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How to Obtain Copies
You may electronically download this document on the U.S. EPA's homepage at
http://vvwv.epa.gov/globalvvarming/mventory. To obtain additional copies of this report,
call the National Center for Environmental Publications and Information (NCEPI) at
(800)490-9198.
For Further Information
Contact Mr. Wiley Barbour, Environmental Protection Agency, Office of Policy, Climate
Policy and Programs Division, (202) 260-6972, barbour.wiley@epa.gov.
For more information regarding climate change and greenhouse gas emissions see
EPA web side at http://www.epa.gov/globalwarming.
Released for printing: April 1999
The photographs on the front and back cover of this year's Greenhouse Gas Inventory of
Emissions and Sinks depict important sources of anthropogenic methane emissions.
Landfills are the largest single anthropogenic source of methane emissions
in the United States. In an environment where the oxygen content is low or
nonexistent (i.e. anaerobic), organic materials, such as yard waste,
household waste, food waste, and paper, are decomposed by bacteria
resulting in the generation of methane.
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 methane to the atmosphere.
When cattle digest food, methane is produced through the process of
enteric fermentation, in which microbes residing in animal digestive
systems break down the feed consumed by the animal. Ruminants, which
include cattle, buffalo, sheep, and goats, have the highest methane
emissions among all animal types because they have a rumen, or large
fore-stomach, in which methane producing fermentation occurs.
Methane is the major component of natural gas. During the production,
processing, transmission, and distribution of natural gas, leaks or fugitive
emissions of methane often occur. Because natural gas is often found in
conjunction with petroleum deposits, leakage from oil wells is also a
source of emissions.
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
April 1999
The Environmental Protection Agency, in cooperation with several other agencies, has
prepared the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997. In accordance
with Decision 3/CP.l of the Framework Convention on Climate Change (FCCC), Annex I
Parties should submit "national inventory data on emissions by sources and removals by sinks."
This Inventory complies with the reporting guidelines established by the Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories. The emissions estimates 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 FCCC.
Each year, advances in scientific understanding and availability of underlying data allow
us to improve the quality and comprehensiveness of the inventory. A new section entitled
"Changes in this Year's U.S. Greenhouse Gas Inventory Report," guides readers to specific areas
where the EPA has expanded coverage, improved methods, or added additional data from
previous inventory publications.
Some of these advances have allowed improved estimates for aviation, agricultural
practices, and natural gas flaring. A new glossary of terms, unit definitions, and conversion
tables have been added to help make this information more accessible to the public. A new table
provides a comparison of recent trends in various environmental and economic variables related
to U.S. greenhouse gas emissions. And finally, an analysis of carbon intensity trends
summarizes how emissions from residential, commercial, industrial, transportation, and electric
utilities have changed over the eight year time span of this report.
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.
Sincerely,
David Gardiner
Assistant Administrator
Office of Policy
Recycled/Recyclable . Printed with Vegetable Oil Based Inks on 100% Recycled Paper (20% Postconsumer)
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Inventory of U.S. Greenhouse
Gas Emissions and Sinks:
199O - 1997
April 1999
U.S. Environmental Protection Agency
Office of Policy
401 M St., SW
Washington, D.C. 20460
U.S.A.
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Acknowledgments
The EPA Office of Policy would like to acknowledge the many individual and organizational contributors to
this document, without whose efforts this report would not be complete. Although the list of researchers, government
employees, and consultants who have provided technical and editorial support is too long to list here, we would like
to thank some key contributors whose work has significantly improved this year's report. In particular, we wish to
acknowledge the efforts of the Energy Information Administration and the Department of Energy for providing
detailed statistics and insightful analysis on numerous energy-related topics; the U.S. Forest Service for preparing the
forest carbon inventory, and the Department of Agriculture's Agricultural Research Service for their work on nitrous
oxide emissions from soils.
Within the EPA, many Offices contributed data, analysis and technical review for this report. The EPA Office
of Atmospheric Programs developed methodologies and provided detailed emission estimates for numerous source
categories, particularly for methane and the synthetic industrial gases. The Office of Mobile Sources 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 contribute analysis and
research for the underlying basis of out estimates.
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, and the Federal Aviation Administration.
We would especially like to thank the staff of the Global Environmental Issues Group at ICF Incorporated for
synthesizing this report and preparing many of the individual analyses.
-------
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). Under a decision of the UNFCCC Conference of the Parties, national inventories
for most 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 the draft document is posted on the EPA web page.1 Copies are also mailed upon request. The
public comment period is 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. The EPA's policy is to allow at least 60
days for public review and comment when proposing new regulations or documents supporting regulatory develop-
ment (unless statutory- or judicial deadlines make a shorter time necessary), and 30 days for non-regulatory docu-
ments of an informational nature such as the Inventory document.
1 See http;//www.epa.gov/globalwarrning/inventory
li Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Table of Contents
Acknowledgments - '
Preface .. .— • • • •—• "
Table of Contents » '"
Ust of Tables, Figures, and Boxes vl
Tables v|
Figures X1
Boxes xil
Changes in This Year's U.S. Greenhouse Gas Inventory Report x/ii
Executive Summary -
Recent Trends in U.S. Greenhouse Gas Emissions ES-2
Global Warming Potentials ES"8
Carbon Dioxide Emissions ES-9
Methane Emissions ES-13
Nitrous Oxide Emissions ES-16
HFCs, PFCs and SF6 Emissions ES-18
Criteria Pollutant Emissions ES-19
1. Introduction — «— •• ——-I""?
What is Climate Change? l~2
Greenhouse Gases • 1"2
Global Warming Potentials 1-6
Recent Trends in U.S. Greenhouse Gas Emissions 1-7
Methodology and Data Sources 1-15
Uncertainty in and Limitations of Emission Estimates 1-15
Organization of Report 1-17
2. Energy • • 2-f
Carbon Dioxide Emissions from Fossil Fuel Combustion 2-3
Stationary Sources (excluding CO2) 2-15
Mobile Sources (excluding CO2) 2-19
Coal Mining 2-24
Natural Gas Systems 2-27
Petroleum Systems 2-29
Natural Gas Flaring and Criteria Pollutant Emissions from Oil and Gas Activities 2-32
International Bunker Fuels 2-33
Wood Biomass and Ethanol Consumption 2-37
3. Industrial Processes 3-1
Cement Manufacture 3-2
Lime Manufacture 3-5
Limestone and Dolomite Use 3-7
Soda Ash Manufacture and Consumption 3-9
Carbon Dioxide Consumption 3-11
Iron and Steel Production 3-12
Ammonia Manufacture 3-13
Ferroalloy Production 3-14
iii
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Petrochemical Production 3-15
Silicon Carbide Production 3-16
Adtpic Acid Production 3-16
Nitric Acid Production 3-18
Substitution of Ozone Depleting Substances 3-19
Aluminum Production 3-22
HCFC-22 Production ; 3.25
Semiconductor Manufacture 3-26
Electrical Transmission and Distribution 3-27
Magnesium Production and Processing 3-29
Industrial Sources of Criteria Pollutants 3.31
4. Solvent Use 4-1
5. Agriculture . : 5.1
Enteric Fermentation 5-2
Manure Management 5.4
Rice Cultivation 5.7
Agricultural Soil Management 5-11
Agricultural Residue Burning 5.17
6, Land-Use Change and Forestry 6-1
Changes in Forest Carbon Stocks 6-1
Changes in Non-Forest Soil Carbon Stocks 6-7
7. Waste , 7.1
Landfills 7-1
Waslewater Treatment 7.4
Human Sewage 7.5
Waste Combustion 7-6
Waste Sources of Criteria Pollutants 7.7
References. „.„. ,..3-1
Executive Summary 8-1
1. Introduction... 8-1
2. Energy 8-1
3. Industrial Processes §-4
4. Solvent Use 8-8
5. Agriculture 8-8
6. Land-Use Change and Forestry 8-12
7. Waste 8-14
.Annexes
ANNEX A: Methodology for Estimating Emissions of CO2 from Fossil Fuel Combustion... A-l
ANNEX B: Methodology for Estimating Emissions of CH4, N2O, and Criteria Pollutants from
Stationary Sources B-l
ANNEX C: Methodology for Estimating Emissions of CH4, N2O, and Criteria Pollutants from
Mobile Sources C-l
ANNEX D: Methodology for Estimating Methane Emissions from Coal Mining D-l
ANNEX E: Methodology for Estimating Methane Emissions from Natural Gas Systems E-l
ANNEX F: Methodology for Estimating Methane Emissions from Petroleum Systems F-l
ANNEX G: Methodology for Estimating Methane Emissions from Enteric Fermentation G-1
ANNEX H: Methodology for Estimating Methane Emissions from Manure Management H-l
ANNEX I: Methodology for Estimating Methane Emissions from Landfills 1-1
ANNEX J: Global Wanning Potential Values j-1
ANNEX K: Ozone Depleting Substance Emissions K-l
!v Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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ANNEX L: Sulfur Dioxide Emissions L-l
ANNEX M: Complete List of Sources M-l
ANNEX N: IPCC Reporting Tables N-l
ANNEX O: IPCC Reference Approach for Estimating CO2 Emissions from Fossil Fuel Combustion O-l
ANNEX P: Sources of Greenhouse Gas Emissions Excluded P-l
ANNEX Q: Constants, Units, and Conversions Q-l
ANNEX R: Abbreviations R-l
ANNEX S: Chemical Symbols S-l
ANNEX T: Glossary T-l
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List of Tables,
Figures, and Boxes
Tables
liable ES-1: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (MMTCE) ES-3
Table ES-2: Annual Percent Change in CO2 Emissions from Fossil Fuel Combustion
for Selected Sectors and Fuels ES-4
Table ES-3: Recent Trends in Various U.S. Data (Index 1990 = 100) , ES-5
Table ES-4: Transportation-Related Greenhouse Gas Emissions (MMTCE) ES-7
Table ES-5: Electric Utility-Related Greenhouse Gas Emissions (MMTCE) ES-8
Table ES-6: Global Warming Potentials (100 Year Time Horizon) ES-9
Table ES-7: U.S. Sources of CO2 Emissions and Sinks (MMTCE) ES-10
Table ES-8: CO2 Emissions from Fossil Fuel Combustion by End-Use Sector (MMTCE)* ES-11
Table ES-9: U.S. Sources of Methane Emissions (MMTCE) ES-14
Table ES-10: U.S. Sources of Nitrous Oxide Emissions (MMTCE) ES-17
Table ES-11: Emissions of MFCs, PFCs, and SF6 (MMTCE) 'f ES-18
Table ES-12: Emissions of Ozone Depleting Substances (Mg) , ES-20
Table ES-13: Emissions of NOX, CO, NMVOCs, and SO2 (Gg) !. ES-21
Table 1-1: Global Warming Potentials and Atmospheric Lifetimes (Years) '. 1-7
Table 1-2: Annual Percent Change in CO2 Emissions from Fossil Fuel Combustion
for Selected Sectors and Fuels 1-8
Table 1-3: Recent Trends in Various U.S. Data (Index 1990=100) 1-9
Table 1-4: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (MMTCE) '. 1-10
Table 1-5: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg) 1-11
Table 1-6: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks by
Chapter/IPCC Sector (MMTCE) 1-12
Table 1-7: Transportation-Related Greenhouse Gas Emissions (MMTCE) '. 1-14
Table 1-8: Electric Utility-Related Greenhouse Gas Emissions (MMTCE) 1-15
Table 1-9: IPCC Sector Descriptions 1-17
Table 1-10: List of Annexes 1-17
Table 2-1: Emissions from Energy (MMTCE) 2-2
Table 2-2: Emissions from Energy (Tg) '. 2-2
Table 2-3: CO2 Emissions from Fossil Fuel Combustion by Fuel Type and Sector (MMTCE) 2-4
Table 2-4: CO2 Emissions from Fossil Fuel Combustion by Fuel Type and Sector (Tg) 2-5
Table 2-5: Non-Energy Use Carbon Stored and CO2 Emissions from International
Bunker Fuel Combustion (MMTCE) 2-6
Table 2-6: Non-Energy Use Carbon Stored and CO2 Emissions from International Bunker
Fuel Combustion (Tg) 2-6
Table 2-7: CO2 Emissions from Fossil Fuel Combustion by End-Use Sector (MMTCE)* 2-7
Table 2-8: CO2 Emissions from Fossil Fuel Combustion in Transportation End-Use Sector (MMTCE) 2-9
Table 2-9: Carbon Intensity from Direct Fossil Fuel Combustion by Sector (MMTCE/EJ) 2-11
Table 2-10: Carbon Intensity from Energy Consumption by Sector (MMTCE/EJ) 2-12
Table 2-11: CO2 Emissions from Fossil Fuel Combustion (Index 1990= 100) 2-13
Table 2-12: CH4 Emissions from Stationary Sources (MMTCE) 2-17
Table 2-13: N2O Emissions from Stationary Sources (MMTCE) 2-17
Table 2-14: CH4 Emissions from Stationary Sources (Gg) ', 2-18
Table 2-15: N2O Emissions from Stationary Sources (Gg) 2-18
vi Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Table 2-16: NOX, CO, and NMVOC Emissions from Stationary Sources in 1997 (Gg) 2-19
Table 2-17: CH4 Emissions from Mobile Sources (MMTCE) 2-20
Table 2-18: N2O Emissions from Mobile Sources (MMTCE) 2-20
Table 2-19: CH4 Emissions from Mobile Sources (Gg) 2-21
Table 2-20: N2O Emissions from Mobile Sources (Gg) 2-21
Table 2-21: NOX, CO, and NMVOC Emissions from Mobile Sources in 1997 (Gg) 2-22
Table 2-22: CH4 Emissions from Coal Mining (MMTCE) 2-25
Table 2-23: CH4 Emissions from Coal Mining (Tg) 2-25
Table 2-24: Coal Production (Thousand Metric Tons) 2-27
Table 2-25: CH4 Emissions from Natural Gas Systems (MMTCE) 2-28
Table 2-26: CH4 Emissions from Natural Gas Systems (Tg) 2-28
Table 2-27: CH4 Emissions from Petroleum Systems (MMTCE) 2-30
Table 2-28: CH4 Emissions from Petroleum Systems (Gg) 2-30
Table 2-29: Uncertainty in CH4 Emissions from Petroleum Systems (Gg) 2-31
Table 2-30: CO2 Emissions from Natural Gas Flaring 2-32
Table 2-31: NOX, NMVOCs, and CO Emissions from Oil and Gas Activities (Gg) 2-32
Table 2-32: Total Natural Gas Reported Vented and Flared (million ft3) and Thermal
Conversion Factor (Btu/ft3) 2'33
Table 2-33: Emissions from International Bunker Fuels (MMTCE) 2-35
Table 2-34: Emissions from International Bunker Fuels (Gg) 2-35
Table 2-35: Civil Aviation Jet Fuel Consumption for International Transport (million gallons) 2-36
Table 2-36: Marine Vessel Distillate and Residual Fuel Consumption for
International Transport (million gallons) 2-36
Table 2-37: CO2 Emissions from Wood Consumption by End-Use Sector (MMTCE) 2-38
Table 2-38: CO2 Emissions from Wood Consumption by End-Use Sector (Tg) 2-38
Table 2-39: CO2 Emissions from Ethanol Consumption 2-38
Table 2-40: Woody Biomass Consumption by Sector (Trillion Btu) 2-39
Table 2-41: Ethanol Consumption 2-39
Table 3-1: Emissions from Industrial Processes (MMTCE) 3~3
Table 3-2: Emissions from Industrial Processes (Tg) 3-3
Table 3-3: CO2 Emissions from Cement Production 3"4
Table 3-4: Cement Production (Thousand Metric Tons) •. 3~5
Table 3-5: Net CO2 Emissions from Lime Manufacture 3-6
Table 3-6: CO2 Emissions from Lime Manufacture (Tg) 3-6
Table 3-7: Lime Production and Lime Use for Sugar Refining and PCC (Thousand Metric Tons) 3-6
Table 3-8: CO2 Emissions from Limestone & Dolomite Use (MMTCE) 3-8
Table 3-9: CO2 Emissions from Limestone & Dolomite Use (Tg) 3-8
Table 3-10: Limestone & Dolomite Consumption (Thousand Metric Tons) 3-9
Table 3-11: CO2 Emissions from Soda Ash Manufacture and Consumption 3-9
Table 3-12: CO2 Emissions from Soda Ash Manufacture and Consumption (Tg) 3-10
Table 3-13: Soda Ash Manufacture and Consumption (Thousand Metric Tons) 3-10
Table 3-14: CO2 Emissions from Carbon Dioxide Consumption 3-11
Table 3-15: Carbon Dioxide Consumption 3-11
Table 3-16: CO2 Emissions from Iron and Steel Production 3-12
Table 3-17: Pig Iron Production 3-12
Table 3-18: CO2 Emissions from Ammonia Manufacture 3-13
Table 3-19: Ammonia Manufacture 3-13
Table 3-20: CO2 Emissions from Ferroalloy Production 3-14
Table 3-21: Production of Ferroalloys (Metric Tons) 3-15
Table 3-22: CH4 Emissions from Petrochemical Production • 3-15
Table 3-23: Production of Selected Petrochemicals (Thousand Metric Tons) , 3-16
Table 3-24: CH4 Emissions from Silicon Carbide Production 3-16
Table 3-25: Production of Silicon Carbide 3-16
Table 3-26: N2O Emissions from Adipic Acid Production 3-17
vii
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Table 3-27: Adipic Acid Production 3_17
Table 3-28: N2O Emissions from Nitric Acid Production 3_18
Table 3-29: Nitric Acid Production ...".............."."! 3-18
Table 3-30: Emissions of HFCs and PFCs fromODS Substitution (MMTCE) 3-19
Table 3-31: Emissions of HFCs and PFCs from ODS Substitution (Mg) 3-19
Table 3-32: CO2 Emissions from Aluminum Production 3-23
Table 3-33: PFC Emissions from Aluminum Production (MMTCE) 3-23
Table 3-34: PFC Emissions from Aluminum Production (Mg) 3-24
Table 3-35: Production of Primary Aluminum 3_25
Table 3-36: HFC-23 Emissions from HCFC-22 Production ZZZZZZZZZZ!! 3-26
Table 3-37: PFC Emissions from Semiconductor Manufacture 3-27
Table 3-38: SF6 Emissions from Electrical Transmission and Distribution 3-28
Table 3-39: SF6 Emissions from Magnesium Production and Processing 3-29
Table 3-40: 1997 Potential and Actual Emissions of HFCs, PFCs, and SF6
from Selected Sources (MMTCE) 3.30
Table 3-41: NOX, CO, and NMVOC Emissions from Industrial Processes (Gg) , 3-31
Table 4-1: Emissions of NOX, CO, and NMVOC from Solvent Use (Gg) '. 4-2
Table 5-1: Emissions from Agriculture (MMTCE) 5_2
Table 5-2: Emissions from Agriculture (Tg) 5_2
Table 5-3: CH4 Emissions from Enteric Fermentation (MMTCE) 5.3
Table 5-4: CH4 Emissions from Enteric Fermentation (Tg) 5.3
Table 5-5: Cow Populations (thousands) and Milk Production (million kilograms) , 5-4
Table 5-6: CH4 and N2O Emissions from Manure Management (MMTCE) 5-6
Table 5-7: CH4 Emissions from Manure Management (Tg) 5.5
Table 5-8: N2O Emissions from Manure Management (Gg) 5.5
Table 5-9: CH4 Emissions from Rice Cultivation (MMTCE) 5.9
Table 5-10: CH4 Emissions from Rice Cultivation (Gg) 5.9
Table 5-11: Area Harvested for Rice-Producing States (hectares) 5.10
Table 5-12: Primary Cropping Flooding Season Length (days) 5-11
Table 5-13: N2O Emissions from Agricultural Soil Management (MMTCE) 5-12
Table 5-14: N2O Emissions from Agricultural Soil Management (Gg N2O) 5-12
Table 5-15: Commercial Fertilizer Consumption (Metric Tons of Nitrogen) 5-16
Table 5-16: Animal Excretion (Metric Tons of Nitrogen) 5_16
Table 5-17: Bean, Pulse, and Alfalfa Production (Metric Tons of Product) 5-16
Table 5-18: Corn and Wheat Production (Metric Tons of Product) 5-16
Table 5-19: Histosol Area Cultivated (Hectares) ' ZZs-16
Table 5-20: Direct N2O Emissions from Agricultural Cropping Practices (MMTCE) 5-17
Table 5-21: Direct N2O Emissions from Pasture, Range, and Paddock Animals (MMTCE) 5-17
Table 5-22: Indirect N2O Emissions (MMTCE) 5_17
Table 5-23: Emissions from Agricultural Residue Burning (MMTCE) 5-18
Table 5-24: Emissions from Agricultural Residue Burning (Gg) 5-19
Table 6-1: Net CO2 Flux from Land-Use Change and Forestry (MMTCE) 6-2
Table 6-2: Net CO2 Flux from Land-Use Change and Forestry (Tg CO2) 6-2
Table 6-3: Net CO2 Flux from U.S. Forests (MMTCE) ZZ!Z!" 6-4
Table 6-4: Net CO2 Flux from U.S. Forests (Tg CO2) '.'.'.""". 6-4
Table 6-5: U.S. Forest Carbon Stock Estimates (Tg of Carbon) 6-6
Table 6-6: CO2 Flux From Non-Forest Soils (MMTCE) ', ZZZ 6-8
Table 6-7: CO2 Flux From Non-Forest Soils (Tg CO2) !".ZZ!" 6-8
Table 6-8: Areas of Cultivated Organic Soils and Quantities of Applied Minerals 6-9
vili Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Table 7-1: Emissions from Waste (MMTCE) 7-2
Table 7-2: Emissions from Waste (Tg) 7-2
Table 7-3: CH4 Emissions from Landfills (MMTCE) 7-3
Table 7-4: CH4 Emissions from Landfills (Tg) 7-3
Table 7-5: CH4 Emissions from Domestic Wastewater Treatment 7-5
Table 7-6: U.S. Population (millions) and Wastewater BOD Produced (Gg) 7-5
Table 7-7: N2O Emissions from Human Sewage 7-5
Table 7-8: U.S. Population (millions) and Average Protein Intake (kg/person/year) 7-6
Table 7-9: N2O Emissions from Waste Combustion 7-6
Table 7-10: Municipal Solid Waste Generation (Metric Tons) and Percent Combusted 7-7
Table 7-11: U.S. Municipal Solid Waste Combusted by Data Source (Metric Tons) 7-7
Table 7-12: Emissions of NOX, CO, and NMVOC from Waste (Gg) 7-8
Table A-l: 1997 Energy Consumption Data and CO2 Emissions from Fossil Fuel
Combustion by Fuel Type A-4
Table A-2: 1996 Energy Consumption Data and CO2 Emissions from Fossil Fuel
Combustion by Fuel Type A-5
Table A-3: 1995 Energy Consumption Data and CO2 Emissions from Fossil Fuel
Combustion by Fuel Type A-6
Table A-4: 1994 Energy Consumption Data and CO2 Emissions from Fossil Fuel
Combustion by Fuel Type A-7
Table A-5: 1993 Energy Consumption Data and CO2 Emissions from Fossil Fuel
Combustion by Fuel Type A-8
Table A-6: 1992 Energy Consumption Data and CO2 Emissions from Fossil Fuel
Combustion by Fuel Type A-9
Table A-7: 1991 Energy Consumption Data and CO2 Emissions from Fossil Fuel
Combustion by Fuel Type A-10
Table A-8: 1990 Energy Consumption Data and CO2 Emissions from Fossil Fuel
Combustion by Fuel Type A-ll
Table A-9: 1997 Emissions From International Bunker Fuel Consumption A-12
Table A-10: 1997 Non-Energy Use Carbon Stored In Products A-12
Table A-ll: Key Assumptions for Estimating Carbon Dioxide Emissions A-13
Table A-12: Annually Variable Carbon Content Coefficients by Year (MMTCE/QBtu) A-14
Table A-13: Electricity Consumption by End-Use Sector (Billion Kilowatt-hours) A-14
Table B-l: Fuel Consumption by Stationary Sources for Calculating CH4 and N2O Emissions (TBtu) B-2
Table B-2: CH4 and N2O Emission Factors by Fuel Type and Sector (g/GJ) B-2
Table B-3: NOX Emissions from Stationary Sources (Gg) B-3
Table B-4: CO Emissions from Stationary Sources (Gg) B-4
Table B-5: NMVOC Emissions from Stationary Sources (Gg) B-5
Table C-l: Vehicle Miles Traveled for Gasoline Highway Vehicles (109 Miles) C-3
Table C-2: Vehicle Miles Traveled for Diesel Highway Vehicles (109 Miles) C-3
Table C-3: VMT Profile by Vehicle Age (years) and Vehicle/Fuel Type for Highway
Vehicles (percent of VMT) C-4
Table C-4: Fuel Consumption for Non-Highway Vehicles by Fuel Type (U.S. gallons) C-4
Table C-5: Control Technology Assignments for Gasoline Passenger Cars (percentage of VMT) C-5
Table C-6: Control Technology Assignments for Gasoline Light-Duty Trucks (percentage of VMT) C-6
Table C-7: Control Technology Assignments for California Gasoline Passenger
Cars and Light-Duty Trucks (percentage of VMT) C-6
Table C-8: Control Technology Assignments for Gasoline Heavy-Duty Vehicles (percentage of VMT) .... C-6
Table C-9: Control Technology Assignments for Diesel Highway VMT C-7
Table C-10: Emission Factors (g/km) for CH4 and N2O and "Fuel Economy" (g CO2/km)
for Highway Mobile Sources C-7
IX
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Table C-11: Emission Factors for CH4 and N2O Emissions from Non-Highway
Mobile Sources (g/kgfuel) C-8
Table C-12: NOX Emissions from Mobile Sources, 1990-1997 (Gg) C-8
Table C-13: CO Emissions from Mobile Sources, 1990-1997 (Gg) .' C-9
Table C-14: NMVOCs Emissions from Mobile Sources, 1990-1997 (Gg) ! C-9
Table D-l: Mine-Specific Data Used to Estimate Ventilation Emissions D-2
Table D-2: Coal Basin Definitions by Basin and by State D-4
Table D-3: Annual Coal Production (thousand short tons) D-5
Table D-4: Coal Surface and Post-Mining Methane Emission Factors (ft3 per short ton) D-5
Table D-5: Underground Coal Mining Methane Emissions (billion cubic feet) D-6
Table D-6: Total Coal Mining Methane Emissions (billion cubic feet) , D-6
Table E-l: 1992 Data and Emissions (Mg) for Venting and Flaring from Natural Gas
Field Production Stage \ E-2
Table E-2: Activity Factors for Key Drivers , E-3
Table E-3: CH4 Emission Estimates for Venting and Flaring from the Field Production Stage (Mg) E-4
Table F-l: CH4 Emissions from Petroleum Production Field Operations .". .'...„ F-3
Table F-2: CH4 Emissions from Petroleum Storage '. F-3
Table F-3: CH4 Emissions from Petroleum Refining F-3
Table F-4: CH4 Emissions from Petroleum Transportation: Loading Alaskan Crude
Oil onto Tankers (Barrels/day) '. F-4
Table F-5: CH4 Emissions from Petroleum Transportation: Crude Oil Transfers to
Terminals (Barrels/day) F-4
Table F-6: CH4 Emissions from Petroleum Transportation: Ballast Emissions (Barrels/day) F-4
Table F-7: Total CH4 Emissions from Petroleum Transportation F-5
Table G-l: Livestock Population (thousand head) G-2
Table G-2: Dairy Cow CH4 Emission Factors and Milk Production Per Cow G-2
Table G-3: CH4 Emission Factors Beef Cows and Replacements (kg/head/yr) G-2
Table G-4: Methane Emissions from Livestock Enteric Fermentation (Tg) G-3
Table G-5: Enteric Fermentation CH4 Emission Factors '. G-3
Table H-l: Livestock Population (1000 head) '. H-2
Table H-2: Dairy Cow and Swine CH4 Conversion Factors !. H-3
Table H-3: Dairy Cow and Swine Constants '. H-3
Table H-4: CH4 Emissions from Livestock Manure Management (Tg) H-4
Table M: Municipal Solid Waste (MSW) Contributing to CH4 Emissions (Tg) .' 1-2
Table 1-2: CH4 Emissions from Landfills (Tg) 1-3
Table 1-3: Municipal Solid Waste Landfill Size Definitions (Tg) 1-3
Table J-l: Global Warming Potentials and Atmospheric Lifetimes (years) J-l
Table K-l: Emissions of Ozone Depleting Substances (Mg) K-2
Table L-l: SO2 Emissions (Gg) L-2
Table L-2: SO2 Emissions from Electric Utilities (Gg) L-2
Table O-l: 1997 U.S. Energy Statistics (physical units) O-5
Table 0-2: Conversion Factors to Energy Units (heat equivalents) O-6
Table O-3: 1997 Apparent Consumption of Fossil Fuels (TBtu) O-7
Table O-4: 1997 Potential Carbon Emissions O-8
Table O-5: 1997 Non-Energy Carbon Stored in Products O-9
x Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table O-6: Reference Approach CO2 Emissions from Fossil Fuel Consumption
(MMTCE unless otherwise noted) O-9
Table O-7: 1997 Energy Consumption in the United States: Sectoral vs. Reference Approaches (TBtu) .. O-9
Table O-8: 1997 CO2 Emissions from Fossil Fuel Combustion by Estimating Approach (MMTCE) O-10
Table O-9: 1996 Energy Consumption in the United States: Sectoral vs. Reference Approaches (TBtu) O-10
Table O-10: 1996 CO2 Emissions from Fossil Fuel Combustion by Estimating Approach (MMTCE) .... O-10
Table Q-l: Guide to Metric Unit Prefixes Q-l
Table Q-2: Conversion Factors to Energy Units (heat equivalents) Q-3
Table S-l: Guide to Chemical Symbols S-l
Figures
Figure ES-1: U.S. GHG Emissions by Gas ES-2
Figure ES-2: Annual Percent Change in U.S. GHG Emissions ES-2
Figure ES-3: Absolute Change in U.S. GHG Emissions Since 1990 ES-2
Figure ES-4: 1997 Greenhouse Gas Emissions by Gas ES-4
Figure ES-5: U.S. Greenhouse Gas Emissions Per Capita and Per Dollar of Gross Domestic Product ES-6
Figure ES-6: 1997 Sources of CO2 ES-9
Figure ES-7: 1997 U.S. Energy Consumption by Energy Source ES-10
Figure ES-8: U.S. Energy Consumption (Quadrillion Btu) ES-10
Figure ES-9: 1997 CO2 Emissions from Fossil Fuel Combustion by Sector and Fuel Type ES-11
Figure ES-10: 1997 End-Use Sector Emissions of CO2 from Fossil Fuel Combustion ES-11
Figure ES-11: 1997 Sources of CH4 ES-14
Figure ES-12: 1997 Sources of N2O ES-16
Figure ES-13: 1997 Sources of HFCs, PFCs, and SF6 , ES-18
Figure 1-1: U.S. GHG Emissions by Gas 1-7
Figure 1-2: Annual Percent Change in U.S. GHG Emissions 1-7
Figure 1-3: Absolute Change in U.S. GHG Emissions Since 1990 1-8
Figure 1-4: U.S. Greenhouse Gas Emissions Per Capita and Per Dollar of Gross Domestic Product 1-9
Figure 1-5: U.S. GHG Emissions by Chapter/IPCC Sector 1-12
Figure 2-1: 1997 Energy Chapter GHG Sources 2-1
Figure 2-2: 1997 U.S. Energy Consumption by Energy Source 2-3
Figure 2-3: U.S. Energy Consumption (Quadrillion Btu) 2-3
Figure 2-4: 1997 CO2 Emissions from Fossil Fuel Combustion by Sector and Fuel Type 2-3
Figure 2-5: Fossil Fuel Production Prices 2-4
Figure 2-6: 1997 End-Use Sector Emissions of CO2 from Fossil Fuel Combustion 2-6
Figure 2-7: Motor Gasoline Retail Prices (Real) 2-7
Figure 2-8: Motor Vehicle Fuel Efficiency 2-8
Figure 2-9: Heating Degree Days 2-8
Figure 2-10: Electric Utility Retail Sales by End-Use Sector 2-10
Figure 2-11: Change in CO2 Emissions from Fossil Fuel Combustion Since 1990 by End-Use Sector .... 2-12
Figure 2-12: Mobile Source CH4 and N2O Emissions 2-22
Figure 3-1: 1997 Industrial Processes Chapter GHG Sources 3-1
Figure 5-1: 1997 Agriculture Chapter GHG Sources 5-1
Figure 7-1: 1997 Waste Chapter GHG Sources 7-1
xi
-------
Boxes
Box ES-1: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data f ES-5
Box ES-2: Greenhouse Gas Emissions from Transportation Activities ES-6
Box ES-3: Electric Utility-Related Greenhouse Gas Emissions ES-8
Box ES-4: Emissions of Ozone Depleting Substances ES-20
Box ES-5: Sources and Effects of Sulfur Dioxide ES-22
j
Box 1-1: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data ', 1-9
Box 1-2: Greenhouse Gas Emissions from Transportation Activities 1-13
Box 1-3: Electric Utility-Related Greenhouse Gas Emissions ! 1-14
Box 2-1: Sectoral Carbon Intensity Trends Related to Fossil Fuel and Overall Energy Consumption 2-11
Box 3-1: Potential Emission Estimates of MFCs, PFCs, and SF6 ', 3-30
xii Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Changes in This Year's
U.S. Greenhouse Gas
Inventory Report
Each year the EPA not only revises the estimates presented in the official U.S. Greenhouse Gas Inventory of
Emissions and Sinks but also attempts to improve the analyses themselves through the use of better methods or data.
A summary of the latest changes and additions to this report is provided below:
• An expanded discussion of emissions from International Bunker Fuels has been included in the Energy chapter.
Emissions of CH4, N2O, CO, NOX, and NMVOCs from these fuels have been estimated for the first time. Carbon
dioxide emissions from aircraft have nearly doubled because of the inclusion of fuels consumed by foreign
flagged air carriers for the first time. Previously, only U.S. flagged air carriers were able to be included. A new
source of data for consumption of fuels for marine bunkers has also resulted in minor changes in the estimates
from ships and boats.
• Nitrous oxide emissions from the combustion of jet fuel in aircraft were estimated for the first time using a
simplified methodology based on the emission factors presented in IPCC/UNEP/OECD/IEA (1997).
• A new comparison of recent trends in various environmental and economic variables related to U.S. greenhouse
gas emissions is presented in Box 1-1.
• An new analysis of sectoral (i.e., residential, commercial, industrial, transportation, and electric utility) carbon
intensities and emission trends from CO2 Emissions from Fossil Fuel Combustion is presented in Box 2-1.
• Carbon stored through the non-energy uses of fossil fuels was given a more detailed treatment in Table 2-5 and
Table 2-6.
• The estimates for CO2 emissions from Natural Gas Flaring were revised slightly and made more consistent with
methane emission estimates under the venting portion of Petroleum Systems.
• Wood consumed as fuel is no longer reported by EIA separately for the commercial and residential end-use
sectors; therefore, CH4 and N2O emission estimates from wood burned under Stationary Sources for these two
sectors were not disaggregated by end-use sector.
• Estimates of potential emissions for select HFCs, PFCs, and SF6 sources have been presented for the first time in
Box 3-1.
• Nitrous oxide emission estimates from Agricultural Soil Management have been revised to account for the appli-
cation of additional quantities of animal manure applied to soils. This revision was based on a better understand-
ing of the ultimate fate of unmanaged animal manure.
• Useful constants, unit definitions, and conversion factors have been included for the first time in Annex Q. A list
of abbreviations and chemical symbols has also been included in Annex R and Annex S, respectively.
• A detailed glossary of terms related to greenhouse gas emissions and inventories has been provided for the first
time in Annex T.
XIII
-------
-------
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 gas (GHG) emissions. This
inventory adheres to both (1) a comprehensive and detailed methodology for estimating sources and sinks of anthro-
pogenic 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 differ-
ent emission sources and greenhouse gases to climate change. Moreover, systematically and consistently estimating
national and international emissions is a prerequisite for evaluating the cost-effectiveness and feasibility of mitigation
strategies and emission reduction technologies.
This chapter summarizes the latest information on U.S. anthropogenic greenhouse gas emission trends from
1990 through 1997 To ensure that the U.S. emissions inventory is comparable to those of other UNFCCC signatory
countries, 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). For
most source categories, the IPCC default methodologies were expanded, resulting in a more comprehensive and
detailed estimate of emissions.
Naturally occurring greenhouse gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous ox-
ide (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 hydrochlorofiuorocarbons (HCFCs) are halocarbons that contain chlorine, while halocarbons that con-
tain bromine are referred to as halons. Other fluorine containing halogenated substances include hydrofluorocarbons
(HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).
There are also several gases that 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. These
gases—referred to as ozone precursors—include carbon monoxide (CO), oxides of nitrogen (NOX), and nonmethane
volatile organic compounds (NMVOCs).2 Aerosols—extremely small particles or liquid droplets often produced by
emissions of sulfur dioxide (SO2)—can also affect the absorptive characteristics of the atmosphere.
Although CO2, CH4, and N2O occur naturally in the atmosphere, their atmospheric concentrations have been affected
by human activities. Since pre-industrial time (i.e., since about 1750), concentrations of these greenhouse gases have
increased by 28,145, and 13 percent, respectively (IPCC 1996). This build-up has altered the composition of the earth's
atmosphere, and may affect the global climate system.
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 Also referred to in the U.S. Clean Air Act as "criteria pollutants."
Executive Summary ES-1
-------
Beginning in the 1950s, the use of CFCs and other
stratospheric ozone depleting substances (ODSs) in-
creased by nearly 10 percent per year until the mid-1980s,
when international concern about ozone depletion led to
the signing of the Montreal Protocol on Substances that
Deplete the Ozone Layer. Since then, the consumption
of ODSs has been undergoing a phase-out. In contrast,
use of ODS substitutes such as MFCs, PFCs, and SF6 has
grown significantly during this time.
Recent Trends in U.S.
Greenhouse Gas Emissions
Total U.S. greenhouse gas emissions rose in 1997
to 1,813.6 million metric tons of carbon equivalents
(MMTCE)3 (11.1 percent above 1990 baseline levels). The
single year increase in emissions from 1996, to 1997 was
1.3 percent (23.1 MMTCE), down from the previous year's
increase of 3.3 percent. 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-1 provides a detailed summary of U.S. greenhouse gas
emissions and sinks for 1990 through 1997.
Figure ES-4 illustrates the relative contribution of
the direct greenhouse gases to total U.S. emissions in
1997. The primary greenhouse gas emitted by human
activities was CO2. The largest source of CO2 and of over-
all greenhouse gas emissions in the United States was
Figure ES-1
TOJh'l Change in U.S. GHG Emissions
1,750
1,500
1,250
1,000
750
500
250-
U.S. GHG Emissions by Gas
• HFCs, PFCs, & SFg • Methane
• Nitrous Oxide Carbon Dioxide
1.632 1.620 1.645 1.675 1713 1J2i -
1990 1991 1992 1993 1994 1995 1996 1997
3.3%
1991 1992 1993 1994 1995 1996 1997
fossil fuel combustion. Methane emissions resulted pri-
marily from decomposition of wastes in landfills, ma-
nure and enteric fermentation associated with domestic
livestock, natural gas systems, and coal mining. Emis-
sions of N2O were dominated by agricultural soil man-
agement and mobile source fossil fuel combustion. The
substitution of ozone depleting substances and emissions
of HFC-23 during the production of HCFC-22 were the
primary contributors to aggregate HFC emissions. PFC
emissions came mainly from primary aluminum produc-
tion, while electrical transmission and distribution sys-
tems emitted the majority of SF6.
As the largest source of U.S. GHG emissions, CO2
from fossil fuel combustion accounted for 81 percent of
emissions in 1997 when each gas is weighted by its Glo-
Figure ES-3
1991 1992 1993 1994 1995 1996 1997
* Estimates we presented in units of millions of metric tons of carbon equivalents (MMTCE), which weights each gas by its GWP value, i
Global Warming Potential (see following section).
ES-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table ES-1: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (MMTCE)
Gas/Source
1990
1991 1992 1993 1994 1995 1996 1997
C02
Fossil Fuel Combustion
Natural Gas Flaring
Cement Manufacture
Lime Manufacture
Limestone and Dolomite Use
Soda Ash Manufacture and Consumption
Carbon Dioxide Consumption
Land-Use Change and Forestry (Sink)3
International Bunker Fuelsb
CH
Stationary Sources
Mobile Sources
Coal Mining
Natural Gas Systems
Petroleum Systems
Petrochemical Production
Silicon Carbide Production
Enteric Fermentation
Manure Management
Rice Cultivation
Agricultural Residue Burning
Landfills
Wastewater Treatment
International Bunker Fuelsb
H20
Stationary Sources
Mobile Sources
Adipic Acid Production
Nitric Acid Production
Manure Management
Agricultural Soil Management
Agricultural Residue Burning
Human Sewage
Waste Combustion
: International Bunker Fuels'1
MFCs, PFCs, and SF6
- Substitution of Ozone Depleting Substances
' Aluminum Production
HCFC-22 Production
Semiconductor Manufacture
Electrical Transmission and Distribution
Magnesium Production and Processing
Total Emissions
Net Emissions (Sources and Sinks)
1,344.3
1,327.2
2.3
8.9
3.3
1.4
1.1
0.2
(311.5)
27.1
169.9
2.3
1.4
24.0
32.9
1.6
0.3
+
32.7
14.9
2.5
0.2
56.2
0.9
+
95.7
3.8
13.6
4.7
3.3
2.6
65.3
0.1
2.1
0.1
0.2
22.2
0.3
4.9
9.5
0.2
5.6
1.7
1,632.1
1,320.6
1,329.8
1,312.6
2.6
8.7
3.2
1.3
1.1
0.2
(311.5)
27.8
171.0
2.4
1.4
22.8
33.3
1.6
0.3
+
32.8
15.4
2.5
0.2
57.6
0.9
+
97.6
3.8
14.2
4.9
3.3
2.8
66.2
0.1
2.1
0.1
0.2
21.6
0.2
4.7
8.4
0.4
5.9
2.0
1,620.0
1,308.5
1,349.6
1,332.4
2.6
8.8
3.3
1.2
1.1
0.2
(311.5)
29.0
172.5
2.4
1.4
22.0
33.9
1.6
0.3
+
33.2
16.0
2.8
0.2
57.8
0.9
+
100.1
3.9
15.2
4.6
3.4
2.8
68.0
0.1
2.2
0.1
0.2
23.0
0.4
4.1
9.5
0.6
6.2
2.2
1,645.2
1,333.7
1,379.2
1,360.6
3.5
9.3
3.4
1.1
1.1
0.2
(208.6)
29.9
172.0
2.4
1.4
19.2
34.1
1.6
0.4
+
33.6
16.1
2.5
0.2
59.7
0.9
+
100.4
3.9
15.9
4.9
3.5
2.9
67.0
0.1
2.2
0.1
0.3
23.4
1.4
3.5
8.7
0.8
6.4
2.5
1,675.0
1,466.5
1,403.5
1,383.9
3.6
9.6
3.5
1.5
1.1
0.2
(208.6)
27.4
175.5
2.4
1.4
19.4
33.5
1.6
0.4
+
34.5
16.7
3.0
0.2
61.6
0.9
+
108.3
4.0
16.7
5.2
3.7
2.9
73.4
0.1
2.2
0.1
0.2
25.9
4.0
2.8
8.6
1.0
6.7
2.7
1,713.2
1,504.7
1,419.2
1,397.8
4.5
9.9
3.7
1.9
1.2
0.3
(208.6)
25.4
178.6
2.5
1.4
20.3
33.2
1.6
0.4
+
34.9
16.9
2.8
0.2
63.6
0.9
+
105.4
4.0
17.0
5.2
3.7
2.9
70.2
0.1
2.3
0.1
0.2
30.8
9.5
2.7
7.4
1.2
7.0
3.0
1,733.9
1,525.4
1,469.3
1,447.7
4.3
9.9
3.8
2.0
1.2
0.3
(208.6)
25.4
178.3
2.5
1.4
18.9
33.7
1.5
0.4
+
34.5
16.6
2.5
0.2
65.1
0.9
+
108.2
4.1
17.4
5.4
3.9
3.0
72.0
0.1
2.3
0.1
0.2
34.7
11.9
2.9
8.5
1.4
7.0
3.0
1,790.5
1,582.0
1,487.9
1,466.0
4.2
10.2
3.9
2.1
1.2
0.3
(208.6)
26.6
179.6
2.2
1.4
18.8
33.5
1.6
0.4
+
34.1
17.0
2.7
0.2
66.7
0.9
+
109.0
4.1
17.5
3.9
3.8
3.0
74.1
0.1
2.3
0.1
0.2
37.1
14.7
2.9
8.2
1.3
7.0
3.0
1,813.6
1,605.0
+ Does not exceed 0.05 MMTCE
a Sinks are only included in net emissions total. Estimates of net carbon sequestration due to land-use change and forestry activities exclude
non-forest soils, and are based partially upon projections of forest carbon stocks.
b Emissions from International Bunker Fuels are not included in totals. . . ,
Note: Totals may not sum due to independent rounding.
Executive Summary ES-3
-------
Figure ES-4
1997 Greenhouse Gas Emissions by Gas
HFCs, PFCs & SFg 2.0%
> - 6.0%"
|CH4-9.9%
CO2 - 82.0%
bal Warming Potential.4 Emissions from this source grew
by 11 percent (138.8 MMTCE) from 1990 to 1997 and
were responsible for over three-quarters of the increase
In national emissions during this period. The annual in-
crease in CO2 emissions from this source was 1.3 per-
cent in 1997, down from the previous year when emis-
sions increased by 3.6 percent.
The dramatic increase in fossil fuel combustion-
related CO2 emissions in 1996 was primarily a function
of two factors: 1) fuel switching by electric utilities from
natural gas to more carbon intensive coal as gas prices
rose sharply due to weather conditions, which drove up
residential consumption of natural gas for heating; and
2) higher petroleum consumption for transportation. In
1997, by comparison, electric utility natural gas consump-
tion rose to regain much of the previous year's decline as
the supply available rose due to lower residential con-
sumption. Despite this increase in natural gas consump-
tion by utilities and relatively stagnant U.S. electricity
consumption, coal consumption rose in 1997 to offset
the temporary shut-down of several nuclear power plants.
Petroleum consumption for transportation activities in
1997 also grew by less than one percent, compared to
over three percent the previous year (see Table ES-2).
The annual increase in CO2 emissions from petroleum in
1997 is based on motor gasoline sales data from the
U.S. Energy Information Administration; it is expected
to be revised upward with the publication of future en-
ergy statistics.
Overall, from 1990 to 1997, total emissions of CO2,
CH4, and N2O increased by 143.5 (11 percent), 9.7 (6
percent), and 13.4 MMTCE (14 percent), respectively.
During the same period, weighted emissions of HFCs,
PFCs, and SF6 rose by 14.9 MMTCE (67 percent). De-
spite being emitted in smaller quantities relative to the
other principle greenhouse gases, emissions of HFCs,
PFCs, and SF6 are significant because of their extremely
high Global Wanning 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, which was estimated to be 11
percent of total emissions in 1997.
Other significant trends in emissions from addi-
tional source categories over the eight year period from
1990 through 1997 included the following:
• Aggregate HFC and PFC emissions resulting from
the substitution of ozone depleting substances (e.g.,
CFCs) increased dramatically (by 14.4 MMTCE).
This increase was partly offset, however, by reduc-
tions in PFC emissions from aluminum production
(41 percent) and HFC emissions from HCFC-22 pro-
duction (14 percent), both as a result of voluntary
industry emission reduction efforts and, in the former
case, from falling domestic aluminum production.
• Combined N2O and CH4 emissions from mobile
source fossil fuel combustion rose by 3.9 MMTCE
(26 percent), primarily due to increased rates of N2O
generation in highway vehicles.
Table ES-2: Annual Percent Change in C02
Emissions from Fossil Fuel Combustion for
Selected Sectors and Fuels
Sector
Electric Utility
Electric Utility
Residential
Transportation*
Fuel
Type
Coal
Natural Gas
Natural Gas
Petroleum
1995
to 1996
5,7%
-14.6%
8:i%
3,4%
1996
to 1997
2.9%
8.7%
-4.4%
0.3%
Excludes emissions from International Bunker Fuels.
4 See section below entitled Global Warming Potential.
ES-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Methane emissions from the decomposition of waste
in municipal and industrial landfills rose by 10.5
MMTCE (19 percent) as the amount of organic mat-
ter in landfills steadily accumulated.
Emissions from coal mining dropped by 5.2
MMTCE (21 percent) as the use of methane from
degasification systems increased significantly.
Nitrous oxide emissions from agricultural soil man-
agement increased by 8.8 MMTCE (13 percent) as
fertilizer consumption and cultivation of nitrogen fix-
ing crops rose.
• An additional domestic adipic acid plant installed
emission control systems in 1997; this was estimated
to have resulted in a 1.4 MMTCE (27 percent) de-
cline in emissions from 1996 to 1997 despite an in-
crease in production.
The following sections describe the concept of
Global Warming Potentials (GWPs), present the anthro-
pogenic sources and sinks of greenhouse gas emissions
in the United States, briefly discuss emission pathways,
summarize the emission estimates, and explain the rela-
tive importance of emissions from each source category.
Box ES-1: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data
There are several ways to assess a nation's greenhouse gas emitting intensity. These measures of intensity could be based on
aggregate energy consumption because energy-related activities are the largest sources of emissions, on fossil fuel consumption
only because almost all energy-related emissions involve the combustion of fossil fuels, on electricity consumption because
electric utilities were the largest sources of U.S. greenhouse gas emissions in 1997, on total gross domestic product as a measure
of national economic activity, or on a per capita basis. Depending upon which of these measures was used, the United States could
appear to have reduced or increased its national greenhouse gas intensity. Table ES-3 provides data 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 1.5 percent since 1990. This rate is slightly slower than that for total energy or fossil fuel consumption—
thereby indicating an improved or lower greenhouse gas emitting intensity—and much slower than that for either electricity con-
sumption or overall gross domestic product. Emissions, however, are growing faster than national population, thereby indicating a
worsening or higher greenhouse gas emitting intensity on a per capita basis (see Figure ES-5). Overall, atmospheric C02 concen-
• trations—a function of many complex anthropogenic and natural processes—are increasing at 0.4 percent per year.
Table ES-3: Recent Trends in Various U.S. Data (Index 1990 = 100)
Variable
1990
1991 1992 1993 1994 1995 1996 1997 Growth
GHG Emissions3
Energy Consumption5
Fossil Fuel Consumption0
Electricity Consumption0
GDPd
Population6
Atmospheric C02 Concentration*
100
100
100
100
100
100
100
99
100
99
102
99
101
100
101
101
101
102
102
102
101
103
104
104
105
104
103
101
105
106
106
108
108
104
101
106
108
107
111
110
105
102
110
112
110
114
114
106
102
111
112
112
115
118
107
103
1.5%
1.6%
1.6%
2.0%
2.5%
1.0%
0.4%
aGWP weighted values
b Energy content weighted values. Source: DOE/EIA
c Source: DOE/EIA
d Gross Domestic Product in chained 1992 dollars (BEA1998)
e (U.S. Census Bureau 1998)
f Mauna Loa Observatory, Hawaii (Keeling and Whorf 1998)
a Average annual growth rate
Executive Summary ES-5
-------
Figure ES-5
Ell Dollar of Gross Domestic Product
108
Emissions per capita
Emissions per $GDP
92 J
1990 1991 1992 1993 1994 1995 1996 1997
Box ES-2: Greenhouse Gas Emissions from Transportation Activities
ii'ii»™ in(Sas»9 a" overthe wor|d> '"eluding in tne United States.,Since ttieJ^Os^h? umber,, of highway
;;; Vehicles registered in the United States has increased taster than .the., overall population, agcording to the FedeVal Highway Admin-
,1,: fetation, Likewise, tfte, number of miles driven— up 1 8 percent from i 990 to 1 997— and gallons of" gasoline Consumed each year
! til ttw United States have increased relatively steadily since the 1 980s, according to the Energy Information Administration. These
- ^crSem,ln,miPl!?r y£c^,,f£a^ are th,e res""i of a confluence of factors including population growth, economic growth, increas-
l Iflg Urban" "sprawC'and" low fuel prices.
f< i , ,.. ..... . if i
= One of the unintended consequences of these changes is a slowing of progress toward cleaner air in both urban and rural parts of
:: Ito.fiflynlry. Passenger cars, trucks, motorcycles, and buses emit significant quantities of air pollutants with! local, regional, and
I ^zl::6*6'?:^0^!!!"1:^,8 are ro3!0/ soulces of ca/bon !™nPxlde (P°), carbon dioxide (C02),,, methane |(CH4), nonmethane
•- : Wtaie organic compounds (NMVO'c'sj, nitrogen oxides (I\!0X), nitrous oxide (I\J20), and hydrofluorocarbons; (HFCs). Motor ve-
::;; f&tes^. ^ Jr/iportaflt contributors to many serious air pollution problems, including ground-level ozone or smog, acid rain, fine
'lilii'iilllllil'lil'iiP yplllll i'J ihlWii'i'ii1'!, ^l'*il!!!B'^ii^M^M!ll:l!ll!li1lW .iLifililii! „ /"ii'l'i f'!'1'.'!!!111 ',',i ', I .J'lii'Wl'lli,, "! I'.'i '"l'i '" ...... ii :!' '"Jli'1, , , i .,! 'IIK VJ"1 1 'i* i .i':'"1'!,!1'!, ''.ii niiiht1,!1!!!!,1!!11, ' ,;,,, p," * ...... :", I ',,i,:,'L ...... "^jf , '.i :', ,• : '
ce, ...... teiSI0,sj,|lje,, &, MSi,,^^^ ...... fedijn, jasoline, developed strict emissiori 'Standards, for new
passingeFcTCan! ..... emission'contrpTpragrams,ji-equiredms^
Snd maintenance programs, antJ more recently, introduced the use of reformulated gasoline to mitigate the a'ir pollution impacts
from motor vehicles. New vehicles are now equipped with advanced emissions controls, which are designed to reduce emissions
Of nitofisn oxides, hydrocarbons, and carbon monoxide.
this report reflects new data on the role that automotive catalytic converters play in emissions of I\I20, a powerful greenhouse gas.
The EPA's Office of Mobile Sources has conducted a series of tests in order to measure the magnitude of I\J20 emissions from
gasoline-fueled passenger cars and light-duty trucks equipped with catalytic converters.. Results show thatN20 emissions are
lower lhan the IPCC default factors, and the United States has shared this data with the IPCC. In this report, ndw emission factors
developed from these measurements and from previously ; published ^literature were usedjp .calculate 'e^sjons from.' mobile
sources in the United States (see Annex C). "_" ..... "_'*_ " " '' ' ' ""'' "' "' ...... "' ' '[ "\ ""_' ^'J^ | '" ......... i ...... ]|""~ ' '"^ ''"" ^ ..... [ ..... "^" " "" " ^ "
Table ES-4 summarizes greenhouse gas emissions from all transportation-related activities. Overall, transportation activities—
excluding international bunker fuels— accounted for an almost constant 26 percent of total U.S. areenhouse gas emissions from
1990 to 1997, These emissions were primarily C02 from fuel combustion, which increased by 10 percent fjom 1990 to 1997.
However, because of larger increases in N20 and HFC emissions during this period, overall emissions from transportation activities
aclually increased by 12 percent.
ES-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table ES-4: Transportation-Related Greenhouse Gas Emissions (MMTCE)
Gas/Vehicle Type
1990 1991 1992 1993 1994 1995 1996 1997
C02
Passenger Cars3
Light-Duty Trucks3
Other Trucks
Buses
Aircraft
Boats and Vessels
Locomotives
Other"
International Bunker Fuels0
CH4
Passenger Cars
Light-Duty Trucks
Other Trucks and Buses
Aircraft
Boats and Vessels
Locomotives
Otherd
International Bunker Fuels0
MZ0
Passenger Cars
Light-Duty Trucks
Other Trucks and Buses
Aircraftd
Boats and Vessels
Locomotives
Other"
International Bunker Fuels0
MFCs
Mobile Air Conditioners6
Total0
405.0
169.3
77.5
57.3
2.7
50.5
16.4
7.5
23.8
27.1
1.4
0.8
0.4
0.1
+
+
+
0.1
+
13.6
8.7
3.4
0.7
0.5
0.1
0.1
0.2
0.2
+
+
420.0
396.7
167.8
77.2
55.1
2.9
48.4
15.9
6.9
22.5
27.8
1.4
0.7
0.4
0.1
+
+
+
0.1
+
14.2
9.1
3.7
0.7
0.5
0.1
0.1
0.2
0.2
+
+
412.3
402.4
172.0
77.2
56.7
2.9
. 47.4
16.4
7.4
22.4
29.0
1.4
0.7
0.4
0.1
+
+
+
0.1
+
15.2
9.7
3.9
0.7
0.5
0.1
0.1
0.2
0.2
0.2
0.2
419.1
406.8
173.5
80.5
59.9
3.1
47.6
11.7
6.8
23.8
29.9
1.4
0.7
0.4
0.2
+
+
+
0.1
+
15.9
10.1
4.2
0.7
0.5
0.1
0.1
0.2
0.3
0.7
0.7
424.8
422.1
172.5
87.2
62.7
3.3
49.6
13.9
8.0
24.9
27.4
1.4
0.7
0.4
0.2
+
+
+
0.1
+
16.7
10.0
5.1
0.8
0.5
0.1
0.1
0.2
0.2
1.3
1.3
441.5
430.7
175.6
89.2
64.2
3.5
48.3
16.8
8.1
24.9
25.4
1.4
0.7
0.4
0.2
+
+
+
0.1
+
17.0
10.1
5.2
0.8
0.5
0.1
0.1
0.2
0.2
2.5
2.5
451.6
445.3
160.8
109.9
68.3
3.0
50.5
18.5
8.8
25.5
25.4
1.4
0.6
0.5
0.2
+
+
+
0.1
+
17.4
8.9
6.8
0.9
0.5
0.1
0.1
0.2
0.2
3.6
3.6
467.7
446.5
162.6
111.1
69.5
3.0
50.1
15.4
9.0
25.8
26.6
1.4
0.6
0.5
0.2
+
+
+
0.1
+
17.5
9.1
6.8
0.9
0.5
0.1
0.1
0.2
0.2
4.5
4.5
469.9
+ Does not exceed 0.05 MMTCE
Note: Totals may not sum due to independent rounding.
a In 1996, the U.S. Federal Highway Administration modified the definition of light-duty trucks to include minivans and sport utility vehicles.
Previously, these vehicles were included under the passenger cars category. Hence the sharp drop in G02 emissions for passenger cars from
1995 to 1996 was observed. This gap, however, was offset by an equivalent rise in C02 emissions from light-duty trucks.
b "Other" C02 emissions include motorcycles, construction equipment, agricultural machinery, pipelines, and lubricants.
c Emissions from International Bunker Fuels are not included in totals.
d "Other" CH4 and N20 emissions include motorcycles, construction equipment, agricultural machinery, 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.
e Includes primarily HFC-134a
Executive Summary ES-7
-------
Box ES-3: Electric Utility-Related Greenhouse Gas Emissions
Like transportation, activities related to the generation, transmission, and distribution of electricity in the United States result in
greenhouse gas emissions. Table ES-5 presents greenhouse gas emissions from electric utility-related activities. Aggregate emis-
sions from electric utilities of all greenhouse gases increased by 1 1 .8 percent from 1 990 to 1 997, and accounted for just under 30
percent of total U.S. greenhouse emissions during the same period. The majority of these emissions resulted from the combustion
of coal in boilers to produce steam that is passed through a turbine to generate electricity. Overall, the generation of electricity
results !n a larger portion of total U.S. greenhouse gas emissions than any other activity.
•: •• |
Table ES-5: Electric Utility-Related Greenhouse Gas Emissions (MMTCE)
Gas/Fuel Type or Source 1990 1991 1992 1993 1994 1995 1996 1997
CO-,
Coal
Natural Gas
Petroleum
Geoihermal
CH4
Stationary Sources (Utilities)
N20
Stationary Sources (Utilities)
SFS
Electrical Transmission and Distribution
Total
+ Does not exceed 0.05 MMTCE
Note; Totals may not sum due to independent rounding.
476.8
409.0
41.2
26.6
0.1
0.1
0.1
2.0
2.0
5.6
5.6
484.6
473.4
407.2
41.1
25.1
0.1
0.1
0.1
2.0
2.0
5.9
5.9
481.4
472.5
411.8
40.7
19.9
0.1
0.1
0.1
2.0
2.0
6.2
6.2
480.8
490.7
428.7
39.5
22.5
0.1
0.1
0.1
2.1
2.1
6.4
6.4
499.3
494.8
430.2
44.0
20.6
+
0.1
0.1
2.1
2,1
6.7
6.7
503.7
494.1
433.0
47.2|
14.0,
+
0.1
0.1;
2.1
2.1,,;
7.0
7.0,;
503.3
513.2
457.5
40.3
15.4
+
0.1
0.1
2.2
2.2
7.0
7.0
522.5
532.3
470.9
43.8
17.6
+
0.1
0.1
2.3
2.3
7.0
7.0
541.7
Global Warming Potentials
Gases in the atmosphere can contribute to the green-
house effect both directly and indirectly. Direct effects
occur when the gas itself is a greenhouse gas; Indirect ra-
diative forcing occurs when chemical transformations of
the original gas produce a gas or gases that are greenhouse
gases, or when a gas influences the atmospheric lifetimes
of other gases. The concept of a Global Warming Poten-
tial (GWP) has been developed to compare the ability of
each greenhouse gas to trap heat in the atmosphere rela-
tive to another gas. Carbon dioxide was chosen as the ref-
erence gas to be consistent with IPCC guidelines.
Global Warming Potentials are not provided for the
criteria pollutants CO, NOX, NMVOCs, and SO2 because
there is no agreed upon method to estimate the contribu-
tion of gases that indirectly affect radiative forcing to
climate change (IPCC 1996).
All gases in this executive summary are presented
in units of million metric tons of carbon equivalents
(MMTCE). Carbon comprises 12/44ths of carbon diox-
ide by weight. In order to convert emissions reported in
teragrams (Tg) of greenhouse gas to MMTCE, the fol-
lowing equation was used:
a
The GWP of a greenhouse gas is the ratio of glo-
bal warming, or radiative forcing (both direct and indi-
rect), from one unit mass of a greenhouse gas to that of
one unit mass of carbon dioxide over a period of time.
While any time period can be selected, the 100 year
GWPs recommended by the IPCC and employed by the
United States for policy making and reporting purposes
were used in this report (IPCC 1996). A tabulation of
GWPs is given below in Table ES-6.
ES-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table ES-6: Global Warming Potentials
(100 Year Time Horizon)
Gas
Figure ES-6
GWP
Carbon dioxide (C02)
Methane (CH4)*
Nitrous oxide (N20)
HFC-23
HFC-125
HFC-134a
HFC-143a
HFC-1523
HFC-227ea
HFC-236fa
HFC-4310mee
CF4
C2F6
Q p
SF6
1
21
310
11,700
2,800
1,300
3,800
140
2,900
6,300
1,300
6,500
9,200
7,000
7,400
23,900
Source: (IPCC 1996)
* The methane GWP 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.
Carbon Dioxide Emissions
The global carbon cycle is made up of large car-
bon flows and reservoirs. Hundreds of billions of tons of
carbon in the form of CO2 are absorbed by oceans and
living biomass (sinks) and are emitted to the atmosphere
annually through natural processes (sources). When in
equilibrium, carbon fluxes among these various reser-
voirs are roughly balanced.
Since the Industrial Revolution, this equilibrium
of atmospheric carbon has been altered. Atmospheric
concentrations of CO2 have risen about 28 percent (IPCC
1996), principally because of fossil fuel combustion,
which accounted for almost 99 percent of total U.S. CO2
emissions in 1997. Changes in land-use and forestry prac-
tices can also emit CO2 (e.g., through conversion of for-
est land to agricultural or urban use) or can act as a sink
for CO2 (e.g., through net additions to forest biomass).
Figure ES-6 and Table ES-7 summarize U.S.
sources and sinks of CO2, while the remainder of this
section discusses CO2 emission trends in greater detail.
Fossil Fuel Combustion
Cement Manufacture
Natural Gas Flaring
Lime Manufacture
Limestone and
Dolomite Use
Soda Ash Manufacture
and Consumption
Carbon Dioxide I
Manufacture |
1,466
Portion of All
Emissions
4 6 8 10 12
MMTCE
Energy
Energy-related activities accounted for almost all
U.S. CO2 emissions for the period of 1990 through 1997.
Carbon dioxide from fossil fuel combustion was the main
contributor, although CH4 and N2O were also emitted.
In 1997, approximately 85 percent of the energy con-
sumed in the United States was produced through the
combustion of fossil fuels. The remaining 15 percent
came from renewable or other energy sources such as
hydropower, biomass, and nuclear energy (see Figure ES-
7 and Figure ES-8). Energy-related activities other than
fuel combustion, such as those associated with the pro-
duction, transmission, storage, and distribution of fossil
fuels, also emit GHGs (primarily CH4). A discussion of
specific trends related to CO2 emissions from energy con-
sumption is presented below.
Fossil Fuel Combustion
As fossil fuels are combusted, the carbon stored in
them is almost entirely emitted as CO2. The amount of
carbon in fuels per unit of energy content varies signifi-
cantly by fuel type. For example, coal contains the high-
est amount of carbon per unit of energy, while petro-
leum has about 25 percent less carbon than coal, and
natural gas has about 45 percent less. From 1990 through
1997, petroleum supplied the largest share of U.S. en-
ergy demands, accounting for an average of 39 percent
Executive Summary ES-9
-------
Table ES-7: U.S. Sources of C02 Emissions and Sinks (MMTCE)
Source
Fossil Fuel Combustion
Cement Manufacture
Natural Gas Flaring
Umf Manufacture
Umistone and Dolomite Use
Soda Ash ManufacUp anc), Consumption
Carbon Dioxide Consumption
Land-Use Change and Forestry (Sink)3
International Bunker Fuels6
Total Emissions
Net Emissions (Sources and Sinks)
1990
1,327.2
8.9
2.3
3.3
1.4
1.1
0.2
(311.5)
27.1
1,344.3
1,032.8
1991
1,312.6
8.7
2.6
3.2
1.3
1.1
0.2
(311.5)
27.8
1,329.8
1,018.3
1992
1,332.4
8.8
2.6
3.3
1.2
1.1
0.2
(311.5)
29.0
1,349.6
1,038.1
1993
1,360.6
9.3
3.5
3.4
1.1
1.1
0.2
(208.6)
29.9
1,379.2
1,170.6
1994
1,383.9
9.6
3.6
3,5
1.5
1.1
0.2
(208.6)
27.4
1,403.5
1,194.9
1995
1,397.8'
9.9:
4.5,;
3.7;
1.g:
1.2,
0.3,;
(208.6)
25.4i
1,419.2
1,210.6
1996
1,447.7
9.9
4.3
3.8
2.0
1.2
0.3
(208.6)
25.4
1,469.3
1,260.7
1997
1,466.0
10.2
4.2
3.9
2.1
1.2
0.3
(208.6)
26.6
1
1
,487.9
,279.3
* Sfc*s are only Included in net emissions total. Estimates of net carbon sequestration due to land-use change and forestry activities exclude
non-test soils, and are based partially upon projections of forest carbon stocks. j
11 Emissions from Internationa! Bunker Fuels are not included in totals. [
Note: Totals may not sum due to independent rounding.
Figure ES-7
Figure ES-8
Nuclear-7.1%
Renewable - 7.6%
Coal-22.8%
Natural Gas-24%
Petroleum - 38.6%
of total energy consumption. Natural gas and coal fol-
lowed in order of importance, accounting for an average
of 24 and 22 percent of total energy consumption, re-
spectively. Most petroleum was consumed in the trans-
portation sector, while the vast majority of coal was used
by electric utilities, and natural gas was consumed largely
in the industrial and residential sectors.
Emissions of CO2 from fossil fuel combustion in-
creased at an average annual rate of 1.5 percent from
1990 to 1997. The fundamental factors behind this trend
include (1) a robust domestic economy, (2) relatively low
energy prices, and (3) fuel switching by electric utilities.
After 1990, when CO2 emissions from fossil fuel com-
bustion were 1,327.2 MMTCE, there was a slight de-
100
I
a so
o
1 60-1
o
I
c
Ul
40
Total Energy
Renewable & Nuclear
1990 1991 1992 1993 1994 1995 1996 1997
cline in emissions in 1991, followed by a relatively steady
increase to 1,466.0 MMTCE in 1997 J Overall, CO2 emis-
sions from fossil fuel combustion increased by 11 per-
cent over the eight year period and rose by 1.3 percent in
the final year.
Of all emissions related to fossil fuel combustion
from 1996 to 1997, emissions from coal grew the most
(an increase of 12.1 MMTCE or 2.3 percent). Alone,
emissions from coal combustion by electric utilities in-
creased by 2.9 percent from 1996 to 1997. Emissions
from natural gas remained almost unchanged as increased
consumption by electric utilities and the commercial sec-
tor were offset by decreases in the residential and indus-
trial sectors.
ES-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table ES-8: C02 Emissions from Fossil Fuel Combustion by End-Use Sector (MMTCE)*
End-Use Sector
1990
1991 1992 1993 1994 1995 1996 1997
Residential
Commercial
Industrial
Transportation
U.S. Territories
Total
253.
206.
453.
405.
9.
1,327
,0
.8
.3
,0
.1
.2
257
206
441
396
10
1,312
.1
.4
.8
.7
.6
.6
255.7
205.3
459.3
402.4
9.7
1,332.4
271.6
212.1
459.5
406.8
10.5
1,360.6
268.6
214.1
467.8
422.1
11.3
1,383.9
269.8
218.4
466.8
430.7
12.0
1,397.8
285.4
225.9
478.8
445.3
12.2
1,447.7
286.1
237.1
483.7
446.5
12.6
1,466.0
* Emissions from fossil fuel combustion by electric utilities are allocated based on electricity consumption by each end-use sector.
Note: Totals may not sum due to independent rounding.
Emissions from the combustion of petroleum prod-
ucts in 1997 increased 1.5 percent from the previous
year, accounting for about 33 percent of the increase in CO2
emissions from fossil fuel combustion.
The four end-use sectors contributing to CO2 emis-
sions from fossil fuel combustion include: industrial, trans-
portation, residential, and commercial. Electric utilities
also emit 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, utility
emissions have been distributed to each end-use sector
based upon their aggregate electricity consumption. Emis-
sions from utilities are addressed separately after the end-
use sectors have been discussed. Emissions from U.S. ter-
ritories are also calculated separately due to a lack of end-
use-specific consumption data. Table ES-8, Figure ES-9,
and Figure ES-10 summarize CO2 emissions from fossil
fuel combustion by end-use sector.
Industrial End-Use Sector. Industrial CO2 emis-
sions resulting from direct fossil fuel combustion and
from the generation of electricity consumed by the sec-
tor accounted for 33 percent of U.S. emissions from fos-
sil fuel consumption. About two-thirds of these emissions
result from producing steam and process heat from fos-
sil fuel combustion, while the remaining third results from
consuming electricity for powering motors, electric fur-
naces, ovens, and lighting.
Transportation End-Use Sector. Transportation
activities—excluding international bunker fuels—ac-
counted for 30 percent of CO2 emissions from fossil fuel
combustion in 1997. Virtually all of the energy consumed
in this end-use sector came from petroleum products. Two
thirds of the emissions resulted from gasoline consump-
tion in motor vehicles. The remaining emissions came
from other transportation activities, including the com-
bustion of diesel fuel in heavy-duty vehicles and jet fuel
in aircraft.
Figure ES-9
Figure ES-10
500-
400-
g300
• Natural Gas
• Petroleum
• Coal
Executive Summary ES-11
-------
Residential and Commercial End-Use Sectors. The
residential and commercial sectors accounted for 19 and
16 percent, respectively, of CO2 emissions from fossil
fuel consumption in 1997. Both sectors relied heavily on
electricity for meeting energy needs, with 64 and 73 per-
cent, respectively, of their emissions attributable to elec-
tricity consumption for lighting, heating, cooling, and
operating appliances. The remaining emissions were
largely due to the consumption of natural gas and petro-
leum, primarily for meeting heating and cooking needs.
