) "APC Year-End Statistics for 2002,"
American Plastics Council website, accessed June 2003
.
APC (2000) as reported in "Facts & Figures for the
Chemical Industry," Chemical and Engineering News,
Vol. 78 (26), June 26, 2000. American Plastics Council.
Arlington, VA. Available online at .
CM A (1999) U.S. Chemical Industry Statistical
Handbook. Chemical Manufacturer's Association.
Washington, DC.
Connolly, U. (2000) Personal communication between
Suzanne Bratis of ICF Consulting and Una Connelly of
National Asphalt Pavement Association. August 2000.
(Tel: 859-288-4960).
Dow (2003) "Dow Products and Services," . Accessed 2002.
DuPont (1995) "DuPont Dibasic Ester Solvents Page,"
DuPont Nylon, . Accessed 2002.
EIA (2003) Monthly Energy Review, July 2003 and
Unpublished Supplemental Tables on Petroleum Product
detail. Energy Information Administration, U.S. Department
of Energy, Washington, DC, DOE/EIA-0035(2003/07).
EIA (200la) Annual Energy Review 1999. Energy
Information Administration, U.S. Department of Energy,
Washington, DC. DOE/EIA-0384(99).
EIA (200 Ib) Manufacturing Energy Consumption Survey
(MECS) 1998, U.S. Department of Energy, Energy
Information Administration, Washington D.C. Available
online at
-------
EIIP (1999) Methods for Estimating Greenhouse Gas
Emissions from Combustion of Fossil Fuels, Emissions
Inventory Improvement Program: State and Territorial Air
Pollution Program Administrators/Association of Local
Air Pollution Control Officials and U.S. Environmental
Protection Agency, EIIP Document Series Volume VIII,
Chapter 1. (STAPPA/ALAPCO/EPA), Washington DC,
August 2000. Accessed August 28, 2000 .
EIIP (1998) "Area Sources" Asphalt Paving, Emissions
Inventory Improvement Program: State and Territorial Air
Pollution Program Administrators/Association of Local
Air Pollution Control Officials and U.S. Environmental
Protection Agency, EIIP Document Series Volume III,
Chapter 17. (STAPPA/ALAPCO/EPA), Washington DC,
August 2000. Accessed July 27, 2000 .
Eldredge-Roebuck (2000) Personal communication
between Joe Casola of ICE Consulting and Brandt
Eldredge-Roebuck of the American Plastics Council. July,
112000. (Tel: 703-253-0611).
EPA (2002a) National Air Quality and Emissions Trends
Report data, 1900-2000. U.S. Environmental Protection
Agency, Office of Air Quality Planning and Standards,
Research Triangle Park, NC. Received in a 1/28/02 email
to Marian Van Pelt from Michael Gillenwater.
EPA (2002b) Pesticides Industry Sales and Usage,
1998 and 1999 Market Estimates, U.S. Environmental
Protection Agency, Office of Prevention, Pesticides and
Toxic Substances, Washington, DC. Accessed July 2003
.
EPA (2001) Inventory of U.S. Greenhoue Gas Emissions
and Sinks: 1990-1999, U.S. Environmental Protection
Agency, Office of Atmospheric Programs, Washington,
DC.EPA236-R-01-001.
EPA (2000a) Biennial Reporting System (BRS). U.S.
Environmental Protection Agency, Envirofacts Warehouse.
Washington, DC. Available online at .
EPA (2000b) Toxics Release Inventory, 1998.
U.S. Environmental Protection Agency, Office of
Environmental Information, Office of Information
Analysis and Access, Washington, DC. Available online at
.
EPA (2000c) Hot Mix Asphalt Plants Emission Assessment
Report (Draft Report), AP-42. U.S. Environmental
Protection Agency, Office of. Air Quality Planning ?nd
Standards, Research Triangle Park, NC, June. Available
online at (accessed July 25, 2000).
EPA (1999) Pesticides Industry Sales and Usage:
1996 and 1997 Market Estimates. U.S. Environmental
Protection Agency, Office of Prevention, Pesticides and
Toxic Substances, Washington, DC. Available online at
.
EPA (1998) Pesticides Industry Sales and Usage,
1994 and 1995 Market Estimates, U.S. Environmental
Protection Agency, Office of Prevention, Pesticides and
Toxic Substances, Washington, DC. Accessed July 2003
.
EPA (1995) Asphalt Paving Operations, AP-42, U.S.
Environmental Protection Agency, Office of Air Quality
Planning and Standards, Research Triangle Park, NC.
FEE (2001) as reported in "Production: slow gains in
output of chemicals and products lagged behind U.S.
economy as a whole," Chemical and Engineering News,
Vol. 79 (26), June 25, 2001. Fiber Economics Bureau.
Washington, DC. Available online at .
IFF (2002) "Fragrance Ingredients: Alpha Pinene,"
International Flavors & Fragrances Inc. . Accessed 2002.
IISRP (2000) as reported in ACS (2001) "Facts & Figures
for the Chemical Industry," Chemical and Engineering
News, Vol. 78 (26), June 26, 2000. International Institute
of Synthetic Rubber Producers. Houston, Texas.
Available online in IISRP's February 18, 2000, News
Release: .
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories.
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
IPCS (1999) "Safe Work," International Labour
Organization, International Programme on Chemical
Safety, . Accessed
summer-fall 2003.
James, A. (2000) Personal communication between
Suzanne Bratis of ICF Consulting and Alan James of Akzo
Nobel Coatings, Inc. July 2000. (Tel: 614-294-3361).
Johnson, G. L. (2003) Personal communication between
Caren Mintz of ICF Consulting and Greg Johnson of
Liskow & Lewis, on behalf of the International Carbon
Black Association (ICBA). Data received in an email on
November 5, 2003.
References 11-5
-------
Kelly, P. (2000) Personal communication between Tom
Smith of ICF Consulting and Peter Kelly of Asphalt
Roofing Manufacturers Association. August 2000. (Tel:
301-348-2002).
Lide, D. R. (1995) CRC Handbook of Chemistry and
Physics. CRC Press, Ann Arbor.
Marland, G. and R. M. Rotty (1984) "Carbon dioxide
emissions from fossil fuels: a procedure for estimation and
results for 1950-1982." Tellus. 36B, 4, 232-261.
Miller, T. (1999) Material Safety Data Sheet, Carbon
Black. Continental Carbon Company. Published
September 1, 1999. Downloaded from , October
10, 2003.
NPRA (2001) Selected Petrochemical Statistics
- U.S. Trade, Production and Consumption. National
Petrochemical & Refiners Association, Washington, DC.
PAN (2002) "Pesticides Database." Pesticide Action
Network North America, . Accessed
summer-fall 2003.
Rinehart, T. (2000) Personal communication between
Thomas Rinehart of U.S. Environmental Protection
Agency, Office of Solid Waste, and Randall Freed of ICF
Consulting. July 2000. (Tel: 703-308-4309).
RMA (2002) U.S. Scrap Tire Markets 2001.
Rubber Manufacturers Association, Washington, DC.
December 2002.
SPI (2000) The Society of the Plastics Industry Website,
.
Accessed June 28, 2000.
STMC (2003) Scrap Tire Facts and Figures. Scrap Tire
Management Council of the Rubber Manufacturers
Association. Washington, DC. Downloaded from and July 7, 2003.
Tooly, L. (2001) Personal communication between Robert
Lanza of ICF Consulting and Lee Tooly of EPA's Office of
Air Quality Planning and Standards. Access file sent in an
email on August 20, 2001.
U.S. Bureau of the Census (2003) U.S International Trade
Commission (USITC) Trade Dataweb, . Accessed fall 2002-spring 2003.
U.S. Census Bureau (1999) 1997 Economic Census,
Manufacturing - Industry Series, Petroleum Lubricating
Oil and Grease Manufacturing, document number
EC97M-3241D, and Petroleum Refining, document
number EC97M-3241A (2 reports).
Wood, A. (2003) "Compendium of Pesticide Common
Names" on Alan Wood's Web Site. . Accessed summer-
fall 2003.
Stationary Combustion (excluding C02)
EIA (2003) Monthly Energy Review, July 2003 and
Unpublished Supplemental Tables on Petroleum
Product detail. Energy Information Administration, U.S.
Department of Energy, Washington, DC, DOE/EIA-
0035(2003/07).
EPA (2003) E-mail correspondence containing preliminary
ambient air pollutant data between EPA OAP and EPA
OAQPS. December 22, 2003.
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories.
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Gas Inventories Programme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
SAIC/EIA (2001). "Monte Carlo Simulations of
Uncertainty in U.S. Greenhouse Gas Emission Estimates."
Final Report. Prepared by Science Applications
International Corporation (SAIC) for Energy Information
Administration (EIA), Office of Integrated Analysis and
Forecasting, U.S. Department of Energy, Washington,
D.C. 22 June.
Mobile Combustion (excluding C02)
AAR (2003) Railroad Facts, 2002 Ed. Policy and
Economics Department, Association of American
Railroads, Washington, DC.
Barton, P. and J. Simpson (1994) "The effects of aged
catalysts and cold ambient temperatures on nitrous oxide
emissions." Mobile Source Emissions Division (MSED),
Environment Canada, MSED Report #94-21.
Benson, D. (2002) Personal communication. Unpublished
data developed by the Upper Great Plains Transportation
Institute, North Dakota State University and American
Short Line & Regional Railroad Association.
Brasil, T. and W. McMahon (1999) "Exhaust Emission
Test Results from a 1998 Ford F-150 LPG/Gasoline Bi-
Fueled Light-Duty Truck using Six LPG Fuel Blends." Air
Resources Board, July 1999. (Available online at .)
BEA (1991 through 2003) Unpublished BE-36 survey
data. Bureau of Economic Analysis (BEA), U.S.
Department of Commerce.
11-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Browning, L. (2003) "VMT Projections for Alternative
Fueled and Advanced Technology Vehicles through
2025," 13th CRC On-Road Vehicle Emissions Workshop,
April 2003.
BTS (2002) National Transportation Statistics 2002.
Bureau of Transportation Statistics, U.S. Department of
Energy, Washington, DC, BTS02-08. (Available online at
.)
CARB (2000) Public Meeting to Consider Approval of
Revisions to the State's On-mad Motor Vehicle Emissions
Inventory: Technical Support Document. California Air
Resources Board, California Environmental Protection
Agency. May 2000.
Census (2000) Vehicle Inventory and Use Survey. U.S.
Census Bureau. Washington, DC, database CD-EC97-VIUS.
CRC (1997) Auto/Oil Air Quality Improvement Research
Program: Program Final Report. Coordinating Research
Council, January 1997.
Dasch, J. M. (1992) Journal of the Air and Waste
Management Association. "Nitrous Oxide Emissions from
Vehicles," 42(l):63-67, January.
DESC (2002) Unpublished data from the Defense Fuels
Automated Management System (DFAMS), Defense
Energy Support Center, Defense Logistics Agency, U.S.
Department of Defense.
DOC (1991 through 2003) Unpublished "Report of
Bunker Fuel Oil Laden on Vessels Cleared for Foreign
Countries." Form-563, Foreign Trade Division, Bureau of
the Census, U.S. Department of Commerce.
DOE (1993 through 2003) Transportation Energy Data
Book. Office of Transportation Technologies, Center for
Transportation Analysis, Energy Division, Oak Ridge
National Laboratory, ORNL-6959.
DOT (1991 through 2003) Fuel Cost and Consumption,
Federal Aviation Administration, U.S. Department of
Transportation, Bureau of Transportation Statistics,
Washington, DC, DAI-10.
EIA (2002a) Alternative Fuels Data Tables. Energy
Information Administration, U.S. Department of Energy,
Washington, DC. (Available online at .)
EIA (2002b) Personal Communication with Joel Lou.
Residual and Distillate Fuel Oil Consumption for
Vessel Bunkering (Both International and Domestic) for
American Samoa, U.S. Pacific Islands, and Wake Island.
EIA (2003a) Monthly Energy Review, July 2003 and
Unpublished Supplemental Tables on Petroleum
Product detail. Energy Information Administration, U.S.
Department of Energy, Washington, DC, DOE/EIA-
0035(2003/07).
EIA (2003b) International Energy Annual 2001, "World
Petroleum Supply and Disposition, 2000" . Table 3.1.
EIA (2003c) Personal Communication with Charles
Esser. Residual and Distillate Fuel Oil Consumption for
Vessel Bunkering (Both International and Domestic) for
American Samoa, U.S. Pacific Islands, and Wake Island.
EIA (1991 through 2003) Fuel Oil and Kerosene Sales.
Energy Information Administration, U.S. Department of
Energy, Washington, DC, DOE/EIA-0535-annual.
EPA (2003a) Annual Certification Test Results
Report. Office of Transportation and Air Quality, U.S.
Environmental Protection Agency. Available online at
.
EPA (2003b) Confidential engine family sales
data submitted to EPA by manufacturers. Office of
Transportation and Air Quality, U.S. Environmental
Protection Agency.
EPA (2003c) E-mail correspondence containing
preliminary ambient air pollutant data between EPA OAP
and EPA OAQPS. December 22, 2003.
EPA (2000) Mobile6 Vehicle Emission Modeling Software.
Office of Mobile Sources, U.S. Environmental Protection
Agency. Ann Arbor, Michigan.
EPA (1999) Emission Facts: The History of Reducing
Tailpipe Emissions. Office of Mobile Sources, May, EPA
420-F-99-017. Available online at .
EPA (1998) Emissions of Nitrous Oxide from Highway
Mobile Sources: Comments on the Draft Inventory of U.S.
Greenhouse Gas Emissions and Sinks, 1990-1996. Office
of Mobile Sources, Assessment and Modeling Division,
U.S. Environmental Protection Agency, August, EPA420-
R-98-009. Available online at .
EPA (1994b) Milestones in Auto Emissions Control. Office
of Mobile Sources, August, EPA 400-F-92-014. Available
online at .
EPA (1993) Automobiles and Carbon Monoxide. Office
of Mobile Sources, January, EPA 400-F-92-005. Available
online at .
EPA/DOE (2001) Fuel Economy 2001 Datafile. U.S.
Environmental Protection Agency, Department of Energy.
Washington, DC, dataset Olguide0918. Available online at
.
References 11-7
-------
FHWA (1996 through 2003, draft version) Highway
Statistics. Federal Highway Administration, U.S.
Department of Transportation. Washington, DC, report
FHWA-PL-96-023-annual.
FHWA (2002b) "Traffic Volume Trends - December
2002," accessed December 2, 2003. Available online
.
ICF (2001) Revised U.S. VMT estimates and N2O
emission factors. Memorandum from ICF Consulting to
Ed Coe, Office of Transportation and Air Quality, U.S.
Environmental Protection Agency. December 2001.
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines jor National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
Lipman, T. and M. Delucchi (2002) "Emissions of Nitrous
Oxide and Methane from Conventional and Alternative
Fuel Motor Vehicles," Climate Change, Volume 53,
pp.477-516. (Available on the internet at < http://ist-
socrates.berkeley.edu/~rael/Climatic_Change.pdf>)
Norbeck, J., T. Truex, M. Smith, and T. Durbin (1998)
"Inventory of AFVs and AFV Comparison: OEM vs.
Retrofits," CE-CERT, University of California Riverside,
Final Report 98-VE-RT2W-008-FR, September 1998
Available online at .
NREL (2002) Truck Engine/Fuel System Specification
Data, Center for Transportation Technologies and Systems,
National Renewable Energy Laboratory, U.S. Department
of Energy, Washington, DC. Available online at .
Prigent, M. and G. De Soete (1989) "Nitrous oxide N2O
in engines exhaust gases—a first appraisal of catalyst
impact," Society of Automotive Engineers, SAE Paper
890492.
Smith, L. R. and P. M. Carey (1982) "Characterization of
exhaust emissions from high mileage catalyst-equipped
automobiles," Society of Automotive Engineers, SAE
Paper 820783.
Unnasch, S. and L. Browning (2000) "Fuel Cycle Energy
Conversion Efficiency Analysis."
Unnasch, S., L. Browning and E. Kassoy (2001)
"Refinement of Selected Fuel-Cycle Emissions Analyses,
Final Report to ARB."
Urban, C. M. and R. J. Garbe (1980) "Exhaust Emissions
from Malfunctioning Three-Way Catalyst-Equipped
Automobiles," Society of Automotive Engineers, SAE
Paper 800511.
Wang, M.G. (1999) "GREET 1.5 - Transportation Fuel
Cycle Model" Report No. ANL/ESD-39.
Weaver, C. S. and L.-M. Chan (1996) "Mobile source
emission factors for global warming gases," Draft Final
Report, 24 June, submitted to ICF, Inc. by Engine, Fuel,
and Emissions Engineering, Inc., Sacramento, CA.
Coal Mining
AAPG (1984). Coalbed Methane Resources of the United
States, AAPG Studies in Geology Series #17, 1984.
Coal Age (2002). Keystone Coal Industry Manuals 1991-
2002. Primedia Buisness Magazines & Media. Chicago, IL.
DOE (1983). Methane Recovery from Coalbeds: A
Potential Energy Source, U.S. Department of Energy,
(DOE/METC/83-76).
EIA (2002). Personal Communication on September 30,
2002, U.S. Department of Energy, Energy Information
Administration, Washington, DC.
EIA (2000). Coal Industry Annual 1991-1999.
U.S. Department of Energy, Energy Information
Administration, Washington, DC, Table 3.
EPA (2002). 2002 Base Year Greenhouse Gas Inventory
Preparation Guidelines memorandum. U.S. Environmental
Protection agency, Air And Radiation, June 2003.
EPA (1996). Evaluation and Analysis of Gas Content and
Coal Properties of Major Coal Bearing Regions of the
United States, U.S. Environmental Protection Agency,
EPA/600/R-96-065.
EPA (1990). Methane Emissions from Coal Mining: Issues
and Opportunities for Reduction. U.S. Environmental
Protection Agency, Air and Radiation, September.
GRI (1988). A Geologic Assessment of Natural Gas from
Coal Seams Topical Reports, Gas Research Institute 1986-88.
Mutmansky, J. M. and Y. Wang (2000). Analysis of
Potential Errors in Determination of Coal Mine Annual
Methane Emissions, Mineral Resources Engineering, Vol.
9, No. 4, December 2000.
USBM (1986). Circular 9067, Results of the Direct
Method Determination of the Gas Contents of U.S. Coal
Basins. U.S. Bureau of Mines.
Abandoned Coal Mines
EPA 2003, "Methane Emissions Estimates &
Methodology for Abandoned Coal Mines in the U.S.",
Draft Final Report, Washington DC, June 2003.
Garcia, F., and J. Cervik 1987, Method Factors for
Anemometer Measurement at Pipe Outlets, U.S. Bureau of
Mines, RI 9061, Pittsburgh, PA.
Garcia, F, F. E. McCall, and M. A. Trevits 1994,
Proceedings of the 7th U.S. Mine Ventilation Symposium,
A Case Study of Methane Gas Migration Through Sealed
11-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Mine Gob Into Active Mine Workings, U.S. Bureau of
Mines, Pittsburgh, PA.
Irani, M. C., E. D. Thimons, T. G. Bobick, Maurice Deul,
and M. G. Zabetakis 1972, Methane Emissions From U.S.
Coal Mines, A Survey, U.S. Bureau of Mines, Information
Circular 8558, Pittsburgh, PA.
Kirchgessner, D.A., S.D. Piccot, and S.S. Masemore 2001,
An Improved Inventory of Methane Emissions from Coal
Mining in the U.S., Journal of Air and Waste Management
Association, Volume 50:1904-1919, March 2001.
Masemore, S., S. Piccot, E. Ringler, and W. P. Diamond
1996, Evaluation and Analysis of Gas Content and Coal
Properties of Major Coal Bearing Regions of the United
States, EPA-600/R-96-065, Washington, DC.
Mutmansky, Jan M., and Yanbei Wang 2000, Analysis of
Potential Errors in Determination of Coal Mine Annual
Methane Emissions, Pennsylvania State University,
Department of Energy and Geo-Environmental
Engineering, University Park, PA.
Seidle, J.P. and L.E. Am 1990, "Use of Conventional
Reservoir Models for Coalbed Methane Simulation,"
Paper CIM/SPE 90-118, presented at the CIM/SPE
International Technical Meeting, Calgary, Alberta (June
10-13, 1990).
Petroleum Systems
API (2002) Basic Petroleum Data Book. American
Petroleum Institute, Washington, DC.
DOI (1998-2002) Offshore Development Activity. Minerals
Management Service, U.S. Department of Interior.
Available online at .
EIA (2003) Monthly Energy Review. Energy Information
Administration, U.S. Department of Energy, Washington,
DC. Available online at .