Electric Utilities. The United States relies on elec-
tricity to meet a significant portion of its energy demands,
especially for lighting, electric motors, heating, and air
conditioning. Electric utilities are responsible for con-
suming 28 percent of overall U.S. energy and emitted 36
percent of CO2 from fossil fuel consumption in 1997.
The type of fuel combusted by utilities 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, hydro-
electric, or geothermal energy. However, electric utili-
ties rely on coal for over half of their total energy re-
quirements and accounted for 88 percent of all coal con-
sumed in the United States in 1997. Consequently,
changes in electricity demand have a significant impact
on coal consumption and associated CO2 emissions.
Natural Gas Flaring
Carbon dioxide is produced when methane from
oil wells is flared (i.e., combusted) to relieve rising pres-
sure or to dispose of small quantities of gas that are not
commercially marketable. In 1997, flaring activities
emitted approximately 4.2 MMTCE, or about 0.3 per-
cent of U.S. CO2 emissions.
Biomass Combustion
Biomass—in the form of fuel wood and wood
waste—is used primarily by the industrial end-use sec-
tor, while the transportation end-use sector is the pre-
dominant use of biomass-based fuels, such as ethanol
from corn and woody crops. Ethanol and ethanol blends,
such as gasohol, are typically used to fuel public trans-
port vehicles.
Although these fuels do emit CO2, in the long run
the CO2 emitted from biofuel consumption does not in-
crease 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 crop lands are accounted for under Land-Use Change
and Forestry.
Gross CO2 emissions from biomass combustion
were 59.1 MMTCE, with the industrial sector account-
ing for 79 percent of the emissions, and the residential
sector, 18 percent. Ethanol consumption by the trans-
portation sector accounted for only 3 percent of CO2
emissions from biomass combustion.
Industrial Processes
Emissions are often produced as a by-product of
various non-energy-related activities. For example, in-
dustrial processes can chemically transform raw materi-
als. This transformation often releases greenhouse gases
such as CO2. The production processes that emit CO2
include cement manufacture, lime manufacture, lime-
)i
stone and dolomite use (e.g., in iron and steel making),
soda ash manufacture and consumption, and CO2 con-
sumption. Total CO2 emissions from these sources were
approximately 17.8 MMTCE in 1997, accounting for
about 1 percent of total CO2 emissions. Since 1990, emis-
sions from each of these sources increased, except for
emissions from soda ash manufacture and consumption,
which remained relatively constant.
Cement Manufacture (10.2 MMTCE)
Carbon dioxide is produced primarily during the
production of clinker, an intermediate product from which
finished Portland and masonry cement are made. Spe-
cifically, CO2 is created when calcium carbonate (CaCO3)
is heated in a cement kiln to form lime and CO2. This
lime combines with other materials to produce clinker,
while the CO2 is released into the atmosphere.
ES-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Lime Manufacture (3.9 MMTCE)
Lime is used in steel making, construction, pulp
and paper manufacturing, and water and sewage treat-
ment. It is manufactured by heating limestone (mostly
calcium carbonate, CaCO3) in a kiln, creating calcium
oxide (quicklime) and CO2, which is normally emitted
to the atmosphere.
Limestone and Dolomite Use (2.1 MMTCE)
Limestone (CaCO3) and dolomite (CaCO3MgCO3)
are basic raw materials used by a wide variety of indus-
tries, including the construction, agriculture, chemical,
and metallurgical industries. 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 desulfur-
ization systems to remove sulfur dioxide from the ex-
haust gases.
Soda Ash Manufacture and
Consumption (1.2 MMTCE)
Commercial soda ash (sodium carbonate, Na2CO3)
is used in many consumer products, such as glass, soap and
detergents, paper, textiles, and food. During the manufac-
turing of soda ash, some natural sources of sodium carbon-
ate 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.
Carbon Dioxide Consumption (0.3 MMTCE)
Carbon dioxide is used directly in many segments
of the economy, including food processing, beverage
manufacturing, chemical processing, and a host of in-
dustrial and other miscellaneous applications. For the
most part, the CO2 used in these applications is eventu-
ally released to the atmosphere.
Land-Use Change and Forestry
When humans alter the biosphere through changes
in land-use and forest management practices, they alter the
natural carbon flux between biomass, soils, and the atmo-
sphere. In the United States, improved forest management
practices and the regeneration of previously cleared forest
areas have resulted in a net uptake (sequestration) of car-
bon in U.S. forest lands, which cover about 298 million
hectares (737 million acres) (Powell et al. 1993). This up-
take is an ongoing result of land-use changes in previous
decades. For example, because of improved agricultural
productivity and the widespread use of tractors, the rate of
clearing forest land for crop cultivation and pasture slowed
greatly 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 brought out of crop production, primarily be-
tween 1920 and 1950, and were allowed to revert to forest
land or were actively reforested.
Since the early 1950s, the managed growth of pri-
vate forest land in the East has nearly doubled the biom-
ass density there. The 1970s and 1980s saw a resurgence
of federally sponsored tree-planting programs (e.g., the
Forestry Incentive Program) and soil conservation pro-
grams (e.g., the Conservation Reserve Program), which
have focused on reforesting previously harvested lands,
improving timber-management, combating soil erosion,
and converting marginal cropland to forests.
In 1997, the CO2 flux from land-use change and
forestry activities was estimated to have been a net up-
take of 208.6 MMTCE. This carbon was sequestered in
trees, understory, litter, and soils in forests, U.S. wood
product pools, and wood in landfills. This net carbon
uptake represents an offset of about 14 percent of the
CO2 emissions from fossil fuel combustion in 1997. The
amount of carbon sequestered through U.S. forestry and
land-use practices is estimated to have declined by about
a third between 1990 and 1997 largely due to the matu-
ration of existing U.S. forests and the slowed expansion
of Eastern forest cover.
Methane Emissions
Atmospheric methane (CH4) is an integral compo-
nent of the greenhouse effect, second only to CO2 as a
contributor to anthropogenic greenhouse gas emissions.
Methane's overall contribution to global warming is sig-
nificant because it is estimated to be 21 times more ef-
fective at trapping heat in the atmosphere than CO2 (i.e.,
the GWP value of methane is 21). Over the last two cen-
turies, methane's concentration in the atmosphere has
more than doubled (IPCC 1996). Scientists believe these
Executive Summary ES-13
-------
atmospheric increases were due largely to increasing
emissions from anthropogenic sources, such as landfills,
natural gas and petroleum systems, agricultural activi-
ties, coal mining, stationary and mobile source fossil fuel
combustion, wastewater treatment, and certain industrial
processes (see Figure ES-11 and Table ES-9).
Figure ES-11
Landfills
Enteric Fermentation
Natural Gas Systems
Coal Mining
Manure Management
Rica Cultivation
Stationary Sources
PcUoloum Systems
Mobile Sources
Wastewatcr Treatment
Petrochemical Production
Agricultural Residua Burning
Silicon Carbide Production
Portion of All
<0.05
0 10 20 30 40 50 60
MMTCE
Landfills
Landfills are the largest single anthropogenic
source of methane emissions in the,United States. In an
environment where the oxygen content is low or nonex-
istent, organic materials, such as yard waste, household
waste, food waste, and paper, are decomposed by bacte-
ria, resulting in the generation of methane and biogenic
CO2. Methane emissions from landfills are affected by
site-specific factors such as waste composition, moisture,
and landfill size.
Methane emissions from U.S. landfills in 1997 were
66.7 MMTCE, a 19 percent increase since 1990 due to
the steady accumulation of wastes in landfills. Emissions
from U.S. municipal solid waste landfills, which received
about 61 percent of the solid waste generated in the United
States, accounted for 93 percent of total landfill emis-
sions, while industrial landfills accounted for the remain-
der. Approximately 14 percent of the methane generated
in U.S. landfills in 1997 was recovered and combusted,
I
often for energy.
A regulation promulgated in March 1996 requires
the largest U.S. landfills to begin collecting and com-
busting their landfill gas to reduce emissions of
nonmethane volatile organic compounds (NMVOCs). It
Table ES-9: U.S. Sources of Methane Emissions (MMTCE)
Source
1990 1991 1992 1993 1994 1995 1996 1997
Landjpls _,'„ ,'.,," '
Enteric Fermentation
Natural Gas Systems
Coal Mining
Manure Management
Rice Cu|t(vation '" '. "~
Stationary Sources
Pe^rojgum Systems
Mobile"' Sources
Wasiwater Treatment
Petrochemical Production
Agricultural Residue Burning
Silicon" Carbide Production
International Bunker Fuels*
Total
, 56,2
32.7
32^9
24.0
14.9
2.5
2.3
1.6
1.4
0.9
0.3
0.2
+
','" H-
169.9
57,6.
32.8
33.3
22.8
15.4
2.5
2.4
1.6
1.4
P.9
0.3
0,2
+
". ±,,",
171=0
57.8
33.2
33.9
22.0
16.0
2.8
2.4
1.6
1.4
0.9
0.3
0.2
+
„ +"
172,5
59.7
33.6
34.1
19.2
16.1
2.5
2.4
1.6
1.4
,,,,0.9,
0.4
0.2
+
.'..+. ".
172.0
,, 61,6.
34.5
33.5
m'4
16.7
3.0
2.4
1.6
1.4
„ ,0,9 „
0.4
0,2.
•f _
.' , ,-t,
175,5
,63.6 ,
34.9
33.2
20.3 ;
16.9 !
2.8
2.5
1.6 ;
1.4
0.9 ;
0.4
0=2 ';
t ,
-l- .
178.6
65.1
34.5
33.7
„ 1,8.9
16.6
2.5
2,5
1.5
1.4
0.9
0.4
0.2
+
+
178.3
66.7
34.1
33.5
18.8
17.0
2.7
2.2
1.6
1.4
0.9
0.4
0.2
,„ , +
179.6
•f Doss not exceed 0.05 MMTCE
* Emissions from International Bunker Fuels are not included in totals.
Note; Totals may not sum due to Independent rounding.
ES-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
is estimated that by the year 2000, this regulation will
have reduced landfill methane emissions by more than
50 percent. Furthermore, the EPA is currently reviewing
site-specific information on landfill gas recovery and
anticipates that this new information will lead to a higher
estimate of the national recovery total, and thus, lower
net methane emissions. This new information will be
available in future inventories.
Natural Gas and Petroleum Systems
Methane is the major component of natural gas. Dur-
ing the production, processing, transmission, and distribu-
tion of natural gas, fugitive emissions of methane often oc-
cur. 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 main-
tenance procedures and equipment conditions. In 1997,
emissions from U.S. natural gas systems were estimated to
be 33.5 MMTCE, accounting for approximately 19 percent
of U.S. methane emissions.
Methane emissions from the components of petro-
leum systems—including crude oil production, crude oil
refining, transportation, and distribution—generally oc-
cur as a result of system leaks, disruptions, and routine
maintenance. In 1997, emissions from petroleum sys-
tems were estimated to be 1.6 MMTCE, or 1 percent of
U.S. methane emissions. EPA is reviewing new informa-
tion on methane emissions from petroleum systems and
anticipates that future emission estimates will be higher
for this source.
From 1990 to 1997, combined methane emissions
from natural gas and petroleum systems increased by
about 2 percent as the number of gas producing wells
and miles of distribution pipeline rose.
Coal Mining
Produced millions of years ago during the forma-
tion of coal, methane trapped within coal seams and sur-
rounding rock strata is released when the coal is mined.
The quantity of methane released to the atmosphere dur-
ing coal mining operations depends primarily upon the
depth and type of the coal that is mined.
Methane from surface mines is emitted directly to
the atmosphere as the rock strata overlying the coal seam
are removed. Because methane in underground mines is
explosive at concentrations of 5 to 15 percent in air, most
active underground mines are required to vent this meth-
ane, typically to the atmosphere. At some mines, meth-
ane-recovery systems may supplement these ventilation
systems. U.S. recovery of methane has been increasing
in recent years. During 1997, coal mining activities emit-
ted 18.8 MMTCE of methane, or 10 percent of U.S.
methane emissions. From 1990 to 1997, emissions from
this source decreased by 22 percent due to increased use
of the methane collected by mine degasification systems.
Agriculture
Agriculture accounted for 30 percent of U.S. meth-
ane emissions in 1997, with enteric fermentation in do-
mestic livestock and manure management accounting for
the majority. Other agricultural activities contributing
directly to methane emissions included rice cultivation
and agricultural waste burning.
Enteric Fermentation (34.1 MMTCE)
During animal digestion, methane is produced
through the process of enteric fermentation, in which mi-
crobes residing in animal digestive systems break down the
feed consumed by the animal. Ruminants, which include
cattle, buffalo, sheep, and goats, have the highest methane
emissions among all animal types because they have a ru-
men, or large fore-stomach, in which methane-producing
fermentation occurs. Non-ruminant domestic animals, such
as pigs and horses, have much lower methane emissions. In
1997, enteric fermentation was the source of about 19 per-
cent of U.S. methane emissions, and more than half of the
methane emissions from agriculture. From 1990 to 1997,
emissions from this source increased by 5 percent due mainly
to increased livestock populations.
Manure Management (17.0 MMTCE)
The decomposition of organic animal waste in an
anaerobic environment produces methane. The most
important factor affecting the amount of methane pro-
duced is how the manure is managed, because certain
types of storage and treatment systems promote an oxy-
Executive Summary ES-15
-------
gen-free environment. In particular, liquid systems tend
to encourage anaerobic conditions and produce signifi-
cant quantities of methane, whereas solid waste manage-
ment approaches produce little or no methane. Higher
temperatures and moist climatic conditions also promote
methane production.
Emissions from manure management were about
9 percent of U.S. methane emissions in 1997, and about
a third of the methane emissions from agriculture. From
1990 to 1997, emissions from this source increased by
14 percent because of larger farm animal populations and
expanded use of liquid manure management systems.
Rice Cultivation (2.7 MMTCE)
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 or-
ganic matter in the soil decomposes, releasing methane
to the atmosphere, primarily through the rice plants. In
1997, rice cultivation was the source of slightly over 1
percent of total U.S. methane emissions, and about 5
percent of U.S. methane emissions from agriculture.
Emissions estimates from this source did not change sig-
nificantly from 1990 levels.
Agricultural Residue Burning (0.2 MMTCE)
Burning crop residue releases a number of green-
house gases, including methane. Agricultural residue
burning is considered to be a net source of methane emis-
sions because, unlike CO2, methane released during burn-
ing is not reabsorbed by crop regrowth during the next
growing season. Because field burning is not common
in the United States, it was responsible for only 0.1 per-
cent of U.S. methane emissions in 1997.
Other Sources
Methane is also produced from several other
sources in the United States, including fossil fuel com-
bustion, wastewater treatment, and some industrial pro-
cesses. Fossil fuel combustion by stationary and mobile
sources was responsible for methane emissions of 2.2
and 1,4 MMTCE, respectively in 1997. The majority of
emissions from stationary sources resulted from the com-
bustion of wood in the residential and industrial sectors.
The combustion of gasoline in highway vehicles was re-
sponsible for the majority of the methane emitted from
mobile sources. Wastewater treatment was a smaller
source of methane, emitting 0.9 MMTCE in 1996. Meth-
ane emissions from two industrial sources—petrochemi-
cal and silicon carbide production—-were also estimated,
totaling 0.4 MMTCE.
Nitrous Oxide Emissions
Nitrous oxide (N2O) is a greenhouse gas that is
produced both naturally, from a wide variety of biologi-
cal sources in soil and water, and anthropogenically by a
variety of agricultural, energy-related, industrial, and
waste management activities. While N2O emissions are
much lower than CO2 emissions, N2O is approximately
310 times more powerful than CO2 at trapping heat in
the atmosphere (IPCC 1996). During the past two centu-
ries, atmospheric concentrations of N2O have risen by
approximately 13 percent. The main anthropogenic ac-
tivities producing N2O in the United States were fossil
fuel combustion in motor vehicles, agricultural soil man-
agement, and adipic and nitric acid production (see Fig-
ure ES-12 and Table ES-10).
Agricultural Soil Management
Nitrous oxide (N2O) is produced naturally in soils
through microbial processes of nitrification and denitri-
fication. A number of anthropogenic activities add to
the amount of nitrogen available to be emitted as N2O by
these microbial processes. Direct additions of nitrogen
Figure ES-12
Agricultural Soil Management
Mobile Sources
Stationary Sources
Adipic Acid
Nitric Acid
Manure Management |
Human Sewage I
Agricultural Residue Burning 0.1
Waste Combustion 0.1
10 20 30 40 50 60 70
MMTCE
ES-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table ES-10: U.S. Sources of Nitrous Oxide Emissions (MMTCE)
1990 1991 1992 1993 1994 1995 1996 1997
Agricultural Soil Management
Mobile Sources
Stationary Sources
Adipic Acid Production
Nitric Acid Production
Manure Management
Human Sewage
Agricultural Residue Burning
Waste Combustion
International Bunker Fuels*
Total
65.3 .
13.6
3.8
4.7
3.3
2.6
2.1
0.1
0.1
0.2
95.7
66.2
14.2
3.8
4.9
3.3
2.8
2.1
0.1
0.1
0.2
97.6
68.0
15.2
3.9
4.6
3.4
2.8
2.2
0.1
0.1
0.2
100.1
67.0
15.9
3.9
4.9
3.5
2.9
2.2
0.1
0.1
0.3
100.4
73.4
16.7
4.0
5.2
3.7
2.9
2.2
0.1
0.1
0.2
108.3
70.2
17.0
4.0
5.2
3.7
2.9
2.3
0.1
0.1
0.2
105.4
72.0
17.4
4.1
5.4
3.9
3.0
2.3
0.1
0.1
0.2
108.2
74.1
17.5
4.1
3.9
3.8
3.0
2.3
0.1
0.1
0.2
109.0
' Emissions from International Bunker Fuels are not included in totals.
Note: Totals may not sum due to independent rounding.
fertilizers, cultivation of nitrogen-fixing crops, cultiva-
tion of Mgh-organic-content soils, the application of live-
stock manure on croplands and pasture, the incorpora-
tion of crop residues in soils, and direct excretion by
animals onto soil. Indirect emissions result from volatil-
ization and subsequent atmospheric deposition of am-
monia (NH3) and oxides of nitrogen (NOX) and from
leaching and surface run-off. These indirect emissions
originate from nitrogen applied to soils as fertilizer and
from managed and unmanaged livestock wastes.
In 1997, agricultural soil management accounted
for 74.1 MMTCE, or 68 percent of U.S. N2O emissions.
From 1990 to 1997, emissions from this source increased
by 13 percent as fertilizer consumption and cultivation
of nitrogen fixing crops rose.
Fossil Fuel Combustion
Nitrous oxide is a product of the reaction that oc-
curs between nitrogen and oxygen during fossil fuel com-
bustion. Both mobile and stationary sources emit N2O,
and the volume emitted varies according to the type of
fuel, technology, and pollution control device used, as
well as maintenance and operating practices. For ex-
ample, catalytic converters installed to reduce mobile
source pollution can result in the formation of N2O.
In 1997, N2O emissions from mobile sources totaled
17.5 MMTCE, or 16 percent of U.S. N2O emissions. Emis-
sions of N2O from stationary sources were 4.1 MMTCE, or
4 percent of U.S. N2O emissions. From 1990 to 1997, com-
bined N2O emissions from stationary and mobile sources
increased by 22 percent, primarily due to increased rates of
N2O generation in motor vehicles.
Adipic Acid Production
The majority of the adipic acid produced in the
United States is used to manufacture nylon 6,6. Adipic
acid is also used to produce some low-temperature lu-
bricants, and to add a "tangy" flavor to foods.
In 1997, U.S. adipic acid production emitted 3.9
MMTCE of N2O, or 4 percent of U.S. N2O emissions.
By the end of 1997, all but one of the four adipic acid
plant in the United States were believed to have installed
emission control systems that almost eliminate N2O emis-
sions. Even though adipic acid production increased from
1990 to 1997, emissions from this source decreased by
17 percent, due to the installation of control systems on
additional production plants.
Nitric Acid Production
Nitric acid production is another industrial source
of N2O emissions. Used primarily to make synthetic com-
mercial fertilizer, this raw material is also a major com-
ponent 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 atmo-
sphere. In 1997, N2O emissions from nitric acid produc-
tion were 3.8 MMTCE, or 4 percent of U.S. N2O emis-
sions. From 1990 to 1997, emissions from this source
increased by 14 percent as nitric acid production grew.
Executive Summary ES-17
-------
Manure Management
Nitrous oxide is produced as part of microbial nitrifi-
cation and denitrification processes in managed and
unmanogcd manure, the latter of which is addressed under
agricultural soil management. Total N2O emissions from
managed manure systems hi 1997 were 3.0 MMTCE, ac-
counting for 3 percent of U.S. N2O emissions. Emissions
increased by 15 percent from 1990 to 1997.
Other Sources
Other sources of N2O included agricultural reside
burning, waste combustion, and human sewage in waste-
water treatment systems. In 1997, agricultural residue
burning and municipal solid waste combustion each
emitted approximately O.I MMTCE of N2O. Although
N2O emissions from wastewater treatment were not fully
estimated because of insufficient data availability, the
human sewage component of domestic wastewater re-
sulted in emissions of 2.3 MMTCE in 1997.
HFCs, PFCs and SF6 Emissions
Hydrofluorocarbons (HFCs) andperfluorocarbons
(PFCs} are categories of synthetic chemicals that have
been introduced as alternatives to the ozone depleting
substances (ODSs), which are being phased out under
the Montreal Protocol and Clean Air Act Amendments
Of 1990. Because HFCs and PFCs do not directly de-
plete the stratospheric ozone layer, they are not controlled
by the Montreal Protocol.
These compounds, however, along with sulfur
hexafluoride (SF6), are potent greenhouse gases. In addi-
tion to having high global warming potentials, SF6 and many
HFCs and PFCs have extremely long atmospheric lifetimes,
resulting in their essentially irreversible accumulation in the
atmosphere. Sulfur hexafluoride, itself, is the most potent
greenhouse gas the IPCC has evaluated.
In addition to their use as substitutes for ozone de-
pleting substances, the other industrial sources of these gases
are aluminum production, HCFC-22 production, semicon-
ductor manufacturing, electrical transmission and distribu-
tion, and magnesium production and processing. Figure ES-
13 and Table ES-11 present emission estimates for HFCs,
PFCs, and SF6, which totaled 37.1 MMTCE in 1997.
Figure ES-13
Illll lillill iiiOgSf, ,PFt»d':an| Sr"
Substitution of Ozone
Depleting Substances
HCFC-22 Production
Electrical Transmission
and Distribution
Magnesium Production
and Processing
Aluminum Production
Semiconductor
Manufacture
Portion of All
Emissions
5 10
MMTCE
15
Table ES-11: Emissions of MFCs, PFCs, and SF6 (MMTCE)
Source
1990 1991 1992
1993
Substitution of Ozone Depleting Substances
HCFC-22 Production
Electrical Transmission and Distribution
Magnesium Production and Processing
Aluminum Production
Semiconductor Manufacture
Total
0.3
9.5
5.6
1.7
4.9
0.2
22.2
0.2
8.4
5.9
2.0
4.7
0.4
21.6
0.4
9.5
6.2
2.2
4.1
0.6
23.0
1.4
8.7
6.4
2.5
3.5
0.8
23.4
4.0
8.6
67
2.7
28
1.0
25.9
9.5
7.4
7 o
30
27
1.2
30.8
11.9
8.5
7 n
30
2 Q
1.4
34.7
14.7
8.2
7 n
Q n
9 Q
1.3
37.1
ES-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Substitution of Ozone Depleting
Substances
The use and subsequent emissions of HFCs and PFCs
as ODS substitutes increased dramatically from small
amounts in 1990 to 14.7 MMTCE in 1997. This increase
was 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 hi refrigeration applications. This
trend is expected to continue for many years, and will ac-
celerate in the early part of the next century as HCFCs, which
are interim substitutes in many applications, are themselves
phased-out under the provisions of the Copenhagen Amend-
ments to the Montreal Protocol.
Other Industrial Sources
HFCs, PFCs, and SF6 are also emitted from a num-
ber of other industrial processes. During the production
of primary aluminum, two PFCs (CF4 and C2F6) are emit-
ted as intermittent by-products of the smelting process.
Emissions from aluminum production were estimated to
have decreased by 41 percent between 1990 and 1997
due to voluntary emission reductions efforts by the in-
dustry and falling domestic aluminum production.
HFC-23 is a by-product emitted during the pro-
duction of HCFC-22. Emissions from this source were
8.2 MMTCE in 1997, and have decreased by 14 percent
since 1990 due mainly to voluntary efforts by industry.
The semiconductor industry uses combinations of
HFCs, PFCs, and SF6 for plasma etching and chemical
vapor deposition processes. For 1997, it was estimated
that the U.S. semiconductor industry emitted a total of
1.3 MMTCE. These gases were not widely used in the
industry in 1990.
The primary use of SF6 is as a dielectric in electri-
cal transmission and distribution systems. Fugitive emis-
sions of SF6 occur from leaks in and servicing of substa-
tions and circuit breakers, especially from older equip-
ment. Estimated emissions from this source increased by
25 percent from 1990, to 7.0 MMTCE in 1997.
Lastly, SF6 is also used as a protective covergas for
the casting of molten magnesium. Estimated emissions
from primary magnesium production and magnesium
casting were 3.0 MMTCE in 1997, an increase of 76
percent since 1990.
Criteria Pollutant Emissions
In the United States, carbon monoxide (CO), ni-
trogen oxides (NOX), nonmethane volatile organic com-
pounds (NMVOCs), and sulfur dioxide (SO2) are com-
monly referred to as "criteria pollutants," as termed in
the Clean Air Act. Carbon monoxide is produced when
carbon-containing fuels are combusted incompletely.
Nitrogen oxides (i.e., NO and NO2) are created by light-
ning, fires, fossil fuel combustion, and in the stratosphere
from nitrous oxide. NMVOCs—which include such com-
pounds as propane, butane, and ethane—are emitted pri-
marily from transportation, industrial processes, and non-
industrial consumption of organic solvents. In the United
States, SO2 is primarily emitted from the combustion of
fossil fuels and by the metals industry.
In part because of their contribution to the forma-
tion of urban smog (and acid rain in the case of SO2),
criteria pollutants are regulated under the Clean Air Act.
These gases also indirectly affect the global climate by
reacting with other chemical compounds in the atmo-
sphere to form compounds that are greenhouse gases.
Unlike other criteria pollutants, SO2 emitted into the at-
mosphere is believed to affect the Earth's radiative bud-
get negatively; therefore, it is discussed separately.
The most important of the indirect climate change
effects of criteria pollutants is their role as precursors of
tropospheric ozone. In this role, they contribute to ozone
formation and alter the atmospheric lifetimes of other
greenhouse gases. For example, CO interacts with the
hydroxyl radical—the major atmospheric sink for meth-
ane emissions—to form CO2. Therefore, increased at-
mospheric concentrations of CO limit the number of
hydroxyl molecules (OH) available to destroy methane.
' NOX and CO emission estimates from agricultural burning were estimated separately, and therefore not taken from EPA (1998).
Executive Summary ES-19
-------
Box ES-4: Emissions of Ozone Depleting Substances
i
Chtorofluorocarbons (CFCs) and other halogenated compounds were first emitted into the atmosphere this century. This family of
man-made compounds Includes CFCs, halons, methyl chloroform, carbon tetrachloride, methyl bromide, and
hydrochlorofluorocarbons (HCFCs). These substances have been used in a variety of industrial applications, including refrigera-
tion, air conditioning, foam blowing, solvent cleaning, sterilization, fire extinguishing, coatings, paints, and aerosols.
Because these compounds have been shown to deplete stratospheric ozone, they are typically referred to as ozone depleting
substances (ODSs), In, addition, they are potent greenhouse gases.
Recognizing the harmful effects of these compounds on the ozone layer, in 1987 many governments signed the Montreal Protocol
on Substances that Deplete the Ozone Layer to limit the production and importation of a number of CFCs and other halogenated
compounds. The United States furthered its commitment to phase-out ODSs by signing and ratifying the Copenhagen Amendments
to tr® Montresl Protocol In 1992. Under these amendments, the United States committed to ending the production and importation
of hajons by 1994, and CFCs by 1996.
£'; ! . ' ' '' .' '. !|
The IPCC Guidelines do not include reporting instructions for estimating emissions of ODSs because their use! is being phased-out
undifjhe Montreal "Protocol. The United States believes, however, that a greenhouse gas emissions inventory is incomplete
Without these emissions; therefore, estimates for several Class I and Class II ODSs are provided in Table ES-12. Compounds are
grouped by class according to their ozone depleting potential. Class I compounds are the primary ODSs; Class II compounds
Include partially halogenated chlorine compounds (HCFCs), some of which were developed as interim replacements for CFCs.
Because these HCFC compounds are only partially halogenated, their hydrogen-carbon bonds are more vulnerable to oxidation in
the troposphere and, therefore, pose only one-tenth to one-hundredth the threat to stratospheric ozone compared to CFCs.
it should be noted that the effects of these compounds on radiative forcing are not provided. Although many ODSs have relatively
high direct GWPs, their indirect effects from ozone—also a greenhouse gas—destruction are believed to have negative radiative
forcing effects, and therefore could significantly reduce the overall magnitude of their radiative forcing effects. Given the uncertain-
ties surrounding the net effect of these gases, emissions are reported on an unweighted basis.
Table ES-12: Emissions of Ozone Depleting Substances (Wig)
Compound
PHI1 , ' ": • si i ';'ii
Class I
CFC-1 1
CFC-12
CRJ-1.13
CFC-114
CFC~115
Carbon Tetrachlpride
Mefiyl Chloroform
Halon-1211
Halon-1301
Class II
HCFC-22
HCFC-123
HCFC-124
HCFC-141b
HCFS-l42b
HCFC-225ca/cb
1990
53,500
112,600
26,350
4,700
4,200
32,300
158,300
1,000
1,800
79,789
+-
+
+
. +
+ ..
1991
48,300
103,500
20,550
3,600
4,000
31,000
154,700
1,100
1,800
79,540
+
+
+
+
+
1992
45,100
80,500
17,100
3,000
3,800
21,700
108,300
1,000
1,700
79,545
285
429
+
3,526
, , +
1993
45,400
79,300
17,100
3,000
3,600
18,600
92,850
1,100
1,700
71,224
570
2,575
1,909
9,055
-)-
1994
36,600
57,600
8,550
1,600
3,300
15,500
77,350
1,000
1,400
71,386
844
4,768
6,529
14,879
+
1995
36,200
51,800
8,550
1,600
3,000
4,700
46,400
1,100
1,400
74,229
1,094
5,195
11,608
21,058
565
1996
i
ii
26,600
;35,500
_l_
300
3,200
+
+
: 1,100
,1,400
1
77,472
: 1,335
5,558
,14,270
27,543
579
1997
25,100
23,100
+
100
2,900
+
1,100
1,300
79,620
1,555
5,894
12,113
28,315
593
Sourcji EPA Of eeqfAjj-and .Radiation estimates
Dots "not exceed 10 M§
ES-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Since 1970, the United States has published esti-
mates of annual emissions of criteria pollutants (EPA
1998).5 Table ES-13 shows that fuel combustion accounts
for the majority of emissions of these gases. In 1997,
fossil fuel combustion by mobile sources emitted 49, 81,
and 41 percent of U.S. NOX, CO, and NMVOC emis-
sions, respectively. Industrial processes—such as the
manufacture of chemical and allied products, metals pro-
cessing, and industrial uses of solvents—were also sig-
nificant sources of CO, NOX, and NMVOCs.
Table ES-13: Emissions of NOX, CO, NMVOCs, and S02 (Gg)
Gas/Activity
1990
1991 1992 1993 1994 1995 1996 1997
NOX
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Industrial Processes
Solvent Use
Agricultural Burning
Waste
CO
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Industrial Processes
Solvent Use
Agricultural Burning
Waste
NMVOCs
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Industrial Processes
Solvent Use
Agricultural Burning
Waste
SOZ
Stationary Fossil Fuel Combustion
Mobile Fossil Fuel Combustion
Oil and Gas Activities
Industrial Processes
Solvent Use
Agricultural Burning
Waste
21,139
9,
10,
83,
4
66
9
18
7
3
5
21
18
1
1
,884
,231
139
771
1
30
83
,056
,999
,429
302
,580
4
763
979
,723
912
,952
555
,193
,217
MA
895
,870
,407
,728
390
,306
+
MA
38
21,213
9,779
10,558
110
648
2
30
86
84,776
5,313
70,256
313
7,166
4
712
1,012
18,838
975
8,133
581
2,997
5,245
IMA
907
21,258
17,959
1,729
343
1,187
+
NA
39
21,460
9,914
10,659
134
629
2
34
87
81,764
5,583
68,503
337
5,480
5
824
1,032
18,453
1,011
7,774
574
2,825
5,353
NA
916
21,076
17,684
1,791
377
1,186
+
NA
39
21,685
10,080
10
,749
111
603
2
28
112
81,696
5
68
5
1
18
7
2
5
20
,068
,974
337
,500
4
681
,133
,622
901
,819
588
,907
,458
NA
949
,729
17,459
1
1
,708
347
,159
1
NA
56
21,964
9,993
10,949
106
774
2
37
103
85,729
5
70
7
1
19
8
3
5
20
17
1
1
,007
,655
307
,787
5
858
,111
,191
898
,110
587
,057
,590
NA
949
,187
,134
,524
344
,135
1
NA
48
21,432
9,822
10,732
100
656
3
30
89
76,699
5,383
63,846
316
5,370
5
703
1,075
18,360
973
7,354
582
2,873
5,609
NA
968
17,741
14,724
1,525
334
1,116
1
NA
42
21,160
9,543
10,636
100
754
3
34
91
78,350
5,424
63,205
316
7,523
5
786
1,091
17,209
978
7,156
469
2,521
5,691
NA
393
17,972
15,253
1,217
334
1,125
1
NA
42
21,267
9,729
10,519
104
781
3
37
94
75,158
4,369
60,794
330
7,689
6
843
1,127
17,129
780
6,949
488
2,622
5,882
NA
407
18,477
15,658
1,252
349
1,175
1
NA
44
Source: (EPA 1998) except for estimates from agricultural burning.
+ Does not exceed 0.5 Gg
NA (Not Available)
Note: Totals may not sum due to independent rounding.
Executive Summary ES-21
-------
Box ES-5: Sources and Effects of Sulfur Dioxide
Sulfjir dioxide (S02j emitted into the atmosphere through natural and anthropogenic processes affects the Earth's radiative budget
iBJBJ i «t ' ,:,„ hil!• ,' 1 Liamii nil 111. . 1 i',,,!"1,. v.'i ;, '"'inn1: ?h ' 'i ' „ .: • r v, i. ,r, . , ., "rif ]'« ; '' v : ' ij ii" , ' ,i"' a>
tnrouajh its photochemical transformation into sulfate aerosols that can (1) scatter sunlight back to space, thereby reducing the
radiation reaching the Earth's surface; (2) affect cloud formation; and (3) affect atmospheric chemical composition (e.g., strato-
spheric OHone, by providing surfaces for heterogeneous chemical reactions). The overall effect of S02 derived aerosols on radiative
forcing is believed to be negative (IPCC1996|. However, because S02 is short-lived and unevenly distributed ih the atmosphere, its
. ratfljjye^orcipgjmpacts are highly uncertain. ]'\ \ ' ' / ' ' , , , "" ',' . ' ""
Suite dipxide, j.s, alsg jjt major contributor to the formation of urban smog, which can cause significant increases in acute and
chronic respiratory diseases. Once S02 is emitted, it is chemically transformed in the atmosphere and returns to the Earth as the
primary source of acid rain. Because of these harmful effects, the United States has regulated Sp? emissions in the Clean Air Act.
Eteciric utilities are trie largest source of S02 emissions in the United States, accounting for 64 percent in 1997. Coal combustion
contributes nearly all of those emissions (approximately 96 percent). Sulfur dioxide emissions have significantly decreased in
recent years, primarily as a result of electric utilities switching from high sulfur to low sulfur coal. '
ES-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
1. Introduction
report presents estimates by the United States government of U.S. anthropogenic greenhouse gas emissions
and sinks for the years 1990 through 1997. A summary of these estimates is provided in Table 1-4 and Table 1-
5 by gas and source category. 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.1'2 This report also discusses the methods and data used to calculate these emission estimates.
In June of 1992, the United States signed the United Nations Framework Convention on Climate Change
(UNFCCC). The objective of the UNFCCC is "to achieve...stabilization of greenhouse gas concentrations in the
atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system."3'4
Parties to the Convention, by signing, make commitments "to 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.. "5 The United States views this report as
an opportunity to fulfill this commitment under UNFCCC.
In 1988, preceding the creation of the UNFCCC, the Intergovernmental Panel on Climate Change (IPCC) was
jointly established by the World Meteorological Organization (WMO) and the United Nations Environment Programme
(UNEP). The charter of the IPCC is to assess available scientific information on climate change, assess the environ-
mental and socio-economic impacts of climate change, and formulate response strategies (IPCC 1996). Under Work-
ing Group 1 of the IPCC, nearly 140 scientists and national experts from more than thirty countries corroborated 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 Revised 1996 IPCC Guidelines were accepted by the IPCC at its Twelfth Session (Mexico City, 11-13
September 1996). The information provided in this inventory is presented in accordance with these guidelines, unless
otherwise noted. Additionally, in order to fully comply with the Revised 1996 IPCC Guidelines, the United States has
provided a copy of the IPCC reporting tables in Annex N and estimates of carbon dioxide emissions from fossil fuel
combustion using the IPCC Reference Approach in Annex O.
* See the section below entitled Global Warming Potentials for an explanation of GWP values.
2 See the section below entitled What is Climate Change? for an explanation of radiative forcing.
3 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).
4 Article 2 of the Framework Convention on Climate Change published by the UNEP/WMO Information Unit on Climate Change.
5 Article 4 of the Framework Convention on Climate Change published by the UNEP/WMO Information Unit on Climate Change (also
identified in Article 12).
Introduction 1-1
-------
Overall, the purpose of an inventory of anthropo-
genic greenhouse gas emissions is (1) to provide a basis
for the ongoing development of methodologies for esti-
mating sources and sinks of greenhouse gases; (2) to pro-
vide a common and consistent mechanism through which
Parties to the UNFCCC can estimate emissions and com-
pare the relative contribution of individual sources, gases,
and nations to climate change; and (3) as a prerequisite
for evaluating the cost-effectiveness and feasibility of
pursuing possible mitigation strategies.
What is Climate Change?
Climate change refers to long-term fluctuations hi
temperature, precipitation, wind, and other elements of the
Earth's climate system.6 Natural processes such as solar-
irradiance variations, variations in the Earth's orbital pa-
rameters,7 and volcanic activity can produce variations in
climate. The climate system can also be influenced by
changes in the concentration of various gases in the atmo-
sphere, which affect the Earth's absorption of radiation.
The Earth naturally absorbs and reflects incoming
solar radiation and emits longer wavelength terrestrial
(thermal) radiation back into space. On average, the ab-
sorbed solar radiation is balanced by the outgoing ter-
restrial radiation emitted to space. A portion of this ter-
restrial radiation, though, is itself absorbed by gases in
the atmosphere. The energy from this absorbed terres-
trial radiation warms the Earth's surface and atmosphere,
creating what is known as the "natural greenhouse ef-
fect." Without the natural heat-trapping properties of these
atmospheric gases, the average surface temperature of
the Earth would be about 34°C lower (IPCC 1996).
Under the United Nations FCCC, the definition of
climate change is "a change of climate which is attrib-
uted directly or indirectly to human activity that alters
the composition of the global atmosphere and which is
in addition to natural climate variability observed over
comparable time periods."8 Given that definition, in its
1995 assessment of the science of climate change, the
IPCC concluded that:
Human activities are changing the atmospheric
concentrations and distributions of greenhouse
gases and aerosols. These changes can produce
a radiative forcing by changing either the re-
flection or absorption of solar radiation, or the
emission and absorption of terrestrial radiation
(IPCC 1996).
The IPCC went on to report in its assessment that
the "[g]lobal mean surface temperature [of the Earth] has
increased by between about 0.3 and 0.6 °C since the late
19* century..." (IPCC 1996) and finally concluded with
the following statement:
Our ability to quantify the human influence on
global climate is currently limited because the
expected signal is still emerging from the noise
of natural variability, and because there are un-
certainties in key factors. These include the
magnitude and patterns of long term natural
variability and the time-evolving pattern of forc-
ing by, and response to, changes in concentra-
tions of greenhouse gases and aerosols, and land
surface changes. Nevertheless, the balance of
the evidence suggests that there is a discernable
human influence on global climate (IPCC 1996).
Greenhouse Gases
Although the Earth's atmosphere consists mainly
of oxygen and nitrogen, neither play a significant role in
this greenhouse effect because both are essentially trans-
parent to terrestrial radiation. The greenhouse effect is
primarily a function of the concentration of water vapor,
carbon dioxide, and other trace gases in the atmosphere
that absorb the terrestrial radiation leaving the surface of
the Earth (IPCC 1996). Changes in the atmospheric con-
centrations of these greenhouse gases can alter the bal-
ance of energy transfers between the atmosphere, space,
land, and the oceans. 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).
" The Earth's climate system comprises the atmosphere, oceans, biosphere, cryosphere, and geosphere.
*7
' For cxumptc, eccentricity, precession, and inclination.
* Article t of the Framework Convention on Climate Change published by the UNEP/WMO Information Unit on Climate Change.
1-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Climate change can be driven by changes in the
atmospheric concentrations of a number of
radiatively active gases and aerosols. We have
clear evidence that human activities have af-
fected concentrations, distributions and life
cycles of these gases (IPCC 1996).
Naturally occurring greenhouse gases include wa-
ter vapor, carbon dioxide (CO2), methane (CH4), nitrous
oxide (N2O), and ozone (O3). Several classes of haloge-
nated substances that contain fluorine, chlorine, or bro-
mine are also greenhouse gases, but they are, for the most
part, emitted solely by human activities. Chlorofiuoro-
carbons (CFCs) and hydrochlorofluorocarbons (HCFCs)
are halocarbons that contain chlorine, while halocarbons
that contain bromine are referred to as halons. Other fluo-
rine containing halogenated substances include
hydrofluorocarbons (HFCs), perfluorocarbons (PFCs),
and sulfur hexafluoride (SF6). There are also several gases
that, although they do not have a direct radiative forcing
effect, do influence the formation and destruction of
ozone, which does have such a terrestrial radiation ab-
sorbing effect. These gases—referred to here as ozone
precursors—include carbon monoxide (CO), oxides of
nitrogen (NOx), and nonmethane volatile organic com-
pounds (NMVOCs).9 Aerosols—extremely small par-
ticles or liquid droplets often produced by emissions of
sulfur dioxide (SO2)—can also affect the absorptive char-
acteristics of the atmosphere.
Carbon dioxide, methane, and nitrous oxide are
continuously emitted to and removed from the atmo-
sphere by natural processes on Earth. Anthropogenic
activities, however, can cause additional quantities of
these and other greenhouse gases to be emitted or se-
questered, thereby changing their global average atmo-
spheric concentrations. Natural activities such as respi-
ration 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 anthropo-
genic activities—generally do not alter average atmo-
spheric greenhouse gas concentrations over decadal
timeframes. Climatic changes resulting from anthropo-
genic activities, however, could have positive or nega-
tive feedback effects on these natural systems.
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 Glo-
bal Wanning Potentials (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 at-
mosphere, 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 activi-
ties are not believed to directly affect the average global
concentration of water vapor; however, the radiative forc-
ing produced by the increased concentrations of other green-
house gases may indirectly affect the hydrologic cycle. A
warmer atmosphere has an increased water holding capac-
ity; yet, increased concentrations of water vapor affects the
formation of clouds, which can both absorb and reflect so-
lar and terrestrial radiation.
Carbon Dioxide (CO2). In nature, carbon is cycled
between various atmospheric, oceanic, land biotic, ma-
rine 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 carbon dioxide is
part of this global carbon cycle, and therefore its fate is a
complex function of geochemical and biological pro-
cesses. Carbon dioxide concentrations in the atmosphere,
as of 1994, increased from approximately 280 parts per
million by volume (ppmv) in pre-industrial10 times to 358
ppmv, a 28 percent increase (IPCC 1996).11 The IPCC
has stated that "[t]here is no doubt that this increase is
largely due to human activities, in particular fossil fuel
combustion..." (IPCC 1996). Forest clearing, other bio-
mass burning, and some non-energy production processes
(e.g., cement production) also emit notable quantities of
carbon dioxide.
9 Also referred to in the U.S. Clean Air Act as "criteria pollutants."
Introduction 1-3
-------
In its latest scientific 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—al-
though the magnitude and significance of the effects are
not fully resolved" (IPCC 1996).
Methane (CH4). Methane is primarily produced
through anaerobic decomposition of organic matter in
biological systems. Agricultural processes such as wet-
land 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-prod-
uct of coal mining and incomplete fossil fuel combus-
tion. The average global concentration of methane in the
atmosphere was 1,720 parts per billion by volume (ppbv)
in 1994, a 145 percent increase from the pre-industrial
concentration of 700 ppbv (IPCC 1996). It is estimated
that 60 to 80 percent of current CH4 emissions are the
result of anthropogenic activities. Carbon isotope mea-
surements indicate that roughly 20 percent of methane
emissions are from fossil fuel consumption, and an equal
percentage is produced by natural wetlands, which will
likely increase with rising temperatures and rising mi-
crobial action (IPCC 1996).
Methane is removed from the atmosphere by re-
acting with the hydroxyl radical (OH) and is ultimately
converted to CO,. Increasing emissions of methane,
though, reduces the concentration of OH, and thereby
the rate of further methane removal (IPCC 1996).
Nitrous Oxide (N^O). Anthropogenic sources of
N,O emissions include agricultural soils, especially the
use of synthetic and manure fertilizers; fossil fuel com-
bustion, especially from mobile sources; adipic (nylon)
and nitric acid production; wastewater treatment and
waste combustion; and biomass burning. The atmospheric
concentration of nitrous oxide (N2O) in 1994 was about
312 parts per billion by volume (ppbv), while pre-indus-
trial concentrations were roughly 275 ppbv. The major-
ity of this 13 percent increase has occurred after the pre-
industrial period and is most likely due to anthropogenic
activities (IPCC 1996). Nitrous oxide is removed from
the atmosphere primarily by the photolytic action of sun-
light in the stratosphere.
Ozone (O3). Ozone is present in both the upper
stratosphere,12 where it shields the Earth from harmful
levels of ultraviolet radiation, and at lower concentra-
tions in the troposphere13, where it is the main compo-
nent of anthropogenic photochemical "smog". During
the last two decades, emissions of anthropogenic chlo-
rine and bromine-containing halocarbons, such as chlo-
rofluorocarbons (CFCs), have depleted stratospheric
ozone concentrations. This loss of pzone in the strato-
sphere has resulted in negative radiative forcing, repre-
senting an indirect effect of anthropogenic emissions of
chlorine and bromine compounds (IPCC 1996).
Tropospheric ozone, which is also a greenhouse gas,
is produced from the oxidation of methane and from reac-
tions with precursor gases such as carbon monoxide (CO),
nitrogen oxides (NOx), and non-methane volatile organic
compounds (NMVOCs). This latter group of ozone precur-
sors are included in the category referred to as "criteria pol-
lutants" in the United States under the Clean Air Act14 and
its subsequent amendments. The tropospheric concentra-
tions of both ozone and these precursor gases are short-
lived and, therefore, spatially variable,
Halocarbons. Halocarbons are for the most part man-
made chemicals that have both direct and indirect radiative
forcing effects. Halocarbons that contain chlorine—chlo-
rofluorocarbons (CFCs), hydrochlorofluorocarbons
(HCFCs), methyl chloroform, and carbon tetrachloride—
and bromine—halons, methyl bromide, and
'"The pre-industrial period is considered as the time preceding the year 1750 (IPCC 1996).
1' Carton 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 1996). ',
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.
• 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.
1-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
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 at-
mosphere is reduced because they cause stratospheric ozone
depletion, which is itself an important greenhouse gas in
addition to shielding the Earth from harmful levels of ultra-
violet radiation. 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 pro-
duction and importation of HCFCs by non-Article 515 coun-
tries beginning in 1996, and then followed by a complete
phase-out by the year 2030. The ozone depleting gases cov-
ered under the Montreal Protocol and its Amendments are
not covered by the UNFCCC; however, they are reported in
this inventory under Annex K.
Hydrofluorocarbons (HFCs), perfluorocarbons
(PFCs), and sulfur hexafluoride (SF6) are not ozone deplet-
ing substances, and therefore are not covered under the
Montreal Protocol. They are, however, powerful greenhouse
gases. HFCs—primarily used as replacements for ozone
depleting substances but also emitted as a by-product of the
HCFC-22 manufacturing process—currently have a small
aggregate radiative forcing impact; however, it is anticipated
that their contribution to overall radiative forcing will in-
crease (EPCC1996). PFCs and SF6 are predominantly emit-
ted from various industrial processes including aluminum
smelting, semiconductor manufacturing, electric power
transmission and distribution, and magnesium casting. Cur-
rently, the radiative forcing impact of PFCs, and SF6 is also
small; however, because they have extremely long atmo-
spheric lifetimes, their concentrations tend to irreversibly
accumulate in the atmosphere.
Carbon Monoxide (CO). 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 radi-
cal) that would otherwise assist in destroying CH4 and tro-
pospheric ozone. Carbon monoxide is created when car-
bon-containing fuels are burned incompletely. Through
natural processes in the atmosphere, it is eventually oxi-
dized to CO2. Carbon monoxide concentrations are both
short-lived in the atmosphere and spatially variable.
Nitrogen Oxides (NOJ. 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 strato-
sphere, where it has positive radiative forcing effects. (NOx
emissions injected higher in the stratosphere16 can lead to
stratospheric ozone depletion.) Nitrogen oxides are created
from lightning, soil microbial activity, biomass burning (both
natural and anthropogenic fires), fossil fuel combustion, and,
in the stratosphere, from nitrous oxide (N2O). Concentra-
tions of NOx are both relatively short-lived in the atmosphere
and spatially variable.
Nonmethane Volatile Organic Compounds
(NMVOCs). Nonmethane volatile organic compounds
include compounds such as propane, butane, and ethane.
These compounds participate, along with NOx, in the
formation of tropospheric ozone and other photochemi-
cal oxidants. NMVOCs are emitted primarily from trans-
portation and industrial processes, as well as biomass
burning and non-industrial consumption of organic sol-
vents. 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 vol-
canic activity or by anthropogenic processes such as fuel
combustion. Their effect upon radiative forcing is to both
absorb radiation and to alter cloud formation, thereby
affecting the reflectivity (i.e., albedo) of the Earth. Aero-
sols are removed from the atmosphere primarily by pre-
cipitation, and generally have short atmospheric lifetimes.
Like ozone precursors, aerosol concentrations and com-
position vary by region (IPCC 1996).
14 [42 U.S.C § 7408, CAA § 108]
^ Article 5 of the Montreal Protocol covers several groups of countries, especially developing countries, with low consumption rates of ozone
depleting substances. Developing countries with per capita consumption of less than 0.3 kg of certain ozone depleting substances (weighted by
their ozone depleting potential) receive financial assistance and a grace period of ten additional years in the phase-out of ozone depleting
substances. ,
16 Primarily from fuel combustion emissions from high altitude supersonic aircraft.
Introduction 1-5
-------
Anthropogenic aerosols in the troposphere are pri-
marily the result of sulfur dioxide (SO2)17 emissions from
fossil fuel and biomass burning. Overall, aerosols tend
to produce a negative radiative forcing effect (i.e., net
cooling effect on the climate), although because they are
short-lived in the atmosphere—lasting days to weeks—
their concentrations respond rapidly to changes in emis-
sions.1* Locally, the negative radiative forcing effects of
aerosols can offset the positive forcing of greenhouse
gases (1PCC 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). Emissions of sulfur dioxide are
provided in Annex L of this report.
Global Warming Potentials
A Global Wanning Potential (GWP) is intended as a
quantified measure of the relative radiative forcing impacts
of a particular greenhouse gas (see Table 1-1). It is defined
as the cumulative radiative forcing—both direct and indi-
rect effects—over a specified time horizon resulting from
the emission of a unit mass of gas relative to some refer-
ence gas (IPCC 1996). Direct effects occur when the gas
itself is a greenhouse gas. 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 the atmospheric lifetimes of other gases.
The reference gas used is CO2> in which case GWP weighted
emissions are measured in million metric tons of carbon
equivalents (MMTCE). Carbon comprises 12/44ths of car-
bon dioxide by weight In order to convert emissions re-
ported in teragrams (Tg) of a gas to MMTCE, the following
equation is used:
Tg = Teragrams (equivalent to million metric tons)
GWP = Global Warming Potential
MMTCE = (Tg of gas) X (GWP) X Hj
\'¥*l
where,
MMTCE = Million Metric Tons of Carbon
Equivalents
= Carbon to carbon dioxide molecular weight
ratio.
GWP values allow policy makers to compare the
impacts of emissions and reductions of different gases.
According to the IPCC, GWPs typically have an uncer-
tainty 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.
In addition to communicating emissions in units
of mass, Parties may choose also to use global
warming potentials (GWPs) to reflect their inven-
tories and projections in carbon dioxide-equiva-
lent terms, using information provided by the In-
tergovernmental Panel on Climate Change (IPCC)
in its Second Assessment Report. Any use of GWPs
should be based on the.effects of the greenhouse
gases over a 100-year time horizon. In addition,
Parties may also use other time horizons.19
Greenhouse gases with long atmospheric lifetimes
(e.g., CO2, CH4, N2O, HFCs, PFCs,;!and SF6) tend to be
evenly distributed throughout the atmosphere, and conse-
quently global average concentrations can be determined.
The short-lived gases such as water vapor, tropospheric
ozone, ozone precursors (e.g., NOx, CO, and NMVOCs),
and tropospheric aerosols (e.g., SO2 products), however, vary
regionally, and consequently it is difficult to quantify their
global radiative forcing impacts. No GWP values are at-
tributed to these gases that are short-lived and spatially in-
homogeneous in the atmosphere. Other greenhouse gases
not yet listed by the Intergovernmental Panel on Climate
Change (IPCC), but are already or soon will be in commer-
cial use include: HFC-245fa, hydrofluoroethers (HFEs), and
nitrogen trifluoride (NF3).
A more detailed technical discussion on the deri-
vation of and uncertainties in GWP values can be found
in Annex J.
' Sulfur dioxide is a primary anthropogenic contributor to the formation of "acid rain" and other forms of atmospheric acid deposition.
15t
10 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).
19 Framework Convention on Climate Change; FCCC/CP/1996/15/Add.l; 29 October 1996; Report of the Conference of the Parties at its
second session; held at Geneva from 8 to 19 July 1996; Addendum; Part Two: Action taken by the Conference of the Parties at its second
session; Decision 9KP.2; Communications from Parties included in Annex I to the Convention: guidelines, schedule and process for consider-
ation; Annex: Revised Guidelines for the Preparation of National Communications by Parties Included in Annex I to the Convention; p. 18.
1-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 1-1: Global Warming Potentials and
Atmospheric Lifetimes (Years)
Atmospheric
Gas
Carbon dioxide (C02)
Methane (GH/
Nitrous oxide (N20)
HFC-23
HFC-125
HFC-134a
HFC-1433
HFC-152a
HFC-227ea
HFC-236fa
HFC-4310mee
CF4
C2F6
C4F10
C6F1<
SFR
Source: {IPCC 1996)
a 1 00 year time horizon
Lifetime
50-200
12±3
120
264
32.6
14.6
48.3
1.5
36.5
209
17.1
50,000
10,000
2,600
3,200
3,200
b The methane 6WP includes the direct effects
effects due to the production
of tropospheric
stratospheric water vapor. The indirect effect
GWPa
1
21
310
11,700
2,800
1,300
3,800
140
2,900
6,300
1,300
6,500
9,200
7,000
7,400
23,900
and those indirect
ozone and
due to the
production of C02 is not included.
Recent Trends in U.S.
Greenhouse Gas Emissions
Total U.S. greenhouse gas (GHG) emissions rose
in 1997 to 1,813.6 million metric tons of carbon equiva-
lents (MMTCE) (11.1 percent above 1990 baseline lev-
els). The single year increase in emissions from 1996 to
1997 was 1.3 percent (23.1 MMTCE), down from the
previous year's increase of 3.3 percent. Figure 1-1
through Figure 1-3 illustrate the overall trends in total
U.S. emissions by gas, annual changes, and absolute
changes since 1990.
The largest source of U.S. GHG emissions was
carbon dioxide (CO2) from fossil fuel combustion, which
accounted for 81 percent of weighted emissions in 1997.
Emissions from this source grew by 11 percent (138.8
MMTCE) over the from 1990 to 1997 and were respon-
sible for over three-quarters of the increase in national
emissions during this period. The annual increase in CO2
emissions from this source was 1.3 percent in 1997, also
down from the previous year's high when increased fos-
sil fuel consumption drove up emissions by 3.6 percent.
The dramatic increase in fossil fuel combustion-re-
lated CO2 emissions in 1996 was primarily a function of
two factors: 1) fuel switching by electric utilities from natu-
"ral gas to more carbon intensive coal as gas prices rose
sharply due to weather conditions, which drove up residen-
tial consumption of natural gas for heating; and 2) higher
petroleum consumption for transportation. In 1997, by com-
parison, electric utility natural gas consumption rose to re-
gain much of the previous year's decline as the supply avail-
able rose due to lower residential consumption. Despite this
increase in natural gas consumption by utilities and rela-
tively stagnant U.S. electricity consumption, coal consump-
tion rose in 1997 to offset the temporary shut-down of sev-
eral nuclear powerplants. Petroleum consumption for trans-
portation activities in 1997 also grew by less than one per-
Figure 1-1
• MFCs, PFCs, & SF6
• Nitrous Oxide
• Methane
: Carbon Dioxide
1,750-1,632 1,620 1.645
1,675 L713 1.734 ^
1,791 1,814
1990 1991 1992 1993 1994 1995 1996 1997
Figure 1-2
1991 1992 1993 1994 1995 1996 1997
Introduction 1-7
-------
Figure 1-3
:IISi!i!IM
180
150
120
9°
60
30
0
-30
181.5
158.4
-12.1
13.1
1991 1992 1993 1994 1995 1996 1997
cent, compared to over three percent the previous year (see
Table 1-2). The annual increase of CO2 emissions from pe-
troleum in 1997 is based on motor gasoline sales data from
the U.S. Energy Information Administration; it is expected
to be revised upward with the publication of future energy
statistics.
Other significant trends in emissions from addi-
tional source categories over the eight year period from
1990 through 1997 included the following:
* Aggregate HFC and PFC emissions resulting from
the substitution of ozone depleting substances (e.g.,
CFCs) increased dramatically (by 14.4 MMTCE).
This increase was partly offset, however, by reduc-
tions in PFC emissions from aluminum production
(41 percent) and HFC emissions from HCFC-22 pro-
duction (14 percent), both as a result of voluntary
industry emission reduction efforts and, hi the former
case, from falling domestic aluminum production.
• Combined N20 and CH4 emissions from mobile
source fossil fuel combustion rose by 3.9 MMTCE
(26 percent), primarily due to increased rates of N2O
generation in highway vehicles.
• Methane emissions from the decomposition of waste
in municipal and industrial landfills rose by 10.5
MMTCE (19 percent) as the amount of organic mat-
ter in landfills steadily accumulated.
• Emissions from coal mining dropped by 5.2
MMTCE (21 percent) as the use of methane from
dcgasification systems increased significantly.
Table 1-2: Annual Percent Change in C02
Emissions from Fossil Fuel Combustion for
Selected Sectors and Fuels
Sector
Electric Utility
Electric Utility
Residential
Transportation*
Fuel
type
Coal
Natural Gas
Natural Gas
Petroleum
1995to
1996
5.7%
-14.6%
8.1%
3.4%
1996to
1997
2.9%
8.7%
-4.4%
0.3%
Excludes emissions from International Bunker Fuels.
• Nitrous oxide emissions from agricultural soil man-
agement increased by 8.8 MMTCE (13 percent) as
fertilizer consumption and cultivation of nitrogen
fixing crops rose.
• An additional domestic adipic acid plant installed
emission control systems in 1997; this was estimated
to have resulted in a 1.4 MMTCE (27 percent) de-
cline in emissions from 1996 to 1997 despite an in-
crease in production.
Overall, from 1990 to 1997 total emissions of CO2,
CH4, and N2O increased by 143.5 (11 percent), 9.7 (6
percent), and 13.4 MMTCE (14 percent), respectively.
During the same period, weighted emissions of HFCs,
PFCs, and SF6 rose by 14.9 MMTCE (67 percent). De-
spite being emitted in smaller quantities relative to the
other principal greenhouse gases, emissions of HFCs,
PFCs, and SF6 are significant because of their 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, which was estimated to be 11
percent of total emissions in 1997.
As an alternative, emissions; can be aggregated
across gases by the IPCC defined sectors, referred to here
as chapters. Over the eight year period of 1990 to 1997,
total emissions in the Energy, Industrial Processes, Agri-
culture, and Waste chapters climbed by 140.2 (10 per-
cent), 17.6 (39 percent), 13.0 (11 percent), and 10.8
MMTCE (18 percent), respectively. Estimates of the
quantity of carbon sequestered in the Land-Use Change
and Forestry chapter, although based on projections, de-
clined in absolute value by 103.0 MMTCE (33 percent).
1-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Box 1-1: Recent Trends in Various U.S. Greenhouse Gas Emissions-Related Data
There are several ways to assess a nation's greenhouse gas emitting intensity. These measures of intensity could be based on
aggregate energy consumption because energy-related activities are the largest sources of emissions, on fossil fuel consumption
only because almost all energy-related emissions involve the combustion of fossil fuels, on electricity consumption because
electric utilities were the largest sources of U.S. greenhouse gas emissions in 1997, on total gross domestic product as a measure
of national economic activity, or on a per capita basis. Depending upon which of these measures was used, the United States could
appear to have reduced or increased its national greenhouse gas intensity. Table 1 -3 provides data 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 1.5 percent since 1990. This rate is slightly slower than that for total energy or fossil fuel consumption—
thereby indicating an improved or lower greenhouse gas emitting intensity—and much slower than that for either electricity
consumption or overall gross domestic product. Emissions, however, are growing fasterthan national population, thereby indicating
a worsening or higher greenhouse gas emitting intensity on a per capita basis (see Figure 1 -4). Overall, atmospheric C02 concentra-
tions—a function of many complex anthropogenic and natural processes—are increasing at 0.4 percent per year.
Table 1-3: Recent Trends in Various U.S. Data (Index 1990=100)
Variable
1990
1991 1992 1993 1994 1995 1996 1997 Growth Rate"
GHG Emissions3
Energy Consumption"
Fossil Fuel Consumption0
Electricity Consumption0
GDP"
Population6
Atmospheric CO,, Concentration'
100
100
100
100
100
100
100
99
100
99
102
99
101
100
101
101
101
102
102
102
101
103
104
104
105
104
103
101
105
106
106
108
108
104
101
106
108
107
111
110
105
102
110
112
110
114
114
106
102
111
112
112
115
118
107
103
1.5%
1.6%
1.6%
2.0%
2.5%
1.0%
0.4%
a GWP weighted values
b Energy content weighted values. Source: DOE/EIA
c Source: DOE/EIA
" Gross Domestic Product in chained 1992 dollars (BEA 1998)
e (U.S. Census Bureau 1998)
' Mauna Loa Observatory, Hawaii (Keeling and Whorf 1998)
s Average annual growth rate
Figure 1-4
., . _
108 n
1990 1991 1992 1993 1994 1995 1996 1997
Introduction 1-9
-------
Table 1-4 summarizes emissions and sinks from all
U.S. anthropogenic sources in weighted units of MMTCE,
while unweighted gas emissions and sinks in teragrams (Tg)
are provided in Table 1-5. Alternatively, emissions and sinks
are aggregated by chapter in Table 1-6 and Figure 1-5.
Table 1-4: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (MMTCE)
Gas/Source
1990 1991 1992 1993 1994 1995 1996 1997
CO,
Fossil Fuel Combustion
Natural Gas Flaring
Cement Manufacture
Urns Manufacture
Limestone and Dolomite Use
Soda Ash Manufacture and Consumption
Carbon Dioxide Consumption
Land-Use Change and Forestry (Sink)1
International Bunker Fuels"
CH4
Stationary Sources
Mobile Sources
Coal Mining
Natural Gas Systems
Petroleum Systems
Petrochemical Production
Silicon Carbide Production
Entiric Fermentation
Manure Management
Rice Cultivation
Agricultural Residue Burning
Landfills
Waste water Treatment
International Bunker Fuels"
MjO
Stationary Sources
Mobile Sources
Adipic Acid Production
Nitrfc Acid Production
Manure Management
Agricultural Soil Management
Agricultural Residue Burning
Human Sewage
Waste Combustion
International Bunker Fuels"
HFCs, PFCs, and SF,
Substitution of Ozone Depleting Substances
Atupnurn Production
HCFC:22 Production
Semiconductor Manufacture
Electrical Transmission and Distribution
Magnesium Production and Processing
Total Emissions
Net Emissions (Sources and Sinks)
1,344.3
1,327.2
2.3
8.9
3.3
1.4
1.1
0.2
(311.5)
27.1
169.9
2.3
1.4
24.0
32.9
1.6
0.3
+
32.7
14.9
2.5
0.2
56.2
0.9
_f.
95.7
3.8
13.6
4.7
3.3
2.6
65.3
0.1
2.1
0.1
0.2
22.2
0.3
4.9
9.5
0.2
5.6
1.7
1,632.1
1,320.6
1,329.8
1,312.6
2.6
8.7
3.2
1.3
1.1
0.2
(311.5)
27.8
171.0
2.4
1.4
22.8
33.3
1.6
0.3
+
32.8
15.4
2.5
0.2
57.6
0.9
i
97.6
3.8
14.2
4.9
3.3
2.8
66.2
0.1
2.1
0.1
0.2
21.6
0.2
4.7
8.4
0,4
5.9
2.0
1,620.0
1,308.5
1,349.6
1,332.4
2.6
8.8
3.3
1.2
1.1
0.2
(311.5)
29.0
172.5
2.4
1.4
22.0
33.9
1.6
0.3
+
33.2
16.0
2.8
0.2
57.8
0.9
i
100.1
3.9
15.2
4.6
3.4
2.8
68.0
0.1
2.2
0.1
0.2
23.0
0.4
4.1
9.5
0.6
6.2
2.2
1,645.2
1,333.7
1,379.2
1,360.6
3.5
9.3
3.4
1.1
1.1
0.2
(208.6)
29.9
172.0
2.4
1.4
19.2
34.1
1.6
0.4
+
33.6
16.1
2.5
0.2
59.7
0.9
i
100.4
3.9
15.9
4.9
3.5
2.9
67.0
0.1
2.2
0.1
0.3
23.4
1.4
3.5
8.7
0.8
6.4
2.5
1,675.0
1,466.5
1,403.5
1,383.9
3.6
9.6
3.5
1.5
1.1
0.2
(208.6)
27.4
175.5
2.4
1.4
19.4
33.5
1.6
0.4
-j.
34.5
16.7
3.0
0.2
61.6
0.9
i
108.3
4.0
16.7
5,2
3.7
2,9
73.4
0.1
2.2
0.1
0.2
25.9
4.0
2.8
8.6
1.0
6.7
2.7
1,713.2
1,504.7
1,419.2
1,397.8:
4.5
9.9'
3.7
1.9,;
1.2
0.3
(208.6)
25.4
178.6
2.5
1.4
20.3
33.2
1.5;
0.4,
+
34.9 "
16.9
2.8,'
0.2
63.6 :
0.9
• :l
T ,ij
105.4
4.0 !
17.0
5.2 "
3-7,
2.9
70.2
0.1
2.3;
0.1
0.2,
30.8
9.5
2.7!
7.4
1.2
7.0
3.0
1,733.9
1,525.4
1,469.3
1,447.7
4.3
9.9
3.8
2.0
1.2
0.3
(208.6)
25.4
178.3
2.5
1.4
18.9
33.7
1.5
0.4
+
34.5
16.6
2.5
0.2
65.1
0.9
,
108.2
4.1
17.4
5.4
3.9
3.0
72.0
0.1
2.3
0.1
0.2
34.7
11.9
2.9
8.5
1.4
7.0
3.0
1,790.5
1,582.0
1,487.9
1,466.0
4.2
10.2
3.9
2.1
1.2
0.3
(208.6)
26.6
179.6
2.2
1.4
18.8
33.5
1.6
0.4
+
34.1
17.0
2.7
0.2
66.7
0.9
,
109.0
4.1
17.5
3.9
3.8
3.0
74.1
0.1
2.3
0.1
0.2
37.1
14.7
2.9
8.2
1.3
7.0
3.0
1,813.6
1,605.0
+ Does not exceed 0.05 MMTCE
* Sinks are only Included In net emissions total. Estimates of net carbon sequestration due to land-use change and forestry activities exclude
non-fpfBSt soils, and are based partially upon projections of forest carbon stocks.
• Emissions from International Bunker Fuels are not included in totals.
Note; totals may not sura due to independent rounding. ]
1-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 1-5: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks (Tg)
Gas/Source
1990
1991 1992 1993 1994 1995 1996 1997
C02
Fossil Fuel Combustion
Natural Gas Flaring
Cement Manufacture
Lime Manufacture
Limestone and Dolomite Use
Soda Ash Manufacture and Consumption
Carbon Dioxide Consumption
Land-Use Change and Forestry (Sink)3
International Bunker Fuels"
CH4
Stationary Sources
Mobile Sources
Coal Mining
Natural Gas Systems
Petroleum Systems
Petrochemical Production
Silicon Carbide Production
Enteric Fermentation
Manure Management
Rice Cultivation
Agricultural Residue Burning
Landfills
Wastewater Treatment
International Bunker Fuels"
N20
Stationary Source
Mobile Sources
Adipic Acid
Nitric Acid
Manure Management
Agricultural Soil Management
Agricultural Residue Burning
Human Sewage
Waste Combustion
International Bunker Fuels"
MFCs, PFCs, and SF6
Substitution of Ozone Depleting Substances
Aluminum Production
HCFC-22 Production'
Semiconductor Manufacture
Electrical Transmission and Distribution"
Magnesium Production and Processing"
NO
CO
NMVOCs
4,929.2
4,866.2
8.4
32.6
11.9
5.1
4.1
0.8
(1,142.2)
99.3
29.7
0.4
0.3
4.2
5.7
0.3
0.1
+
5.7
2.6
0.4
+
9.8
0.2
+
1.1
+
0.2
0.1
+
+
0.8
+
+
+
+
M
M
M
+
M
+
+
21.1
83.1
18.7
4,875.8
4,812.8
9.6
31.9
11.7
4.9
4.0
0.8
(1,142.2)
101.9
29.9
0.4
0.2
4.0
5.8
0.3
0.1
+
5.7
2.7
0.4
+
10.0
0.2
-t-
1.2
+
0.2
0.1
+
+
0.8
+
+
4-
+
M
M
M
+
M
+
+
21.2
84.8
18.8
4,948.5
4,885.4
9.4
32.1
12.1
4.5
4.1
0.9
(1,142.2)
106.4
30.1
0.4
0.2
3.8
5.9
0.3
0.1
+
5.8
2.8
0.5
+
10.1
0.2
+
1.2
+
0.2
0.1
+
+
0.8
+
+
+
+
M
M
M
+
M
+
+
21.5
81.8
18.5
5,057.0
4,988.7
13.0
33.9
12.4
4.1
4.0
0.9
(764.7)
109.6
30.0
0.4
0.2
3.4
5.9
0.3
0.1
+
5.9
2.8
0.4
+
10.4
0.2
+
1.2
+
0.2
0.1
+
+
0.8
+
+
+
+
M
M
M
-t-
M
+
+
21.7
81.7
18.6
5,146.1
5,074.4
13.1
35.4
12.8
5.5
4.0
0.9
(764.7)
100.4
30.7
0.4
0.2
3.4
5.8
0.3
0.1
+
6.0
2.9
0.5
+
10.8
0.2
+
1.3
+
0.2
0.1
- +
+
0.9
+
+
+
+
M
M
M
+
M
+
+
22.0
85.7
19.2
5,203.6
5,125.1
16.4
36.1
13.6
7.0
4.3
1.0
(764.7)
93.3
31.2
0.4
0.2
3.6
5.8
0.3
0.1
+
6.1
3.0
0.5
+
11.1
0.2
+
1.2
+
0.2
0.1
+
+
0.8
+
+
+
+
M
M
M
+
M
+
+
21.4
76.7
18.4
5,387.4
5,308.3
15.7
36.4
14.1
7.5
4.3
1.1
(764.7)
93.0
31.1
0.4
0.2
3.3
5.9
0.3
0.1
+
6.0
2.9
0.4
+
11.4
0.2
+
1.3
+
0.2
0.1
+
+
0.9
+
+
+
+
M
M
M
+
M
+
+
21.2
78.3
17.2
5,455.6
5,375.2
15.2
37.5
14.2
7.8
4.4
1.2
(764.7)
97.5
31.4
0.4
0.2
3.3
5.8
0.3
0.1
+
6.0
3.0
0.5
+
11.6
0.2
+
1.3
+
0.2
+
+
+
0.9
+
+
+
+
M
M
M
+
M
+
+
21.3
75.2
17.1
+ Does not exceed 0.05 Tg
M Mixture of multiple gases
a Sinks are not included in C02 emissions total. Estimates of net carbon sequestration due to land-use change and forestry activities exclude
non-forest soils, and are based partially upon projections of forest carbon stocks.
" Emissions from International Bunker Fuels are not included in totals.
c HFC-23 emitted
" SF6 emitted
Note: Totals may not sum due to independent rounding.
Introduction 1-11
-------
Figure 1-5
Industrial Processes
i i|ii|i|i|ii|iiii|iiftifl ipfumMiiii ..... (i nin!i"i|ii npf
m iJM ^ -"ik
Land-Use Change and Fprestry (sink)
1990 1991 1992 1993 1994 1995 1996 1997
Table 1-6: Recent Trends in U.S. Greenhouse Gas Emissions and Sinks by Chapter/IPCC Sector (MMTCE)
Chapter/IPCC Sector
1990 1991 1992 1993 1994 1995 1996 1997
Energy
Industrial Processes
Agriculture
Land-Use Change and Forestry (Sink)*
Waste
TftaS Irojssioris
Net Emissions (Sources and Sinks)
~ ' , ;;, 73T1 ,':. ,llr , , i '. ,. ;• in ; , .,..; ., , , . -j, .. ..,' . 1 ,' " ~- ',' '. ;
1,409.0 1,394.6 1,415.2 1,442.6 1,466.3 1,482.1 1,531.6 1,549.2
45.4 44.8 46.0 47.2 51.2 57.0 61.6 63.0
118.4 120.0 123.1 122.4 130.9 128.0 128.9 131.4
(311.5) (311.5) (311.5) (208.6) (208.6) (208.6) (208.6) (208.6)
59.2 60.6 60.9 62.8 64,8 66,9 [ 68.4 70.0
1,632.1 1,620.0 1,645.2 1,675.0 1,713.2 1,733.9 1,790.5 1,813.6
1,320.6 1,308.5 1,333.7 1,466.5 1,504.7 1,525.4 1,582.0 1,605.0
* Sbfe..afgest sois, and are based partially upon projections of forest carbon stocks.
!e: Totals may "riot "sum" due" "to independent rounding.
" :!;i|"! •. ":" ij'i*i;- iwi '•!''. s; ,• • SIM ;:,''C.. i": .. •.-.-• 'i,',:'.' ;•'.•:
1-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Box 1-2: Greenhouse Gas Emissions from Transportation Activities
Motor vehicle usage is increasing all over the world, including in the United States. 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 Admin-
istration. Likewise, the number of miles driven—up 18 percent from 1990 to 1997—and gallons of gasoline consumed each year
in the United States have increased relatively steadily since the 1980s, according to the Energy Information Administration. These
increases in motor vehicle usage are the result of a confluence of factors including population growth, economic growth, increas-
ing urban sprawl, and low fuel prices.
One of the unintended consequences of these changes is a slowing of progress toward cleaner air in both urban and rural parts of
the country. Passenger cars, trucks, motorcycles, and buses emit significant quantities of air pollutants with local, regional, and
global effects. Motor vehicles are major sources of carbon monoxide (CO), carbon dioxide (C02), methane (CH4), nonmethane
volatile organic compounds (NMVOCs), nitrogen oxides (NOX), nitrous oxide (N20), and hydrofluorocarbons (MFCs). Motor ve-
hicles are also important contributors to many serious air pollution problems, including ground level ozone or smog, acid rain, fine
particulate matter, and global warming. Within the United States and abroad, government agencies have taken strong actions to
reduce these emissions. Since the 1970s, the EPA has reduced lead in gasoline, developed strict emission standards for new
passenger cars and trucks, directed states to enact comprehensive motor vehicle emission control programs, required inspection
and maintenance programs, and more recently, introduced the use of reformulated gasoline to mitigate the air pollution impacts
from motor vehicles. New vehicles are how equipped with advanced emissions controls, which are designed to reduce emissions
of nitrogen oxides, hydrocarbons, and carbon monoxide.
This report reflects new data on the role that automotive catalytic converters play in emissions of N20, a powerful greenhouse gas.
The EPA's Office of Mobile Sources has conducted a series of tests in order to measure the magnitude of N20 emissions from
gasoline-fueled passenger cars and light-duty trucks equipped with catalytic converters. Results show that N20 emissions are
lower than the IPCC default factors, and the United States has shared this data with the IPCC. In this report, new emission factors
developed from these measurements and from previously published literature were used to calculate emissions from mobile
sources in the United States (see Annex C).
Table 1-7 summarizes greenhouse gas emissions from all transportation-related activities. Overall, transportation activities-
excluding international bunker fuels—accounted for an almost constant 26 percent of total U.S. greenhouse gas emissions from
1990 to 1997. These emissions were primarily C02 from fuel combustion, which increased by 10 percent from 1990 to 1997.
However, because of larger increases in N20 and HFC emissions during this period, overall emissions from transportation activities
actually increased by 12 percent.
Introduction 1-13
-------
Table 1-7: Transportation-Related Greenhouse Gas Emissions (MMTCE)
Gas7\fehlclB type 1990 1991 1992 1993 1994
1995
1996 1997
co,
Passenger Cars1
Light-Duty Trucks*
Otter Trucks
Buses
Aircraft
Boats and Vessels
Locomotives
Other*'
International Bunker fuels'
CH4
Passenger Cars
Light-Duty Trucks
Other Trucks and Buses
Aircraft
Boats and Vessels
Locomotives
Other1
International Bunker Fuelsc
H,0
Passenger Cars
Llgl-Duty trucks
Other Trucks and Buses
Aircraft"
Boats and Vessels
Locomotives
Other*
International Bunker Fuelsc
HFCs
Mobfle Air Conditioners'
Total'
405.0
169.3
77.5
57.3
2.7
50.5
16.4
7.5
23.8
27.1
1.4
0.8
0.4
0.1
+
+
+
0.1
+
13.6
8.7
3.4
0.7
0.5
0.1
0.1
0.2
0.2
+
+
420.0
396.7
167.8
77.2
55.1
2.9
48.4
15.9
6.9
22.5
27.8
1.4
0.7
0.4
0.1
+
+
+
0.1
_l_
14.2
9.1
3.7
0.7
0.5
0,1
0.1
0.2
0.2
+
+
412.3
402.4
172.0
77.2
56.7
2.9
47.4
16.4
7.4
22.4
29.0
1.4
0.7
0.4
0.1
+
+
+
0.1
_l_
15.2
9.7
3.9
0.7
0.5
0.1
0.1
0.2
0,2
0.2
0.2
419.1
406.8
173,5
80.5
59.9
3.1
47.6
11.7
6.8
23.8
29.9
1.4
0.7
0.4
0.2
+
+
_l_
0.1
+
15.9
10.1
4.2
0.7
0.5
0.1
0,1
0.2
0.3
0.7
0.7
424.8
422.1
172.5
87.2
62.7
3.3
49.6
13.9
8.0
24.9
27,4
1.4
0.7
0.4
0.2
+
+
0.1
_l_
16.7
.. 1Q.Q.
5.1
0.8
0.5
0.1
0.1
0.2
0.2
1.3
1.3
441.5
430.7
175.6!
89.2!
64.2!
3.5
48.3
16.8
8.1!
24.9!
25.4;
1-4
0.7
0.4
0.2
+ i
+ '
0.1;
17.0
10.1
5.2
0.8;
0.5!
0.1,;
0.1
0.2;
0.2
2.5
2.5
451.6
445.3
160.8
109.9
68.3
3.0
50.5
18.5
8.8
25,5
25.4
1.4
0.6
0.5
0.2
+i
+
0.1
17.4
8,9
6.8
0.9
0.5
0.1
0.1
0.2
0.2
3.6
3.6
467.7
446.5
162.6
111.1
69.5
3.0
50.1
15.4
9.0
25.8
26.6
1.4
0.6
0.5
0.2
+
+
0.1
17.5
9.1
6.8
0.9
0.5
0.1
0.1
0.2
0.2
4.5
4.5
469.9
'+' Does not exceed O.OS MMTCE
Note; Totals may not sum due to independent rounding. !
" In 1996, the U.S. Federal Highway Administration modified the definition of light-duty trucks to include minivans and sport utility vehicles.
Previously, these vehictes werejncluded under the passenger cars category. Hence the sharp drop in C02 emissions for passenger cars from
1985 Un996 was observed. This gap, however, was offset by an equivalent rise in C02 emissions from light-duty trucks!
* *0ttwr" CO, emissions include motorcycles, construction equipment, agricultural machinery, pipelines, and lubricants. '.
1 Emissions from International Bunker Fuels are not included in totals. ;
* "Other* CH« and NjO emissions include motorcycles, construction equipment, agricultural machinery, gasoline-poweredlrecreational,
Industrial, lawn and garden, light commercial, logging, airport service, other equipment; and diesel-powered recreational, industrial, lawn and
garden, light construction,, airport service. !
«includes primarily HFC-134a '.
Box 1-3: Electric Utility-Related Greenhouse Gas Emissions
1 Like {fihsportition, activities related to the generation, transmission, and distribution of electricity in the United States result in
greenhouse gas emissions. Table i-8 presents greenhouse gas emissions from electric utility-related activities. Aggregate emis-
sions from electric utilities of all greenhouse gases from electric utilities increased by 11.8 percent from )990 to 1997, and
accounted for Just under 30 percent of total U.S. greenhouse emissions during the same period. The majority of these emissions
„ resufW from, tne combustion of coal in boilers to produce steam that is passed through a turbine to generate electricity. Overall, the
generation of electricity results in a larger portion of total U.S. greenhouse gas emissions than any other activity.
1-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 1-8: Electric Utility-Related Greenhouse Gas Emissions {MMTCE)
Gas/Fuel Type or Source
1990 1991 1992 1993 1994 1995 1996 1997
C02
Coal
Natural Gas
Petroleum
Geothermal
GH4
Stationary Sources (Utilities)
M20
Stationary Sources (Utilities)
SF6
Electrical Transmission and Distribution
Total
476.8
409.0
41.2
26.6
0.1
0.1
0.1
2.0
2.0
5.6
5.6
484.6
473.4
407.2
41.1
25.1
0.1
0.1
0.1
2.0
2.0
5.9
5.9
481.4
472.5
411.8
40.7
19.9
0.1
0.1
0.1
2.0
2.0
6.2
6.2
480.8
490.7
428.7
39.5
22.5
0.1
0.1
0.1
2.1
2.1
6.4
6.4
499.3
494.8
430.2
44.0
20.6
+
0.1
0.1
2.1
2.1
6.7
6.7
503.7
494.1
433.0
47.2
14.0
+
0.1
0.1
2.1
2.1
7.0
7.0
503.3
513.2
457.5
40.3
15.4
+
0.1
0.1
2.2
2.2
7.0
7.0
522.5
532.3
470.9
43.8
17.6
+
0.1
0.1
2.3
2.3
7.0
7.0
541.7
+ Does not exceed 0.05 MMTCE
Note: Totals may not sum due to independent rounding.
Methodology and Data Sources
Emissions of greenhouse gases from various
sources have been estimated using methodologies that
are consistent with the Revised 1996IPCC Guidelines
for National Greenhouse Gas Inventories (IPCC/UNEP/
OECD/IEA 1997), except were noted otherwise. To the
extent possible, the present U.S. inventory relies on pub-
lished 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/actors are factors
that relate quantities of emissions to an activity. For some
sources, IPCC default methodologies and emission fac-
tors have been employed. However, for emission sources
considered to be major sources in the United States, the
IPCC default methodologies were expanded and more
comprehensive methods were applied.
Inventory emission estimates from energy consump-
tion and production activities are based primarily on the
latest official fuel consumption data from the Energy Infor-
mation Administration of the Department of Energy (EIA).
Emission estimates for NOx, CO, and NMVOCs were taken
directly, except where noted, from the United States Envi-
ronmental Protection Agency's (EPA) report, National Air
Pollutant Emission Trends 1900 -1997 (EPA 1998), which
is an annual EPA publication that provides the latest esti-
mates of regional and national emissions for ozone precur-
sors (i.e., criteria 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
criteria pollutants are conceptually similar to the IPCC rec-
ommended methodologies, the large number of sources EPA
used in developing its estimates makes it difficult to repro-
duce the methodologies from EPA (1997) in this inventory
document. In these instances, the sources containing de-
tailed documentation of the methods used are referenced
for the interested reader. For agricultural sources, the EPA
criteria pollutant emission estimates were supplemented
using available 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.
Carbon dioxide emissions from fuel combusted in
ships or aircraft engaged in the international transport of
passengers or cargo are not included in U.S. totals, but
are reported separately as international bunkers in ac-
cordance with IPCC reporting guidelines (IPCC/UNEP/
OECD/IEA 1997). Carbon dioxide emissions from fuel
combusted within U.S. territories, however, are included
in U.S. totals.
Uncertainty in and Limitations of
Emission Estimates
While the current U.S. emissions inventory pro-
vides a solid foundation for the development of a more
detailed and comprehensive national inventory, it has
several strengths and weaknesses.
Introduction 1-15
-------
First, this inventory by itself does not provide a
complete picture of past or future emissions in the United
States; it only provides an inventory of U.S. emissions
Tor the years 1990 through 1997. However, the United
States believes that common and consistent inventories
taken over a period of time can and will contribute to
understanding future emission trends. The United States
produced its first comprehensive inventory of greenhouse
gas emissions and sinks in 1993, and intends to update
this inventory annually in conjunction with its commit-
ments under the UNFCCC. The methodologies used to
estimate emissions will be periodically updated as meth-
ods and information improve, and as further guidance is
received from the IPCC.
Secondly, there are uncertainties associated with
the emissions estimates. Some of the current estimates,
such as those for C02 emissions from energy-related ac-
tivities and cement processing, are considered to be fairly
accurate. For other categories of emissions, however, a
lack of data or an incomplete understanding of how emis-
sions are generated limit the scope or accuracy of the
estimates presented. Despite these uncertainties, the Re-
vised 1996 IPCC Guidelines for National Greenhouse
Gas Inventories (IPCC/UNEP/OECD/IEA1997) require
that countries provide single point estimates for each gas
and emission or removal source category. Within the dis-
cussion of each emission source, specific factors affect-
ing the accuracy of the estimates are discussed.
Finally, while the IPCC methodologies provided
in the Revised 1996 IPCC Guidelines represent baseline
methodologies for a variety of source categories, many
of these methodologies continue to be improved and re-
fined as new research and data becomes available. The
current U.S. inventory uses the IPCC methodologies
when applicable, and supplements them with other avail-
able 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. Quanti-
tative estimates of some of the sources and sinks of green-
house gas emissions are not available at this time. In par-
ticular, emissions from some land-use activities and in-
dustrial processes are not included in the inventory ei-
ther because data are incomplete or because methodolo-
gies do not exist for estimating emissions from these
source categories. See Annex P for a discussion of the
sources of greenhouse gas emissions excluded from this
report.
Improving the accuracy of emission factors. Fur-
ther 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 methane and nitrous
oxide emissions from stationary and mobile source fos-
sil fuel combustion are highly uncertain.
Collecting detailed activity data. Although meth-
odologies exist for estimating emissions for some sources,
problems arise in obtaining activity data at a level of de-
tail in which aggregate emission factors can be applied.
For example, the ability to estimate emissions of meth-
ane and nitrous oxide from jet aircraft is limited due to a
lack of activity data by aircraft type and number of land-
ing and take-off cycles.
Applying Global Warming Potentials. GWP values
have several limitations including that they are not ap-
plicable to unevenly distributed gases and aerosols such
as tropospheric ozone and its precursors. They are also
intended to reflect global averages and, therefore, do not
account for regional effects. Overall, the main uncertain-
ties in developing GWP values are the estimation of at-
mospheric lifetimes, assessing indirect effects, choosing
the appropriate integration time horizon, and assessing
instantaneous radiative forcing effect which is dependent
upon existing atmospheric concentrations. According to
the IPCC, GWPs typically have an uncertainty of ±35
percent (IPCC 1996). Additional discussion on the un-
certainties related to the use of GWP weighting values
can be found in Annex J.
Emissions calculated for the U.S. inventory reflect
current best estimates; in some cases; however, estimates
are based on approximate methodologies, assumptions,
and incomplete data. As new information becomes avail-
able in the future, the United States will continue to im-
prove and revise its emission estimates.
1-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Organization of Report
In accordance with the IPCC guidelines for report-
ing contained in the Revised 1996 IPCC Guidelines for
National Greenhouse Gas Inventories (IPCC/UNEP/
OECD/IEA 1997), this U.S. inventory of greenhouse gas
emissions is segregated into six sector-specific chapters,
listed below in Table 1-9.
Within each chapter, emissions are identified by
the anthropogenic activity that is the source of the green-
house gas emissions being estimated (e.g., coal mining).
Overall, the following organizational structure is consis-
tently applied throughout this report:
Chapter/IPCC Sector: Overview of emis-
sion trends for each IPCC defined sector
Table 1-9: IPCC Sector Descriptions
Source: Description of source pathway and emis-
sion trends from 1990 through 1997
— Methodology: Description of analytical meth-
ods employed to produce emission estimates
— Data Sources: Identification of primary
data references, primarily for activity data and
emission factors
— Uncertainty: Discussion of relevant issues
related to the uncertainty in the emission es-
timates presented
Special attention is given to carbon dioxide from
fossil fuel combustion relative to other sources because
of its share of emissions relative to other sources. For
example, each energy consuming end-use is treated in-
dividually. Additional information for certain source cat-
egories and other topics is also provided in several An-
nexes listed in Table 1-10.
Chapter/IPCC Sector
Activities Included
Energy
Industrial Processes
Solvent Use
Agriculture
Land-Use Change and Forestry
Waste
Emissions of all greenhouse gases resulting from stationary and mobile energy activities
including fuel combustion and fugitive fuel emissions.
By-product or fugitive emissions of greenhouse gases from industrial processes not
directly related to energy activities such as fossil fuel combustion.
Emissions, of primarily non-methane volatile organic compounds (NMVOCs), resulting
from the use of solvents.
Anthropogenic emissions from agricultural activities except fuel combustion and sewage
emissions, which are addressed under Energy and Waste, respectively.
Emissions and removals from forest and land-use change activities, primarily carbon dioxide.
Emissions from waste management activities.
Source: (IPCC/UNEP/OECD/IEA 1997)
Table 1-10: List of Annexes
ANNEX A Methodology for Estimating Emissions of C02
from Fossil Fuel Combustion
ANNEX B Methodology for Estimating Emissions of
CH4, N20, and Criteria Pollutants from
Stationary Sources
ANNEX C Methodology for Estimating Emissions of
CH4, N20, and Criteria Pollutants from Mobile
Sources
ANNEX D Methodology for Estimating Methane
Emissions from Coal Mining
ANNEX E Methodology for Estimating Methane
Emissions from Natural Gas Systems
ANNEX F Methodology for Estimating Methane
Emissions from Petroleum Systems
ANNEX G Methodology for Estimating Methane
Emissions from Enteric Fermentation
ANNEX H Methodology for Estimating Methane Emissions
from Manure Management
ANNEX I Methodology for Estimating Methane Emissions
from Landfills
ANNEX J Global Warming Potential Values
ANNEX K Ozone Depleting Substance Emissions
ANNEX L Sulfur Dioxide Emissions
ANNEX M Complete List of Sources
ANNEX N IPCC Reporting Tables
ANNEX 0 IPCC Reference Approach for Estimating C02
Emissions from Fossil Fuel Combustion
ANNEX P Sources of Greenhouse Gas Emissions Excluded
ANNEX Q Constants, Units, and Conversions
ANNEX R Abbreviations
ANNEX S Chemical Symbols
ANNEX! Glossary
Introduction 1-17
-------
-------
2. Energy
E:
Figure 2-1
Fossil Fuel Combustion
Natural Gas Systems
Coal Mining
Mobile Sources
Stationary Sources |
Natural Gas Flaring |
Petroleum Systems |
1,466
'nergy-related activities were the primary source of U.S. anthropogenic greenhouse gas emissions, accounting for 85
ipercent of total emissions annually on a carbon equivalent basis in 1997. This included 99, 32, and 20 percent of the
nation's carbon dioxide (CO^, methane (CH^, 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 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 2-1). Due to the relative importance of fossil fuel combustion-related CO2 emissions, they
are considered separately from other emissions. Fossil fuel combustion also emits CH4 and N2O, as well as criteria
pollutants such as nitrogen oxides (NOX), carbon monoxide (CO), and non-methane volatile organic compounds (NMVOCs).
Fossil fuel combustion—from stationary and mobile sources—-was the second largest source N2O emissions in the United
States, and overall energy-related activities are the largest
sources of criteria 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 emis-
sions consist primarily of 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 emis-
sions totals in the Energy chapter because biomass fuels are
of biogenic origin. It is assumed that the carbon released
when biomass is consumed is recycled as U.S. forests and
crops regenerate, causing no net addition of CO2 to be added 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.
Overall, emissions from energy-related activities have increased from 1990 to 1997 due, in part, to the strong perfor-
mance of the U.S. economy. Over this period, the U.S. Gross Domestic Product (GDP) grew approximately 18 percent, or at
an average annual rate of 2.5 percent. This robust economic activity increased the demand for fossil fuels, with an associated
increase in greenhouse gas emissions. Table 2-1 summarizes emissions for the Energy chapter in units of million metric tons
of carbon equivalents (MMTCE), while unweighted gas emissions in teragrams (Tg) are provided in Table 2-2. Overall,
emissions due to energy-related activities were 1,549.2 MMTCE in 1997, an increase of 10 percent since 1990.
Portion of All
Emissions
20
40
MMTCE
60
Energy 2-1
-------
Table 2-1: Emissions from Energy (MMTCE)
Gas/Source
1990 1991 1992 1993 1994
1995
1996 1997
co2 ' ' '
Fossil Fuel Combustion
Natural Gas Flaring
International Bunker Fuels*
Biomass-Ethanol*
Biomass-Wood*
Non-Energy Use Carbon Stored*
CH4
Stationary Sources
Mobile Sources
Coal Mining
Natural Gas Systems
Petroleum Systems
International Bunker Fuels*
N20
Stationary Sources
Mobile Sources
International Bunker Fuels*
Total
1,329.4
1,327.2
2.3
27.1
1.6
55.6
(68.9)
62.2
2.3
1.4
24.0
32.9
1.6
+
17.4
3.8
13.6
0.2
1,409.0
1,315.2
1,312.6
2.6
27.8
1.2
56.2
(68.5)
61.4
2.4
1.4
22.8
33.3
1.6
+
18.0
3.8
14.2
0.2
1,394.6
1,334.9
1,332.4
2.6
29.0
1.5
59.0
(70.3)
61.3
2.4
1.4
22.0
33.9
1.6
+
19.0
3.9
15.2
0.2
1,415.2
1,364.1
1,3,60.6
3.5
29.9
1.7
58.8
(73.2)
58.6
2.4
1.4
19.2
34.1
1.6
+
19.9
3.9
15.9
0.3
1,442.6
"l,387.5
1.383,8,.
3.6
27.4
1.8
59.7
(78.1)
58.2
2.4
1.4
19.4
33.5
1.6
-1-
20.7
4,0
16.7
0.2
1,466,3
I
1,402.2 1
U97,8, 1
4.5;
25.4 1
2.0,
59.7
(79.1)
58.9
2.5
1.4:
20.3;
33.2
1.6;
+
20.9
4.0,;
17.0;
0.2
1,482.1 , 1
,452.0
,447.7
4.3
25.4
1.4
62.4
(80.7)
58.1
2.5
1.4
18.9
33.7
1.5
+
21.6
4.1
17.4
0.2
,531.6
1,470.1
1,466.0
4.2
26.6
1.8
57.2
(83.6)
57.4
2.2
1.4
18.8
33.5
1.6
+
21.7
4.1
17.5
0.2
1,549.2
* These values are presented for informational purposes only and are not included or are already accounted for in totals. I
Note: totals may not sum due fci independent rounding.
Table 2-2: Emissions from Energy (Tg)
„ Gas^Source
1990 1991 1992 1993 1994 1995 1996 1997
C02 4,874.6
Fossl Fuel Combustion 4,866.2
Natural Gas Flaring
BjQfiass-Ettjanot*
Biomass-Wood*
InteirjaJioM, Bunker fuels*
Non-Energy Use Carbon Stored*
CH4
Stationary Sources
Mobile Sources
Coal Mining
Natural Gas Systems
Petroleum Systems
International Bunker Fuels*
N20
Stationary Sources
Mobie Sources
Jnteirjatifina! Bunker Fuels*
+ Doqs not exceed 0,05 Tg
8.4
5.7
203.8
99.3
(252.7)
10.9
0.4
0.3
4.2
5.7
0.3
4,822.4
4,812.8
9.6
4.5
205.9
101.9
(251.2)
10.7
0.4
0.2
4.0
5.8
0.3
4,894.8
4,885.4
9.4
5.5
216.5
106.4
(257.8)
10.7
0.4
0.2
3.8
5.9
0.3
5,001.7 5,087.5 5,141.6
4,988.7 5,074.4 5,125.1
13.0 13.1 16.4
6.1 6.7 7.2
215.4 219.0 219.1
109.6 100.4 93.3
5,324.0 5,390.4
5,308.3 5,375,2
15.7 15.2
5.1 6.7
228.8 209.8
93.0 97.5
(268.5) (286.5) (289.9)' (295.9) (306.6)
10.2 10.2 10.3
0.4 0.4 0.4
0.2 0.2 0.2
3.4 3.4 3.6
10.1 10.0
0.4 0.4
0.2 0.2
3.3 3.3
5.9 5J 5J,, 5,9 '.::"5.8
0.3 0.3 0.3 0.3 0.3
„ +. , , + + ,„+,,, + + ; + +
0.2
+
0.2
+
0.2
+
0.2
+
0.2
4.
0.2
-t-
0.2 0,2 0.2
+ + +
0.2 0.2 0.2
+ ± +
0.3 0.3
0.2 0.2
+ +
* These values are presented for informational purposes only and are not included or are already accounted for in totals. l[
Mote: Totals may not sum due to independent rounding
:. • • . . . • •
2-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Carbon Dioxide Emissions
from Fossil Fuel Combustion
In 1997, the majority of energy consumed in the
United States, 85 percent, was produced through the com-
bustion of fossil fuels such as coal, natural gas, and petro-
leum (see Figure 2-2 and Figure 2-3). Of the remaining, 7
percent was supplied by nuclear electric power and 8 per-
cent by renewable energy technologies (EIA 1998a).
As fossil fuels are combusted, the carbon stored in
the fuels is emitted as CO2 and smaller amounts of other
gases, including methane (CH4), carbon monoxide (CO),
and non-methane volatile organic compounds (NMVOCs).
These other gases are emitted as a by-product of incom-
plete fuel combustion. The amount of carbon in fuels var-
ies significantly by fuel type. For example, coal contains
Figure 2-2
Nuclear-7.1%
| Renewable - 7.6%
|
I Coal - 22.8%
Natural Gas - 24%
Petroleum - 38.6%
Figure 2-3
1990 1991 1992 1993 1994 1995 1996 1997
the highest amount of carbon per unit of useful energy.
Petroleum has roughly 75 percent of the carbon per unit of
energy as coal, and natural gas has only about 55 percent.1
Petroleum supplied the largest share of U.S. energy de-
mands, accounting for an average of 39 percent of total
energy consumption over the period of 1990 through 1997.
Natural gas and coal followed in order of importance, ac-
counting for an average of 24 and 22 percent of total con-
sumption, respectively. Most petroleum was consumed in
the transportation sector, while the vast majority of coal
was used by electric utilities, with natural gas consumed
largely in the industrial and residential sectors (see Figure
2-4)(EIA1998a).
Emissions of CO2 from fossil fuel combustion in-
creased at an average annual rate of 1.4 percent from
1990 to 1997. The major factor behind this trend was a
robust domestic economy, combined with relatively low
energy prices. For example, petroleum prices have
changed little in real terms since the 1970s, with coal
prices actually having declined by more than 60 percent
in real terms compared to the 1975 price (EIA 1998a)
(see Figure 2-5). After 1990, when CO2 emissions from
fossil fuel combustion were 1,327.2 MMTCE (4,866.2
Tg), there was a slight decline of emissions in 1991 due
to a national economic downturn, followed by an in-
crease to 1,466.0 MMTCE (5,375.2 Tg) in 1997 (see
Figure 2-5: Fossil Fuel Production Prices and Table 2-3
and Table 2-4). Overall, CO2 emissions from fossil fuel
combustion increased by 10.5 percent over the eight year
period and rose by 1.3 percent hi the final year.
Figure 2-4
500
Based on national aggregate carbon content of all coal, natural gas, and petroleum fuels combusted in the United States.
Energy 2-3
-------
Figure 2-5
Fossil Fpe Prodiltioii Prices
-Crude Oil
- Natural Gas
Bituminous Coal,
— Subbituminous
Coal, and Lignite
Anthracite Coal
1975 1978 1981 1984 1987 1990 1993 1996
Table 2-3: C02 Emissions from Fossil Fuel Combustion by Fuel Type and Sector (MMTCE)
Fuel/Sector
1990 1991 1992 1993 1994 1995 1996 1997
Coal
VResierlaf
Commercial
Industrial
Transportation
Electric Utilities
U,S, Territories
I ' iiiiiiim ii,iK I'ln MI Km jd iiHiihi'jiiiiiiiimri ii.onijiiniij, • .ii,,» iu i
Natural Gas
Residential
Commercial
Industrial
Transportation
Eteclric Utilities
U.S. Territories
Petroleum
Residential
Commercial
Industrial
^Jransjiprtatton
-•""Becic'OIIes "' ' ""
U.S. Territories
Geothermal*
Tola?
481.6
1.6
2.4
68.5
+
409.0
0.2
273™5
65.1
38.8
118.6
9.8
41.2
.
572.0
23^
18,0,
100.0
394.5
26.6
8.9
0.1
1,327.2
475.9
1.4
2.2
64.8
+
407.2
tu..,.
278.4
67.5
40.4
120.5
8.9
41.1
.
558.3
m,
17:1
94.3
,.,W&
25.1
10.4
0.1
1,312.6
478.3
1.5
2.2
62.6
+
411.8
0.2
286.5
69.4
41.5
126.1
8.8
40.7
_
567.5
2i8,,
16.1
104.3
392.9
19.9
9.5
0.1
1,332.4
494.7
1.5
2.2
62.2
+
428.7
0,2,,
297.0
73.4
43.1
131.7
9.3
39.5
_
568.8
26,2
14.9
98.0
3J6J
22.5
10.3
0.1
1,360.6
496.7
1.4
2.1
62.7
+
430,2
0,3,,,,
301.9
71, ,8
42,9
133.1
10.2
44.0
_
585.2
25,3
14,9
102.0
41,1 2
20.6
11.1
0.0
1,383.9
I
498.8
1.4
2.1 '
62.1 „
+ i
433.0
0,3,,
314.5
.71,7...
44.8 •
140.41
10.4
47.2 ,
_
584.4
,„ , 25J
15.0
98.2 ;
... 419,1,,;,
14.0 ;
11,8
0.0
1,397.8
— • : ^ !i-
521.1
1.4
2,1
59.9
+
457.5
0.3
319.3
... ,77.5
46.7
144.3
10.6
40.3
607.2
27.2
14.6
103,9
,,,,434.1,
15.4
12.0
0.0
1,447.7
533.3
1.4
, 2.1
58.5
+
470.9
0.3
319.4
74.1
48.6
142^5
10.5
43.8
613.3
27.7
14,4
...106,0
,,435.3
17.6
12.4
0.0
1,466.0
- Not applicable
* Does not exceed 0.05 MMTCE .,'. ,^"'..". '. „"!' ','",' j
* MU^ouph not technically a fossil fuel, geothermal energy-related C02 emissions are included for reporting purposes.
Mote1 Totals may not sum due to independent rounding.
2-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-4: C09 Emissions from Fossil Fuel Combustion by Fuel Type and Sector (Tg)
Fuel/Sector
1990 1991 1992 1993 1994 1995 1996 1997
Coal
Residential
Commercial
Industrial
Transportation
Electric Utilities
U.S. Territories
Natural Gas
Residential
Commercial
Industrial
Transportation
Electric Utilities
U.S. Territories
Petroleum
Residential
Commercial
Industrial
Transportation
Electric Utilities
U.S. Territories
Geothermal*
Total
1,765.9
5.8
8.7
251.0
+
1,499.7
0.6
1,002.9
238.5
142.4
434.9
36.0
151.1
-
2,097.2
87.7
66.1
366.6
1,446.4
97.6
32.7
0.2
4,866.2
1,744.
5.
8.
8
3
0
237.6
-f
1,493.
2
0.7
1,020.8
247.3
148.2
441.8
32.8
150.6
-
2,047.0
89
62
345
1,419
91
38
0
4,812
.4
.6
.7
.2
.9
.2
.2
.8
1,753.8
5.4
8.1
229.5
+
1,510.0
0.8
1,050.5
254.5
152.3
462.3
32.1
149.3
-
2,080.9
90.9
59.1
382.3
1,440.7
73.1
34.8
0.2
4,885.4
1,814.
5.
8.
0
3
1
228.0
H
1,571.7
0.9
1,088.8
269.1
158.2
482.8
33.9
144
-
2,085
96
54
359
1,455
82
37
0
4,988
.9
.6
.1
.7
.5
.2
.5
.7
.2
.7
1,821.3
5.2
7.9
229.9
+
1,577.4
0.9
1,107.1
263.3
157.4
488.0
37.2
161.2
-
2,145.8
92.8
54.7
374.2
1,507.9
75.6
40.6
0.2
5,074.4
1,828.9
5.1
7.6
227.7
+
1,587.5
0.9
1,153.3
263.0
164.3
514.9
38.1
173.0
-
2,142.8
94.4
54.9
360.1
1,538.9
51.3
43.2
0.1
5,125.1
1,910.9
5.2
7.8
219.5
+
1,677.4
1.0
1,170.8
284.2
171.2
529.0
38.7
147.7
-
2,226.4
99.7
53.6
381.1
1,591.8
56.5
43.9
0.1
5,308.3
1,955.3
5.2
7.8
214.6
4
1,726.7
1.0
1,171.1
271.6
178.1
522
38
.3
.6
160.5
-
2,248
101
52
388
1,595
64
45
0
5,375
.6
.5
.7
.5
.9
.6
.3
.1
.2
- Not applicable
+ Does not exceed 0.05 Tg
* Although not technically a fossil fuel, geothermal energy-related C02 emissions are included for reporting purposes.
Note: Totals may not sum due to independent rounding.
Since 1990, consumption of all fossil fuels in-
creased, with about 37 percent of the change in CO2
emissions from fossil fuel combustion coming from coal,
33 percent from natural gas, and 30 percent from petro-
leum. From 1996 to 1997, absolute emissions from coal
grew the most (an increase of 12.1 MMTCE or 2.3 per-
cent), while emissions from natural gas changed the least
(an increase of 0.1 MMTCE or less than 0.1 percent).
During the same time period, emissions from electric
utility petroleum and natural gas combustion increased
the most on a percentage basis by 14.4 and 8.7 percent,
respectively. See Box 2-1 for additional discussion on
overall emission trends.
In 1997, combustion of fossil fuels by electric utili-
ties increased, in part, to offset the temporary shutdown of
£
several nuclear power plants and two plant closings. As a
result, in 1997 the U.S. coal industry produced the largest
amount of coal ever and electric utilities consumed record
quantities. Electric utilities increased consumption by 2.8
percent from 1996 levels. The aggregate consumption of
coal hi sectors other than electric utilities actually declined
by 2.6 percent (EIA 1998f) during this period. The net in-
crease in coal consumption by all sectors was responsible
for 66 percent of the total increase in CO2 emissions from
fossil fuel combustion.
Continued low prices encouraged the consump-
tion of petroleum products in 1997, which increased by
1.3 percent from the previous year. This rise in petro-
leum use accounted for 33 percent of the increase in
CO2 emissions from fossil fuel combustion.
From 1996 to 1997, emissions from natural gas
held steady. Consumption decreases in the industrial and
residential sectors offset increases in the commercial and
electric utility sectors.
Fossil fuels also have applications other than com-
bustion for energy. For example, some petroleum prod-
ucts can be used for manufacturing plastics, asphalt, or
lubricants. A portion of the carbon consumed for these
non-energy uses is sequestered for long periods of time.
In addition, as required by the IPCC (IPCC/UNEP/
OECD/IEA1997) CO2 emissions from the consumption
of fossil fuels for aviation and marine international trans-
Energy 2-5
-------
port activities (i.e., bunker fuels) are reported separately,
and not included in national emission totals. Both esti-
mates for non-energy use carbon stored and international
bunker fuel emissions for the United States are provided
in Table 2-5 and Table 2-6.
End-Use Sector Contributions
When analyzing CO2 emissions from fossil fuel com-
bustion, four end-use sectors can be identified: industrial,
transportation, residential, and commercial. Electric utili-
ties also emit C02; however, these emissions occur as they
combust fossil fuels to provide electricity to one of the four
end-use sectors. For the discussion below, electric utility
emissions have been distributed to each end-use sector
based upon their share of national electricity consumption.
Emissions from electric utilities are addressed separately
after the end-use sectors have been discussed. Emissions
from U.S. territories are also calculated separately due to a
lack of end-use-specific consumption data. Table 2-7 and
Figure 2-6 summarize CO2 emissions from fossil fuel com-
bustion by end-use sector.
Industrial End-Use Sector
The industrial end-use sector accounted for ap-
proximately one-third of CO2 emissions from fossil fuel
combustion. On average, nearly 64 percent of these emis-
sions resulted from the direct consumption of fossil fu-
els in order to meet industrial demand for steam and
process heat. The remaining 36 percent resulted from
Figure 2-6
SOOi IB From Electricity
400
300
200
100
Table 2-5: Non-Energy Use Carbon Stored and C02 Emissions from
International Bunker Fuel Combustion (MMTCE)
Category/Sector
1990 1991 1992 1993 1994 1995 1996 1997
Non-Energy Use Carbon Stored
Industrial
Transportation
Territories
International Bunker Fuels*
Aviatjon/
Marine*
68.9
67.0
1.8
0.2
27.1
10.5
16.6
68.5
66.7
1.6
0.2
27.8
10.5
17.3
70.3
68.6
1.6
0.1
29.0
11.0
18.0
73.2
71.4
1.7
0.2
29.9
11.2
18.7
78.1
76,3
1.7
0.1
27.4
11.6
15,8
79.1
77.2
1.7 :
0.1 !
25,4
12.4
13.0
80.7
78.8
1.6
0.2
25.4
12.8
12.6
83.6
81.7
1.7
0.2
26.6
13.9
12.7
Exeitfes military Internatiofial bunkers fuels. See international Bunker Fuels for additional detail.
Note; Totals may not sum due to independent rounding.
Table 2-6: Non-Energy Use Carbon Stored and C02 Emissions from
International Bunker Fuel Combustion (Tg)
Category/Sector
1990 1991 1992 1993 1994 1995 1996 1997
Non-Energy Use Carbon Stored
Industrial
Transportation
Territories
International Bunker Fuels*
:Aylajlpn*
Marine*'
252.7
245.6
6.5
0.6
99.3
38.4
60.8
251.2
244.5
5.8
0.9 ..
101.9
38.4
63.5
257.8
251.4
6.0
0.4
106.4
40.4
66.0
268.5
261.8
6.1
0.6
109.6
41.1
68.5
286.5
279.6
6.3
0.5
100.4
42,5
57.9
289.9
283.2 ,
6.2
0.5 :
93.3
45.5
47.8
295.9
289.0
6.0
0.8
93.0
47.0
46.0
306.6
299.4
6.4
0.9
97.5
51.0
46.6
* Excludes military international bunkers fuels. See International Bunker Fuels for additional detail.
tec Totals may not sum due to independent rounding.
2-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-7: C02 Emissions from Fossil Fuel Combustion by End-Use Sector (MMTCE)*
End-Use Sector
1990
1991 1992
1993
1994 1995 1996 1997
Residential
Commercial
Industrial
Transportation
U.S. Territories
Total
253.0
206.8
453.3
405.0
9.1
1,327.2
257.1
206.4
441.8
396.7
10.6
1,312.6
255.7
205.3
459.3
402.4
9.7
1,332.4
271.6
212.1
459.5
406.8
10.5
1,360.6
268.6
214.1
467.8
422.1
11.3
1,383.9
269.8
218.4
466.8
430.7
12.0
1,397.8
285.4
225.9
478.8
445.3
12.2
1,447.7
286.1
237.1
483.7
446.5
12.6
1,466.0
* Emissions from fossil fuel combustion by electric utilities are allocated based on electricity consumption by each end-use sector.
Note: Totals may not sum due to independent rounding.
the consumption of electricity for uses such as motors,
electric furnaces, ovens, and lighting. Although indus-
try accounted for the largest share of end-use sector emis-
sions, from 1990 to 1997 its emissions grew the least in
percentage terms (7 percent). During the same period,
coal consumption by industry declined by 15 percent,
while natural gas and petroleum consumption increased
by 20 and 6 percent, respectively.
The industrial end-use sector was also the largest
user of fossil fuels for non-energy applications. Fossil
fuels can be used for producing products such as fertil-
izers, plastics, asphalt, or lubricants, that 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 manufac-
ture of materials like plastics can also store carbon, if
the material is not burned. Carbon stored by industrial
non-energy uses of fossil fuels rose 22 percent between
1990 and 1997, to 81.7 MMTCE (306.6 Tg CO2).
Transportation End-Use Sector
Transportation was second to the industrial end-
use sector in terms of U.S. CO2 emissions from fossil
fuel combustion emissions, accounting for slightly over
30 percent—excluding international bunker fuels. Al-
most all of the energy consumed in this end-use sector
came from petroleum-based products, with nearly two-
thirds due to gasoline consumption in automobiles and
other highway vehicles. Other uses, including diesel fuel
for the trucking industry and jet fuel for aircraft, ac-
counted for the remainder.
Following the overall trend in U.S. energy con-
sumption, fossil fuel combustion for transportation grew
steadily after declining in 1991, resulting in a 10 per-
cent increase in CO2 emissions to 446.5 MMTCE
(1,637.1 Tg) in 1997. This increase was primarily the
result of greater motor gasoline, distillate fuel oil (e.g.,
diesel), and jet fuel consumption. It was slightly offset
by decreases in the consumption of aviation gasoline,
LPG, lubricants, and residual fuel. Overall, motor ve-
hicle fuel efficiency stabilized in the 1990s after increas-
ing steadily since 1977 (EIA 1998a). This trend was due,
in part, to a decline in gasoline prices and new motor
vehicle sales being increasingly dominated by less fuel-
efficient light-duty trucks and sport-utility vehicles (see
Figure 2-7 and Figure 2-8). Moreover, declining petro-
leum prices during these years—with the exception of
1996—combined with a stronger economy, were largely
responsible for an overall increase in vehicle miles trav-
eled by on-road vehicles ().
Table 2-8 below provides a detailed breakdown of
CO2 emissions by fuel category and vehicle type for the
transportation end-use sector. On average 60 percent of
the emissions from this end-use sector were the result
Figure 2-7
1972 1975 1978 1981 1984 1987 1990 1993 1996
Energy 2-7
-------
Figure 2-8
Motor Vehicle Fuel Efficiency
All Motor Vehicles
1975 1978 1981 1984 1987 1990 1993 1996
of the combustion of motor gasoline in passenger cars
and light-duty trucks. Diesel highway vehicles and jet
aircraft were also significant contributors, each account-
ing for, on average, 13 percent of CO2 emissions from
the transportation end-use sector. It should be noted that
the U.S. Department of Transportation's Federal High-
way Administration altered its definition of light-duty
trucks in 1995 to include sport-utility vehicles and
minivans; previously these vehicles were included un-
der the passenger cars category. As a consequence of
this reclassification, a discontinuity exists in the time
series in Table 2-8 for both passenger cars and light-
duty trucks.2 In future editions of this report a consis-
tent classification scheme across the entire time series
will be applied by incorporating adjustments in the al-
location of fuel consumption for the period 1990 to 1995
to eliminate this discontinuity.
The annual increase in CO2 emissions from motor
gasoline in 1997 is based on fuel sales data from the
U.S. Energy Information Administration; it is expected
to be revised upward with the publication of future en-
ergy statistics. Carbon stored in lubricants used for trans-
portation activities were 1.7 MMTCE (6.4 Tg) in 1997.
Residential and Commercial End-Use Sectors
From 1990 to 1997, the residential and commercial
end-use sectors, on average, accounted for 19 and 16 per-
cent, respectively, of CO2 emissions from fossil fuel com-
bustion. Both the residential and commercial end-use sec-
tors were heavily reliant on electricity for meeting energy
needs, with about two-thirds of their emissions attribut-
able to electricity consumption for lighting, heating, cool-
ing, and operating appliances. The remaining emissions
were largely due to the direct consumption of natural gas
and petroleum products, primarily for heating and cooking
needs. Unlike in other major end-use sectors, emissions
from residences did not decline in 1991, but instead de-
creased in 1992 and 1994, then grew steadily through 1997
(see Figure 2-9). This difference in overall trends compared
to other end-use sectors is because energy consumption in
residences is affected proportionately more by the weather
than by prevailing economic conditions. The commercial
end-use sector, however, is primarily dependent on elec-
tricity for lighting and is affected more by the number of
commercial consumers. Coal consumption was a small
component of energy use in both the residential and com-
mercial sectors.
Figure 2-9
o"
o
v-
II
To
o
1
_c
120
110-
100
90(
80
1!
Heating Degree Days3
Normal
(4,576 Heating Degree Days)
• • •
• • »
>
)90 1991 1992 1993 1994 1995 1996 1997
I
Electric Utilities
The United States relied on electricity to meet a
significant portion of its energy requirements. Electric-
ity was consumed primarily in the residential, commer-
cial, and industrial end-use sectors for uses such as light-
ing, heating, electric motors, and air conditioning (see
Figure 2-10). To generate this electricity, utilities con-
sumed 28 percent of national fossil fuels on an energy
content basis and were collectively the largest produc-
ers of CO2 emissions from fossil fuel combustion, ac-
counting for 36 percent in 1997. Electric utilities were
responsible for a larger share of these CO2 emissions
See Box 1 -2 in the Introduction chapter for a discussion on emissions of all greenhouse gases from transportation related activities.
Degree days arc relative measurements of outdoor air temperature. Heating degree days are deviations of the mean daily temperature below 65°
R Excludes Alaska and Hawaii. Normals are based on data from 1961 through 1990.
2-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-8: C02 Emissions from Fossil Fuel Combustion in Transportation End-Use Sector (MMTCE)
Fuel/Vehicle Type
1990
1991 1992
1993
1994 1995 1996 1997
Motor Gasoline
Passenger Cars*
Light-Duty Trucks*
Other Trucks
Motorcycles
Buses
Construction Equipment
Agricultural Machinery
Boats (Recreational)
Distillate Fuel Oil (Diesel)
Passenger Cars*
Light-Duty Trucks*
Other Trucks
Buses
Construction Equipment
Agricultural Machinery
Boats (Freight)
Locomotives
Marine Bunkers
Jet Fuel
General Aviation
Commercial Air Carriers
Military Vehicles
Aviation Bunkers
Aviation Gasoline
General Aviation
Residual Fuel Oil
Boats (Freight)
Marine Bunkers
Natural Gas
Passenger Cars*
Light-Duty Trucks*
Buses
Pipeline
I.PG
Light-Duty Trucks*
Other Trucks
Buses
Electricity
Buses
Locomotives
Pipeline
Lubricants
Total (including bunkers)
260.9
167.3
74.9
11.3
0.4
0.6
0.6
1.2
4.6
75.7
2.0
2.5
45.8
2.2
2.9
6.5
5.0
7.3
1.4
60.1
1.7
32.0
16.0
10.5
0.8
0.8
21.9
6.8
15.2
9.8
+
+
+
9.8
0.4
0.1
0.2
+
0.7
+
0.1
0.6
1.8
432.1
259.5
165.9
74.7
11.2
0.4
0.6
0.6
1.2
4.8
72.6
1.9
2.4
43.7
2.2
2.9
6.3
4.8
6.8
1.6
58.1
1.5
29.6
16.5
10.5
0.8
0.8
22.0
6.3
15.7
8.9
+
+
+
8.9
0.3
0.1
0.2
+
0.7
+
0.1
0.5
1.6
424.5
263.4
170.0
74.6
11.2
0.4
0.6
0.6
1.2
4.7
75.3
2.0
2.5
45.2
2.3
2.9
6.4
5.1
7.3
1.6
57.6
1.3
30.5
14.8
11.0
0.8
0.8
23.0
6.7
16.4
8.8
+
+
+
8.8
0.3
0.1
0.2
+
0.7
+
0.1
0.5
1.6
431.4
269.3
171.5
77.8
11.7
0.5
0.7
0.6
2.0
4.6
77.3
2.1
2.6
48.0
2.3
2.9
6.4
4.7
6.6
1.6
58.1
1.3
30.9
14.6
11.2
0.7
0.7
19.4
2.4
17.1
9.3
+
+
+
9.2
0.3
0.1
0.2
+
0.7
+
0.1
0.5
1.6
436.7
273.7
170.5
84.2
10.4
0.5
0.9
0.6
2.1
4.5
82.5
2.0
2.8
52.0
2.4
2.9
6.4
4.6
7.9
1.5
60.4
1.2
32.0
15.6
11.6
0.7
0.7
19.1
4.8
14.3
10.2
+
+
+
10.1
0.5
0.2
0.3
+
0.7
+
0.1
0.5
1.7
449.4
279.9
173.5
85.9
10.9
0.5
0.8
0.7
2.2
5.3
83.8
2.1
3.0
53.0
2.7
2.8
6.2
4.4
8.0
1.7
60.0
1.4
32.8
13.4
12.4
0.7
0.7
18.5
7.1
11.4
10.4
+
+
+
10.4
0.5
0.3
0.3
+
0.7
+
0.1
0.5
1.7
456.2
285.2
158.7
106.1
11.1
0.5
0.6
0.7
2.1
5.4
89.8
2.1
3.6
57.0
2.4
3.0
6.6
5.1
8.7
1.4
62.7
1.5
33.9
14.5
12.8
0.7
0.7
19.2
8.0
11.2
10.6
+
+
+
10.5
0.3
0.1
0.1
+
0.7
+
0.1
0.5
1.6
470.7
288.3
160.4
107.2
11.3
0.5
0.6
0.7
2.2
5.5
91.6
2.1
3.7
58.1
2.4
3.0
6.7
5.2
8.8
1.6
63.3
1.5
33.9
14.0
13.9
0.7
0.7
15.9
4.8
11.1
10.5
+
+
+
10.5
0.3
0.1
0.2
+
0.7
+
0.1
0.5
1.7
473.1
Note: Totals may not sum due to independent rounding. Estimates include emissions from the combustion of both aviation and marine
international bunker fuels in civilian vehicles only. Military international bunker fuels are not estimated separately.
+ Does not exceed 0.05 MMTCE
*ln 1996, the U.S. Federal Highway Administration modified the definition of light-duty trucks to include minivans and sport utility vehicles.
Previously, these vehicles were included under the passenger cars category. Hence the sharp drop in emissions for passenger cars from 1995
to 1996 occurred. This gap, however, was offset by an equivalent rise in emissions from light-duty trucks.
Energy 2-9
-------
Figure 2-10
1,100 - Residential
1,000
_,. 900
1 800 •
J 70° 1
S 600
500
400
300
1972 1975 1978 1981 1984 1987 1990 1993 1996
Industrial
mainly because they rely on more carbon intensive coal
for a majority of their primary energy. Some of the elec-
tricity consumed in the United States was generated us-
ing low or zero CO2 emitting technologies such as hy-
droelectric or nuclear energy; however, in 1997 the com-
bustion of coal was the source of 57 percent of the elec-
tricity consumed in the United States (EIA 1998b).
Electric utilities were the dominant consumer of
coal in the United States, accounting for 87 percent in
1997. Consequently, changes in electricity demand have
a significant impact on coal consumption and associ-
ated CO3 emissions. In fact, electric utilities consumed
record amounts of coal (922 million short tons) in 1997.
Overall, emissions from coal burned at electric utilities
increased by 15 percent from 1990 to 1997. This increase
!n coal-related emissions from electric utilities was alone
responsible for 45 percent of the overall rise in CO2 emis-
sions from fossil fuel combustion.
In addition to the increase in consumption of coal
by electric utilities, consumption of botii natural gas and
petroleum rose by 9 and 14 percent in 1997.respectively
(EIA 1998e). Electric utility natural gas use increased
significantly in 1994 and 1995, as prices and supply sta-
bilized following a series of cold winters and a period of
industry restructuring. However, in 1996 gas prices
paid by electric utilities increased by a dramatic 33 per-
cent (EIA 1997a), making gas-based electricity genera-
tion less economical. Consequently, natural gas con-
sumption by electric utilities declined by 15 percent in
1996. The rebound in 1997 regained half of the previous
year's decline. This increased gas consumption occurred
mostly in California, where hydroelectric and nuclear
generation each fell by 10 percent, and in New York,
where nuclear generation fell by 16 percent. Over the
1990 to 1997 period, emissions from natural gas burned
at electric utilities rose by 6 percent. Fuel oil was the
most expensive fossil fuel delivered to electric utilities
in 1997, 62 percent more costly than natural gas on an
energy content basis. Consequently, petroleum consti-
tuted a small portion of electric utility fossil fuel con-
sumption (4 percent in 1997) and occurred mostly in
the eastern United States.
In 1997, consumption of all fossil fuels for pro-
ducing electricity increased to accommodate the tem-
porary shut-down of several nuclear power plants across
the country and two plant closings. Total nuclear power
plants electricity generation fell off by 7 percent account-
ing for 1.5 percent of total national generation (45.3 bil-
lion kilowatt hours) (EIA 1998b).
2-10 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Box 2-1: Sectoral Carbon Intensity Trends Related to Fossil Fuel and Overall Energy Consumption
Fossil fuels are the predominant source of energy in the United States, and carbon dioxide (C02) is emitted as a product from their
complete combustion. Useful energy, however, can be generated from many other sources that do not emit C02 in the energy
conversion process.4 In the United States, useful energy is also produced from renewable (i.e., hydropower, biofuels, geothermal,
solar, and wind) and nuclear sources.
Energy-related C02 emissions can be reduced by not only reducing total energy consumption (e.g., through conservation mea-
sures) but also by lowering the carbon intensity of the energy sources employed (i.e., fuel switching from coal to natural gas). The
amount of carbon emitted—in the form of C02—from the combustion of fossil fuels is dependent upon the carbon content of the
fuel and the fraction of that carbon that is oxidized. Fossil fuels vary in their carbon content, ranging from 13.7 MMTCE/EJ for
natural gas to 26.4 MMTCE/EJ for coal and petroleum coke.5 In general, the carbon intensity of fossil fuels is the highest for coal
products, followed by petroleum and then natural gas. Other sources of energy, however, may be directly or indirectly carbon
neutral (i.e., 0 MMTCE/EJ). Energy generated from nuclear and many renewable sources do not result in direct emissions of C02.
Biofuels such as wood and ethanol are also considered to be carbon neutral, as the C02 emitted during combustion is assumed to
be offset by the carbon sequestered in the growth of new biomass.6 The overall carbon intensity of the U.S. economy is then
dependent upon the combination of fuels and other energy sources employed to meet demand.
Table 2-9 provides a time series of the carbon intensity for each sector of the U.S. economy. The time series incorporates only the
energy consumed from the direct combustion of fossil fuels in each sector. For example, the carbon intensity for the residential
sector does not include the energy from or emissions related to the consumption of electricity for lighting^ wood for heat. Looking
only at this direct consumption of fossil fuels, the residential sector exhibited the lowest carbon intensity, which was related to the
large percentage of energy derived from natural gas for heating. The carbon intensity of the commercial sector was greater than the
residential sector for the period from 1990 to 1996, but then declined to an equivalent level as commercial businesses shifted away
from petroleum to natural gas. The industrial sector was more dependent on petroleum and coal than either the residential or
commercial sectors, and thus had a higher carbon intensity over this period. The carbon intensity of the transportation sector was
closely related to the carbon content of petroleum products (e.g., motor gasoline and jet fuel), which were the primary sources of
energy. Lastly, the electric utility sector had the highest carbon intensity due to its heavy reliance on coal for generating electricity.
Table 2-9: Carbon Intensity from Direct Fossil Fuel Combustion by Sector (MMTCE/EJ)
Sector
1990 1991 1992 1993 1994 1995 1996 1997
Residential
Commercial"
Industrial3
Transportation
Electric Utilities"
All Sectors0
14.7
15.2
16.6
18.1
22.4
18.6
14.7
15.1
16.5
18.1
22.4
18.6
14.6
15.0
16.5
18.1
22.4
18.6
14.6
14.9
16.4
18.1
22.5
18.6
14.6
14.9
16.4
18.1
22.4
18.6
14.6
14.8
16.3
18.1
22.4
18.5
14.6
14.8
16.3
18.1
22.6
18.5
14.7
14.7
16.3
18.1
22.6
18.6
a Does not include electricity or renewable energy consumption.
b Does not include electricity produced using nuclear or renewable energy.
c Does not include nuclear or renewable energy consumption.
Note: Excludes non-energy fuel use emissions and consumption. Exajoule (EJ) = 1018 joules = 0.9479 QBtu.
4 CO2 emissions, however, may be generated from upstream activities (e.g., manufacture of the technologies).
5 One exajoule (EJ) is equal to 1018 joules or 0.9478 QBtu.
6 This statement assumes that there is no net loss of biomass-based carbon due to biofuel consumption.
Energy 2-11
-------
In contrast to Table 2-9, Table 2-10 presents carbon intensity values that incorporate energy consumed from all sources (i.e., fossil
fuels. renewaWes, anj, nuclear). In, add-on, the ..emissions related to the generation of ^electricity^have been , attributed to both
efecfSc utilities and'C sector in which that,,,,ejectiicity was eventually consumed/ This table, therefore, provides a more complete
picture of the actual carbon Intensity of each sector per unit of energy consumed. Both the residential and commercial sectors
obtain a large portion of their energy from electricity. The residential sector, however, also uses significant Quantities of biofuels
sucf] as wood, thereby lowering its carbon intensity. The industrial sector uses biofuels in even greater quantities than the residen-
tial sector. The carbon intensity of electric utilities differs greatly from the scenario in Table 2-9 where only the energy consumed
from the direct combustion of fossil fuels was included. This difference is due almost entirely to the inclusion ;of electricity genera-
tion from nuclear and hydropower sources, which do not emit carbon dioxide. Also in contrast with the previous scenario in Table
; 2-9 ftp transportation sector in Table 2-10 emerges as the most carbon intensive when all sources of energy are included, due to
Its almost complete reliance on petroleum products and relatively minor amount of biomass based fuels such as ethanol.
Table 2-10: Carbon Intensity from Energy Consumption by Sector (MMTCE/EJ)
Sector
1990 1991 1992 1993 1994 1995 1996
Resieria!1
Commercial"
Industrial*
transportation'
Electric Utilities6
,AJ| %ctorse, , , , ,,...,
14.5
15.2
14.8
18.0
15.3
15,8
14.3
15.0
14.6
18.1
15.0
15.6
14.4
15.1
14.6
18.1
15.2
15.7
14.5
15.2
14.6
18.0
15.3
15.7
145
15.1
.. 14,6,,,
18.0
15.2
15.7
14.2,;
148"
HA;.
18.0'
14.8
15.5
14.3
149
14.4
18.0
15.0
15.5
14.7
15 1
14.5
18.0
15.3
15.7
„* Iwlifeelectrtfily (frqm fosslfuel, nuclear, and renewable sources) and direct renewable,,energy consumption.'
s te!«teselec]rielty generation from nuclear and renewable sources.
_" ;piffjjewabje, ,ap?rgy consumption. , , ;
8s,nofi;-eii|{gy fuel, use emissions and cpnsumntipn. Assumed that residential consumed all qf the biofue|-b?se,d energy and 50
"'solar wie^y InlecqmbTriid EIA residential/commercial sector category Exajouie (EJ) ='id1' joules =" 0.9479 QBtu.
IIIT
................
, "Si!;'!''
.,!»!! ..... . Mi ...... HI
litiiliiiii:;
'il'UKillUI1
By comparing the values in Table 2-9 and Table 2-10, there
are a couple oFpbservationsJh'at^anbe.made. The usage
of renewable and nuclear energy sources have resulted in a
significantly lower carbon Intensity of the U.S. economy,
especially for the Industrial and electric utility sectors. How-
ever, over the eight year period of 1990 through 1997, the
Carbon intensity of U.S. fossil fuel consumption has been
fairly constant, and changes in the usage of renewable and
nuclear energy technologies have not altered this trend.
Figure 2-11 and Table 2-11 present the detailed C02 emis-
sion trends underlying the carbon Intensity differences and
changes described In Table 2-9. In Figure 2-11 changes in
bpth overall erid^use-r^Iated emissions and electjcjty-re-
laled ^missions for each year since 1990 are highlighted In
"feble 2-11 values are normalized in the year 1990 to one-.
hundred (100), thereby highlighting changes overtime.
Figure 2-11
Change in C02 Emissions from Fossil Fuel Combustion
60
45
30
15J
0
Dark shaded columns relate to changes in ^missions from electricity
consumption. Lightly shaded columns relate to changes in emissions from both
electricity and direct fossil fuel combustion.
Residentia
Transportation
In olher words, the emissions from the generation of electricity are intentionally double counted by attributing them both to utilities and the
sector in which electricity consumption occurred.
2-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-11: C02 Emissions from Fossil Fuel Combustion (Index 1990 = 100)
Sector/Fuel Type
1990 1991
1992
1993 1994 1995 1996 1997 % Of'97
Residential
Coal
Natural Gas
Petroleum
Commercial
Coal
Natural Gas
Petroleum
Industrial
Coal
Natural Gas
Petroleum
Transportation
Coal
Natural Gas
Petroleum
Electric Utility
Coal
Natural Gas
Petroleum
U.S. Territories
Coal
Natural Gas
Petroleum
All Sectors
100
100
100
100
100
100
100
100
100
100
100
100
100
-
100
100
100
100
100
100
100
100
-
100
100
103
91
104
102
101
91
104
95
97
95
102
94
98
-
91
98
99
100
100
94
117
110
-
117
99
106
92
107
104
101
93
107
89
102
91
106
104
99
-
89
100
99
101
99
75
107
126
-
106
100
112
92
113
110
102
92
111
83
102
91
111
98
100
-
94
101
103
105
96
84
116
137
-
115
103
109
90
110
106
101
90
110
83
104
92
112
102
104
-
103
104
104
105
107
77
125
146
-
124
104
109
87
110
108
104
87
115
83
105
91
118
98
106
-
106
106
104
106
115
53
132
148
-
132
105
117
89
119
114
107
89
120
81
107
87
122
104
110
-
108
110
108
112
98
58
135
152
-
134
109
114
89
114
116
110
89
125
80
107
85
120
106
110
-
107
110
112
115
106
66
139
152
-
139
110
7.0%
0.1%
5.1%
1.9%
4.4%
0.1%
3.3%
1.0%
20.9%
4.0%
9.7%
7.2%
30.4%
-
0.7%
29.7%
36.3%
32.1%
3.0%
1.2%
0.9%
0.0%
-
0.8%
100.0%
- Not applicable
Note: Totals may not sum due to independent rounding.
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. methodol-
ogy is presented in Annex A, and is characterized by the
following steps:
1. Determine fuel consumption by fuel type and
sector. By aggregating consumption data by sector (e.g.,
commercial, industrial, etc.), primary fuel type (e.g.,
coal, petroleum, gas), and secondary fuel category (e.g.,
motor gasoline, distillate fuel oil, etc.), estimates of to-
tal U.S. fossil fuel consumption for a particular year were
made.8 The United States does not include territories in
its national energy statistics; therefore, fuel consump-
tion data for territories was collected separately.
2. Determine the total carbon content of fuels con-
sumed. 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 maxi-
mum amount of carbon that could potentially be released
to the atmosphere if all of the carbon were converted to
CO2. The carbon content coefficients used by the United
States are presented in Annex A.
3. Subtract the amount of carbon stored in prod-
ucts. Non-fuel 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 ex-
ample, asphalt made from petroleum can sequester up
to 100 percent of the carbon for extended periods of time,
while other products, such as lubricants or plastics, lose
or emit some carbon when they are used and/or burned
as waste. Aggregate U.S. energy statistics include con-
sumption of fossil fuels for non-energy uses; therefore,
8 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 12.6 MMTCE of emissions in 1997.
Energy 2-13
-------
the portion of carbon sequestered through these uses was
subtracted from potential carbon emission estimates. The
amount of carbon sequestered or stored in non-energy
uses of fossil fuels was based on the best available data
on the end-uses and ultimate fate of the various energy
products. These non-energy uses occurred in the indus-
trial and transportation sectors and U.S. territories.
4. Adjust for carbon that does not oxidize during
combustion. Because combustion processes are not 100
percent efficient, some of the carbon contained in fuels
is not emitted to the atmosphere. Rather, it remains be-
hind as soot, ash, or other by-products of inefficient com-
bustion. The estimated amount of carbon not oxidized
due to inefficiencies during the combustion process was
assumed to be I percent for petroleum and coal and 0.5
percent for natural gas (see Annex A).
5. Subtract emissions from international bunker
fuels. According to the IPCC guidelines (IPCC/UNEP/
OECD/IEA 1997) emissions from international trans-
port activities, or bunker fuels, should not be included
in national totals. Because U.S. energy consumption sta-
tistics include these bunker fuels—distillate fuel oil, re-
sidual fuel oil, and jet fuel—as part of consumption by
the transportation sector, emissions from international
transport activities were calculated separately and sub-
tracted from emissions from die transportation sector.
The calculations for emissions from bunker fuels fol-
lows the same procedures used for emissions from con-
sumption of all fossil fuels (i.e., estimation of consump-
tion, determination of carbon content, and adjustment
for the fraction of carbon not oxidized.
6. Allocate transportation emissions by vehicle
type. Because the transportation end-use sector was the
largest direct consumer of fossil fuels in the United
Slates,9 a more detailed accounting of carbon dioxide
emissions is provided. Fuel consumption data by vehicle
type and transportation mode were used to allocate emis-
sions by fuel type calculated for the transportation end-
use sector. Specific data by vehicle type were not avail-
able for 1997; tiierefore, the 1996 percentage allocations
were applied to 1997 fuel consumption data in order to
estimate emissions in 1997. Military vehicle jet fuel con-
sumption was assumed to account for the difference be-
tween total U.S. jet fuel consumption (as reported by
DOE/EIA) and civilian air carrier consumption for both
domestic and international flights (as reported by DOT/
BTS and BEA). '
Data Sources
Data on fuel consumption for the United States
and its territories, carbon content of fuels, and percent
of carbon sequestered in non-energy uses were obtained
directly from the Energy Information Administration
(EIA) of the U.S. Department of Energy (DOE). Fuel
consumption data were obtained primarily from the
Monthly Energy Review (EIA 1998e) and various EIA
databases. U.S. marine bunker fuel consumption data
for distillate and residual fuel oil was taken from Fuel
Oil and Kerosene Sales (EIA 1998c). Marine bunker fuel
consumption in U.S. territories was collected from in-
ternal EIA databases used to prepare the International
Energy Annual (EIA 1998d). Jet fuel consumption for
aviation international bunkers was taken from Fuel Cost
and Consumption, which are monthly data releases by
the Department of Transportation's Bureau of Transpor-
tation Statistics (DOT/BTS 1998), and unpublished data
from the Bureau of Economic Analysis (BEA 1998). The
data collected by DOT/BTS includes fuel consumed for
international commercial flights both originating and ter-
minating in the United States. One-half of this value was
assumed to have been purchased in the United States.10
IPCC (IPCC/UNEP/OECD/IEA 1997) provided
combustion efficiency rates for petroleum and natural gas.
Bechtel (1993) provided the combustion efficiency rates
for coal. Vehicle type fuel consumption data for the alloca-
tion of transportation sector emissions Were primarily taken
from the Transportation Energy Databook prepared by the
Center for Transportation Analysis at Oak Ridge National
Laboratory (DOE 1993, 1994, 1995, 1996, 1997, 1998).
All jet fuel and aviation gasoline were assumed to have
been consumed in aircraft.
f Electric utilities arc not considered a final end-use sector, because they consume energy solely to provide electricity to the other sectors.
ltf See section titled International Bunker Fuels for a more detailed discussion.
2-14 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Carbon intensity estimates were developed using
nuclear and renewable energy data from EIA (1998a)
and fossil fuel consumption data as discussed above and
presented in Annex A.
For consistency of reporting, the IPCC has rec-
ommended that national inventories report energy data
(and emissions from energy) 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 catego-
ries are estimated from energy production data (account-
ing for imports, exports, stock changes, and losses). The
resulting quantities are referred to as "apparent consump-
tion." 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 collected through sur-
veys at the point of delivery or use and aggregated to
determine national totals.
Uncertainty
For estimates of CO2 from fossil fuel combustion,
the amount of CO2 emitted, in principle is directly related
to the amount of fuel consumed, the fraction of the fuel
that is oxidized, and the carbon content of the fuel. There-
fore, a careful accounting of fossil fuel consumption by
fuel type, average carbon contents of fossil fuels consumed,
and consumption of products with long-term carbon stor-
age should yield an accurate estimate of CO2 emissions.
There are uncertainties, however, concerning the
consumption data sources, carbon content of fuels and
products, and combustion efficiencies. For example,
given the same primary fuel type (e.g., coal), the amount
of carbon contained in the fuel per unit of useful energy
can vary. Non-energy uses of the fuel can also create
situations where the carbon is not emitted to the atmo-
sphere (e.g., plastics, asphalt, etc.) or is emitted at a de-
layed rate. The proportions of fuels used in these non-
fuel production processes that result in the sequestra-
tion of carbon have been assumed. Additionally, ineffi-
ciencies 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 uncer-
tainty in the CO2 estimates.
Other sources of uncertainty are fuel consumption
by U.S. territories and bunker fuels consumed by the
military. The United States does not collect as detailed
energy statistics for its territories as for the fifty states
and the District of Columbia. Therefore both estimating
emissions and bunker fuel consumption by these terri-
tories is difficult. It is also difficult to determine the geo-
graphic boundaries of where military bunker fuels are
consumed. The U.S. Department of Defense currently
does not collect energy consumption data sufficiently
detailed to estimate military bunker fuel emissions.
For the United States, however, these uncertain-
ties are believed to be relatively small. U.S. CO2 emis-
sion estimates from fossil fuel combustion are consid-
ered accurate within one or two percent. See, for ex-
ample, Marland and Pippin (1990).