EIA (2001) Annual Energy Review. Energy Information
Administration, U.S. Department of Energy, Washington,
DC. Available online at .
EIA (2002) Petroleum Supply Annual 1990-2002 Volume
1. Energy Information Administration, U.S. Department of
Energy, Washington, DC.
EPA (1999) Estimates of Methane Emissions from the U.S.
Oil Industry (Draft Report). Office of Air and Radiation,
U.S. Environmental Protection Agency, Washington, DC.
OGJ (2002a) Oil and Gas Journal 1990-2002, Pipeline
Economics Issue, August or September.
OGJ (2002b) Oil and Gas Journal 1990-2002, Worldwide
Refining Issue, late December.
Radian (1996a) Methane Emissions from the Natural Gas
Industry, V7: Blow and Purge Activities. Prepared for the
Gas Research Institute and EPA. April 1996.
Radian (1996b) Methane Emissions from the Natural Gas
Industry, VI1: Compressor Driver Exhaust. Prepared for
GRI and EPA. April 1996.
Radian (1996c) Methane Emissions from the Natural Gas
Industry, VI2: Pneumatic Devices. Prepared for GRI and
EPA. April 1996.
Radian (1996d) Methane Emissions from the Natural Gas
Industry, VI3: Chemical Injection Pumps. Prepared for
GRI and EPA. April 1996.
Radian (1996e) Methane Emissions from the U.S. Petroleum
Industry. Draft. Prepared for GRI and EPA. June 1996.
Radian (1996f) Methane and Carbon Dioxide Emissions
Estimate From U.S. Petroleum Sources. Prepared for API.
July 1996.
United States Army Corps of Engineers (1995-2001)
Waterbome Commerce of the United States, Part 5: National
Summaries. U.S. Army Corps of Engineers, Washington, DC.
Natural Gas Systems
AGA (1991-1998) Gas Facts. American Gas Association,
Washington, DC.
API (2003) "Table 12 - Section HI - Producing Oil Wells
in the United States by State." Basic Petroleum Data Book.
American Petroleum Institute. August 2002. Volume XXII,
Number 2.
Alabama State Oil and Gas Board (2003). Available online
at .
DOI (1998-2002) Offshore Development Activity. Minerals
Management Service, U.S. Department of Interior.
Available online at .
EIA (1993, 1996, 1997, 1998a). Table 1, Summary
Statistics for Natural Gas in the United States. Natural
Gas Annual. Energy Information Administration,
Department of Energy, Washington, DC. Available online
at .
EIA (2003b). "Table 2 - Supply and Disposition of Dry
Natural Gas in the United States 1996-2002." Natural
Gas Monthly. Energy Information Administration,
Department of Energy, Washington, DC. Available online
at .
EIA (2001, 2003c). "Table 3 - Natural Gas Consumption
in the United States." Natural Gas Monthly. Energy
Information Administration, Department of Energy,
Washington, DC. Available on line at .
EIA (2003d). "Table 6 - Number of Producing Gas and
Gas Condensate Wells by State." Historical Natural Gas
Annual 1930-2000. Energy Information Administration,
Department of Energy, Washington, DC. Available online
at .
References 11-9
-------
EIA (2001, 2003e). "Table 7 - Marketed Production of
Natural Gas by State." Natural Gas Monthly. Energy
Information Administration, Department of Energy,
Washington, DC. Available online at .
EIA (2003f). "Table 95 - Natural Gas Consumption in
the United States, 1930-2000." Natural Gas Annual,
2000. Energy Information Administration, Department of
Energy, Washington, DC. Available online at . Gas Consumption in the Transportation section
is now labeled Vehicle Fuel.
EIA (1998g). "Table 100, Natural Gas Consumption in
the United States, 1994-1998." Natural Gas Annual, 1998.
Energy Information Administration, Department of Energy,
Washington, DC. Available online at .
EPA (2001) The Power of Partnerships: Energy Star
and other Voluntary Programs. U.S. EPA, Climate
Protection Partnerships Division. EPA 430-R-01-009.
July 2001. Available online at .
OPS (2003b). Natural Gas Distribution Annuals Data.
Office of Pipeline Safety, Department of Transportation.
Washington, DC. Available online at .
Wyoming Oil and Gas Conservation Commission (2003).
Available online at .
Waste Combustion
APC (2000) as reported in "Facts & Figures for the
Chemical Industry," Chemical and Engineering News,
Vol. 78 (26), June 26, 2000. American Plastics Council.
Arlington, VA. Available online at .
De Soete, G. G. (1993) Nitrous Oxide from Combustion and
Industry: Chemistry, Emissions and Control. In Van Amstel,
A. R. (ed) Proc. of the International Workshop Methane and
Nitrous Oxide: Methods in National Emission Inventories
and Options for Control, Amersfoort (NL) 3-5 February.
DeZan, D. (2000) Personal communication between Diane
DeZan of the Fiber Economics Bureau and Joe Casola of
ICF Consulting, August 4, 2000.
Eldredge-Roebuck, B. (2000) Personal communication
between Brandt Eldredge-Roebuck of the American Plastics
Council and Joe Casola of ICF Consulting, July 11, 2000.
EIA (Energy Information Administration). 2002.
AEO2002 (Annual Energy Outlook), Appendix C, High
Oil Price Case, Table 2. Energy Consumption by Sector
and Source. Available online at .
EPA (2003) Characterization of Municipal Solid
Waste in the United States: 2001 Update. (Draft) U.S.
Environmental Protection Agency, Office of Solid Waste
and Emergency Response, EPA. Washington, DC.
EPA (2002a) Characterization of Municipal Solid Waste
in the United States: 2000 Update. U.S. Environmental
Protection Agency, Office of Solid Waste and Emergency
Response, EPA. Washington, DC, EPA530-R-02-001.
EPA (2002b) Solid Waste Management and Greenhouse
Gases: A Life-Cycle Assessment of Emissions and Sinks. U.S.
Environmental Protection Agency, Office of Solid Waste and
Emergency Resposne, Washington, DC, EPA530-R-98-013.
EPA (2001) Municipal Solid Waste in the United States:
1999 Facts and Figures. U.S. Environmental Protection
Agency, Office of Solid Waste, EPA. Washington, DC,
EPA530-R-01-014.
EPA (2000a) Characterization of Municipal Solid Waste
in the United States: 1999 Update Fact Sheet (and Data
Tables). U.S. Environmental Protection Agency, Office of
Solid Waste, EPA. Washington, DC, EPA530-F-00-024.
EPA (2000b) Characterization of Municipal Solid Waste in
the United States: Source Data on the 1999 Update. U.S.
Environmental Protection Agency, Office of Solid Waste,
EPA. Washington, DC, EPA530-F-00-024.
EPA (1999) Characterization of Municipal Solid Waste in
the United States: 1998 Update. Report No. EPA530-R-
99-021. U.S. Environmental Protection Agency, Office of
Solid Waste, EPA. Washington, DC.
EPA (1998) Characterization of Municipal Solid Waste
in the United States: 1997 Update. U.S. Environmental
Protection Agency, Office of Solid Waste, EPA.
Washington, DC, EPA530-R-98-007.
EPA (1997) Characterization of Municipal Solid Waste
in the United States: 1996 Update. U.S. Environmental
Protection Agency, Office of Solid Waste, EPA.
Washington, DC, EPA530-R-97-015.
11-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
EPA (1996) Characterization of Municipal Solid Waste
in the United States: 1995 Update. U.S. Environmental
Protection Agency, Office of Solid Waste, EPA.
Washington, DC.
EPA (1995) Compilation of Air Pollutant Emission
Factors, AP-42, Fifth Edition, Volume I: Stationary Point
and Area Sources, Introduction. Office of Air Quality
Planning and Standards, U.S. EPA. Research Triangle
Park, NC. October.
FEE (2000) as reported in "Facts & Figures for the
Chemical Industry," Chemical and Engineering News,
Vol. 78 (26), June 26, 2000. Fiber Economics Bureau.
Washington, DC. Available online at .
Glenn, Jim (1999) "11th Annual BioCycle Nationwide
Survey: The State of Garbage in America." BioCycle,
April 1999. JG Press, Emmaus, PA.
Goldstein, N. and C. Madtes (2001) "13th Annual BioCycle
Nationwide Survey: The State of Garbage in America,"
BioCycle, December 2001. JG Press, Emmaus, PA.
Goldstein, N. and C. Madtes (2000) "12th Annual BioCycle
Nationwide Survey: The State of Garbage in America, Part
I," BioCycle, November 2000. JG Press, Emmaus, PA.
IISRP (2000) as reported in "Facts & Figures for the
Chemical Industry," Chemical and Engineering News, Vol.
78 (26), June 26, 2000. International Institute of Synthetic
Rubber Producers. Houston, Texas. Available online in
IISRP's February 18, 2000, News Release: .
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories.
Intergovernmental Panel on Climate Change, IPCC
National Greenhouse Gas Invnetories Programme Technical
Support Unit, Kanagawa, Japan. Available online at .
IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories, Paris:
Intergovernmental Panel on Climate Change, United Nations
Environment Programme, Organization for Economic Co-
Operation and Development, International Energy Agency.
Johnke (1999), as cited in Good Practice Guidance and
Uncertainty Management in National Greenhouse Gas
Inventories, Intergovernmental Panel on Climate Change,
2000.
Kearney, A.T. (1992) Scrap Tire Use/Disposal Study 1992
Update. Scrap Tire Management Council, Washington, DC.
Kearney, A.T. (1990) Scrap Tire Use/Disposal Study Final
Report. Scrap Tire Management Council, Washington, DC.
Miller, T. (1999) Material Safety Data Sheet, Carbon Black.
Continental Carbon Company. Published September 1,
1999. Downloaded from , October 10, 2003.
RMA (2002) U.S. Scrap Tire Markets 2001.
Rubber Manufacturers Association, Washington, DC.
December 2002.
STMC (2003) Scrap Tire Facts and Figures. Scrap Tire
Management Council of the Rubber Manufacturers
Association. Washington, DC. Downloaded from and , July 7, 2003.
STMC (2002) Scrap Tire Facts and Figures. Scrap
Tire Management Council of the Rubber Manufacturers
Association. Washington, DC. Downloaded from
,
October 22, 2002.
STMC (2001) Scrap Tire Facts and Figures. Scrap
Tire Management Council of the Rubber Manufacturers
Association. Washington, DC. Downloaded from
,
Septembers, 2001.
STMC (2000) Scrap Tire Facts and Figures. Scrap Tire
Management Council of the Rubber Manufacturers
Association. Washington, DC. Downloaded from , July 26, 2000.
STMC (1999) Scrap Tire Use/Disposal Study 1998/1999
Update Executive Summary. Scrap Tire Management
Council of the Rubber Manufacturers Association.
Washington, DC. Published September 15, 1999.
Downloaded from ,
July 26, 2000.
STMC (1997) Scrap Tire Use/Disposal Study 1996 Update.
Scrap Tire Management Council, Washington, DC.
STMC (1995) Scrap Tire Use/Disposal Study 1994 Update.
Scrap Tire Management Council, Washington, DC.
UK: Environment Agency (1999), as cited in Good
Practice Guidance and Uncertainty Management in
National Greenhouse Gas Inventories, Intergovernmental
Panel on Climate Change, 2000.
U.S. Census Bureau (2000) Annual Projections of the
Total Resident Population as of July 1: Middle, Lowest,
Highest, and Zero International Migration Series, 1999
to 2100, February,
-------
Natural Gas Flaring and Ambient
Air Pollutant Emissions from Oil and
Gas Activities
Barns, D. and Edmonds, J. (1990) "An Evaluation of the
Relationship Between the Production and Use of Energy
and Atmospheric Methane Emissions." DOE/NBB-0088P.
Pacific Northwest Laboratory. Richland, WA.
EIA (2003) Natural Gas Annual 2001, DOE/EIA
0131(01)-annual, Energy Information Administration, U.S.
Department of Energy, Washington, DC. February 2003.
EIA (2001) Natural Gas Annual 2000, DOE/EIA
0131(00)-annual, Energy Information Administration, U.S.
Department of Energy, Washington, DC. October 2001.
EPA (2003) E-mail correspondence containing preliminary
ambient air pollutant data between EPA OAP and EPA
OAQPS. December 22, 2003.
MMS (2003) Emissions Inventories ofOCS Production
and Development Activities in the Gulf of Mexico. A report
by the Minerals Management Service. MMS OCS Report
2002 -073.
International Bunker Fuels
BEA (1991 through 2003) Unpublished BE-36 survey
data. Bureau of Economic Analysis (BEA). U.S.
Department of Commerce, Washington, DC.
DESC (2003) Unpublished data from the Defense Fuels
Automated Management System (DFAMS). Defense
Energy Support Center, Defense Logistics Agency, U.S.
Department of Defense, Washington, DC.
DOC (1991 through 2003) Unpublished "Report of Bunker
Fuel Oil Laden on Vessels Cleared for Foreign Countries."
Foreign Trade Division, Bureau of the Census, U.S.
Department of Commerce, Washington, DC. Form-563.
DOT (1991 through 2003) Fuel Cost and Consumption.
Airline Information, Bureau of Transportation Statistics,
U.S. Department of Transportation, Washington, DC.
EIA (2003) Monthly Energy Review, July 2003 and
Unpublished Supplemental Tables on Petroleum
Product detail. Energy Information Administration, U.S.
Department of Energy, Washington, DC, DOE/EIA-
0035(2003/07).
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories.
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
NASA (1996) Scheduled Civil Aircraft Emission
Inventories for 1992: Database Development and
Analysis. Prepared for Langley Research Center, NASA
Contractor Report # 4700, April.
USAF (1998) Fuel Logistics Planning. U.S. Air Force
pamphlet AFPAM23-221, 1 May.
Wood Biomass and Ethanol Consumption
EIA (1997) Renewable Energy Annual. Energy
Information Administration, U.S. Department of Energy.
Washington, DC. March. DOE/EIA-0603(96)
EIA (2003) Annual Energy Review 2002. Energy
Information Administration, U.S. Department of Energy.
Washington, DC. July. Tables 10.2a and 10.2b. DOE/EIA-
0384(2002).
EIA (1994) Estimates of U.S. Biomass Energy
Consumption 1992. Energy Information Administration,
U.S. Department of Energy. Washington, DC. May. DOE/
EIA-0548(92).
Lindstrom, P. (2003) Personal communication between
Matthew Stanberry of ICF Consulting and Perry
Lindstrom of the Energy Information Administration.
November 2003.
Industrial Processes
Iron and Steel Production
AISI (2003) 2002 Annual Statistical Report, American
Iron and Steel Institute, Washington, DC.
AISI (2002) 2001 Annual Statistical Report, American
Iron and Steel Institute, Washington, DC.
AISI (2001) 2000 Annual Statistical Report, American
Iron and Steel Institute, Washington, DC.
AISI (1996) 1995 Annual Statistical Report, American
Iron and Steel Institute, Washington, DC.
AISI (1995) 1994 Annual Statistical Report, American
Iron and Steel Institute, Washington, DC.
DOE (1997) Office of Industrial Technologies - Energy
and Environmental Profile of the U.S. Aluminum Industry,
July 1997.
EIA (2003) Quarterly Coal Report January-December
2002, Energy Information Administration, U.S.
Department of Energy, Washington, DC. DOE/EIA-0121
EIA (2002) Quarterly Coal Report January-March 2002,
Energy Information Administration, U.S. Department of
Energy, Washington, DC. DOE/EIA-0121 (2002/1Q).
EIA (2001) U.S. Coal, Domestic and International Issues,
Energy Information Administration, U.S. Department of
Energy, Washington, DC, March 2001.
EIA (2000) Quarterly Coal Report October-December
2000, Energy Information Administration, U.S.
Department of Energy, Washington, DC. DOE/EIA-0121
(2000/4Q).
11-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Gas Inventories Programme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
USGS (2002) Minerals Yearbook: Aluminum Annual
Report 2001. U.S. Geological Survey, Reston, VA.
USGS (200la) Minerals Yearbook: Iron and Steel Annual
Report 2000. U.S. Geological Survey, Reston, VA.
USGS (2001b) Minerals Yearbook: Aluminum Annual
Report 2000. U.S. Geological Survey, Reston, VA.
USGS (2000a) Minerals Yearbook: Iron and Steel Annual
Report 1999. U.S. Geological Survey, Reston, VA.
USGS (2000b) Minerals Yearbook: Aluminum Annual
Report 1999. U.S. Geological Survey, Reston, VA.
USGS (1999) Minerals Yearbook: Iron and Steel Annual
Report 1998. U.S. Geological Survey, Reston, VA.
USGS (1998) Minerals Yearbook: Aluminum Annual
Report 1997. U.S. Geological Survey, Reston, VA.
USGS (1997) Minerals Yearbook: Iron and Steel Annual
Report 1996. U.S. Geological Survey, Reston, VA.
USGS (1995a) Minerals Yearbook: Iron and Steel Annual
Report 1994. U.S. Geological Survey, Reston, VA.
USGS (1995b) Minerals Industries Surveys: Aluminum
Annual Review 1994. U.S. Geological Survey, U.S.
Department of the Interior. Washington, DC. May.
USGS (1993) Minerals Yearbook: Iron and Steel Annual
Report 1992. U.S. Geological Survey, Reston, VA.
Cement Manufacture
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Gas Inventories Programme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
IPCC (1996) Climate Change 1995: The Science of
Climate Change, Intergovernmental Panel on Cliamte
Change; J.T. Houghton, L.G. Meira Filho, B.A. Callander,
N. Harris, A. Kattenberg, and K. Maskell, eds.; Cambridge
University Press. Cambridge, U.K.
USGS (2003) Mineral Yearbook: Cement Annual Report
2002. U.S. Geological Survey, Reston, VA.
USGS (2002) Mineral Yearbook: Cement Annual Report
2001. U.S. Geological Survey, Reston, VA.
USGS (2001) Mineral Yearbook: Cement Annual Report
2000. U.S. Geological Survey, Reston, VA.
USGS (2000) Mineral Yearbook: Cement Annual Report
1999. U.S. Geological Survey, Reston, VA.
USGS (1999) Mineral Yearbook: Cement Annual Report
1998. U.S. Geological Survey, Reston, VA.
USGS (1998) Minerals Yearbook: Cement Annual Report
1997. U.S. Geological Survey, Reston, VA.
USGS (1997) Minerals Yearbook: Cement Annual Report
1996. U.S. Geological Survey, Reston, VA.
USGS (1996) Minerals Yearbook: Cement Annual Report
1995. U.S. Geological Survey, Reston, VA.
USGS (1995a) Cement: Annual Report 1993. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC. June.
USGS (1995b) Cement: Annual Report 1994. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC.
USGS (1992) Cement: Annual Report 1990. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC. April.
Ammonia Manufacture and
Urea Application
EIA (1998) Manufacturing Energy Consumption Survey
(MECS) U.S. Department of Energy, Energy Information
Administration, Washington D.C. Available online at
, August 2002.
U.S. Census Bureau (2003) Current Industrial Reports
Fertilizer Materials and Related Products:Annual Reports
2002 Summary. Available online at .
U.S. Census Bureau (2002a) Current Industrial Reports
Fertilizer Materials and Related Products: First Quarter
2002. June 2002. Available online at .
References 11-13
-------
U.S. Census Bureau (2002b) Current Industrial Reports
Fertilizer Materials and Related Products: Fourth Quarter
200L March 2002. Available online at .
U.S. Census Bureau (2002c) Current Industrial Reports
Fertilizer Materials and Related Products: Third Quarter
2001. January 2002. Available online at .
U.S. Census Bureau (200la) Current Industrial Reports
Fertilizer Materials and Related Products: Second
Quarter 2001. September 2001. Available online at
.
U.S. Census Bureau (2001b) Current Industrial Reports
Fertilizer Materials and Related Products .'Annual Report
2000. Available online at .
U.S. Census Bureau (2000) Current Industrial Reports
Fertilizer Materials and Related Products:Annual Report
1999. Available online at .
U.S. Census Bureau (1999) Current Industrial Reports
Fertilizer Materials and Related Products:Annual Report
1998. Available online at .
U.S. Census Bureau (1998) Current Industrial Reports
Fertilizer Materials and Related Products:Annual Report
1997. Available online at .
U.S. Census Bureau (1994) Current Industrial Reports
Fertilizer Materials Annual Report 1993, Report No.
MQ28B.
U.S. Census Bureau (1993) Current Industrial Reports
Fertilizer Materials Annual Report 1992, Report No.
MQ28B.
U.S. Census Bureau (1992) Current Industrial Reports
Fertilizer Materials Annual Report 1991, Report No.
MQ28B.