Stationary Sources (excluding C02)
Stationary sources encompass all fuel combustion
activities except those related to transportation activi-
ties (i.e., mobile combustion). Other than carbon diox-
ide (CO2), which was addressed in the previous section,
gases from stationary combustion include the greenhouse
gases methane (CH4) and nitrous oxide (N2O) and the
criteria pollutants nitrogen oxides (NOX), carbon mon-
oxide (CO), and non-methane volatile organic com-
pounds (NMVOCs). Emissions of these gases from sta-
tionary sources depend upon fuel characteristics, tech-
nology type, usage of pollution control equipment, and
ambient environmental conditions. Emissions also vary
with the size and vintage of the combustion technology
as well as maintenance and operational practices.
Nitrous oxide and NOX emissions from stationary
combustion are closely related to air-fuel mixes and com-
bustion temperatures, as well as the characteristics of
any pollution control equipment that is employed. Car-
bon monoxide emissions from stationary combustion are
generally a function of the efficiency of combustion and
the use of emission controls; they are highest when less
oxygen is present in the air-fuel mixture than is neces-
sary for complete combustion. These conditions are most
Energy 2-15
-------
likely to occur during start-up and shut-down and dur-
ing fuel switching (e.g., the switching of coal grades at
a coal-burning electric utility plant). Methane and
NMVOC emissions from stationary combustion are be-
lieved to be a function of the CH4 content of the fuel
and post-combustion controls.
Emissions of OH4 increased slightly from 1990 to
1996, but fell below the 1990 level in 1997 to 2.2
MMTCE (391 Gg). This decrease in emissions was pri-
marily due to lower wood consumption in the residen-
tial and commercial sectors. Nitrous oxide emissions
rose 8 percent since 1990 to 4.1 MMTCE (49 Gg) in
1997. The largest source of N2O emissions was coal com-
bustion by electric utilities, which alone accounted for
53 percent of total N2O emissions from stationary com-
bustion in 1997. Overall, though, stationary combustion
is a small source of CH4 and N2O in the United States.
In general, stationary combustion was a signifi-
cant source of NOX and CO emissions, and a smaller
source of NMVOCs. In 1997, emissions of NOX from
stationary' combustion represented 46 percent of national
NOX emissions, while CO and NMVOC emissions from
stationary combustion contributed approximately 6 and
5 percent, respectively, to the national totals for the same
year. From 1990 to 1997, emissions of NOX were fairly
constant, while emissions of CO and NMVOCs de-
creased by 13 and 14 percent, respectively.
The decrease in CO and NMVOC emissions from
1990 to 1997 can largely be attributed to decreased resi-
dential and commercial wood consumption, which is the
most significant source of these pollutants in the Energy
sector. Overall, NOX emissions from energy varied due to
fluctuations in emissions from electric utilities. Table 2-
12, Table 2-13, Table 2-14, and Table 2-15 provide CH4
and N20 emission estimates from stationary sources by
sector and fuel type. Estimates of NOX, CO, and NMVOC
emissions in 1997 are given in Table 2-16."
Methodology
Methane and nitrous oxide emissions were esti-
mated by multiplying emission factors (by sector and
fuel type) by fossil fuel and wood consumption data.
Methane and nitrous oxide emission estimates for sta-
tionary combustion activities were grouped into four
sectors—industrial, commercial/institutional, residen-
tial, and electric utilities—and were based on national
coal, natural gas, fuel oil, and wood consumption data.
For NOX, CO, and NMVOCs, the major source cat-
egories included in this section are those used in EPA
(1998): coal, fuel oil, natural gas, wood, other fuels (in-
cluding LPG, coke, coke oven gas, and others), and sta-
tionary internal combustion. The EPA estimates emis-
sions of NOX, CO, and NMVOCs, by sector and fuel
source using a "bottom-up" estimating procedure. In
other words, emissions were calculated either for indi-
vidual sources (e.g., industrial boilers) or for multiple
sources combined, using basic activity data as indica-
tors of emissions. Depending on the source category,
these basic activity data may include fuel consumption,
fuel deliveries, tons of refuse burned, raw material pro-
cessed, etc.
The EPA derived the overall emission control effi-
ciency of a source category 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 source combustion, as de-
scribed above, is similar to the methodology recommended
by the IPCC (IPCC/UNEP/OECD/EEA 1997).
More detailed information on the methodology for
calculating emissions from stationary sources including
emission factors and activity data is provided in Annex B.
ii
Data Sources
Emissions estimates for NOX, CO, and NMVOCs
in this section were taken directly from the EPA's Draft
National Air Pollutant Emissions Trends: 1900 - 1997
(EPA 1998). U.S. energy data were provided by the U.S.
Energy Information Administration's Annual Energy
Review (EIA 1998a) and Monthly Energy Review (EIA
1998b). Emission factors were provided by the Revised
1996 IPCC Guidelines for National Greenhouse Gas
Inventories (IPCC/UNEP/OECD/IEA 1997).
" See Annex B for a complete time series of criteria pollutant emission estimates for 1990 through 1997.
2-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-12: CH4 Emissions from Stationary Sources (MMTCEJ
Sector/Fuel Type
Electric Utilities
Coal
Fuel Oil
Natural gas
Wood
Industrial
Coal
Fuel Oil
Natural gas
Wood
Commercial/Institutional
Coal
Fuel Oil
Natural gas
Wood*
Residential
Coal
Fuel Oil
Natural Gas
Wood
Total
1990
0.1
0.1
+
+
+
0.8
0.2
0.1
0.2
0.3
0.1
+
0.1
0.1
NA
1.3
0.1
0.1
0.1
0.9
2.3
1991
0.1
0.1
+
+
+
0.8
0.1
0.1
0.2
0.3
0.1
+
+
0.1
NA
1.3
0.1
0.1
0.1
1.0
2.4
1992
0.1
0.1
+
+
+
0.8
0.1
0.1
0.2
0.3
0.1
+
+
0.1
NA
1.4
0.1
0.1
0.1
1.1
2.4
1993
0.1
0.1
+
+
+
0.8
0.1
0.1
0.3
0.3
0.1
+
+
0.1
NA
1.3
0.1
0.1
0.1
1.0
2.4
1994
0.1
0.1
+
+
+
0.9
0.1
0.1
0.3
0.3
0.1
+
+
0.1
NA
1.3
0.1
0.1
0.1
0.9
2.4
1995
0.1
0.1
+
+
+
0.9
0.1
0.1
0.3
0.3
0.1
+
+
0.1
NA
1.4
0.1
0.1
0.1
1.0
2.5
1996
0.1
0.1
+
+
+
0.9
0.1
0.1
0.3
0.4
0.1
+
+
0.1
NA
1.4
0.1
0.1
0.1
1.1
2.5
1997
0.1
0.1
+
+
+
0.9
0.1
0.1
0.3
0.3
0.1
+
+
0.1
NA
1.1
0.1
0.1
0.1
0.8
2.2
+ Does not exceed 0.05 MMTCE
NA (Not Available)
* Commercial/institutional emissions from the combustion of wood are included under the residential sector.
Note: Totals may not sum due to independent rounding.
Table 2-13: N20 Emissions from Stationary Sources (MMTCE)
Sector/Fuel Type
1990 1991 1992 1993 1994 1995 1996 1997
Electric Utilities
Coal
Fuel Oil
Natural gas
Wood
Industrial
Coal
Fuel Oil
Natural gas
Wood
Commercial/Institutional
Coal
Fuel Oil
Natural gas
Wood*
Residential
Coal
Fuel Oil
Natural Gas
Wood
Total
2.0
1.9
0.1
+
+
1.4
0.3
0.4
0.1
0.6
0.1
+
+
+
NA
0.3
+
0.1
+
0.2
3.81
2.0
1.9
0.1
+
+
1.4
0.3
0.4
0.1
0.6
0.1
+
+
+
NA
0.3
+
0.1
+
0.2
3.78
2.0
1.9
+
+
+
1.5
0.3
0.4
0.1
0.7
0.1
+
+
+
NA
0.3
+
0.1
+
0.2
3.85
2.1
2.0
0.1
+
+
1.5
0.3
0.4
0.1
0.7
0.1
+
+
+
NA
0.3
+
0.1
+
0.2
3.93
2.1
2.0
+
+
+
1.5
0.3
0.5
0.1
0.7
0.1
+
+
+
NA
0.3
+
0.1
+
0.2
3.97
2.1
2.0
+
+
+
1.5
0.3
0.4
0.1
0.7
0.1
+
+
+
NA
0.3
+
0.1
+
0.2
3.96
2.2
2.1
+
+
+
1.5
0.3
0.5
0.1
0.7
0.1
+
+
+
NA
0.3
+
0.1
+
0.2
4.13
2.3
2.2
+
+
+
1.5
0.3
0.5
0.1
0.7
0.1
+
+
+
NA
0.3
+
0.1
+
0.2
4.13
+ Does not exceed 0.05 MMTCE
NA (Not Available)
* Commercial/institutional emissions from the combustion of wood are included under the residential sector.
Note: Totals may not sum due to independent rounding.
Energy 2-17
-------
Table 2-14: CH4 Emissions from Stationary Sources (Gg)
Sector/Fuel Type
111 I. II II II '
Electric Utilities
Coal
FuiOil
Natural gas
Wood
Industrial
Coal
Fuel Oil
Natural gas
Wood
Commercial/Institutional
Coal
Fuel Oil : ,
Natural pas i
'WboB'"*
Residential
Coal
FuelOii
Natural Gas
Wood
Total
+ Does not exceed 0.5 Gg
NA {Not Available)
1990
23
16
4
3
1
140
27
17
40
55
23
1
9
13
NA
218
19
13
21
166
404
1991
23
16
4
3
1
138
26
16
41
55
23
1
9
13
NA
227
17
13
22
175
410
1992
22
16
3
3
1
143
25
17
43
58
23
1
8
14
NA
237
17
13
23
184
425
1993
23
17
3
3
1
146
25
17
45
59
23
1
8
14
NA
224
17
14
24
169
415
1994
i1 ' •' I'l ' ' ,
23
17
3
3
1
149
25
18
46
61
23
1
3,,
14,
NA
220
17
13
24
166
414
1995
23
17
2
3 „
+ „
149
24
17
48
59 ,
23
1
8 „
15 „
NA
236
16
14 :
24
183 ;
431
ii
1996
23
18
2
3
1
154
24
18
49
63
24
1
7
15
NA
240
17
14
26
183
441
1997
24
19
2
3
1
151
23
19
49
61
24
1
7
16
NA
191
17
15
24
135
391
* Commercial/Institutional emissions from the combustion of wood are included under the residential sector.
Note: Totals may not sum due to independent rounding.
Table 2-15: N20 Emissions from Stationary
Secior/FuenVpe
Electric Utilities
: Coal
Fuel Oil
Natural gas
Wood
Industrial
Coal
Fuel Oil
Natural gas
Wood
Commercial/Institutional
Coal
Fuel Oil
Natural gas
Wood*
Residential
Coal
Fuel Oil
Natural Gas
Wood
Total
+ Doss not exceed 0,5 Gg
• NAlffat, Available}
Sources
1990
24
23
1
+
+
17
4
5
1
7
1
+
1
+
NA
3
+
1
+
2
45
(Gg)
1991
24
22
1
+
+
17
4
5
1
7
1
+
1
+
NA
4
+
1
+
2
45
1992
24
23
1
+
+
17
3
5
1
8
1
+
+
+
NA
4
+
1
-1-
2
46
1993
25
24
1
+
+
17
3
5
1
8
1
+
+
+
NA
4
+
1
+
2
46
1994
25
24
1
+
+
18
3
5
1
8
1
+
+
+
NA
4
_j-
1
+
2,,,,',,
47
I
1995
25
24 ;
+
+ ''
+ ... j
18
3
5 ;
1 ',
8 :
1 ,
+ i
+ '
+
NA
4
+ I
1 ;
_i_
.2. .!...
47
Ii
1996
26
25
+
+
+
18
3
5
1
8
1
_l_
+
+
NA
4
_l_
1
1
2
49
1997
27
26
+
+
_)_
18
3
6
1
8
1
+
+
+
NA
3
+
1
+
'.. 2 .
49
* CommerciaVtnstllutionat emissions from the combustion of wood are included under the residential sector. .
Nois: totals may not sum due to independent rounding.
••;
: ' ',: •
I'
•; , -
2-18 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-16: NOX, CO, and NMVOC Emissions from Stationary Sources in 1997 (Gg)
Sector/Fuel Type
N0y
CO
NMVOC
Sector/Fuel Type
N0y
CO
NMVOC
Electric Utilities
Coal
Fuel Oil
Natural gas
Wood
Internal Combustion
Industrial
Coal
Fuel Oil
Natural gas
Wood
Other Fuels3
Internal Combustion
5,605
5,079
120
262
NA
144
2,967
557
218
1,256
NA
118
818
368
230
11
71
NA
56
1,007
91
66
329
NA
288
233
46
26
3
7
NA
9
197
5
11
70
NA
48
62
Commercial/Institutional
Coal
Fuel Oil
Natural gas
Wood
Other Fuels"
Ftesidential
Coal"
Fuel Oilb
Natural 6asb
Wood
Other Fuels3
Total
379
36
97
219
I\!A
27
779
NA
NA
NA
31
748
9,729
235
14
17
51
NA
152
2,759
NA
NA
NA
2,520
239
4,369
22
1
3
10
NA
8
515
NA
NA
NA
478
37
780
NA (Not Available)
a "Other Fuels" include LP6, waste oil, coke oven gas, coke, and non-residential wood (EPA 1998).
b Coal, fuel oil, and natural gas emissions are included in the "Other Fuels" category (EPA 1998).
Note: Totals may not sum due to independent rounding. See Annex B for emissions in 1990 through 1996.
Uncertainty
Methane emission estimates from stationary sources
are highly uncertain, primarily due to difficulties in calcu-
lating 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 dif-
ferent sectors), rather than specific emission processes (i.e.,
by combustion technology and type of emission control).
The uncertainties associated with the emission estimates
of these gases are greater than with estimates of CO2 from
fossil fuel combustion, which are mainly a function of 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 criteria
pollutants, uncertainties are partly due to assumptions con-
cerning combustion technology types, age of equipment,
emission factors used, and projections of growth.
Mobile Sources (excluding C02)
Mobile sources emit greenhouse gases other than
CO2, including methane (CEy, nitrous oxide (N2O), and
the criteria pollutants carbon monoxide (CO), nitrogen
oxides (NOX), and non-methane volatile organic compounds
(NMVOCs).
As with combustion in stationary sources, N2O and
NOX emissions are closely related to fuel characteris-
tics, air-fuel mixes, and 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 and CO emissions. Carbon monox-
ide emissions from mobile source combustion are sig-
nificantly affected by combustion efficiency and pres-
ence of post-combustion emission controls. Carbon mon-
oxide emissions are highest when air-fuel mixtures have
less oxygen than required for complete combustion. This
occurs especially in idle, low speed and cold start con-
ditions. Methane and NMVOC emissions from motor
vehicles are a function of the CH4 content of the motor
fuel, the amount of hydrocarbons passing unco'mbusted
through the engine, and any post-combustion control of
hydrocarbon emissions, such as catalytic converters.
Emissions from mobile sources were estimated by
transport mode (e.g., highway, air, rail, and water) and fuel
type—motor gasoline, diesel fuel, jet fuel, aviation gas,
natural gas, liquefied petroleum gas (LPG), and residual
fuel oil—and vehicle type. Road transport accounted for
the maj ority of mobile source fuel consumption, and hence,
the majority of mobile source emissions. Table 2-17 through
Table 2-20 provide CH4 and N2O emission estimates from
mobile sources by vehicle type, fuel type, and transport
mode. Estimates of NOX, CO, and NMVOC emissions in
1997 are given in Table 2-21.12
12 See Annex C for a complete time series of criteria pollutant emission estimates for 1990 through 1997.
Energy 2-19
-------
Table 2-17: CH4 Emissions from Mobile Sources (MMTCE)
Fuel JVpe/Vehicle Type
Gasoline Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft
Other*
Total
* Does not exceed 0.05 MMTCE
Mote: Totals may not sum due to independent rounding.
* "Other" Includes snowmobiles, small gasoline powered
(Basel powered utility equipment
1990
1.3
0.8
0.4
0.1
+
0.1
+
+
0.1
0.1
+
+
+
+
+
+
1.4
1991
1.2
0.7
0.4
0.1
+
0.1
+
+
0.1
0.1
+
•f
+
+
+
+
1.4
utility equipment,
1992
1.2
0.7
0.4
0.1
+
0.1
+
+
0.1
0.1
+
+
+
+
+
+
1.4
1993 1994
1.2
0.7
0.4
0.1
+
0.1
+
+
0.1
0.1
-f-
+
+
+
+
+
1.4
heavy-duty gasoline powered
1.2
0.7
0.4
0.1
+
0.1
+
+
0.1
0.1
+
+
+
+
+
+
1.4
ii
1995
I
1.2
0.7:
0.4
0.1;
+
0-1
+ ;!
+ I
0.1
0.1
+
+ i
+ :
+
+ ;
+ i
1.4
1996 1997
1.2
0.6
0.5
0.1
+
0.1
+
+
0.1
0.1
+
+
+
+
+
+
1.4
1.2
0.6
0.5
0.1
+
0.1
+
+
0.1
0.1
+
+
+
+
+
+
1.4
utility equipment, and heavy-duty
Table 2-18: N20 Emissions from Mobile Sources (MMTCE)
Fuel Type/Vehicle Type
Total
1990 1991 1992 1993 1994 1995 1996 1997
Gasoline Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heayy-Duty Vehicles
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
'Aircraft
Other*
12.3
8.6
3.4
0.2
+
0.5
+
+
0.5
0.8
0.1
0.1
0.1
-f
0.5
+
12.9
9.0
3.7
0.2
+
0.5
+
+
0.5
0.8
0.1
0.1
0.1
+
0.5
+
~ —
13.8
9.7
3.9
0.2
+
0.5
+
+
0.5
0.8
0.1
0.1
0.1
+
0.5
+
14.6
10.1
4.2
0.3
+
0.5
+
+
0,5
0.8
0.1
0.1
0.1
_l_
0.5
+
^^"
15.3
9.9
5.1
0.3
+
0.6
+
,,,,+
0.5
0.8
o.i
0.1
0.1
,. -t,
0.5
+
i
15.6
10.1
5.2
0.3,
+
0.6
+ \
0.5 '
0.8
0.1 ,;
0.1 ;
0.1 ;
+ i,
0.5,;
16.0
8.9
6.8
0.3
0.6
+
0.6
0.8
0.1
0.1
0.1
0.5
16.1
9.0
6.7
0.3
0.6
+
0.6
0.8
0.1
0.1
0.1
0.5
13.6
14.2
15.2
15.9
16.7
17.0
17.4
17.5
jsmiy 'riot sum due to independent rounding. "
* "Oflwr" Includes snowmobiles, small gasoline powered utility equipment, heavy-duty gasoline powered utility equipment, and heavy-duty
(flesel powered utility equipment.
2-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-19: CH4 Emissions from Mobile Sources (Gg)
Fuel Type/Vehicle Type
1990 1991 1992 1993 1994 1995 1996 1997
Gasoline Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft
Other*
Total
220
133
67
16
4
10
+
+
10
22
4
3
6
1
8
1
252
214
128
66
16
4
10
+
+
10
21
4
2
5
1
7
1
245
211
127
65
15
4
10
-t-
+
10
21
4
. 3
6
1
7
1
243
209
123
66
16
4
11
+
+
10
21
4
2
5
1
7
1
241
211
115
75
17
4
11
+
+
11
21
4
2
6
1
7
1
244
209
114
74
17
4
11
+
+
11
22
4
3
6
1
7
1
242
212
98
94
16
4
12
+
+
11
22
4
3
6
1
7
1
246
210
100
91
16
4
12
+
+
11
20
3
2
6
1
7
1
242
+ 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 2-20: N20 Emissions from Mobile Sources (Gg)
Fuel Type/Vehicle Type
1990
1991 1992
1993
1994 1995 1996 1997
Gasoline Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft
Other*
Total
145
102
41
2
+
6
+
+
5
10
1
1
1
+
6
+
161
153
107
44
3
+
6
+
+
5
9
1
1
1
+
6
+
169
164
115
46
3
+
6
+
+
6
10
1
1
1
+
5
- +
179
173
120
50
3
+
6
+
+
6
9
1
1
1
+
5
+
188
181
117
60
3
+
7
+
+
6
10
1
1
1
+
6
+
197
184
119
61
4
+
7
+
+
6
10
2
1
1
+
6
+
201
189
105
80
4
+
7
+
+
7
10
1
1
1
+
6
+
206
191
107
80
4
+
7
+
+
7
9
1
1
1
+
6
+
207
+ 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.
Energy 2-21
-------
Table 2-21: NOX, CO, and NMVOC Emissions from Mobile Sources in 1997 (Gg)
Fuel Type/Vehicle Type NDX CO NMVOCs
Gasoline Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Motorcycles
Diesel Highway
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
4,629
2,597
1,725
296
11
1,753
31
11
1,711
44,225
24,356
16,659
3,039
171
1,368
27
10
1,332
4,528
2,467
1,785
243
33
217
11
5
201
Fuel Type/Vehicle Type NOX CO NMVOCs
Non-Highway
Ships and Boats
Locomotives
Farm Equipment
Construction Equipment
Aircraft3
Otherb
Total
4,137
273
861
962
1,120
161
759
10,519
15,201
• 1,704
; 105
298
'. 1,080
, 918
11 1,096'
60,794
2,205
468
45
116
219
170
1,186
6,949
* WrWflfl estimates Include only emissions related to LTD cycles, and therefore do not include cruise altitude emissions.
* "Ofw* inctudes oasojjne powered recreational, industrial, lawn and garden, light commercial, logging, airport service, other equipment; and
(fe^l'poweretf rtcrealiortal. Industrial, lawn and garden, light construction, airport service. !|
Note: TMsIs may not sum due to independent rounding. See Annex C for emissions In 1990 through 1996. |
Mobile sources were responsible for a small portion
of national CH4 emissions but were the second largest
source of N2O in the United States. From 1990 to 1997,
CH4 emissions declined by 4 percent, to 1.4 MMTCE (242
Gg). Nitrous oxide emissions, however, rose 29 percent to
17.5 MMTCE (207 Gg) (see Figure 2-12). The reason for
this conflicting trend was that the control technologies em-
ployed on highway vehicles in the United States lowered
CO, NOX, NMVOC, and CH4 emissions, but resulted in
higher average N2O emission rates. Fortunately, since 1994
improvements in the emission control technologies installed
on new vehicles have reduced emission rates of both NOX
and N2O per vehicle mile traveled. Overall, CH4 and N2O
emissions were dominated by gasoline-fueled passenger
cars and light-duty gasoline trucks.
Figure 2-12
16
ui 12
o
I 8
4
0
N00
CH,
1990 1991 1992 1993 1994 1995 1996 1997
Emissions of criteria pollutants generally increased
from 1990 through 1994, after which there were de-
creases of 4 (NOX) to 14 (CO) percent by 1997. A drop
in gasoline prices combined with a strengthening U.S.
economy caused the initial increase. These factors
pushed the vehicle miles traveled (VMT) by road sources
up, resulting in increased fuel consumption and higher
emissions. Some of this increased activity was later off-
set by an increasing portion of the U.S. vehicle fleet
meeting established emissions standards.
Fossil-fueled motor vehicles comprise the single
largest source of CO emissions in the United States and
are a significant contributor to NOX and NMVOC emis-
sions. In 1997, CO emissions from mobile sources con-
tributed 81 percent of total CO emissions and 49 and 41
!i
percent of NOX and NMVOC emissions, respectively.
Since 1990, emissions of CO and NMVOCs from mo-
bile sources decreased by 8 and 13 percent, respectively,
while emissions of NOX increased by 3 percent.
I
Methodology
Estimates for CH4 and N2O emissions from mo-
bile combustion were calculated by multiplying emis-
sion factors by measures of activity for each category.
Depending upon the category, activity data included such
information as fuel consumption, fuel deliveries, and
vehicle miles traveled (VMT). Emission estimates from
highway vehicles were based on VMT and emission fac-
tors by vehicle type, fuel type, model year, and control
2-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
technology. Fuel consumption data was employed as a
measure of activity for non-highway vehicles and then
fuel-specific emission factors were applied.13 A com-
plete discussion of the methodology used to estimate
emissions from mobile sources is provided in Annex C.
The EPA (1998a) provided emissions estimates of
NOX, CO, and NMVOCs for eight categories of high-
way vehicles14, aircraft, and seven categories of off-high-
way vehicles15.
Data Sources
Emission factors used in the calculations of CH4
and N2O emissions are presented in Annex C. The Re-
vised 1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA
1997) provided emission factors for CH4, and were de-
veloped using MOBILESa, a model used by the Envi-
ronmental Protection Agency (EPA) to estimate exhaust
and running loss emissions from highway vehicles. The
MOBILE5a model uses information on ambient tem-
perature, vehicle speeds, national vehicle registration dis-
tributions, gasoline volatility, and other variables in or-
der to produce these factors (EPA 1997).
Emission factors for N2O from gasoline highway
vehicles came from a recent EPA report (1998b). This re-
port developed 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 Ve-
hicle and Fuel Emissions Laboratory (NVFEL). These
emission factors for gasoline highway vehicles are lower
than the U.S. default values in the Revised 1996 IPCC
Guidelines, but are higher than the European default val-
ues, both of which were published before the more recent
tests and literature review conducted by the NVFEL. 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. More de-
tails may be found in EPA (1998b).
Emission factors for gasoline vehicles other than
passenger cars were scaled from those for passenger cars
with the same control technology, based on their rela-
tive fuel economy. This scaling was supported by lim-
ited data showing that light-duty trucks emit more N2O
than passenger cars with equivalent control technology.
The use of fuel-consumption ratios to determine emis-
sion factors is considered a temporary measure only, to
be replaced as soon as additional testing data are avail-
able. For more details, see EPA (1998b). Nitrous oxide
emission factors for diesel highway vehicles were taken
from the European default values found in the Revised
1996IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997).
There is little data addressing N2O emissions from U.S.
diesel-fueled vehicles, and in general, European coun-
tries have had more experience with diesel-fueled ve-
hicles. U.S. default values in the Revised 1996 IPCC
Guidelines were used for non-highway vehicles.
Activity data were gathered from several U.S. gov-
ernment sources including EIA (1998a), EIA (1998b),
FHWA (1998), BEA (1998), DOC (1998) FAA (1998),
andDOT/BTS (1998). Control technology data for high-
way vehicles were obtained from the EPA's Office of
Mobile Sources. Annual VMT data for 1990 through
1997 were obtained from the Federal Highway
Administration's (FHWA) Highway Performance Moni-
toring System database, as noted in EPA (1998a).
Emissions estimates for NOX, CO, NMVOCs were
taken directly from the EPA's National Air Pollutant
Emissions Trends, 1900 - 1997 (EPA 1998a).
Uncertainty
Mobile source emission estimates can vary sig-
nificantly due to assumptions concerning fuel type and
composition, technology type, average speeds, type of
emission control equipment, equipment age, and oper-
ating and maintenance practices. Fortunately, detailed
activity data for mobile sources were available, includ-
13 The consumption of international bunker fuels is not included in these activity data, but are estimated separately under the International Bunker
Fuels source category.
14 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.
15 These categories included: gasoline and diesel farm tractors, other gasoline and diesel farm machinery, gasoline and diesel construction equip-
ment, snowmobiles, small gasoline utility engines, and heavy-duty gasoline and diesel general utility engines.
Energy 2-23
-------
ing VMT by vehicle type for highway vehicles. The al-
location of this VMT to individual model years was done
using the profile of U.S. vehicle usage by vehicle age in
1990 as specified in MOBILE 5a. Data to develop a tem-
porally variable profile of vehicle usage by model year
instead of age was not available.
Average emission factors were developed based
on numerous assumptions concerning the age and model
of vehicle; percent driving in cold start, warm start, and
cruise conditions; average driving speed; ambient tem-
perature; and maintenance practices. The factors for
regulated emissions from mobile sources—CO, NOX, and
hydrocarbons—have been extensively researched, and
thus involve lower uncertainty than emissions of unregu-
lated gases. Although methane has not been singled out
for regulation in the United States, overall hydrocarbon
emissions from mobile sources—a component of which
is methane—are regulated.
Compared to methane, CO, NOX, and NMVOCs,
there is relatively little data available to estimate emis-
sion factors for nitrous oxide. Nitrous oxide is not a cri-
teria pollutant, and measurements of it in automobile
exhaust have not been routinely collected. Research data
has shown that N2O emissions from vehicles with cata-
lytic converters are greater than those without emission
controls, and that vehicles with aged catalysts emit more
than new ones. The emission factors used were, there-
fore, derived from aged cars (EPA 1998b). The emis-
sion 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. Cur-
rently, N2O gasoline highway emission factors for ve-
hicles other than passenger cars are scaled based on those
for passenger cars and their relative fuel economy. Ac-
tual measurements should be substituted for this proce-
dure when they become available. Further testing is
needed to reduce the uncertainty in emission factors for
all classes of vehicles, using realistic driving regimes,
environmental conditions, and fuels.
Although aggregate jet fuel and aviation gasoline
consumption data has been used to estimate emissions
from aircraft, the recommended method for estimating
emissions in the Revised 1996 IPCC Guidelines is to
use data by specific aircraft type (IPCC/UNEP/OECD/
IEA 1997). The IPCC also recommends that cruise alti-
tude emissions be estimated separately using fuel con-
sumption data, while landing and take-off (LTO) cycle
data be used to estimate near-ground level emissions.
The EPA is attempting to develop revised estimates based
on this more detailed activity data, and these estimates
are to be presented in future inventories.
U.S. jet fuel and aviation gasoline consumption is
currently all attributed to the transportation sector by
EIA, and it is assumed here that it is all used to fuel
aircraft. However it is likely that some fuel purchased
by airlines is not necessarily be used in aircraft, but in-
stead 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.
Overall, uncertainty for N2O emissions estimates is
considerably higher than for CH4, CO, NOX, or NMVOC;
however, all these gases involve far more uncertainty than
CO2 emissions from fossil fuel combustion.
Lastly, in EPA (1998), U.S. aircraft emission esti-
mates for CO, NOx, and NMVOCs are based upon landing
and take-off (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
presented here overestimate IPCC-defmed domestic CO,
NOX, and NMVOC emissions by including LTO cycles by
aircraft on international flights but underestimate because
they do not include emissions from aircraft on domestic
flight segments at cruising altitudes.
Coal Mining
All underground and surface coal mining liberates
(i.e., releases) methane as part of normal operations. The
amount of methane liberated during mining is primarily
dependent upon the amount of methane stored in the
coal and the surrounding strata. This in situ methane
content is a function of the quantity of methane gener-
ated during the coal formation process and its ability to
migrate through the surrounding strata over time. The
2-24 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
degree of coalification—defined by the rank or quality
of the coal formed—determines the amount of methane
generated during the coal formation process; higher
ranked coals generate more methane. The amount of
methane that remains in the coal and surrounding strata
also depends upon geologic characteristics such as pres-
sure within a coal seam. Deeper coal deposits tend to
retain more of the methane generated during coalifica-
tion. Accordingly, deep underground coal seams gener-
ally have higher methane contents than shallow coal seams
or surface deposits.
Underground, versus surface, coal mines contrib-
ute the largest share of methane emissions. All under-
ground coal mines employ ventilation systems to en-
sure that methane levels remain within safe concentra-
tions. These systems can exhaust significant amounts of
methane to the atmosphere in low concentrations. Addi-
tionally, over twenty gassy U.S. coal mines supplement
ventilation systems with degasification systems.
Degasification systems are wells drilled from the sur-
face or boreholes drilled inside the mine that remove
large volumes of methane before or after mining. In
1997, 14 coal mines collected methane from
degasification systems and sold this gas to a pipeline,
thus reducing emissions to the atmosphere. Surface coal
Table 2-22: CH4 Emissions from Coal Mining (MMTCE)
1991
mines also release methane as the overburden is removed
and the coal is exposed. Additionally, after coal has been
mined, small amounts of methane retained in the coal
are released during processing, storage, and transport.
Total methane emissions in 1997 were estimated
to be 18.8 MMTCE (3.3 Tg), declining 22 percent since
1990 (see Table 2-22 and Table 2-23). Of this amount,
underground mines accounted for 65 percent, surface
mines accounted for 14 percent, and post-mining emis-
sions accounted for 21 percent. With the exception of
1995, total methane emissions declined every year dur-
ing this period. In 1993, emissions from underground
mining dropped to a low of 2.8 Tg, primarily due to la-
bor strikes at many of the large underground mines. In
1995, there was an increase in methane emissions from
underground mining due to particularly high emissions
at the gassiest coal mine in the country. Overall, with
the exception of 1995, total methane emitted from un-
derground mines declined in each year because of in-
creased gas recovery and use. Surface mine emissions and
post-mining emissions remained relatively constant from
1990 to 1997.
In 1994, EPA's Coalbed Methane Outreach Pro-
gram (CMOP) began working with the coal industry and
Activity
1990
1992 1993 1994 1995 1996 1997
Underground Mining
Liberated
Recovered & Used
Surface Mining
Post- Mining (Underground)
Post-Mining (Surface)
17.1
18.8
(1.6)
2.8
3.6
0.5
16.4
18.1
(1.7)
2.6
3.4
0.4
15.6
17.8
(2.1)
2.6
3.3
0.4
13.3
16.0
(2.7)
2.5
3.0
0.4
13.1
16.3
(3.2)
2.6
3.3
0.4
14.2
17.7
(3.4)
2.4
3.3
0.4
12.6
16.5
(3.8)
2.5
3.4
0.4
12.3
16.8
(4.6)
2.6
3.5
0.4
Total
24.0
22.8
22.0
19.2
19.4 20.3
18.9
18.8
Note: Totals may not sum due to independent rounding.
Table 2-23: CH4 Emissions from Coal Mining (Tg)
1990 1991 1992 1993 1994 1995 1996 1997
Underground Mining
Liberated
Recovered & Used
Surface Mining
Post- Mining (Underground)
Post-Mining (Surface)
Total
3.0
3.3
(0.3)
0.5
0.6
0.1
4.2
2.9
3.2
(0.3)
0.4
0.6
0.1
4.0
2.7
3.1
(0.4)
0.4
0.6
0.1
3.8
2.3
2.8
(0.5) .
0.4
0.5
0.1
3.4
2.3
2.8
(0.6)
0.5
0.6
0.1
3.4
2.5
3.1
(0.6)
0.4
0.6
0.1
3.6
2.2
2.9
(0.7)
0.4
0.6
0.1
3.3
2.1
2.9
(0.8)
0.5
0.6
0.1
3.3
Note: Totals may not sum due to independent rounding.
Energy 2-25
-------
other stakeholders to identify and remove obstacles to
investments in coal mine methane recovery and use
projects. Reductions attributed to CMOP were estimated
to be 0,7,0.8, 1.0, and 1.3 MMTCE in 1994, 1995,1996
and 1997, respectively.
Methodology
The methodology for estimating methane emis-
sions from coal mining consists of two main steps. The
first step involved estimating methane emissions from
underground mines. Because of the availability of ven-
tilation system measurements, underground mine emis-
sions can be estimated on a mine-by-mine basis and then
summed to determine total emissions. The second step
involved estimating emissions from surface mines and
post-mining activities by multiplying basin-specific coal
production by basin-specific emissions factors.
Underground mines. Total methane emitted from
underground mines was estimated as the quantity of
methane liberated from ventilation systems, plus meth-
ane liberated from degasification systems, minus meth-
ane recovered and used. The Mine Safety and Heath
Administration (MSHA) measures methane emissions
from ventilation systems for all mines with detectable16
methane concentrations. These mine-by-mine measure-
ments were used to estimate methane emissions from
ventilation systems.
Some of the gassier underground mines also use
degasification systems (e.g., wells or boreholes) that re-
move methane before or after mining . This methane
can then be collected for use or vented to the atmosphere.
Various approaches were employed to estimate the quan-
tity of methane collected by each of the more than twenty
mines using these systems, depending on available data.
For example, some mines have reported to EPA the
amounts of methane liberated from their degasification
systems. For mines that sell recovered methane to a pipe-
line, pipeline sales data was used to estimate
degasifieation emissions. Finally, for those mines for
which no other data was available, default recovery ef-
ficiency values were developed, depending on the type
of degasification system employed.
Finally, the amount of methane recovered by
degasification systems and then used (i.e., not vented)
was estimated. This calculation was complicated by the
fact that methane is rarely recovered and used during
the same year in which the particular coal seam is mined.
In 1997, 14 active coal mines sold recovered methane to
a pipeline operator. Emissions avoided for these projects
were estimated using gas sales data reported by various
state agencies, and information supplied by coal mine
operators regarding the number of years in advance of
mining that gas recovery occurred. Additionally, some
of the state agencies provided individual well produc-
tion information, which was used to assign gas sales to
a particular year.
Surface Mines and Post-Mining Emissions. Sur-
face mining and post-mining methane emissions were
estimated by multiplying basin-specific coal production
by basin-specific emissions factors. For surface mining,
emissions factors were developed by assuming that sur-
face mines emit from one to three times as much meth-
ane as the average in situ methane .content of the coal.
This accounts for methane released from the strata sur-
rounding the coal seam. For this analysis, it is assumed
that twice the average in-situ methane content is emit-
ted. For post-mining emissions, the emission factor was
assumed to be from 25 to 40 percent of the average in
situ methane content of coals mined in the basin. For
this analysis, it is assumed that 32.5 percent of the aver-
age in-situ methane content is emitted.
Data Sources
i
The Mine Safety and Health Administration pro-
vided mine-specific information on methane liberated
from ventilation systems at underground mines. EPA
developed estimates of methane liberated from
degasification systems at underground mines based on
available data for each of the mines employing these
systems. The primary sources of data for estimating
16 MSHA records coat mine methane readings with concentrations of greater than 50 ppm (parts per million) methane. Readings below this
threshold are considered non-detectable.
2-26 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
emissions avoided at underground mines were gas sales
data published by state petroleum and natural gas agen-
cies, information supplied by mine operators regarding
the number of years in advance of mining that gas re-
covery occurred, and reports of gas used on-site. An-
nual coal production data was taken from the Energy
Information Agency's Coal Industry Annual (see Table
2-24) (EIA 1991, 1992, 1993, 1994, 1995, 1996, 1997,
1998). Data on in situ methane content and emissions
factors were taken from EPA (1993).
Table 2-24: Coal Production
(Thousand Metric Tons)
Natural Gas Systems
Year
Underground Surface
Total
1990
1991
1992
1993
1994
1995
1996
1997
384,247
368,633
368,625
318,476
362,063
359,475
371,813
381,620
546,814
532,653
534,286
539,211
575,525
577,634
593,311
607,163
931,061
901,285
902,911
857,687
937,588
937,109
965,125
988,783
Uncertainty
The emission estimates from underground venti-
lation systems were based upon actual measurement data
for mines with detectable methane emissions. Accord-
ingly, the uncertainty associated with these measure-
ments is estimated to be low. Estimates of methane lib-
erated from degasification systems are less certain be-
cause EPA assigns default recovery efficiencies for a
subset of U.S. mines. Compared to underground mines,
there is considerably more uncertainty associated with
surface mining and post-mining emissions because of
the difficulty in developing accurate emissions factors
from field measurements. Because underground emis-
sions comprise the majority of total coal mining emis-
sions, the overall uncertainty is estimated to be only ±15
percent.17 Currently, the estimate does not include emis-
sions from abandoned coal mines because of limited
data. The EPA is conducting research on the feasibility
of including an estimate in future years.
Methane emissions from natural gas systems are
generally process related, with normal operations, rou-
tine maintenance, and system upsets being the primary
contributors. Emissions from normal operations include:
natural gas combusting engine and turbine exhaust, bleed
and discharge emissions from pneumatic devices, and
fugitive emissions from system components. Routine
maintenance emissions originate from pipelines, equip-
ment, and wells during repair and maintenance activi-
ties. Pressure surge relief systems and accidents can lead
to system upset emissions.
The U.S. natural gas system encompasses hundreds
of thousands of wells, hundreds of processing facilities,
hundreds of thousands of miles of transmission pipe-
lines, and over a million miles of distribution pipeline.
The system, though, can be divided into four stages, each
with different factors affecting methane emissions, as
follows:
Field Production. In this initial stage, wells are
used to withdraw raw gas from underground formations.
Emissions arise from the wells themselves, treatment
facilities, gathering pipelines, and process units such as
dehydrators and separators. Fugitive emissions and emis-
sions from pneumatic devices accounted for the major-
ity of emissions. Emissions from field production have
increased absolutely and as a proportion of total emis-
sions from natural gas systems—approximately 27 per-
cent between 1990 and 1996—due to an increased num-
ber of producing gas wells and related equipment, and
then leveled off in 1997 at 9.5 MMTCE.
Processing. In this stage, processing plants remove
various constituents from the raw gas before it is in-
jected into the transmission system. Fugitive emissions
from compressors, including compressor seals, were the
primary contributor from this stage. Processing plants
accounted for about 12 percent of methane emissions from
natural gas systems during the period of 1990 through 1997.
7 Preliminary estimate
Energy 2-27
-------
Transmission and Storage. Natural gas transmis-
sion involves high pressure, large diameter pipelines that
transport gas long distances from field production areas
to distribution centers or large volume customers. From
1990 to 1997, total natural gas transmission pipeline
milage varied, with an overall decline from about
280,000 miles to about 260,000 miles. Throughout the
transmission system, compressor stations pressurize the
gas to move it through the pipeline. Fugitive emissions
from compressor stations and metering and regulating
stations accounted for the majority of the emissions from
transmission. Pneumatic devices and engine exhaust
were smaller sources of emissions from transmission fa-
cilities. Methane emissions from the transmission stage
accounted for approximately 35 percent of the emissions
from natural gas systems.
Natural gas is also injected and stored in under-
ground formations during periods of low demand, and
withdrawn, processed, and distributed during periods of
high demand. Compressors and dehydrators were the
primary contributors from these storage facilities. Less
than one percent of total emissions from natural gas sys-
tems can be attributed to these facilities.
Distribution. The distribution of natural gas requires
the use of low-pressure pipelines to deliver gas to custom-
ers. The distribution network consisted of nearly 1.4 mil-
lion miles of pipeline in 1996, increasing from a 1990 fig-
ure of just over 1.3 million miles (AGA 1996). Distribu-
tion system emissions, which accounted for approximately
27 percent of emissions from natural gas systems, resulted
mainly from fugitive emissions from gate stations and non-
plastic piping. An increased use of plastic piping, which
has lower emissions than other pipe materials, has reduced
the growth in emissions from this stage.
Overall, natural gas systems emitted 33.5 MMTCE
(5.9 Tg) of methane in 1997 (see Table 2-25 and Table
2-26). Emissions rose slightly from 1990 to 1997, re-
flecting an increase in the number of producing gas wells
and miles of distribution pipeline. Initiated in 1993,
EPA's Natural Gas STAR program is working with the
gas industry to promote profitable practices that reduce
methane emissions. The program is estimated to have
reduced emissions by 0.7, 1.2, 1.3 and 1.6 MMTCE in
1994, 1995, 1996, and 1997, respectively.
i
Methodology
The foundation for the estimate of methane emis-
sions from the U.S. natural gas industry is a detailed
study by the Gas Research Institute and EPA (GRI/EPA
1995). The GRI/EPA study developed over 100 detailed
emission factors and activity levels through site visits
to selected gas facilities, and arrived at a national point
Table 2-25: CH4 Emissions from
: H! ill1 .i „, I,1 'I,!,,:.. • l 'ii'llllll: • ' '{
Re d Production
,il'! lllllllllil.l : i ' " 'III "'"'I11 . n'JIilllll
Processing
Transmission and Storage
Distribution
total
Natural Gas Systems (MMTCE)
, .» i , , ,
1990 1991 1992
8.0 8.2 8.5
4.0 4.0 4.0
12.6 12.7 12.9
8.3 8.4 8.6 "
32.9 33.3 33.9
1993
"8.7"""
4.0
12.6
8.8
34.1
1994
I ,,'V ', i1
8.8
4.2"
12.5
8.7
33T
j
, i
1995
•.•,•..• I,
9.1
4.1-
12.5"
8.7 "
,. , . I
33.2
1996
"9.5'
4.1
12.4
9.1
33J
1
1997 •
9.5 " I
4.1 I
12.7 •
8.9 •
33.5 1
reductions from Natural Gas STAR program. Totals may not sum due to independent rounding. H
Natural Gas Systems (Tg)
i
1990 1991 1992
1.4 1.4 1.5
0.7 0.7 0.7
2.2 2.2 2.3
1.4 1.5 1.5
5.7 5.8 5.9
1993
' ,",'". 'i '
i.5
0.7
2.2
1.5
5.9
1994
:iiliin-'":
,1,5,,,
0.7
2.2
1.5
5.8
Note; 1994 through 1997 totals Include reductions from Natural Gas STAR program. Totals may not sum due to
'
I
1995
it
1,6,
0.7
2.2
1.5
5.8
1996
1.7
0.7
2.2
1.6
5.9
1
1997 •
1.7 ' 1
0.7 •
2.2 •
1.5
5.9
independent rounding.
i
2-28 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
estimate for 1992. Since publication of this study, EPA
conducted additional analysis to update the activity data
for some of the components of the system, particularly
field production equipment. Summing emissions across
individual sources in the natural gas system provided a
1992 baseline emission estimate from which the emis-
sions for the period 1990 through 1997 were derived.
Apart from the year 1992, detailed statistics on
each of the over 100 activity levels were not available
for the time series 1990 through 1997. To estimate these
activity levels, aggregate annual statistics were obtained
on the main driving variables, including: number of pro-
ducing wells, number of gas plants, miles of transmis-
sion pipeline, miles of distribution pipeline, and miles
of distribution services. By assuming that the relation-
ships among these variables remained constant (e.g., the
number of heaters per well remained the same), the sta-
tistics on these variables formed the basis for estimat-
ing other activity levels.
For the period 1990 through 1995, the emission
factors were held constant. A gradual improvement in
technology and practices is expected to reduce the emis-
sion factors slightly over time. To reflect this trend, the
emission factors were reduced by about 0.2 percent per
year starting with 1996, a rate that, if continued, would
lower the emission factors by 5 percent in 2020. See
Annex E for more detailed information on the method-
ology and data used to calculate methane emissions from
natural gas systems.
Data Sources
Activity data were taken from the American Gas
Association (AGA 1991,1992,1993,1994, 1995,1996,
1997), the Energy Information Administration's Annual
Energy Outlook (EIA 1997a), Natural Gas Annual (EIA
1997b), and Natural Gas Monthly (EIA 1998), and the
Independent Petroleum Association of America (IPAA
1997). The U.S. Department of Interior (DOI1997,1998)
supplied offshore platform data. All emission factors
were taken from GRI/EPA (1995).
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, scal-
ing up from model facilities introduces a degree of uncer-
tainty. Additionally, highly variable emission rates were
measured among many system components, making the
calculated average emission rates uncertain. Despite the
difficulties associated with estimating emissions from this
source, the uncertainty in the total estimated emissions are
believed to be on the order of ±40 percent.
Petroleum Systems
One of the gases emitted from the production and
refining of petroleum products is methane. The activi-
ties that lead to methane emissions include: production
field treatment and separation, routine maintenance of
production field equipment, crude oil storage, refinery
processes, crude oil tanker loading and unloading, and
venting and flaring. Each stage is described below:
Production Field Operations. Fugitive emissions
from oil wells and related production field treatment and
separation equipment are the primary source of emis-
sions from production fields. From 1990 to 1997, these
emissions accounted for about 10 percent of total emis-
sions from petroleum systems. Routine maintenance,
which includes the repair and maintenance of valves,
piping, and other equipment, accounted for less than 1
percent of total emissions from petroleum systems.
Emissions from production fields are expected to de-
cline in the future as the number of oil wells decreases.
Crude Oil Storage. Crude oil storage tanks emit meth-
ane during two processes. "Breathing losses" from roof
seals and joints occur when the tank is in use, and while
tanks are being drained or filled. "Working losses" occur
as the methane hi the air space above the liquid is displaced.
Piping and other equipment at storage facilities can also
produce fugitive emissions. Between 1990 and 1997, crude
oil storage emissions accounted for less than 1 percent of
total emissions from petroleum systems.
Energy 2-29
-------
Refining. Waste gas streams from refineries are a
source of methane emissions. Based on Tilkicioglu and
Winters (1989), who extrapolated waste gas stream emis-
sions to national refinery capacity, emissions estimates
from this source accounted for approximately 3 percent
of total methane emissions from the production and re-
fining of petroleum.
Ttinker Operations. The loading and unloading of
crude oil tankers releases methane. From 1990 to 1997,
emissions from crude oil transportation on tankers ac-
counted for roughly 2 percent of total emissions from
petroleum systems.
Venting and Flaring. Gas produced during oil pro-
duction that cannot be contained or otherwise used is
released into the atmosphere or flared. Vented gas typi-
cally has a high methane content; however, it is assumed
that flaring destroys the majority of the methane in the
gas (about 98 percent depending upon the moisture con-
tent of the gas). Venting and flaring may account for up
to 85 percent of emissions from petroleum systems.
There is considerable uncertainty in the estimate of
emissions from this activity.
In 1997 methane emissions from petroleum sys-
tems were 1.6 MMTCE (271 Gg) and have remained
essentially constant since 1990. Emission estimates are
provided below in Table 2-27 and Table 2-28.
Methodology
The methodology used for estimating emissions
from each stage is described below:
Production Field Operations^ Emission estimates
were calculated by multiplying emission factors (i.e.,
emissions per oil well) with their corresponding activ-
ity data (i.e., number of oil wells). To estimate emis-
sions for 1990 to 1997, emission factors developed to
estimate 1990 emissions were multiplied by updated
activity data for 1990 through 1997. Emissions estimates
from petroleum systems excluded associated natural gas
wells to prevent double counting with the estimates for
Natural Gas Systems.
Crude Oil Storage. Tilkicioglu and Winters (1989)
estimated crude oil storage emissions on a model tank farm
facility with fixed and floating roof tanks. Emission fac-
tors developed for the model facility were applied to pub-
lished crude oil storage data to estimate emissions.
Table 2-27: CH4 Emissions from Petroleum Systems (MMTCE)
ll'i.
I-':
,
Stage
^rgtlijgtlon, Field Operations
^^Sl^ioja1 ge
f|e;ft,[jjj>g
.fanner Operations
Renting and Flaring
Total
19!
, 0.
"" 4
0.
4
1.
1.
30
1
1
3
6
1991
0.1
0.1
4
1.3
1.6
1992
, 0,1
0.1
+
1.3
1.6
19!
0,
4
0.
4
1.
1.
93
,1,
.1
,3
6
1994
„ ,0,1,,
0.1
4
1.3
1.6
1995
.'.oX'
0.1
4
1.3
1.6
1996
0.1
0.1
4
1.3
1.5
1997
, ,0.1
0.1
4
1.3
1.6
,t D«3 not exceed 0.05 MMTCE
Hole1 Totals may not sum due to independent rounding.
Table 2-28: CH4 Emissions from Petroleum Systems (Gg)
1! '
1 ::
Stage
„,._... ; ;»^^^^^
production Field Operations
Crude 01 Storage
Refining
Tanker Operations
Venting and Flaring
Total
1990
24
2
10
6,
231
272
1991
25
2
10
6
231
273
1992
..'I'^i'.tilF'H!111"!111':
24'""
2
10
5
231
272
1993
:<'i »HW,ta
24
2
10
5
231
272
1994
24
2
10
5
231
272
1995
23
2
10
5 ;
231
271
1996
23
2
9
5
231
271
1997
23
2
9
5
231
271
it
tote: totals may not sum due to independent rounding.
2-30 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Refining. Tilkicioglu and Winters (1989) also es-
timated methane emissions from waste gas streams based
on measurements at ten refineries. These data were ex-
trapolated to total U.S. refinery capacity to estimate
emissions from refinery waste gas streams for 1990. To
estimate emissions for 1991 through 1997, the emissions
estimates for 1990 were scaled using updated data on
U.S. refinery capacity.
Tanker Operations. Methane emissions from
tanker operations are associated with the loading and
unloading of domestically-produced crude oil trans-
ported by tanker, and the unloading of foreign-produced
crude transported by tanker. The quantity of domestic
crude transported by tanker was estimated as Alaskan
crude oil production less Alaskan refinery crude utiliza-
tion, plus 10 percent of non-Alaskan crude oil produc-
tion. Crude oil imports by tanker were estimated as to-
tal imports less imports from Canada. An emission fac-
tor based on the methane content of hydrocarbon va-
pors emitted from crude oil was employed (Tilkicioglu
and Winters 1989). This emission factor was multiplied
by updated activity data to estimate total emissions for
1990 through 1997.
Venting and Flaring. Although venting and flar-
ing data indicate that the amount of venting and flaring
activity has changed over time, there is currently insuf-
ficient data to assess the change in methane emissions
associated with these fluctuations. Given the consider-
able uncertainty in the emissions estimate for this stage,
and the inability to discern a trend in actual emissions,
the 1990 emissions estimate was held constant for the
years 1991 through 1997.
See Annex F for more detailed information on the
methodology and data used to calculate methane emis-
sions from petroleum systems.
Data Sources
Data on the number of oil wells in production fields
were taken from the American Petroleum Institute (API
1998) as was the number of oil wells that do not pro-
duce natural gas. Crude oil storage, crude oil stocks,
crude oil production, utilization, and import data were
obtained from the U.S. Department of Energy (EIA 1991,
1992, 1993, 1994, 1995, 1996, 1997, 1998). U.S. refin-
ery capacity and Alaskan refinery crude capacity data
were extrapolated based on estimates for 1990 through
1996 (EIA 1990, 1991, 1992, 1993, 1994, 1995, 1997).
Emission factors were taken from Tilkicioglu and Win-
ters (1989) and EPA (1993).
Uncertainty
There are significant uncertainties associated with
all aspects of the methane emissions estimates from petro-
leum systems. Published statistics are inadequate for esti-
mating activity data at the level of detail required. Simi-
larly, emission factors for each stage remain uncertain. In
particular, there is insufficient information to estimate an-
nual venting and flaring emissions using published statis-
tics. EPA is currently undertaking more detailed analyses
of emissions from this source and anticipates that new in-
formation will be available for future inventories. Prelimi-
nary work suggests that emission estimates will increase.
Table 2-29 provides emission estimate ranges given the
uncertainty in the venting and flaring estimates.
Tahle 2-29: Uncertainty in CH4 Emissions from Petroleum Systems (Gg)
Stage
1990 1991 1992 1993 1994 1995 1996 1997
Venting and Flaring (point estimate)
Low
High
Total (point estimate)
Low
High
231
93
462
272
103
627
231
93
462
273
103
631
231
93
462
272
103
628
231
93
462
272
103
627
231
93
462
272
103
625
231
93
462
271
102
621
231
93
462
271
102
620
231
93
462
271
102
621
Energy 2-31
-------
Natural Gas Flaring and
Criteria Pollutant Emissions
from Oil and Gas Activities
The flaring of natural gas from oil wells is a small
source of carbon dioxide (CO2). In addition, oil and gas
activities also release small amounts of nitrogen oxides
(NOX), carbon monoxide (CO), and nonmethane vola-
tile organic compounds (NMVOCs). This source ac-
counts for only a small proportion of overall emissions
of each of these gases. Emissions of CO2, NOX, and CO
from petroleum and natural gas production activities are
all less than 1 percent of national totals, while NMVOC
emissions are roughly 3 percent of national totals.
Carbon dioxide emissions from petroleum produc-
tion result from natural gas that is flared (i.e., combusted)
at the production site. Barns and Edmonds (1990) noted
that of total reported U.S. venting and flaring, approxi-
mately 20 percent may be vented, with the remaining
80 percent flared; however, it is now believed that flar-
ing accounts for an even greater proportion, although
some venting still occurs. Methane emissions from vent-
ing are accounted for under Petroleum Systems. For
1997, the CO2 emissions from the flaring were estimated
to be approximately 4.2 MMTCE (15.2 Tg), an increase
of 82 percent since 1990 (see Table 2-30).
Criteria pollutant emissions from oil and gas pro-
duction, transportation, and storage, constituted a relatively
small and stable portion of the total emissions of these gases
for the 1990 to 1997 period (see Table 2-31).
Methodology
The estimates for CO2 emissions were prepared us-
ing an emission factor of 14.92 MMTCE/QBtu of flared
gas, and an assumed flaring efficiency of 100 percent. The
quantity of flared gas was estimated as the total reported
vented and flared gas minus a constant 12,031 million cu-
bic feet, which was assumed to be vented.18
Criteria pollutant emission estimates for NOX, CO,
and NMVOCs were determined using industry-published
production data and applying average emission factors.
Table 2-30: C02 Emissions from Natural
Gas Flaring
Year
MMTCE
Tg
1990
1991
1992
1993
1994
1995
1996
1997
2.3
2.6
2.6
3.5
3.6
4.5
4.3
4.2
: 8.4
9.6
„ 9-4
13.0
:: 13.1
16.4
, 15.7
. 15.2
Table 2-31: NOX, NMVOCs, and CO Emissions from
Oil and Gas Activities (Gg)
Year
NO,
CO
NMVOCs
1990
1991
1992
1993
1994
1995
1996
1997
139
110
134
111
106
100
100
104
302
313
337
337
307
316
316
330
555
581
574
588
587
582
469
488
Data Sources
Activity data in terms of total natural gas vented
and flared for estimating CO2 emissions from natural
gas flaring were taken from EIA's Natural Gas Annual
(EIA 1998). The emission and thermal conversion fac-
tors were also provided by EIA (see Table 2-32)
EPA (1998) provided emission estimates for NOX,
CO, and NMVOCs from petroleum refining, petroleum
product storage and transfer, and petroleum marketing
operations. Included are gasoline, crude oil and distil-
late 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 prima-
rily arise from assumptions concerning what proportion
of natural gas is flared and the flaring efficiency. The
portion assumed vented as methane in the methodology
for Petroleum Systems is currently held constant over
'* Sec the methodological discussion under Petroleum Systems for the basis of the portion of natural gas assumed vented.
2-32 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-32: Total Natural Gas Reported Vented
and Flared (million ft3) and Thermal Conversion
Factor (Btu/ft3)
Year
1990
1991
1992
1993
1994
1995
1996
1997
IB period
Vented and Flared
150,415
169,909
167,519
226,743
228,336
283,739
272,117
263,819
1990 through 1997 due
Thermal
Conversion Factor
1,106
1,108
1,110
1,106
1,105
1,106
1,106
1,106
to the uncertaintii
involved in the estimate. Uncertainties in criteria pol-
lutant emission estimates are partly due to the accuracy
of the emission factors used and projections of growth.
International Bunker Fuels
Emissions resulting from the combustion of fuels
used for international transport activities, termed inter-
national bunker fuels under the UN Framework Con-
vention on Climate Change (UNFCCC), are currently
not included in national emission totals, but are reported
separately on the basis of fuel sold in each country. The
decision to report emissions from international bunker
fuels separately, instead of allocating them to a particu-
lar country, was made by the Intergovernmental Negoti-
ating Committee in establishing the Framework Con-
vention on Climate Change.19 These decisions are re-
flected in the Revised 1996IPCC Guidelines, in which
countries are requested to report emissions from ships
or aircraft that depart from their ports and are engaged
in international transport separately from national to-
tals (IPCC/UNEP/OECD/IEA 1997). The Parties to the
UNFCCC have yet to decide on a methodology for allo-
cating these emissions.20
Greenhouse gases emitted from the combustion of
international bunker fuels, like other fossil fuels, include
carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O),
carbon monoxide (CO), oxides of nitrogen (NOX),
nonmethane volatile organic compounds (NMVOCs), par-
ticulate matter, and sulfur dioxide (SO^.21 Two transport
modes are addressed under the IPCC definition of interna-
tional bunker fuels: aviation and marine. 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, mili-
tary aviation comprises aircraft under the control of na-
tional armed forces, and general aviation applies to recre-
ational and small corporate aircraft. The IPCC Guidelines
further define international bunker fuel use as the fuel com-
busted for civil (commercial) aviation purposes by aircraft
arriving or departing on international flight segments. How-
ever, as mentioned above, only the fuel used by aircraft
taking-off (i.e., departing) from the United States are re-
ported here. The standard fuel used for civil aviation is
kerosene-type jet fuel, while the typical fuel used for gen-
eral aviation is aviation gasoline.22
Emissions of CO2 from aircraft are a function of
fuel use, whereas emissions per flight or ton-mile in the
case of cargo, are a function of flight path, fuel effi-
ciency of the aircraft and its engines, occupancy, and
load factor. Methane, N2O, CO, NOX, and NMVOC emis-
sions depend upon engine characteristics, flight condi-
tions, and flight phase (i.e., take-off, climb, cruise, de-
cent, 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
19 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) (contact secretariat@unfccc.de).
20 See FCCC/SBSTA/1996/9/Add.l and Add.2 for a discussions of allocation options for international bunker fuels (see http://www.unfccc.de/
fccc/docs/1996/sbsta/09aO 1 .pdf and /09a02.pdf).
21 Sulfur dioxide emissions from jet aircraft and marine vessels, although not estimated here, are mainly determined by the sulfur content of the
fuel. On average jet fuel has a sulfur content around 0.05 percent, while distillate diesel fuel averages around 0.3 percent and residual fuel oil
around 2.3 percent.
22 Naphtha-type jet fuel is used primarily by the military in turbojet and turboprop aircraft engines.
Energy 2-33
-------
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 air-
craft, near or in the ozone layer, is higher than that of
subsonic aircraft. At this higher altitude, NOX emissions
contribute to ozone depletion.23 At the cruising altitudes
of subsonic aircraft, however, NOX emissions contrib-
ute to the formation of ozone. At these lower altitudes,
the positive radiative forcing effect of ozone is most po-
tent.2"' The vast majority of aircraft NOX emissions oc-
cur at these lower cruising altitudes of commercial sub-
sonic aircraft25 (NASA 1996).
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, mili-
tary (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 larg-
est of the four categories. 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 at-
mospheric impacts of NOX from shipping are relatively
minor, as the emissions occur at ground level.
Overall, aggregate greenhouse gas emissions in
1997 from the combustion of international bunker fuels
from both aviation and marine activities decreased by 1
percent since 1990, to 26.8 MMTCE (see Table 2-33).
Although emissions from international flights depart-
ing from the United States have increased significantly
(33 percent), emissions from international shipping voy-
ages departing the United States appear to have decreased
by a greater absolute amount.26 The majority of these
emissions were in the form of carbon dioxide; however,
small amounts of CH4 and N2O were also emitted. Of
the criteria pollutants, emissions of NOX by aircraft at
cruising altitudes are of primary concern because of their
effects on ozone formation (see Table 2-38).
Emissions from both aviatior^ and marine interna-
tional transport activities are expected to grow in the
future as both air traffic and trade increase, although
emission rates should decrease over time due to techno-
logical changes.27 ;
Methodology
Emissions of CO2 were estimated through the ap-
plication of carbon content and fraction oxidized fac-
tors to fuel consumption activity data. This approach is
analogous to that described under CO2 from Fossil Fuel
Combustion. A complete description of the methodol-
ogy and a listing of the various factors employed can be
found in Annex A.
Emission estimates for CH4, N2O, CO, NOX, and
NMVOCs were calculated by multiplying emission fac-
tors by measures of fuel consumption by fuel type and
mode. Activity data for aviation included solely jet fuel
consumption statistics, while the marine mode included
both distillate diesel and residual fuel oil.
Data Sources
Carbon content and fraction oxidized factors for kero-
sene-type jet fuel, distillate fuel oil, and residual fuel oil
were taken directly from the Energy Information Adminis-
i
tration (EIA) of the U.S. Department of Energy and are
presented in Annex A. Heat content and density conver-
sions were taken from EIA (1998). Emission factors used
in the calculations of CH4, N2O, CO, NOX, and NMVOC
emissions were taken from the Revised 19961PCC Guide-
lines (IPCC/UNEP/OECD/ffiA 1997). For aircraft emis-
D In 1996, there were only around a dozen civilian supersonic aircraft in service around the world which flew at these altitudes, however.
** However, at this lower altitude, ozone does little to shield the earth from ultraviolet radiation.
15 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.
11 Most emission related international aviation and marine regulations are under the rubric of the International Civil Aviation Organization (ICAO)
Of the Internntkmat Maritime Organization (IMO), which develop international codes, recommendations, and conventions, such as the Interna-
tional Convention of the Prevention of Pollution from Ships (MARPOL).
2-34 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-33: Emissions from International Bunker Fuels (MMTCE)
Gas/Mode
1990
1991
1992
1993
1994
1995
1996
1997
C02
Aviation
Marine
CH4
Aviation
Marine
N20
Aviation
Marine
Total
27.1
10.5
16.6
+
+
+
0.2
0.1
0.1
27.3
27.8
10.5
17.3
+
+
+
0.2
0.1
0.1
28.0
29.0
11.0
18.0
+
+
+
0.2
0.1
0.1
29.3
29.9
11.2
18.7
+
+
+
0.3
0.1
0.1
30.2
27.4
11.6
15.8
+
+
+
0.2
0.1
0.1
27.6
25.4
12.4
13.0
+
+
+
0.2
0.1
0.1
25.7
25.4
12.8
12.6
+
+
+
0.2
0.1
0.1
25.6
26.6
13.9
12.7
+
+
+
0.2
0.1
0.1
26.8
+ Does not exceed 0.05 MMTCE
Note: Totals may not sum due to independent rounding. Excludes emissions from military fuel consumption. Includes aircraft cruise altitude
emissions.
Table 2-34: Emissions from International Bunker Fuels (Gg)
Gas/Mode
1990
1991
1992
1993
1994
1995
1996
1997
C02
Aviation
Marine
CH4
Aviation
Marine
N20
Aviation
Marine
CO
Aviation
Marine
NOX
Aviation
Marine
NMVOC
Aviation
Marine
99,258
38,432
60,826
2
1
1
3
1
1
99
63
35
1,777
152
1,625
53
9
43
101,925
38,450
63,475
2
1
1
3
1
2
100
63
37
1,849
152
1,697
54
9
45
106,404
40,413
65,990
2
1
1
3
1
2
105
66
39
1,923
160
1,764
57
10
47
109,605
41,100
68,505
2
1
1
3
1
2
108
68
40
1,993
162
1,831
59
10
49
100,377
42,491
57,886
2
1
1
3
1
1
104
70
34
1,716
168
1,547
52
10
41
93,296
45,528
47,768
2
1
+
3
1
1
103
75
28
1,459
180
1,278
45
11
34
92,991
46,957
46,034
2
1
+
3
1
1
104
77
27
1,417
186
1,231
44
12
33
97,542
50,974
46,568
2
1
+
3
2
1
111
84
27
1,448
202
1,246
46
13
33
Note: Totals may not sum due to independent rounding. Excludes emissions from military fuel consumption. Includes aircraft cruise altitude
emissions.
sions, 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 distil-
late diesel or residual fuel oil the following values, in the
same units, except where noted, were employed: 0.03 for
CH4,0.08 for N20, 1.9 for CO, 87 for NOX, and 0.052 g/
MJ for NMVOCs.
Activity data on aircraft fuel consumption were col-
lected from two government agencies. Jet fuel consumed
by U.S. flagged air carriers for international flight segments
was supplied by the Bureau of Transportation Statistics
(DOT/BTS 1998). 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 pur-
chased 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) un-
der the U.S. Department of Commerce (BEA 1998). Ap-
proximate average fuel prices paid by air carriers for air-
craft on international flights were taken from DOT/BTS
Energy 2-35
-------
(1998) and used to convert the BEA expenditure data to
gallons of fuel consumed. Final jet fuel consumption esti-
mates arc presented in Table 2-39.
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 un-
published data collected by the Foreign Trade Division
of the U.S. Department of Commerce's Bureau of the
Census (DOC 1998). These fuel consumption estimates
arc presented in Table 2-36.
Uncertainty
Emission estimates related to the consumption of
international bunker fuels are subject to the same uncer-
tainties as those from domestic aviation and marine mo-
bile source emissions; however, additional uncertainties
result from the difficulty in collecting accurate fuel con-
sumption activity data for international transport activi-
ties separate from domestic transport activities.28 For
example, smaller aircraft on shorter routes often carry
sufficient fuel to complete several flight segments with-
out refueling in order to minimize time spent at the air-
port gate or take advantage of lower fuel prices at par-
ticular airports. This practice, called tankering, when
done on international flights, complicates the use of fuel
sales data for estimating bunker fuel emissions.
i
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/BTS (1998) in-
ternational flight segment fuel data used for U.S. flagged
carriers does not include smaller air carriers and unfor-
tunately defines flights departing to Canada and some
flights to Mexico as domestic instead of international.
ii
As for the BEA (1998) data on foreign flagged carriers,
there is some uncertainty as to the average fuel price,
|j
and to the completeness of the data. It was also not pos-
sible 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.29
Table 2-35: Civil Aviation Jet Fuel Consumption for International Transport (million gallons)
1990
1991 1992 1993 1994 1995 1996 1997
U.S. Carriers
foreign Carriers'
Total
^bte-'foJals may not
1,982 1,970 2,069 2,078 2J55 2,256 ' 2,329"' 2,482
2,062 2,075 2,185 2,252 2,326 2,549 '2,629 2,900
4,043 4,045 4,254 4,330 4,482 4,804 4,958 5,382
sumduelo independent rbundlng.lxcludes military tt
Table 2-36: Marine Vessel Distillate and Residual Fuel Consumption for
International Transport (million gallons)
Fuel type
1990 1991 1992 1993 1994
1995 1996
1997
Residual Fuel Oil
- Distillate Diesel Fuel & Other
4,761
521
4,920
600
5,137
598
5,354
595
4,475
561
3,567
609
••I
3,504
510
3,495
573
: Noja; Excludes military fuel consumption. The density of residual fuel oil and distillate diesel fuel were assumed to be 3.575 and 3.192 kg/
"gallon, respectively. ' ' "
!(1 Sec uncertainly discussions under CO2 from Fossil Fuel Combustion and Mobile Source 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. !
2-36 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Although aggregate fuel consumption data has
been used to estimate emissions from aviation, the rec-
ommended method for estimating emissions in the Re-
vised 1996IPCC Guidelines is to use data by specific
aircraft type (IPCC/UNEP/OECD/IEA 1997). The IPCC
also recommends that cruise altitude emissions be esti-
mated separately using fuel consumption data, while
landing and take-off (LTO) cycle data be used to esti-
mate near-ground level emissions.30 The EPA is devel-
oping revised estimates based on this more detailed ac-
tivity data, and these estimates are to be presented in
future inventories.
There is also concern as to the reliability of the ex-
isting DOC (1998) data on marine vessel fuel consump-
tion reported at U.S. customs stations due to the signifi-
cant degree of inter-annual variation. Of note is that fuel
consumption data were not available for the year 1990;
therefore, an average of 1989 and 1991 data was employed.
No estimates of bunker fuel emissions resulting
from military aviation or marine activities have been
presented here because of a lack of detailed fuel con-
sumption data from the U.S. Department of Defense
(DOD). The DOD is developing their own institutional
greenhouse gas inventory, and therefore, future U.S. in-
ventories are expected to include estimates of military
bunker fuel emissions.
Wood Biomass and
Ethanol Consumption
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
carbon dioxide (CO2). However, in the long run the car-
bon dioxide emitted from biomass consumption does
not increase atmospheric carbon dioxide concentrations,
assuming the biogenic carbon emitted is offset by the
uptake of CO2 resulting from the growth of new biom-
ass. As a result, CO2 emissions from biomass combus-
tion 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 res-
ervoirs in wooded or crop lands are accounted for under
the Land-Use Change and Forestry sector.
In 1997, CO2 emissions due to burning of woody
biomass within the industrial and residential/commer-
cial sectors and by electric utilities were about 57.2
MMTCE (209.8 Tg) (see Table 2-37 and Table 2-38).
As the largest consumer of woody biomass, the indus-
trial sector in 1997 was responsible for 81 percent of the
CO2 emissions in from this source. The combined resi-
dential/commercial31 sector was the second largest emit-
ter, making up 18 percent of total emissions from woody
biomass. The commercial end-use sector and electric
utilities accounted for the remainder.