U.S. Census Bureau (1991) Current Industrial Reports
Fertilizer Materials Annual Report 1990, Report No.
MQ28B.
U.S. ITC (2002) United States International Trade
Commission Interactive Tariff and Trade Data Web,
Version 2.5.0. Accessed online at . Accessed August, 2002.
Lime Manufacture
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Gas Inventories Programme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
Males, E. (2003) Public review comments received in a
memorandum from Eric Males, National Lime Association
to Mr. William N. Irving & Mr. Leif Hockstad,
Environmental Protection Agency. Memorandum dated
March 6, 2003.
USGS (2003) Mineral Yearbook: Lime Annual Report
2002. U.S. Geological Survey, Reston, VA.
USGS (2002) Mineral Yearbook: Lime Annual Report
2001. U.S. Geological Survey, Reston, VA.
USGS (2001) Mineral Yearbook: Lime Annual Report
2000. U.S. Geological Survey, Reston, VA.
USGS (2000) Mineral Yearbook: Lime Annual Report
1999. U.S. Geological Survey, Reston, VA.
USGS (1999) Minerals Yearbook: Lime Annual Report
1998. U.S. Geological Survey, Reston, VA.
USGS (1998) Minerals Yearbook: Lime Annual Report
1997. U.S. Geological Survey, Reston, VA.
USGS (1997) Minerals Yearbook: Lime Annual Report
1996. U.S. Geological Survey, Reston, VA.
USGS (1996) Minerals Yearbook: Lime Annual Report
1995. U.S. Geological Survey, Reston, VA.
USGS (1995) Minerals Yearbook: Lime Annual Report
1994. U.S. Geological Survey, Reston, VA.
USGS (1994) Lime: Annual Report 1993. U.S. Geological
Survey, U.S. Department of the Interior, formerly Bureau
of Mines. Washington, DC. September.
USGS (1992) Lime: Annual Report 1991. U.S. Geological
Survey, U.S. Department of the Interior, formerly Bureau
of Mines. Washington, DC. November.
Limestone and Dolomite Use
Tepordei (2003) Telephone Conversations between Matthew
Stanberry of ICF Consulting and Valentin Tepordei,
Commodity Specialist, USGS, 23 October- 31 October.
Tepordei (2002) Telephone Conversations between Matthew
Stanberry of ICF Consulting and Valentin Tepordei,
Commodity Specialist, USGS, 29 October- 8 November.
USGS (2003a) Mineral Yearbook: Crushed Stone Annual
Report 2002. U.S. Geological Survey, Reston, VA.
USGS (2003b) Mineral Yearbook: Magnesium Annual
Report 2002. U.S. Geological Survey, Reston, VA.
USGS (2002a) Mineral Yearbook: Crushed Stone Annual
Report 2001. U.S. Geological Survey, Reston, VA.
USGS (2002b) Mineral Yearbook: Magnesium Annual
Report 2001. U.S. Geological Survey, Reston, VA.
USGS (2001 a) Mineral Yearbook: Crushed Stone Annual
Report 2000. U.S. Geological Survey, Reston, VA.
USGS (2001b) Mineral Yearbook: Magnesium Annual
Report 2000. U.S. Geological Survey, Reston, VA.
11-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
USGS (2000a) Mineral Yearbook: Crushed Stone Annual
Report 1999. U.S. Geological Survey, Reston, VA.
USGS (2000b) Mineral Yearbook: Magnesium Annual
Report 1999. U.S. Geological Survey, Reston, VA.
USGS (1999a) Mineral Yearbook: Crushed Stone Annual
Report 1998. U.S. Geological Survey, Reston, VA.
USGS (1999b) Mineral Yearbook: Magnesium Annual
Report 1998. U.S. Geological Survey, Reston, VA.
USGS (\998a) Mineral Yearbook: Crushed Stone Annual
Report 1997. U.S. Geological Survey, Reston, VA.
USGS (1998b) Mineral Yearbook: Magnesium Annual
Report 1997. U.S. Geological Survey, Reston, VA.
USGS (1997a) Minerals Yearbook: Crushed Stone Annual
Report 1996. U.S. Geological Survey, Reston, VA.
USGS (1997b) Mineral Yearbook: Magnesium Annual
Report 1996. U.S. Geological Survey, Reston, VA.
USGS (1996a) Minerals Yearbook: Crushed Stone Annual
Report 1995. U.S. Geological Survey, Reston, VA.
USGS (1996b) Mineral Yearbook: Magnesium Annual
Report 1995. U.S. Geological Survey, Reston, VA.
USGS (1995a) Crushed Stone: Annual Report 1993.
U.S. Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC. January.
USGS (1995b) Crushed Stone: Annual Report 1994.
U.S. Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC.
USGS (1995c) Magnesium: Annual Report 1994. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC.
USGS (1993) Crushed Stone: Annual Report 1991. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC. March.
Soda Ash Manufacture and Consumption
USGS (2003) Minerals Yearbook: Soda Ash Annual
Report 2002. U.S. Geological Survey, Reston, VA.
USGS (2002) Minerals Yearbook: Soda Ash Annual
Report 2001. U.S. Geological Survey, Reston, VA.
USGS (2001) Minerals Yearbook: Soda Ash Annual
Report 2000. U.S. Geological Survey, Reston, VA.
USGS (2000) Minerals Yearbook: Soda Ash Annual
Report 1999. U.S. Geological Survey, Reston, VA.
USGS (1999) Minerals Yearbook: Soda Ash Annual
Report 1998. U.S. Geological Survey, Reston, VA.
USGS (1998) Minerals Yearbook: Soda Ash Annual
Report 1997. U.S. Geological Survey, Reston, VA.
USGS (1997) Minerals Yearbook: Soda Ash Annual
Report 1996. U.S. Geological Survey, Reston, VA.
USGS (1996) Minerals Yearbook: Soda Ash Annual
Report 1995. U.S. Geological Survey, Reston, VA.
USGS (1995) Minerals Yearbook: Soda Ash Annual
Report 1994. U.S. Geological Survey, Reston, VA.
USGS (1994) Soda Ash: Annual Report 1993. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC. July.
Titanium Dioxide Production
Chemical Market Reporter (2000). May 22, 2000.
Gambogi, J.(2002). Telephone conversation between Philip
Groth of ICF Consulting and Joseph Gambogi, Commodity
Specialist, U.S. Geologocial Survey, 13 November.
Onder, H, and E.A. Bagdoyan (1993) Everything You've
Always Wanted to Know about Petroleum Coke. Allis
Mineral Systems.
USGS (2003) Mineral Yearbook: Titanium Annual Report
2002. U.S. Geological Survey, Reston, VA.
USGS (2002) Mineral Yearbook: Titanium Annual Report
2001. U.S. Geological Survey, Reston, VA.
USGS (2001) Mineral Yearbook: Titanium Annual Report
2000. U.S. Geological Survey, Reston, VA.
USGS (2000) Mineral Yearbook: Titanium Annual Report
1999. U.S. Geological Survey, Reston, VA.
USGS (1999) Minerals Yearbook: Titanium Annual Report
1998. U.S. Geological Survey, Reston, VA.
USGS (1998) Minerals Yearbook: Titanium Annual Report
1997. U.S. Geological Survey, Reston, VA.
USGS (1997) Minerals Yearbook: Titanium Annual Report
1996. U.S. Geological Survey, Reston, VA.
USGS (1996) Minerals Yearbook: Titanium Annual Report
1995. U.S. Geological Survey, Reston, VA.
USGS (1995) Minerals Yearbook: Titanium Annual Report
1994. U.S. Geological Survey, Reston, VA.
USGS (1994) Minerals Yearbook: Titanium Annual Report
1993. U.S. Geological Survey, Reston, VA.
USGS (1993) Minerals Yearbook: Titanium Annual Report
1992. U.S. Geological Survey, Reston, VA.
USGS (1992) Minerals Yearbook: Titanium Annual Report
1991. U.S. Geological Survey, Reston, VA.
USGS (1991) Minerals Yearbook: Titanium Annual Report
1990. U.S. Geological Survey, Reston, VA.
Phosphoric Acid
USGS (2003). Electronic mail from Mr. Stephen M
Jasinski, USGS Commodity Specialist, Phosphate Rock,
[sjasinsk@usgs.gov] to Mr. Robert Lanza, ICF Consulting,
July 30, 2003.
References 11-15
-------
USGS (2003a). Electronic mail from Mr. Stephen M
Jasinski, USGS Commodity Specialist, Phosphate Rock,
[sjasinsk@usgs.gov] to Mr. Robert Lanza, ICF Consulting,
August 11,2003.
USGS (2002). Minerals Yearbook. Phosphate Rock Annual
Report 2001. U.S. Geological Survey, Reston, VA.
USGS (2001). Minerals Yearbook. Phosphate Rock Annual
Report 2000. U.S. Geological Survey, Reston, VA.
USGS (2000). Minerals Yearbook. Phosphate Rock Annual
Report 1999. U.S. Geological Survey, Reston, VA.
USGS (1999). Minerals Yearbook. Phosphate Rock Annual
Report 1998. U.S. Geological Survey, Reston, VA.
USGS (1998). Minerals Yearbook. Phosphate Rock Annual
Report 1997. U.S. Geological Survey, Reston, VA.
USGS (1997). Minerals Yearbook. Phosphate Rock Annual
Report 1996. U.S. Geological Survey, Reston, VA.
USGS (1996). Minerals Yearbook. Phosphate Rock Annual
Report 1995. U.S. Geological Survey, Reston, VA.
USGS (1995). Minerals Yearbook. Phosphate Rock Annual
Report 1994. U.S. Geological Survey, Reston, VA.
EFMA (2000).European Fertilizer Manufacturers
Association Best Available Techniques for Pollution
Prevention and Control in the European Fertilizer Industry
-- Booklet No. 4 of 8: Production of Phosphoric Acid.
Available online at
FIPR (2003). Florida Institute of Phosphate Research,
Analyses of Some Phosphate Rocks, facsimile from Mr.
Gary Albarelli, FIPR, Bartow, Florida, to Mr. Robert
Lanza, ICF Consulting, July 29, 2003
FIPR (2003a). Florida Institute of Phosphate Research,
personal communication of Mr. Michael Lloyd,
Laboratory Manager, FIPR, Bartow, Florida, to Mr. Robert
Lanza, ICF Consulting, August 2003.
Ferroalloy Production
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
Onder, H, and E.A. Bagdoyan (1993) Everything You've
Always Wanted to Know about Petroleum Coke. Allis
Mineral Systems.
USGS (2003) Mineral Yearbook: Silicon Annual Report
2002. U.S. Geological Survey, Reston, VA
USGS (2002) Mineral Yearbook: Silicon Annual Report
2001. U.S. Geological Survey, Reston, VA.
USGS (2001) Mineral Yearbook: Silicon Annual Report
2000. U.S. Geological Survey, Reston, VA.
USGS (2000) Mineral Yearbook: Silicon Annual Report
1999. U.S. Geological Survey, Reston, VA.
USGS (1999) Minerals Yearbook: Silicon Annual Report
1998. U.S. Geological Survey, Reston, VA.
USGS (1998) Minerals Yearbook: Silicon Annual Report
1997. U.S. Geological Survey, Reston, VA.
USGS (1997) Minerals Yearbook: Silicon Annual Report
1996. U.S. Geological Survey, Reston, VA.
USGS (1996) Minerals Yearbook: Silicon Annual Report
1995. U.S. Geological Survey, Reston, VA.
USGS (1995) Minerals Yearbook: Silicon Annual Report
1994. U.S. Geological Survey, Reston, VA.
USGS (1994) Silicon: Annual Report 1993. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC.
USGS (1993) Silicon: Annual Report 1992. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC.
USGS (1992) Silicon: Annual Report 1991. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC.
USGS (1991) Silicon: Annual Report 1990. U.S.
Geological Survey, U.S. Department of the Interior,
formerly Bureau of Mines. Washington, DC.
Carbon Dioxide Consumption
Denbury Resources Inc. (2002) Annual Report, 2002,
Page 14.
Denbury Resources Inc. (2002) Annual Report, 2001,
Page 22.
Broadhead, R. (2003) Electronic mail from Mr. Ron
Broadhead, New Mexico Bureau of Geology and Mineral
Resources [ron@gis.nmt.edu] to Ms. Robin Petrusak, ICF
Consulting, Septembers, 2003.
Sim, PH. (2001) Ammonia Shutdowns Drain CO2 Supply
and Boost Prices. Chemical Week. August 22, 2001.
U.S. Census Bureau (2002). Current Industrial Reports
Industrial Gases: 2002.
U.S. Census Bureau (2000). Current Industrial Reports
Industrial Gases: 2000.
U.S. Census Bureau (1998). Current Industrial Reports
Industrial Gases: 1998.
U.S. Census Bureau (1996). Current Industrial Reports
Industrial Gases: 1996.
U.S. Census Bureau (1994). Manufacturing Profile
Industrial Gases: 1994.
U.S. Census Bureau (1992). Current Industrial Reports
Industrial Gases: 1992. Data provided by Mr. Kevin
Woynes of the U.S. Census Bureau.
11-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Petrochemical Production
ACC (2003) Guide to the Business of Chemistry. American
Chemistry Council. Arlington, VA.
ACC (2002) Guide to the Business of Chemistry. American
Chemistry Council. Arlington, VA.
CMA (1999) U.S. Chemical Industry Statistical
Handbook. Chemical Manufacturer's Association.
Washington, DC.
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
Johnson, G. L. (2003) Personal communication between
Caren Mintz of ICE Consulting and Greg Johnson of
Liskow & Lewis, on behalf of the International Carbon
Black Association (ICBA). Data received in an email on
Novembers, 2003.
Silicon Carbide Production
IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
USGS (2003) Minerals Yearbook: Manufactured Abrasives
Annual Report 2002. U.S. Geological Survey, Reston, VA.
USGS (2002) Minerals Yearbook: Manufactured Abrasives
Annual Report 2001. U.S. Geological Survey, Reston, VA.
USGS (2001) Minerals Yearbook: Manufactured Abrasives
Annual Report 2000. U.S. Geological Survey, Reston, VA.
USGS (2000) Minerals Yearbook: Manufactured Abrasives
Annual Report 1999. U.S. Geological Survey, Reston, VA.
USGS (1999) Minerals Yearbook: Manufactured Abrasives
Annual Report 1998. U.S. Geological Survey, Reston, VA.
USGS (1998) Minerals Yearbook: Manufactured Abrasives
Annual Report 1997. U.S. Geological Survey, Reston, VA.
USGS (1997) Minerals Yearbook: Manufactured Abrasives
Annual Report 1996. U.S. Geological Survey, Reston, VA.
USGS (1996) Minerals Yearbook: Manufactured Abrasives
Annual Report 1995. U.S. Geological Survey, Reston, VA.
USGS (1995) Minerals Yearbook: Manufactured Abrasives
Annual Report 1994. U.S. Geological Survey, Reston, VA.
USGS (1994) Manufactured Abrasives: Annual Report
1993. U.S. Geological Survey, U.S. Department of the
Interior, formerly Bureau of Mines. Washington, DC.
USGS (1993) Manufactured Abrasives: Annual Report
1992. U.S. Geological Survey, U.S. Department of the
Interior, formerly Bureau of Mines. Washington, DC.
USGS (1992) Manufactured Abrasives: Annual Report
1991. U.S. Geological Survey, U.S. Department of the
Interior, formerly Bureau of Mines. Washington, DC.
USGS (1991) Manufactured Abrasives: Annual Report
1990. U.S. Geological Survey, U.S. Department of the
Interior, formerly Bureau of Mines. Washington, DC.
Nitric Acid Production
C&EN (2003) "Facts and Figures in the Chemical Industry."
Chemical and Engineering News, July 27,2003, pg 56.
C&EN (2002) "Facts and Figures in the Chemical
Industry." Chemical and Engineering News, June 24,
2002, pg 62.
C&EN (2001) "Facts and Figures in the Chemical
Industry." Chemical and Engineering News, June 25,
2001,pg46.
Choe, J.S., P.J. Cook, and F.P. Petrocelli (1993)
"Developing N2O Abatement Technology for the Nitric
Acid Industry." Prepared for presentation at the 1993
ANPSG Conference. Air Products and Chemicals, Inc.,
Allentown, PA.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Inventories Porgramme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000, pg 3.35.
EPA (1997) Compilation of Air Pollutant Emission
Factors, AP-42, U.S. Environmental Protection Agency,
Office of Air Quality Planning and Standards, Research
Triangle Park, NC, October.
Adipic Acid Production
ACC (2003) "Adipic Acid Production." Table 3.12
- Production of the Top 100 Chemicals. American
Chemistry Council Guide to the Business of Chemistry,
August 2003.
C&EN (1995) "Production of Top 50 Chemicals Increased
Substantially in 1994." Chemical and Engineering News.
73(15): 17. April 10.
C&EN (1994) "Top 50 Chemicals Production Rose
Modestly Last Year." Chemical & Engineering News,
72(15): 13. April 11.
C&EN (1993) "Top 50 Chemicals Production Recovered
Last Year." Chemical & Engineering News, 71(15): 11.
April 12.
C&EN (1992) "Production of Top 50 Chemicals Stagnates
in 1991." Chemical and Engineering News, 70(15): 17.
April 13.
Childs, D. (2003). Personal communication between Dave
Childs of DuPont, USA and Duncan Rotherham of ICF
Consulting, USA. August 7, 2003.
References 11-17
-------
Childs, D. (2002). Personal communication between
Dave Childs of DuPont, USA and Laxmi Palreddy of ICF,
Consulting, USA. August 8, 2002.
CMR (2001) "Chemical Profile: Adipic Acid." Chemical
Market Reporter, July 16, 2001.
CMR (1998) "Chemical Profile: Adipic Acid." Chemical
Market Reporter, June 15, 1998.
CW (1999) "Product Focus: Adipic Acid/Adiponitrile."
Chemical Week, March 10, 1999, pg. 31.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Inventories Porgramme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000, pg 3.34.
Reimer, R. (1999). Personal communication between Ron
Reimer of DuPont, USA and Heike Mainhardt of ICF,
Consulting. May 19, 1999.
Reimer, R.A., C.S. Slaten, M. Seapan, T.A. Koch, and
V.G. Triner (1999) "Implementation of Technologies for
Abatement of N2O Emissions Associated with Adipic
Acid Manufacture." Presented at the Second International
Symposium on Non-CO2 Greenhouse Gases, September
8-10, 1999, Noordwijkerhout, the Netherlands.
Thiemens, M.H., and W.C. Trogler (1991) "Nylon
production; an unknown source of atmospheric nitrous
oxide." Science: 251:932-934.
Substitution of Ozone Depleting
Substances
IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories, Paris:
Intergovernmental Panel on Climate Change, United Nations
Environment Programme, Organization for Economic Co-
Operation and Development, International Energy Agency.
HCFC-22 Production
Rand, S., M. Branscome, and D. Ottinger (1999)
"Opportunities for the Reduction of HFC-23 Emissions
from the Production of HCFC-22." In: Proceedings from
the Joint IPCC/TEAP Expert Meeting On Options for the
Limitation of Emissions ofHFCs and PFCs. Petten, the
Netherlands, 26-28 May 1999.
ARAP (2003). Electronic mail communication between Sally
Rand, EPA, and Dave Stirpe, Executive Director, Alliance for
Responsible Atmospheric Policy. August 18,2003.
Electrical Transmission and Distribution
M. Maiss and CAM Brenninkmeijer (2000) "A reversed
trend in emissions of SF6 to the atmosphere?" Non-CO2
Greenhouse Gases: Scientific Understanding, Control, and
Implementation, Proceedings of the Second International
Symposium, Noordwijkerhout, The Netherlands, 8-10
September 1999, Kluwer Academic Publishers, 2000, p. 199.
O'Connell, P. F. Heil, J. Henriot, G. Mauthe, H. Morrison, L.
Neimeyer, M. Pittroff, R. Probst, J.P. Tailebois, (2002), SF6 in
the Electric Industry, Status 2000, Cigre, February 2002.
RAND (2002) Katie D. Smythe, RAND Environmental
Science and Policy Center, "Production and Distribution
of SF6 by End-Use Application," International Conference
on SF6 and the Environment: Emission Reduction
Strategies. San Diego, CA, November 21-22, 2002.
Aluminum Production
EPA (1993) Proceedings: Workshop on Atmospheric
Effects, Origins, and Options for Control of Two Potent
Greenhouse Gases: CF4 and C2F6, Sponsored by the
U.S. Environmental Protection Agency, Global Change
Division, Office of Air and Radiation, April 21-22.