Since 1990, emissions of CO2 from biomass burn-
ing increased by a maximum of 12 percent in 1996, be-
fore falling back to a 3 percent increase in 1997. The
decrease in emissions from 1996 to 1997 was due to a
26 percent decline in woody biomass consumption in
the residential/commercial sector.
Biomass-derived fuel consumption in the United
States consisted mainly of ethanol use in the transporta-
tion sector. Ethanol is primarily produced from corn
grown in the Midwest, and was used mostly in the Mid-
west and 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 per-
cent gasoline, 10 percent ethanol blend known as gaso-
hol. Ethanol and ethanol blends are often used to fuel
public transport vehicles such as buses, or centrally fu-
eled fleet vehicles. Ethanol and ethanol blends are be-
lieved to burn "cleaner" than gasoline (i.e., lower in NOX
and hydrocarbon emissions), and have been employed
30 It should be noted that in the EPA's Draft National Air Pollutant Emissions Trends, 1900 -1997 (EPA 1998), 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 (1998) is also likely to include emissions from ocean-going vessels departing from U.S. ports on international voyages.
31 For this emissions source, data are not disaggregated into residential and commercial sectors.
Energy 2-37
-------
Table 2-37: C02 Emissions from Wood Consumption by End-Use Sector (MMTCE)
End-Use Sector
1990 1991 1992 1993 1994 1995 1996 1997
Electric Utility
industrial
Resrafintia^Commerclal
Total
0.5
42.4
12.7
55.6
0.5
42.3
13.4
56.2
0.5
44.5
14.1
59.0
0.4
45.4
12.9
58.8
0.4
4,6.6
127
59.7
I
0.4
45.4 L
14,0
59.7
0.4
48.0
14,0
62.4
0.4
46.4
10.4
57.2
Note: Totals may not sum due to independent rounding.
ii
Table 2-38: C02 Emissions from Wood Consumption by End-Use Sector (Tg)
End-Use Sector 1990 1991 1992 1993 1994 1995 1996 1997
Etelc Utility
Industrial
;itsljJppM?CQ:rprnf;cli|
Total
17
155.6
46,4,,
203.8
1.7
155.2
4.9.0
205.9
17
163.2
5,1,5
216.5
1.6
166.5
47.3,
215.4
1.6
170.9
, 4,6,5
219.0
1.4,,
166.5,
51 .£,...
219.1
16
175.8
51.4
228.8
1.5,
170.3
38.0
209.8
' Mole: Totals may not sum due to independent rounding.
in urban areas with poor air quality. However, because
ethanol is a hydrocarbon fuel, its combustion emits CO2.
In 1997, the United States consumed an estimated
97 trillion Btus of ethanol (1.3 billion gallons). Emis-
sions of CO2 in 1997 due to ethanol fuel burning were
estimated to be approximately 1.8 MMTCE (6.7 Tg) (see
Table 2-39). Between 1990 and 1991, emissions of CO2
due to ethanol fuel consumption fell by 21 percent. Af-
ter this decline, emissions from ethanol steadily in-
creased through 1997, except for a sharp decline in 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, reaching close to normal levels at the
end of the year. However, total 1996 ethanol production
Table 2-39: C02 Emissions from
Ethanol Consumption
Year
MMTCE
1990 1
1991 1
, ,,1912 ;
ji , i" ,1 1993
' " ' 1 1 1^94
I SSM^Sfe 2
1996 - 1
" ' : 1997 1
.6
.2
,,5
,7
A" "
.0
.4
.8
5.7
4.5
5,5
6.1
", l,6"7 "i ,;;,;:
7,2
5.1
6.7
fell far short of the 1995 level (EIA, 1997). Production
in 1997 returned to normal historic levels.
Methodology
Woody biomass emissions were estimated by
converting U.S. consumption data in energy units (17.2
million Btu per short ton) to megagrams (Mg) of dry
matter using EIA assumptions. Once consumption data
for each sector were converted to megagrams of dry
matter, the carbon content of the dry fuel was estimated
based on default values of 45 to 50" percent carbon in
dry biomass. The amount of carbon released from com-
bustion was estimated using 87 percent for the fraction
oxidized (i.e., combustion efficiency). Ethanol con-
sumption data in energy units were also multiplied by
a carbon coefficient (18.96 mg C/Btu) to produce car-
bon emission estimates.
Data Sources
Woody biomass consumption data were provided
by EIA (1998) (see Table 2-40). The factor for convert-
ing energy units to mass was supplied by EIA (1994).
Carbon content and combustion efficiency values were
taken from the Revised 1996IPCC Guidelines (IPCC/
UNEP/OECD/IEA 1997).
2-38 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 2-40: Woody Biomass Consumption
by Sector (Trillion Btu)
Year
1990
1991
1992
1993
1994
1995
1996
1997
Industrial
1,948
1,943
2,042
2,084
2,138
2,084
2,200
2,132
Residential/
Commercial
581
613
645
' 592
582
641
644
475
Electric
Utility
21
21
22
20
20
17
20
19
Table 2-41: Ethanol Consumption
Year Trillion Btu
1990
1991
1992
1993
1994
1995
1996
82
65
79
88
97
104
74
Emissions from ethanol were estimated using con-
sumption data from EIA (1998) (see Table 2-41). The
carbon coefficient used was provided by OTA (1991).
Uncertainty
The combustion efficiency factor used is believed
to under estimate the efficiency of wood combustion pro-
cesses in the United States. The IPCC emission factor
has been used because better data are not yet available.
Increasing the combustion efficiency would increase
emission estimates. In addition, according to EIA (1994)
commercial wood energy use is typically not reported
because there are no accurate data sources to provide
reliable estimates. Emission estimates from ethanol pro-
duction are more certain than estimates from woody bio-
mass consumption due to better activity data collection
methods and uniform combustion techniques.
Energy 2-39
-------
-------
3. 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 cement production, lime manufacture, limestone
and dolomite use (e.g., flux stone, flue gas desulfurization, and glass manufacturing), soda ash production and use,
CO2 consumption, iron and steel production, ammonia manufacture, ferroalloy production, aluminum production,
petrochemical production (including carbon black, ethylene, dicholoroethylene, styrene, and methanol), silicon car-
bide production, adipic acid production, and nitric acid production (see Figure 3-1).1
In addition to the three Figure 3-1
greenhouse gases listed above,
there are also industrial sources of
several classes of man-made flu-
orinated compounds called
hydrofluorocarbons (HFCs),
perfluorocarbons (PFCs), and sul-
fur 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,
they will continue to accumulate
in the atmosphere as long as emis-
sions continue. Sulfur hexafluo-
ride, itself, is the most potent
greenhouse gas the EPCC has ever
evaluated. Usage of these gases,
especially HFCs, is growing rap-
Substitution of Ozone Depleting Substances
Cement Manufacture
HCFC-22 Production
Electrical Transmission and Distribution
Adipic Acid
Lime Manufacture
Nitric Acid
Magnesium Production and Processing
Aluminum Production
Limestone and Dolomite Use ^H
Semiconductor Manufacture H
Soda Ash Manufacture and Consumption HJ
Petrochemical Production |
Carbon Dioxide Consumption |
Silicon Carbide Production <0.05
Portion of All
Emissions
6 8 10
MMTCE
12 14
1 Carbon dioxide emissions from iron and steel production, ammonia manufacture, ferroalloy production, and aluminum production are
included in the Energy chapter under Fossil Fuel Combustion of industrial coking coal, natural gas, and petroleum coke.
Industrial Processes 3-1
-------
idly 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, 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 pro-
duction and processing.
In 1997, industrial processes generated emission
of 63.0 MMTCE, or 3.5 percent of total U.S. greenhouse
gas emissions. Carbon dioxide emissions from all indus-
trial processes were 17.8 MMTCE (65.2 Tg) in the same
year. This amount accounted for only 1 percent of na-
tional CO2 emissions. Methane emissions from petro-
chemical and silicon carbide production resulted in emis-
sions of approximately 0.4 MMTCE (0.1 Tg) in 1997,
which was less than 1 percent of U.S. CH4 emissions.
Nitrous oxide emissions from adipic acid and nitric acid
production were 7.8 MMTCE (0.1 Tg) in 1997, or 7 per-
cent of total U.S. N2O emissions. In the same year, com-
bined emissions of HFCs, PFCs and SF6 totaled 37.1
MMTCE. Overall, emissions from industrial processes
increased by 39 percent from 1990 to 1997.
Emission estimates are presented in this chapter
for several industrial processes that are actually accounted
for within the Energy chapter. Although CO2 emissions
from iron and steel production, ammonia manufacture,
ferroalloy production, and aluminum production are not
the result of the combustion of fossil fuels for energy,
their associated emissions are captured in the fuel data
for industrial coking coal, natural gas, industrial coking
coal, and petroleum coke, respectively. Consequently, if
til emissions were attributed to their appropriate chap-
ter, then emissions from energy would decrease by
roughly 33 MMTCE in 1997, and industrial process
emissions would increase by the same amount.
Greenhouse gases are also emitted from a number
of industrial processes not addressed in this chapter. For
example, caprolactam—a chemical feedstock for the
manufacture of nylon 6,6—and urea production are be-
lieved to be industrial sources of N2O emissions. How-
ever, emissions for these and other sources have not been
estimated at this time due to a lack of information on the
emission processes, manufacturing data, or both. As more
information becomes available, emission estimates for
these processes will be calculated and included in future
greenhouse gas emission inventories, although their con-
tribution is expected to be small.2
i
The general method employed to estimate emis-
sions for industrial processes, as recommended by the
Intergovernmental Panel on Climate Change (IPCC),
generally involved multiplying production data for each
process by an emission factor per unit of production. The
emission factors used were either derived using calcula-
tions that assume precise and efficient chemical reactions
or were based upon empirical data in published refer-
ences. As a result, uncertainties in the emission coeffi-
ii
cients can be attributed to, among other things, ineffi-
ciencies in the chemical reactions associated with each
production process or to the use of empirically derived
emission factors that are biased and, therefore, may not
represent U.S. national averages. Additional sources of
uncertainty specific to an individual source category are
discussed in each section.
Table 3-1 summarizes emissions for the Industrial
•I
Processes chapter in units of million metric tons of car-
bon equivalents (MMTCE), while unweighted gas emis-
sions in teragrams (Tg) are provided in Table 3-2.
Cement Manufacture
Cement manufacture is an energy and raw mate-
rial intensive process resulting in the generation of car-
bon dioxide (CO2) from both the energy consumed in
making the cement and the chemical process itself.3 Ce-
* Sec, Annex P for a discussion of emission sources excluded.
* The COj emissions related to the consumption of energy for cement manufacture are accounted for under CO2 from Fossil Fuel Combustion
in the Energy chapter.
3-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 3-1: Emissions from Industrial Processes (MMTCE)
Gas/Source
1990 1991 1992 1993 1994 1995 1996 1997
C02
Cement Manufacture
Lime Manufacture
Limestone and Dolomite Use
Soda Ash Manufacture and Consumption
Carbon Dioxide Consumption
Iron and Steel Production*
Ammonia Manufacture*
Ferroalloy Production*
Aluminum Production*
CH4
Petrochemical Production
Silicon Carbide Production
N20
Adipic Acid Production
Nitric Acid Production
HFCs, PFCs, and SFB
Substitution of Ozone Depleting Substances
Aluminum Production
HCFC-22 Production
Semiconductor Manufacture
Electrical Transmission and Distribution
Magnesium Production and Processing
Total
14.9
8.9
3.3
1.4
1.1
0.2
23.9
6.3
0.5
1.6
0.3
0.3
+
8.1
4.7
3.3
22.2
0.3
4.9
9.5
0.2
5.6
1.7
45.4
14.6
8.7
3.2
1.3
1.1
0.2
19.2
6.4
0.4
1.7
0.3
0.3
+
8.3
4.9
3.3
21.6
0.2
4.7
8.4
0.4
5.9
2.0
44.8
14.6
8.8
3.3
1.2
1.1
0.2
20.7
6.7
0.4
1.6
0.3
0.3
+
8.0
4.6
3.4
23.0
0.4
4.1
9.5
0.6
6.2
2.2
46.0
15.1
9.3
3.4
1.1
1.1
0.2
21.0
6.4
0.4
1.5
0.4
0.4
+
8.4
4.9
3.5
23.4
1.4
3.5
8.7
0.8
6.4
2.5
47.2
16.0
9.6
3.5
1.5
1.1
0.2
21.6
6.6
0.4
1.3
0.4
0.4
+
8.9
5.2
3.7
25.9
4.0
2.8
8.6
1.0
6.7
2.7
51.2
16.9
9.9
3.7
1.9
1.2
0.3
22.2
6.5
0.4
1.4
0.4
0.4
+
9.0
5.2
3.7
30.8
9.5
2.7
7.4
1.2
7.0
3.0
57.0
17.3
9.9
3.8
2.0
1.2
0.3
21.6
6.6
0.5
1.4
0.4
0.4
+
9.2
5.4
3.9
34.7
11.9
2.9
8.5
1.4
7.0
3.0
61.6
17.8
10.2
3.9
2.1
1.2
0.3
23.5
7.1
0.5
' 1.4
0.4
0.4
+
7.8
3.9
3.8
37.1
14.7
2.9
8.2
1.3
7.0
3.0
63.0
+ Does not exceed 0.05 MMTCE
* Emissions from these sources are accounted for in the Energy chapter and are not included in the Industrial Processes totals.
Note: Totals may not sum due to independent rounding.
Table 3-2: Emissions from Industrial Processes (Tg)
Gas/Source
1990 1991 1992 1993 1994 1995 1996 1997
C02
Cement Manufacture
Lime Manufacture
Limestone and Dolomite Use
Soda Ash Manufacture and Consumption
Carbon Dioxide Consumption
Iron and Steel Production3
Ammonia Manufacture3
Ferroalloy Production3
Aluminum Production3
CH4
Petrochemical Production
Silicon Carbide Production
H20
Adipic Acid Production
Nitric Acid Production
HFCs, PFCs, and SF6
Substitution of Ozone Depleting Substances
Aluminum Production
HCFC-22 Production"
Semiconductor Manufacture
Electrical Transmission and Distribution0
Magnesium Production and Processing0
54.6
32.6
11.9
5.1
4.1
0.8
87.6
23.1
1.8
6.0
0.1
0.1
+
0.1
0.1
+
M
M
M
+
M
+
+
53.4
31.9
11.7
4.9
4.0
0.8
70.6
23.4
1.6
6.1
0.1
0.1
+
0.1
0.1
+
M
M
M
+
M
+
+
53.7
32.1
12.1
4.5
4.1
0.9
75.8
24.4
1.6
5.9
0.1
0.1
+
0.1
0.1
+
M
M
M
+
M
+
+
55.3
33.9
12.4
4.1
4.0
0.9
77.1
23.4
1.5
5.4
0.1
0.1
+
0.1
0.1
+
M
M
M
+
M
+
+
58.6
35.4
12.8
5.5
4.0
0.9
79.0
24.3
1.6
4.8
0.1
0.1
+
0.1
0.1
+
M
M
M
+
M
+
+
62.0
36.1
13.6
7.0
4.3
1.0
81.4
23.7
1.6
5.0
0.1
0.1
+
0.1
0.1
+
M
M
M
+
M
+
+
63.4
36.4
14.1
7.5
4.3
1.1
79.0
24.2
1.7
5.3
0.1
0.1
+
0.1
0.1
+
M
M
M
+
M
+
+
65.2
37.5
14.2
7.8
4.4
1.2
86.1
26.1
1.8
5.3
0.1
0.1
+
0.1
0.1
+
M
M
M
+
M
+
+
+ Does not exceed 0.05 Tg
M (Mixture of gases)
a Emissions from these sources are accounted for in the Energy
chapter and are not included in the Industrial Processes totals.
6 HFC-23 emitted
0 SF6 emitted
Note: Totals may not sum due to independent rounding.
Industrial Processes 3-3
-------
ment production accounts for about 2.4 percent of total
global industrial and energy-related CO2 emissions (IPCC
1996), and the United States is the world's third largest
cement producer. Cement is manufactured in almost ev-
ery state and is used in all of them. Carbon dioxide, emit-
ted from the chemical process of cement production, rep-
resents one of the largest sources of industrial CO2 emis-
sions in the United States.
During cement production process, calcium car-
bonate (CaCO3) is heated in a cement kiln at a tempera-
lure of l,93(PC (3,500°F) to form lime (i.e., calcium ox-
ide or CaO) and CO2. This process is known as calcina-
tion 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, re-
sults in additional CO2 emissions. However, this addi-
tional lime is already accounted for in the Lime Manu-
facture source category in this chapter; therefore, the
additional emissions from making masonry cement from
clinker are not counted in this source's total. They are
presented here for informational purposes only.
In 1997, U.S. clinker production—including Puerto
Rico—totaled 73,889 thousand metric tons, and U.S.
masonry cement production reached 3,473 thousand
metric tons (USGS 1998). The resulting emissions of CO2
from clinker production were estimated to be 10.2
MMTCE (37.5 Tg) (see Table 3-3). Emissions from ma-
sonry production from clinker raw material were esti-
mated to be 0.02 MMTCE (0.09 Tg) in 1997, but again
are accounted for under Lime Manufacture.
After falling in 1991 by 2 percent from 1990 lev-
els, cement production emissions have grown every year
since. Overall, from 1990 to 1997 emissions increased
by 15 percent. In 1997, output by cement plants increased
3 percent over 1996, to 73,889 thousand metric tons.
Cement is a critical component of the construction in-
dustry; therefore, the availability of public construction
funding, as well as overall economic growth, will have
considerable influence on cement production in the fu-
Table 3-3: C02 Emissions from Cement Production*
Year
MMTCE
Tg
1990
1991
1992
1993
1994
1995
1996
1997
8.9
8.7
8.8
, ,!„,
9.3
9.7
9.9
9.9 "
10.2 ;
32.6
31.9
32.1
33.9
35.4
36.1
36.4
37.5
* Totals exclude C02 emissions from making masonry cement
from clinker, which are accounted for under Lime Manufacture.
I
ture. In the near term, a strong domestic economy and
the passage of the Federal Highway Act are two key fac-
tors that may lift the market for construction materials
and, thus, create growth in the cement industry.
Methodology
Carbon dioxide emissions from cement manufac-
ture are created by the chemical reaction of carbon-con-
taining minerals (i.e., calcining limqstone). 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 pro-
portional to the lime content of the clinker. During calci-
nation, 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 ap-
plying 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/UNEP/OECD/IEA 1997) and a con-
stant reflecting the mass of CO2 released per unit of lime.
This yields an emission factor of 0.507 tons of CO2 per
ton of clinker produced. The emission factor was calcu-
lated as follows:
EFclinker = 0.646 CaO x
44.01 g/mole CO2
56.08 g/mole CaO
0.507 tons CO2/ton clinker
3-4 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
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 approxi-
mately 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 percentage (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 pro-
duction are accounted for in the section on CO2 emis-
sions from Lime Manufacture. Thus, these emissions
were estimated in this chapter for informational purposes
only, and are not included in the cement emission totals.
Data Sources
The activity data for cement and clinker produc-
tion (see Table 3-4) were taken from U.S. Geological
Survey (USGS 1992,1995,1996,1997,1998); the 1997
figure was adjusted, as stated below, from USGS, Min-
eral Industry Surveys: Cement in December 1997. The
data were compiled by USGS through questionnaires sent
to domestic clinker and cement manufacturing plants.
For 1997, clinker figures were not yet available. Thus, as
recommended by the USGS, clinker production was es-
timated for 1997 by subtracting 5 percent from Portland
cement production (Portland cement is a mixture of clin-
ker and approximately 5 percent gypsum) and by sub-
tracting imported clinker.
Uncertainty
The uncertainties contained in these estimates are
primarily due to uncertainties in the lime content of clin-
ker and in the amount of lime added to masonry cement.
For example, the lime content of clinker varies from 64
Table 3-4: Cement Production
(Thousand Metric Tons)
Year
Clinker
Masonry
1990
1991
1992
1993
1994
1995
1996
1997
64,355
62,918
63,415
66,957
69,786
71,257
71,706
73,889
3,209
2,856
3,093
2,975
3,283
3,603
3,469
3,473
to 66 percent. Also, some amount of CO2 is reabsorbed
when the cement is used for construction. As cement re-
acts with water, alkaline substances such as calcium hy-
droxide are formed. During this curing process, these
compounds may react with CO2 in the atmosphere to cre-
ate calcium carbonate. This reaction only occurs in
roughly the outer 0.2 inches of surface area. Since the
amount of CO2 reabsorbed is thought to be minimal, it is
not considered in this analysis.
Lime Manufacture
Lime, or calcium oxide (CaO), is an important
manufactured product with many industrial, chemical,
and environmental applications. Lime has historically
ranked fifth in total production of all chemicals in the
United States. Its major uses are in steel making, flue
gas desulfurization (FGD) at coal-fired electric power
plants, construction, pulp and paper manufacturing, and
water purification. 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 driven 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)4 production.
Lime production in the United States—including
Puerto Rico—was reported to be 19,300 thousand metric
1 Precipitated calcium carbonate is a specialty filler used in premium-quality coated and uncoated papers.
Industrial Processes 3-5
-------
tons in 1997 (USGS 1998). This resulted in CO2 emissions
of 3.9 MMTCE (14.2 Tg) (seeTable 3-5 and Table 3-6).
Domestic lime manufacture has increased every
year since 1991, when it declined by 1 percent from 1990
levels. Production in 1997 increased 1 percent over that
in 1996 to about 19,300 thousand metric tons. Overall,
from 1990 to 1997, CO2 emissions increased by 19 per-
cent. This increase is attributed in part to growth in de-
mand for environmental applications. In 1993, the U.S.
Environmental Protection Agency (EPA) completed regu-
lations under the Clean Air Act capping sulfur dioxide
(SO2) emissions from electric utilities. This action re-
sulted in greater lime consumption for flue gas desulfu-
rization systems, which increased by 16 percent in 1993
(USGS 1994). At the turn of the century, over 80 percent
ofltme consumed in the United States went for construc-
tion uses. However by the 1990s over 90 percent was
consumed for chemical and industrial purposes, of which
28 percent were environmental uses (USGS 1997).
Table 3-5: Net C02 Emissions from Lime
Manufacture
• III
.1 lllllll1
IT i
Year
i" 1,1990
1991
1992
1993
1994
1995
1996
1997
MMTCE
3;g •
3.2
"3.3
3 A
3.5
3.7
3.8
3.9
Table 3-6: C02 Emissions from Lime
Manufacture (Tg)
Methodology
During the calcination stage of lime manufacture,
CO2 is driven off as a gas and normally exits the system
with the stack gas. The mass of CO? released per unit of
lime produced can be calculated based on stoichiometry:
(44.01 g/mole CO2) -r (56.08 g/mole CaO) =
0.785 g CO2/g CaO
,1
Lime production in the United States was 19,300
thousand metric tons in 1997 (USGS 1998), resulting in
potential CO2 emissions of 15.1 Tg. Some of the CO2
generated during the production process, however, was
recovered for use in sugar refining and precipitated cal-
cium carbonate (PCC) production. Combined lime manu-
facture by these producers was 1,470 thousand metric
tons in 1997, generating 1.2 Tg of CO2. It was assumed
that approximately 80 percent of the CO2 involved in
sugar refining and PCC was recovered.
Data Sources
The activity data for lime manufacture and lime
consumption by sugar refining and precipitated calcium
carbonate (PCC) for 1990 through 1992 (see Table 3-7)
were taken from USGS (1991, 1992); for 1993 through
1994 from Michael Miller (1995); for 1995 through 1996
from USGS (1997); and for 1997 from USGS (1998).
Uncertainty
The term "lime" is actually a general term that in-
cludes various chemical and physical forms of this com-
modity. Uncertainties in the emission estimate can be at-
tributed to slight differences in the chemical composition
of these products. For example, although much care is taken
:: ; •:„.„•,_::::„::::- ::;:_:; :;:::::::::.,,:;;:: ,.; :„:;;: ,::,:::,:,::, Net
IP , s, . , , fpr Potential Recovered* Emissions
» > :*iii . :iiiiii!it:iii! mFHWM lEiiiiiii i: i i i
1990 12.5 (0.5) 11.9
;;;,;:".; ,1,991 12J ; (0.6) 1.1.7
1992 12.7 (0.6) 12.1
;;: ,„;:;:: isss 13:2 ; (os) 12.4
" "l!;!;!;"l:; ":1994 137 (09) 128
^9S 14.5 (0.9) 13.6
1 JIli ,19,96 "j^.O (0.9) 14.1
"997 15.1 (0.9) 14.2
* For sugar refMng and precipitated calcium carbonate
production
Ne'e: Totals may not sum due to independent rounding.
Table 3-7: Lime Production and Lime Use for Sugar
Refining and PCC (Thousand Metric Tons)
Year Production Use
1990
1991
1992
1993
-f QQ/1
i yy't
1995
1996
1997
• ' ''.'•• ",;", •;".
15,859
15,694
16,227
16,800
17,400
18,500
19,100
19,300
'•'•' :;:";" "' '•i'r:!
826
964
1,023
1,310
1,377
1,504
1,428
1,470
:; ", . . ;
3-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
to avoid contamination during the production process, lime
typically contains trace amounts of impurities such as iron
oxide, alumina and silica. Due to differences in the lime-
stone 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. In most processes that use lime (e.g., water soft-
ening), CO2 reacts with the lime to create calcium carbon-
ate. This is not necessarily true about lime consumption in
the steel industry, however, which is the largest consumer
of lime. 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.
As more information becomes available, this emission esti-
mate will be adjusted accordingly.
In some cases, lime is generated from calcium car-
bonate by-products at paper mills and water treatment
plants.5 The lime generated by these processes is not in-
cluded in the USGS data for commercial lime consump-
tion. In the paper industry, mills which employ the sul-
fate process (i.e., Kraft) consume lime in order to
causticize a waste sodium carbonate solution (i.e., black
liquor). Most sulfate mills recover the waste calcium car-
bonate after the causticizing operation and calcine it back
into lime—thereby generating CO2—for reuse in the
pulping process. However, some of these mills capture
the CO2 released in this process to be used as precipi-
tated calcium carbonate (PCC). Further research is nec-
essary to determine to what extent CO2 is released to the
atmosphere through generation of lime by paper mills.
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 pro-
cess. Further research is necessary to determine the de-
gree to which lime recycling is practiced by water treat-
ment plants in the United States.
Limestone and Dolomite Use
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 environ-
mental 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 as part of a process to generate CO2 as a by-prod-
uct. For example, limestone can be used as a flux or pu-
rifier in metallurgical furnaces, as a sorbent in flue gas
desulfurization (FGD) systems for utility and industrial
plants, or as a raw material in glass manufacturing.
In 1997, approximately 15,288 thousand metric
tons of limestone and 2,239 thousand metric tons of do-
lomite were used for these applications. Overall, both
limestone and dolomite usage resulted in aggregate CO2
emissions of 2.1 MMTCE (7.8 Tg) (see Table 3-8 and
Table 3-9).
Emissions in 1997 increased 4 percent from the
previous year. Although they decreased slightly in 1991,
1992, and 1993, CO2 emissions from this source have
since increased 53 percent from the 1990 baseline. In
the future, gradual increases in demand for crushed stone
are anticipated based on the volume of work on highway
and other infrastructure projects, and the overall growth
in the U.S. economy. The increases will also be influ-
enced by construction activity for both publicly and pri-
vately funded projects.
Methodology
Carbon dioxide emissions were calculated by mul-
tiplying the amount of limestone consumed by an aver-
age carbon content for limestone, approximately 12.0
percent for limestone and 13.2 percent for dolomite
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 [CaCOJ. 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 to the atmosphere.
6 Limestone and dolomite are collectively referred to as limestone by the industry, and intermediate varieties are seldom distinguished.
Industrial Processes 3-7
-------
Table 3-8: C02 Emissions from Limestone & Dolomite Use (MMTCE)
1990 1991 1992 1993 1994
1995 1996 1997
Flux Stone
Glass, Making
FGB
.Mi .
0.8
+
0.5
, 1.4
0.7
+
0.6
1.3
0.6
0.1
0.5
1.2
0.5
0.1
0.5
1.1
0.8
0.1
0.6
1.5
II '
1.1
0.1
0.7
1-9
1 2
0.2
0.7
2.0
1 2
0.2
0.8
2.1
4 Does not exceed 0.05 MMTCE
Note; Totals may not sum due to Independent rounding.
Table 3-9: C02 Emissions from Limestone & Dolomite Use (Tg)
Activity
1990 1991 1992 1993 1994 1995 1996
Flux Stone
Umeslone
Dolomite
Glass Making
Limestone
Dolomite
FGD
Total
3.0
2.6
0.5
0.2
0.2
MA
1.9
5.1
2.7
2.3
0.4
0.2
0.2
NA
2.0
4.9
2.3
2.0
0.4
0.2
0.2
NA
2.0
4.5
1.9
1.6
0.3
0.3
0.3
NA
1.9
4.1
3.0
2.1
0.8
0.4
0.4
NA
2.2
5.5
3.9
2.5
1.4
0.5
0.4
0.1
2.6
7.0
4.2
3.3
09
0.6
0.4
0.1
2.7
7.5
4.5
35
1 0
0 6
0.5
0.1
2.8
7.8
NA (Hot Available)
Note: Totals may not sum due to independent rounding.
(based on stoiehiometry). Assuming that all of the car-
bon was released into the atmosphere, the appropriate
emission factor was multiplied by the annual level of
consumption for flux stone, glass manufacturing, and
FGD systems to determine emissions.
Data Sources
Consumption data for 1990 through 1997 of lime-
stone and dolomite used as flux stone and in glass manu-
facturing (see Table 3-10) were obtained from the USGS
(1991,' 1993, 1996, 1997, 1998). Consumption data for
limestone used in FGD were taken from unpublished
survey data in the Energy Information Administration's
Form EI-767, "Steam Electric Plant Operation and De-
sign Report," (EIA 1997).
For 1990, 1994, and 1997, the USGS did not pro-
vide a breakdown of limestone and dolomite production
by end-use. Consumption figures for these years were
estimated by assuming that limestone and dolomite ac-
counted for the same percentage of total crushed stone
consumption for a given year as the average of the per-
centages for the years before and after (exception: 1990
and 1997 consumption were estimated using the percent-
ages for only 1991 and 1996, respectively). Also, start-
ing in 1996, USGS discontinued reporting glass manu-
facture separately. From 1996 onward, limestone used
in glass manufacture is estimated based on its percent of
total crushed stone for 1995.
It should be noted that there is a large quantity of
crushed stone reported to the USGS under the category
"unspecified uses". A portion of this consumption is be-
lieved to be limestone or dolomite used as flux stone and
for glass manufacture. The quantity listed for "unspeci-
fied uses" was, therefore, allocated to each reported end-
use according to each end-uses fraction of total consump-
tion in that year.7
Uncertainty
Uncertainties in this estimate are due to variations
in the chemical composition of limestone. In addition to
calcite, limestone may contain smaller amounts of mag-
nesia, silica, and sulfur. The exact specifications for lime-
stone or dolomite used as flux stone vary with the pyro-
metallurgical process, the kind of ore processed, and the
1 This approach was recommended by USGS.
3-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 3-10: Limestone & Dolomite Consumption (Thousand Metric Tons)
Activity
1990
1991 1992 1993 1994 1995 1996 1997
Flux Stone
Limestone
Dolomite
Glass Making
Limestone
Dolomite
FGD
5,797
932
430
NA
4,369
5,213
838
386
NA
4,606
4,447
737
495
NA
4,479
3,631
632
622
NA
4,274
4,792
1,739
809
NA
5,080
5,734
2,852
958
216
5,839
7,569
1,899
1,011
228
6,115
7,967
1,999
1,064
240
6,257
NA (Not Available)
final use of the slag. Similarly, the quality of the lime-
stone used for glass manufacturing will depend on the
type of glass being manufactured. Uncertainties also ex-
ist 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. Furthermore,
some of the limestone reported as "limestone" is believed
to actually be dolomite, which has a higher carbon con-
tent than limestone.
Soda Ash Manufacture and
Consumption
Soda ash (sodium carbonate, Na2CO3) is a white
crystalline solid that is readily soluble in water and
strongly 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 de-
tergents, 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 pro-
duces 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 two states produce natural soda ash: Wyo-
ming and California. Of these two states, only Wyoming
has net emissions of CO2. This difference is a result of
the production processes employed in each state.8 Dur-
ing the production process used in Wyoming, natural
sources of sodium carbonate are heated and transformed
into a crude soda ash that requires further refining. Car-
bon dioxide (CO2) is generated as a by-product of this
reaction, and is eventually emitted into the atmosphere.
In addition, CO2 may also be released when soda ash is
consumed.
In 1997, CO2 emissions from the manufacture of
soda ash from trona were approximately 0.5 MMTCE
(1.7 Tg). Soda ash consumption in the United States also
generated 0.8 MMTCE (2.8 Tg) of CO2 in 1997. Total
emissions from this source in 1997 were then 1.2
MMTCE (4.4 Tg) (see Table 3-11 and Table 3-12). Emis-
sions have fluctuated since 1990. These fluctuations were
strongly related to the behavior of the export market and
the U.S. economy. Emissions in 1997 increased by 3
percent from the previous year, and have increased 7
percent since 1990.
Table 3-11: C02 Emissions from Soda Ash
Manufacture and Consumption
Year
MMTCE
1990
1991
1992
1993
1994
1995
1996
1997
1.1
1.1
1.1
1.1
1.1
1.2
1.2
1.2
8 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 precipi-
tates 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 never actually released.
Industrial Processes 3-9
-------
Table 3-12: C02 Emissions from Soda Ash
Manufacture and Consumption (Tg)
Year Manufacture Consumption Total
'•i'li '"."in,, ' « i y o v
1 ,i "'il '".: "illlillllllhiiii.iiiiiiiiliii III i III III
: - 1981
' ' 1992
1993
•'•:.:• 1994
1995
1996
1997
l&.
1.4
T.5
1.4
1.4
1.6
1.6
1.7
1 i1 i'ii|ll|,i,l!lB*ii* ',
2.6
2.6
2.6
2.6
2.7
2.7
2.8
HIM :: • ,!,•,, TiH.il i,
4.0
4.1
4.1
4.0
4.3
4.3
4.4
MT'ToWs may not" sum du'eto independent rounding.
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 1997 was
glass making, 49 percent; chemical production, 26 percent;
soap and detergent manufacturing, 12 percent; distributors,
5 percent; flue gas desulfurization, 3 percent; pulp and pa-
per production and miscellaneous, 2 percent each; and wa-
ter treatment, 1 percent (USGS 1998).
Domestic soda ash is expected to grow between 1
to 1.5 percent per year, while world demand is forecast
at 2 to 3 percent annually for the next several years (USGS
1998). Exports are a driving force behind increasing U.S.
soda ash production capacity. U.S. soda ash exports in-
creased 9 percent in 1997 to a record 3.8 million metric
ions (OSGS 1998). The majority of the increase in soda
ash consumption is expected to come from Asia and South
America (e.g., the automotive manufacturing industry).
However, the economic problems in Asia that began in
laic 1997 will have a direct impact on U.S. soda ash ex-
ports. It is estimated that exports to Asia in 1998 will be
about 2 percent less than that of 1997 (USGS 1998).
Based on this formula, approximately 10.27 met-
ric tons of trona are required to generate one metric ton
of CO2. Thus, the 17.1 million metric tons of trona mined
in 1997 for soda ash production (USGS 1998) resulted
in CO2 emissions of approximately 0.5 MMTCE (1.7 Tg).
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 pur-
poses, additional CO2 is usually emitted. In these applica-
tions, 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.
Data Sources
The activity data for trona production and soda ash
consumption (see Table 3-13) were taken from USGS
(1993, 1994, 1995, 1998). Soda ash manufacture and
consumption data were collected by the USGS from vol-
untary 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 consid-
ered to be relatively certain. Both the emissions 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 infor-
mation characterizing the emissions from each end-use
is limited. Therefore, uncertainty exists as to the accu-
racy of the emission factors.
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 diox-
ide and water are generated as a by-products of the cal-
cination process. Carbon dioxide emissions from the cal-
cination of trona can be estimated based on the follow-
ing chemical reaction:
2(Na3H(CO3)2 *2H2O) -> 3Na2CO3 + 5H2O + CO2
[trona] [soda ash]
Table 3-13: Soda Ash Manufacture and
Consumption (Thousand Metric Tons)
, , , I, „, ,„ , ,,
Year Manufacture* Consumption
1990
J9iJ
' ' 1992
1993
'• 1994
1995
1996
1997
14,734
14,674
14,900
14,500
14,600
16,500
16,300
17,100
6,527
6,287
6,360
6,350
6,240
6,510 !
6,470
,,,6,670
* Ejoda ash manufactured from trona ore only.
3-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Carbon Dioxide Consumption
Carbon dioxide (CO2) is used for a variety of applica-
tions, including food processing, chemical production,
carbonated beverages, and enhanced oil recovery (EOR).
Carbon dioxide used for EOR is injected into the ground to
increase reservoir pressure, and is therefore considered se-
questered.9 For the most part, however, CO2 used in non-
EOR applications will eventually enter the atmosphere.
Carbon dioxide is produced from a small number of
natural wells, as a by-product from the production of chemi-
cals (e.g., ammonia), or separated from crude oil and natu-
ral gas. Depending on the raw materials that are used, the
by-product CO2 generated during these production processes
may already be accounted for in the CO2 emission estimates
from fossil fuel consumption (either during combustion or
from non-fuel uses). For example, ammonia is manufac-
tured using primarily natural gas as a feedstock. Carbon
dioxide emissions from this process are accounted for in
the Energy chapter under Fossil Fuel Combustion and, there-
fore, are not included here.
In 1997, CO2 emissions from this source not ac-
counted for elsewhere were 0.3 MMTCE (1.2 Tg) (see
Table 3-14). This amount represents an increase of 8
percent from the previous year and is 54 percent higher
than emissions in 1990.
Methodology
Carbon dioxide emission estimates were based on
CO2 consumption with the assumption that the end-use
applications, except enhanced oil recovery, eventually
release 100 percent of the CO2 into the atmosphere. Car-
bon dioxide consumption for uses other than enhanced
oil recovery was about 6,143 thousand metric tons in
1997. The Freedonia Group estimates that, in the United
States, there is an 80 to 20 percent split between CO2
produced as a by-product and CO2 produced from natu-
ral wells. Thus, emissions are equal to 20 percent of CO2
consumption. The remaining 80 percent was assumed to
already be accounted for in the CO2 emission estimates
from other categories (the most important being Fossil
Fuel Combustion).
Delta Sources
Carbon dioxide consumption data (see Table 3-15)
were obtained from Freedonia Group Inc. (1994, 1996).
Data for 1996 were obtained by personal communication
with Paul Ita of the Freedonia Group Inc. (1997). The
Freedonia Group does not provide estimates for 1997. There-
fore, data for 1997 were estimated using the annualized
growth rate of carbon dioxide consumption from 1993 to
1996. Percent of carbon dioxide produced from natural wells
was obtained fr6m Freedonia Group Inc. (1991).
Table 3-14: C02 Emissions from Carbon
Dioxide Consumption
Year
MMTCE
Tg
1990
1991
1992
1993
1994
1995
1996
1997
0.2
0.2
0.2
0.3
0.2
0.3
0.3
0.3
0.8
0.8
0.9
0.9
0.9
1.0
1.1
1.2
Table 3-15: Carbon Dioxide Consumption
Year
Thousand Metric Tons
1990
1991
1992
1993
1994
1995
1996
1997
4,000
4,200
4,410
4,559
4,488
4,842
5,702
6,143
9 It is unclear to what extent the CO2 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 CO2, 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 remains sequestered.
Industrial Processes 3-11
-------
Uncertainty
Uncertainty exists in the assumed allocation of
carbon dioxide produced from fossil fuel by-products (80
percent) and carbon dioxide produced from wells (20
percent). In addition, it is possible that CO2 recovery
exists in particular end-use sectors. Contact with several
organizations did not provide any information regarding
recovery. More research is required to determine the
quantity, if any, that may be recovered.
Iron and Steel Production
In addition to being an energy intensive process,
the production of iron and steel also generates process-
related emissions of CO2. Iron is produced by first re-
ducing iron oxide (ore) with metallurgical coke in a blast
furnace, to produce pig iron (impure iron of about 4 to
4,5 percent carbon by weight). Carbon dioxide is pro-
duced as the coke used in this process is oxidized. Steel
(less than 2 percent carbon by weight) is produced from
pig iron in a variety of specialized steel furnaces. The
majority of COj emissions come from the production of
iron, with smaller amounts evolving from the removal of
carbon from pig iron to produce steel.
Additional CO2 emissions also occur from the use
of limestone or dolomite flux in iron and steel produc-
tion; however, these emissions are accounted for under
Limestone and Dolomite Use.
Emissions of CO2 from iron and steel production
in 1997 were 23.5 MMTCE (86.1 Tg). Emissions fluctu-
ated significantly from 1990 to 1997 due to changes in
domestic economic conditions and changes in imports
and exports. CO2 emissions from this source are not in-
cluded in totals for the Industrial Processes chapter be-
cause they are accounted for with Fossil Fuel Combus-
tion emissions from industrial coking coal in the Energy
chapter.10 Emissions estimates are presented here for in-
formational purposes only (see Table 3-16).
Table 3-16: C02 Emissions from Iron and Steel
Production
Year
MMTCE
Tg
1990
1991
1992
1993
1994
1995
1996
1997
23.9
19.2
20.6
21.0
21.6
22.2
21.6
23.5
i
87.6
1 •
70.6
75.8
77.1
: 79.0
81.4
79.0
; 86.1
Methodology
Carbon dioxide emissions were calculated by mul-
tiplying annual estimates of pig iron production by the
ratio of CO2 emitted per unit of iron produced (1.6 met-
ric ton CO2/ton iron). The emission factor employed was
applied to both pig iron production and integrated pig
iron plus steel production; therefore, emissions were es-
timated using total U.S. pig iron production for all uses
including making steel.
Data Sources
The emission factor was taken from the Revised 1996
IPCC Guidelines (IPCC/UNEP/OECD/TEA1997). Produc-
tion data for 1990 through 1996 (see Table 3-17) came from
the U.S. Geological Survey's (USGS) Minerals Yearbook-
Volume I-Metals and Minerals (USqS 1996, 1997); data
for 1997 were obtained from USGS (1998).
!
Table 3-17: Pig Iron Production
1990
1991
1992
'"' "• " "" '1993
1994
1995
"" ' "1996 "
1997
54,750
44,1,00
47,4,00
48,200
49,400
50,900
iJg^OQ
53,800
10 Although the CO2 emissions from the use of industrial coking coal as a reducing agent should be included in the Industrial Processes
sector, information to distinguish individual non-fuel uses of fossil fuels is unfortunately not available in DOEi/EIA fuel statistics.
3-12 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Uncertainty
The emission factor employed was assumed to be
applicable to both pig iron production and integrated pig
iron plus steel production. This assumption was made
because the uncertainty in the factor is greater than the
additional emissions generated when steel is produced
from pig iron. Using plant-specific emission factors could
yield a more accurate estimate, but these factors were
not available. The most accurate alternative would be to
calculate emissions based on the amount of reducing
agent used, rather than on the amount of iron or steel
produced; however, these data were also not available.
Ammonia Manufacture
Table 3-18: C02 Emissions from Ammonia
Manufacture
Emissions of CO2 occur during the production of
ammonia. In the United States, roughly 98 percent of
synthetic ammonia is produced by catalytic steam reform-
ing of natural gas, and the remainder is produced using
naphtha (a petroleum fraction) or the electrolysis of brine
at chlorine plants (EPA 1997). The former two fossil fuel-
based reactions produce carbon monoxide and hydro-
gen gas; however, the latter reaction does not lead to CO2
emissions. Carbon monoxide (CO) in the first two pro-
cesses is transformed into CO2 in the presence of a cata-
lyst (usually a metallic oxide). The hydrogen gas is di-
verted and combined with nitrogen gas to produce am-
monia. The CO2, included in a gas stream with other pro-
cess impurities, is absorbed by a scrubber solution. In
regenerating the scrubber solution, CO2 is released.
(catalyst)
CH4 + H2O -
3H2 + N2
4H2 + CO2
» 2NH
Emissions of CO2 from ammonia production in
1997 were 7.1 MMTCE (26.1 Tg). Carbon dioxide emis-
sions from this source are not included in totals for the
Industrial Processes chapter because these emissions are
accounted for with non-energy use of natural gas under
Fossil Fuel Combustion in the Energy chapter.11 Emis-
sions estimates are presented here for informational pur-
poses only (see Table 3-18).
Year
MMTCE
Tg
1990
1991
1992
1993
1994
1995
1996
1997
6.3
6.4
6.7
6.4
6.6
6.5
6.6
7.1
23.1
23.4
24.4
23.4
24.3
23.7
24.2
26.1
Methodology
Emissions of CO2 were calculated by multiplying
annual estimates of ammonia production by an emission
factor (1.5 ton CO2/ton ammonia). It was assumed that all
ammonia was produced using catalytic steam reformation,
although small amounts may have been produced using
chlorine brines. The actual amount produced using this lat-
ter method is not known, but assumed to be small.
Data Sources
The emission factor was taken from the Revised
1996IPCC Guidelines (IPCC/UNEP/OECD/IEA1997).
Production data (see Table 3-19) came from the Census
Bureau of the U.S. Department of Commerce (Census
Bureau 1998) as reported in Chemical and Engineering
News, "Facts & Figures for the Chemical Industry."
Table 3-19: Ammonia Manufacture
Year Thousand Metric Tons
1990
"1991
1992
1993
1994
1995
1996
1997
15,425
15,576
16,261
15,599
16,211
15,788
16,114
17,415
11 Although the CO2 emissions from the use of natural gas as a feedstock should be included in the Industrial Processes chapter,
information to distinguish individual non-fuel uses of fossil fuels is unfortunately not available in DOE/EIA fuel statistics.
Industrial Processes 3-13
-------
Uncertainty
It is uncertain how accurately the emission factor
used represents an average across all ammonia plants.
By using natural gas consumption data for each ammo-
nia plant, more accurate estimates could be calculated.
However, these consumption data are often considered
confidential and are difficult to acquire. All ammonia
production in this analysis was assumed to be from the
same process; however, actual emissions could differ
because processes other than catalytic steam reforma-
tion may have been used.
Ferroalloy Production
Carbon dioxide is emitted from the production of
several ferroalloys. Ferroalloys are composites of iron
and other elements often including silicon, manganese,
and chromium. When incorporated in alloy steels,
ferroalloys are used to alter the material properties of the
steel. Estimates from two types of ferrosilicon (50 and
75 percent silicon) and silicon metal (about 98 percent
silicon) have been calculated. Emissions from the pro-
duction of ferrochromium and ferromanganese are not
included here because of the small number of manufac-
turers of these materials. As a result, government infor-
mation disclosure rules prevent the publication of pro-
duction data for them. Similar to emissions from the pro-
duction of iron and steel, CO2is emitted when metallur-
gical coke is oxidized during a high-temperature reac-
tion with iron and the selected alloying element. Due to
the strong reducing environment, CO is initially pro-
duced. The CO is eventually oxidized, becoming CO2. A
representative reaction equation for the production of 50
percent ferrosilicon is given below:
Fe2O3 + 2SiO2 + 1C -» 2FeSi + 7CO
Table 3-20: C02 Emissions from
Ferroalloy Production
Year
MMTCE
1990
1991
1992
1993
1994
'"' "; ""''1995 "
1996
1997
0.5
0.4
0.4
0.4
0.4
8.4
0.5
0.5
; 1.8
1 1.6'" '=:"""
1.6
1,5
; 1.6
. 1.7
, 1-8
Emissions of CO2 from ferroalloy production in
1997 were 0.5 MMTCE (1.8 Tg). Carbon dioxide emis-
sions from this source are not included in the totals for
the Industrial Processes chapter because these emissions
are accounted for in the calculations for industrial cok-
ing coal under Fossil Fuel Combustion in the Energy
chapter.12 Emission estimates are presented here for in-
formational purposes only (see Table 3-20).
Methodology
Emissions of CO2 were calculated by multiplying
annual estimates of ferroalloy production by material-spe-
cific emission factors. Emission factors were applied to pro-
duction data for ferrosilicon 50 and 75 percent (2.35 and
3.9 metric ton CO2/metric ton, respectively) and silicon metal
(4.3 metric ton CO2/metric ton). It was assumed that all
ferroalloy production was produced using coking coal, al-
though some ferroalloys may have been produced with
wood, other biomass, or graphite carbon inputs.
Data Sources
Emission factors were taken from the Revised 1996
IPCC Guidelines (IPCC/UNEP/OECD/IEA1997). Produc-
tion data for 1990 through 1996 (see Table 3-21) came from
the Minerals 'Yearbook: Volume I—petals and Minerals
published in USGS (1991,1992, 199J3,1994, 1995, 1996,
1997); data for 1997 were obtained from USGS (1998).
It
11 Although the CO2 emissions from the use of industrial coking coal as a reducing agent should be included in the Industrial Processes
chapter, information to distinguish individual non-fuel uses of fossil fuels is unfortunately not available in DdE/EIA fuel statistics.
3-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 3-21: Production of Ferroalloys
(Metric Tons)
Table 3-22: CH4 Emissions from
Petrochemical Production
Year
1990
1991
1992
1993
1994
1995
1996
1997
Ferrosilicon
50%
321,385
230,019
238,562
199,275
198,000
181,000
182,000
175,000
Ferrosilicon
75%
109,566
101,549
79,976
94,437
112,000
128,000
132,000
147,000
Silicon
Metal
145,744
149,570
164,326
158,000
164,000
163,000
175,000
187,000
Uncertainty
Although some ferroalloys may be produced us-
ing wood or other biomass as a carbon source, informa-
tion and data regarding these practices were not avail-
able. Emissions from ferroalloys produced with wood
would not be counted under this source because wood-
based carbon is of biogenic origin.13 Emissions from
ferroalloys produced with graphite inputs would be
counted in national totals, but may generate differing
amounts of CO2 per unit of ferroalloy produced com-
pared to the use of coking coal. As with emissions from
iron and steel production, the most accurate method for
these estimates would be basing calculations on the
amount of reducing agent used in the process, rather than
on the amount of ferroalloys produced. These data were
not available, however.
Petrochemical Production
Small amounts of methane (CH4) are released dur-
ing the production of some petrochemicals. Emissions
are presented here from the production of five chemi-
cals: carbon black, ethylene, ethylene dichloride, styrene,
and methanol. Aggregate emissions of CH4 from petro-
chemical production in 1997 were 0.4 MMTCE (75 Gg)
(see Table 3-22). Production levels of all five chemicals
increased from 1990 to 1997.
Year
MMTCE
1990
1991
1992
1993
1994
1995
1996
1997
0.3
0.3
0.3
* 0.4
0.4
0.4
0.4
0.4
56
57
60
66
70
70
74
75
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/met-
ric ton carbon black, 1 kg CH4/metric ton ethylene, 0.4
kg CH4/metric ton ethylene dichloride14, 4 kg CH4/met-
ric 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 methane emissions, there were not
sufficient data to estimate their emissions.
Data Sources
Emission factors were taken from the Revised 1996
IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997). An-
nual production data (see Table 3-23) came from the
Chemical Manufacturers Association Statistical Hand-
book (CMA 1998).
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 emissions estimates, however, such data were not
available. There may also be other significant sources of
methane arising from petrochemical production activi-
ties which have not been included in these estimates.
12 Although the CO2 emissions from the use of industrial coking coal as a reducing agent should be included in the Industrial Processes
chapter, information to distinguish individual non-fuel uses of fossil fuels is unfortunately not available in DOE/EIA fuel statistics.
Industrial Processes 3-15
-------
Table 3-23: Production of Selected Petrochemicals (Thousand Metric Tons)
Chemical
Carbon Black
••;; Ethgene
_ : ' : Ithyiene Dlehloride
Styrene
Melhanol
1990
1,
16,
6,
3,
3,
306
542
282
637
785
1991
1,225
18,124
6,221
3,681
3,948
1992
1,365
18,563
6,872
4,082
3,666
1993
1,452
18,714
8,141
4,565
4,782
1994
1,492
20,201
8,482
5,112
4,932
1995
1,524
19,470
7,831
5,167
5,123
I
,!:,:. „
1996
,1,560
20,990
8,596
5,387
5,262
1997
1,588
21,886
9,152
5,171
5,455
Silicon Carbide Production
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 car-
bon in the form of petroleum coke. Methane is produced
during this reaction from volatile compounds in the pe-
troleum coke. Although CO2 is also emitted from this
production process, the requisite data were unavailable
for these calculations. Regardless, they are already ac-
counted for under CO2 from Fossil Fuel Combustion in
the Energy chapter. Emissions of CH4 from silicon car-
bide production in 1997 (see Table 3-24) were 1 Gg (less
than 0,05 MMTCE).
Table 3-24: CH4 Emissions from Silicon
Carbide Production
Year
MMTCE
Gg
Ill III 111
•ill
111 111
199d +
1991 +
1992 +
1993 +
1994 f "
1995 "" ' "7 "
1996 +
1997 + '
-j
1
'!.' "!".'.! i"
1
" i~"m
' "" "T
1
i
+ Does not exceed 0.05 MMTCE
Methodology
Emissions of CH4 were calculated by multiplying
annual estimates of silicon carbide production by an
emission factor (11.6 kg CH4/metric ton silicon carbide).
This emission factor was derived empirically from mea-
surements taken at Norwegian silicon carbide plants
(IPCC/UNEP/OECD/IEA 1997).
Data Sources
The emission factor was taken from the Revised
1996IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997).
Production data for 1990 through 1997 (see Table 3-25)
came from the Minerals Yearbook: yolume I-Metals and
Minerals published in USGS (1991, 1992, 1993, 1994,
1995, 1996, 1997, 1998). \
Table 3-25: Production of Silicon Carbide
Year
1990
1991
1992
1993
1994
: .',: 1995
1996,,,
1997
Metric Tons
105,000
78,900
84,300
74,900
84,700
75,400
73,600
68,200
• i
Uncertainty
The emission factor used here was based on one study
of Norwegian plants. The applicability of this factor to av-
erage 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 pro-
duced. These data were not available, however.
Adipic Acid Production
Adipic acid production has been identified as a sig-
nificant anthropogenic source of nitrous oxide (N2O)
emissions. Adipic acid is a white crystalline solid used
in the manufacture of synthetic fibers, coatings, plastics,
urethane foams, elastomers, and synthetic lubricants.
3-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Commercially, it is the most important of the aliphatic
dicarboxylic acids, which are used to manufacture poly-
esters. Ninety percent of all adipic acid produced in the
United States is used in the production of nylon 6,6. It is
also used to provide some foods with a "tangy" flavor.
Adipic acid is produced through a two-stage pro-
cess during which N2O is generated in the second stage.
This second stage involves the oxidation of a ketone-
alcohol with nitric acid. Nitrous oxide is generated as a
by-product of this reaction and is emitted in the waste
gas stream. In the United States, this waste gas is treated
to remove nitrogen oxides (NOX), other regulated pollut-
ants, and in some cases N2O. There are currently four
plants in the United States that produce adipic acid. Since
1990, two of these plants have employed emission con-
trol measures destroying roughly 98 percent of the N2O
in their waste gas stream before it is released to the at-
mosphere (Radian 1992). During 1997, a third plant in-
stalled comparable N2O emission controls that operated
for approximately a quarter of the year.
Adipic acid production for 1997 was estimated to
be 860 thousand metric tons. Nitrous oxide emissions
from this source were estimated to be 3.9 MMTCE (46
Gg) in 1997 (see Table 3-26),
Table 3-26: N20 Emissions from Adipic Acid
Production
Year
MMTCE
1990
1991
1992
1993
1994
1995
1996
1997
4.7
4.9
4.6
4.9
5.2
5.2
5.4
3.9
56
58
54
58
62
62
63
46
Adipic acid production reached its highest level in
thirteen years in 1997, growing about 3 percent from the
previous year. Though production continues to increase,
emissions have been significantly reduced, due to the
widespread installation of pollution control measures
mentioned above.
Methodology
Nitrous oxide emissions were calculated by multi-
plying adipic acid production by the ratio of N2O emit-
ted per unit of adipic acid produced and adjusting for the
actual percentage of N2O released as a result of plant-
specific emission controls. Because emissions of N2O in
the United States are not regulated, emissions have not
been well characterized. However, on the basis of ex-
periments (Thiemens and Trogler 1991), the overall re-
action stoichiometry for N2O production in the prepara-
tion of adipic acid was estimated at approximately 0.3
kg of N2O per kilogram of product.
Data Sources
Adipic acid production data for 1990 through 1995
(see Table 3-27) were obtained from Chemical and En-
gineering News, "Facts and Figures" and "Production of
Top 50 Chemicals" (C&EN 1992, 1993, 1994, 1995,
1996). The 1996 and 1997 data were projected from the
1995 manufactured total based upon suggestions from
industry contacts. The emission factor was taken from
Thiemens, M.H. and W.C. Trogler (1991). Adipic acid
plant capacities were obtained from Chemical Market
Reporter (June 15, 1998).
Table 3-27: Adipic Acid Production
Year Thousand Metric Tons
1990
1991
1992
1993
1994
1995
1996
1997
735
771
708
765
815
816
835
860
Uncertainty
Because N2O emissions are controlled in some
adipic acid production facilities, the amount of N2O that
is actually released will depend on the level of controls
in place at a specific production plant. Thus, in order to
calculate accurate emission estimates, it is necessary to
have production data on a plant-specific basis. In most
Industrial Processes 3-17
-------
cases, however, these data are confidential. As a result,
plant-specific production figures were estimated by al-
locating total adipic acid production using existing plant
capacities. This creates a degree of uncertainty in the
adipic acid production data used to derive the emission
estimates as it is necessary to assume that all plants op-
erate at equivalent utilization levels.
The emission factor was based on experiments
(Thiemens and Trogler 1991) that attempt to replicate the
industrial process and, thereby, measure the reaction sto-
ichiometry for N2O production in the preparation of adipic
acid. However, the extent to which the lab results are repre-
sentative of actual industrial emission rates is not known.
Nitric Acid Production
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 manufac-
tured 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. While
the waste gas stream may be cleaned of other pollutants
such as nitrogen dioxide, there are currently no control
measures aimed at eliminating N2O.
Nitric acid production reached 8,232 thousand
metric tons in 1997 (C&EN 1998). Nitrous oxide emis-
sions from this source were estimated at 3.8 MMTCE
(45 Gg) (see Table 3-28). Nitric acid production for 1997
decreased 1 percent from the previous year, but has in-
creased 13 percent since 1990.
Table 3-28: N20 Emissions from Nitric
Acid Production
Methodology
Nitrous oxide emissions were calculated by multi-
plying nitric acid production by the amount of N2O emit-
ted per unit of nitric acid produced. Off-gas measure-
ments at one nitric acid production facility showed N2O
emission rates to be approximately 2 to 9 g N2O per kg
of nitric acid produced (Reimer et al. 1992). In calculat-
ing emissions, the midpoint of this range was used (5.5
kg N2O/metric ton HNO3).
Data Sources
!
Nitric acid production data for 1990 through 1997
(see Table 3-29) were obtained from Chemical and En-
gineering News, "Facts and Figures" (C&EN 1998). The
emission factor range was taken from Reimer, R.A.,
Parrett, R.A., and Slaten, C.S. (1992).
Table 3-29: Nitric Acid Production
Year
Thousand Metric Tons
1990
1991
1992
1993
1994
1995
1996
1997
7;f§6 '"
7,191
7,381
7,4,88
8,005
8,020
8,3,51
8,232
Uncertainty
These emission estimates are highly uncertain due
to a lack of information on manufacturing processes and
emission controls. Although no abatement techniques are
specifically directed at removing N2O at nitric acid plants,
existing control measures for other pollutants may have
some impact upon N2O emissions. The emission factor
range of 2 to 9 g N2O per kg of nitric acid produced is
I,,,;, lilSfiar !!'; ifi'wfflfil
ii; • ,: !•'
:••• •,':'•
i; ' ;v
*• .:
""fikjfi
IllvfrfSa, :• ,r
1992
; : f993
1994
«;^19;i|§H.tii: ,.
;«»;':;.1997
•Wn.
3.3
3.4
"is: ::
3.7
3.7
"19
3.8
, , ,,, ., ,, ,, , ., , aigmjuucuiL, itaumg iu luiinci uuueiuuiuy wiien appiy-
Gg ing the midpoint value.
40"
iii, ii i|,:i;ii,|iiii,1 '" IL iis1,"! i1!' in; ' f • nn II
40
40
'1 '..41
43
44
46
45
'• ' ll 1 ' ,, ' II, 1 II, II, III ll
3-18
inventory of U.S. Greenhouse Gas Emissions and Sinks: 1 990-1 997
-------
Substitution of Ozone
Depleting Substances
Hydrofluorocarbons (HFCs) and perfluorocarbons
(PFCs) are used primarily 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 199015. Ozone depleting sub-
stances—chlorofluorocarbons (CFCs), halons, carbon tet-
rachloride, methyl chloroform, and
hydrochlorofluorocarbons (HCFCs)—are used in a variety
of industrial applications including refrigeration and air
conditioning equipment, sol vent cleaning, foam production,
sterilization, fire extinguishing, and aerosols. Although
HFCs and PFCs, unlike ODSs, are not harmful to the strato-
spheric ozone layer, they are powerful greenhouse gases.
Emission estimates for HFCs and PFCs used as substitutes
for ODSs are provided in Table 3-30 and Table 3-31.
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 re-
frigerant 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-40416. In 1993, use of HFCs in foams and aerosols
Table 3-30: Emissions of HFCs and PFCs from ODS Substitution (MMTCE)
Gas
1990 1991 1992 1993 1994 1995 1996 1997
HFC-23
HFC-125
HFC-1 34a
HFC-1 43a
HFC-236fa
HFC-4310m.ee
C4F10
^6^14
Others*
Total
+ + + + +
+ + 0.2 0.4 1.2
0.2 0.2 0.2 1.0 1.9
+ + + + +
+ + + + +
+ + + + +
+ + + + +
+ + + + +
0.1 + + + . 0.8
0.3 0.2 0.4 1.4 4.0
+
2.2
3.4
0.1
+
0.2
+
+
3.5
9.5
0.1
2.4
4.8
0.2
0.1
0.4
0.1
+
3.7
11.9
0.1
2.7
6.4
0.4
0.3
0.5
0.2
+
4.0
14.7
+ Does not exceed 0.05 MMTCE
* Others include HFC-152a, HFC-227ea, and PFC/PFPEs, which are a proxy for a diverse collection of PFCs and perfluoropolyethers (PFPEs)
employed for solvent applications. For estimating purposes, the GWP value used for PFC/PFPEs was based upon C6F14.
Note: Totals may not sum due to independent rounding.
Table 3-31: Emissions of HFCs and PFCs from ODS Substitution (Wig)
Gas
1990 1991 1992 1993 1994 1995 1996
1997
HFC-23
HFC-125
HFC-1 34a
HFC-1 43a
HFC-236fa
HFC-4310mee
C4F10
C6F14
Others*
+ + + +
+ + 236 481
564 564 626 2,885
4- + + 12
4 + 4-4
4 + + +
4 + + +
444 +
.
+
1,628
5,410
43
+
+
+
+
-
9
2,823
9,553
94
+
611
22
2
-
26
3,172
13,605
226
79
1,030
64
6
-
43
3,572
17,960
427
175
1,479
105
12
-
- Not applicable
+ Does not exceed 0.5 Mg
* Others include HFC-152a, HFC-227ea, and PFC/PFPEs, which are a proxy for a diverse collection of PFCs and perfluoropolyethers (PFPEs)
employed for solvent applications.
15 [42 U.S.C § 7671, CAA § 601]
16 R-404 contains HFC-125, HFC-143a, and HFC-134a.
Industrial Processes 3-19
-------
began, and in 1994 these compounds also found appli-
cations as solvents and sterilants. In 1995, ODS substi-
tutes 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 increased dramatically, from
small amounts in 1990, to 14.7 MMTCE in 1997. This
increase was the result of efforts to phase-out CFCs and
Other ODSs in the United States. This trend is expected
to continue for many years, and will accelerate in the
early part of the next century as HCFCs, which are in-
terim substitutes in many applications, are themselves
phased-out under the provisions of the Copenhagen
Amendments to the Montreal Protocol.
Methodology and Data Sources
The EPA used a detailed vintaging model of ODS-
containing equipment and products to estimate the ac-
tual—versus potential—emissions of various ODS sub-
stitutes, 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 "vin-
tages" of new equipment that enter service in each end-
use. Tliis vintaging model predicts ODS and ODS sub-
stitute use in the United States based on modeled esti-
mates 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 equip-
ment 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.
The major end-use categories defined in the
vintaging model to characterize ODS use in the United
States were: refrigeration and air conditioning, aerosols,
solvent cleaning, fire extinguishing equipment, steriliza-
tion, and foams.
The vintaging model estimates HFC and PFC use
and emissions resulting from their use as replacements
for ODSs by undertaking the following steps:
Step 1: Estimate ODS Use in the United States Prior
to Phase-out Regulations
The model begins by estimating CFC, halon, methyl
chloroform, and carbon tetrachloride use prior to the re-
strictions on the production of these compounds in the
United States. For modeling purposes, total ODS use was
divided into more than 40 separate end-uses. The method-
ology used to estimate baseline ODS use varied depending
on the end-use under consideration. The next section de-
scribes the methodology used for estimating baseline ODS
use in the refrigeration, air conditioning, and fire extinguish-
ing (halon) end-uses. The subsequent section details the
methodology used for all other end-uses.
Step 1.1: Estimate Baseline ODS Use for
Refrigeration, Air Conditioning, and Fire
Extinguishing
For each equipment type, the model estimates the
total stock of ODS-containing equipment during the pe-
riod 1985 to 1997. The key data required to develop stock
estimates for each end-use were as follows:
• Total stock of ODS-containing equipment in use in
the United States in 1985
• The annual rate of growth in equipment consump-
tion in each end-use
• The retirement function for equipment in each
end-use
Historical production and consumption data were
collected for each equipment type to develop estimates
of total equipment stock in 1985. For some end-uses, the
only data available were estimates of ODS usage. In these
cases, the total 1985 stock was estimated by dividing to-
tal ODS use by the average charge of ODS in a typical
piece of equipment.
Stocks of ODS-containing equipment change over
time. In the vintaging model, the growth in equipment
stocks in each end-use was simulated after 1985 using
growth rates that define the total number of pieces of
new equipment added to the stock each year. The model
also uses a retirement function to calculate the length of
time each piece of equipment is expected to remain hi
service. These retirement functions are a critical part of
the vintaging model because they determine the speed at
which the stock of equipment turns over and is replaced
by new equipment. In this analysis, point estimates of
3-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
the average lifetime of equipment in each end-use were
used to develop retirement functions. These retirement
functions assume 100 percent survival of equipment up
to this average age and zero percent survival thereafter.
Given these data, the total equipment stock in ser-
vice in a given year t was estimated as the equipment
stock in the year 0-1), plus new equipment added to the
stock in year t, minus retirements in year t.
Annual ODS use was then estimated for each equip-
ment type during the period 1985 through 1997. Because
control technologies can reduce particular kinds of ODS
use, use estimates were broken down by type of use (e.g.,
use in new equipment at manufacture and use required
to maintain existing equipment). Baseline estimates of
ODS use were based on the following data collected for
each equipment type:
• ODS charge size (the number of kilograms of ODS
installed in new equipment during manufacture)
* ODS required to maintain existing equipment (In
many end-uses, chemical must be regularly added
to equipment to replace chemical emitted from the
equipment. Such emissions result from normal leak-
age and from loss during servicing of the equipment.)
With these data, ODS usage for each refrigeration,
air conditioning, and fire extinguishing end-use was cal-
culated using the following equation:
(Total stock of existing equipment in use) ' (ODS
required to maintain each unit of existing equipment) +
(New equipment additions)' (ODS charge size)
Step 1.2: Estimate Baseline ODS Use in Foams,
Solvents, Sterilization, and Aerosol End-Uses
For end-uses other than refrigeration, air condition-
ing, and fire extinguishing, a simpler approach was used
because these end-uses do not require partial re-filling
. of existing equipment each year. Instead, such equipment
either does not require any ODS after initial production
(e.g., foams and aerosols), or requires complete re-fill-
ing or re-manufacturing of the equipment each year (e.g.,
solvents and sterilants). ODS use does not need to be
differentiated between new and existing equipment for
these end-uses. Thus, it is not necessary to track the stocks
of new and existing equipment separately over time.
The approach used for these end-uses was to esti-
mate total ODS use in 1985 based on available industry
data. Future ODS use was estimated using growth rates
that predict ODS consumption growth in these end-uses
over time, based upon input from industry.
Step 2: Specification and Implementation of
Control Technologies
Having established a baseline for ODS equipment
in 1985, the vintaging model next defines controls that
may be undertaken for purposes of reducing ODS use
and emissions within each end-use. The following con-
trols were implemented in the model:
• Replacement of ODS used in the manufacturing of
new equipment or in the operation of existing equip-
ment (i.e., retrofits) with alternative chemicals, such
as HFCs and PFCs
• Replacement of ODS-based processes or products
with alternative processes or products (e.g., the use
of aqueous cleaning to replace solvent cleaning with
CFC-113)
• Modification of the operation and servicing of equip-
ment to reduce use and emission rates through the
application of engineering and recycling controls
Assumptions addressing these types of controls in
each end-use were used to develop "substitution sce-
narios" that simulate the phase-out of ODSs in the United
States by end-use. These scenarios represent EPA's best
estimates of the use of control technologies towards the
phase-out ODS in the United States, and are periodically
reviewed by industry experts.
In addition to the chemical substitution scenarios,
the model also assumes that a portion of ODS substi-
tutes are recycled during servicing and retirement of the
equipment. Recycling is assumed to occur in the refrig-
eration and air conditioning, fire extinguishing, and sol-
vent end-uses.
The substitution scenarios defined for each equip-
ment type were applied to the relevant equipment stocks.
The equipment life-cycle was then simulated after the
imposition of controls. Substitute chemical use and emis-
sions—including HFCs and PFCs—were calculated for
each scenario using the methods described below.
Industrial Processes . 3-21
-------
Step 3: Estimate ODS Substitute Use and
Emissions (HFC's and PFCs)
ODS substitute use (i.e., HFC and PFC use) was
calculated using the same routine described above for
refrigeration, air conditioning, and fire extinguishing
equipment. In terms of chemical usage, a key question
was whether implementation of a given ODS substitute
in an end-use changed the quantity of chemical required
to manufacture new equipment or service existing equip-
ment. In this analysis, it was assumed that the use of ODS
alternatives in new equipment—including HFCs and
PFCs—did not change the total charge of initial chemi-
cal used in the equipment in each end-use. For certain
refrigeration and air conditioning end-uses, however, it
was assumed that new equipment manufactured with
HFCs and PFCs would have lower leak rates than older
equipment, Existing ODS-containing equipment that was
retrofitted with HFCs or PFCs was assumed to have a
higher leak rate than new HFC/PFC equipment.
The use of HFCs and PFCs in all other end-uses
was calculated by simply replacing ODS use with the
chemical alternatives defined in the substitution scenarios.
The use of HFCs and PFCs was not assumed to change
the quantity of chemical used in new or existing equip-
ment for these end-uses.
The vintaging model estimates HFC and PFC emis-
sions over the lifetime of equipment in each end-use.
Emissions may occur at the following points in the life-
time of the equipment:
• Emissions upon manufacture of equipment
• Annual emissions from equipment (due to normal
leakage, and if applicable, servicing of equipment)
• Emissions upon retirement of equipment
The emissions that occur upon manufacture of re-
frigeration and air conditioning equipment were assumed
to be less man 0.1 percent. Annual emissions of HFCs and
PFCs fifom equipment—due to normal leakage and servic-
ing—were assumed to be constant each year over the life of
tire equipment. The quantity of emissions at disposal is a
function of the prevalence of recycling at disposal.
Emissions for open cell foam were assumed to be
100 percent in the year of manufacture. Closed cell foams
were assumed to emit a portion of total HFC/PFC use
upon manufacture, a portion at a constant rate over the
lifetime of the foam, and the rest at disposal. There were
no foam recycling technologies in use in the United
States; therefore, HFCs and PFCs remaining in closed
cell foam were assumed to be emitted by the end of the
product lifetime.