Gariepy, B. and G. Dube (1992) 'Treating Aluminum with
Chlorine." U.S. Patent 5,145,514. Issued September 8,1992.
IAI (2000), Anode Effect Survey 1994-1997 and
Perfluorocarbon Compounds Emissions Survey 1990-
1997, International Aluminum Institute, London, United
Kingdom. 2000.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Gas Inventories Programme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
Ko, M.K.W., N.D. Sze, W.-C. Wang, G. Shia, A. Goldman,
FJ. Murcray, D.G. Murcray, and C.P. Rinsland (1993)
"Atmospheric Sulfur Hexafluoride: Sources, Sinks, and
Greenhouse Wanning." Journal of Geophysical Research,
98, 10499-10507.
MacNeal, J., T. Rack, and R. Corns (1990) "Process for
Degassing Aluminum Melts with Sulfur Hexafluoride."
U.S. Patent 4,959,101. Issued September 25, 1990.
Maiss, M. and C.A.M. Brenninkmeijer (1998)
"Atmospheric SF6: Trends, Sources and Prospects,"
Environmental Science and Technology, v. 32, n. 20, pp.
3077-3086.
Ten Eyck, N. and M. Lukens (1996) "Process for
Treating Molten Aluminum with Chlorine Gas and
Sulfur Hexafluoride to Remove Impurities." U.S. Patent
5,536,296. Issued July 16, 1996.
USGS (2003) Mineral Commodity Summaries. U.S.
Geological Survey, Reston, VA. January.
11-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
USGS (2002) Mineral Yearbook: Aluminum Annual
Report 2001. U.S. Geological Survey, Reston, VA.
USGS (2001) Minerals Yearbook: Aluminum Annual
Report 2000. U.S. Geological Survey, Reston, VA.
USGS (2000) Minerals Yearbook: Aluminum Annual
Report 1999. U.S. Geological Survey, Reston, VA.
USGS (1998) Minerals Yearbook: Aluminum Annual
Report 1997. U.S. Geological Survey, Reston, VA.
USGS (1995) Mineral Industry Surveys: Aluminum
Annual Review 1994. U.S. Geological Survey, U.S.
Department of the Interior, formerly Bureau of Mines.
Washington, DC. May.
Victor, D.G. and G.J. MacDonald (1998) "A Model for
Estimating Future Emissions of Sulfur Hexafluoride and
Perfluorcarbons." Interim Report for the International
Institute for Applied Systems Analysis (IIASA), July,
1998. Downloaded from the IIASA website , May 23, 2000.
Zurecki, Z. (1996) "Effect of Atmosphere Composition on
Homogenizing Al-Mg and Al-Li Alloys." Gas Interactions
in Nonferrous Metals Processing - Proceedings of the
1996 125th The Minerals, Metals & Materials Society
(TMS) Annual Meeting (Anaheim, CA, USA), pp. 77-93.
Semiconductor Manufacture
Burton, C.S., and R, Beizaie (2001) "EPA's PFC
Emissions Model (PEVM) v. 2.14: Description and
Documentation" prepared for Office of Global Programs,
U. S. Environmental Protection Agency, Washington, DC.
20001 November 2001.
Burton, C.S., and D. Lieberman (2003) "PFC Reduction/
Climate Partnership: Emission and Documentation
Trends," Draft Report, prepared for Office of Atmospheric
Programs, U. S. Environmental Protection Agency,
Washington, DC. 2001. August 2003.
International SEMATECH. International Technology
Roadmap: 2000 Update,
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Gas Inventories Programme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
Semiconductor Equipment and Materials International.
World Fab Watch, 2003 Edition.
Strategic Marketing Associates (2003) Personal
communication September 5, 2003 between C. S. Burton
and George Burns, President of Strategic Marketing
Associates, PO Box 1217, Santa Cruz, CA 95061.
VLSI Research, Inc. (2003) Document 327031, Volume
Dl.l, Table 2.2.2-1 - Worldwide Silicon Demand by
Wafer Size. May 2003. Available online at .
VLSI Research, Inc. (2003) Document 327028, Volume
Dl.l, Table 2.2.2-2 - Worldwide Silicon Demand by
Linewidth. May 2003. Available online at .
VLSI Research, Inc. (2003) Document 327029, Volume
Dl.l, Table 2.2.2-3 - Worldwide Silicon Demand by
Device Type. May 2003. Available online at .
VSLI Research, Inc. (2003) Personal communication
September 5, 2003 between C. S. Burton and Marta
Hernandez, Analyst at VLSI Research Inc., 1754
Technology Drive, Suite 117, San Jose, CA 95110.
Magnesium Production and Processing
Bartos S., J. Marks, R. Kantamaneni, and C. Laush (2003)
"Measured SF6 Emissions from Magnesium Die Casting
Operations," Magnesium Technology, 2003.
Gjestland, H. and D. Magers (1996) "Practical Usage
of Sulphur [Sulfur] Hexafluoride for Melt Protection in
the Magnesium Die Casting Industry," #13,1996 Annual
Conference Proceedings, Ube City, Japan, International
Magnesium Association.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Gas Inventories Programme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
RAND (2002) Katie D. Smythe, RAND Environmental
Science and Policy Center, "Production and Distribution
of SF6 by End-Use Application," International Conference
on SF6 and the Environment: Emission Reduction
Strategies. San Diego, CA, November 21-22).
USGS (2002). Minerals Yearbook: Magnesium Annual
Report 2001. U.S. Geological Survey, Reston, VA.
Avaiable online at .
USGS (2003). Personal communication with Deborah A.
Kramer. U.S. Geological Survey, Reston, VA. August, 2003.
Industrial Sources of Ambient
Air Pollutants
EPA (2003) E-mail correspondence containing preliminary
ambient air pollutant data between EPA OAP and EPA
OAQPS. December 22, 2003.
EPA (1997) Compilation of Air Pollutant Emission
Factors, AP-42, U.S. Environmental Protection Agency,
Office of Air Quality Planning and Standards, Research
Triangle Park, NC, October.
References 11-19
-------
Solvent and Other Product Use
Nitrous Oxide Product Usage
CGA (2002) "CGA/NWSA Nitrous Oxide Fact Sheet."
Compressed Gas Association. March 25, 2002. Available
online at .
Heydorn, B. (1997) "Nitrous Oxide - North America."
Chemical Economics Handbook, SRI Consulting. May 1997.
Kirt-Otthmer (1990) "Anesthetics." Kirk-Otthmer
Encyclopedia of Chemical Technology, Volume 2, pp.
781-782.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, National
Greenhouse Inventories Porgramme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
Tupman, M. (2002) Personal communication between
Martin Tupman of Airgas Nitrous Oxide and Laxmi
Palreddy of ICF Consulting, USA. July 3, 2002.
Tupman, M. (2003) Personal communication between
Martin Tupman of Airgas Nitrous Oxide and Daniel
Lieberman of ICF Consulting, USA. August 8, 2003.
Solvent Use
EPA (2003) E-mail correspondence containing preliminary
ambient air pollutant data between EPA OAP and EPA
OAQPS. December 22, 2003.
EPA (1997) Compilation of Air Pollutant Emission
Factors, AP-42, U.S. Environmental Protection Agency,
Office of Air Quality Planning and Standards, Research
Triangle Park, NC, October.
Agriculture
Enteric Fermentation
Becket, J.L. and J.W. Oltjen (1993) Estimation of the
water requirement for beef production in the United
States. Journal of Animal Science. 71:818-826.
Crutzen, P.J., I. Aselmann, and W. Seiler (1986). "Methane
Production by Domestic Animals, Wild Ruminants, Other
Herbivores, Fauna, and Humans." Tellus 386:271-284.
Donovan, K. (1999) Personal Communication between
Kacey Donovan of University of California, Davis and
Staff at ICF Consulting.
Donovan, K. and L. Baldwin (1999). Results of the
AAMOLLY model runs for the Enteric Fermentation
Model. University of California, Davis.
EPA (2000) Draft Enteric Fermentation Model
Documentation. U.S. Environmental Protection Agency,
Office of Air and Radiation, Washington, DC. June 13, 2000.
EPA (1993). Anthropogenic Methane Emissions in the
United States: Estimates for 1990, Report to Congress.
Office of Air and Radiation, U.S. Environmental
Protection Agency, Washington, DC.
FAO (2002). FAOSTAT Statistical Database. Food and
Agriculture Organization of the United Nations. Available
online at . Accessed June, 19, 2002.
Feedstuffs (1998). "Nutrient requirements for pregnant
replacement heifers." Feedstuffs, Reference Issue, p. 50.
IPCC (2000). Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories.
Chapter 4. IPCC National Greenhouse Gas Inventories
Programme Technical Support Unit, Kanagawa, Japan.
Data also available at .
IPCC/UNEP/OECD/IEA (1997). Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Cooperation and Development, International
Energy Agency.
Johnson, D. (2002). Personal Communication between
Don Johnson of Colorado State University, Fort Collins,
and ICF Consulting.
Johnson, D. (1999). Personal Communication between
Don Johnson of Colorado State University, Fort Collins,
and David Conneely of ICF Consulting.
NRC (1999). 1996 Beef NRC, Appendix Table 22.
National Research Council.
NRC (2000). Nutrient Requirements of Beef Cattle:
Seventh Revised Edition: Update 2000, Table 11-1,
Appendix Table 1. National Research Council.
USDA (2003a). Cattle, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
January 31, 2003. Data also available from .
USDA (2003b). Hogs and Pigs, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. June 27, 2003. Data also available from
.
USDA (2003c). Livestock Slaughter, U.S. Department
of Agriculture, National Agriculture Statistics Service,
Washington, DC. January 24 - June 20, 2003. Data also
available from .
USDA (2003d). Milk Production, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 14, 2003. Data also available
from .
11-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
USDA (2003e). Sheep and Goats, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. January 31, 2003. Data also available
from .
USDA (2003f). Cattle on Feed, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 14, 2003. Data also available
from .
USDA (2002a). Cattle, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
February 1, 2002. Data also available from .
USDA (2002b). Hogs and Pigs, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. June 28, 2002. Data also available from
.
USDA (2002c). Livestock Slaughter, U.S. Department
of Agriculture, National Agriculture Statistics Service,
Washington, DC. January 25 - June 21, 2002. Data also
available from .
USDA (2002d). Milk Production, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 15, 2002. Data also available
from .
USDA (2002e). Sheep and Goats, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 1, 2002. Data also available
from .
USDA (2002f). Cattle on Feed, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 15, 2002. Data also available
from .
USDA (2001a). Cattle, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
January 26, 2001. Data also available from .
USDA (2001 b). Hogs and Pigs, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. December 28, 2001. Data also available
from .
USDA (2001c). Livestock Slaughter, U.S. Department
of Agriculture, National Agriculture Statistics Service,
Washington, DC. January 19 - December 21, 2001. Data
also available from .
USDA (2001d). Milk Production, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 16, 2001. Data also available
from .
USDA (200le). Sheep and Goats, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. January 26, 2001. Data also available
from .
USDA (2001f). Cattle on Feed, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 16, 2001. Data also available
from .
USDA (2000a). Cattle, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
January 28, 2000. Data also available from .
USDA (2000b). Hogs and Pigs, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. December 28, 2000. Data also available
from.
USDA (2000c). Livestock Slaughter, U.S. Department
of Agriculture, National Agriculture Statistics Service,
Washington, DC. January 21 - December 22, 2000. Data
also available from .
USDA (2000d). Milk Production, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 16, 2000. Data also available
from .
USDA (2000e). Sheep and Goats, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. January 28. Data also available from
.
USDA (2000f). Cattle on Feed, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 18, 2000. Data also available
from .
USDA (1999a). Cattle, Final Estimates 1994-1998, U.S.
Department of Agriculture, National Agriculture Statistics
Service, Washington DC. 1999. Data also available from
.
USDA (1999b). Hogs and Pigs, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. December 28, 1999. Data also available
from .
USDA (1999c). Livestock Slaughter, U.S. Department
of Agriculture, National Agriculture Statistics Service,
Washington, DC. January 22 - December 23, 1999. Data
also available from .
USDA (1999d). Milk Cows and Milk Production - Final
Estimates 1993-1997, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
January 1999. Data also available from .
USDA (1999e). Sheep and Goats, Final Estimates 1994-
98, U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC, 1999. Data also
available from .
USDA (1998). Hogs and Pigs, Final Estimates 1993-97,
U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. Data also available
from .
References 11-21
-------
USDA (1996). Beef Cow/Calf Health and Productivity
Audit (CHAPA): Forage Analyses from Cow/Calf Herds
in 18 States, National Animal Health Monitoring System,
Washington DC. March 1996. Data also available from
.
USDA (1995a). Cattle, Final Estimates 1989-93, U.S.
Department of Agriculture, National Agriculture Statistics
Service, Washington, DC. January. Data also available
from.
USDA (1995b). Dairy Outlook, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 27. Data also available from
.
USDA (1994a). Hogs and Pigs, Final Estimates 1988-
92, U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. December. Data also
available from .
USDA (1994b). Sheep and Goats, Final Estimates 1988-
93, U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. January 31. Data also
available from .
USDA: APHIS :VS (1998) Beef '97, National Animal Health
Monitoring System, Fort Collins, CO. 1998. Data also
available from .
USDA:APHIS:VS (1994) Beef Cow/CalfHealth and
Productivity Audit. National Animal Health Monitoring
System, Fort Collins, CO. Data also available from .
USDA:APHIS:VS (1993) Beef Cow/Calf Health and
Productivity Audit. National Animal Health Monitoring
System, Fort Collins, CO. August. Data also available
from .
Western Dairyman (1998). "How Big Should Heifers Be at
Calving?" The Western Dairyman, Sept. 1998, p. 12.
Manure Management
Anderson, S. (2000) Telephone conversation between
Lee-Ann Tracy of ERG and Steve Anderson, Agricultural
Statistician, U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC. 31 May.
ASAE (1999) ASAE Standards 1999, 46th Edition,
American Society of Agricultural Engineers, St. Joseph, MI.
Bryant, M.P., V.H. Varel, R.A. Frobish, and H.R. Isaacson
(1976) In: H.G. Schlegel (ed.). Seminar on Microbial
Energy Conversion. E. Goltz KG. Gottingen, Germany.
347 pp.
Deal, P. (2000) Telephone conversation between Lee-Ann
Tracy of ERG and Peter B. Deal, Rangeland Management
Specialist, Florida Natural Resource Conservation Service,
21 June.
EPA (200la) Cost Methodology Report for Beef and Dairy
Animal Feeding Operations. EPA-821-R-01-019, January.
EPA (200 Ib) Development Document for the Proposed
Revisions to the National Pollutant Discharge Elimination
System Regulation and the Effluent Guidelines for
Concentrated Animal Feeding Operations EPA-821-R-01-
003, January.
EPA (2000) AgSTAR Digest, U.S. Environmental
Protection Agency, Office of Air and Radiation. Spring.
EPA (1993) Anthropogenic Methane Emissions in the
United States: Estimates for 1990, Report to Congres,
U.S. Environmental Protection Agency, Office of Air and
Radiation. April.
EPA (1992) Global Methane Emissions from Livestock
and Poultry Manure, U.S. Environmental Protection
Agency, Office of Air and Radiation, February.
ERG (2003) Methodology for Estimating Uncertainty for
Manure Management Greenhouse Gas Inventory. Contract
No. GS-10F-0036, Task Order 005. Memorandum to EPA
from ERG. September 26, 2003.
ERG (2001) Summary of development of MDP Factor for
methane conversion factor calculations. September 2001.
ERG (2000a) Calculations: Percent Distribution of
Manure for Waste Management Systems. August 2000.
ERG (2000b) Summary of B0 Literature Review. June 2000.
FAO (2003) Yearly U.S. total horse population data from the
Food and Agriculture Organization of the United Nations
database, . Accessed June 2003.
Groffman, P.M., R. Brumme, K. Butterbach-Bahl, K.E.
Dobbie, A.R. Mosier, D. Ojima, H. Papen, W.J. Parton,
K.A. Smith, and C. Wagner-Riddle. (2000) "Evaluating
annual nitrous oxide fluxes at the ecosystem scale." Global
Biogeochemcial Cycles, 14(4): 1061-1070.
Hashimoto, A.G. (1984) "Methane from Swine Manure:
Effect of Temperature and Influent Substrate Composition
on Kinetic Parameter (k)." Agricultural Wastes. 9:299-308.
Hashimoto, A.G., V.H. Varel, and Y.R. Chen (1981)
"Ultimate Methane Yield from Beef Cattle Manure; Effect
of Temperature, Ration Constituents, Antibiotics and
Manure Age." Agricultural Wastes. 3:241-256.
Hill, D.T. (1984) "Methane Productivity of the Major
Animal Types." Transactions of the ASAE. 27(2):530-540.
Hill, D.T. (1982) "Design of Digestion Systems for
Maximum Methane Production." Transactions of the
ASAE. 25(1):226-230.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change, NGGIP.
Chapter 4, Agriculture.
Johnson, D. (2000) Telephone conversation between
Lee-Ann Tracy of ERG and Dan Johnson, State Water
Management Engineer, California Natural Resource
Conservation Service, 23 June.
11-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Lange, J. (2000) Telephone conversation between
Lee-Ann Tracy of ERG and John Lange, Agricultural
Statistician, U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC. 8 May.
Martin, J. (2000) "A Comparison of the Performance
of Three Swine Waste Stabilization Systems," paper
submitted to Eastern Research Group, Inc. October, 2000.
Miller, P. (2000) Telephone conversation between
Lee-Ann Tracy of ERG and Paul Miller, Iowa Natural
Resource Conservation Service, June 12, 2000.
Milton, B. (2000) Telephone conversation between Lee-
Ann Tracy of ERG and Bob Milton, Chief of Livestock
Branch, U.S. Department of Agriculture, National
Agriculture Statistics Service, May 1, 2000.
Morris, G.R. (1976) Anaerobic Fermentation of Animal
Wastes: A Kinetic and Empirical Design Fermentation.
M.S. Thesis. Cornell University.
NOAA (2003) National Oceanic and Atmospheric
Administration (NOAA), National Climate Data Center
(NCDC) Downloaded "O106.tmp" on July 27, 2003 from
(for all states
except Alaska and Hawaii); downloaded "all-1994.tar",
"all-1995.tar", "all-1996.tar", "all-1997.tar", "all-1998.
tar", and "all-1999.tar" in April 2000 and "all-2000.tar"
in July 2001 from (for Alaska and Hawaii).
Peterson, K., and H. Jacobs (2003) 1990-2002
Vaolatile Solids and Nitrogen Excretion Rates Deliverable
Under EPA Contract No. GS-10F-0124J, Task Order 004-
02. Memorandum to EPA from ICF Consulting. August
28, 2003.
Peterson, K., J. King, and D, Johnson (2002) Methodology
and Results for Revised Diet Characterizatoin Analysis
Deliverable under EPA contract no. 68-W7-0069, task
order 505-01. Memorandum to EPA from ICF Consulting.
July 31,2002.
Poe, G., N. Bills, B. Bellows, P. Crosscombe, R. Koelsch,
M. Kreher, and P. Wright (1999) Staff Paper Documenting
the Status of Dairy Manure Management in New
York: Current Practices and Willingness to Participate
in Voluntary Programs, Department of Agricultural,
Resource, and Managerial Economics, Cornell University,
Ithaca, New York, September.
Safley, L.M., Jr. and P.W. Westerman (1992) "Performance
of a Low Temperature Lagoon Digester." Biological
Wastes. 9060-8524/92/S05.00.
Safley, L.M., Jr. and P.W. Westerman (1990)
"Psychrophilic Anaerobic Digestion of Animal Manure:
Proposed Design Methodology." Biological Wastes.
34:133-148.
Safley, L.M., Jr. and P.W. Westerman (1989) "Anaerobic
Lagoon Biogas Recovery Systems." Biological Wastes.
27:43-62.
Safley, L.M., Jr. (2000) Telephone conversation between
Deb Bartrain of ERG and L.M. Safley, President, Agri-
Waste Technology, June and October.
Stettler, D. (2000) Telephone conversation between
Lee-Ann Tracy of ERG and Don Stettler, Environmental
Engineer, National Climate Center, Oregon Natural
Resource Conservation Service, 27 June.
Summers, R. and S. Bousfield (1980) "A Detailed Study of
Piggery-waste Anaerobic Digestion." Agricultural Wastes.
2:61-78.
Sweeten, J. (2000) Telephone conversation between Indra
Mitra of ERG and John Sweeten, Texas A&M University,
June 2000.
UEP (1999) Voluntary Survey Results - Estimated
Percentage Participation/Activity, Caged Layer
Environmental Management Practices, Industry data
submissions for EPA profile development, United Egg
Producers and National Chicken Council. Received from
John Thorne, Capitolink. June 2000.
USDA (2003a) Cattle, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
January 31, 2003. Data also available from .
USDA (2003b) Cattle on Feed Cattle, U.S. Department
of Agriculture, National Agriculture Statistics Service,
Washington, DC. January 17, 2003. Data also available
from .
USDA (2003c) Hogs and Pig, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. March 28, 2003. Data also available
from .
USDA (2003d) Chicken and Eggs Annual Summary, U.S.
Department of Agriculture, National Agriculture Statistics
Service, Washington, DC. January 30, 2003. Data also
available from .
USDA (2003e) Poultry Production and Value Annual
Summary, U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC. April
29, 2003, revised May 3, 2003. Data also available from
.
USDA (2003f) Sheep and Goats, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. January 31, 2003. Data also available
from .
USDA (2002a) Cattle, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
February 1, 2002. Data also available from .
USDA (2002b) Cattle on Feed Cattle, U.S. Department
of Agriculture, National Agriculture Statistics Service,
Washington, DC. January 18, 2002. Data also available
from .
References 11-23
-------
USDA (2002c) Hogs and Pig, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. March 28, 2002. Data also available
from .
USDA (2002d) Chicken and Eggs Annual Summary, U.S.
Department of Agriculture, National Agriculture Statistics
Service, Washington, DC. January 29, 2002, revised
March 22, 2002. Data also available from .
USDA (2002e) Poultry Production and Value Annual
Summary, U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC. April
29, 2002, revised May 3, 2002. Data also available from
.
USDA (2002f) Sheep and Goats, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. February 1, 2002. Data also available
from .
USDA (2001a) Cattle, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
January 26, 2001. Data also available from .
USDA (2001b) Cattle on Feed Cattle, U.S. Department
of Agriculture, National Agriculture Statistics Service,
Washington, DC. January 19, 2001. Data also available
from .
USDA (2001c) Hogs and Pig, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. March 30, 2001. Data also available
from .
USDA (2001d) Chicken and Eggs - 1999 Summary Cattle,
U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. January.
USDA (2001e) Poultry Production and Value - 1999
Summary, U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC. April.
USDA (200If) Sheep and Goats, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. January. Data also available from
.
USDA (2001g) Published Estimates Database, U.S.
Department of Agriculture, National Agricultural Statistics
Service, Washington, DC. Downloaded from , September 26, 2001.
USDA (2000a) Cattle, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
January 28, 2000. Data also available from .
USDA (2000b) Cattle on Feed Cattle, U.S. Department
of Agriculture, National Agriculture Statistics Service,
Washington, DC. April 14, 2000. Data also available from
.
USDA (2000c) Hogs and Pig, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. March 24, 2000. Data also available
from .
USDA (2000d) Chicken and Eggs -1999 Summary Cattle,
U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. January.
USDA (2000e) Poultry Production and Value -1999
Summary, U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC. April.
USDA (2000f) Sheep and Goats, U.S. Department of
Agriculture, National Agriculture Statistics Service,
Washington, DC. January. Data also available from
.
USDA (2000g) Chicken and Eggs - Final Estimates
1988-1993, U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC.
Downloaded from , May 3, 2000.
USDA (2000h) Re-aggregated data from the National
Animal Health Monitoring System's (NAHMS) Dairy '96
study provided by Stephen L. Ott of the U.S. Department
of Agriculture, Animal and Plant Health Inspection
Service. June 19.
USDA (2000i) Layers '99 - Pan II: References of
1999 Table Egg Layer Management in the U.S., U.S.
Department of Agriculture, Animal and Plant Health
Inspection Service (APHIS), National Animal Health
Monitoring System (NAHMS). January.
USDA (1999a) Cattle - Final Estimates 1994-98, U.S.
Department of Agriculture, National Agriculture Statistics
Service, Washington, DC. January. Data also available
from.
USDA (1999b) Poultry Production and Value - Final
Estimates 1994-97, U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC. March.
USDA (1999c) Sheep and Goats - Final Estimates
1994-1998, U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC. January.
USDA (1999d). Miscellaneous Livestock and Animal
Specialties Inventory and Sales: 1997 and 1992, Table
25, U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. Accessed May 2000
.
USDA (1999e) 1992 and 1997 Census of Agriculture
(CD-ROM), U.S. Department of Agriculture, National
Agriculture Statistics Service, Washington, DC.
USDA (1998a) Hogs and Pigs - Final Estimates 1993-
97, U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. December. Data also
available from .
11-24 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
USDA (1998b) Chicken and Eggs - Final Estimates 1994-
97, U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. December.
USDA (1998c) Nutrients Available from Livestock
Manure Relative to Crop Growth Requirements, Resource
Assessment and Strategic Planning Working Paper 98-
1, U.S. Department of Agriculture, Natural Resources
Conservation Service. February.
USDA (1998d) Re-aggregated data from the National
Animal Health Monitoring System's (NAHMS) Swine '95
study aggregated by Eric Bush of the U.S. Department of
Agriculture, Centers for Epidemiology and Animal Health.
USDA (1996a) Agricultural Waste Management Field
Handbook, National Engineering Handbook (NEH), Part
651, U.S. Department of Agriculture, Natural Resources
Conservation Service. July.
USDA (1996b) Swine '95: Grower/Finisher Part II:
Reference of 1995 U.S. Grower/Finisher Health &
Management Practices, U.S. Department of Agriculture,
Animal Plant Health and Inspection Service, Washington,
DC. June.
USDA (1995a) Cattle - Final Estimates 1989-93, U.S.
Department of Agriculture, National Agriculture Statistics
Service, Washington, DC. January. Data also available
from .
USDA (1995b) Poultry Production and Value - Final
Estimates 1989-1993, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
January.
USDA (1994a) Hogs and Pigs - Final Estimates 1988-
92, U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. December. Data also
available from .
USDA (1994b) Sheep and Goats - Final Estimates 1989-
1993, U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. January 31, 1994.
Wright, P. (2000) Telephone conversation between Lee-
Ann Tracy of ERG and Peter Wright, Cornell University,
College of Agriculture and Life Sciences, June 23, 2000.
Rice Cultivation
Bollich, P. (2000) Telephone conversation between Payton
Decks of ICF Consulting and Pat Bollich, Professor with
Louisiana State University Agriculture Center. May 17, 2000.
Bossio, D.A., W. Horwath, R.G. Mutters, and C. van
Kessel (1999) "Methane pool and flux dynamics in a rice
field following straw incorporation." Soil Biology and
Biochemistry 31:1313-1322.
Cicerone R.J., C.C. Delwiche, S.C. Tyler, and P.R.
Zimmerman (1992) "Methane Emissions from
California Rice Paddies with Varied Treatments." Global
Biogeochemical Cycles 6:233-248.
Deren, C. (2002) Telephone conversation between
Caren Mintz and Dr. Chris Deren, Everglades Research
and Education Centre at the University of Florida. August
15,2002.
Guethle, D. (2003) Telephone conversation between Caren
Mintz of ICF Consulting and David Guethle, Agronomy
Specialist, Missouri Cooperative Extension Service. June
19, 2003.
Guethle, D. (2002) Telephone conversation between Caren
Mintz of ICF Consulting and David Guethle, Agronomy
Specialist, Missouri Cooperative Extension Service.
August 19, 2002.
Guethle, D. (2001) Telephone conversation between Caren
Mintz of ICF Consulting and David Guethle, Agronomy
Specialist at Missouri Cooperative Extension Service.
September 4, 2001.
Holzapfel-Pschorn, A., R. Conrad, and W. Seller (1985)
"Production, Oxidation, and Emissions of Methane in Rice
Paddies." FEMS Microbiology Ecology 31:343-351.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories.
IPCC National Greenhouse Gas Inventories Programme
Technical Support Unit, Kanagawa, Japan. Available online
at .
IPCC/UNEP/OECD/ffiA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories. Paris:
Intergovernmental Panel on Climate Change, United Nations
Environment Programme, Organization for Economic Co-
Operation and Development, International Energy Agency.
Kirstein, A. (2003) Telephone conversation between Caren
Mintz of ICF Consulting and Arthur Kirstein, Coordinator,
Agricultural Economic Development Program, Palm Beach
County Cooperative Extension Service, FL. August 13, 2003.
Klosterboer, A. (2003) Telephone conversation between
Caren Mintz of ICF Consulting and Arlen Klosterboer, retired
Extension Agronomist, Texas A&M University. July 7, 2003.
Klosterboer, A. (2002) Telephone conversation
between Caren Mintz of ICF Consulting and Arlen
Klosterboer, Extension Agronomist, Texas A&M University.
August 19, 2002.
Klosterboer, A. (200la) Telephone conversation between
Caren Mintz of ICF Consulting and Arlen Klosterboer,
Extension Agronomist, Texas A&M University. August
6,2001.
Klosterboer, A. (200 Ib) Telephone conversation between
Caren Mintz of ICF Consulting and Arlen Klosterboer,
Extension Agronomist, Texas A&M University. October
8,2001.
Klosterboer, A. (2000) Telephone conversation
between Payton Decks of ICF Consulting and Arlen
Klosterboer, Extension Agronomist, Texas A&M
University. May 18,2000.
References 11-25
-------
Klosterboer, A. (1999) Telephone conversation between
Catherine Leining of ICF Consulting and Arlen
Klosterboer, Extension Agronomist, Texas A & M
University. June 10, 1999.
Klosterboer, A. (1997) Telephone conversation between
Holly Simpkins of ICF Incorporated and Arlen
Klosterboer, Texas A & M University. December 1, 1997.
Lee, D. (2003) Telephone conversation and email
correspondence between Caren Mintz of ICF Consulting
and Danny Lee, OK Farm Service Agency, Stillwater, OK.
July 2, 2003.
Lindau, C.W. and P.K. Bollich (1993) "Methane
Emissions from Louisiana First and Ratoon Crop Rice."
Soil Science 156:42-48.
Lindau, C.W., P.K Bollich, and R.D. DeLaune
(1995) "Effect of Rice Variety on Methane Emission
from Louisiana Rice." Agriculture, Ecosystems and
Environment 54:109-114.
Linscombe, S. (2003) Telephone conversation between
Caren Mintz of ICF Consulting and Steve Linscombe,
Professor with the Rice Research Station at Louisiana
State University Agriculture Center. June 10, 2003.
Linscombe, S. (2002) Telephone conversation between
Caren Mintz of ICF Consulting and Steve Linscombe,
Professor with the Rice Research Station at Louisiana
State University Agriculture Center. August 21, 2002.
Linscombe, S. (2001a) Telephone conversation between
Caren Mintz of ICF Consulting and Steve Linscombe,
Research Agronomist, Rice Research Station in Crowley,
LA. July 30-August 1, 2001.
Linscombe, S. (2001b) Email correspondence between
Caren Mintz of ICF Consulting and Steve Linscombe,
Research Agronomist, Rice Research Station in Crowley,
LA. October 4, 2001.
Linscombe, S. (1999a) Telephone conversation between
Catherine Leining of ICF Consulting and Steve
Linscombe, Research Agronomist, Rice Research Station
in Crowley, LA. June 3, 1999.
Linscombe, S. (1999b) Telephone conversation between
Payton Decks of ICF Consulting and Steve Linscombe,
Research Agronomist, Rice Research Station in Crowley,
LA. August 9, 1999.
Mayhew, W. (1997) Telephone conversation between
Holly Simpkins of ICF Incorporated and Walter Mayhew,
University of Arkansas, Little Rock. November 24, 1997.
Mutters, C. (2003) Telephone conversation between Caren
Mintz of ICF Consulting and Mr. Cass Mutters, Rice Farm
Advisor for Butte, Glen, and Tehama Counties. University
of California Cooperative Extension Service. June 23, 2003.
Mutters, C. (2002) Telephone conversation between Caren
Mintz of ICF Consulting and Mr. Cass Mutters, Rice Farm
Advisor for Butte, Glen, and Tehama Counties. University of
California Cooperative Extension Service. August 27,2002.
Mutters, C. (2001) Telephone conversation between
Caren Mintz of ICF Consulting and Cass Mutters, Rice
Farm Advisor for Butte, Glen, and Tehama Counties,
University of California Cooperative Extension Service.
Septembers, 2001.
Saichuk, J. (1997) Telephone conversation between
Holly Simpkins of ICF Incorporated and John Saichuk,
Louisiana State University. November 24, 1997.
Sass, R.L., F.M Fisher, P.A. Harcombe, and F.T. Turner
(199la) "Mitigation of Methane Emissions from Rice
Fields: Possible Adverse Effects of Incorporated Rice
Straw." Global Biogeochemical Cycles 5:275-287.
Sass, R.L., F.M. Fisher, F.T. Turner, and M.F. Jund (1991b)
"Methane Emissions from Rice Fields as Influenced by
Solar Radiation, Temperature, and Straw Incorporation."
Global Biogeochemical Cycles 5:335-350.
Sass, R.L., F.M. Fisher, P.A. Harcombe, and F.T. Turner
(1990) "Methane Production and Emissions in a Texas
Rice Field." Global Biogeochemical Cycles 4:47-68.
Sass, R.L., F.M. Fisher, and Y.B. Wang (1992) "Methane
Emission from Rice Fields: The Effect of Floodwater
Management." Global Biogeochemical Cycles 6:249-262.
Schueneman, T. (200la) Telephone conversation between
Caren Mintz of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida.
July 30, 2001.
Schueneman, T. (2001 b) Telephone conversation between
Caren Mintz of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida.
October 9, 2001.
Schueneman, T. (2000) Telephone conversation between
Payton Decks of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida.
May 16, 2000.
Schueneman, T. (1999a) Telephone conversation
between Catherine Leining of ICF Consulting and Tom
Schueneman, Palm Beach County Agricultural Extension
Agent, Florida. June 7, 1999.
Schueneman, T. (1999b) Telephone conversation between
Payton Decks of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida.
August 10, 1999.
Schueneman, T. (1999c) Telephone conversation between
John Venezia of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida.
August 7, 1999.
Schueneman, T. (1997) Telephone conversation between
Barbara Braatz of ICF Incorporated and Tom Schueneman,
County Extension Agent, Florida. November 7, 1997.
Slaton, N. (200la) Telephone conversation between Caren
Mintz of ICF Consulting and Nathan Slaton, Extension
Agronomist - Rice, University of Arkansas Division of
Agriculture Cooperative Extension Service. August 23,2001.
11-26 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Slaton, N. (2001b) Telephone conversation between Caren
Mintz of ICF Consulting and Nathan Slaton, Extension
Agronomist - Rice, University of Arkansas Division of
Agriculture Cooperative Extension Service. October 3,2001.
Slaton, N. (2000) Telephone conversation between Payton
Deeks of ICF Consulting and Nathan Slaton, Extension
Agronomist - Rice, University of Arkansas Division of
Agriculture Cooperative Extension Service. May 20, 2000.
Slaton, N. (1999) Telephone conversation between
Catherine Leining of ICF Consulting and Nathan Slaton,
Extension Agronomist - Rice, University of Arkansas
Division of Agriculture Cooperative Extension Service.
June 3, 1999.
Stevens, G. (1997) Telephone conversation between
Holly Simpkins of ICF Incorporated and Gene Stevens,
Extension Specialist, Missouri Commercial Agriculture
Program, Delta Research Center. December 17, 1997.
Street, J. (2003) Telephone conversation and email
correspondence between Caren Mintz of ICF Consulting
and Joe Street, Rice Specialist, Mississippi State
University, Delta Research Center. June 19, 2003.
Street, J. (2002) Telephone conversation and email
correspondence between Caren Mintz of ICF Consulting
and Joe Street, Rice Specialist, Mississippi State
University, Delta Research Center. August 19, 2002.
Street, J. (2001) Telephone conversation between Caren
Mintz of ICF Consulting and Dr. Joe Street, Mississippi
State University, Delta Research and Extension Center and
Delta Branch Station. 3 October.
Street, J. (1997) Telephone conversation between
Holly Simpkins of ICF Incorporated and Dr. Joe Street,
Mississippi State University, Delta Research and
Extension Center and Delta Branch Station. 1 December.
USDA (2003) Crop Production 2002 Summary. National
Agricultural Statistics Service, U.S. Department of
Agriculture. Available online at . Accessed June 2003.
USDA (2002) Crop Production 2001 Summary. National
Agricultural Statistics Service, U.S. Department of
Agriculture. Available online at . Accessed June 2002.
USDA (2001) Crop Production 2000 Summary. National
Agricultural Statistics Service, U.S. Department of
Agriculture. Available online at . Accessed July 2001.
USDA (1998) Field Crops Final Estimates 1992-97.
Statistical Bulletin Number 947 a. National Agricultural
Statistics Service, U.S. Department of Agriculture.
Available at . Accessed
July 2001.
USDA (1994) Field Crops Final Estimates 1987-1992.
Statistical Bulletin Number 896. National Agricultural
Statistics Service, U.S. Department of Agriculture. Available
at . Accessed July 2001.
Wilson, C. (2003) Telephone conversation between Caren
Mintz of ICF Consulting and Dr. Chuck Wilson, Rice
Specialist at the University of Arkansas Cooperative
Extension Service. June 11, 2003.
Wilson, C. (2002) Telephone conversation between Caren
Mintz of ICF Consulting and Dr. Chuck Wilson, Rice
Specialist at the University of Arkansas Cooperative
Extension Service. August 23, 2002.
Agricultural Soil Management
AAPFCO (2003) Commercial Fertilizers 2002.
Association of American Plant Food Control Officials
and The Fertilizer Institute, University of Kentucky,
Lexington, KY.
AAPFCO (2002) Commercial Fertilizers 2001.
Association of American Plant Food Control Officials
and The Fertilizer Institute, University of Kentucky,
Lexington, KY.
AAPFCO (2000a) 1999-2000 Commercial Fertilizers
Data. ASCII files. Available: David Terry, Secretary,
AAPFCO.
AAPFCO (2000b) Commercial Fertilizers 2000.
Association of American Plant Food Control Officials,
University of Kentucky, Lexington, KY.
AAPFCO (1999) Commercial Fertilizers 1999.
Association of American Plant Food Control Officials,
University of Kentucky, Lexington, KY.
AAPFCO (1998) Commercial Fertilizers 1998.
Association of American Plant Food Control Officials,
University of Kentucky, Lexington, KY.
AAPFCO (1997) Commercial Fertilizers 1997.
Association of American Plant Food Control Officials,
University of Kentucky, Lexington, KY.
AAPFCO (1996) Commercial Fertilizers 1996.
Association of American Plant Food Control Officials,
University of Kentucky, Lexington, KY.
AAPFCO (1995) Commercial Fertilizers 1995.
Association of American Plant Food Control Officials,
University of Kentucky, Lexington, KY.
Anderson, S. (2000) Telephone conversation
between Lee-Ann Tracy of ERG and Steve Anderson,
Agricultural Statistician, U.S. Department of Agriculture,
National Agriculture Statistics Service, Washington, DC.
May 31,2000.
ASAE (1999) ASAE Standards 1999.46th Edition,
American Society of Agricultural Engineers, St. Joseph, MI.
References 11-27
-------
Barnard, G.W. and Kristoferson, L.A. (1985) Agricultural
Residues as Fuel in the Third World. Technical Report No.
5. Earthscan, London, UK.
Bastian, R. (2003) Telephone conversation between
Caren Mintz of ICF Consulting and Robert Bastian,
Office of Water, U.S. Environmental Protection Agency,
Washington, DC, August 13, 2003.
Bastian, R. (2002) Telephone conversation between
Caren Mintz of ICF Consulting and Robert Bastian,
Office of Water, U.S. Environmental Protection Agency,
Washington, DC, August 23, 2002.
Bastian, R. (2001) Telephone conversation between
Caren Mintz of ICF Consulting and Robert Bastian,
Office of Water, U.S. Environmental Protection Agency,
Washington, DC, September-October.
Bastian, R. (1999) Telephone conversation between
Marco Alcaraz of ICF Consulting and Robert Bastian,
Office of Water, U.S. Environmental Protection Agency,
Washington, DC, August.
Beuselinck, PR. and WF. Grant (1995) "Birdsfoot
Trefoil." In: Forages, Volume I: An Introduction to
Grassland Agriculture, Barnes, R.F., Miller, D.A., and
Nelson, C.J. (eds.), pp. 237-248, Iowa State University
Press, Ames, IA.
Brady, N.C. and R.R. Weil (1999) The Nature and
Properties of Soils. Prentice Hall, Upper Saddle River,
New Jersey, 881 pp.
Brandt, R. (2001) Telephone conversation between Caren
Mintz of ICF Consulting and Rhonda Brandt, Commodity
Specialist in the Crops Branch of the National Agricultural
Statistics Service, USDA.