Emissions were assumed to occur at manufacture,
during normal operation, and upon retirement of fire
extinguishing systems. Emissions at manufacture were
assumed to be negligible and emissions upon disposal
were assumed to be minimal because of the use of re-
covery technologies.
For solvent applications, 15 percent of the chemi-
cal used in equipment was assumed to be emitted in that
year. The remainder of the used solvent was assumed to
be disposed rather than emitted or recycled.
For sterilization applications, all chemicals that
were used in the equipment were assumed to be emitted
in that year.
All HFCs and PFCs used in aerosols were assumed
to be emitted in the same year. No technologies were
known to exist that recycle or recover aerosols.
Uncertainty
Given that emissions of ODS substitutes occur from
thousands of different kinds of equipment and from mil-
lions of point and mobile sources throughout the United
States, emission estimates must be made using analyti-
cal tools such as the EPA vintaging model or the meth-
ods outlined in IPCC/UNEP/OECD/IEA (1997). Though
EPA's model is more comprehensive than the IPCC meth-
odology, significant uncertainties still exist with regard
to the levels of equipment sales, equipment characteris-
tics, and end-use emissions profiles that were used to
estimate annual emissions for the various compounds.
i
Aluminum Production
.
Aluminum is a light-weight, malleable, and corro-
sion resistant metal that is used in many manufactured
products including aircraft, automobiles, bicycles, and
kitchen utensils. The United States was the largest pro-
ducer of primary aluminum with 17 percent of the world
total in 1997 (USGS 1998). The United States was also a
3-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
major importer of primary aluminum. The production of
primary aluminum—in addition to consuming large quan-
tities of electricity—results in emissions of several green-
house gases including carbon dioxide (CO2) and two
perfluorocarbons (PFCs): perfluoromethane (CF4) and
perfluoroethane (C2F6).
Occasionally, sulfur hexafiuoride (SF6) is also used
by the aluminum industry as a fluxing and degassing
agent in experimental and specialized casting operations.
In these cases it is normally mixed with argon, nitrogen,
and/or chlorine and blown through molten aluminum;
however, this practice is not used by primary aluminum
production firms in the United States and is not believed
to be extensively used by secondary casting firms. Where
it does occur, the concentration of SF6 in the mixture is
small and a portion of the SF6 is decomposed in the pro-
cess (Waite and Bernard 1990, Corns 1990). It has been
estimated that 230 Mg of SF6 were used by the alumi-
num industry in the United States and Canada (Maiss
and Brenninkmeijer 1998); however, this estimate is
highly uncertain. Emissions of SF6 have not been esti-
mated for this source.
Carbon dioxide is emitted during the aluminum
smelting process when alumina (aluminum oxide, A12O3)
is reduced to aluminum using the Hall-Heroult reduc-
tion process. The reduction of the alumina occurs through
electrolysis in a molten bath of natural or synthetic cryo-
lite (Na3AlF6). The reduction cells contain a carbon lin-
ing 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 produc-
tion were estimated at 1.4 MMTCE (5.3 Tg) in 1997 (see
Table 3-32). The CO2 emissions from this source, however,
are accounted for under the non-fuel use portion of CO2
from Fossil Fuel Combustion of petroleum coke and tar
pitch in the Energy chapter. Thus, to avoid double count-
ing, CO2 emissions from aluminum production are not in-
cluded in totals for the Industrial Processes chapter. They
are provided here for informational purposes only.
In addition to CO2 emissions, the aluminum pro-
duction industry was also the largest source of PFC emis-
sions in the United States. During the smelting process,
when the alumina ore content of the electrolytic bath falls
below critical levels required for electrolysis, rapid volt-
age increases occur, termed "anode effects". These an-
ode 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. The more frequent and long-lasting
the anode effects, the greater the emissions.
Primary aluminum production-related emissions of
PFCs are estimated to have declined 41 percent since
1990 to 2.5 MMTCE of CF4 (1,430 Mg) and 0.4 MMTCE
of C2F6 (140 Mg) in 1997, as shown in Table 3-33 and
Table 3-34. This decline was both due to reductions in
domestic aluminum production and actions taken by alu-
minum smelting companies to reduce the frequency and
duration of anode effects under EPA's Voluntary Alumi-
num Industrial Partnership (VAIP).
Table 3-32: C02 Emissions from Aluminum
Production
Year
MMTCE
Tg
1990
1991
1992
1993
1994
1995
1996
1997
1.6
1.7
1.6
1.5
1.3
1.4
1.4
1.4
6.0
6.1
5.9
5.4
4.8
5.0
5.3
5.3
Table 3-33: PFC Emissions from Aluminum
Production (MMTCE)
Year
CF,
C,F,
2r6
Total
1990
1991
1992
1993
1994
1995
1996
1997
4.3
4.1
3.6
3.1
2.5
2.4
2.5
2.5
0.6
0.6
0.5
0.4
0.4
0.3
0.4
0.4
4.9.
4.7
4.1
3.5
2.8
2.7
2.9
2.9
Note: Totals may not sum due to independent rounding.
Industrial Processes 3-23
-------
Table 3-34: PFC Emissions from Aluminum
Production (Mg)
"•' Hi i ill nil
Yaar CF4 C2F6
, . III!
•-_
I"
HIE'! f!
1990
1991
1992
1993
1994
1995
1996
mi
II 111 Illllllllil I
2,430
2,330
2,020,
1,750
1,400
i;330
1,430
: :: 1:430
ii ' ' :
240
230
200
170
140
130
140
140 ;
U.S. primary aluminum production for 1997, to-
taling 3,603 thousand metric tons, increased only slightly
from 1996. Changes in U.S. primary aluminum produc-
tion are due in part to imports, mainly from Russia and
other republics of the Former Soviet Union. For example,
in 1994 these countries exported 60 percent more ingots
(metal cast for easy transformation) to the United States
than in 1993, leading to a significant decline in domestic
production. However, imports from Russia have declined
from their peak level in 1994 (USGS 1998).
The transportation industry remained the largest
domestic consumer of aluminum, accounting for about
29 percent (USGS 1998). The "big three" automakers
have announced new automotive designs that will ex-
pand the use of aluminum materials in the near future.
The U.S. Geological Survey believes that demand for
and production of aluminum will continue to increase.
Methodology
Carbon dioxide is generated during alumina reduc-
tion to aluminum metal following the reaction below:
2A12O3 + 3C -> 4A1 + 3CO2
The quantity of CO2 released was estimated from
the production of primary aluminum metal and the car-
bon consumed by the process. During alumina reduc-
tion, approximately 1.5 to 2.2 metric tons of CO2 are
emitted for each metric ton of aluminum produced
(Abrahamson 1992). In previous inventories, the mid-
point (1.85) of this range was used for the emission fac-
tor. However, for this year's report—and adjusting ear-
lier years—the emission factor was revised to 1.5 metric
tons CO2 per metric ton of aluminum smelted based on a
mass balance for a "typical" aluminum smelter (Drexel
University Project Team 1996). Ttiis value is at the low
end of the Abrahamson (1992) range.
The CO2 emissions from this source are already ac-
counted for under CO2 Emissions frpm Fossil Fuel Com-
bustion in the Energy chapter.n Thus, to avoid double count-
ing, CO2 emissions from aluminum production are not in-
cluded in totals for the Industrial Processes chapter.
PFC emissions from aluminum production were
estimated using a per unit production emission factor for
the base year 1990. The emission factor used is a func-
tion of several operating variables including average an-
ode effect frequency and duration. Total annual emis-
sions for 1990 were then calculated based on reported
annual production levels. The five components of the per
unit production emission factor are:
• Amount of CF4 and C2F6 emitted during every
minute of an anode effect, per ampere of current
• Average duration of anode effects
• Average frequency of anode effects
• Current efficiency for aluminum smelting
• Current required to produce a metric ton of alumi-
num, assuming 100 percent efficiency
Using available data for the United States, this
methodology yields a range in the emission factor of 0.01
to 1.2 kg CF4 per metric ton of aluminum produced in
1990 (Jacobs 1994). The emission factor for C2F6 was
estimated to be approximately an order of magnitude
!
lower. Emissions for 1991 through 1996 were estimated
with emission factors that incorporated data on reduc-
tions in anode effects reported to the VAIP by aluminum
companies.
Data Sources
Primary aluminum production data for 1990 through
1997 (see Table 3-35) were obtained from USGS, Mineral
Industry Surveys: Aluminum Annual Report (USGS 1998,
1995). The USGS requested data from the 13 domestic pro-
ducers, all of whom responded. The CO2 emission factor
" Although the carbon contained in the anode is considered a non-fuel use of petroleum coke or tar pitch and should be included in the Industrial
Processes chapter, information to distinguish individual non-fuel uses of fossil fuels is unfortunately not available in DOE/EIA fuel statistics.
3-24 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
range was taken from Abrahamson (1992). The mass bal-
ance for a "typical" aluminum smelter was taken from Drexel
University Project Team (1996).
PFC emission estimates were provided by the EPA's
Atmospheric Pollution Prevention Division in coopera-
tion with participants in the Voluntary Aluminum Indus-
trial Partnership (VAIP).
Table 3-35: Production of Primary Aluminum
Year
Thousand Metric Tons
1990
1991
1992
1993
1994
1995
1996
1997
4,048
4,121
4,042
3,695
3,299
3,375
3,577
3,603
Uncertainty
Uncertainty exists as to the most accurate CO2
emission factor for aluminum production. Emissions vary
depending on the specific technology used by each plant.
However, evidence suggests that there is little variation
in CO2 emissions from plants utilizing similar technolo-
gies (IPCC/UNEP/OECD/IEA 1997). A less uncertain
method would be to calculate 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.
For PFC emission estimates, the value for emis-
sions per anode effect minute per ampere was based on a
limited number of measurements that may not be repre-
sentative of the industry as a whole (EPA 1993). For ex-
ample, the emission factor may vary by smelter technol-
ogy type, among other factors. The average frequency of
anode effects and the current efficiency are well docu-
mented; however, insufficient measurement data existed
to quantify a relationship between PFC emissions and
anode effect minutes. Future inventories will incorpo-
rate additional data reported to VAIP by aluminum com-
panies and ongoing research into PFC emissions from
aluminum production.
Emissions of SF6 from aluminum fluxing and de-
gassing have not been estimated. Uncertainties exist as
to the quantity of SF6 used by the aluminum industry
and its rate of destruction as it is blown through molten
aluminum.
HGFC-22 Production
Trifluoromethane (HFC-23 or CHF3) is generated
as a by-product during the manufacturing of
chlorodifluoromethane (HCFC-22), which is primarily
employed as a substitute for ozone depleting sub-
stances—mainly in refrigeration and air conditioning
systems—and as a chemical feedstock for manufactur-
ing synthetic polymers. Because of its stratospheric ozone
depleting properties, HCFC-22 production for non-feed-
stock uses is scheduled to be phased out by 2020 under
the U.S. Clean Air Act.18 Feedstock production, in con-
trast, 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 pro-
duces SbClxFy, (where x + y = 5), which reacts with the
chlorinated hydrocarbons to replace chlorine atoms with
fluorine. The HF and chloroform are introduced by sub-
merged 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-flu-
orinated 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. 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 un-
wanted by-product, or may be captured for use in a limited
number of applications.
Emissions of HFC-23 in 1997 were estimated to
be 8.2 MMTCE (2,570 Mg). This represents a 14 per-
cent decline from emissions in 1990 (see Table 3-36).
18 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 3-25
-------
In the future, production of HCFC-22 in the United
States is expected to increase initially and then decline
as non-feedstock HCFCs production is phased-out; feed-
stock production is anticipated to continue growing
steadily, mainly for manufacturing Teflon® and other
chemical products. All U.S. producers of HCFC-22 are
participating in a voluntary program with the EPA to re-
duce HFC-23 emissions.
Table 3-36: HFC-23 Emissions from HCFC-22
Production
Year
MMTCE
1990
1991
1992
1993
1994
1995
1996
1997
9.5
§S4
9,5
8.7
8J
7.4
8.5
LT-Tal'I "
3.0
2.6
3.0
2.7
2.7
2.3
2.7
2.6
Methodology
EPA studied the conditions of HFC-23 generation,
methods for measuring emissions, and technologies for
emissions control. This effort was undertaken in coop-
eration with the manufacturers of HCFC-22.
Earlier emission estimates assumed that HFC-23
emissions were between 2 and 4 percent of HCFC-22
production on a mass ratio basis. The methodology em-
ployed for this report was based upon measurements of
critical feed components at individual HCFC-22 produc-
tion plants. Individual producers also measured HFC-23
concentrations in the process stream by gas chromatog-
raphy. Using measurements of feed components and
HFC-23 concentrations in process streams, the amount
Of HFC-23 generated was estimated. HFC-23 concen-
trations were determined at the point the gas leaves the
chemical reactor; therefore, estimates also include fugi-
tive emissions.
Data Sources
Emission estimates were provided by the EPA's
Atmospheric Pollution Prevention Division in coopera-
tion with the U.S. manufacturers of HCFC-22.
Uncertainty
A high level of confidence has been attributed to
the HFC-23 concentration data employed because mea-
surements were conducted frequently and accounted for
day-to-day and process variability. It is estimated that
the emissions reported are within 20 percent of the true
value. This methodology allowed for determination of
reductions in HFC-23 emissions during a period of in-
creasing HCFC-22 production. The use of a constant
emission factor would not have allowed for such an as-
sessment. By 1996, the rate of HFC-23 generated as a
percent of HCFC-22 produced dropped, on average, be-
low 2 percent in the United States.
Semiconductor Manufacture
The semiconductor industry uses multiple long-
lived fluorinated gases in plasma etching and chemical
vapor deposition (CVD) processes. The gases most com-
monly employed are trifluorpmethane (HFC-23),
perfluoromethane (CF4), perfluoroethane (C2F6), and sul-
fur hexafluoride (SF6), although other compounds such
as nitrogen trifluoride (NF3) andperfiuoropropane (C3F8)
and perfluorocyclobutane (c-C4F8) are also used. The
exact combination of compounds is specific to the pro-
cess employed.
!l
Plasma etching is performed to provide pathways
for the conducting material to connect individual circuit
components in the silicon, using HFCs, PFCs, SF6 and
other gases in plasma. The etching process creates fluo-
rine atoms that react at the semiconductor surface ac-
cording to prescribed patterns to selectively remove sub-
strate material. A single semiconductor wafer may re-
quire as many as 100 distinct process steps that utilize
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
HF in plasma, which etches away residual material from
chamber walls, electrodes, and chamber hardware. The
majority of the gas flowing into the chamber flows
unreacted through the chamber and, without recovery
systems, is emitted into the atmosphere.
I
3-26 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
In addition to being directly used in the manufac-
turing processes, these gases can also be transformed
during the process into a different HFC or PFC com-
pound, which is then exhausted into the atmosphere. For
example, when either CHF3 or C2F6 is used in cleaning
or etching, CF4 is often generated and emitted as a pro-
cess by-product.
For 1997, it was estimated that total weighted emis-
sions of all greenhouse gases by the U.S. semiconductor
industry were 1.3 MMTCE. These gases were not widely
used in 1990, hence, emissions in 1990 were estimated to
be only 0.2 MMTCE. Combined emissions of all gases are
presented in Table 3-37 below. It is expected that the rapid
growth of this industry and the increasing complexity of
microchips will increase emissions in the future.
Table 3-37: PFC Emissions from Semiconductor
Manufacture
Year
MMTCE*
1990
1991
1992
1993
1994
1995
1996
1997
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.3
* Combined radiative forcing effect of all gases
Methodology
An estimate of emissions was developed based on
the approximate sales of the four main gases (HFC-23,
CF4, C2F6, and SF6) to semiconductor firms. Estimates
were confirmed with data reported to the EPA by a sub-
set of firms in the industry who have engaged in volun-
tary monitoring efforts. Further study of gas emission
rates is also underway.
Data Sources
Emission estimates were provided by the EPA's
Atmospheric Pollution Prevention Division in coopera-
tion with the U.S. semiconductor industry.
Uncertainty
Emission estimates for this source are believed to
be highly uncertain due to the lack of detailed gas con-
sumption data and the complex chemical reactions in-
volved in the processes used. For example, in the etch-
ing process the gas molecules are disrupted by a plasma
into varied recombinant formulations specific to each tool
and operation. Therefore, a portion of the gases consumed
may be destroyed or transmuted into other gases. Be-
cause of these uncertainties, unweighted emissions by
gas are not presented.
Another greenhouse gas, NF3, has not been evalu-
ated by the IPCC and was not included in this inventory
of greenhouse gas emissions. It has been estimated that
the atmospheric lifetime of NF3, before it undergoes pho-
todissociation in the stratosphere, is about 700 years, re-
sulting in a 100 year global warming potential (GWP)
value of approximately 8,000 (Molina, Wooldridge, and
Molina 1995). As the understanding of the emission char-
acteristics of this gas improves, NF3 will be included in
future inventories.
Electrical Transmission and
Distribution
The largest use for sulfur hexafluoride (SF6), both
domestically and internationally, is as an electrical insu-
lator in equipment that transmits and distributes electric-
ity. It has been estimated that 30 percent of the world-
wide use of SF6 is leaked from electrical transmission
and distribution equipment (Maiss and Brenninkmeijer
1998). 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 al-
lows for more compact substations in dense urban areas.
Fugitive emissions of SF6 can escape from gas-in-
sulated substations and switchgear through seals, espe-
cially from older equipment. It can also be released dur-
Industrial Processes 3-27
-------
ing equipment installation and when equipment is
opened for servicing, which typically occurs every few
years. In the past, some utilities vented SF6 to the atmo-
sphere during servicing; however, it is believed that in-
creased 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 7.0 MMTCE
(1,020 SVfg) in 1997. This quantity amounts to a 25 percent
increase over the estimate for 1990 (see Table 3-38).
Table 3-38: SF6 Emissions from Electrical
Transmission and Distribution
•It 1 Year
i 1 1Bar
1990
1991
.:::..: 1992
1993
1994
1995
':;;,;;~::;:j99i;
1997
MMTCE
i n in in i in linn i
5.6
5.9
6.2
6.4
6.7
7,0
7D
7.0
Mg
II III II I III "li ' ,
859
902
945
988
1,031
1,074
:.: it M :.; • ;
1,074
Methodology
The EPA developed its methodology for estimat-
ing SF6 emissions from electrical transmission and dis-
tribution systems in 1994. The method estimates actual
emissions of SF6 using a top-down, or production-based
approach. Specifically, emissions were calculated based
upon the following factors: 1) the estimated U.S. pro-
duction capacity for SF6, 2) the estimated utilization of
this production capacity, 3) the fraction of U.S. SF6 pro-
duction estimated to be sold annually for use in electri-
cal equipment, and 4) the fraction of these sales estimated
to replace emitted gas.
Based on information gathered from chemical
manufacturers, the EPA estimated in 1994 that U.S. pro-
duction capacity for SF6 was 3.0 thousand metric tons. It
was assumed that plants were operating at 90 percent
capacity, which was consistent with industry averages
and implied that 2.7 thousand metric tons of SF6 were
produced in 1994. The EPA further assumed that 75 per-
cent of U.S. SF6 sales were made to electric utilities and
electrical transmission and distribution equipment manu-
facturers. This assumption is consistent with the estimate
given in Ko, et al. (1993) that worldwide, 80 percent of
j
SF6 sales is for electrical transmission and distribution
systems. Seventy-five percent of annual U.S. production
in 1994 was 2.0 thousand metric tons.
Finally, the EPA assumed that approximately 50
percent of this production, or 1.0 thousand metric tons,
replaced gas emitted into the atmosphere in 1994. This
amount is equivalent to 6.5 MMTCE. The EPA's esti-
mate was based on information that emissions rates from
this equipment were significant and atmospheric mea-
surements that indicated that most of the SF6 produced
internationally since the 1950s had been released. Emis-
sions from electrical equipment were known to occur
from the service and disposal of the equipment and leaks
during operation. Leaks from older equipment were re-
ported to release up to 50 percent of the equipment's
charge per year, although leaks from newer equipment
were reported to release considerably less (e.g., under 1
percent of the charge per year).
It was assumed that emissions have remained con-
stant at 7 MMTCE since 1994.
ii
Data Sources
Emission estimates were provided by the EPA's
Atmospheric Pollution Prevention Division in coopera-
tion with U.S. electric utilities and chemical producers.
Uncertainty
There is currently little verifiable data for estimat-
ing SF6 emissions from electrical transmission and dis-
tribution systems. Neither U.S. gas consumption nor
emission monitoring data were available when these es-
timates were developed. The EPA has recently launched
a voluntary program with electrical power systems to
reduce emissions of SF6 from equipment used to trans-
mit and distribute electricity such as high voltage circuit
breakers, substations, transformers, and transmission
lines. The EPA anticipates that better information on SF6
emissions from electrical equipment will be provided
through its voluntary agreements with electrical utilities
that use SF6 in equipment.
3-28 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Magnesium Production and
Processing
The magnesium metal production and casting in-
dustry uses sulfur hexafluoride (SF6) as a covergas to
prevent the violent oxidation of molten magnesium in
the presence of air. Small concentrations of SF6 in com-
bination with carbon dioxide and/or air are blown over
the molten magnesium metal to induce and stabilize the
formation of a protective crust. A minute portion of the
SF6 applie,d reacts with the magnesium to form a thin
molecular film of mostly magnesium oxide and some
magnesium fluoride. No significant conversion or de-
struction of SF6 occurs in the magnesium casting pro-
cesses, and it is currently assumed that all SF6 is emitted
to the atmosphere. The industry adopted the use of SF6
to replace salt fluxes, sulfur dioxide (SO2), and boron
trifluoride (BF3), which are toxic and more corrosive at
higher concentrations. The SF6 technique is used by pro-
ducers of primary magnesium metal and most magne-
sium part casters.
For 1997, a total of 3.0 MMTCE (460 Mg) of SF6
was estimated to have been emitted by the magnesium
industry, 76 percent more than was estimated for 1990
(see Table 3-39). There are no significant plans for ex-
pansion of primary production in the United States, but
demand for magnesium metal for die casting has begun
to expanded as auto manufacturers have begun to design
more magnesium parts into vehicle models.
Table 3-39: SF6 Emissions from Magnesium
Production and Processing
Year
MMTCE
Mg
1990
1991
1992
1993
1994
1995
1996
1997
1.7
2.0
2.2
2.5
2.7
3.0
3.0
3.0
260
300
340
380
420
460
460
460
Methodology
Emissions were estimated based upon usage infor-
mation supplied to the EPA by primary magnesium pro-
ducers. Consumption was assumed to equal emissions in
the same year. Although not directly employed, the Nor-
wegian Institute for Air Research (NIAR 1993) has re-
ported a range of emission factors for primary magne-
sium production as being from 1 to 5 kg of SF6 per met-
ric ton of magnesium. A survey of magnesium die cast-
ers has also reported an average emission factor of 4.1
kg of SF6 per metric ton of magnesium parts die cast
(Gjestland and Magers 1996).
Data Sources
Emission estimates were provided by the EPA's
Atmospheric Pollution Prevention Division in coopera-
tion with the U.S. primary magnesium metal producers
and casting firms.
Uncertainty
There are a number of uncertainties in these esti-
mates, including the assumption that SF6 does not react
nor decompose during use. In reality, it is possible that
the melt surface reactions and high temperatures associ-
ated with molten magnesium would cause some gas deg-
radation. Like other sources of SF6 emissions, verifiable
SF6 consumption data for the United States were not avail-
able. Sulfur hexafluoride may also be used as a covergas
for the casting of molten aluminum with a high magne-
sium content; however, it is uncertain to what extent this
practice actually occurs.
Industrial Processes 3-29
-------
Box 3-1: Potential Emission Estimates of HFCs, PFCs, and SF6
; ;;., Emissions.ofHF Cs,PFCsand SF6 from industrial processes can be estimated in two ways, either as potential emissions or as
actual emissions. Emission estimates contained within the rest of this chapter are "actual emissions," defined by the Revised 1996
: fCC g«&fefes for National Greenhouse Gas Inventories (IPCC 1997) as estimates that take into account the time lag between
conlirnplin and emissions^ In contrast, "potential emissions" are defined to be equal to the amount of a chemical consumed in
;: j&sqynjry, minus the amount of a chemical recovered for destruction or export in the year of consideration. Potential emissions will
i toenerpy be greater for a given yearthan actual emissions, since some amount of chemical consumed will be stored in products
.,,„,.. iiiiim innii"1,. :.!;::< in
if. 1,1? wuipment and wl not be emitted to,,,the atmosphere until a later date. Because all chemicals consumed will eventually be
fl" "i'W' 'I'l i i1 iilflllBf Hi i I'llnll IllliJIiillllllllllf llllll!|:1llllllllllllllllll!lii I Illllllllii J!1 iP :SB ilillllBfiiBBBWIIBiBB Blliiif !1B]B!BB'. illRilli ".,; V BUBBI: BE! V 1;iB"!l|i;iB!lBi!!BIBIIIIIii M IBIWJil: ill Bl|J 11BB,B 'ii if'! \;" Bllllill!l!i!|l!iiBi: BBIIBIIBB nBilBBBI!.' BlBBBBIiiiBBillB.I \ I" BIBBilB ilBEEKBlEI'V i,1 iB!!!!!!?!!!!?!!!1;1;!" B!: ! B ; lIlflilSiiiBBBBl; „ ,.', I" i' i '111
!' 'Iroitfed Wo the atmosphere unless they are destroyed, in the long term the cumulative emission estimates using the two ap-
Ii' "i, \ 'w\ in HE ' , BII E> i >i ,r, ii"" >'»ii;' ii, E
f ] Jra||jff should be equivalent. Although actual emissions are considered to be the more accurate estimation approach for a single
« • year, estimates of potential emissions are presented here for completeness.
Separate estimates of potential emissions were not made for industrial processes that fall into the following categories: .
• By-product emissions. Some emissions do not result from trie consumption or use of a chemical, but are trie unintended by-
; -;i: ,;'rjffi3uei, gfiiiofrwprocess! FoFsuc'ti en^sTwiK'which ihciude" errifssions bf"CF4' and"c^'^imm aluminum production and of
5 HFC-23 from HCFC-22 production, the distinction between potential and actual emissions is not relevant.!
* :!"'!!!s2iMl2^ '.'.
sumed that there is no delay between consumption and emission and that no destruction of the chemical takes place. It this
Case, actual emissions equal potential'Emissions. ' ,
II I Illllll III III I I 111 II III III I Illllllllll III I 111 I Illllllllll I III IIIIIIIIIIE III III I 111 I IIIIIIIIWnHiira rilTllfWlllW^ 1111 liB' i',,'l: JHllllHilh'.!'!'!!'!'''!!!* 'i'i;,li!llllllllllV',lllll|lllilllLilil^^^^ :,< , ,(»'llln lilliMBu "" I" ' '. ',ii,rt'
• Emissions that are not easily defined. In some processes, such as semiconductor manufacture, the gases used in the process
I HiJii,.^..Illllllllll , , 1 , , . . , , i,i,.iii>UB^ i.,>.|H!i. i jir' j'ji1 n, ,s i' ' <.„ s,
ijljiiijjjblp 3-^Q presents potential emission estimates for HFCs and PFCs from the substitution of ozone depleting "substances and SF6
«> ii missions from, electrical transmission and distribution and other miscellaneous sources such as tennis shoes and sound insulat-
, . ' .0 ' IIIM^^^^^^^^ . ^ ,||| ||||,||M^^^^^^^^^ ^ Uv u,j io,,,,,u OMUUU u,,u oumiu mju.ui
Hi 'wmoows.™ Potential emissions associated with the substitution for ozone depleting substances were calculated through a
..combination of EPA's Vintaging Model and information provided by U.S. chemical manufacturers. For other SF6 sources, estimates
| "fieti Based on in as5U"^e-Jj {]_§. SFg production capacity and plant utilization to estimate total sales. The portion of this amount
used for magnesium processing and assumed to be used for semiconductor manufacture were subtracted. This value of U.S.
lion reported by other countries. The two values were consistent within 25 percent.
Table 3-40:1997 Potential and Actual Emissions of HFCs, PFCs, and SF6 from Selected Sources (MMTCE)
liiHiiiii'i! inw',i, Illilliiiiiiiiiiiiiiiii il iii il in iii nil iiinm in iiiiiiiilllili i i ii ilililii I mi n i i nun mi nun i 11 in minim« iiviiimnm i n n mi i • nun iiiiiiiiiiiiiiiin n mi mn n inn iimm n i in n iiinnnnim n \\ \ \\\\ n n ill n MI i i
Potential Actual
s Depleting Substances 25.7 14.7
:'AItininiiiri RodlicHon : 2"9
~ lCFC-22 Production - 8.2 | '.'Z.1'.. I
Senjconductor Manufacture - 1.3 , '. ,
••;:;(pa;gpesium Production and Processing 3.0 3.0
::::;'|lSi%.§l:6,Sotirces* 14..8,,,, 7.0 ' , . ,, '. ]
[lnmm"1"-"lm ,| i-• T i _.....' .. . ^ _
.-slnncHis ^lecirlcil ffansmission and Distribution and, in the case of' potential emissions, other miscellaneous sources. '
-' Rii; 'totals may not sum due to independent rounding.
" Sec Annex P for a discussion of sources of SF6 emissions excluded from the actual emissions estimates in this report.
3-30 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Industrial Sources of
Criteria Pollutants
In addition to the main greenhouse gases addressed
above, many industrial processes generate emissions of
criteria air pollutants. Total emissions of nitrogen oxides
(NOX), carbon monoxide (CO), and nonmethane volatile
organic compounds (NMVOCs) from non-energy indus-
trial processes from 1990 to 1997 are reported by appli-
cation category in Table 3-41.
Methodology and Data Sources
The emission estimates for this source were taken
directly from the EPA's National Air Pollutant Emissions
Trends, 1900-1997 (EPA 1998). Emissions were calcu-
lated 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 pro-
cessed, etc.
Activity data were used in conjunction with emis-
sion factors, which together relate the quantity of emis-
sions to the activity, Emission factors are generally avail-
able from the EPA's Compilation of Air Pollutant Emis-
sion Factors, AP-42 (EPA 1997). The EPA currently de-
rives the overall emission control efficiency of a source
category from a variety of information sources, includ-
ing published reports, the 1985 National Acid Precipita-
tion 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 accurate
estimates of activity data.
Table 3-41: NOX, CO, and NMVOC Emissions from Industrial Processes (Gg)
Gas/Source
1990 1991 1992
1993
1994 1995 1996 1997
MOX
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 & Allied Product Manufacturing
Metals Processing
Storage and Transport
Other Industrial Processes
Miscellaneous*
771
152
88
3
343
185
9,580
1,074
2,395
69
487
5,556
3,193
575
111
1,356 '
364
787
648
149
69
5
319
106
7,166
1,022
2,333
25
497
3,288
2,997
644
112
1,390
355
496
629
148
74
4
328
75
5,480
1,009
2,264
15
494
1,697
2,825
649
113
1,436
376
252
603
141
75
4
336
48
5,500
992
2,301
46
538
1,623
2,907
636
112
1,451
401
306
774
145
82
5
353
189
7,787
1,063
2,245
22
544
3,912
3,057
627
114
1,478
397
441
656
144
89
5
362
56
5,370
1,109
2,159
22
566
1,514
2,873
599
113
1,499
409
253
754
144
89
5
366
150
7,523
1,109
2,157
22
576
3,658
2,521
396
64
1,190
398
473
781
151
93
6
382
150
7,689
1,168
2,237
24
601
3,660
2,622
415
66
1,249
416
476
* Miscellaneous includes the following categories: catastrophic/accidental release, other combustion, health services, TSDFs (Transport,
Storage, and Disposal Facilities under the Resource Conservation and Recovery Act), cooling towers, and fugitive dust. It does not include
agricultural fires or slash/prescribed burning, which are accounted for under the Agricultural Burning source.
Note: Totals may not sum due to independent rounding.
Industrial Processes 3-31
-------
-------
4. Solvent Use
use of solvents and other chemical products can result in emissions of various ozone precursors (i.e.,
criteria pollutants).1 Nonmethane volatile organic compounds (NMVOCs), commonly referred to as "hy-
drocarbons," are the primary gases emitted from most processes employing organic or petroleum based solvents,
along with small'amounts of carbon monoxide (CO) and oxides of nitrogen (NOX) whose emissions are associated
with control devices used to reduce NMVOC emissions. Surface coatings accounted for just under a majority of
NMVOC emissions from solvent use (46 percent in 1997), while "non-industrial"2 uses accounted for about 33
percent and dry cleaning for 3 percent. Overall, solvent use accounted for approximately 34 percent of total U.S.
emissions of NMVOCs in 1997, and increased 13 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 recom-
mended 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 solvents 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 many of these industrial applications also employ thermal incineration
as a control technology, CO and NOX combustion by-products are also reported with this source category.
Total emissions of nitrogen oxides (NOX), nonmethane volatile organic compounds (NMVOCs), and carbon monox-
ide (CO) from non-energy industrial processes from 1990 to 1997 are reported by detailed source category in Table 4-1.
Methodology
Emissions were calculated by aggregating solvent use data based on information relating to solvent uses from differ-
ent 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 emission factors to the type 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.
1 Solvent usage in the United States also results in the emission of small amounts of hydrofluorocarbons (HFCs) and hydrofluoroethers
(HFEs), which are included under Substitution of Ozone Depleting Substances in the Industrial Processes chapter.
2 "Non-industrial" uses include cutback asphalt, pesticide application adhesives, consumer solvents, and other miscellaneous applications.
Solvent Use 4-1
-------
Table 4-1: Emissions of NOX, CO, and NMVOC from Solvent Use (Gg)
Activity
1990 1991 1992 1993 1994 1995 1996 1997
B0j<
" Digressing
Graphic Arts
Dry Cleaning
;;jSurf§ceCoa|ing
Other industrial Processes8
"t Ng|;l|tIus|r]aXPrJ)cessesS
CQ
DegreasFng
Graphic Arts
Dfy Cleaning
Surface Coating
Other Industrial Processes8
* Noji -Industrial processes''
NMVOCs
i Decreasing
Graphic Arts
6g Cleaning
Surface Coating
Other Industrial Processes8
rtan-Wustnal Processes'1
1
+
+
+
1
+
, „, t
4
+
+
+
+
4
" " ' „!, !_, ,,t
5,217
675
249
195
2,289
85
1,724
2
-f-
+
+
1
+
,, ...t,
4
+
+
+
1
., ,,,,,,l,3
5,245
651
273
198
2,287
89
1,746
2
+
1
+
2
+
H-
" ' 5 '
+
+
+
1
3
t,
5,353
669
280
203
2,338
93
1,771
2
-j.
1
+
2
+
±
4
+
+
+
1
3
^T"'
5,458
683
292
204
2,387
93
1,798
2
+
1
_l_
2
+
±, ,
5
+
+
1
1
3
5,590
703
302
207
2,464
90
1,825
11 i
3 . .
+
1
+
2
+
+
'5 "
+ '
+ "'-
1 '
1
3
+
5,609
716
,,,307,,,,
,209,,;,,
2,4,3,2,
,8,7,, ;.
1,858
3 ,„
1
2
_l_
+
5
+
+
1
1 „
3
+
5,691
599
,,,,35,3
1,72
2,613
48
1,905
3
1
2
+
6
+
+
1
1
3
5,882
628
373
174
2,713
51, „
1,943
* Inqlixfep rubber and plasiitc^_anuf?cturirii~ and other miscelianebus applications!
f tnctades cutback asphalt, pesticide application adhesives, consumer solvents, and other miscellaneous applications.
Note: Totals may not sum due to independent rounding.
; :-f Does not exceed GJLGg ...'..'.. ..".'." , ". . , '.''..
Data Sources
The emission estimates for this source were taken
directly from the EPA's National Air Pollutant Emissions
Trends, 1900-1997 (EPA 1998). Emissions were calcu-
lated either for individual sources or for many sources
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 emis-
sion factors, which together relate the quantity of emis-
sions to the activity. Emission factors are generally avail-
able from the EPA's Compilation of Air Pollutant Emis-
sion Factors, AP-42 (EPA 1997).; The EPA currently
derives the overall emission control efficiency of a source
category from a variety of information sources, includ-
ing published reports, the 1985 National Acid Precipita-
tion and Assessment Program emissions inventory, and
other EPA data bases.
Uncertainty
Uncertainties in these estimates are partly due to
the accuracy of the emission factors used and the reli-
ability of correlations between activity data and actual
emissions.
4-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
5. Agriculture
Figure 5-1
Agricultural activities contribute directly to emissions of greenhouse gases through a variety of processes. The
Agriculture chapter includes the following sources: enteric fermentation in domestic livestock, livestock manure
management, rice cultivation, agricultural soil activities, and agricultural residue burning (see Figure 5-1). Several other
agricultural activities, such as irrigation and tillage practices, may also generate anthropogenic greenhouse gas emissions;
however, the impacts of these practices are too uncertain to estimate emissions.1 Agriculture-related land-use activities,
such as conversion of grassland to cultivated land, are discussed in the Land-Use Change and Forestry chapter.
In 1997, agricultural activities were responsible for
emissions of 131.4 MMTCE, or 7 percent of total U.S.
greenhouse gas emissions. Methane (CH4) and nitrous ox-
ide (N2O) were the primary greenhouse gases emitted by
agricultural activities. Methane emissions from enteric
fermentation and manure management represent about 19 and
9 percent of total CH4 emissions from anthropogenic ac-
tivities, respectively. Of all domestic animal types, beef and
dairy cattle were by far the largest emitters of methane. Rice
cultivation and agricultural crop waste burning were minor
sources of methane. Agricultural soil management activi-
ties such as fertilizer application and other cropping prac-
tices were the largest source of U.S. N2O emissions, ac-
counting for 68 percent. Manure management and agricul-
tural residue burning were also smaller sources of N2O emissions.
Table 5-1 and Table 5-2 present emission estimates for the Agriculture chapter. Between 1990 and 1997, CH4
emissions from agricultural activities increased by 8 percent while N2O emissions increased by 13 percent. In addi-
tion to CH4 and N2O, agricultural residue burning was also a minor source of the criteria pollutants carbon monoxide
(CO) and nitrogen oxides (NOX).
Agricultural Soil
Management
Enteric
Fermentation
Portion of All
Emissions
Manure
Management
Rice Cultivation
Agricultural 0 4
Residue Burning
10 20 30 40 50 60 70
' Irrigation associated with rice cultivation is included in this inventory.
Agriculture 5-1
-------
Table 5-1: Emissions from Agriculture (MMTCE)
Gas/Source
CH4 I:,,;::;,,1;;:,,::;;,,,,:
i Enteric Fermentation
Manure Management
Rica Cultivation
Agricultural Residue Burning
[ f| HfflfjJS lfeP9enlent
'IlilllgHlural'Soil Management
| ;;|' ilflliylyral fiesldue Burning
' :'foti """ " "
1990
50.3
32 J
14.9
2.5
0.2
68.1
2.6
65.3""
0.1
118.4
;:; ; ,: Nets: Totals may not sum due to independent rounding.
Table 5-2: Emissions from Agriculture (Tg)
Gas/Source 1990
CH<
Enteric fermentation
Manure Management
Rice Cultivation , II ,,,''' „„,'„„,„"'„'",',
Agricultural Residue Burninp
N20
Manure Management
Agricultural Soil Management
Agncuilural Residue Burning
+• Does nol exceed O.dS Tg
Note: Totals may not sum due to independent rounding
8.8
5.7
2.6
0.4
+
0.8
+
0.8
+
1991
50.9""
318
'"15V4
2.5
0.2
69.1
2.8
66.2
0.1
120.0
1991
8.9
"5.7"
2.7
""J-i,
+
0.8
+
0.8
+
1992
52.2
33.2
i'6.6
2,8,,,,
0.2
70.9
2.8
68,0
0.1
123.1
1992
9.1
5.8
2.8
'..',PJ.
+
0.8
+
0.8
+
1993
52.5"
33.6
16.1"
2,5
0.2
69.9
2.9
67.0
0.1
122.4
1993
9.2
5.9
2.8
'j_o.4_
+
0.8
+
0.8
+
1994 1995
54.5 54.8
34.5 34.9
167 16.9
3.0 2.8
0.2 0.2
76.4 73.2
2.9 2.9
73.4 70.2
0.1 0.1
130.9 128.0
:
1994 1995
1996 1997
53.8 54.1
34.5 34.1
16.6 17.0
2.5 2,7
0.2 0.2
75.1 77.2
3.0 3.0
72.0 74.1
0.1 0.1
128.9 131.4
,
1996 1997
9.5 9.6 9.4 9.4
6.0 6.1 6.0 6.0
2.9 3.0 2.9 3.0
,. "..'.iDL ".,o,5\ ,,o:4 0.5
+ + ; + +
0.9 0.9
' "+ +
0.9 0.8
+ +
0.9 0.9
+ +
0.9 0.9
+ +
Enteric Fermentation
Methane (CH4) is produced as part of the normal
digestive processes in animals. During digestion, mi-
crobes resident in an animal's digestive system ferment
food consumed by the animal. This microbial fermenta-
tion process, referred to as enteric fermentation, produces
methane as a by-product, which can be exhaled, or eruc-
tated, by the animal. The amount of methane produced
and excreted by an individual animal depends primarily
upon the animal's digestive system, and the amount and
lype of feed it consumes.
Among domestic animal types, the ruminant ani-
mals (e.g.. cattle, buffalo, sheep, goats, and camels) are
the major emitters of methane 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 soluble products that
can be utilized by the animal. The microbial fermenta-
tion that occurs in the rumen enables ruminants to digest
coarse plant material that non-ruminant animals cannot.
Ruminant animals, consequently, have the highest meth-
ane emissions among all animal types.
Non-ruminant domestic animals (e.g., pigs, horses,
mules, rabbits, and guinea pigs) also produce methane
through enteric fermentation, although this microbial
fermentation occurs in the large intestine. These non-ru-
minants have significantly lower methane emissions than
ruminants because the capacity of the large intestine to
produce methane is lower.
In addition to the type of digestive system, an
animal's feed intake also affects methane excretion. In
general, a higher feed intake leads to higher methane
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 var-
ies among animal types as well as among different man-
agement practices for individual animal types.
Methane emissions estimates for livestock are
shown in Table 5-3 and Table 5-4. Total livestock emis-
5-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 5-3: CH* Emissions from Enteric Fermentation (MMTCE)
Animal Type
Dairy Cattle
Beef Cattle
Other
Sheep
Goats
Horses
Hogs
Total
1990
8.4
22.6
1.6
0.5
0.1
0.5
0.5
32.7
1991
8.4
22.8
1.7
0.5
0.1
0.6
0.5
32.8
1992
8.4
23.1
1.7
0.5
0.1
0.6
0.5
33.2
1993
8.4
23.6
1.6
0.5
0.1
0.6
0.5
33.6
1994
8.4
24.5
1.6
0.4
0.1
0.6
0.5
34.5
1995
8.4
24.9
1.6
0.4
0.1
0.6
0.5
34.9
1996
8.3
24.6
1.6
0.4
0.1
0.6
0.5
34.5
1997
8.3
24.3
1.6
0.3
0.1
0.6
0.5
34.1
Note: Totals may not sum due to independent rounding.
Table 5-4: CH4 Emissions from Enteric Fermentation (Tg)
Animal Type
1990 1991 1992 1993 1994 1995 1996 1997
Dairy Cattle
Beef Cattle
Other
Sheep
Goats
Horses
Hogs
Total
1.5
4.0
0.3
0.1
+
0.1
0.1
5.7
1.5
4.0
0.3
0.1
+
0.1
0.1
5.7
1.5
4.0
0.3
0.1
+
0.1
0.1
5.8
1.5
4.1
0.3
0.1
+
0.1
0.1
5.9
1.5
4.3
0.3
0.1
+
0.1
0.1
6.0
1.5
4.3
0.3
0.1
+
0.1
0.1
6.1
1.5
4.3
0.3
0.1
+
0.1
0.1
6.0
1.5
4.2
0.3
0.1
+
0.1
0.1
6.0
+ Does not exceed 0.05 Tg
Note: Totals may not sum due to independent rounding.
sions in 1997 were 34.1 MMTCE (6.0 Tg). Emissions
from dairy cattle remained relatively constant from 1990
to 1997 despite a steady increase in milk production.
During this time, emissions per cow increased due to a
rise in milk production per dairy cow (see Table 5-5);
however, this trend was offset by a decline in the dairy
cow population. Beef cattle emissions continued to de-
cline, caused by the second consecutive year of declin-
ing cattle populations. Methane emissions from other
animals have remained relatively constant.
Methodology
Livestock emission estimates fall into two catego-
ries: cattle and other domesticated animals. Cattle, due
to their large population, large size, and particular diges-
tive characteristics, account for the majority of methane
emissions from livestock in the United States and are
handled separately. Also, cattle production systems in the
United States are well characterized in comparison with
other livestock management systems. Overall, emissions
estimates were derived using emission factors, which
were multiplied by animal population data.
While the large diversity of animal management
practices cannot be precisely characterized and evalu-
ated, significant scientific literature exists that describes
the quantity of methane produced by individual rumi-
nant animals, particularly cattle. A detailed model that
incorporates this information and other analyses of feed-
ing practices and production characteristics was used to
estimate emissions from cattle populations.
To derive emission factors for the various types of
cattle found in the United States, a mechanistic model of
rumen digestion and animal production was applied to
data on thirty-two different diets and nine different cattle
types (Baldwin et al. 1987a and b).2 The cattle types were
defined to represent the different sizes, ages, feeding
systems,'and management systems that are typically
found in the United States. Representative diets were
2 The basic model of Baldwin et al. (1987a and b) was revised somewhat to allow for evaluations of a greater range of animal types and
diets. See EPA (1993).
Agriculture 5-3
-------
defined for each category of animal, reflecting the feeds
and forages consumed by cattle type and region. Using
this model, emission factors were derived for each com-
bination of animal type and representative diet. Based
upon the level of use of each diet in the five regions,
average regional emission factors for each of the nine
cattle types were derived.3 These emission factors were
then multiplied by the applicable animal populations from
each region.
For dairy cows and beef cows and replacements,
emission estimates were developed using regional emis-
sion factors. Dairy cow emission factors were modified
to reflect changing (primarily increasing) milk produc-
tion per cow over time in each region. All other emission
factors were held constant over time. Emissions from
other cattle types were estimated using national average
emission factors.
Emissions estimates for other animal types were
based upon average emission factors representative of
entire populations of each animal type. Methane emis-
sions from these animals accounted for a minor portion
of total methane emissions from livestock in the United
States. Also, the variability in emission factors for each
of these other animal types (e.g., variability by age, pro-
duction system, and feeding practice within each animal
type) Ik smaller than for cattle.
See Annex G for more detailed information on the
methodology and data used to calculate methane emis-
sions from enteric fermentation.
Data Sources
The emission estimates for all domestic livestock
were determined using a mechanistic model of rumen
digestion and emission factors developed in EPA (1993).
For dairy cows and beef cows and replacements, regional
emission factors were used from EPA (1993). Emissions
from other cattle types were estimated using national
average emission factors from EPA (1993). Methane
emissions from sheep, goats, pigs, and horses were esti-
mated by using emission factors utilized in Crutzen et al.
(1986) and annual population data from USDA statisti-
cal reports. These emission factors are representative of
typical animal sizes, feed intakes, and feed characteris-
tics in developed countries. The methodology employed
in EPA (1993) is the same as those recommended in IPCC
(1997). All livestock population data were taken from
USDA statistical reports. See the following section on
manure management for a complete listing of reports
cited. Table 5-5 below provides a summary of cattle popu-
lation and milk production data.
Table 5-5: Cow Populations (thousands) and Milk
Production (million kilograms)
Year
'"BiiryCow11
Population
Beef Cow
Population
Milk
Production
1990
,1991
1992
1993
1994
1995
1996
1997
10,007
9,883
9,714
9,679
,9,514
9,494
9,409
9,304
32,677
„„ 3,2,960 ;
33,453
34,132 "
35,325 ;
35,628
35,414
34,486 '
67,006
,66,995
68,441
68,304
69,702
70,500
69,976
71,035
Uncertainty
The diets analyzed using the rumen digestion model
include broad representations of the types of feed con-
sumed within each region. Therefore, the full diversity
of feeding strategies employed in the United States is
not represented and the emission factors used may be
biased. The rumen digestion model, however, has been
validated by experimental data. Animal population and
production statistics, particularly for beef cows and other
grazing cattle, are also uncertain. Overall, the uncertainty
in the emission estimate is estimated to be roughly "20
percent (EPA 1993). \
Manure Management
The management of livestock manure produces
methane (CH4) and nitrous oxide (N2O) emissions. Meth-
ane is produced by the anaerobic decomposition of ma-
nure. Nitrous oxide is produced as part of the agricul-
tural nitrogen cycle through the denitrification of the or-
ganic nitrogen in livestock manure and urine.
1 Feed intifcc of bulls does not vary significantly by region, so only a national emission factor was derived for ^this cattle type.
5-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
When livestock and poultry manure is stored or
treated in systems that promote anaerobic conditions (e.g.,
as a liquid in lagoons, ponds, tanks, or pits), the decom-
position of materials in manure tends to produce meth-
ane. When manure is handled as a solid (e.g., in stacks or
pits) or deposited on pastures and range lands, it tends to
decompose aerobically and produce little or no meth-
ane. Air temperature and moisture also affect the amount
of methane produced because they influence the growth
of the bacteria responsible for methane formation. Meth-
ane production generally increases with rising tempera-
ture and residency time. Also, for non-liquid based ma-
nure systems, moist conditions (which are a function of
rainfall and humidity) favor methane production. Al-
though the majority of manure is handled as a solid, pro-
ducing little methane, the general trend in manure man-
agement, particularly for dairy and swine producers, is
one of increasing usage of liquid systems.
The composition of the manure also affects the
amount of methane produced. Manure composition de-
pends upon the diet of the animals. The greater the en-
ergy content and digestibility of the feed, the greater the
potential for methane emissions. For example, feedlot
cattle fed a high energy grain diet generate manure with
a high methane-producing capacity. Range cattle feed-
ing on a low energy diet of forage material produce ma-
nure with only half the methane-producing capacity of
feedlot cattle manure.
The amount of N2O produced can also vary de-
pending on the manure and urine composition, the type
of bacteria involved in the process, and the amount of
oxygen and liquid in the manure system. Nitrous oxide
emissions result from livestock manure and urine that is
managed using liquid and slurry systems, as well as ma-
nure and urine that is collected and stored. Nitrous oxide
emissions from unmanaged livestock manure and urine
on pastures, ranges, and paddocks, as well as from ma-
nure and urine that is spread onto fields is accounted for
and discussed under Agricultural Soil Management.
Table 5-6, Table 5-7, and Table 5-8 (note, Table 5-
8 is in units of gigagrams) provide estimates of methane
and nitrous oxide emissions from manure management.
Emission quantities are broken down by animal catego-
ries representing the major methane producing groups.
Estimates for methane emissions in 1997 were 17.0
MMTCE (3.0 Tg). Emissions have increased each year
from 1990 through 1995; however, emissions decreased
slightly in 1996 with a decline in animal populations,
including swine. In 1997, emissions from this source in-
creased above even 1995 levels, mostly due to revived
swine production and higher poultry production. Under
the AgSTAR Program of the U.S. Climate Change Ac-
tion Plan, methane emissions from manure have been
reduced through methane recovery efforts. The AgSTAR
Program reported a reduction of 0.1 MMTCE of meth-
ane in both 1996 and 1997.
Total N2O emissions from managed manure sys-
tems in 1997 were estimated to be 3.0 MMTCE (35 Gg).
The 15 percent increase in emissions from 1990 to 1997
can be attributed to an increase in the population of poul-
try and swine over the eight year period. The proportion
of beef cattle in feedlots, which were assumed to use
managed manure systems, also increased. Again,
unmanaged livestock manure is accounted for under
Agricultural Soil Management. Methane emissions were
mostly unaffected by this shift in the beef cattle popula-
tion because feedlot cattle use solid storage systems,
which produce little methane.
In general, changes in the emission estimates over
time reflect variations in animal populations. The esti-
mates also reflect a regional redistribution of dairies to
the southwestern states, which have larger average farm
sizes, and an increase in feed consumption by dairy cows
to accommodate increased milk production per cow.
Regional shifts in the hog population were also assessed.
Methodology
The methods presented in EPA (1993) form the
basis of the methane emissions estimates for each ani-
mal type. The calculation of emissions requires the fol-
lowing information:
• Amount of manure produced (amount per head times
number of head)
• Portion of the manure that is volatile solids (by ani-
mal type)
• Methane producing potential of the volatile solids
(by animal type)
Agriculture 5-5
-------
Table 5-6: CH4 and N20 Emissions from Manure Management (MMTCE)
Gas/AnimalType
1990 1991 1992 1993 1994 1995 1996 1997
CH,
• biry Cattle
Beef Cattle
;",,: Swine,, ,
.; Steep"
, i ' , i iiiiiii i * i < >,' i. . ',. ' • ' ,, .,
".'"I':' GpjlS , vi , ih,.
•: P2i|ry
::; "Horses" " 1",.' .^Z* ',"","" _ ""„,,' ',','"" '. "
Dairy Cattle
"Beef Cattfe " , """" , ™ ' '" [ ,
Swfns
Sfiie'p
"", 'Goats',^ ",',' ;_ ^ , , „„ \
'••'• Poultry " ' ' ' ' '
Horses
Total
14.9
4.3
1.1
,7.8,
,,+ „„
.t,
1.5
0-2
2.6
0.1
o!i
0.0
0.0
1.3
0.0
17.6
15.4
4.3
1.2
S-2
1.5
0.2
2.8
0.1
1.2
0.1
P.,
"its'
.0,0.
18.2
,-*•' QMS not exceed 0.05 MMTCE
, Hots; Totals may not sum due to independent rounding.
Table 5-7: CH4 Emissions from Manure Management (Tg)
III III 1 iilll lllilll ,' • . .',"", .';,(: 'In"-!. ir '.• • ... '; !n i .;
Animal Type 1990 1991
JIIIIIIIIL I II II II IIIIIII :• >• . .. !.. '''.' ' !', ': :. i
Dairy Cattle
Beef Cattle
Swine
: Sheep
Goats
Poultry
Horses
Total
0.7
0.2
1.4
0.3
2.6
0.8
0,2
1,4
0.3
2.7
+ Does not exceed 0.05 Tg
.....fiote: Totals maynot sum due to independent rounding.
Table 5-8: N20 Emissions from Manure Management (Gg)
AnlrnalTVpe 1990 1991
,• Dairy" Cattle
Beef Cattle
;;8w(rl
• ,„; Sheep
Goats
": Pouftry
"Hoi^es
Total
+ Does not exceed 0.5 Gg
i Note: Totals may not sum due to independent rounding.
•IHIII I I M I ' III I 'III III ^l fl | ' ll » ' , l.!| .If'li" »,', ;
"l
13
,1-
15
1
31
1'
15
.,,.,1
16
1
33
16.0
4.4
1.2
8,6,,
,,t,,,
'"•L6
0.2
2.8
0.1
1.2
0.1
o.d
0,0
1.4
0,0
18.7
1992
0,8
, Q,2
1.5
0.3
2.8
1992
"l" '
14
,,. 1
16
1
33
16.1
4.4
1.2
8,6
I!.', UP. I '.
0.2
2.9
0.1
1.2
QJ
0.0
0.0
1.4
0,0,
19.0
1993
"".a i1.1,,;!!,"!!,',!'1:'
.... 0,8
0:2
1.5
0.3
2.8
1993
i '
15
„ 1
17
1
34
'•::,:i ' .... V .•
16.7
..4.5
1.2
±
ZL
0.2
2.9
QJ..
1.2
0,1
0.0
fll,
1.5
0,1
19.7
i • l'!'1,,,:1"
1994
"I ;«,Mi.|l'".i !'•
QJ,
0,2,,
1.6
0.3
2.9
1994
'i "'
15,.
j
17
1
35
'If; 'ill!1, 't. i
16,9
4.5
1.3
9,2
... . ll '
0.2'
2.9
' tif ..
0,0
D.Q..,
,o,'l
19.8
• ll
1995
l|1!' ,'"i|,, i 1: '•!
... ,^,,
1-6
0.3
2.9
;:>. i
. ! . „
1995
.14. „
.. 1
is ;
1 ;
34
. -.'."s !i"vi
i
16.6
4.5
1.3
,8,8
, ..+
""i.7
0.2
3.0
„ , 0.1
1.2
0.1
,0.0
o.o, „„
1.5
0.1
19.5
I! "
i ill" . Ml
1996
0.8
0.2
1.5
0.3
2.9
1996
"l
14 ...
1
18
1
35
• ' JJ'"'!!'!1 ,,, .1
17,0
4.6
1.3
9.3
,, „ + , .
..' t8 „„„„„
0.2
3.0
0.1
1.2
0.1
0.0
0,0
1.6
0.1
20.0
1997
",,!" t
0.8
0,2
1.6
0.3
3.0
: ' if
1997
' "l
15
1
19
1
36
',:•:; . ,i
5-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
• Extent to which the methane producing potential is
realized for each type of manure management sys-
tem (by state and manure management system)
• Portion of manure managed in each manure man-
agement system (by state and animal type)
For dairy cattle and swine—the two largest emit-
ters of methane—estimates were developed using state-
level animal population data. For other animal types, 1990
emission estimates from the detailed analysis presented
in EPA (1993) were scaled at the national level using the
population of each livestock type. Nitrous oxide emis-
sions were estimated by first determining manure man-
agement system usage. Manure system usage for dairy
cows and swine were based on the farm size distribu-
tion. Total Kjeldahl nitrogen4 production was calculated
for all livestock using livestock population data and ni-
trogen excretion rates. The total amount of nitrogen from
manure was reduced by 20 percent to account for the
portion that volatilizes to NH3 and NOX (IPCC/UNEP/
OECD/IEA 1997). Nitrous oxide emission factors were
then applied to total nitrogen production to estimate N2O
emissions. Throughout the time series the estimates of
the portion of manure and urine which is managed in
each of the manure management systems in each state
remained fixed.
See Annex H for more detailed information on the
methodology and data used to calculate methane emis-
sions from manure management. The same activity data
was also used to calculate N2O emissions.
Data Sources
Annual livestock population data for all livestock
types except horses were obtained from the U.S. Depart-
ment of Agriculture's National Agricultural Statistics Ser-
vice (USDA 1994a, b; 1995a-j; 1996a-f; 1997a-f, 1998a-
h). Horse population data were obtained from the FAOSTAT
database (FAO 1998). Data on farm size distribution for
dairy cows and swine were taken from the U.S. Depart-
ment of Commerce (DOC 1995, 1987). Manure manage-
ment system usage data for other livestock were taken from
EPA (1992). Nitrogen excretion rate data were developed
by the American Society of Agricultural Engineers (ASAE
1995). Nitrous oxide emission factors were taken from
IPCC/UNEP/OECD/IEA (1997). Manure management sys-
tems characterized as "Other" generally refers to deep pit
and litter systems. The IPCC N2O emission factor for "other"
systems (0.005 kg N2O/kg N excreted), was determined to
be inconsistent with the characteristics of these manage-
ment systems. Therefore, in its place the solid storage/dry-
lot emission factor was used.
Uncertainty
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
state and the exact methane generating characteristics of
each type of manure management system. Because of
significant shifts in the dairy and swine sectors toward
larger farms, it is believed that increasing amounts of
manure are being managed in liquid manure manage-
ment systems. The existing estimates capture a portion
of these shifts as the dairy and swine populations move
regionally toward states with larger average farm sizes.
However, changes in farm size distribution within states
since 1992 are not captured by the method. The methane
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.
The N2O emission factors published in IPCC/
UNEP/OECD/IEA (1997) were also derived using lim-
ited information. The IPCC factors are global averages;
U.S.-specific emission factors may be significantly dif-
ferent. Manure and urine in anaerobic lagoons and liq-
uid/slurry management systems produce methane at dif-
ferent rates, and would in all likelihood produce N2O at
different rates, although a single emission factor was used.
Rice Cultivation
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
Total Kjeldahl nitrogen is a measure of organically bound nitrogen and ammonia nitrogen.
Agriculture 5-7
-------
floodwater causing anaerobic conditions in the soil to
develop, Under such conditions, methane is produced
through anaerobic decomposition of soil organic matter
by methanogenic bacteria. However, not all of the meth-
ane that is produced is released into the atmosphere. As
much as 60 to 90 percent of the methane produced is
oxidised by aerobic methanotrophic bacteria in the soil
(Holzapfel-Psehorn et al. 1985, Sass et al. 1990). Some
of the methane is also leached away as dissolved meth-
ane in floodwater that percolates from the field. The re-
maining non-oxidized methane is transported from the
submerged soil to the atmosphere primarily by diffusive
transport through the rice plants. Some methane also es-
capes 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
methane emissions, Upland rice fields are not flooded,
and therefore are not believed to produce methane. In
deepwater rice fields (i.e., fields with flooding depths
greater than one meter), lower stems and roots of the
rice plants are dead, and thus effectively block the pri-
mary methane transport pathway to the atmosphere.
Therefore, while deepwater rice growing areas are be-
lieved to emit methane, die quantities released are likely
to be significantly less than the quantities released from
areas with more shallow flooding depths. Also, some
flooded fields are drained periodically during the grow-
ing season, either intentionally or accidentally. If water
is draiped and soils are allowed to dry sufficiently, meth-
ane emissions decrease or stop entirely. This is due to
soil aeration, which not only causes existing soil meth-
ane to oxidize but alsp inhibits further methane produc-
tion in soils. All rice in the United States is grown under
continuously flooded conditions; none is grown under
deepwater conditions.
Other factors that influence methane emissions
from flooded rice fields include soil temperature, soil
type, fertilization practices, cultivar selection, and other
cultivation practices (e.g., tillage, seeding and weeding
practices). Many studies have found, for example, that
methane emissions increase as soil temperature increases.
SevcraJ studies have also indicated that some types of
synthetic nitrogen fertilizer inhibit methane generation,
while organic fertilizers enhance methane emissions.
However, while it is generally acknowledged that these
factors influence methane emissions, the extent of their
I!
influence, individually or in combination, has not been
well quantified.
Rice cultivation is a small spurce of methane in
the United States. Only seven states grow rice: Arkan-
sas, California, Florida, Louisiana, Mississippi, Missouri,
and Texas. Methane emissions frop rice cultivation in
1997 were estimated to have been 2.7 MMTCE (475 Gg).
Table 5-9 and Table 5-10 present annual emission esti-
mates for each state. There was nq apparent trend over
the seven year period. Between 1994 and 1996, rice ar-
eas declined fairly steadily in almost all states, and the
national total declined by about 8 percent each year; in
1997, however, rice areas increased by about 7 percent
(see Table 5-11). '
The factors that affect the rice area harvested vary
from state to state. In Florida, the state having the small-
est harvested rice area, rice acreage is driven by sugar-
cane acreage. Sugarcane fields are flooded each year to
control pests, and on this flooded land a rice crop is grown
along with a ratoon crop of sugarcane (Schudeman
1997a). In Missouri, rice acreage is; affected by weather
(rain during the planting season may prevent the plant-
ing of rice), prices of soybeans relative to rice (if soy-
bean prices are higher, then soybeans may be planted on
some of the land which would otherwise have been
planted in rice), and government support programs
(which, beginning in 1996, were being phased-out)
(Stevens 1997). In Mississippi, rice acreage is driven by
both the price of rice and the price of soybeans. Rice in
Mississippi is usually rotated with soybeans, but if soy-
bean prices increase relative to rice prices, then some of
the acreage that would have been planted in rice, is in-
stead planted in soybeans (Street 1997). In Texas, rice
production, and thus, harvested area, are driven by both
government programs and the cost of production
(Klosterboer 1997). California rice area is influenced by
water availability as well as government programs and
commodity prices. In recent years, California was able
to grow more rice due to recovery from a drought, as
well as price increases associated with gaining access to
the Japanese market (Scardaci 1997). In Louisiana, rice
5-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 5-9: GH4 Emissions from Rice Cultivation (MMTCE)
State
1990 1991 1992 1993 1994 1995 1996 1997
Arkansas
California
Florida
Louisiana
Mississippi
Missouri
Texas
Total
0.9
0.5
+
0.6
0.2
0.1
0.3
2.5
0.9
0.4
+
0.6
0.1
0.1
0.3
2.5
1.0
0.5
+
0.7
0.2
0.1
0.3
2.8
0.9
0.5
+
0.6
0.2
0.1
0.2
2.5
1.1
0.6
+
0.7
0.2
0.1
0.3
3.0
1.0
0.5
+
0.7
0.2
0.1
0.3
2.8
0.9
0.6
+
0.6
0.1
0.1
0.2
2.5
1.0
0.6
+
0.6
0.1
0.1
0.2
2.7
+ Does not exceed 0.05 MMTCE
Note: Totals may not sum due to independent rounding.
Table 5-10: CH4 Emissions from Rice Cultivation (Gg)
State
1990 1991 1992 1993 1994 1995 1996 1997
Arkansas
California
Florida
Louisiana
Mississippi
Missouri
Texas
Total
156
79
3
111
27
11
52
439
164
70
5
104
24
12
50
429
180
79
5
126
30
15
51
486
160
88
5
108
27
12
43
443
185
98
5
126
34
16
52
516
175
94
5
116
32
15
46
482
152
101
4
99
23
12
40
431
178
103
5
111
26
14
38
475
Note: Totals may not sum due to independent rounding.
area is influenced by government programs, weather
conditions (such as rainfall during the planting season),
as well as the price of rice relative to that of corn and
other crops (Saichuk 1997). Arkansas rice area has been
influenced in the past by government programs. The
phase-out of these programs began in 1996, and com-
modity prices in the spring had a greater effect on the
amount of land planted in rice (Mayhew 1997).
Methodology
The Revised 1996IPCC Guidelines (IPCC/UNEP/
OECD/EEA 1997) recommend applying a seasonal emis-
sion factor to the annual harvested rice area to estimate an-
nual CH4 emissions. This methodology assumes that a sea-
sonal emission factor is available for all growing conditions,
including season lengths. Because season lengths are vari-
able both within and among states in the United States, and
because flux measurements have not been taken under all
growing conditions hi the United States, the previous IPCC
methodology (IPCC/UNEP/OECD/IEA 1995) has been
applied here, using season lengths that vary slightly from
the recommended approach. The 1995 IPCC Guidelines
recommend multiplying a daily average emission factor by
growing season length and annual harvested area. The IPCC
Guidelines suggest that the "growing" season be used to
calculate emissions based on the assumption that emission
factors are derived from measurements over the whole grow-
ing season rather than just the flooding season. Applying
this assumption to the United States, however, would result
in an overestimate of emissions because the emission fac-
tors developed for the United States are based on measure-
ments over the flooding, rather than the growing, season.
Therefore, the method used here is based on the number of
days of flooding during the growing season and a daily av-
erage emission factor, which is multiplied by the harvested
area. Agricultural statisticians hi each of the seven states in
the United States that produce rice were contacted to deter-
mine water management practices and flooding season
lengths in each state. Although all contacts reported that
rice growing areas were continually flooded, flooding sea-
son lengths varied considerably among states; therefore,
emissions were calculated separately for each state.
Agriculture 5-9
-------
The climatic conditions of southwest Louisiana,
Texas, and Florida also allow for a second, or ratoon,
rice crop. This second rice crop is produced from re-
growth on the stubble after the first crop has been har-
vested. The emission estimates presented here account
for this additional harvested area.
Because the number of days that the rice fields re-
main permanently flooded varies considerably with plant-
ing system and cultivar type, a range for the flooding
season length was adopted for each state. The harvested
areas J(nd flooding season lengths for each state are pre-
sented in Table 5-11 and Table 5-12, respectively.
If , ': .. ,
Data Sources
Data on harvested rice area for all states except
Florida were taken from U.S. Department of Agriculture's
Crop Production 1997 Summary (USDA 1998). Har-
vested rice areas in Florida from 1990 to 1996 were ob-
tained from Tom Schudeman (1997a), aFlorida Agricul-
tural Extension Agent. Harvested rice areas in Florida in
1997 were obtained from Terrie Smith of Sem-Chi Rice
(1998). Acreages for the ratoon crops were estimated by
assuming that the ratooned areas were equal to about 30
percent of the primary crop in Louisiana, 40 percent in
Texas (Lindau and Bollich 1993); 5Q percent of the pri-
mary crop in Florida in 1990 through 1996 (Schudeman
1995), and 67 percent of the primary crop in Florida in
1997 (Smith, 1998). Information about flooding season
lengths was obtained from agricultural extension agents
in every rice-producing state. Daily methane emission
factors were taken from results of field studies performed
in California (Cicerone et al. 1983), Texas (Sass et al.
1990, 1991a, 1991b, 1992) and Louisiana (Lindau et al.
1991, Lindau and Bollich 1993). Based on the maximal
I
and minimal estimates of the emission rates measured in
these studies, a range of 0.1065 to 0.5639 g/m2/day was
applied to the harvested areas and flooding season lengths
in each state.5 Since these measurements were taken in
rice growing areas, they are representative of soil tern-
i
peratures, and water and fertilizer management practices
typical of the United States.
Uncertainty
There are three sources of uncertainty in the cal-
culation of CH4 emissions from rice cultivation. The larg-
est uncertainty is associated with the emission factor.
Daily average emissions, derived from field measure-
ments in the United States, vary from state to state by as
Table 5-11: Area Harvested for Rice-Producing States (hectares)
Ik, ;i win illllliiiii! -is;? MI iiiiiiitiiiiiT «M
-jigaiCTop 1990,
.
iiilialPliiS
fioridg
::::::;, Plimafy
platoon
"Lltalslana
Primary
iiiiiirs'Ratoon
Mississippi
[ ' ' Missouri
Priowry
: Ratoon
485|D33
°IS9 854
"" '4"978
2,489
220,558
66,168
101,174
32,376
142,857
57,143
^,273,229
1991
•IIIIW
509,91.5
141,071
8,580
4,290
206,394
61,918
89,033
37,232
138,810
55,524
1,255,767
(ill'iigij'i'iliiiliillil i
-------
Table 5-12: Primary Cropping Flooding Season
Length (days)
State
Low
High
Arkansas
California
Florida*
Louisiana*
Mississippi
Missouri
Texas*
75
123
90
90
75
80
60
100
153
120
120
82
100
80
* These states have a second, or "ratoon", cropping cycle which
may have a shorter flooding season than the one listed in the
table.
much as two orders of magnitude (IPCC/UNEP/OECD/
IEA 1997). This variability is due to differences in culti-
vation practices, such as ratooning and fertilizer use, as
well as differences in soil and climatic conditions. A range
(0.3352 g/m2/day ±68 percent) has been used in these
calculations to reflect this variability. Based on this range,
methane emissions from rice cultivation in 1997 were
estimated to have been approximately 0.7 to 4.8 MMTCE
(121 to 830 Gg).
Another source of uncertainty is in the flooding
season lengths used for each state. Flooding seasons in
each state may fluctuate from year to year and thus a
range has been used to reflect this uncertainty.
The last source of uncertainty centers around the
ratoon, or second crop. Rice fields for the ratoon crop
typically remain flooded for a shorter period of time than
for the first crop. Studies indicate, however, that the meth-
ane emission rate of the ratoon crop may be significantly
higher than that of the first crop. The rice straw produced
during the first harvest has been shown to dramatically
increase methane emissions during the ratoon cropping
season (Lindau and Bollich 1993). It is not clear to what
extent the shorter season length and higher emission rates
offset each other. As scientific understanding improves,
these emission estimates can be adjusted to better reflect
these variables.
Agricultural Soil Management
Nitrous oxide (N2O) is produced naturally in soils
through the microbial processes of nitrification and denitri-
fication.6 A number of agricultural activities add nitrogen
to soils, thereby increasing the amount of nitrogen avail-
able for nitrification and denitrification, and ultimately the
amount of N2O emitted. These activities may add nitrogen
to soils either directly or indirectly. Direct additions occur
through various cropping practices (i.e., application of syn-
thetic and organic fertilizers, application of animal wastes,
production of nitrogen-fixing crops, incorporation of crop
residues, and cultivation of high organic content soils, called
histosols), and through animal grazing (i.e., direct deposi-
tion of animal wastes on pastures, range, and paddocks by
grazing animals). Indirect additions occur through two
mechanisms: 1) volatilization of applied nitrogen (i.e., fer-
tilizer and animal waste) and subsequent atmospheric depo-
sition of that nitrogen as ammonia (NH3) and oxides of ni-
trogen (NOX); and 2) surface runoff and leaching of applied
nitrogen. Other agricultural soil management practices, 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 sig-
nificant uncertainties as to the effects of these other prac-
tices, they have not been estimated.