Carpenter, G.H. (1992) "Current Litter Practices
and Future Needs." In: 7992 National Poultry Waste
Management Symposium Proceedings, Blake, J.P., Donald,
J.O., and Patterson, P.H. (eds.), pp. 268-273, Auburn
University Printing Service, Auburn, AL.
Cropper, J. (2000) Telephone Conversation between
Payton Decks of ICF Consulting and Jim Cropper, Natural
Resource Conservation Service, Pennsylvania, May 24,
June 6, and June 13,2000.
Daly, C, G.H. Taylor, W.P. Gibson, T. Parzybok, G.L.
Johnson, and PA. Pasteris (1998) "Development of high-
quality spatial datasets for the United States." in: Proc.,
1st International Conference on Geospatial Information in
Agriculture and Forestry, Lake Buena Vista, FL. June 1-3,
1998, pp.I-512-1-519.
Daly, C., R.P. Neilson, and D.L. Phillips (1994) "A
statistical-topographic model for mapping climatological
precipitation over mountainous terrain." Journal of
Applied Meteorology, 3 3:140-15 8.
Deal, P. (2000) Telephone conversation between Lee-Ann
Tracy of ERG and Peter B. Deal, Rangeland Management
Specialist, Florida Natural Resource Conservation Service,
June 21,2000.
Del Grosso, S.J., W.J. Parton, A.R. Mosier, M.D. Hartman,
J. Brenner., D.S. Ojima, and D.S. Schimel (2001)
"Simulated interaction of carbon dynamics and nitrogen
trace gas fluxes using the DAYCENT model." In M.
Schaffer, L. Ma, & S. Hansen (eds.), Modeling Carbon
and Nitrogen Dynamics for Soil Management: 303-332.
Boca Raton, Florida: CRC Press.
Deren, C. (2002). Telephone conversation between
Caren Mintz and Dr. Chris Deren, Everglades Research
and Education Centre at the University of Florida. August
15,2002.
EPA (1999) Biosolids Generation, Use and Disposal in the
United States. Office of Solid Waste, U.S. Environmental
Protection Agency. Available online at .
EPA (1993) Federal Register. Part II. Standards for the
Use and Disposal of Sewage Sludge; Final Rules. U.S.
Environmental Protection Agency, 40 CFR Parts 257, 403
and 503.
Eve, M. (2001) E-mail from Marlen Eve of the Natural
Resources Ecology Laboratory to Barbara Braatz and
Caren Mintz of ICF Consulting, containing statistics on
U.S. histosol areas cultivated in 1982, 1992, and 1997,
which were extracted from the 1997 National Resources
Inventory, September .21, 2001
Evers, G.W. (2000) Telephone and E-mail Conversation
between Barbara Braatz of ICF Consulting and Gerald W.
Evers, Texas Agricultural Experiment Center, Texas A&M
University, July 7 and July 10, 2000.
FAO (2003) Yearly U.S. total horse population data from the
Food and Agriculture Organization of the United Nations
database, Accessed July 2003.
Gerrish, J. (2000) Telephone Conversation between
Barbara Braatz of ICF Consulting and Dr. Jim Gerrish,
Forage Systems Research Center, University of Missouri,
July 7, 2000.
Hoveland, C.S. (2000) Telephone Conversation
between Barbara Braatz of ICF Consulting and Carl
S. Hoveland, Department of Agronomy, University of
Georgia, July 7, 2000.
Hoveland, C.S. and G.W. Evers (1995) "Arrowleaf,
Crimson, and Other Annual Clovers." In: Forages, Volume
I: An Introduction to Grassland Agriculture, Barnes, R.F.,
Miller, D.A., and Nelson, C.J. (eds.), pp. 249-260, Iowa
State University Press, Ames, IA.
11-28 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories.
IPCC National Greenhouse Gas Inventories Programme
Technical Support Unit, Kanagawa, Japan. Available online
at .
IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
Johnson, D. (2000) Telephone conversation between
Lee-Ann Tracy of ERG and Dan Johnson, State Water
Management Engineer, California Natural Resource
Conservation Service, June 23, 2000.
Karkosh, R. (2000) Telephone conversation between
Barbara Braatz of ICF Consulting and Roy Karkosh,
Crops Branch, National Agricultural Statistics Service,
U.S. Department of Agriculture, July 17, 2000.
Ketzis, J. (1999) Telephone and Email conversations
between Marco Alcaraz of ICF Consulting and Jen Ketzis
regarding the Animal Science Department Computer
Model (Cornell Net Carbohydrate and Protein System),
Cornell University, June/July.
Kirstein, A. (2003) Telephone conversation between Caren
Mintz of ICF Consulting and Arthur Kirstein, Coordinator,
Agricultural Economic Development Program, Palm
Beach County Cooperative Extension Service, FL, August
13,2003.
Lange, J. (2000) Telephone conversation between Lee-Ann
Tracy of ERG and John Lange, Agricultural Statistician,
U. S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC, May 8, 2000.
Lee, D. (2003) Telephone coversation and email
correspondence between Caren Mintz of ICF Consulting
and Danny Lee, Farm Service Agency, Stillwater, OK,
July-August.
Metcalf and Eddy, Inc. (1991) Wastewater Engineering:
Treatment, Disposal, and Reuse, Third Edition, McGraw-
Hill Publishing Company, NY.
Miller, P. (2000) Telephone conversation between
Lee-Ann Tracy of ERG and Paul Miller, Iowa Natural
Resource Conservation Service, June 12, 2000.
Milton, B. (2000) Telephone conversation between Lee-
Ann Tracy of ERG and Bob Milton, Chief of Livestock
Branch, U.S. Department of Agriculture, National
Agriculture Statistics Service, May 1, 2000.
Nevison, C. (2000) "Review of the IPCC methodology
for estimating nitrous oxide emissions associated with
agricultural leaching and runoff." Chemosphere-Global
Change Science 2:493-500.
Ogle, S. (2002) E-mail from Stephen Ogle of the Natural
Resources Ecology Laboratory to Barbara Braatz of ICF
Consulting, containing revised statistics on U.S. histosol
areas cultivated in 1982, 1992, and 1997, which were
extracted from the 7997 National Resources Inventory by
Marlen Eve, January 9, 2002.
Parton, W.J., M.D. Hartman, D.S. Ojima, and D.S. Schimel
(1998) "DAYCENT: Its land surface submodel: description
and testing." Global Planetary Change 19:35-48.
Pederson, G.A. (2000) Telephone conversation between
Barbara Braatz of ICF Consulting and Dr. Gary A.
Pederson, Department of Agronomy, Mississippi State
University, July 24 and 25, 2000.
Pederson, G.A. (1995) "White Clover and Other Perennial
Clovers." In: Forages, Volume I: An Introduction to
Grassland Agriculture, Barnes, R.F., Miller, D.A., and
Nelson, C.J. (eds.), pp. 227-236, Iowa State University
Press, Ames, IA.
Poe, G., N. Bills, B. Bellows, P. Crosscombe, R. Koelsch,
M. Kreher, and P. Wright (1999) Documenting the Status
of Dairy Manure Management in New York: Current
Practices and Willingness to Participate in Voluntary
Programs. Staff Paper, Dept. of Agricultural, Resource,
and Managerial Economics, Cornell University, Ithaca,
NY, September.
Safley, L.M. (2000) Telephone conversation between Deb
Bartram of ERG and L.M. Safley, President, Agri-Waste
Technology, June.
Safley, L.M., M.E. Casada, J.W. Woodbury, and J.F. Roos
(1992) Global Methane Emissions from Livestock and
Poultry Manure. EPA/400/1-91/048, Office of Air and
Radiation, U.S. Environmental Protection Agency. February.
Schueneman, T. (2001) Telephone conversation between
Caren Mintz of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida,
July 30, 2001.
Schueneman, T. (1999) Telephone conversation between
Payton Decks of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida,
August 10, 1999.
Schueneman, T., and C. Deren (2002) "An Overview
of the Florida Rice Industry" SS-AGR-77, Agronomy
Department, Florida Cooperative Extension Service,
Institute of Food and Agricultural Sciences, University of
Florida. Revised November 2002.
Stettler, D. (2000) Telephone conversation between
Lee-Ann Tracy of ERG and Don Stettler, Environmental
Engineer, National Climate Center, Oregon Natural
Resource Conservation Service, June 27, 2000.
Strehler, A., and W. Stutzle (1987) "Biomass Residues".
In: Biomass, Hall, D.O. and Overend, R.P. (eds.), pp. 75-
102, John Wiley and Sons, Ltd. Chichester, UK.
References 11-29
-------
Sweeten, J. (2000) Telephone conversation between
Indra Mitra of ERG and John Sweeten, Texas A&M
University, June.
Taylor, N.L., and R.R. Smith (1995) "Red Clover."
In: Forages, Volume I: An Introduction to Grassland
Agriculture, Barnes, R.R, Miller, D.A., and Nelson, C.J.
(eds.), pp. 217-226, Iowa State University Press, Ames, IA.
Turn, S.Q., B.M. Jenkins, J.C. Chow, L.C. Pritchett, D.
Campbell, T. Cahill, and S.A. Whalen (1997) "Elemental
characterization of particulate matter emitted from
biomass burning: Wind tunnel derived source profiles
for herbaceous and wood fuels." Journal of Geophysical
Research 102 (D3): 3683-3699.
TVA (1994) Commercial Fertilizers 1994. Tennessee
Valley Authority, Muscle Shoals, AL.
TVA (1993) Commercial Fertilizers 1993. Tennessee
Valley Authority, Muscle Shoals, AL.
TVA (1992a) Commercial Fertilizers 1992. Tennessee
Valley Authority, Muscle Shoals, AL.
TVA (1992b) Fertilizer Summary Data 1992. Tennessee
Valley Authority, Muscle Shoals, AL.
TVA (1991) Commercial Fertilizers 1991. Tennessee
Valley Authority, Muscle Shoals, AL.
USDA (2003a) Crop Production 2002 Summary. National
Agricultural Statistics Service, U.S. Department of
Agriculture, Washington, DC. Available online at . Accessed May 2003.
USDA (2003b) Cattle, National Agriculture Statistics
Service, U.S. Department of Agriculture, Washington, DC.
January 31, 2003. Data also available online at .
USDA (2003c) Cattle on Feed, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. January 17, 2003. Data also available
online at .
USDA (2003d) Hogs and Pigs, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. March 28, 2003. Data also available
online at .
USDA (2003e) Chickens and Eggs Annual Summary,
National Agriculture Statistics Service, U.S. Department of
Agriculture, Washington, DC. January 30, 2003. Data also
available online at .
USDA (2003f) Poultry - Production and Value 2002
Summary, National Agriculture Statistics Service, U.S.
Department of Agriculture, Washington, DC. April 29,
2003. Data also available online at .
USDA (2003g) Sheep and Goats, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. January 31,2003. Data also available
online at .
USDA (2002a) Crop Production 2001 Summary. National
Agricultural Statistics Service, U.S. Department of
Agriculture, Washington, DC. Available online at . Accessed August 2002.
USDA (2002b) Cattle, National Agriculture Statistics
Service, U.S. Department of Agriculture, Washington, DC.
February 1, 2002. Data also available online at .
USDA (2002c) Cattle on Feed, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. January 18, 2002. Data also available
online at .
USDA (2002d) Hogs and Pigs, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. March 28, 2002. Data also available
online at .
USDA (2002e) Chickens and Eggs Annual Summary,
National Agriculture Statistics Service, U.S. Department
of Agriculture, Washington, DC. January 29, revised
March 22, 2002. Data also available online at .
USDA (2002f) Poultry - Production and Value 2001
Summary, National Agriculture Statistics Service, U.S.
Department of Agriculture, Washington, DC. April 29,
revised May 3, 2002. Data also available online at .
USDA (2002g) Sheep and Goats, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. February 1,2002. Data also available
online at .
USDA (200la) Crop Production 2000 Summary. National
Agricultural Statistics Service, U.S. Department of
Agriculture, Washington, DC. Available online at . Accessed July 2001.
USDA (2001b) Cattle, National Agriculture Statistics
Service, U.S. Department of Agriculture, Washington, DC.
January 26, 2001. Data also available online at .
USDA (2001c) Cattle on Feed Cattle, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. January 19, 2001. Data also available
online at .
USDA (200Id) Hogs and Pigs, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. March 30, 2001. Data also available
online at .
USDA (200 le) Chicken and Eggs - 2000 Summary,
National Agriculture Statistics Service, U.S. Department
of Agriculture, Washington, DC. January.
USDA (2001f) Poultry Production and Value - 2000
Summary, National Agriculture Statistics Service, U.S.
Department of Agriculture, Washington, DC. April.
11-30 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
USDA (200 Ig) Sheep and Goats, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. January. Data also available online at
.
USDA (2000a) Cattle on Feed, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. April 14, 2000. Data also available
online at .
USDA (2000b) Cattle, National Agriculture Statistics
Service, U.S. Department of Agriculture, Washington, DC.
January 28, 2000. Data also available online at .
USDA (2000c) Chicken and Eggs -1999 Summary Cattle,
National Agriculture Statistics Service, U.S. Department
of Agriculture, Washington, DC. January.
USDA (2000d) Chicken and Eggs - Final Estimates
1988-1993, National Agriculture Statistics Service, U.S.
Department of Agriculture, Washington, DC. May 3, 2000.
USDA (2000e) Hogs and Pigs, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. March 24, 2000 Data also available
online at .
USDA (2000f) Poultry Production and Value -1999
Summary, National Agriculture Statistics Service, U.S.
Department of Agriculture, Washington, DC. April.
USDA (2000g) Sheep and Goats, National Agriculture
Statistics Service, U.S. Department of Agriculture,
Washington, DC. January.
USDA (2000h) 7997 National Resources Inventory.
U.S. Department of Agriculture, Natural Resources
Conservation Service, Washington, DC.
USDA (2000i) Crop Production 1999 Summary. National
Agricultural Statistics Service, Agricultural Statistics Board,
U.S. Department of Agriculture, Washington, DC. Available
online at .
USDA (1999b) Poultry Production and Value - Final
Estimates 1994-97, National Agriculture Statistics Service,
U.S. Department of Agriculture, Washington, DC. March.
USDA (1999c) Sheep and Goats - Final Estimates
1994-1998, National Agriculture Statistics Service, U.S.
Department of Agriculture, Washington, DC. January.
USDA (1999d), Miscellaneous Livestock and Animal
Specialties Inventory and Sales: 1997 and 1992, Table
25. U.S. Department of Agriculture, National Agriculture
Statistics Service, Washington, DC. Accessed May 2000
at .
USDA (1999e) 7992 and 1997 Census of Agriculture
(CD-ROM), National Agriculture Statistics Service, U.S.
Department of Agriculture.
USDA (1998a) Chicken and Eggs - Final Estimates
1994-97, National Agriculture Statistics Service, U.S.
Department of Agriculture, Washington, DC. December.
USDA (1998b) Field Crops Final Estimates 1992-97.
Statistical Bulletin Number 947 a. National Agricultural
Statistics Service, U.S. Department of Agriculture, GPO,
Washington, DC. Available online at . Accessed July 2001.
USDA (1998c) Hogs and Pigs - Final Estimates 1993-97,
National Agriculture Statistics Service, U.S. Department
of Agriculture, Washington, DC. December. Data also
available online at .
USDA (1998d) Nutrients Available from Livestock
Manure Relative to Crop Growth Requirements, Resource
Assessment and Strategic Planning Working Paper 98-
1, U.S. Department of Agriculture, Natural Resources
Conservation Service. February.
USDA (1996) Agricultural Waste Management Field
Handbook, National Engineering Handbook (NEH), Part
651, U.S. Department of Agriculture, Natural Resources
Conservation Service. July.
USDA (1995a) Cattle - Final Estimates 1989-93, National
Agriculture Statistics Service, U.S. Department of
Agriculture, Washington, DC. January. Data also available
online at .
USDA (1995b) Poultry Production and Value - Final
Estimates 1989-1993, National Agriculture Statistics
Service, U.S. Department of Agriculture, Washington, DC.
USDA (1994a) Field Crops: Final Estimates, 1987-1992.
Statistical Bulletin Number 896. National Agriculture
Statistics Service, U.S. Department of Agriculture, GPO,
Washington, DC. Available online at .
USDA (1994b) Hogs and Pigs - Final Estimates 1988-92,
National Agriculture Statistics Service, U.S. Department
of Agriculture, Washington, DC. December. Data also
available online at .
USDA (1994c) Sheep and Goats - Final Estimates
1989-1993, National Agriculture Statistics Service, U.S.
Department of Agriculture, Washington, DC. January.
Wright, P. (2000) Telephone conversation between Lee-
Ann Tracy of ERG and Peter Wright, Cornell University,
College of Agriculture and Life Sciences, June 23, 2000.
Field Burning of Agricultural Residues
Barnard, G., and L. Kristoferson (1985) Agricultural
Residues as Fuel in the Third World. Earthscan Energy
Information Programme and the Beijer Institute of the
Royal Swedish Academy of Sciences. London, England.
References 11-31
-------
Bollich, P. (2000) Telephone conversation between Payton
Decks of ICF Consulting and Pat Bollich, Professor with
Louisiana State University Agriculture Center, May 17, 2000.
California Air Resources Board (2001) Progress Report
on the Phase Down and the 1998-2000 Pause in the Phase
Down of Rice Straw Burning in the Sacramento Valley Air
Basin, Proposed 2001 Report to the Legislature, June.
California Air Resources Board (1999) Progress Report on
the Phase Down of Rice Straw Burning in the Sacramento
Valley Air Basin, Proposed 1999 Report to the Legislature,
December.
Cibrowski, P. (1996) Telephone conversation between
Heike Mainhardt of ICF Incorporated and Peter Cibrowski,
Minnesota Pollution Control Agency, July 29, 1996.
Deren, C. (2002) Telephone conversation between Caren
Mintz of ICF Consulting and Dr. Chris Deren, Everglades
Research and Education Centre at the University of
Florida, August 15, 2002.
EPA (1994) International Anthropogenic Methane
Emissions: Estimates for 1990, Report to Congress. EPA
230-R-93-010. Office of Policy Planning and Evaluation,
U.S. Environmental Protection Agency. Washington, DC.
EPA (1992) Prescribed Burning Background Document and
Technical Information Document for Prescribed Burning
Best Available Control Measures. EPA-450/2-92-003. Office
of Air Quality Planning and Standards, U.S. Environmental
Protection Agency. Research Triangle Park, NC.
Fife, L. (1999) Telephone conversation between Catherine
Leining of ICF Consulting and Les Fife, President and
General Manager, Fife Environmental, June 9, 1999.
Guethle, D. (2003) Telephone conversation between Caren
Mintz of ICF Consulting and David Guethle, Agronomy
Specialist, Missouri Cooperative Extension Service, June
19, 2003.
Guethle, D. (2002) Telephone conversation between Caren
Mintz of ICF Consulting and David Guethle, Agronomy
Specialist, Missouri Cooperative Extension Service,
August 19, 2002.
Guethle, D. (2001) Telephone conversation between Caren
Mintz of ICF Consulting and David Guethle, Agronomy
Specialist, Missouri Cooperative Extension Service, July
31,2001.
Guethle, D. (2000) Telephone conversation between
Payton Decks of ICF Consulting and David Guethle,
Agronomy Specialist, Missouri Cooperative Extension
Service, May 17,2000.
Guethle, D. (1999) Telephone conversation between
Payton Deeks of ICF Consulting and David Guethle,
Agronomy Specialist, Missouri Cooperative Extension
Service, August 6, 1999.
ILENR (1993) Illinois Inventory of Greenhouse Gas
Emissions and Sinks: 1990. Office of Research and
Planning, Illinois Department of Energy and Natural
Resources. Springfield, IL.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories.
IPCC National Greenhouse Gas Inventories Programme
Technical Support Unit, Kanagawa, Japan. Available online
at .
IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
Jenkins, B.M., S.Q. Turn, and R.B. Williams (1992)
Atmospheric emissions from agricultural burning in
California: determination of burn fractions, distribution
factors, and crop specific contributions. Agriculture,
Ecosystems and Environment 38:313-330.
Ketzis, J. (1999) Telephone conversation between Marco
Alcaraz of ICF Consulting and Jen Ketzis of Cornell
University, June/July.
Kirstein, A. (2003) Telephone coversation between Caren
Mintz of ICF Consulting and Arthur Kirstein, Coordinator,
Agricultural Economic Development Program, Palm
Beach County Cooperative Extension Service, Florida,
August 13, 2003.
Klosterboer, A. (2003) Telephone conversation between
Caren Mintz of ICF Consulting and Arlen Klosterboer,
retired Extension Agronomist, Texas A&M University.
July 7, 2003.
Klosterboer, A. (2002) Telephone conversation between
Caren Mintz of ICF Consulting and Arlen Klosterboer,
Extension Agronomist, Texas A&M University, August
19, 2002.
Klosterboer, A. (2001) Telephone conversation between
Caren Mintz of ICF Consulting and Arlen Klosterboer,
Extension Agronomist, Texas A&M University, August
6,2001.
Klosterboer, A. (2000) Telephone conversation
between Payton Deeks of ICF Consulting and Arlen
Klosterboer, Extension Agronomist, Texas A&M
University, May 18, 2000.
Klosterboer, A. (1999a) Telephone conversation
between Catherine Leining of ICF Consulting and
Arlen Klosterboer, Extension Agronomist, Texas A&M
University, June 10, 1999.
Klosterboer, A. (1999b) Telephone conversation between
Payton Deeks of ICF Consulting and Arlen Klosterboer,
Extension Agronomist, Texas A&M University, August
12, 1999.
11-32 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Lee, D. (2003). Telephone conversation and email
correspondence between Caren Mintz of ICF Consulting
and Danny Lee, OK Farm Service Agency, Stillwater, OK.
July 2, 2003.
Lindberg, J. (2003) Email correspondence between Caren
Mintz of ICF Consulting and Jeff Lindberg, California Air
Resources Board, June-July.
Lindberg, J. (2002) Telephone conversation and email
correspondence between Caren Mintz of ICF Consulting
and Jeff Lindberg, California Air Resources Board,
September 12-23,2002.
Linscombe, S. (2003) Telephone conversation between
Caren Mintz of ICF Consulting and Steve Linscombe,
Professor with the Rice Research Station at Louisiana
State University Agriculture Center. June 10, 2003.
Linscombe, S. (2002) Email correspondence between
Caren Mintz of ICF Consulting and Steve Linscombe,
Research Agronomist, Louisiana State University
Agricultural Center, August 21, 2002.
Linscombe, S. (2001) Email correspondence between
Caren Mintz of ICF Consulting and Steve Linscombe,
Research Agronomist, Louisiana State University
Agricultural Center, July 30 -August 1, 2001.
Linscombe, S. (1999a) Telephone conversation between
Catherine Leining of ICF Consulting and Steve
Linscombe, Research Agronomist, Louisiana State
University Agricultural Center, June 3, 1999.
Linscombe, S. (1999b) Telephone conversation between
Payton Decks of ICF Consulting and Steve Linscombe,
Research Agronomist, Louisiana State University
Agricultural Center, August 9, 1999.
Mutters, C. (2003) Telephone conversation between Caren
Mintz of ICF Consulting and Mr. Cass Mutters, Rice Farm
Advisor for Butte, Glen, and Tehama Counties. University
of California Cooperative Extension Service, June 23, 2003.
Mutters, C. (2002) Telephone conversation between Caren
Mintz of ICF Consulting and Cass Mutters, Rice Farm
Advisor for Butte, Glen, and Tehama Counties, University of
California Cooperative Extension Service, August 27,2002.
Mutters, C. (2001) Telephone conversation between Caren
Mintz of ICF Consulting and Cass Mutters, Rice Farm
Advisor for Butte, Glen, and Tehama Counties, University of
California Cooperative Extension Service, August 27,2001.
Mutters, C. (2000) Telephone conversation between
Payton Deeks of ICF Consulting and Cass Mutters, Rice
Farm Advisor for Butte, Glen, and Tehama Counties,
University of California Cooperative Extension Service.
Najita, T. (2001) Telephone conversation between Caren
Mintz of ICF Consulting and Theresa Najita, Air Pollution
Specialist, California Air Resources Board, July 31, 2001.
Najita, T. (2000) Telephone conversation between Payton
Deeks of ICF Consulting and Theresa Najita, Air Pollution
Specialist, California Air Resources Board, August 17, 2000.
Noller, J. (1996) Telephone conversation between Heike
Mainhardt of ICF Incorporated and John Noller, Missouri
Department of Natural Resources, July 30, 1996.
Oregon Department of Energy (1995) Report on Reducing
Oregon's Greenhouse Gas Emissions: Appendix D
Inventory and Technical Discussion. Oregon Department
of Energy. Salem, OR.
Schueneman, T. (2001) Telephone conversation between
Caren Mintz of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida,
July 30, 2001.
Schueneman, T. (2000) Telephone conversation between
Payton Deeks of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida,
May 16, 2000.
Schueneman, T. (1999a) Telephone conversation
between Catherine Leining of ICF Consulting and Tom
Schueneman, Palm Beach County Agricultural Extension
Agent, Florida, June 7, 1999.
Schueneman, T. (1999b) Telephone conversation between
Payton Deeks of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida,
August 10, 1999.
Schueneman, T. (1999c) Telephone conversation between
John Venezia of ICF Consulting and Tom Schueneman,
Palm Beach County Agricultural Extension Agent, Florida,
September 2, 1999.
Schueneman, T.J. and C.W. Deren (2002) "An Overview
of the Florida Rice Industry" SS-AGR-77, Agronomy
Department, Florida Cooperative Extension Service,
Institute of Food and Agricultural Sciences, University of
Florida. Revised November 2002.
Slaton, N. (2001) Telephone conversation between Caren
Mintz of ICF Consulting and Nathan Slaton, Extension
Agronomist - Rice, University of Arkansas Division of
Agriculture Cooperative Extension Service.
Slaton, N. (2000) Telephone conversation between Payton
Deeks of ICF Consulting and Nathan Slaton, Extension
Agronomist - Rice, University of Arkansas Division of
Agriculture Cooperative Extension Service, May 20, 2000.
Slaton, N. (1999a) Telephone conversation between
Catherine Leining of ICF Consulting and Dr. Nathan
Slaton, Extension Agronomist - Rice, University of
Arkansas Division of Agriculture Cooperative Extension
Service, June 3, 1999.
Slaton, N. (1999b) Telephone conversation between
Payton Deeks of ICF Consulting and Dr. Nathan Slaton,
Extension Agronomist - Rice, University of Arkansas
Division of Agriculture Cooperative Extension Service,
August 6, 1999.
References 11-33
-------
Street, J. (2003) Telephone conversation between Caren
Mintz of ICF Consulting and Joe Street, Rice Specialist,
Mississippi State University, Delta Research Center, June
19, 2003.
Street, J. (2002) Telephone conversation and email
correspondence between Caren Mintz of ICF Consulting
and Joe Street, Rice Specialist, Mississippi State
University, Delta Research Center, August 19, 2002.
Street, J. (2001) Telephone conversation and email
correspondence between Caren Mintz of ICF Consulting
and Joe Street, Rice Specialist, Mississippi State
University, Delta Research Center, August 1, 2001.
Street, J. (2000) Telephone conversation between Payton
Deeks of ICF Consulting and Joe Street, Rice Specialist,
Mississippi State University, Delta Research Center, May
17, 2000.
Street, J. (1999a) Telephone conversation between
Catherine Leining of ICF Consulting and Joe Street, Rice
Specialist, Mississippi State University, Delta Research
Center, June 8, 1999.
Street, J. (1999b) Telephone conversation between Payton
Deeks of ICF Consulting and Joe Street, Rice Specialist,
Mississippi State University, Delta Research Center,
August 6, 1999.
Strehler, A., and W. Stutzle (1987) "Biomass Residues."
In: Hall, D.O. and Overend, R.P. (eds.) Biomass. John
Wiley and Sons, Ltd. Chichester, UK.
Turn, S.Q., B.M. Jenkins, J.C. Chow, L.C. Pritchett, D.
Campbell, T. Cahill, and S.A. Whalen (1997) "Elemental
characterization of paniculate matter emitted from
biomass burning: Wind tunnel derived source profiles
for herbaceous and wood fuels." Journal of Geophysical
Research 102(D3):3683-3699.
University of California (1977) Emission Factors From
Burning of Agricultural Waste Collected in California.
University of California, Davis.
USDA (2003) Crop Production 2002 Summary. National
Agricultural Statistics Service, Agricultural Statistics
Board, U.S. Department of Agriculture, Washington, DC.
Available online at .
USDA (2002) Crop Production 2001 Summary. National
Agricultural Statistics Service, Agricultural Statistics
Board, U.S. Department of Agriculture, Washington, DC.
Available online at .
USDA (2001) Crop Production 2000 Summary. National
Agricultural Statistics Service, Agricultural Statistics
Board, U.S. Department of Agriculture, Washington, DC.
Available online at .
USDA (2000) Crop Production 1999 Summary. National
Agricultural Statistics Service, Agricultural Statistics
Board, U.S. Department of Agriculture, Washington, DC.
Available online at .
USDA (1998) Field Crops, Final Estimates 1992-1997.
Statistical Bulletin No. 947a. National Agricultural
Statistics Service, Agricultural Statistics Board, U.S.
Department of Agriculture, Washington, DC. Available
online at .
USDA (1994) Field Crops, Final Estimates 1987-1992.
Statistical Bulletin No. 896. National Agricultural
Statistics Service, Agricultural Statistics Board, U.S.
Department of Agriculture, Washington, DC. Available
online at .
Wilson, C. (2003) Telephone conversation between Caren
Mintz of ICF Consulting and Dr. Chuck Wilson, Rice
Specialist, University of Arkansas Cooperative Extension
Service. June 11,2003.
Wilson, C. (2002) Telephone conversation between Caren
Mintz of ICF Consulting and Dr. Chuck Wilson, Rice
Specialist, University of Arkansas Division of Agriculture
Cooperative Extension Service, August 23, 2002.
Wilson, C. (2001) Telephone conversation between Caren
Mintz of ICF Consulting and Dr. Chuck Wilson, Rice
Specialist, University of Arkansas Division of Agriculture
Cooperative Extension Service, August 1, 2001.
Wisconsin Department of Natural Resources (1993)
Wisconsin Greenhouse Gas Emissions: Estimates for
1990. Bureau of Air Management, Wisconsin Department
of Natural Resources, Madison, WI.
Land-Use Change and Forestry
EPA (1998) Greenhouse Gas Emissions from Management
of Selected Materials in Municipal Solid Waste. U.S.
Environmental Protection Agency, Office of Solid Waste and
Emergency Response, Washington, DC. EPA530-R-98-013.
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency. Paris, France.
Changes in Forest Carbon Stocks
Adams, D.M., and R.W. Haynes. (1980) "The Timber
Assessment Market Model: Structure, Projections, and
Policy Simulations." Forest Science Monograph 22,
Society of American Foresters, Bethesda, MD, 64 pp.
11-34 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Alig, R.J. (1985) "Econometric Analysis of Forest Acreage
Trends in the Southeast." Forest Science 32: 119-134.
Birdsey, R. A., and G. M. Lewis. (2003). Current and
Historical Trends in Use, Management, and Disturbance
of U. S. Forestlands. Pages 15-34 in J. M. Kimble, L. S.
Heath, R. A. Birdsey, and R. Lai, editors. The Potential
of U.S. Forest Soils to Sequester Carbon and Mitigate the
Greenhouse Effect. CRC Press, New York.
Birdsey, R. (1996). Carbon Storage for Major Forest
Types and Regions in the Conterminous United States.
Pages 1-26 and 261-379 (appendices 262 and 263) in
R. N. Sampson and D. Hair, editors. Forest and Global
Change Volume 2: Forest Management Opportunities
for Mitigating Carbon Emissions. American Forests,
Washington DC.
Birdsey, R., and L. S. Heath (2001). Forest Inventory
Data, Models, and Assumptions for Monitoring Carbon
Flux. Pages 125-135 in Soil Carbon Sequestration and
the Greenhouse Effect. Soil Science Society of America,
Madison, WI.
Birdsey, R.A., and L.S. Heath (1995) "Carbon Changes
in U.S. Forests." hi: Productivity of America's Forests and
Climate Change. Gen. Tech. Rep. RM-271. Rocky Mountain
Forest and Range Experiment Station, Forest Service, U.S.
Department of Agriculture, Fort Collins, CO, pp. 56-70.
EPA (2003). Inventory of U. S. Greenhouse Gas Emissions
and Sinks: 1990 - 2001. EPA 430-R-02-003, USEPA,
(United States Environmental Protection Agency), Office
of Atmospheric Programs, Washington, DC.
Prayer, W.E., and G.M. Furnival (1999) "Forest Survey
Sampling Designs: A History." Journal of Forestry 97(12):
4-10.
Gillespie, A.J.R. (1999) "Rationale for a National Annual
Forest Inventory Program." Journal of Forestry 97(12):
16-20.
Haynes, R.W. (2003) An Analysis of the Timber Situation
in the United States: 1952-2050. Gen. Tech. Rep. PNW-
GTR-560., U.S. Department of Agriculture, Forest Service,
Pacific Northwest Research Station, Portland, OR.
Heath, L.S., J.E., Smith, and R.A. Birdsey (2003). Carbon
Trends in U. S. Forestlands: A Context for the Role of
Soils in Forest Carbon Sequestration. Pages 35-45 in J. M.
Kimble, L. S. Heath, R. A. Birdsey, and R. Lai, editors.
The Potential of U. S. Forest Soils to Sequester Carbon
and Mitigate the Greenhouse Effect. Lewis Publishers
(CRC Press), Boca Raton, FL.
Heath, L. S., and I.E. Smith (2000a) "Soil Carbon
Accounting and Assumptions for Forestry and Forest-
related Land Use Change." In: The Impact of Climate
Change on America's Forests. Joyce, L.A., and Birdsey,
R.A. Gen. Tech. Rep. RMRS-59. Rocky Mountain
Research Station, Forest Service, U.S. Department of
Agriculture, Fort Collins, CO, pp. 89-101.
Heath, L.S., and J. E. Smith (2000b) "An Assessment
of Uncertainty in Forest Carbon Budget Projections."
Environmental Science & Policy 3:73-82.
Heath, L.S., R.A. Birdsey, C. Row, and A.J. Plantinga
(1996) "Carbon Pools and Fluxes in U.S. Forest Products."
In: Apps, MJ. and Price, D.T. (eds.) Forest Ecosystems,
Forest Management and the Global Carbon Cycle.
Springer-Verlag, Berlin, pp. 271-278.
Heath, L.S., and R.A. Birdsey (1993) "Carbon Trends of
Productive Temperate Forests of the Coterminous United
States." Water, Air, and Soil Pollution 70: 279-293.
Howard, J. L. (2001) U.S. timber production, trade,
consumption, and price statistics 1965-1999. Res. Pap.
FPL-RP-595. Madison, WI: U.S. Department of Agriculture,
Forest Service, Forest Products Laboratory: 90 p.
Howard, J.L. (2001) U.S. Timber Production, Trade,
Consumption, and Price Statistics 1965-1999. Res. Pap.
RP-595. U.S. Department of Agriculture, Forest Service,
Forest Products Laboratory, Madison, WI, 90 p.
Ince, P. J. (1994) Recycling and Long-Range Timber
Outlook. Gen. Tech. Rep. RM-242. Rocky Mountain
Forest and Range Experiment Station, Forest Service, U.S.
Department of Agriculture. Fort Collins, CO, 66 p.
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency. Paris, France.
Johnson, M. G., and J.S. Kern (2003). Quantifying the
organic carbon held in forested soils of the United States
and Puerto Rico. Pages 47-72 in J. M. Kimble, L. S.
Heath, R. A. Birdsey, and R. Lai, editors. The Potential of
U. S. Forest Soils to Sequester Carbon and Mitigate the
Greenhouse Effect. Lewis Publishers (CRC Press), Boca
Raton, FL.
Johnson, D.W., and PS. Curtis (2001) "Effects of Forest
Management on Soil C and N Storage: Meta-analysis."
Forest Ecology and Management, 140(2): 227-238.
May, D.M. (1998) The North Central Forest Inventory &
Analysis Timber Product Output Database—A regional
composite approach. General Technical Report NC-200,
U.S. Department of Agriculture, Forest Service, North
Central Research Station, St. Paul, MN, 16 pp.
Mills, J.R., and J.C. Kincaid (1992) The Aggregate
Timberland Assessment System-ATLAS: A Comprehensive
Timber Projection Model. Gen. Tech. Rep. PNW-281.
Pacific Northwest Research Station, Forest Service, U.S.
Department of Agriculture, Portland, OR, 160 pp.
Phillips, D.L., S.L. Brown, P.E. Schroeder, and R.A. Birdsey
(2000). Toward error analysis of large-scale forest carbon
budgets. Global Ecology and Biogeography 9:305-313.
References 11-35
-------
Plantinga, A.J., and R.A. Birdsey (1993) "Carbon Fluxes
Resulting from U.S. Private Timberland Management."
Climatic Change 23:37-53.
Row, C, and R.B. Phelps (1996) Wood Carbon Flows
and Storage After Timber Harvest. Pages 27-58 in R. N.
Sampson and D. Hair, editors. Forest and Global Change
Volume 2: Forest Management Opportunities for Mitigating
Carbon Emissions. American Forests, Washington DC.
Skog, K.E., and G.A. Nicholson (1998) "Carbon Cycling
Through Wood Products: The Role of Wood and Paper
Products in Carbon Sequestration." Forest Products
Journal 48:75-83.
Smith, J.E., L.S. Heath, and J.C. Jenkins (2003). Forest
volume-to-biomass models and estimates of mass for live
and standing dead trees of U.S. forests. General Technical
Report NE-298. USDA Forest Service, Newtown Square,
Pennsylvania, 57 pp.
Smith, W.B., J.S. Vissage, D.R. Darr, and R.M. Sheffield
(2001) Forest Resources of the United States, 1997. Gen.
Tech. Rep. NC-219. North Central Research Station,
Forest Service, U.S. Department of Agriculture, St. Paul,
MN, 191 pp.
Smith, J.E., and L.S. Heath (2002). A model of forest floor
carbon mass for United States forest types. Res. Paper NE-
722. USDA Forest Service, Northeastern Research Station,
Newtowne Square, PA
Smith, I.E., and L.S. Heath (2000) "Considerations
for Interpreting Probabilistic Estimates of Uncertainty
of Forest Carbon." In: The Impact of Climate Change
on America's Forests. Gen. Tech. Rep. RMRS-59.
Rocky Mountain Research Station, Forest Service, U.S.
Department of Agriculture, Fort Collins, CO, pp. 102-111.
Smith, J. E., and L.S. Heath (In press) Carbon stocks and
projections on public forestlands in the United States,
1952-2040. Environmental Management.
Ulrich, A.H. (1989) U.S. Timber Production, Trade,
Consumption, and Price Statistics, 1950-1987. USDA
Miscellaneous Publication No. 1471, U.S. Department of
Agriculture, Forest Service, Washington, DC, 77 pp
USDA (1991) State Soil Geographic Data Base
(STATSGO): Data Users Guide. U.S. Department of
Agriculture, Soil Conservation Service, National Resource
Conservation Service. Miscellaneous Publication Number
1492, U.S. Government Printing Office.
USDA Forest Service (1964) The Demand and Price
Situation for Forest Products, 1964. Misc. Pub. 983,
Washington, DC.
Waddell, K.L., D.D. Oswald and D.S. Powell (1989) Forest
Statistics of the United States, 1987. Resource Bulletin PNW-
RB-168. Pacific Northwest Research Station, Forest Service,
U.S. Department of Agriculture, Portland, OR, 106 pp.
Changes in Carbon Stocks in Urban Trees
Cairns, M.A., S. Brown, E.H. Helmer, and G.A.
Baumgardner (1997) "Root Biomass Allocation in the
World's Upland Forests." Oceologia 111: 1-11.
deVries, R.E. (1987) A Preliminary Investigation of the
Growth and Longevity of Trees in Central Park. New
Brunswick, NJ: Rutgers University, M.S. thesis.
Dwyer, J.F., D.J. Nowak, M.H. Noble, and S.M Sisinni
(2000) Connecting People with Ecosystems in the
21st Century: An Assessment of Our Nation's Urban
Forests. General Technical Report PNW-GTR-490,
U.S. Department of Agriculture, Forest Service, Pacific
Northwest Research Station, Portland, OR.
Fleming, L.E. (1988) Growth Estimation of Street Trees
in Central New Jersey. New Brunswick, NJ: Rutgers
University, M.S. thesis.IPCC/UNEP/OECD/IEA
(1997) Revised 1996 IPCC Guidelines for National
Greenhouse Gas Inventories, Paris: Intergovernmental
Panel on Climate Change, United Nations Environment
Programme, Organization for Economic Co-Operation and
Development, International Energy Agency. Paris, France.