Estimates of annual N2O emissions from agricul-
tural soil management were underestimated in the previ-
ous U.S. Inventory because the animal waste portion of
direct N2O emissions from agricultural cropping prac-
tices included only animal wastes managed as "daily
spread." However, of the total animal waste nitrogen pro-
duced in the U.S., all of it (i.e., nitrogen from animal
wastes managed as daily spread and managed in animal
waste management systems) will eventually be applied
to soils with the exception of that which volatilizes, runs
off, is used for feed, and is directly deposited by grazing
animals. The present inventory accounts for total animal
waste nitrogen, and, as a consequence, the emission esti-
6 Nitrification is the aerobic microbial oxidation of ammonium to nitrate, and denitrification is the anaerobic microbial reduction of nitrate to
dinitrogen gas (IPCC/UNEP/OECD/TEA 1997). Nitrous oxide is a gaseous intermediate product in the reaction sequences of both processes,
which leaks from microbial cells into the soil atmosphere.
Agriculture 5-11
-------
mates provided below are higher (by about five percent)
than previous estimates.
The revised estimates of annual N2O emissions
from agricultural soil management range from 65.3 to
74.1 MMTCE (773 to 876 Gg N2O) for the years 1990
to 1997 (Table 5-13 and Table 5-14). Emission levels
increased fairly steadily from 1990 to 1997 except for
the year 1993, when emissions declined slightly, and the
year 1994, when emissions increased sharply. These fluc-
tuations are largely a reflection of annual variations in
synthetic nitrogen fertilizer consumption and crop pro-
duction. Synthetic nitrogen fertilizer consumption, and
production of corn and most beans and pulses, peaked in
1994 due to the 1993 flooding of the North Central re-
gion and the intensive cultivation that followed. Over the
eight-yew period, total emissions of N2O increased by
13 percent.
Methodology and Data Sources
This N2O source category is divided into three com-
ponents: '(I) direct emissions from agricultural soils due
to cropping practices; (2) direct emissions from agricul-
tural soils due to grazing animals; and (3) emissions from
soils indirectly induced by agricultural applications of
I
nitrogen. The emission estimates for all three compo-
nents follow the methodologies in the Revised 1996IPCC
Guidelines aPCC/UNEP/OECD/IEA 1997).
;!
Direct N20 Emissions from Agricultural Soils
Estimates of N2O emissions from this component
are based on the total amount of nitrogen that is applied
to soils through cropping practices. These practices are
(1) the application of synthetic and organic fertilizers,
(2) the application of animal waste through both daily
spread and eventual application of wastes that had been
managed in waste management systems (e.g., lagoons),
(3) the production of nitrogen-fixing crops, (4) the in-
corporation of crop residues into the soil, and (5) the
cultivation of histosols.
Annual synthetic and organic fertilizer consumption
data for the U.S. were taken from annual publications on
commercial fertilizer statistics (AAPFCO1995,1996,1997;
TVA 1990,1992a,b, 1994). Organic fertilizers included in
these publications are manure, compost, dried blood, sew-
age sludge, tankage7, and other organic. The manure por-
tion of the organic fertilizers was subtracted from the total
organic fertilizer consumption data to avoid double count-
ing8. Fertilizer consumption data are recorded in "fertilizer
Table 5-13: N20 Emissions from Agricultural Soil Management (MMTCE)
1990 1991 1992 1993 1994 1995 1996 1997
iillii Dlprt
um ^cultural Soils
Grazing Animals
Indirect . ^ ' . ,",
JtoJ__ ";"'
Mii'totals may not stint' due to independent rounding.
iii iiiii iiii in HI 1 1 iiiiiii 1 iiiiiii ill in iiiiiii iiiiiiiiiiiiiiiiiiiiiiii iiiiiiH in iiiiiii i iiiiiiiiiiiii i iiiiiliiliiiiH hi iiiii i iiii iik in ill iiiiiiiii ii iiiiiiiiii nil i in lit
36.5
10.1
18.8
65.3
37.0
10.1
19.1
66.2
38,4
10.4
19.2
68.0
36.7
10.5
'19,7
67.0
42.1
10.8
SOU
73.4
39.0
11.0
20,1 |
70.2
11 1
40.8
10.8
20,4
72.0
43.0
10.7
..'.20.4. '
74.1
Table 5-14: N20 Emissions from Agricultural Soil Management (Gg N20)
1990 1991 1992 1993 1994 1995 1996 1997
I
Direct
Agricultural Soils 431
Graztng Animals 119
Indirect 222
Tbta| 773
Hots. Totals may not sum due to independent rounding'!
438
120
225
783
454
123
227
804
434
125
233
792
498
128
241'
868
i" •
461 |
131 i
238 .1
830
i
• i
482,
128
241
851
509
126
241
816
J Tankage is dried Jiiimal residue, usually freed from fat and gelatin.
* The manure is accounted for when estimating the total amount of nitrogen from manure applied to soils.
5-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
year" totals (July to June) which were converted to calen-
dar year totals by assuming that approximately 35 percent
of fertilizer usage occurred from July to December (TVA
1992b). July to December values were not available for cal-
endar year 1997, so a "least squares line" statistical test us-
ing the past seven data points was used to arrive at an ap-
proximate total. Data on the nitrogen content of synthetic
fertilizers were available in published consumption reports;
however, data on non-manure organic fertilizer consump-
tion did not include nitrogen content information. To con-
vert to units of nitrogen, it was assumed that 4.1 percent of
non-manure organic fertilizers (on a mass basis) was nitro-
gen (Terry 1997). Annual consumption of commercial fer-
tilizers (synthetic and non-manure organic) in units of ni-
trogen are presented in Table 5-15. The total amount of ni-
trogen consumed from synthetic and non-manure organic
fertilizers was reduced by 10 percent and 20 percent, re-
spectively, to account for the portion that volatilizes to NH3
and NOX (IPCC/UNEP/OECD/IEA 1997).
To estimate the amount of animal waste nitrogen
applied to soils, it was assumed that of the total animal
waste nitrogen produced in the U.S., all of it will eventu-
ally be applied to soils with three exceptions. These ex-
ceptions are (1) the portion of nitrogen that will volatil-
ize, (2) the nitrogen in the poultry waste that is used as
feed for ruminants (i.e., approximately 10% of the poul-
try waste produced in the U.S.), and (3) the nitrogen in
the waste that is directly deposited onto fields by graz-
ing animals9. Annual animal population data for all live-
stock types, except horses, were obtained from the USDA
National Agricultural Statistics Service (USDA 1994b,c,
1995a-j, 1996a-g, 1997a-g, 1998a-g). Horse population
data were taken from U.S. Department of Commerce's
Bureau of Census (DOC 1987) and FAO (1996). Popu-
lation data (by animal type) were multiplied by an aver-
age animal mass constant (ASAE 1995) to derive total
animal mass for each animal type. Total Kjeldahl nitro-
gen10 excreted per year (manure and urine) was then cal-
culated using daily rates of N excretion per unit of ani-
mal mass (ASAE 1995) (see Table 5-16). The amount of
animal waste nitrogen directly deposited by grazing ani-
mals, derived using manure management system usage
data and farm size (Safely et al. 1992, DOC 1995) as
described in the "Direct N2O Emissions from Grazing
Animals" section, was then subtracted from the total ni-
trogen. Ten percent of the poultry waste nitrogen pro-
duced in managed systems and used as feed for rumi-
nants was then subtracted. Finally, the total amount of
nitrogen from manure applied to soils was then reduced
by 20 percent to account for the portion that volatilizes
to NH3 and NOX (IPCC/UNEP/OECD/IEA 1997).
Annual production statistics for nitrogen-fixing
crops (beans, pulses, and alfalfa) were taken from U.S.
Department of Agriculture reports (USDA 1994a, 1997h,
1998h). These statistics are presented in Table 5-17. Crop
product values for beans and pulses were expanded to
total crop dry biomass, in mass units of dry matter, by
applying residue to crop ratios and dry matter fractions
for residue from Strehler and Stutzle (1987). Crop prod-
uct values for the alfalfa were converted to dry matter
mass units by applying a dry matter fraction value esti-
mated at 80 percent (Mosier 1998). To convert to units
of nitrogen, it was assumed that 3 percent of the total
crop dry mass for all crops was nitrogen (IPCC/UNEP/
OECD/IEA 1997).
To estimate the amount of nitrogen applied to soils
through crop residue incorporation, it was assumed that
all residues from corn, wheat, bean, and pulse produc-
tion, except the fractions that are burned in the field after
harvest, are plowed under. Annual production statistics
were taken from U.S. Department of Agriculture (USDA
1994a, 1997h, 1998h). These statistics are presented in
Table 5-17 and Table 5-18. Crop residue biomass, in dry
matter mass units, was calculated from the production
statistics by applying residue to crop mass ratios and dry
matter fractions for residue from Strehler and Stutzle
(1987). For wheat and corn, nitrogen contents were taken
from Barnard and Kristoferson (1985). For beans and
pulses, it was assumed that 3 percent of the total crop
residue was nitrogen (IPCC/UNEP/OECD/IEA 1997).
9 An additional exception is the nitrogen in the waste that will runoff from waste management systems due to inadequate management.
There is insufficient information with which to estimate this fraction of waste nitrogen.
10 Total Kjeldahl nitrogen is a measure of organically bound nitrogen and ammonia nitrogen.
Agriculture 5-13
-------
The crops whose residues were burned in the field are
corn, wheat, soybeans, and peanuts. For these crop types,
the total residue nitrogen was reduced by 3 percent to
subtract the fractions burned in the field (see the Agri-
cultural Residue Burning section of this chapter).
Total crop nitrogen in the residues returned to soils
was then added to the unvolatilized applied nitrogen from
commercial Fertilizers and animal wastes, and the nitro-
gen fixation from bean, pulse, and alfalfa cultivation. The
sum was multiplied by the IPCC default emission factor
(0.0125 kg N2O-N/kg N applied) to estimate annual N2O
emissions from nitrogen applied to soils.
Statistics on the area of histosols cultivated annu-
ally were not available, so an estimate for the year 1982
(Mausbach and Spivey 1993) was used for all years in
the 1990 to 1997 series (see Table 5-19). The area esti-
mate was derived from USDA land-use statistics. The
histosol area cultivated was multiplied by the IPCC de-
fault emission factor (5 kg N2O-N/ha cultivated) to esti-
mate annual N2O emissions from histosol cultivation.
Annual N2O emissions from nitrogen applied to soils
were then added to annual N2O emissions from histosol
cultivation to estimate total direct annual N2O emissions
from agricultural cropping practices (see Table 5-20).
Direct N20 Emissions from Grazing Animals
Estimates of N2O emissions from this component
were based on animal wastes that are not used as animal
feed, or applied to soils, or managed in manure manage-
ment systems, but instead are deposited directly on soils
by animals in pastures, range, and paddocks.11 It was
assumed that all unmanaged wastes, except for dairy cow
wastes, fall into this category (Safely et al. 1992). Esti-
mates of nitrogen excretion by these animals were de-
rived from animal population and weight statistics, in-
formation on manure management system usage in the
United States, and nitrogen excretion values for each
animal type.
Annual animal population data for all livestock
types, except horses, were obtained from the USDA Na-
tional Agricultural Statistics Service (USDA 1994b,c,
1995a-j, 1996a-g, 1997a-g, 1998a-g). Horse population
data were taken from U.S. Department of Commerce's
Bureau of Census (DOC 1987) and FAO (1996). Ma-
nure management system usage for all livestock types,
except swine, was taken from Safely et al. (1992). Be-
cause these data were not available for swine, the swine
population values were allocated to manure management
system types using information on farm size distribution
reported by the U.S. Department of Commerce (DOC
', i!
1995). Swine populations in the larger farm categories
were assumed to utilize manure collection and storage
management systems; all the wastes from smaller farms
were assumed to be managed as pasture, range, and pad-
dock. Population data for animals whose wastes were
managed in pasture, range, and paddock were multiplied
by an average animal mass constant (ASAE 1995) to
derive total animal mass for each animal type. Total
Kjeldahl nitrogen excreted per year was then calculated
for each animal type using daily rates of N excretion per
unit of animal mass (ASAE 1995). Annual nitrogen ex-
cretion was men summed over all animal types (see Table
5-16), and reduced by 20 percent to account for the por-
tion that volatilizes to NH3 and NOX. The remainder was
multiplied by the IPCC default emission factor (0.02 kg
N2O-N/kg N excreted) to estimate N2O emissions (see
Table 5-21).
Indirect N20 Emissions from Nitrogen Applied to
Agricultural Soils
This component accounts for N2O that is emitted
indirectly from nitrogen applied as fertilizer and excreted
by livestock. Through volatilization, some of this nitro-
gen enters the atmosphere as NH3 and NOX, and subse-
quently returns to soils through atmospheric deposition,
thereby enhancing N2O production. Additional nitrogen
is lost from soils through leaching and runoff, and enters
groundwater and surface water systems, from which a
portion is emitted as N2O. These two indirect emission
pathways are treated separately, although the activity data
used are identical.
11 The Revised 1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997) indicate that emissions from animal wastes managed in solid storage
and dtylol should also be included in the emissions from soils (see footnote "c" in Table 4-22 in the Reference Manual); however, this
Instruction appeared to be an error {and footnote "b" should have been listed next to "Solid storage and drylot" in Table 4-22). Therefore, N2O
emissions from livestock wastes managed in solid storage and drylot are reported under Manure Management, rather than here. (See Annex H
for a dlieussion of the activity data used to calculate emissions from the manure management source category.)
5-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Estimates of total nitrogen applied as fertilizer and
excreted by all livestock (i.e., wastes from all unmanaged
and managed systems) were derived using the same ap-
proach as was employed to estimate the direct soil emis-
sions. Annual application rates for synthetic and non-
manure organic fertilizer nitrogen were derived as de-
scribed above from commercial fertilizer statistics for
the United States (AAPFCO 1995, 1996, 1997; TVA
1990, 1992a and b, 1994). Annual total nitrogen excre-
tion data (by animal type) were derived, also as described
above, using animal population statistics (USDA 1994b,c,
1995a-j, 1996a-g, 1997a-g, 1998a-g; DOC 1987,
1998a,b, d-h; and FAO 1996), average animal mass con-
stants (ASAE 1995), and daily rates of N excretion per
unit of animal mass (ASAE 1995). Annual nitrogen ex-
cretion was then summed over all animal types.
To estimate N2O emissions from volatilization and
subsequent atmospheric deposition, it was assumed that
10 percent of the synthetic fertilizer nitrogen applied, 20
percent of the non-manure organic fertilizer nitrogen
applied, and 20 percent of the total livestock nitrogen
excretion were volatilized to NH3 and NOX, and 1 per-
cent of the total volatilized nitrogen returned to the soils
and was emitted as N2O (IPCC/UNEP/OECD/IEA1997).
These emission levels are presented in Table 5-22.
To estimate N2O emissions from leaching and run-
off, it was assumed that 30 percent of the non-volatilized
nitrogen applied or excreted (i.e., 30 percent of the sum
of 90 percent of synthetic fertilizer nitrogen plus 80 per-
cent of non-manure organic fertilizer nitrogen plus 80
percent of total livestock nitrogen) was lost to leaching
and surface runoff, and 2.5 percent of the lost nitrogen
was emitted as N2O (IPCC/UNEP/OECD/IEA 1997).
These emission levels are also presented in Table 5-22.
Uncertainty
A number of conditions can affect nitrification and
denitrification rates in soils, including: water content,
which regulates oxygen supply; temperature, which con-
trols rates of microbial activity; nitrate or ammonium
concentration, which regulate reaction rates; available
organic carbon, which is required for microbial activity;
and soil pH, which is a controller of both nitrification
and denitrification rates and the ratio of N2O/N2 from
denitrification. These conditions vary greatly by soil
type, climate, cropping system, and soil management
regime. Although numerous emissions measurement data
have been collected under a wide variety of controlled condi-
tions, the interaction of these conditions and their com-
bined effect on the processes leading to N2O emissions
are not fully understood. Moreover, the amount of added
nitrogen from each source (fertilizers, animal wastes,
nitrogen fixation, crop residues, cultivation of histosols,
atmospheric deposition, or leaching and runoff) that is
not absorbed by crops or wild vegetation, but remains in
the soil and is available for production of N2O, is uncer-
tain. Therefore, it is not yet possible to develop statisti-
cally valid estimates of emission factors for all possible
combinations of soil, climate, and management condi-
tions. The emission factors used were midpoint estimates
based on measurements described in the scientific litera-
ture, and as such, are representative of current scientific
understanding. Nevertheless, estimated ranges around
each midpoint estimate are wide; most are an order of
magnitude or larger (IPCC/UNEP/OECD/IEA 1997).
Uncertainties also exist in the activity data used to
derive emission estimates. In particular, the fertilizer sta-
tistics include only those organic fertilizers that enter the
commercial market, so any non-commercial fertilizer use
(other than livestock waste and incorporation of crop
residues) has not been captured. For example, sewage
sludge applied to soils (other than the portion in com-
mercial organic fertilizers) has not been accounted for.
Also, the nitrogen content of organic fertilizers varies by
type, as well as within individual types; however, aver-
age values were used to estimate total organic fertilizer
nitrogen consumed. Conversion factors for the bean,
pulse, and alfalfa production statistics were based on a
limited number of studies, and may not be representa-
tive of all conditions in the United States. It was assumed
that the entire crop residue for corn, wheat, beans, and
pulses was returned to the soils, with the exception of
the fraction burned. A portion of this residue may be dis-
posed of through other practices, such as composting or
landfilling; however, data on these practices are not avail-
able. Statistics on the histosol area cultivated annually
were not available either; the point estimate reported
should be considered highly uncertain. Lastly, the live-
Agriculture 5-15
-------
Table 5-15: Commercial Fertilizer Consumption (Metric Tons of Nitrogen)
Fertilizer Type 1990 1991 1992 1993 1994
Synthetic 10,1(10,726 . 10,271,698 10t335",778 16,727,695 11,171,243 i'O.J
Non-Manure
:, ,„ SlpnlCS 163 1,210 „, 1,256 1,121 ' 1,,101
^hi^BhJiSsii^^^ **' i3de manure gseS.gs commefqiai fertilizer.
Table 5-16: Animal Excretion (Metric Tons of Nitrogen)
~ Hity I'ii'O 1991 1992 1993 1994
BHE^^1 ""' !' JIJ ' " '" '" ;^^^^~^^
I , , ., ,
1 , ' :'•:•:
i
1
1
1995 1996 1997
' l'i' • ' ' I i
511,665 11,164,582 11,214,037
1,368 'l,533 1,534
;
i
..
1995 1996 1997
IS 3,062,628 3,150,736 3,1,3,^107 3,158,899 3,2,15JJJ 3J 85,729 3J.6ZJ.fiQ 3,194,,314
BlPP. & . . . , .
" = P«**fock 4,742,247 4,761,332 4,881,526 4,952,799 5,095,799 5,192,152 5,099,376 5,022,867
Mttanags- ' ' ' ]
;=m|jjt \
'"'il
Ta
„„„-
ip'i
IlllnlJJUl
- =
Ill
111
Ta
„
I'
llJXIleiJlS 7,865,794 7,975,050 8,081,690 8,178,644 8,379,974
ble 5-17: Bean, Pulse, and Alfalfa Production (Metric Tons of Product)
Preset Type 1990 1991 1992 1993 1994
Sp^glDS 52,415,690 54,064,730 59,611,670 50,919,130 69,625,980
PKptS 1,634,590 2,234,650 1,943,380 1,538,770 1,934,370
Dry Edible
BfWS 1,464,690 1,531,550 1,025,800 993,960 1,323,9,00
Bfy.Ed'Bli
,S lOZlpO 168,510 114,990 149,320 102 290
Austrian
sVwSerPeas 5jf60 , 6,300 4,490 7,030 2,310
LwKIs 66^59 104,090 71,030 90,990 84,190
Seed Peas 41,820 41,960 24,360 38,510 34,200
Alfalfa 75.671,002 75,585,727 71,794,602 72,851,472 73,786,780
ble 5-18: Corn and Wheat Production (Metric Tons of Product)
Product Type Id90 1991 1992 1993 1994
Corr||or^ra^ 2,^1,533,597 189^867,775 240,719,220 160,95,3,750 256,6212,90
yfie^ 7^,^92,383 sS.SSo.SM §7,1315,246 65,22.0,410 63,166,750
Table 5-19: Histosol Area Cultivated (Hectares)
Year Hectares
i in iiiiiiiii pin iiiiiiiii ii iiiiiii iiiii i ii ii ii iiiiiii ii ii 111 inn mi ii in ii ii mi iiiiiii iiili iii i inn i mi i limn n in inn nil inn 1 1 in n mi mi
: ' i 1990 843,386
4Q(H Q/10 OOC
: . ; nil in 1 1 i in i iii1 iiiii in 1 ?,1,1 §43,386
1992 ,843,386
1993 843,386
'„ , 199,4 ,8,43,3,86
i 1995 843,386
1996 843,386
1997 843,386
1 „ :
8,448,804
1995
,59,243,170
1.570,100
1,397,610
209,060
5,400
97300
47,540
76,670,720
1995
187305080
59,400,390
1
8,339,367
,1996
64,837,320
1,660,690
1,268,240
121,150
4,670
60,460
24,860
72,136,611
!!
1996
,,,23,6,064,120
62,191,130
i
"
8,291,710
« 1- ii irwi -, i
1
1997
74,223,690
1,608,600
1,332,490
263,810
5,220
108,450
30,940
71,887,135
1997
237,896,540
68,761,480
I
5-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 5-20: Direct N20 Emissions from Agricultural Cropping Practices (MMTCE)
Activity 1990 1991 1992 1993 1994 1995
Note: Totals may not sum due to independent rounding.
1996 1997
Commercial Fertilizers (excluding manure)
Animal Waste Applied to Soils
N Fixation
Crop Residue
Histosol Cultivation
Total
15.1
4.1
10.3
6.4
0.6
36.5
15.4
4.2
10.6
6.3
0.6
37.0
15.5
4.2
11.1
7.1
0.6
38.4
16.0
4.2
9.9
6.0
0.6
36.7
16.7
4.3
12.5
8.0
0.6
42.1
16.2
4.2
11.3
6.8
0.6
39.0
16.7
4.2
11.8
7.5
0.6
40.8
16.8
4.2
13.1
8.4
0.6
43.0
Table 5-21: Direct N20 Emissions from Pasture, Range, and Paddock Animals (MMTCE)
Animal Type
1990 1991 1992 1993 1994 1995 1996 1997
Beef Cattle
Horses
Swine
Sheep
Goats
Poultry
Total
9.0
0.5
0.2
0.2
0.1
+
10.1
9.1
0.5
0.2
0.2
0.1
+
10.1
9.3
0.6
0.2
0.2
0.1
+
10.4
9.5
0.6
0.2
0.2
0.1
+
10.5
9.8
0.6
0.2
0.2
0.1
+
10.8
10.0
0.6
0.2
0.2
0.1
+
11.0
9.8
0.6
0.2
0.2
0.1
+
10.8
9.7
0.6
0.2
0.2
0.0
+
10.7
+ Does not exceed 0.05 MMTCE
Note: Totals may not sum due to independent rounding.
Table 5-22: Indirect N20 Emissions (MMTCE)
Activity 1990
1991 1992 1993 1994 1995 1996 1997
Volatilization & Atmospheric Deposition
Commercial Fertilizer (excluding
Animal Waste
Surface Run-off & Leaching
Commercial Fertilizer (excluding
Animal Waste
Total
manure)
manure)
3
1
2
15
9
6
18
.4
.3
.1
.3
.1
.3
.8
3.5
1.4
2.1
15.6
9.2
6.4
19.1
3
1
2
15
9
6
19
.5
.4
.1
.7
.3
.4
.2
3.6
1.4
2.2
16.1
9.6
6.5
19.7
3.7
1.5
2.2
16.7
10.0
6.7
20.4
3.7
1.4
2.2
16.4
9.7
6.7
20.1
3.7
1.5
2.2
16.7
10.0
6.6
20.4
3.7
1.5
2.2
16.7
10.1
6.6
20.4
Note: Totals may not sum due to independent rounding.
stock excretion values, while based on detailed popula-
tion and weight statistics, were derived using simplify-
ing assumptions concerning the types of management
systems employed.
Agricultural Residue Burning
Large quantities of agricultural crop residues are
produced by fanning activities. There are a variety of
ways to dispose of these residues. For example, agricul-
tural residues can be plowed back into the field,
composted, landfilled, or burned in the field. Alterna-
tively, they can be collected and used as a fuel or sold in
supplemental feed markets. Field burning of crop resi-
dues is not considered a net source of carbon dioxide
(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, how-
ever, a net source of methane (CH4), nitrous oxide (N2O),
carbon monoxide (CO), and nitrogen oxides (NOX),
which are released during combustion. In addition, field
burning may result in enhanced emissions of N2O and
NOX many days after burning (Anderson et al. 1988,
Levine et al. 1988), although this process is highly un-
certain and was not quantified.
Agriculture 5-17
-------
Field burning is not a common method of agricul-
tural 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, peanut, soybeans, bar-
ley, and corn, and of these residues, generally less than 5
percent is burned each year.12 Annual emissions from
tills source over the period 1990 through 1997 averaged
approximately 0.2 MMTCE'(37 Gg) of CH4,0.1 MMTCE
(1 Gg ) of N2O, 771 Gg of CO, and 32 Gg of NOX (see
Table 5-23 and Table 5-24). The average annual emis-
sion estimates for field burning of crop residues from
1990 through 1997 represent approximately 1 percent
of total U.S. CO emissions.
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 burn-
ing, the following equations were used:
]
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)13
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 Resi-
due) x (Combustion Efficiency)
Emissions of CH4 and CO were calculated by mul-
tiplying the amount of carbon released by the appropri-
ate emission ratio (i.e., CH4/C or CO/C). Similarly, N2O
and NOX emissions were calculated by multiplying the
amount of nitrogen released by the appropriate emission
ratio (i.e., N2O/N or NOX/N).
Table 5-23: Emissions from Agricultural Residue Burning (MMTCE)
pa " " "':' ' 1990 1991 1992
1993
1994 1995 1996 1997
!
•; CH<= ,r
llllHlfllSllllllllllIB'"!!!!''!! II II I Illlll III II II III I
•"• • Sugarcane
,;:;,; Core
1 "Soybeans
; Peanuts
N20
Wheat
Rice
i Sugarcane
Corn
barley
Soybeans
Peanuts
Told
0.2
+
0.1
+
+
+
0.1
+
+
+
+
+
0.1
+
0.3
0.2
+
+
0.1
+
+
+
0.1
+
+
+
+
+
0.1
+
0.3
I
0.2 0.2 0.2 0.2
+ + + +
+ + + +
0.1 0.1 0.1 0.1;
+ + + + :
+ + + + !
+ + + + "
0.1 0.1 0.1 0.1
+ + + + ;
+ + • + + ;
+ + + +
0.1 0.0 0.1 0.1
+ + + +
0.3 0.3 0.4 0.3'
0.2 0.2
+ +
+ +
0.1 0.1
+ +
+ 0.1
+ +
0.1 0.1
+ +
+ +
+ +
+ +
+ +
0.1 0.1
+ +
0.3 0.4
t Does not exceed 0.05 MMTCE
Mote totals may not sum due to Independent rounding.
II fj|C frg£(fon of rice straw burned each year is thought to be significantly higher (see "Data Sources" discussion below).
" Burning Efficiency is defined as the fraction of dry biomass exposed to burning that actually burns. Combustion ^Efficiency is defined as
the fraction of catbon in the fiie'that is oxidized completely to CO2. In the methodology recommended by the EPCC, the "burning efficiency" is
assumed to be contained ip the "fraction, of residues burned" factor. However, the number used here, to estimate fhe "fraction of residues
burned** docs not account for the fraction of exposed residue that does not burn. Therefore, a "burning efficiency factor" was added to the
calculations. , !
5-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 5-24: Emissions from Agricultural Residue Burning (Gg)
Gas/Crop Type
1990 1991 1992 1993 1994 1995 1996 1997
CH4
Wheat
Rice
Sugarcane
Corn
Barley
Soybeans
Peanuts
N20
Wheat
Rice
Sugarcane
Corn
Barley
Soybeans
Peanuts
NOX
Wheat
Rice
Sugarcane
Corn
Barley
Soybeans
Peanuts
CO
Wheat
Rice
Sugarcane
Corn
Barley
Soybeans
Peanuts
36
7
4
1
17
1
7
+
1
+
+
+
+
+
1
+
30
1
3
+
11
+ ,
14
+
763
137
88
18
354
15
148
2
34
5
4
1
16
1
7
+
1
+
+
+
+
+
1
+
30
1
3
+
11
+
14
+
712
99
88
20
333
16
153
3
39
6
5
1
19
1
8
+
1
+
+
+
1
+
1
+
34
1
3
+
13
+
16
+
824
124
89
20
404
16
168
3
32
6
4
1
14
1
7
+
1
+
+
+
+
+
1
+
28
1
3
+
9
+
14
+
681
120
84
20
296
14
144
2
41
6
4
1
20
1
9
+
2
+
+
+
1
+
1
+
37
1
3
+
14
+
18
+
858
116
86
20
425
13
194
3
33
5
3
1
16
1
8
+
1
+
+
+
+
+
1
'+
30
1
2
+
10
+
16
+
703
109
65
20
326
13
167
2
37
5
3
1
19
1
9
+
1
+
+
+
1
+
1
+
34
1
2
+
13
+
17
+
786
114
59
19
393
14
183
2
40
6
3
1
19
1
10
+
2
+
+
+
1
+
1
+
37
1
2
0
13
0
20
0
843
127
65
20
406
13
210
2
+ Does not exceed 0.5 Gg
Note: Totals may not sum due to independent rounding.
Data Sources
The crop residues burned in the United States were
determined from various state level greenhouse gas emis-
sion inventories (ILENR 1993, Oregon Department of
Energy 1995, Wisconsin Department of Natural Re-
sources 1993) and publications on agricultural burning
in the United States (Jenkins et al. 1992, Turn et al. 1997,
EPA 1992). Crop production data were taken from the
USDA's Crop Production Summaries (USDA 1993,1994,
1995, 1996, 1997, 1998), except data on the production
of rice in Florida. Data for the years 1996 and 1997 were
obtained from Ken Vaodivia (1997) and Terrie Smith
(1998) respectively, of Sem-Chi Rice. Rice production
data were not available for the years 1990 to 1995, so
they were estimated by applying the 1997 ratio of Florida
rice production to Florida rice area to the total Florida
rice area (both primary and ratoon) for 1990 to 1995.
The 1990 to 1995 Florida rice areas were obtained from
Tom Schudeman (1997), a Florida Agricultural Exten-
sion Agent. The percentage of crop residue burned was
assumed to be 3 percent for all crops, except rice, based
on state inventory data (ILENR 1993, Oregon Depart-
ment of Energy 1995, Noller 1996, Wisconsin Depart-
ment of Natural Resources 1993, and Cibrowski 1996).
For rice, the only data that were available on percentage
of crop residue burned were for California (Jenkins 1997),
which was responsible for about 21 percent of the an-
nual U.S. rice production. Until 1991, 99 percent of
California's rice area was burned each year after harvest.
Since then, California has tightened restrictions on burn-
Agriculture 5-19
-------
ing, such that today, only about half of its rice area is
burned each year. Therefore, a weighted average frac-
tion burned was calculated for rice for each year assum-
ing that the fraction of* rice residue burned in California
declined linearly from 99 to 50 percent between 1991
and 1996, and remained constant at 50 percent in 1997,
while the fraction burned in the rest of the country stayed
constant at 3 percent.
Residue/crop product ratios, residue dry matter
contents, residue carbon contents, and residue nitrogen
contents for all crops except sugarcane, peanuts, and soy-
beans were taken from Strebler and StUtzle (1987). These
data for sugarcane were taken from University of Cali-
fornia £1977) and Turn, et a\. (1997). Residue/crop prod-
uct ratios and residue dry matter contents for peanuts
and soybeans were taken from Strehler and Stutzle
,! i|j
(1987); residue carbon contents for these crops were set
at 0.45 and residue nitrogen contents were taken from
Barnard and Kristoferson (1985) (the value for peanuts
was set equal to the soybean value). The burning effi-
ciency was assumed to be 93 percent, and the combus-
tion efficiency was assumed to be 88 percent for all crop
types (EPA 1994). Emission ratios for all gases were taken
from the Revised 199$ IPCC Guidelines (IPCC/UNEP/
OECD/IEA 1997).
Uncertainty
The largest source of uncertainty in the calculation of
non-CO2 emissions from field burning of agricultural resi-
dues is in the estimates of the fraction of residue of each
crop type burned each year. Data on the fraction burned, or
even the gross amount of residue burned each year, are not
collected at either the national or state level. In addition,
burning practices are highly variable among crops, as well
as among states. The fractions of residue burned used in
these calculations were based upon information collected
ii
by state agencies and in published literature. It is likely that
these emission estimates will continue to change as more
information becomes available.
i
Other sources of uncertainty include the residue/crop
product ratios, residue dry matter contents, burning and
combustion efficiencies, and emission ratios. A residue/crop
product ratio for a specific crop can vary among cultivars,
and for all crops except sugarcane, generic residue/crop
product ratios, rather than ratios specific to the United States,
have been used. Residue dry matter contents, burning and
combustion efficiencies, and emission ratios, all can vary
due to weather and other combustion, conditions, such as
fuel geometiy. Values for these variables were taken from
literature on agricultural biomass burning.
5-20 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
6. Land-Use Change and
Forestry
is chapter provides an assessment of the net carbon dioxide (CO2) flux caused by changes in forest carbon
stocks (trees, understory, forest floor, forest soil, wood products, and landfilled wood), and a preliminary
assessment of the net CO2 flux caused by changes in non-forest soil carbon stocks. Unlike the assessments in other
chapters, which are based on annual activity data, estimates for the Land-Use Change and Forestry chapter are based
on periodic activity data in the form of forest, wood product, and landfilled wood surveys. As a result, the CO2 flux
from forest carbon stocks was calculated on an average annual basis. This annual average value was then applied to
the years between surveys. In addition, because the most recent national compilation of state forest surveys was
completed for the year 1992, and the most recent wood product and landfilled wood surveys were completed for the
year 1990, the estimates of the CO2 flux from forest carbon stocks are based in part on modeled projections of stock
estimates for the year 2000.
Carbon dioxide fluxes caused by changes in forest floor, forest soil, and non-forest soil carbon stocks were not
assessed in previous U.S. greenhouse gas inventories due to insufficient data and lack of accepted guidelines. The
assessment of CO2 flux from forest floor and forest soil carbon stocks in this inventory was based on stock estimates
developed by the U.S. Forest Service, and is consistent with the Revised 1996IPCC Guidelines (IPCC/UNEP/OECD/
IEA 1997). The assessment of CO2 flux from non-forest soils was based on the Revised 1996 IPCC Guidelines, which
includes methodologies for calculating non-forest soil carbon flux from three land-use practices: (1) cultivation of
mineral soils, (2) cultivation of organic soils, and (3) liming of agricultural soils. However, due to insufficient data
about these land-use activities in the United States, this chapter provides only a preliminary assessment of CO2 fluxes
from two of the three land-use practices: cultivation of organic soils and liming of agricultural soils. Because of the
high level of uncertainty associated with these two flux estimates, and the lack of a flux estimate for the third activity,
the non-forest soil flux estimates have not been incorporated into the total fluxes reported for the Land-Use Change
and Forestry chapter.
See Table 6-1 and Table 6-2 for a summary of CO2 fluxes estimated from Land-Use Change and Forestry in the
United States.
Changes in Forest Carbon Stocks
Globally, the most important human activity that affects forest carbon fluxes is deforestation, particularly the
clearing of tropical forests for agricultural use. Tropical deforestation is estimated to have released nearly 6 billion
metric tons of CO2 per year during the 1980s, or about 23 percent of global CO2 emissions from anthropogenic
Land-Use Change and Forestry 6-1
-------
Table 6-1: Net C02 Flux from Land-Use Change and Forestry (MMTCE)
Description
Forests
"' Tries
Uriierstory
Forest 'Floor
" i, 'infill'"! "P 1 1: " '•' " f . hi ' 'i rwiiiii1,'!!" ii'i'iTPin i
,,Sol
Harvesied Wood
..Wood Products
:,Lart[fedWpod
Tola! Net Flux*
1990
(274.2;
1991 1992
(274.2) (274.2)
(9§!6) (95.6)
(2,4),, , (2.4) (2.4)
,,(20.8) (20.8) (20.8)
(155.2) (155.2) (155.2)
(37.3) (37.3) (37.3)
(,17,9) (17.9) (17,9)
(19.4) (19.4) (19.4)
(311.5)
(311.5) (311.5)
1993
III PHI
,(171.3)
' "(i's)
(9.8)
(86,3)
(37.3)
(17.9)
(19.4)
(208.6)
1994
n ii iiiiiiii
(171.3)
(74,0)
(1,3
y
(86,3)
(37.3)
(17.9)
(19.4)
(208.6)
1
1995 1996
( I HI I II ll| II ll 1 1 in
(171.3) (171.3)
(740*) (74.0)
CM) (1-3)
(9.8) (9,8)
(86,33 (86.3)
(37.3) (37.3)
(17.9) (17.9)
(19.4) (19.4)
(208.6) (208.6)
ftolei^Parenlheses indicate seguestration. Totals may, not sum due to independent rounding. Shaded areas indicate val
" edfliSliafoil1 of Klsjoiii'datelnd projections. Mother values "are 'based "on historical data only.
"The total net flux excludes preliminary flux estimates for non-forest soils due to the high level of uncertainty of these es
Table 6-2: Net C02 Flux from Land-Use Change and Forestry (Tg C02)
•i!il,il, :,t vi. ::,! ,i .; i'-iiir si sit i. i. • •. , ' ' i- •,•'•; • , it'.: > •'. •• ''•,• it:;.' -I1!1, „•: « "IP,;*'; ; ifs. ,
Descriplion 1990 1991 1992 1993 1994 199E
Forests
Ureas
Umterstory
FofSs't Floor
Sol
Harvested Wood
Wood Products
LaiffiledWood
Total Net Flux*
(1,005.4)
(350.5)
.":.'.:;: :,(7p)
(569.1)
(136,8)
(65,5)
(71.2)
{1,142,2)
(1,005.4) (1,005.4)
(350.5) (350.5)
(8.8) (8.8)
(76.3) (76.3)
(569.1) (569.1)
(136.8) (136.8)
(65,5) (65,5)
(71,2) (712)
(1,1 42.2) (1,1 42.2)
(627.9)
fTp.f
I'pSJ)
IsI'S)
(65.5)
(7~2)
(764-7)
lii'M : iiiiitii' ':mtf
, (627.9) (627,9
(4r§)
'"" (SI'S),,,',
(isoj
(65,5)
(7i:2) "
(764.7)
(4.6
, (35.8
jes based on
imates.
1996
U|!l li!.'J.|li|ii|,"!'MII|,i
(627.9)
(271.3)
) (4-6)
: :: IMSJ),,
(316.3) (316.3)
(136.8) (136.8)
:,,,(6555
(71.2
(764.7
.i :,(65,.5)
, (71.2)
(764.7)
1997
i ii
(171.3)
(74.0)
(13)
(9.8)
(86.3)
(37.3)
(17.9)
(19-4),
(208.6)
a
Si I' I
1997
(627.9)
(2713)
(4.6)
,„„, (35,8),
(316.3);
(136.8)
,(65.5),
,(71-2)
(764.7)
PaiBrtheses indicate sequestration. Totals may not sum due to independent rounding. Shaded areas indicate valdes based on a
combination of historical data and projections. All other values are based on historical data only. !
*The total net flux excludes preliminary flux estimates for non-forest soils due to the high level of uncertainty of these estimates.
ii
activities. Conversely, during this period about 7 percent
of global CO2 emissions were offset by CO2 uptake due
to forest regrowth in the Northern Hemisphere (Houghton
ct al. 1995).
Given the low rate of change in U.S. forest land
In the United States, the amount of forest land has
remained fairly constant during the last several decades.
The United States covers roughly 2,263 million acres, of
which 33 percent (737 million acres) is forest land
(Powell et al. 1993). the amount of forest land declined
by approximately 5.2 million acres between 1977 and
1987 (USFS 1990, Waddell et al. 1989), and increased
by about 5.3 million acres between 1987 and 1992
(Powell et al. 1993). These changes represent average
fluctuations of only about 0.1 percent per year. Other
major land-use categories in the United States include
range and pasture lands (29 percent), cropland (17 per-
cent), urban areas (3 percent), and other lands (18 per-
cent) (Daugherty 1995).
area, the major influences on the current net carbon flux
from forest land are management activities and 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, inten-
sified management of forests can increase both the rate
of growth and the eventual biomass density of the forest,
thereby increasing the uptake of carbon. The reversion
of cropland to forest land through natural regeneration
also will, over decades, result in increased carbon stor-
age in biomass and soils.
':, II
Forests are complex ecosystems with several in-
ten-elated components, each of which acts as a carbon
storage pool, including:
• Trees (i.e., living trees, standing dead trees, roots,
stems, branches, and foliage)
ii
6-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
• Understory vegetation (i.e., shrubs and bushes)
• The forest floor (i.e., woody debris, tree litter, and
humus)
• Soil
As a result of biological processes in forests (e.g.,
growth and mortality) and anthropogenic activities (e.g.,
harvesting, thinning, and replanting), carbon is continu-
ously cycled through these ecosystem components, as
well as between the forest ecosystem and the atmosphere.
For example, the growth of trees results in the uptake of
carbon from the atmosphere and storage of carbon in
living biomass. As trees age, they continue to accumu-
late carbon until they reach maturity, at which point they
are relatively constant carbon stores. As trees die and
otherwise deposit litter and debris on the forest floor,
decay processes release carbon to the atmosphere and
also increase soil carbon. The net change in forest car-
bon is the sum of the net changes in the total amount of
carbon stored in each of the forest carbon pools over time.
The net change in forest carbon, however, may not
be equivalent to the net flux between forests and the at-
mosphere because timber harvests may not always re-
sult in an immediate flux of carbon to the atmosphere.1
Harvesting in effect transfers carbon from one of the "for-
est pools" to a "product pool." Once in a product pool,
the carbon is emitted over time as CO2 if the wood prod-
uct combusts or decays. The rate of emission varies con-
siderably among different product pools. For example,
if timber is harvested for energy use, combustion results
in an immediate release of carbon. Conversely, if timber
is harvested and subsequently used as lumber in a house-,
it may be many decades or even centuries before the lum-
ber is allowed to decay and carbon is released to the at-
mosphere. If wood products are disposed of in landfills,
the carbon contained in the wood may be released years
or decades later, or may even be stored permanently in
the landfill.
In the United States, improved forest management
practices, the regeneration of previously cleared forest
areas, and timber harvesting and use have resulted in an
annual net uptake (i.e., sequestration) of carbon. Also
due to improvements in U.S. agricultural productivity,
the rate of forest land 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 brought out of crop production,
primarily between 1920 and 1950, and were allowed to
revert to forest land or were actively reforested. The im-
pacts of these land-use changes are still affecting carbon
fluxes from forests in the East. In addition to land-use
changes in the early part of this century, in recent de-
cades carbon fluxes from Eastern forests were affected
by a trend toward managed growth on private land, re-
sulting in a near doubling of the biomass density in east-
ern forests since the early 1950s. More recently, the 1970s
and 1980s saw a resurgence of federally sponsored tree-
planting programs (e.g., the Forestry Incentive Program)
and soil conservation programs (e.g., the Conservation
Reserve Program), which have focused on reforesting
previously harvested lands,"improving timber manage-
ment activities, combating soil erosion, and converting
marginal cropland to forests. In addition to forest regen-
eration and management, forest harvests have also af-
fected net carbon fluxes. Because most of the timber that
is harvested from U.S. forests is used in wood products
and much of the discarded wood products are disposed
of by landfilling—rather than incineration—significant
quantities of this harvested carbon are transferred to long-
term storage pools rather than being released to the at-
mosphere. The size of these long-term carbon storage
pools has also increased steadily over the last century.
As shown in Table 6-3 and Table 6-4, U.S. forest
components, wood product pools, and landfill wood were
estimated to account for an average annual net seques-
tration of 311.5 MMTCE (1,142.2 Tg CO2) from 1990
through 1992, and 208.6 MMTCE (764.7 Tg CO2) from
1993 through 1997. The net carbon sequestration reported
for 1997 represents an offset of about 14 percent of the
1997 CO2 emissions from fossil fuel combustion. The
average annual net carbon sequestration reported for 1993
through 1997 represents a 33 percent decrease relative
1 For this reason, the term "apparent flux" is used in this chapter.
Land-Use Change and Forestry 6-3
-------
Table 6-3: Net C02 Flux from U.S. Forests (MMTCE)
Description
Apparent Forest Flux
,, ,, ^ _
Understory
Fofas} Fkxjr
Forestalls
Apparent Harvested Wood Flux
Apparent Wood Product Flux
Apparent LandOlled Wood Flux
Total Net Flux
1990
(274.2)
(95.6)
(2.4)
(20.8)
(155.2)
, (37.3)
r,[17.9)
. (19.4)
,(311-5)
1991
(274.2)
(95.6)
(2.4)
(20.8)
(155.2)
(37J)
(17,9),
W-4)
(311,5)
1992
(274.2)
(95.6)
(2.4)
(20.8)
(155.2)
Ilzl)
(1,7,9)
(19.4)
(311.5)
1993
(171.3)
:. (74.o)
(1,3)
(9,8}
. 186.3)
(37.3)
.07,9).
(19.4)
(208.6)
1994
(171.3)
(7.P)
(1-3)
(93)
(86,3)
(37,3)
(17-9)
(19.4)
(208.6)
1995
(171.3)
„ (74.0)
(1.3)
(9.8)
(86,3)
(37.3)
(17.9)
(19.4)
(208.6)
1996
(171.3)
, (74,0)
(1.3)
(9.8)
(86,3)
(37.3)
(17.9)
(19.4)
(208.6)
1997
(171.3)
(74.0) .
. (I-3),
(9.8)
(86.3)
(37.3)
(17.9);
(19.4)"
(208.6)
Parentheses indjcats ne^ cajbon "sequestration" (i.e., sequestration or accumulation into the carbon pool minus emissions or harvest
from me carbon pool). The word "apparent" is used to indicate that an estimated flux js a msasure,,fl£JMfiharige in carbon stocks, rather than
ipiBMn* ?r ^r°P ^5 atfflosPhe,rf' T.he sum of the aPParent fluxes ln thjsjajije (i.e.,, total flux) is an estimate of the! actual flux. Shaded
irea? (rtoMe values bas,ed on a combination of historical data and projections. All other values are based on historical data only. Totals may
not aumdut to Independent rounding.
:" "" ' :"'"::"" "I": ' ;::"; ; ;:l:: ': "
Table 6-4: Net C02 Flux from U.S. Forests (Tg C02)
Description
1990 1991 1992 1993 1994 1995 1996 1997
Apparent Forest Flux
tees
(1,005.4) (1,005.4) (1,005.4)
(350.5) (350.5) (350.5)
Forest Floor [[[ P .................
Forest Soils „.' \
Apparent Harvested Wood Flux
Apparent Wood. Product Rux
Ap||re||Ian|||eff'Wood Flux
(8.8)
(76.3)
(569.1)
036.8)
(8.8)
(76.3)
(569.1)
(136.8)
, m-s)
(71.2)
(8.8)
(76.3)
(569.1)
(136.8)
(65.5)
(71.2)
(627.9(
(271.3
i V ii
(627.9
(2,71 • 3
tfrg
(35.8)
,(316,3), ,,(3i0!.35, (316.31
(136.8) (136.8) (136.8
(627.9) (627.9),
'(4.6):
(35.8),:
(316.3) (316.3):
(136.8) (136.8)
(35,8)
(71.2) (71.2) (7,1, .2]
Flyi
(1,142.2) (1,142.2) (1142.2) (764.7) (764.7) (764.7) (764,7) (764JL
Si!ilSIS,JiiJ!!Silln8^ carboy "sequestration" (i.e., sequestration or accumulation into the carbon pool minus emissions or harvest
0 J&U£9JuiS word "aPParentl> is used to indicate that an estimated flux is a measure of net change in carbon stocks, rather than
ux to or from the atmosphere. The sum of the apparent fluxes in this table (i.e., total flux) is an estimate of the factual flux. Shaded
lSi!|fe^ aLBPIPlMl SOS PIPi?ctipns. All other values are based on historical data .only. Totals may
not sun sue to Independent' rounding. ' ,|
L "'' '! "- '- '- " "" - " I '. ! !"
to the average annual net carbon sequestration reported
For 1990 through 1992. This overall decrease in annual
net sequestration was due to changes in the aggregate
age structure of U.S. forests caused by the maturation of
existing forests and the slowed expansion of Eastern for-
est cover. The abrupt shift in annual net sequestration
from 1992 to 1993 is, the result of calculating average
annual fluxes using periodic activity data as well as mod-
ii1 '"i
els that estimate and project decadal rather than annual
stock estimates.
Methodology
The methodology for estimating annual forest car-
bon flux in the United States differs from the method-
I!
ologies employed for other sources because the forest
carbon flux estimates for this source were derived from
periodic surveys of forest carbon stocks rather than an-
nual activity data. Three surveys of forest carbon stocks
were used: (1) timber stocks, (2) wood products, and (3)
landfilled wood. In addition, because national compila-
tions of state forest surveys have not been completed for
1997, projections of forest carbon stocks, rather than
complete historical data, were used to derive some of the
annual flux estimates.
i , •
Timber stock data from forest surveys were used
to derive estimates of carbon contained in the four forest
ecosystem components (trees, understory, forest floor,
and soil) for the survey years. The apparent annual for-
est carbon flux for a specific year was estimated as the
average annual change in the total forest carbon stocks
between the preceding and succeeding timber survey
-------
est surveys were conducted for the years 1987 and 1992,
and a projection has been prepared for the year 2000.
Therefore, the apparent annual forest carbon flux esti-
mate for the years 1990 through 1992 was calculated from
forest carbon stocks reported for 1987 and 1992, and the
apparent annual forest carbon flux estimate for the years
1993 through 1997 was calculated from forest carbon
stocks for 1992 and projected forest carbon stocks for
the year 2000.
Carbon stocks contained in the wood product and
landfilled wood pools were estimated for 1990 using his-
torical forest harvest data, and were estimated for 2000
using projections of forest harvest. Therefore, apparent
annual wood product and landfilled wood fluxes for the
years 1990 through 1997 were calculated from a 1990
historical estimate and a 2000 projection.
The total annual net carbon flux from forests was
obtained by summing the apparent carbon fluxes associ-
ated with changes in forest stocks, wood product pools,
and landfilled wood pools.
The inventory methodology described above is
consistent with the Revised 1996IPCC Guidelines (IPCC/
UKEP/OECD/IEA 1997). The IPCC identifies two ap-
proaches to developing an emissions inventory for Land-
Use Change and Forestry: (1) using average annual sta-
tistics on land-use change and forest management ac-
tivities, and applying carbon density and flux rate data
to these activity estimates to derive total flux values; or
(2) using carbon stock estimates derived from periodic
inventories of forest stocks, and measuring net changes
in carbon stocks over time. The latter approach was em-
ployed because the United States conducts periodic sur-
veys of national forest stocks. In addition, the IPCC iden-
tifies two approaches to accounting for carbon emissions
from harvested wood: (1) assuming that all of the har-
vested wood replaces wood products that decay in the
inventory year so that the amount of carbon in annual
harvests equals annual emissions from harvests; or (2)
accounting for the variable rate of decay of harvested
wood according to its disposition (e.g., product pool,
landfill, combustion). The latter approach was applied
for this inventory using estimates of carbon stored in
wood products and landfilled wood.2 Although there are
large uncertainties associated with the data used to de-
velop the flux estimates presented here, the use of direct
measurements from forest surveys and associated esti-
mates of product and landfilled wood pools is likely to
result in more accurate flux estimates than the alterna-
tive IPCC methodology.
Data Sources
The estimates of forest, product, and landfill car-
bon stocks used in this inventory to derive carbon fluxes
were obtained from Birdsey and Heath (1995), Heath et
al. (1996), and Heath (1997). The amount of carbon in
trees, understory vegetation, the forest floor, and forest
soil in 1987 and 1992 was estimated using timber vol-
ume data collected by the U.S. Forest Service (USFS)
for those years (Waddell et al. 1989, Powell et al. 1993).
The timber volume data include timber stocks on forest
land classified as timberland, reserved forest land, or other
forest land3 in the contiguous United States, but do not
include stocks on forest land in Alaska, Hawaii, U.S. ter-
ritories, or trees on non-forest land (e.g., urban trees).4
The timber volume data include estimates by tree spe-
cies, size class, and other categories.
The amount of carbon in trees, understory vegeta-
tion, the forest floor, and forest soil in 2000 was esti-
mated by Birdsey and Heath (1995) using the FORCARB
forest carbon model (Plantinga and Birdsey 1993) linked
2 This calculation does not account for carbon stored in imported wood products. It does include carbon stored in exports, even if the logs are
processed in other countries (Heath et al. 1996).
3 Forest land in the U.S. 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 1992, there were about 490 million acres of Timberlands, which represented 66 percent
of all forest lands (Powell et al. 1993). Forest land classified as Timberland is unreserved forest land that is producing or is capable of producing crops
of industrial wood. The remaining 34 percent of forest land is classified as Productive Reserved Forest Land, which is withdrawn from timber use by
statute or regulation, or Other Forest Land, which includes unreserved and reserved unproductive forest land.
4 Although forest carbon stocks in Alaska and Hawaii are large compared to the U.S. total, net carbon fluxes from forest stocks in Alaska and
Hawaii are believed to be minor. Net carbon fluxes from urban tree growth are also believed to be minor.
Land-Use Change and Forestry 6-5
-------
to the TAMM/ATLAS forest sector model (Adams and
Hayncs 1980,Alig I985,HaynesandAdams 1985, Mills
and Kincaid 1992). The forest stock projections for 2000,
therefore, are based on multiple variables, including pro-
jections of prices, consumption, and production of tim-
ber and wood products; and projections of forest area,
forest inventory volume, growth, and removals.
The amount of carbon in aboveground and
bclowground tree biomass in forests was calculated by
multiplying timber voiume by conversion factors derived
from studies in the United States (Cost et al. 1990, Koch
1989). Carbon stocks in the forest floor and understory
vegetation were estimated based on simple models (Vogt
IIH .' i ' i
el al. 1986) and review of numerous intensive ecosystem
studies (Birdsey 1992). Soil carbon stocks were calcu-
lated using a model similar to Burke et al. (1989) based
on data from Post et al. (1982).
Carbon stocks in wood products in use and in wood
stored in landfills were estimated by applying the
HARVCARB model (Row and Phelps 1991) to histori-
cal harvest data from the USFS (Powell et al. 1993) and
harvest projections for 2000 (Adams and Haynes 1980,
Mills and Kineaid 1992). The HARVCARB model allo-
cates harvested carbon to disposition categories (prod-
ucts, landfills, energy use, and emissions), and tracks the
accumulation of carbon in different disposition catego-
ries over time.
Tftlble 6-5 presents the carbon stock estimates for
!• ; . tii'i •; , .• i
forests (including trees, understory, forest floor, and for-
est soil), wood products, and landfilled wood used in this
inventory. The increase in all of these stocks over time
indicates that, during the examined periods, forests, for-
est product pools, and landfilled wood all accumulated
carbon (i.e., carbon sequestration by forests was greater
than carbon removed in wood harvests and released
through decay; and carbon accumulation in product pools
and landfills was greater than carbon emissions from these
pools by decay and burning).
Table 6-5: U.S. Forest Carbon Stock Estimates5
(Tg of Carbon)
Description
Forests
Trees
::::" Understory
Forest Floor
FoffistSqi!
Harvested Wood
TV ; Wood Products
, ;,, Landfilled Woqd,
1987
36,353
13,009
558
2,778
2fl,009
NA
NA
NA
1990
NA
NA
NA
NA
NA
3,739
2,061
1,678
1992
37,724
13,487
" 570
2,882
20,785
NA
: NA
NA
2000
~WMf "
"J UflrT*
,iuii''Si'»lifliili*ii'«i'ii'ii.iiiiiii''i'ii!i,
'.:'. I96:o';i
r ?1 475"-
4,1 12"
2,2,40,: ..
J,§Z,2 .,
„ „ ,
stocks do not include forest stocks in
. territories, or treej,,ojingn-forest Jand (e.g.,,,
product stocks inciudejexports, even if the
in other countries, and!exclude imports.
MA, (Not Available)
Note: Forest carbon
Alaska,, Hawaii,, M,
urban trees); wood
logs are processed
'' historical '(ffianS1 pr^'ectton^^ll oBieT vaJuesVre "Basedf on"
•in historical data only. Totals may not sum due to independent
rounding. J
II
Uncertainty
There are considerable uncertainties associated with
the estimates of the net carbon flux from U.S. forests. The
first source of uncertainty stems from the underlying forest
survey data. These surveys are based on a statistical sample
designed to represent a wide variety of growth conditions
present over large territories. Therefore, the actual timber
volumes contained in forests are represented by average
values that are subject to sampling and estimation errors. In
addition, the forest survey data that are currently available
exclude timber stocks on forest land in Alaska, Hawaii, U.S.
territories, and trees on non-forest land (e.g., urban trees);
however, net carbon fluxes from these stocks are believed
to be minor.
The second source of uncertainty results from de-
riving carbon storage estimates for the forest floor, un-
derstory vegetation, and soil from models that are based
on data from forest ecosystem studies. In order to ex-
trapolate results of these studies to all forest lands, it was
assumed that they adequately describe regional or na-
tional averages. This assumption can potentially intro-
duce the following errors: (1) bias from applying data
* Sourcja: Heath (1997), Heath el al. (1996), and Birdsey and Heath (1995).
6-6 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
from studies that inadequately represent average forest
conditions, (2) modeling errors (erroneous assumptions),
and (3) errors in converting estimates from one report-
ing unit to another (Birdsey and Heath 1995). In particu-
lar, the impacts of forest management activities, includ-
ing harvest, on soil carbon are not well understood. Moore
et al. (1981) found that harvest may lead to a 20 percent
loss of soil carbon, while little or no net change in soil
carbon following harvest was reported in another study
(Johnson 1992). Since forest soils contain over 50 per-
cent of the total stored forest carbon in the United States,
this difference can have a large impact on flux estimates.
The third source of uncertainty results from the use
of projections of forest carbon stocks for the year 2000
(Birdsey and Heath 1995) to estimate annual net carbon
sequestration from 1993 to 1997. These projections are
the product of two linked models (FORCARB and
TAMM/ATLAS) that integrate multiple uncertain
variables related to future forest growth and economic
forecasts. Because these models project decadal rather
than annual carbon fluxes, estimates of annual net carbon
sequestration from 1993 to 1997 are calculated as average
annual estimates based on projected long-term changes
in U.S. forest stocks.
The fourth source of uncertainty results from
incomplete accounting of wood products. Because the
wood product stocks were estimated using U.S. harvest
statistics, these stocks include exports, even if the logs
were processed in other countries, and exclude imports.
Haynes (1990) estimates that imported timber accounts
for about 12 percent of the timber consumed in the United
States, and that exports of roundwood and primary
products account for about 5 percent of harvested timber.
Changes in Non-Forest
Soil Carbon Stocks
The amount of organic carbon contained in soils
depends on the balance between inputs of photosyntheti-
cally fixed carbon (i.e., organic matter such as decayed
detritus and roots) and loss of carbon through decompo-
sition. The quantity and quality of organic matter inputs,
and the rate of decomposition, are determined by the
combined interaction of climate, soil properties, and land-
use. Agricultural practices and other land-use activities,
such as clearing, drainage, tillage, planting, crop residue
management, fertilization, and flooding, can modify both
organic matter inputs and decomposition, and thereby
result in a net flux of carbon dioxide (CO2) to or from
soils. The addition of carbonate minerals to soils through
liming operations also results in net emissions of CO2.
Changes in non-forest soil carbon stocks include net
fluxes of CO2 from three categories of land-use/land-
management activities: (1) activities on organic soils,
especially cultivation and conversion to pasture and for-
est; (2) activities on mineral soils, especially land-use
change activities; and (3) liming of soils.6 Organic soils
and mineral soils are treated separately because each re-
sponds differently to land-use practices.
Organic soils contain extremely deep and rich lay-
ers of organic matter. When these soils are cultivated,
tilling or mixing of the soil brings buried organic matter
to the soil surface, thereby accelerating the rate of de-
composition and CO2 generation. Because of the depth
and richness of the organic layer, carbon loss from culti-
vated organic soils can be sustained over long periods of
time (IPCC/UNEP/OECD/IEA1997). Conversion of or-
ganic soils to agricultural uses typically involves drain-
age as well, which also exacerbates soil carbon oxida-
tion. When organic soils are disturbed, through cultiva-
tion and/or drainage, the rate at which organic matter
decomposes, and therefore the rate at which CO2 emis-
sions are generated, is determined primarily by climate,
the composition (decomposability) of the organic mat-
ter, and the specific land-use practices undertaken. The
use of organic soils for upland crops results in greater
carbon loss than conversion to pasture or forests, due to
deeper drainage and/or more intensive management prac-
tices (Armentano and Verhoeven 1990, as cited in IPCC/
UNEP/OECD/IEA 1997).
Mineral soils generally have fairly shallow organic
layers and therefore have low organic carbon contents
6 Fluxes of CO2 from forest soils are excluded from this source because they are included in the previous source category (Changes in Forest
Carbon Stocks).
Land-Use Change and Forestry 6-7
-------
relative to organic soils. Consequently, it is possible to
entirely deplete the carbon stock of a mineral soil within
the first 10 to 20 years of disturbance, depending on the
type of disturbance, climate, and soil type. Once the
majority of the native carbon stock has been depleted,
an equilibrium is reached that reflects a balance between
accumulation from plant residues and loss of carbon
through decomposition. Various land-use practices, such
as incorporation of crop residues and cultivation of cer-
tain crops, can result in a net accumulation of carbon
stocks in mineral soils.
Lime in the form of crushed limestone (CaCO3)
and dolomite (CaMg(CO3)2) is commonly added to ag-
ricultural soils to ameliorate acidification. When these
compounds come in contact with acid soils, they degrade,
thereby generating CO2. The rate of degradation is de-
termined by soil conditions and the type of mineral ap-
plied; it can take several years for agriculturally-applied
lime to degrade completely.
Only two categories of land-use/land-management
activities—agricultural use of organic soils and liming—
are included in the estimates of CO2 emissions presented
here, because insufficient activity data were available to
estimate fluxes from mineral soils. Net annual emissions
of CO^ from organic soils and liming of soils in the United
States over the period 1990 through 1997 totaled approxi-
mately 8 to 9 MMTCE (30 to 32 Tg) (see Table 6-6 and
Table 6-7).
Table 6-6: C02 Flux From Non-Forest Soils
(MMTCE)
in 11 iiiiiiiiiiiiii 11 iiiii i in iiiiiiiiiii i
Table 6-7: C02 Flux From Non-Forest Soils (Tg C02)
PIliiiii'lilillH^
Year
1930
1991
1992
1993
1994
1995
I'll |ggjf
• iiiiriinira!
Soils
NA
NA
NA
NA
NA
NA
P,
HA
Organic
Soils
5.9
5.9
5.9
5.9
5.9
5.9
5r9
5.9
Liming of
Soils
2.2
2.8
2.1
2.1
2.3
2.5
2.4
2*8 '"'
Year
"1990
199!
1992
1993
1994
1995
1996
1997
Mineral
Soils
NA
NA
NA
NA
NA
NA
NA
NA
Organic L
Soils
21.8
21.8
21.8
21.8,
21.8
21.8"
21.8
21.8
iming of
Soils
8.2
10.2
7.8
7.7
8.5
9.3
8.9
10.4
f Thfl C04ftux from non-forest soils has been excluded from
l flux reported fof the Land-Use Change and Forestry
due Jo lh« high level of uncertainty associate!"wild"these
.- tslWaltes,
NA (Not Available) .
Note: The C02 flux from non:forest soils has been excluded from
{JigJaJa!Jffi, rggorted forthe LanjHJse Change and Forestry
chapter due to the FiigK level pFuncertainty" associated with these
f "Estimates.
Annual CO2 emissions from agricultural use of
organic soils were estimated to be 5.9 MMTCE (21.8
Tg) over the 1990 through 1997 period. Organic soil data
were available for only 1982; therefore, emissions from
organic soils were assumed to stay constant at the 1982
level for the years 1990 to 1997. Liming accounted for
net annual CO2 emissions of approximately 2.1 to 2.8
MMTCE (8 to 10 Tg). There was no apparent trend over
the seven year period.
The emission estimates and analysis for this source
: i
are restricted to CO2 fluxes associated with the manage-
ment of non-forest organic soils and liming of soils.
However, it is important to note that land-use and land-
use change activities may also result in fluxes of non-
CO2 greenhouse gases, such as methane (CH4), nitrous
oxide (N2O), and carbon monoxide (CO), to and from
soils. For example, when lands are flooded with fresh-
water, such as during hydroelectric dam construction,
CH4 is produced and emitted to the atmosphere due to
anaerobic decomposition of organic material in the soil
and water column. Conversely, when flooded lands, such
as lakes and wetlands, are drained, anaerobic decompo-
sition and associated CH4 emissions will be reduced. Dry
soils are a sink of CH4, so eventually, drainage may re-
sult in soils that were once a source of CH4 becoming a
sink of CH4. However, once the soils become aerobic,
oxidation of soil carbon and other organic material will
result in elevated emissions of CO2. Moreover, flooding
and drainage may also affect net soil fluxes of N2O and
CO, although these fluxes are highly uncertain. The fluxes
6-8 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
of CH4, and other gases, due to flooding and drainage
are not assessed in this inventory due to a lack of activity
data on the extent of these practices in the United States
as well as scientific uncertainties about the variables that
control fluxes.7
Methodology and Data Sources
The methodologies used to calculate CO2 emissions
from cultivation of organic soils and liming follow the
Revised 1996IPCC Guidelines (IPCC/UNEP/OECD/ffiA
1997).
To estimate annual CO2 emissions from organic
soils, the area under agricultural usage was divided into
broad climatic regions, and the area in each climatic re-
gion was multiplied by an emission factor. (All areas were
cropped rather than utilized for pasture or forestry, so
there was no need to further divide areas into general
land-use types). Annual statistics on the area of organic
soils under agricultural usage were not available for the
years 1990 through 1997; therefore, an estimate for the
area cultivated in 1982 (Mausbach and Spivey 1994) was
used for all years in the 1990 to 1997 series. The area
estimate was derived from USDA land-use statistics.8 Of
the 850,000 hectares of organic soils under cultivation
in 1982, Mausbach and Spivey (1994) estimated that two-
thirds were located in warm, temperate regions and one-
third was located in cool, temperate regions (see Table
6-8). The IPCC default emission factors (10 metric tons
C/hectare/year for warm, temperate regions, 1.0 metric
tons C/hectare/year for cool, temperate regions) were
applied to these areas to estimate annual CO2 emissions
resulting from cultivation of organic soils.
Carbon dioxide emissions from degradation of
limestone and dolomite applied to agricultural soils were
calculated by multiplying the annual amounts of lime-
stone and dolomite applied, by CO2 emission factors
(0.120 metric ton C/metric ton limestone, 0.130 metric
ton C/metric ton dolomite).9 These emission factors are
based on the assumption that all of the carbon in these
materials evolves as CO2. The annual application rates
of limestone and dolomite were derived from estimates
and industry statistics provided in the U.S. Geological
Survey's Mineral Resources Program Crushed Stone
Reports and Mineral Industry Surveys (USGS 1998a,
1998b, 1997a, 1997b, 1996, 1995, 1993). To develop
these data, the Mineral Resources Program obtained pro-
duction and use information by surveying crushed stone
manufacturers. Because some manufacturers were reluc-
tant to provide information, the estimates of total crushed
limestone and dolomite production and use are divided
into three components: (1) production by end-use, as re-
ported 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" produc-
tion). To estimate the total amounts of crushed limestone
and dolomite applied to agricultural soils, it was assumed
Table 6-8: Areas of Cultivated Organic Soils and Quantities of Applied Minerals
Description
1990 1991 1992 1993 1994 1995 1996 1997
Organic Soils Area Cultivated (hectares)
Warm Temperate Regions
Cool Temperate Regions
Applied Minerals (Gg)
Limestone
Dolomite
566,000 566,000 566,000 566,000 566,000 566,000 566,000 566,000
284,000 284,000 284,000 284,000 284,000 284,000 284,000 284,000
16,063 19,820 15,268 15,340 16,730 18,244 17,479 20,286
2,402 3,154 2,283 2,040 2,294 2,751 2,499 3,034
7 However, methane emissions due to flooding of rice fields are included. These are addressed under Rice Cultivation in the Agriculture
chapter.
8 This estimate does not include Alaska, but the area of cultivated organic soils in Alaska is believed to be small and emissions per unit area in
colder regions are relatively low, so this omission is probably quite minor. The estimate also does not include U.S. territories.
9 Note: 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 6-9
-------
that the fractions of "unspecified" and "estimated" pro-
duction that were applied to agricultural soils were equal
to the fraction of "specified" production that was applied
to agricultural soils. In addition, the total crushed lime-
stone and dolomite production figures for 1991, 1993,
1994, and 1995 were revised by the Mineral Resources
Program in later reports, but end uses were not speci-
fied. To estimate the amounts applied to agricultural soils,
it was assumed that the fractions estimated using the pre-
viously published data did not change.
Uncertainty
Uncertainties in the emission estimates presented
result primarily from the underlying activity data used
in the calculations. In particular, statistics on the areas of
organic soil cultivated or managed as pasture or forest
were not available, and the point estimate of total or-
ganic SOU cultivated is highly uncertain. In addition, the
breakdown of the cultivated organic soil area by climate
region was based upon a qualitative assessment of the
location of cultivated organic soils. Furthermore, there
arc uncertainties in the estimates of total limestone and
dolomite applied to agricultural soils, which are based
on estimates as well as reported quantities.
The emission factors used in the calculations are
an additional source of uncertainty. As discussed above,
CO2 emissions from cultivation of organic soils are con-
I!
trolled by climate, the composition of the soil organic
matter, and cultivation practices. Only the first variable
is taken into account, and only in a general way, in de-
riving the emission factors. Moreover, measured carbon
loss rates from cultivated organic soils vary by as much
as an order of magnitude.
The rate of degradation of applied limestone and do-
lomite is determined by soil conditions and the type of min-
eral applied. It can take several years for agriculturally-ap-
plied lime to degrade completely. The approach used to es-
timate CO2 emissions from liming assumed that the amount
of mineral applied in any year was equal to the amount that
degrades in that year, so annual application rates could be
used to derive annual emissions; however, this assumption
may be incorrect. Moreover, soil conditions were not taken
into account in the calculations.
Because the estimates of Confluxes from non-for-
est soils are based on limited and highly uncertain activ-
ity data and cover only a subset of the CO2 fluxes associ-
ated with this source, the estimate of CO2 flux from non-
forest soils has been excluded from the total flux reported
for the Land-Use Change and Forestry chapter.
II
6-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
7. Waste
Certain waste management and treatment activities are sources of greenhouse gas emissions. Particularly the
anaerobic decomposition of organic wastes by bacteria can result in the generation of methane (CH4). Currently,
anaerobic decomposition processes hi landfills are estimated to be the largest anthropogenic source of methane emissions
in the United States, accounting for 37 percent (see Figure 7-1). Smaller amounts of methane 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 esti-
mate. Emissions from the treatment of the human sewage component of wastewater were estimated, however, using a
simplified methodology. Waste combustion, both in incinerators and through open burning, were also a small source of
N2O. Nitrogen oxide (NOX), carbon monoxide (CO), and non-methane volatile organic compounds (NMVOCs) are emit-
ted by each of these sources, but are addressed separately at the end of this chapter. A summary of greenhouse gas emissions
from the Waste sector is presented in Table 7-1 and Table 7-2.