Nowak, D.J. (2002) E-mail from David Nowak of
the USDA Forest Service to Barbara Braatz at ICF
Consulting, containing information on possible urban tree
carbon and forest carbon overlap, January 10, 2002.
Nowak, D.J. (1994) "Atmospheric Carbon Dioxide
Reduction by Chicago's Urban Forest." In: McPherson,
E.G., Nowak, D. J., and Rowntree, R.A. (eds.) Chicago's
Urban Forest Ecosystem: Results of the Chicago Urban
Forest Climate Project. USDA Forest Service General
Technical Report NE-186, Radnor, PA, pp. 83-94.
Nowak, D.J., (1986) "Silvics of an Urban Tree Species:
Norway Maple (Acer platanoides L.)." Syracuse, NY:
State University of New York, College of Environmental
Science and Forestry, M.S. thesis.
Nowak, D.J. and D.E. Crane (2002) "Carbon Storage
and Sequestration by Urban Trees in the United States."
Environmental Pollution 116(3): 381-389.
Nowak, D.J., D.E. Crane, J.C. Stevens, and M. Ibarra
(2002) Brooklyn's Urban Forest, USDA Forest Service
General Technical Report NE-290, Newtown Square, PA.
Nowak, D.J., M.H. Noble, S.M. Sisinni, and J.F. Dwyer
(2001) "Assessing the U.S. Urban Forest Resource."
Journal of Forestry. 99(3): 37-42.
Smith, W.B. and S.R. Shifley (1984) Diameter Growth,
Survival, and Volume Estimates for Trees in Indiana and
Illinois. Res. Pap. NC-257. St. Paul, MN: U.S. Department
of Agriculture, Forest Service, North Central Forest
Experiment Station.
11-36 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Changes in Agricultural Soil Carbon
Stocks
Armentano, T.V. and J.T.A. Verhoeven (1990)
"Biogeochemical Cycles: Global." In: Wetlands and
Shallow Continental Water Bodies. Patten, B.C., et al.
(eds.) SPB Academic Publishing, The Hague, Netherlands,
Volume I, pp. 281-311.
Barbarika, A. (2002) Net enrollment in the Conservation
Reserve Program after 1997 based on active contracts,
Farm Services Agency, Washington, DC. Communication
to Stephen Ogle of the Natural Resource Ecology
Laboratory, Colorado State University, December 2002.
Brady, N.C. and R.R. Weil (1999) The Nature and
Properties of Soils. Prentice Hall, Upper Saddle River,
New Jersey, 881 pp.
CTIC (1998) "1998 Crop Residue Management Executive
Summary," Conservation Technology Information Center,
West Lafayette, Indiana.
Daly, C., G.H. Taylor, W.P. Gibson, T. Parzybok, G.L.
Johnson, and P. A. Pasteris (1998) "Development of High-
quality Spatial Datasets for the United States," in: Proc.,
1st International Conference on Geospatial Information in
Agriculture and Forestry, Lake Buena Vista, FL, June 1-3,
1998, pp. 1-512-1-519.
Daly, C., R.P. Neilson, and D.L. Phillips (1994)
"A Statistical-Topographic Model for Mapping
Climatological Precipitation Over Mountainous Terrain,
Journal of Applied Meteorology, 33:140-158.
Dean, W. E., and E. Gorham (1998) Magnitude and
significance of carbon burial in lakes, reservoirs, and
peatlands. Geology 26:535-538.
ERS (2000) Agricultural Production Management:
Nutrient Management (Chapter 4). In Agricultural
Resources and Environmental Indicators. Available online
at .
Euliss, N., and R. Gleason (2002) Wetland restoration factor
estimates and restoration activity data compiled and provided
by Ned Euliss and Robert Gleason. USGS, Jamestown, North
Dakota, to Stephen Ogle of the National Resource Ecology
Laboratory, Fort Collins, Colorado. August.
Euliss, N.H., Jr., R.A. Gleason, A. Olness, R.L.
McDougal, H.R. Murkin, R.D. Robarts, R.A.
Bourbonniere, and B.G. Warner (In prep) "Prairie
wetlands of North America important for carbon storage".
Eve, M.D., K. Paustian, R. Follett, and E.T. Elliot (2001)
A national inventory of changes in soil carbon from
National Resources Inventory data. Pages 593-610 In: R.
Lai, J.M. Kimble, R.F. Follett, and B.A. Stewart. Methods
for Soil Carbon. CRC Press, Boca Raton, FL.
Hamilton, S.K., A.L. Kutzman, and G.P. Robertson (2002)
"Liming of agricultural soils: A source or a sink for CO2?"
Presented at USDA Symposium on Natural Resource
Management to Offset Greenhouse Gas Emissions,
November 2002, Raleigh, NC.
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency. Paris, France.
Kellogg, R.L., C.H. Lander, D.C. Moffitt, and Gollehon, N.
(2000) "Manure Nutrients Relative to the Capacity of Cropland
and Pastureland to Assimilate Nutrients: Spatial and Temporal
Trends for the United States," U.S. Department of Agriculture,
Publication number npsOO-0579, Washington, DC.
Metherell, A.K., Harding, L.A., Cole, C.V. and Parton, W.J.
(1993) "CENTURY Soil Organic Matter Model Environment."
Agroecosystem version 4.0. Technical documentation, GPSR
Tech. Report No. 4, USDA/ARS, Ft. Collins, CO.
NASS (2002) USDA National Agricultural Statistics
Database. Available online at .
NRCS (2000) "Digital Data and Summary Report: 1997
National Resources Inventory," Revised December
2000, United States Department of Agriculture, Natural
Resources Conservation Service, Resources Inventory
Division, Beltsville, MD.
NRCS (1999) "Soil Taxonomy: A basic system of soil
classification for making and interpreting soil surveys, 2nd
Edition." Agricultural Handbook Number 436, USDA
Natural Resources Conservation Service, Washington, DC.
NRCS (1997) "National Soil Survey Laboratory
Characterization Data," Digital Data, USDA - NRCS,
Lincoln, NE.
NRCS (1981) "Land Resource Regions and Major Land
Resource Areas of the United States," USDA Agriculture
Handbook 296, United States Department of Agriculture,
Natural Resources Conservation Service, National Soil
Survey Center, Lincoln, NE, 156 pp.
Nusser, S.M., F.J. Breidt, and. W.A. Fuller (1998) "Design
and Estimation for Investigating the Dynamics of Natural
Resources, Ecological Applications, 8:234-245.
Nusser, S.M., and J.J. Goebel (1997) "The National
Resources Inventory: A long-term multi-resource
monitoring programme," Environmental and Ecological
Statistics, 4:181-204.
Ogle, S., M. Eve, M. Sperrow, F.J. Breidt, and K. Paustian
(2002) Agricultural Soil C Emissions, 1990-2001:
Documentation to Accompany EPA Inventory Tables.
Natural Resources Ecology Laboratory, Fort Collins, CO,
Provided in 23 September 2002 e-mail from S.M. Ogle to
B.V. Braatz at ICF Consulting.
References 11-37
-------
Ogle, S.M., M.D. Eve, F.J. Breidt, and K. Paustian. In press.
Uncertainty in estimating land use and management impacts
on soil organic carbon storage for U.S. agroecosystems
between 1982 and 1997. Global Change Biology.
Ogle, S.M., F.J. Breidt, and K. Paustian. In prep.
Uncertainty in upscaling field measurements to conduct
national inventories: random error and systematic bias.
Olness, A., N.H. Euliss, Jr., and R.A. Gleason (In press)
Carbon and nitrogen sequestration in northern native
and restored prairie wetlands. Journal of Environmental
Quality.
Parton, W.J., D.S. Ojima, C.V. Cole, and D.S. Schimel
(1994) "A General Model for Soil Organic Matter
Dynamics: Sensitivity to litter chemistry, texture and
management." In: Quantitative Modeling of Soil Forming
Processes. Special Publication 39, Soil Science Society of
America, Madison, WI, pp. 147-167.
Tepordei, V. V. (2003) "Crushed Stone," In: Minerals
Yearbook 2001. U.S. Department of the Interior/U.S.
Geological Survey, Washington, DC. Available online
at . Accessed June 2003.
Tepordei, V. V. (2002) "Crushed Stone," In: Minerals
Yearbook 2000. U.S. Department of the Interior/U.S.
Geological Survey, Washington, DC. Available online at
. Accessed September 2002.
Tepordei, V. V. (2001) "Crushed Stone," In: Minerals
Yearbook 1999. U.S. Department of the Interior/U.S.
Geological Survey, Washington, DC. Available online
at . Accessed August 2001.
Tepordei, V. V. (2000) "Crushed Stone," In: Minerals
Yearbook 1998. U.S. Department of the Interior/U.S.
Geological Survey, Washington, DC. Available online
at . Accessed August 2000.
Tepordei, V. V. (1999) "Crushed Stone," In: Minerals
Yearbook 1997. U.S. Department of the Interior/U.S.
Geological Survey, Washington, DC. Available online
at . Accessed August 2000.
Tepordei, V. V. (1998) "Crushed Stone," In: Minerals
Yearbook 1996. U.S. Department of the Interior/U.S.
Geological Survey, Washington, DC. Available online
at . Accessed August 2000.
Tepordei, V. V. (1997) "Crushed Stone," In: Minerals
Yearbook 1995. U.S. Department of the Interior/U.S.
Geological Survey, Washington, DC. pp. 783-809.
Available online at .
Tepordei, V. V. (1996) "Crushed Stone," In: Minerals
Yearbook 1994. U.S. Department of the Interior/Bureau
of Mines, Washington, DC. (Available online at . Accessed August 2000.
Tepordei, V. V. (1995) "Crushed Stone," In: Minerals
Yearbook 1993. U.S. Department of the Interior/Bureau of
Mines, Washington, DC, pp. 1107-1147.Tepordei, V. V.
(1994) "Crushed Stone," In: Minerals Yearbook 1992. U.S.
Department of the Interior/Bureau of Mines, Washington,
DC, pp. 1279-1303.
Tepordei, V. V. (1993) "Crushed Stone," In: Minerals
Yearbook 1991. U.S. Department of the Interior/Bureau of
Mines, Washington, DC, pp. 1469-1511.
Towery, D. (2001) Adjustments to the CTIC (1998) tillage
data to reflect long-term trends provided by Dan Towery
of the Conservation Technology Information Center,
West Lafayette, Indiana, to Marlen Eve of the National
Resource Ecology Laboratory, Fort Collins, CO. February.
USDA-NRCS (2000) "Digital Data And Summary Report:
1997 National Resources Inventory." Revised December
2000. United States Department of Agriculture, Natural
Resources Conservation Service, Resources Inventory
Division, Beltsville, MD.
USGS (2003) Mineral Industry Surveys: Crushed Stone
and Sand and Gravel in the First Quarter of 2003. U.S.
Geological Survey, Reston, VA. Available online at
.
USGS (2002) Mineral Industry Surveys: Crushed Stone
and Sand and Gravel in the First Quarter of 2002. U.S.
Geological Survey, Reston, VA. Available online at
.
Changes in Yard Trimming
Carbon Stocks in Landfills
Barlaz, M.A. (1998) "Carbon Storage during
Biodegradation of Municipal Solid Waste Components
in Laboratory-Scale Landfills." Global Biogeochemical
Cycles 12: 373-380.
Eleazer, WE., W.S. Odle, Y. Wang, and M. Barlaz (1997)
"Biodegradability of Municipal Solid Waste Components
in Laboratory-Scale Landfills" Environmental Science
Technology, 31:911-917.
EPA (2002) Municipal Solid Waste in the United States:
2000 Facts and Figures. U.S. Environmental Protection
Agency, Office of Solid Waste and Emergency Response,
Washington, DC. EPA530-R-02-001.
11-38 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
EPA (2003) Municipal Solid Waste in the United States:
2001 Facts and Figures. U.S. Environmental Protection
Agency, Office of Solid Waste and Emergency Response,
Washington, DC. EPA/530-R-03-011.
EPA (1999) Characterization of Municipal Solid Waste
in the United States: 1998 Update. U.S. Environmental
Protection Agency, Office of Solid Waste and Emergency
Response, Washington, DC.
Oshins, C., and D. Block (2000) "Feedstock Composition
at Composting Sites." Biocycle 41(9):31-34.
Tchobanoglous, G., H. Theisen, and S.A. Vigil (1993)
Integrated Solid Waste Management, 1st edition. McGraw-
Hill, NY. Cited by Barlaz (1998).
Waste
Landfills
40 CFR Part 60, Subparts Cc (2002) Emission Guidelines
and Compliance Times for Municipal Solid Waste
Landfills, 60.30c-60.36c, Code of Federal Regulations,
Title 40, available online at .
Bingemer, H. and J. Crutzen (1987) "The Production of
Methane from Solid Wastes," Journal of Geophysical
Research, 92:2181-2187.
BioCycle (2001) "13th Annual BioCycle Nationwide
Survey: The State of Garbage in America," N. Goldstein,
BioCycle, December.
EPA (1993) Standards for the Use and Disposal of
Sewage Sludge.
EPA (2003) Landfill Gas-to-Energy Project Database,
Landfill Methane and Outreach Program. March.
EPA (2002a) Municipal Solid Waste in the United States:
2000 Facts and Figures, U.S. Environmental Protection
Agency, Office of Solid Waste and Emergency Response,
Washington, DC. EPA530-R-02-001. June.
EPA (2002b) Solid Waste Management and Greenhouse
Gases: A Life-Cycle Assessment of Emissions and Sinks.
U.S. Environmental Protection Agency, Office of Solid
Waste and Emergency Response, Washington, DC. 2nd
edition. EPA530-R-02-006. May.
EPA (1993) Anthropogenic Methane Emissions in the
United States, Estimates for 1990: Report to Congress,
U.S. Environmental Protection Agency, Office of Air and
Radiation, Washington, DC. EPA/430-R-93-003. April.
EPA (1988) National Survey of Solid Waste (Municipal)
Landfill Facilities, U.S. Environmental Protection Agency,
Washington, DC. EPA/530-SW-88-011. September.
ICF (2002) Personal communication between ICF
Consulting and several flare vendors. August.
IPCC/UNEP/OECD/ffiA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories, Paris:
Intergovernmental Panel on Climate Change, United Nations
Environment Programme, Organization for Economic Co-
Operation and Development, International Energy Agency.
Liptay, K., et al. (1998) "Use of Stable Isotopes to
Determine Methane Oxidation in Landfill Cover Soils,"
JGR Atmospheres, 103D, 8243-8250 pp.
RTI (2003) Personal communication between RTI
International and several flare vendors. July.
Wastewater Treatment
EPA (2002) Development Document for the Proposed
Effluent Limitatons Guidelines and Standards for the Meat
and Poultry Products Industry Point Source Category (40
CFR Part 432). United States Environmental Protection
Agency, Washington, DC, January 2002.
EPA (1997a) Supplemental Technical Development
Document for Effluent Limitations Guidelines and
Standards for the Pulp, Paper, and Paperboard Category.
United States Environmental Protection Agency, Office of
Water. EPA/82 l-R-97-011, Washington, DC, October 1997.
EPA (1997b) Estimates of Global Greenhouse Gas
Emissions from Industrial and Domestic Wastewater
Treatment. United States Environmental Protection
Agency, Office of Policy, Planning, and Evaluation. EPA-
600/R-97-091, Washington, DC, September 1997.
EPA (1996) 7996 Clean Water Needs Survey Report
to Congress. Assessment of Needs for Publicly Owned
Wastewater Treatment Facilities, Correction of Combined
Sewer Overflows, and Management of Storm Water and
Nonpoint Source Pollution in the United States.
(NEEDS Survey) Available online at .
EPA (1993) Development Document for the Proposed
Effluent Limitations Guidelines and Standards for the
Pulp, Paper and Paperboard Point Source Category. EPA-
821-R-93-019. United States Environmental Protection
Agency, Office of Water, Washington, DC, October 1993.
IPCC (2000) Good Practice Guidance and Uncertainty
Management in National Greenhouse Gas Inventories,
Intergovernmental Panel on Climate Change,
Intergovernmental Panel on Climate Change, National
Greenhouse Inventories Porgramme, Montreal, IPCC-
XVI/Doc. 10 (1.IV.2000), May 2000.
Lockwood-Post (2002) Lockwood-Post's Directory
of Pulp, Paper and Allied Trades, Miller-Freeman
Publications, San Francisco, CA.
Metcalf & Eddy, Inc. (1991) Wastewater Engineering:
Treatment, Disposal, Reuse. McGraw-Hill: New York.
ISBN 0-07-041690-7.
References 11-39
-------
Nemerow, Nelson Leonard and Avijit Dasgupta (1991)
Industrial and Hazardous Waste Treatment. Van Nostrand
Reinhold. NY. ISBN 0-442-31934-7.
U.S. Census Bureau (2002) Statistical Abstract of the
United States. Washington, DC. Available online at
.
USDA National Agricultural Statistics Service (2002).
Washington, DC. Available online at .
World Bank (1999) Pollution Prevention and Abatement
Handbook 1998, Toward Cleaner Production. The
International Bank for Reconstruction and Development/
The World Bank. 1818 H Street, N.W. Washington, DC.
20433, USA. ISBN 0-8213-3638-X.
Waste Sources of Ambient Air Pollutants
EPA (2003) E-mail correspondence containing preliminary
ambient air pollutant data between EPA OAP and EPA
OAQPS. December 22, 2003.
EPA (1997) Compilation of Air Pollutant Emission
Factors, AP-42, U.S. Environmental Protection Agency,
Office of Air Quality Planning and Standards, Research
Triangle Park, NC, October.
Human Sewage (Domestic Wastewater)
Czepiel, P., P. Crill, and R. Harriss (1995) Nitrous
oxide emissions from municipal wastewater treatment.
ENVIRON. SCI. TECHNOL. vol. 29, no. 9, pp. 2352-
2356. ISSN-0013-936X.
EPA (1996) 7996 Clean Water Needs Survey Report
to Congress. Assessment of Needs for Publicly Owned
Wastewater Treatment Facilities, Correction of Combined
Sewer Overflows, and Management of Storm Water and
Nonpoint Source Pollution in the United States. (NEEDS
Survey). Available online at , accessed
September 30, 2003.
IPCC/UNEP/OECD/IEA (1997) Revised 1996IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change, United
Nations Environment Programme, Organization for
Economic Co-Operation and Development, International
Energy Agency.
Metcalf and Eddy, Inc. (1991) Wastewater Engineering:
Treatment, Disposal, and Reuse, Third Edition, McGraw-
Hill Publishing Company, NY. ISBN 0-07-041690-7.
Mullick, M.A. (1987) Wastewater Treatment Processes in
the Middle East. The Book Guild Lt. Lewes, Sussex, U.K.
ISBN 0-86-332-336.
U.S. Census Bureau (2001) Monthly Estimates of the
United States Population: April 1, 1980 to July I, 2002,
Population Estimates Program, Population Division, U.S.
Census Bureau, Washington, DC. Available online at
, accessed July , 2003.
11-40 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2002
-------
Solvents and Other Product Use: The smallest sector considered in this inventory, N,O product
usage is the only source of greenhouse gas emissions estimated in this sector. However, ambient
air pollutants are also noted here, as in other sectors.
Land-Use Change and Forestry: The anthropogenic flux in biogenic carbon is estimated as the
net change in carbon stocks over time. The sources estimated include changes in forest carbon
stocks, changes in carbon stocks in urban trees, changes in agricultural soil carbon stocks, and
changes in carbon stocks in landfilled yard trimmings. Net CO., sequestration has been generally
decreasing from 1990 through 2002.
Industrial Processes: Greenhouse gas emissions from this sector are often from mineral, metal, or chemical
products or processes; these processes most often emit CO,, CH4, or N2O. In addition, there are processes
that emit fluorinated compounds, such as MFCs, PFCs, and SF6. Aluminum production, for example, emits
PFCs. These gases are currently emitted in smaller quantities, but they have high global warming potentials,
and emissions from the ozone depleting substance substitutes, in particular, are growing rapidly.
Energy: By far the largest source of emissions from the energy sector is for the combustion of fossil
fuels, accounting for over 95 percent of U.S. energy emissions and 80 percent of total U.S. greenhouse
gas emissions. Within this source, electricity generation accounts for 40 percent of emissions and is
composed of traditional electric utilities, cogenerators, and non-utility power producers.
;inks: 1990-
April 15, 2004
&EPA
EPA 430-R-04-003
-------
-------
-------
ssaujsng lepyjo
O9frOZ OQ 'uoiBujMSBM
(NK)29)
SLuejBojd OMaqdsouJiv JO aoyjo
AouaBv
UO!lO3)OJd IB1U3LUOJ.IAU3
------- |