Overall, in 1997, waste activities generated emissions of 70.0 MMTCE, or 3.9 percent of total U.S. greenhouse
gas emissions.
Figure 7-1
Landfills
66.7
Human
Sewage
Wastewater I
Treatment |
Waste j
Combustion
Portion of All
Emissions
Landfills are the largest anthropogenic source of meth-
ane (CH4) emissions in the United States. In 1997, emis-
sions were approximately 66.7 MMTCE (11.6 Tg). Emis-
sions from municipal solid waste (MSW) landfills, which
received about 61 percent of the total solid waste generated
in the United States, accounted for about 93 percent of total
landfill emissions, while industrial landfills accounted for
the remainder. There were over 2,500 landfills in the U.S.
(BioCycle 1998), with the largest landfills having received
most of the waste and having generated the majority of
emissions.
Methane emissions result from the decomposition of
organic landfill materials such as yard waste, household garbage, food waste, and paper. This decomposition process
is a natural mechanism through which microorganisms derive energy. After being placed in a landfill, organic waste
first decomposes aerobically (in the presence of oxygen) and is then attacked by anaerobic bacteria, which convert
organic matter to substances such as cellulose, amino acids, and sugars. These simple substances are further broken
234
MMTCE
Waste 7-1
-------
Table 7-1: Emissions from Waste (MMTCE)
Gas/Source
1990 1991 1992 1993 1994 1995 1996 1997
atiiu IIIIIH^^
aa ,
ll'ltariffli :
llVasIswater TfBatrnent
•yj,
. '« yun]an,Seffiagg
: riiisiSrriluslon
, "ftfl|a|
"KlfBi Ha!s,5y not sum due to independent rounding.
1 -'1M"! Illllll ill iiil^^^
Table 7-2: Emissions from Waste (Tg)
Gas/Source
CH<
Lat|dfil!s
, Wastewater Treatment
Human Sewage
Waste Combustion
* Does not exceed 0,05 .Tg
Note: Totats may not sum due to independent rounding.
ii
-------
Table 7-3: CH4 Emissions from Landfills (MMTCE)
Activity
1990 1991 1992 1993 1994 1995 1996 1997
MSW Landfills
Industrial Landfills
Recovered
Net Emissions
60
4
(8
56
.6
.2
.6)
.2
61.9
4.3
(8.6)
57.6
63.8
4.4
(10.3)
57.8
65.5
4.5
(10.3)
59.7
67.3
4.6
(10.3)
61.6
69
4
(10
63
.2
.8
.3)
.6
70.6
4.9
(10.3)
65.1
72.0
5.0
(10.3)
66.7
Note: Totals may not sum due to independent rounding.
Table 7-4: CH4 Emissions from Landfills (Tg)
Activity
1990 1991 1992 1993 1994 1995 1996 1997
MSW Landfills
Industrial Landfills
Recovered
Net Emissions
10.
0.
(1-
9.
6
7
5)
8
10.
0,
(1.
10,
.8
.7
.5)
.0
11.1
0.8
(1.8)
10.1
11
0
(1
10
.4
.8
.8)
.4
11.7
0.8
(1.8)
10.8
12.1
0.8
(1.8)
11.1
12.3
0.8
(1.8)
11.4
12.6
0.9
(1.8)
11.6
Note: Totals may not sum due to independent rounding.
Over the next several years, the total amount of
MSW generated is expected to continue increasing. The
percentage of waste landfilled, however, may decline due
to increased recycling and composting practices. In ad-
dition, the quantity of methane that is recovered and ei-
ther flared or used for energy purposes is expected to
increase, partially as a result of a new regulation that will
require large landfills to collect and combust landfill gas.
Methodology
Based on the available information, methane emis-
sions from landfills were estimated to equal methane
production from municipal landfills, plus methane pro-
duced by industrial landfills, minus methane recovered
and combusted, and minus the methane oxidized before
being released into the atmosphere.
The methodology for estimating CH4 emissions
from municipal landfills is based on an updated model
that tracks changes in the population of landfills in the
United States over time. This model is based on the pat-
tern of actual waste disposal by each individual landfill
surveyed by the EPA's Office of Solid Waste in 1987. A
second model was employed to estimate emissions from
the landfill population data (EPA 1993). For each land-
fill in the data set, the amount of waste in place contrib-
uting to methane generation was estimated using its year
of opening, its waste acceptance rate, and total waste
disposed in landfills. Data on national waste disposed in
landfills each year was apportioned by landfill. Emis-
sions from municipal landfills were then estimated by
multiplying the quantity of waste contributing to emis-
sions by emission factors (EPA 1993). For further infor-
mation see Annex I.
To estimate landfill gas recovered per year, data
on current and planned landfill gas recovery projects in
the United States were obtained from Governmental
Advisory Associates (GAA1994). The GAA report, con-
sidered to be the most comprehensive source of infor-
mation on gas recovery in the United States, has esti-
mates for gas recovery in 1990 and 1992. In addition, a
number of landfills were believed to recover and flare
methane without energy recovery and were not included
in the GAA database. To account for the amount of meth-
ane flared without energy recovery, the estimate of gas
recovered was increased by 25 percent (EPA 1993).
The amount of methane oxidized was assumed to
be 10 percent of the methane generated. Methane recov-
ered and oxidized was subtracted from the methane gen-
erated from municipal and industrial landfills to arrive at
net methane emissions. Emissions from industrial sites
were assumed to be seven percent of total emissions from
municipal landfills.
Waste 7-3
-------
Data Sources
I . " !i
The model, including actual waste disposal data
from individual landfills, was developed from a survey
performed by the EPA Office of Solid Waste (EPA 1988).
National landfill waste disposal data for 1988 through
1997 were obtained from BioCycle (1998). Documenta-
tion on the landfill methane emissions methodology
employed is available in EPA's Anthropogenic Methane
Emissions in the United States, Estimates for 1990: Re-
port to Congress (EPA 1993). Emission factors were
taken from Bingemer and Crutzen (1987) and the Gov-
ernmental Advisory Associates (GAA 1994).
Uncertainty
There are several uncertainties associated with the
estimates of methane emissions from landfills. The primary
one concerns the characterization of landfills. There is a
luck of information on the area landfilled and total waste in
place (the fundamental factors that affect methane produc-
tion). In addition, little information is available on the quan-
tity of methane flared at non-energy-related projects and
the number of landfill closures. Finally, the statistical model
used to estimate emissions is based upon methane genera-
tion at landfills that currently have developed energy recov-
ery projects, and may not precisely capture the relationship
between emissions and various physical characteristics of
individual landfills. Overall, uncertainty is estimated to be
roughly ±30 percent.
Waslewater Treatment
The breakdown of organic material in wastewater
treatment systems produces methane when it occurs un-
der anaerobic conditions. During collection and treat-
ment, wastewater may be incidentally as well as deliber-
ately maintained under anaerobic conditions. The meth-
ane produced during deliberate anaerobic treatment is
typically collected and flared or combusted for energy.
However, whenever anaerobic conditions develop, some
of the methane generated is incidentally released to the
atmosphere. Untreated wastewater may also produce
methane if held under anaerobic conditions.
Organic content, expressed in terms of biochemical
oxygen demand (BOD), determines the methane produc-
ing 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
i. ..
decomposition processes: Under anaerobic conditions, how-
ever, wastewater with higher BOD concentrations will pro-
duce more methane than wastewater with lower BOD. The
amount of methane produced is driven by the extent to which
the organic material is broken down under anaerobic ver-
i!i II
sus aerobic conditions.
In 1997, methane emissions from municipal waste-
water were 0.9 MMTCE (0.2 Tg). Emissions have in-
i
creased slightly since 1990 reflecting the increase in the
U.S. human population. No estimates have been devel-
oped to indicate any changes in the manner in which
wastewater is managed in the United States during this
period. Table 7-5 provides emission estimates from do-
mestic wastewater treatment.
At this time, data are not sufficient to estimate
methane emissions from industrial wastewater sources.
Further research is ongoing at the EPA to better quantify
emissions from this source.
Methodology
Wastewater methane emissions are estimated us-
ing the default IPCC methodology (IPCC/UNEP/OECD/
IEA 1997). The total population for each year was mul-
tiplied by a wastewater BOD production rate to deter-
mine total wastewater BOD produced. It was assumed
that, per capita, 0.05 kilograms of wastewater BOD53 is
produced per day and that 15 percent of wastewater
BODS is anaerobically digested. This proportion of BOD
was then multiplied by an emission factor of 0.22 Gg
CH4/Gg BODS.
Data Sources
Human population data for 1990 to 1997 were sup-
plied by the U.S. Census Bureau (1998). The emission fac-
tor employed was taken from Metcalf & Eddy (1972). Table
7-6 provides U.S. population and wastewater BOD data.
Uncertainty
Domestic wastewater emissions estimates are
highly uncertain due to the lack of data on the occur-
rence of anaerobic conditions in treatment systems, es-
7-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 7-5: CH4 Emissions from Domestic
Wastewater Treatment
Year
MMTCE
Tg
1990
1991
1992
1993
1994
1995
1996
1997
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.9
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
pecially incidental occurrences. It is also believed that
industrial wastewater is responsible for significantly more
methane emissions than domestic wastewater treatment.
Human Sewage
Human sewage is transported for treatment in the
form of domestic wastewater. Nitrous oxide (N2O) is
emitted from both domestic and industrial wastewater
containing nitrogen-based organic matter and is produced
through natural processes known as nitrification and deni-
trification. Nitrification occurs aerobically and converts
ammonia into nitrate, while denitrification occurs anaero-
bically, and converts nitrate to N2O. It is estimated that
the amount of N2O emitted from wastewater treatment
plants accounts for approximately 5 to 10 percent of an-
nual global discharge (Spector 1997 McElroy et al. 1978).
Human sewage is believed to constitute a significant por-
tion of the material responsible for N2O emissions from
wastewater (Spector, 1997). There is insufficient infor-
Table 7-6: U.S. Population (millions) and
Wastewater BOD Produced (Gg)
Year
Population BODS*
1990
1991
1992
1993
1994
1995
1996
1997
249.3
252.0
254.9
257.7
260.2
262.7
265.1
267.6
4,554
4,602
4,655
4,706
4,752
4,797
4,842
4,887
* The 5 day biochemical oxygen demand (BOD) measurement
(Metcalf and Eddy 1972)
mation available at this time to estimate emissions from
industrial wastewater and the other components of do-
mestic wastewater. In general, N2O generation in waste-
water systems is affected by temperature, pH, biochemi-
cal oxygen demand (BOD), and nitrogen concentration.
BOD is the amount of dissolved oxygen used by aerobic
microorganisms to completely consume the available
organic matter (Metcalf & Eddy 1972).
Emissions of N2O from human sewage treated in
wastewater systems was estimated to be 2.3 MMTCE (27
Gg) in 1997. An increase in the U.S. population and the
per capita protein intake resulted in an overall increase
of 12 percent in N2O emissions from human sewage be-
tween 1990 and 1997 (see Table 7-7).
Table 7-7: N20 Emissions from Human Sewage
Year
MMTCE
GO
1990
1991
1992
1993
1994
1995
1996
1997
2.1
2.1
2.2
2.2
2.3
2.2
2.3
2.3
24
25
26
26
27
27
27
27
Methodology
Nitrous oxide emissions from human sewage were
estimated using the IPCC default methodology (IPCC/
UNEP/OECD/IEA 1997). The equation in IPCC was
modified slightly to convert N2O-N to N2O by using a
conversion factor of the atomic weight of N2O to that of
N2 (44/28). This is illustrated below:
N2O(s) = (Protein) x (Frac^^) x (NR People) x (EF) x C44/^)
where,
N2O(s) = N2O emissions from human sewage
Protein = Annual, per capita protein consumption
FracNPR = fraction of nitrogen in protein
NR People = U.S. population
EF = Emission factor
(44/28) = The atomic weight ratio of N2O to N2
' The 5 day biochemical oxygen demand (BOD) measurement (Metcalf and Eddy 1972).
Waste 7-5
-------
Data Sources
U.S. population data were taken from the U.S.
Census Bureau (1998). Data on the annual per capita
protein consumption were provided by the United Na-
tions Food and Agriculture Organization (FAO 1998) (see
Table 7-8). Because data on protein intake were unavail-
able for 1997, the average value of per capita protein
consumption over the years 1990 through 1996 was used.
An emission factor has not been specifically estimated
for the United States. As a result, the default IPCC value
(0.01 kg N2O-N/kg sewage-N produced) was applied.
Similarly, the fraction of nitrogen in protein (0.16 kg N/
kg protein) was also obtained from IPCC/UNEP/OECD/
IEA (1997).
Table 7-8: U.S. Population (millions) and Average
Protein Intake (kg/person/year)
Year
Population Protein
1990
1991
1992
1993
1994
1995
249.3
252.0
254.9
257.7
262J
265.1
38.9
39.6
39.8
39.9
40.6
40.3
40.7
Td!'u™
Uncertainty
The U.S. population (NR people) and per capita
protein intake data (Protein) are believed to be fairly ac-
curate. There is significant uncertainty, however, in the
emissfon factor (EF) employed due to regional differ-
ences that would likely affect N2O emissions but are not
accounted for in the default IPCC factor. In contrast, the
fraction of nitrogen in protein (FracNPR) is believed to be
quite accurate. Despite the increase in N2O emissions
from 1990 through 1997, these estimates from human
sewage are significantly lower than other more recent
estimates (Specter 1997) of total N2O emissions from
both domestic and industrial wastewater treatment. EPA
is currently supporting further research to develop a com-
prehensive estimate of emissions from this source.
Waste Combustion
Waste combustion involves the burning of garbage
and non-hazardous solids, called municipal solid waste
i
(MSW), and has been identified as a source of nitrous
oxide (N2O) emissions.4 In 1992, there were over 160
municipal waste combustion plants in the United States
•. i
(EPA 1997b). Emissions from this source are dependent
i
on the types of waste burned and combustion tempera-
tures (De Soete 1993). Nitrous oxide emissions from
i.
MSW combustion were estimated to be 0.1 MMTCE (1
Gg) in 1997, and have fluctuated only slightly since 1990
(see Table 7-9).
I
Table 7-9: N20 Emissions from Waste Combustion
Year
MMTCE
fig
1990
1991
1992
1993
1994
1995
1996
1997
; ,
:"o.i " 1
0.1 1
0.1 : 1
0.1 : 1
0.1 1
0.1 1
0.1 1
0.1 1
.... , ....,„ , . ,,,, I,
Methodology
Estimates of nitrous oxide emissions from MSW
combustion in the United States are based on the meth-
odology outlined in the EPA's Compilation of Air Pol-
lutant Emission Factors (EPA 1997a). According to this
methodology, emissions of N2O from MSW combustion
is the product of the mass of MSW (metric ton MSW)
combusted, the emission factor of N2O emitted per unit
mass of waste combusted (g N2O/metric ton), and an N2O
emissions control removal efficiency. For MSW combus-
tion in the United States, an emission factor of 30 g N2O/
metric ton MSW, and an estimated emissions control re-
moval efficiency of zero percent were used.
Data Sources
Data on the quantity of MSW generated and com-
busted was taken from the April 1908 issue of BioCycle
(Glenn 1998). Table 7-10 provides MSW generation and
* Emissions of COj from the combustion of petroleum-based plastics i
energy use of petroleum.
7-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
percentage combustion data. The emission factor of N2O
emissions per quantity of MSW combusted was taken
from Olivier (1993).
Table 7-10: Municipal Solid Waste Generation
(Metric Tons) and Percent Combusted
Table 7-11: U.S. Municipal Solid Waste Combusted
by Data Source (Metric Tons)
Year
Waste Generation Combusted (%)
1990
1991
1992
1993
1994
1995
1996
1997
266,541,881
254,796,765
264,843,388
278,572,955
293,109,556
296,586,430
297,268,188
309,075,035
11.5
10.0
11.0
10.0
10.0
10.0
10.0
9.0
Uncertainty
As with other combustion-related sources of ni-
trous oxide, emissions are affected by combustion con-
ditions (De Soete, 1993). In part, because insufficient
data exists to provide detailed estimates of N2O emis-
sions for individual combustion facilities, the estimates
presented are highly uncertain. The emission factor for
N2O from MSW combustion facilities used in the analy-
sis is a default used to estimate N2O emissions from fa-
cilities worldwide (Olivier, 1993). As such, it has a range
of uncertainty of an order of magnitude (between 25 and
293 g N2O/metric ton MSW combusted) (Watanabe, et
al. 1992). Due to a lack of relevant information on the
control of N2O emissions from MSW combustion facili-
ties in the U.S., the estimate of zero percent for N2O
emissions control removal efficiency is also uncertain.
MSW combustion activity data used in this analysis, as
published in BioCycle (1998), were compared with data
published by the EPA's Office of Solid Waste (EPA
1997b) and were found to be relatively consistent (see
Table 7-11).
Waste Sources of Criteria Pollutants
In addition to the main greenhouse gases addressed
above, waste generating and handling processes are also
sources of criteria air pollutant emissions. Total emis-
sions of nitrogen oxides (NOX), carbon monoxide (CO),
Year
BioCycle
EPA
1990
1991
1992
1993
1994
1995
1996
1997
30,652,316
25,479,677
29,132,773
27,857,295
29,310,956
29,658,643
29,726,819
30,641,940
28,958,820
30,256,974
29,675,982
29,884,776
29,494,422
30,384,066
NA
NA
NA (Not Available)
and nonmethane volatile organic compounds (NMVOCs)
from waste sources for the years 1990 through 1997 are
provided in Table 7-12.
Methodology and Data Sources
These emission estimates were taken directly from
the EPA's Draft National Air Pollutant Emissions Trends,
1900-1997 (EPA 1998). This EPA report provides emis-
sion estimates of these gases 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 mate-
rial processed) as an indicator of emissions. National
activity data were collected for individual source catego-
ries from various agencies. Depending on the source cat-
egory, these basic activity data may include data on pro-
duction, fuel deliveries, raw material processed, etc.
Activity data were used in conjunction with emis-
sion factors, which relate the quantity of emissions to
the activity. Emission factors are generally available from
the EPA's Compilation of Air Pollutant Emission Fac-
tors, AP-42 (EPA 1997). The EPA currently derives the
overall emission control efficiency of a source category
from a variety of information sources, including pub-
lished 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.
Waste 7-7
-------
Table 7-12: Emissions of NOX, CO, and NMVOC from Waste (Gg)
•Sill !>,,!:• ,!, I .UiitSf I,,,1 Civil!,)' !!::!!•
Gas/Source
.it,-! IL ',' s li ...... •
1990 1991 1992 1993 1994 1995 1996 1997
!,jp; "" '" "
: ^Langlfiijs
„ "'Wastewater treatment
» ,, Jlllliltti!! i, i/ft, 'Will1!!1 "ill! will" '.mm ,
; waste Combustion*
1 Miscellaneous''
*n ' "' '; '"' ll"" ' '""' ' ' :
uu .,
Landfills
Wastewater Treatment
Waste Combustion"
Miscellaneous19
NMVOCs
Lafjfffjlls
Wastewater Treatment
Waste Combustion8
Miiceineoiis8;' '; "" II ;,.
"S3"''
i +_ ^
"" '" "." " '" 82
4-
, '"'" '!!'",' 979 '
1
_l_
978
+
895
58
57
222
..'. , ; „ ".. "558,
86
. -h
, . .. 8^,
' " L
1012
1
_j_
1,011
+
907
60
58
227
562
87
, .+T
..' ,',§6
"i
1032
2
_l_
1,030
+
916
63
61
230
563
112
..,,,,1, ,
i „,' . JT ™ ,!if 1'inl.
107
.'..!.'.! 4..'
1133
2
_l_
1,130
1
949
67 :.
63
256
,,!563 '!
103
, .,,,1 .„
,!',<,; "i "uiiHiiLiiir, i,isi
99
."'. !5". !',!'
1111
2
_i_
1,108
1
949
73
64
248
.'. 564l"l
89
^l
"l','t.
88
1
1075
2
i
1,073
1
968
68
61
237
. 602
i
91
; 1.
i,. <..«.+,
, 89
, , '.1.
1091
; 2
_i_
1,089
; 1
393
" 20
58
240
'.','. 75 •
94
„„ 1
.,„,, .+ ,
93
1 "
1126
2
_l_
1,124
+
408
21
62
246
!"'"79
* Includes waste lncln§r§|ion, afjd open burning (EPA 1998) I
fc Mscgllpaqus .indudesJSDFs (Treatrnent,, Storage, and Disposal Facilities under the Resource Conservation and Recovery Act [42 U.S.C. §
6§24,§WDA § 3004]) arid other waste categories,
Note; Jotals rtiay not sum due to independent rounding. :
7-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
8. References
Executive Summary
EPA (1998) 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/UNEP/OECD/IEA (1997) Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories,
Paris: Intergovernmental Panel on Climate Change,
United Nations Environment Programme, Organization
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IPCC (1996) Climate Change 1995: The Science of Cli-
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Powell, D.S., J.L. Faulkner, D.R. Darr, Z. Zhu, and D.W.
MacCleery (1993) Forest Resources of the United States,
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BEA (1998) Survey of Cur rent Business, Bureau of Eco-
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U.S. Census Bureau (1998) Department of Commerce,
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EPA (1998) National Air Pollutant Emissions Trends
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Agency, Office of Air Quality Planning and Standards,
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IPCC (1996) Climate Change 1995: The Science of Cli-
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Energy
Carbon Dioxide Emissions from
Fossil Fuel Combustion
BEA(1998) Unpublished BE-36 survey data, Bureau of
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Bechtel (1993) A Modified EPRI Class II Estimate for Low
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DOE (1993) Transportation Energy Data Book, Office of
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Division, Oak Ridge National Laboratory, ORNL-6743.
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DOE (1995) Transportation Energy Data Book, Office of
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DOE 0997) Transportation Energy Data Book, Office of
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DOE (1998) Transportation Energy Data Book, Office
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DOT/BTS (1998) Fuel Cost and Consumption, monthly
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EIA (J998a) Annual Energy Review 1997, DOE/EIA-
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EIA (|998b) Electric j^pwer Annual 1997, Volume I, DOE/
El A-Q348(97X1-annual, Energy Information Administra-
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EIA (1998c) Fuel Oil and Kerosene Sales 1997. DOE/
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EIA (1998d) International'Energy Annual 1996, DOE/
EIA-0219(96)-annualr Energy Information Administra-
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EIA (1998e) Monthly Energy Review, DOE/EIA-
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1
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Outlook '91, 67th Annual Outlook Conference. Wash-
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USFS (1990) An Analysis of the Timber Situation in the
United States: 1989 - 2040: A Technical Document Sup-
porting the 1989 USDA Forest Service RPA Assessment.
Gen. Tech. Rep. RM-199. U.S. Forest Service, U.S. De-
partment of Agriculture.
USGS (1998a) Crushed Stone: Annual Report 1996. U.S.
Geological Survey, Reston, VA.
USGS (1998b) Mineral Industry Surveys: CrushedStone
and Sand and Gravel in the Fourth Quarter of 1997.
USGS, Reston, VA
USGS (1997a) CrushedStone: Annual Report 1995. U.S.
Geological Survey, Reston, VA.
USGS (1997b) Mineral Industry Surveys: CrushedStone
and Sand and Gravel in the Fourth Quarter of 1996.
USGS, Reston, VA.
USGS (1996) Crushed Stone: Annual Report 1994. U.S.
Geological Survey, Reston, VA.
USGS (1995) Crushed Stone: Annual Report 1993. U.S.
Geological Survey, Reston, VA.
USGS (1993) Crushed Stone: Annual Report 1991. U.S.
Geological Survey, U.S. Department of the Interior, for-
merly Bureau of Mines. Washington, DC. January.
References 8-13
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Vogt, k.A., C.C. Grier, and DJ. Vogt (1986) Production,
turnover, and nutrient dynamics of above- and
belowground detritus of world forests. Advances in Eco-
logical Research, 15:303-377.
Waddell, Karen L., D.D. Oswald, andD.S. Powell (1989)
forest Statistics of the United States, 1987. Resource
Bulletin PNW-RB-16S. Portland, OR: Pacific Northwest
Research Station, Forest Service, U.S. Department of
Agriculture, 106 p.
Waste
Landfills
Bingemer, H. and Crutzen, J. (1987) "The Production of
Methane from Solid Wastes." Journal of Geophysical
BioCycle (1998). "BioCycle Nationwide Survey: The
State of Garbage in America," April.
EPA (1988). National Survey of Solid Waste (Municipal)
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tember,
EPA (1993) Anthropogenic Methane Emissions in the
United States, Estimates for 1990: Report to Congress,
U.S. Environmental Protection Agency, Office of Air and
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GAA (1994) 1994-1995 Methane Recovery from Land-
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York,.N.Y.
Wastewater Treatment
IPCC/UNEP/OECD/fEA (1997) Revised 1996 IPCC
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Metealf & Eddy, Inc. (1972) Wastewater Engineering:
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U.S. Census Bureau (1998) August 28
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Human Sewage
FAO (1998) FAQSTAT Statistical Database. United
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IPCC/UNEP/OECD/IEA (1997) Revised 1996 IPCC
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United Nations Environment Programme, Organization
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McElroy, M.B., J.W. Elkins, S.C. Wofsy, C.E. Kolb, A.P.
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Metealf and Eddy, Inc. (1972) Wastewater Engineer-
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U.S. Census Bureau (1998) August 28
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Waste Combustion
De Soete, G. G. (1993) Nitrous Oxide from Combustion
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Amstel, A. R. (ed) Proc. Of the International Workshop
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EPA (1997a) Compilation of Air Pollutant Emission Fac-
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fice of Air Quality Planning and Standards, Research
Triangle Park, NC, October.
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fice of Solid Waste, EPA. Washington, DC.
Glenn, Jim (1998) "BioCycle Nationwide Survey: The
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Watanabe, M., Sato, M., Miyazaki, M. and Tanaka, M.
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Paper 3-4. •
8-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1996
-------
Waste Sources of Criteria Pollutants
EPA (1998) Draft National Air Pollutant Emissions
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References 8-15
-------
-------
Annexes
The following seventeen annexes provide additional information to the material presented in the main body of this
report. Annexes A through I discuss methodologies for individual source categories in greater detail than was presented
in the main body of the report and include explicit activity data and emission factor tables. Annex J presents a technical
summary on the derivation of Global Warming Potential values and some of the uncertainties related to their use to
weight greenhouse emission estimates. Annexes K and L summarize U.S. emissions of ozone depleting substances (e.g.,
CFCs and HCFCs) and sulfur dioxide (SO2), respectively. Annex M provides a complete list of emission sources
assessed in this report. Annexes N and O present U.S. greenhouse gas emission estimates in the reporting format
recommended in the Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories
(IPCC/UNEP/OECD/IEA 1997) and the IPCC reference approach for estimating CO2 emissions from fossil fuel
combustion, respectively. Annex P addresses the criteria for the inclusion of an emission source category and some of
the sources which meet the criteria but are nonetheless excluded from U.S. estimates. Annex Q provides some useful
constants, unit definitions, and conversions. Annexes R and S provides a listing of abbreviations and chemical symbols
used. Finally, Annex U contains a glossary of terms related to greenhouse gas emissions and inventories.
List of Annexes
ANNEX A
ANNEX B
ANNEXC
ANNEX D
ANNEXE
ANNEX F
ANNEX G
ANNEX H
ANNEX I
ANNEX!
ANNEX K
ANNEX L ,
ANNEX M
ANNEXN
ANNEX O
ANNEX P
ANNEXQ
ANNEX R
ANNEX S
ANNEX T
Methodology for Estimating Emissions of CO2 from Fossil Fuel Combustion
Methodology for Estimating Emissions of CH4, N2O, and Criteria Pollutants
from Stationary Sources
Methodology for Estimating Emissions of CH4, N2O, and Criteria Pollutants
from Mobile Sources
Methodology for Estimating Methane Emissions from Coal Mining
Methodology for Estimating Methane Emissions from Natural Gas Systems
Methodology for Estimating Methane Emissions from Petroleum Systems
Methodology for Estimating Methane Emissions from Enteric Fermentation
Methodology for Estimating Methane Emissions from Manure Management
Methodology for Estimating Methane Emissions from Landfills
Global Warming Potential Values
Ozone Depleting Substance Emissions
Sulfur Dioxide Emissions
Complete List of Sources
IPCC Reporting Tables
IPCC Reference Approach for Estimating CO2 Emissions from
Fossil Fuel Combustion
Sources of Greenhouse Gas Emissions Excluded
Constants, Units, and Conversions
Abbreviations
Chemical Symbols
Glossary
-------
-------
Annex A
Methodology for Estimating Emissions of C02 from Fossil Fuel Combustion
Carbon dioxide (CO2) emissions from fossil fuel combustion were estimated using a "bottom-up" methodology
characterized by six steps. These steps are described below.
Step 1: Determine Energy Consumption by Fuel Type and Sector
The bottom-up methodology used by the United States for estimating CO2 emissions from fossil fuel combustion
is conceptually similar to the approach recommended by the Intergovernmental Panel on Climate Change (IPCC) for
countries that intend to develop detailed, sectoral-based emission estimates (IPCC/UNEP/OECD/IEA 1997). Basic
consumption data are presented in Columns 2-8 of Table A-l through Table A-8, with totals by fuel type in Column 8
and totals by end-use sector in the last rows. Fuel consumption data for the bottom-up approach were obtained directly
from the Energy Information Administration (EIA) of the U.S. Department of Energy. The EIA data were collected
through surveys at the point of delivery or use; therefore, they reflect the reported consumption of fuel by end-use sector
and fuel type. Individual data elements were supplied by a variety of sources within EIA. Most information was taken
from published reports, although some data were drawn from unpublished energy studies and databases maintained by
EIA.
Energy consumption data were aggregated by end-use sector (i.e., residential, commercial, industrial,
transportation, electric utilities, and U.S. territories), primary fuel type (e.g., coal, natural gas, and petroleum), and
secondary fuel type (e.g., motor gasoline, distillate fuel, etc.). The 1997 total energy consumption across all sectors,
including territories, and energy types was 80,469 trillion British thermal units (TBtu), as indicated in the last entry of
Column 8 in Table A-l. This total includes fuel used for non-energy purposes and fuel consumed as international
bunkers, both of which are deducted in later steps.
There are two modifications made in this report that may cause consumption information herein to differ from
figures given in the cited literature. These are the consideration of synthetic natural gas production and ethanol added
to motor gasoline.
First, a portion of industrial coal accounted for in EIA combustion figures is actually used to make "synthetic
natural gas" via coal gasification. The energy in this gas enters the natural gas stream, and is accounted for in natural
gas consumption statistics. Because this energy is already accounted for as natural gas, it is deducted from industrial
coal consumption to avoid double counting. This makes the figure for other industrial coal consumption in this report
slightly lower than most EIA sources.
Second, ethanol has been added to the motor gasoline stream for several years, but prior to 1993 this addition was
not captured in EIA motor gasoline statistics. Starting in 1993, ethanol was included in gasoline statistics. However,
because ethanol is a biofuel, which is assumed to result in no net CO2 emissions, the amount of ethanol added is
subtracted from total gasoline consumption. Thus, motor gasoline consumption statistics given in this report may be
slightly lower than in EIA sources.
There are also three basic differences between the consumption figures presented in Table A-l through Table A-8
and those recommended in the IPCC emission inventory methodology.
First, consumption data in the U.S. inventory are presented using higher heating values (HHV)1 rather than the
lower heating values (LHV)2 reflected in the IPCC emission inventory methodology. This convention is followed
because data obtained from EIA are based on HHV.
Also referred to as Gross Calorific Values (GCV).
' Also referred to as Net Calorific Values (NCV).
A-1
-------
Second, while EIA's energy use data for the United States includes only the 50 U.S. states and the District of
Columbia, the data reported to the Framework Convention on Climate Change are to include energy consumption within
territories. Therefore, consumption estimates for U.S. territories were added to domestic consumption of fossil fuels.
Energy consumption data from U.S. territories are presented in Column 7 of Table A-l. It is reported separately from
domestic sectoral consumption, because it is collected separately by EIA with no sectoral disaggregation.
Third, the domestic sectoral consumption data in Table A-l include bunker fuels used for international transport
activities and non-energy uses of fossil fuels. The IPCC recommends that countries estimate emissions from bunker
fuels separately and exclude these emissions from national totals, so bunker fuel emissions have been estimated in Table
A-9 and deducted from national estimates (see Step 4). Similarly, fossil fuels used to produce non-energy products that
store carbon rather than release it to the atmosphere are provided in Table A-10 and deducted from national emission
estimates (see Step 3). ;
'i i
Step 2: Determine the Carbon Content of All Fuels
The carbon content of combusted fossil fuels was estimated by multiplying energy consumption (Columns 2
through 8 of Table A-1) by fuel-specific carbon content coefficients (see Table A-11 and Table A-l 2) that reflected the
amount of carbon per unit of energy inherent in each fuel. The resulting carbon contents are sometimes referred to as
potential emissions, or the maximum amount of carbon that could potentially be released to the atmosphere if all carbon
in the fuels were converted to CO2. The carbon content coefficients used in the U.S. inventory were derived by EIA
from detailed fuel information and are similar to the carbon content coefficients contained in the IPCC's default
methodology (IPCC/UNEP/OECD/IEA 1997), with modifications reflecting fuel qualities specific to the United States.
!
Step 3: Adjust for the amount of Carbon Stored in Products
Depending on the end-use, non-energy uses of fossil fuels can result in long term storage of some or all of the
carbon contained in the fuel. For example, asphalt made from petroleum can sequester up to 100 percent of the carbon
contained in the petroleum feedstock for extended periods of time. Other non-energy products, such as lubricants or
plastics also store carbon, but can lose or emit some of this carbon when they are used and/or burned as waste.
The amount of carbon sequestered or stored by non-energy uses of fossil fuel products was based upon data that
addressed the ultimate fate of various energy products, with all non-energy use attributed to the industrial, transportation,
and territories end-use sectors. This non-energy consumption is presented in Table A-10. Non-energy consumption
was then multiplied by fuel-specific carbon content coefficients (Table A-l 1 and Table A-12) to obtain the carbon
conten! of the fuel, or the maximum amount of carbon that could be sequestered if all the carbon in the fuel were stored
in non-energy products (Columns 5 and 6 of Table A-10). This carbon content was then multiplied by the fraction of
carbon assumed to actually have been sequestered in products (Column 7 of Table A-10), resulting in the final estimates
of carbon stored by sector and fuel type, which are presented in Columns 8 through 10 of Table A-10. The portions
of carbon sequestered were based on EIA data.
Step 4: Subtract Carbon from Bunker Fuels.
Emissions from international transport activities, or bunker fuel consumption, were not included in national totals
as recommended by the IPCC"(IPCC/UNEP/OECD/IEA 1997). There is currently disagreement ^internationally as to
how these emissions should be allocated, and until this issue is resolved, countries are asked to report them separately.
EIA energy statistics, however, include bunker fuels—jet fuel, distillate fuel oil, and residual fuel oil—as part of fuel
consumption by the transportation sector. To compensate for this inclusion, bunker fuel emissions were calculated
separately (see Table A-9) and the carbon content of these fuels was subtracted from the transportation sector. The
calculations of bunker fuel emissions followed the same procedures used for other fuel emissions (i.e., estimation of
consumption, determination of carbon content, and adjustment for the fraction of carbon not oxidized).
Step 5: Account for Carbon that Does Not Oxidize During Combustion
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, particulate matter, ash, or other by-products of inefficient
A-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
combustion. The estimated fraction of carbon not oxidized in U.S. energy conversion processes due to inefficiencies
during combustion ranges from 0.5 percent for natural gas to 1 percent for petroleum and coal. Except for coal these
assumptions are consistent with the default values recommended by the IPCC (IPCC/UNEP/OECD/IEA 1997). In the
U.S. unoxidized carbon from coal combustion was estimated to be no more than one percent (Bechtel 1993). Table A-
11 presents fractions oxidized by fuel type, which are multiplied by the net carbon content of the combusted energy to
give final emissions estimates.
Step 6: Summarize Emission Estimates
Actual CO2 emissions in the United States were summarized by major fuel (i.e., coal, petroleum, natural gas,
geothermal) and consuming sector (i.e., residential, commercial, industrial, transportation, electric utilities, and
territories). Adjustments for bunker fuels and carbon sequestered in products were made. Emission estimates are
expressed in terms of million metric tons of carbon equivalents (MMTCE).
To determine total emissions by final end-use sector, emissions from electric utilities were distributed to each end-
use sector according to its share of electricity consumed (see Table A-13).
A-3
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Table A-4: 1994 Energy Consumption Data and C02 Emissions from Fossil Fuel Combustion by Fuel Type
8
10
11
12
13
14
15
Fuel Type
Residential Coal
Commercial Coal
Industrial Coking Coal
Industrial Other Coal
Coke Imports
Transportation Coal
Utility Coal
US Territory Coal (bit)
Total Coal
Natural Gas
Asphalt & Road Oil
Aviation Gasoline
Distillate Fuel Oil
Jet Fuel
Kerosene
LP6
Lubricants
Motor Gasoline
Residual Fuel
Other Petroleum
AvGas Blend Components
Crude Oil
MoGas Blend Components
Misc. Products
Naphtha (<401 deg. F)
Other Oil (>401deg.F)
Pentanes Plus
Petrochemical Feedstocks
Petroleum Coke
Still Gas
Special Naphtha
Unfinished Oils
Waxes
Other Wax & Misc.
Total Petroleum
Geothermal
TOTAL (All Fuels)
Res.
55.5
55.5
4,988.3
0.0
0.0
880.0
0.0
64.9
395.5
0.0
0.0
0.0
1,340.4
6,384.2
Comm.
83.5
83.5
2,980.8
0.0
0.0
464.3
0.0
19.5
69.8
0.0
25.2
174.6
753.3
3,817.6
Consumption (TBtu)
Ind. Trans. Utility
850.6
1,589.4
23.6
0.0
16,895.2
2,463.7 0.0 16,895.2
9,590.2 705.2 3,052.9
1,172.9 0.0 0.0
0.0 38.1 0.0
1,108.8 4,175.0 95.2
0.0 3,154.5 0.0
16.9 0.0 0.0
1,996.5 32.2 0.0
180.9 170.8 0.0
191.9 14,214.1 0.0-
417.6 896.0 846.6
6.1
18.7
0.0
105.9
398.3
838.6
338.7
0.0
793.0 26.3
1,439.4
81.1
(279.2)
40.6
0.0
8,866.8 22,680.7 968.2
0.024
20,920.7 23,385.9 20,916.2
Terr. Total
55.5
83.5
850.6
1,589.4
23.6
0.0
16,895.2
10.3 10.3
10.3 19,508
NA 21,317
1,172.9
38.1
101.4 6,824.7
77.2 3,231.7
101.3
9.2 2,503.1
0.0 351.7
131.5 14,562.7
171.3 2,506.0
72.7 72.7
6.1
18.7
0.0
105:9
398.3
838.6
338.7
0.0
819.4
1,439.4
81.1
(279.2)
40.6
0.0
563.2 35,172.6
0.024
573.4 75,998.0
Emissions (MMTCE)
Res. Comm.
1.4
1.4
71.8
0.0
0.0
17.4
0.0
1.3
6.7
0.0
0.0
0.0
25.3
98.6
2.1
2.1
42.9
0.0
0.0
9.2
0.0
0.4
1.2
0.0
0.5
3.7
14.9
60.0
including Adjustments* and Fraction Oxidized
Ind. Trans. Utility Terr. Total
21.0
41.1
0.7
62.7
133.1
(0.0)
0.0
21.4
0.0
0.3
13.0
1.8
3.7
8.8
0.1
0.4
0.0
2.1
1.8
8.3
2.4
0.0
19.4
24.6
1.6
(5.6)
0.8
(2.9)
102.0
297.8
0.0
0.0
10.2
0.0
0.7
80.9
48.8
0.0
0.5
1.7
273.7
4.8
411.2
421.4
430.2
430.2
44.0
0.0
0.0
1.9
0.0
0.0
0.0
0.0
0.0
18.0
0.7
20.6
0.049
494.8
0.3
0.3
NA
0.0
0.0
2.0
1.5
0.0
0.2
0.0
2.5
3.6
1.3
11.1
11.333
1.4
2.1
21.0
41.1
0.7
0.0
430.2
0.3
496.7
301.9
(0.0)
0.7
132.8
50.3
2.0
21.5
3.5
280.4
39.0
1.3
0.1
0.4
0.0
2.1
1.8
8.3
2.4
0.0
20.1
24.6
1.6
(5.6)
0.8
(2.9)
585.2
0.049
1,383.9
*Adjustments include: international bunker fuel consumption (see Table A-9) and carbon stored in products (see Table A-10)
NA (Not Available)
A-7
-------
Table A-5: 1993 Energy Co nsuwptton Data aid COZ Emissions from Fossil! Fuel Contetion by FtelType
2
/Or— ---11
15
Fuel Type
Residential Coal
Commercial Coal
Industrial Coking Coal
Industrial Other Coal
Coke Imports
Transportation Coal
Utility Coal
US Territory Coal (bit)
Total Coal
Natural Gas
Asphalt & Road Oil
Aviation Gasoline
Distillate Fuel Oil
Jet Fuel
Kerosene
LPG
Lubricants
Motor Gasoline
Residual Fuel
Other Petroleum
AvGas Blend Components
Crude Oil
MoGas Blend Components
Misc. Products
Naphtha (<401 deg. F)
Other Oil (>401deg.F)
Pentanes Plus
Petrochemical Feedstocks
Petroleum Coke
Still Gas
Special Naphtha
Unfinished Oils
Waxes
Other Wax & Misc.
Total Petroleum
Geothermal
TOTAL (All Fuels)
Res.
56.6
56.6
5,097.5
0.0
0.0
912.9
0.0
75.6
398.6
0.0
0.0
0.0
1,387.0
6,541.1
Comm,
85.5
85.5
2,995.8
0.0
0.0
463.9
0.0
14.0
70.3
0.0
29.6
175.0
752.8
3,834.2
Consumption (TBta)
Ind. Trans. Utility
839.5
1,588.0
17.3
0.0
16,841.1
2,444.8 0.0 16,841.1
9,419.6 643.1 2,744.1
1,149.0 0.0 0.0
0.0 38.4 0.0
1,099.7 3,912.9 76.7
0.0 3,028.0 0.0
13.1 0.0 0.0
1,794.4 18.9 0.0
173.1 163.5 0.0
179.4 14,000.5 0.0
451.8 913.4 938.6
0.1
21.2
0.0
94.7
350.6
844.1
332.3
0.0
767.3 36.8
1,430.2
104.6
(396.0)
40.0
0.0
8,449.6 22,075.5 1,052.0
0.026
20,314.0 22,718.6 20,637.3
Terr. Total
56.6
85.5
839.5
1,588.0
17.3
0.0
16,841.1
9.6 9.6
9.6 19,438
NA 20,900
1,149.0
38.4
92.4 6,558.4
66.7 3,094.8
102.7
12.8 2,295.1
0.0 336.5
116.0 14,325.5
153.7 2,632.5
83.3 83.3
0.1
21.2
0.0
94.7
350.6
844.1
332.3
0.0
804.1
1,430.2
104.6
(396.0)
40.0
0.0
525.0 34,242.1
0.026
534.6 74,579.8
Emissions (MMTCE)
Res. Comm.
1.5
1.5
73.4
0.0
0.0
18.0
0.0
1.5
6.7
0.0
0.0
0.0
26.2
101.0
2.2
2.2
43.1
0.0
0.0
9.2
0.0
0.3
1.2
0.0
0.6
3.7
14.9
60.2
including Adjustments* and
Ind. Trans. Utility
20.7
41.1
0.5
62.2
131.7
0.0
0.0
21.2
0.0
0.3
12.1
1.7
3.5
9.5
0.0
0.4
0.0
1.9
1.6
8.3
2.0
0.0
18.9
24.4
2.1
(7.9)
0.8
(2.7)
98.0
291.9
0.0
0.0
9.3
0.0
0.7
75.7
46.9
0.0
0.3
1.6
269.3
2.4
396.9
406.1
428.7
428.7
39.5
0.0
0.0
1.5
0.0
0.0
0.0
0.0
0.0
20.0
1.0
22.5
0.053
490.7
Fraction Oxidized
Terr. Total
0.2
0.2
NA
0.0
0.0
1.8
1.3
0.0
0.2
0.0
2.2
3.3
1.5
10.3
10.524
1.5
2.2
20.7
41.1
0.5
0.0
428.7
0.2
494.7
297.0
0.0
0.7
127.4
48.1
2.0
20.5
3.4
275.5
38.9
1.5
0.0
0.4
0.0
1.9
1.6
8.3
2.0
0.0
19.9
24.4
2.1
(7.9)
0.8
(2.7)
568.8
0.053
1,360.6
*Adjustments include: international bunker fuel consumption (see Table A-9) and carbon stored in products (see Table A-10)
NA (Not Available)
A-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table A-6: 1992 Energy Consumption Data and C02 Emissions from Fossil Fuel Combustion by Fuel Type
10
11
12
13
14
15
Fuel Type
Residential Coal
Commercial Coal
Industrial Coking Coal
Industrial Other Coal
Coke Imports
Transportation Coal
Utility Coal
US Territory Coal (bit)
Total Coal
Natural Gas
Asphalt & Road Oil
Aviation Gasoline
Distillate Fuel Oil
Jet Fuel
Kerosene
LP6
Lubricants
Motor Gasoline
Residual Fuel
Other Petroleum
AvGas Blend Components
Crude Oil
MoGas Blend Components
Misc. Products
Naphtha (<401 deg. F)
Other Oil (>401 deg. F)
Pentanes Plus
Petrochemical Feedstocks
Petroleum Coke
Still Gas
Special Naphtha
Unfinished Oils
Waxes
Other Wax & Misc.
Total Petroleum
Geothermal
TOTAL (All Fuels)
Res.
56.7
56.7
4,821.1
0.0
0.0
864.9
0.0
65.0
382.5
0.0
0.0
0.0
1,312.4
6,190.2
Comm.
85.7
85.7
2,884.2
0.0
0.0
464.0
0.0
11.1
67.5
0.0
79.5
191.2
813.3
3,783.2
Consumption (TBtu)
Ind. Trans. Utility
867.4
1,573.1
27.2
0.0
16,192.0
2,467.7 0.0 16,192.0
8,996.3 608.4 2,828.5
1,102.2 0.0 0.0
0.0 41.1 0.0
1,144.5 3,810.2 67.3
0.0 3,001.3 0.0
9.8 0.0 0.0
1,859.8 18.4 0.0
170.0 160.5 0.0
194.3 13,698.8 0.0
391.3 1,082.0 835.6
0.2
27.4
75.7
100.1
377.3
814.9
322.7
0.0
813.1 30.1
1,447.6
104.6
(355.0)
37.3
0.0
8,637.7 21,812.3 933.0
0.028
20,101.7 22,420.7 19,953.5
Terr. Total
56.7
85.7
867.4
1,573.1
27.2
0.0
16,192.0
8.8 8.8
8.8 18,811
NA 20,138
1,102.2
41.1
78.2 6,429.1
61.9 3,063.2
85.9
11.8 2,340.0
0.0 330.5
114.4 14,087.0
154.6 2,654.7
61.4 61.4
0.2
27.4
75.7
100.1
377.3
814.9
322.7
0.0
843.2
1,447.6
104.6
(355.0)
37.3
0.0
482.3 33,991.0
0.028
491.2 72,940.4
Emissions (MMTCE)
Res. Comm.
1.5
1.5
69.4
0.0
0.0
17.1
0.0
1.3
6.4
0.0
0.0
0.0
24.8
95.7
2.2
2.2
41.5
0.0
0.0
9.2
0.0
0.2
1.1
0.0
1.5
4.1
16.1
59.9
including Adjustments* and Fraction Oxidized
Ind. Trans. Utility Terr. Total
21.2
40.7
0.7
62.6
126.1
(0.0)
0.0
22.1
0.0
0.2
12.7
1.7
3.7
8.2
0.0
0.5
1.5
2.0
1.7
8.1
4.9
0.0
19.0
24.9
2.1
(7.1)
0.7
(2.7)
104.3
292.9
0.0
0.0
8.8
0.0
0.8
73.6
46.6
0.0
0.3
1.6
263.4
6.7
392.9
401.7
411.8
411.8
40.7
0.0
0.0
1.3
0.0
0.0
0.0
0.0
0.0
17.8
0.8
19.9
0.057
472.5
0.2
0.2
NA
0.0
0.0
1.5
1.2
0.0
0.2
0.0
2.2
3.3
1.1
9.5
9.713
1.5
2.2
21.2
40.7
0.7
0.0
411.8
0.2
478.3
286.5
(0.0)
0.8
124.8
47.8
1.7
20.8
3.3
270.8
40.0
1.1
0.0
0.5
1.5
2.0
1.7
8.1
4.9
0.0
19.9
24.9
2.1
(7.1)
0.7
(2.7)
567.5
0.057
1332.4
*Adjustments Include: international bunker fuel consumption (see Table A-9) and carbon stored in products (see Table A-10)
NA (Not Available)
A-9
-------
Tabte A-7: 1991 Energy Consuwptfon Data aid C02 EwJssfens from Fossil Fuel Cowbwtton by Fu«l Type
1
3
10
11
12
13
14
18
Fuel Type
Residential Coal
Commercial Coal
Industrial Coking Coal
Industrial Other Coal
Coke Imports
Transportation Coal
Utility Coal
US Territory Coal (bit)
Total Coal
Natural Gas
Asphalt & Road Oil
Aviation Gasoline
Distillate Fuel Oil
Jet Fuel
Kerosene
LPG
Lubricants
Motor Gasoline
Residual Fuel
Other Petroleum
AvGas Blend Components
Crude Oil
MoGas Blend Components
Misc. Products
Naphtha (<401 deg. F)
Other Oil (>401deg.F)
Pentanes Plus
Petrochemical Feedstocks
Petroleum Coke
Still Gas
Special Naphtha
Unfinished Oils
Waxes
Other Wax & Misc.
Total Petroleum
Geothermal
TOTAL (All Fuels)
Res.
56.3
56.3
4,685.0
0.0
0.0
831.5
0.0
72.3
389.5
0.0
0.0
0.0
1,293.3
6,034.6
Comm.
84.5
84.5
2,807.7
0.0
0.0
481.6
0.0
12.1
68.7
0.0
85.0
213.2
860.6
3,752.8
Consumption (TBIu)
Ind. Trans. Utility
907.3
1,629.2
8.9
0.0
16,012.4
2,545.4 0.0 16,012.4
8,637.2 621.5 2,853.6
1,076.5 0.0 0.0
0.0 41.7 0.0
1,139.2 3,677.6 80.0
0.0 3,025.0 0.0
11.4 0.0 0.0
1,749.3 19.9 0.0
166.7 157.5 0.0
193.3 13,502.6 0.0
335.9 1,031.9 1,076.1
(0.1)
38.9
(25.9)
152.6
298.9
827.3
294.0
0.0
700.2 21.7
1,426.6
88.0
(450.2)
35.1
0.0
8,057.8 21,456.2 1,177.8
0.028
19,240.4 22,077.7 20,043.8
Terr. Total
56.3
84.5
907.3
1,629.2
8.9
0.0
16,012.4
7.8 7.8
7.8 18,706
NA 19,605
1,076.5
41.7
71.4 6,281.3
78.3 3,103.3
95.8
13.8 2,241.2
0.0 324.2
117.0 13,897.9
134.6 2,791.7
122.1 122.1
(0.1)
38.9
(25.9)
152.6
298.9
827.3
294.0
0.0
722.0
1,426.6
88.0
(450.2)
35.1
0.0
537.2 33,382.9
0.028
544.9 71,694.3
Emissions (MMTCE) including Adjustments* and Fraction Oxidized
Res. Comm, Ind. Trans. Utility Terr. Total
1.4
1.4
67.5
0.0
0.0
16.4
0.0
1.4
6.5
0.0
0.0
0.0
24.4
93.3
2.2
2.2
40.4
0.0
0.0
9.5
0.0
0.2
1.2
0.0
1.6
4.5
17.1
59.7
22.6
42.0
0.2
64.8
120.5
(0.0)
0.0
21.9
0.0
0.2
11.0
1.7
3.7
7.1
(0.0)
0.8
(0.5)
3.1
1.3
8.2
4.7
0.0
17.1
24.4
1.7
(9.0)
0.7
(3.7)
94.3
279.6
0.0
0.0
8.9
0.0
0.8
71.0
47.6
0.0
0.3
1.6
259.5
6.3
387.0
396.0
407.2
407.2
41.1
0.0
0.0
1.6
0.0
0.0
0.0
0.0
0.0
22.9
0.6
25.1
0.057
473.5
0.2
0.2
NA
0.0
0.0
1.4
1.5
0.0
0.2
0.0
2.2
2.9
2.2
10.4
10.606
1.4
2.2
22.6
42.0
0.2
0.0
407.2
0.2
475.9
278.4
(0.0)
0.8
121.8
49.1
1.9
19.3
3.2
267.0
43.6
2.2
(0.0)
0.8
(0.5)
3.1
1.3
8.2
4.7
0.0
17.7
24.4
1.7
(9.0)
0.7
(3.7)
558.3
0.057
1,312.6
*Adjustments include: international bunker fuel consumption (see Table A-9) and carbon stored in products (see Table A-10)
NA (Not Available)
A-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table A-8: 1990 Energy Consumption Data and C02 Emissions from Fossil Fuel Combustion by Fuel Type
w
11
12
13
14
15
Fuel Type
Residential Coal
Commercial Coal
Industrial Coking Coal
Industrial Other Coal
Coke Imports
Transportation Coal
Utility Coal
US Territory Coal (bit)
Total Coal
Natural Gas
Asphalt & Road Oil
Aviation Gasoline
Distillate Fuel Oil
Jet Fuel
Kerosene
LP6
Lubricants
Motor Gasoline
Residual Fuel
Other Petroleum
AvGas Bfend Components
Crude Oil
MoGas Blend Components
Misc. Products
Naphtha (<401 deg. F)
Other Oil (>401 deg. F)
Pentanes Plus
Petrochemical Feedstocks
Petroleum Coke
Still Gas
Special Naphtha
Unfinished Oils
Waxes
Other Wax & Misc.
Total Petroleum
Geothermal
TOTAL (All Fuels)
Res.
61.9
61.9
4,518.7
0.0
0.0
837.4
0.0
63.9
365.0
0.0
0.0
0.0
1,266.3
5,846.9
Comm.
92.9
92.9
2,698.1
0.0
0.0
487.0
0.0
11.8
64.4
0.0
110.6
233.1
906.9
3,697.9
Consumption (TBtu)
Ind. Trans. Utility
1,041.8
1,646.1
4.8
0.0
16,087.8
2,692.7 0.0 16,087.8
8,519.7 682.4 2,861.4
1,170.2 0.0 0.0
0.0 45.0 0.0
1,180.9 3,830.5 86.3
0.0 3,129.5 0.0
12.3 0.0 0.0
1,607.7 21.8 0.0
186.3 176.0 0.0
184.1 13,577.1 0.0
417.2 1,030.2 1,139.4
0.2
50.9
53.7
137.8
347.8
753.9
250.3
0.0
719.9 24.7
1,473.2
107.1
(369.0)
33.3
0.0
8,317.9 21,810.1 1,250.4
0.029
19,530.3 22,492.5 20,199.6
Terr. Total
61.9
92.9
1,041.8
1,646.1
4.8
0.0
16,087.8
7.0 7.0
7.0 18,942
NA 19,280
1,170.2
45.0
74.0 6,496.1
61.0 3,190.5
88.0
14.4 2,073.3
0.0 362.3
101.0 13,972.8
121.8 2,941.7
85.9 85.9
0.2
50.9
53.7
137.8
347.8
753.9
250.3
0.0
744.6
1,473.2
107.1
(369.0)
33.3
0.0
458.2 34,009.8
0.029
465.2 72,232.4
Emissions (MMTCE) including Adjustments* and
Res. Comm. Ind. Trans. Utility
1.6
1.6
65.1
0.0
0.0
16.5
0.0
1.2
6.1
0.0
0.0
0.0
23.9
90.6
2.4
2.4
38.8
0.0
0.0
9.6
0.0
0.2
1.1
0.0
2.1
5.0
18.0
59.2
25.9
42.4
0.1
68.5
118.6
0.0
0.0
22.9
0.0
0.2
11.0
1.9
3.5
8.8
0.0
1.0
1.0
2.8
1.6
7.4
3.3
0.0
17.3
25.2
2.1
(7.4)
0.7
(3.4)
100.0
287.1
0.0
0.0
9.8
0.0
0.8
74.2
49.6
0.0
0.4
1.8
260.9
6.8
394.5
404.3
409.0
409.0
41.2
0.0
0.0
1.7
0.0
0.0
0.0
0.0
0.0
24.2
0.7
26.6
0.060
476.9
Fraction Oxidized
Terr. Total
0.2
0.2
NA
0.0
0.0
1.5
1.2
0.0
0.2
0.0
1.9
2.6
1.5
8.9
9.098
1.6
2.4
25.9
42.4
0.1
0.0
409.0
0.2
481.6
273.5
0.0
0.8
126.4
50.8
1.7
18.8
3.6
268.5
47.3
1.5
0.0
1.0
1.0
2.8
1.6
7.4
3.3
0.0
18.0
25.2
2.1
(7.4)
0.7
(3.4)
572.0
0.060
1,327.2
*Adjustments include: international bunker fuel consumption (see Table A-9) and carbon stored in products (see Table A-10)
NA (Not Available)
A-11
-------
.
Table A-9: 1997 Emissions From International Bunker Fuel Consumption
Bunker Fuel Carbon Content Carbon Content
Consumption Coefficient (MMTCE)
Fraction Emissions
Oxidized (MMTCE)
Fuel Type (TBtu) (MMTCE/QBtu)3
Distillate Fuel Oil
Jet Fuel
Residual Fuel OH
Total
79.4
726.5
523.2
1,329.1
19.95
19.33
21.49
1.6
14.0
11.2
26.9
0
0
0
.99 1.6
.99 13.9
.
.99 11.1
26.6
Table A-10: 1997 Non-Energy Use Carbon Stored In Products
i ' "'
• L: 1 :.
Fuel Type
Industrial Coking Coal
Natural Gas
Asphalt 4 Road Oil
LP6
Lubricants
Pentanes Plus
Petrochemical Feedstocks
Naphtha (<401 deg. F)
Other Oil (>401 deg. F)
Still Gas
Petroleum Coke
Special Naphtha
Other Wax & Misc.
DMIIate Fuel Oil
Residual Fuel Oil
Waxes
Miscellaneous
Total
,;,,
'
r.'l
2 3
Non-energy Use
(TBtu)
Ind. Trans.
27.7
391.4
1,223.6
1,651.3
182.3 172.1
295.4
536.4
861.2
2.5
179.0
72.3
46.6
7.5
43.7
97.7
5,618.6 172.1
;i
i:
4
Carbon Content
Coefficient
(MMTCE/QBtu)
25.55
14.47
20.62
16.86
20.24
18.24
18.14
19.95
17.51
27.85
19.86
19.95
21.49
19.81
20.23
5
6
Carbon Content
(MMTCE)
Ind.
0.7
5.7
25.2
27.8
3.7
5.4
9.7
17.2
0.0
5.0
1.4
0.9
0.2
0.9
2.0
105.8
One QBtu is one quadrillion Btu, or 10" Btu. This unit is commonly referred to as a
Trans.
0.0
0.0
0.0
0.0
3.5
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3.5
"Quad."
':;
7 8
9
10
Fraction Carbon Stored (MMTCE)
Sequestered
Ind. Trans.
0.75 0.5 0.0
1.00 5.7 0.0
1.00 25.2 0.0
0.80 22.3 0.0
0.50
.8 1.7
0.80 4.3 0.0
0.75 7.3 0.0
0.50 8.6 0.0
0.80 6.0 0.0
0.50 2.5 0.0
0.00 0.0 0.0
0.50 0.5 0.0
0.50 0.1 0.0
1.00 0.9 0.0
1.00 2.0 0.0
81.7 1.7
•' i
.
•
Total
0.5
5.7
25.2
22.3
3.6
4.3
7.3
8.6
0.0
2.5
0.0
0.5
0.1
0.9
2.0
83.4
A-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table A-11: Key Assumptions for Estimating Carbon Dioxide Emissions
Fuel Type
Coal
Residential Coal
Commercial Coal
Industrial Coking Coal
Industrial Other Coal
Coke Imports
Transportation Coal
Utility Coal
U.S. Territory Coal (bit)
Natural Gas
Petroleum
Asphalt & Road Oil
Aviation Gasoline
Distillate Fuel Oil
Jet Fuel
Kerosene
LPG
Lubricants
Motor Gasoline
Residual Fuel
Other Petroleum
AvGas Blend Components
Crude Oil
MoGas Blend Components
Misc. Products
Naphtha (<401 deg. F)
Other Oil (>401 deg. F)
Pentanes Plus
Petrochemical Feedstocks
Petroleum Coke
Still Gas
Special Naphtha
Unfinished Oils
Waxes
Other Wax & Misc.
Geothermal
Carbon Content Coefficient
(MMTCE/QBtu)
[a]
[a]
[a]
[a]
27.85
NC
[a]
25.14
14.47
20.62
18.87
19.95
[a]
19.72
[a]
20.24
[a]
21.49
20.23
18.87
[a]
19.39
20.23
18.14
19.95
18.24
19.37
27.85
17.51
19.86
20.23
19.81
19.81
2.05
Fraction
Oxidized
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.995
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
0.99
-
Sources: Carbon coefficients and stored carbon from ElA. Combustion efficiency for coal from Bechtel (1993) and for petroleum and natural gas from
IPCC (IPCC/UNEP/OECD/IEA 1997, vol. 2).
- Not applicable
NC (Not Calculated)
[a] These coefficients vary annually due to fluctuations in fuel quality (see Table A-12).
A-13
-------
It:.
Hi!
Table A-12: Annually Variable Carbon Content Coefficients by Year (MMTCE/QBtu)
Fuel Type
Residential Coal
Commercial Coal
industrial Coking Coal
Industrial Other Coal
Utility Coal
LPG
Motor Gasoline
Jet Fuel
Crude 01
1990
25,92
25.92
25.51
25.58
25.68
16.99
19.41
19.40
20.16
Sowct; EIA
Table A-13: Electricity Consumption by
li '• i "'!! ! " i
End-Use Sector
Residential
Commercial
Industrial
Transportation
U.S. Territories*
Tola!
1990
924
839
946
4
2,713
1991
955
856
947
4
2,762
1991
26.00
26.00
25.51
25.60
25.69
16.98
19.41
19.40
20.18
End-Use
1992
936
851
973
4
2,763
1992
26.13
26.13
25.51
25.62
25.69
16.99
19.42
19.39
20.22
Sector
1993
995
886
977
4
2,861
1993
25.97
25.97
25.51
25.61
25.71
16.97
19.43
19.37
20.22
1994
25.95
25.95
25.52
25.63
25.72
17.01
19.45
19.35
20.21
1995
26.00
26^00
25.53
25.63
25.74
17:00
19.38
19.34
20.23
1996
25.92
25.92
25.55
25.61
25.74
16.99
19.36
19.33
20.25
1997
25.92
25.92
25.55
25.61
25.74
16.99
19.35
19.33
20.24
(Billion Kilowatt-hours)
,i. I
1994
1,008
914
1,008
4
2,935
1995
1,043
954
1,013
4
3,013
1996
1,082
981
1,030'
4
3,098
1997
1,072
1,008"
1,036'
4
3,120
*BA atejicfc utility fuel consumption data does not include the U.S. territories.
'-Not applicable
Sowce: EiA
A-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Annex B
Methodology for Estimating Emissions of CH4, N20, and Criteria Pollutants from
Stationary Sources
Estimates of CH4 and N20 Emissions
Methane (CH4) and nitrous oxide (N2O) emissions from stationary source fuel combustion were estimated using
IPCC emission factors and methods. Estimates were obtained by multiplying emission factors (by sector and fuel type)
by fossil fuel and wood consumption data. This "top-down" methodology is characterized by two basic steps, described
below. Data are presented in Table B-l through Table B-5.
Step 1: Determine Energy Consumption by Sector and Fuel Type
Greenhouse gas emissions from stationary combustion activities were grouped into four sectors: industrial,
commercial/institutional, residential, and electric utilities. For CH4 and N2O, estimates were based upon consumption
of coal, gas, oil, and wood. Energy consumption data were obtained from EIA'sMonthly Energy Review (1998b), and
adjusted to lower heating values assuming a 10 percent reduction for natural gas and a 5 percent reduction for coal and
petroleum fuels. Table B-l provides annual energy consumption data for the years 1990 through 1997.
Step 2: Determine the Amount of CH4 and N20 Emitted
Activity data for each sector and fuel type were then multiplied by emission factors to obtain emissions estimates.
Emission factors were taken from the Revised 1996 IPCC Guidelines (IPCC/UNEP/OECD/ffiA 1997). Table B-2
provides emission factors used for each sector and fuel type.
Estimates of NOX, CO, and NMVOC Emissions
For criteria pollutants, the major source categories included were those identified in EPA (1998): coal, fuel oil,
natural gas, wood, other fuels (including bagasse, liquefied petroleum gases, coke, coke oven gas, and others), and
stationary internal combustion (which includes emissions from internal combustion engines not used in transportation).
EPA (1998) periodically estimates emissions of NOX, CO, and NMVOCs by sector and fuel type using a "bottom-up"
estimating procedure. In other words, the emissions were calculated either for individual sources (e.g., industrial
boilers) or for many sources combined, using basic activity data (e.g., fuel consumption or deliveries, etc.) as indicators
of emissions. EPA (1998) projected emissions for years subsequent to their bottom-up estimates. The national activity
data used to calculate the individual categories were obtained from various sources. Depending upon the category, these
activity data may include fuel consumption or deliveries of fuel, tons of refuse burned, raw material processed, etc.
Activity data were used in conjunction with emission factors that relate the quantity of emissions to the activity. Table
B-3 through Table B-7 present criteria pollutant emission estimates for 1990 through 1997.
The basic calculation procedure for most source categories presented in EPA (1998) is represented by the
following equation:
Ep,s = AsxEfp,sx (l-Cp,/100)
where,
E = emissions
p = pollutant
s = source category
A = activity level
EF = emission factor
C = percent control efficiency
B-1
-------
The EPA currently derives the overall emission control efficiency of a category from a variety of sources,
including 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 similar to the methodology recommended by me IPCC
(IPCC/UNEP/OECD/IEA 1997).
if" ' ' ,,it -'« " . ':>-'. : I
I' , ! "('„ i" Si ' • ' i "' ' ii" '
Table B-1: Fuel Consumption by Stationary Sources for Calculating CH4 and N20 Emissions jTBtu)
Fuel/End-Use Sector
Coal
Residential
Commercial/Institutional
Industry
utnis
Petroleum
Residential
ComgiierciaVlristitutlonal
Industry
Utilities
Natural Gas
Residential
Comrpercial'lnstitutionai
Industry
Utilities
Wood
Residential & Commercial
Industrial
Utilities
1990
18,935.3
61.9
92.9
2,692.7
16,087.8
11,741.5
1,266.3
906.9
8,317.9
1,250.4
18,597.9
4,518.7
2,698.1
8,519.7
2,861.4
2550.0
581.0
1947.5
21.5
1991
18,698.6
56.3
84.5
2,545.4
16,012.4
11,389.6
1,293.3
860.6
8,057.8
1,177.8
18,983.5
4,685.0
2,807.7
8,637.2
2,853.6
2577.0
613.0
1942.8
21.2
1992
18,802.1
56.7
85.7
2,467.7
16,192.0
11,696.4
1,312.4
813.3
8,637.7
933.0
19,530.1
4,821.1
2,884.2
8,996.3
2,828.5
2709.0
645.0
2042.4
21.6
1993
19,428.0
56.6
85.5
2,444.8
16,841.1
11,641.5
1,387.0
752.8
8,449.6
1,052.0
20,257.1
5,097.5
2,995.8
9,419.6
2,744.1
2696.0
592.0
2083.5
20.5
1994
19,497.8
55.5
83.5
2,463.7
16,895.2
11,928.7
1,340.4
753.3
8,866.8
968.2
20,612.1
4,988.3
2,980.8
9,590.2
3,052.9
2740.7
582.0
2138.2
20.5
1995
19,567.0
53.7
81.0
2,441.9
16,990.5
11,489.4
1,363.0
756.8
8,711.6
658.0
21,479.2
4,981.3
3,112.9
10,108.6
3,276.4
2741.5
641.0
2083.5
17.0
1996
20,448.3
55.1
133.1
2,357.3
17,952.7
12,000.2
1,440.9
740.9
9,093.6
724.9
21,817.8
5,382.9
3,243.5
10,393.7
2,797.7
2864.0
643.8
2200.5
19.8
1997
20,921.1
55.1
83.1
2,303.0
18,480.0
12,356.8
1,466.9
730.9
9,337.0
822.0
21,843.9
5,145.6
3,373.1
10,285.5
3,039.7
2625.9
475.1
2131.5
19.3
V 1
ill!
Table B-2; CH4 and N20 Emission Factors by Fuel Type and Sector (g/GJ)4
Ilii1: i ' • ... T'1!11 ' :,ii .
.ji, _. Jtfli,,;! , ."I :•;, ;;'ji Jh_ ,, 'hi i „ " ' ' • ."i
Fuel/EridVUse Sector
Coal
;. Residential
CommerclaWnstitutfonal
Industry
Utilities
Petroleum
Residential
Commercial(lnstitub'onal
Industry
" utllitISs
Natural Gas
Residential
Commcrciatlnstitutional
Industry
Utilities
Wood
Residential
CommerciaWnstitutional
Industrial
Utilities
!i
4OJ(Gignjoule)=10'jouIes.
CH4
300
10
10
1
I 10
10
2
3
5
5
5
1
300
300
30
30
One joule = 9.486x10"* Btu
N?0
1.4
1.4
1.4
1.4
0.6
0.6
0.6
0.6
0.1
0.1
0.1
0.1
4.0
4.0
4.0
4.0
l! i
I,
i
f ' '
B-2 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table B-3: NOX Emissions from Stationary Sources (Gg)
Sector/Fuel Type
Electric Utilities
Coal
Fuel Oil
Natural gas
Wood
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 Gasb
Wood
Other Fuels3
Total
1990
6,045
5,119
200
513
NA
213
2,754
530
240
1,072
NA
119
792
336
36
88
181
NA
31
749
NA
NA
NA
42
708
9,884
1991
5,914
5,043
192
526
NA
152
2,703
517
215
1,134
NA
117
720
333
33
80
191
NA
29
829
NA
NA
NA
45
784
9,779
1992
5,901
5,062
154
526
NA
159
2,786
521
222
1,180
NA
115
748
348
35
84
204
NA
25
879
NA
NA
NA
48
831
9,914
1993
6,034
5,211
163
500
NA
160
2,859
534
222
1,207
NA
113
783
360
37
84
211
NA
28
827
NA
NA
NA
40
787
10,080
1994
5,956
5,113
148
536
NA
159
2,855
546
219
1,210
NA
113
767
365
36
86
215
NA
28
817
NA
NA
NA
40
777
9,993
1995
5,792
5,061
87
510
NA
134
2,852
541
224
1,202
NA
111
774
365
35
94
210
NA
27
813
NA
NA
NA
44
769
9,822
1996
5,497
5,027
94
239
NA
137
2,876
543
223
1,212
NA
113
784
366
35
93
212
NA
26
804
NA
NA
NA
44
760
9,543
1997
5,605
5,079
120
262
NA
144
2,967
557
218
1,256
NA
118
818
379
36
97
219
NA
27
779
NA
NA
NA
31
748
9,729
NA (Not Available)
3 "Other Fuels" include LPG, waste oil, coke oven gas, coke,
b Coal, fuel oil, and natural gas emissions are included in the
Note: Totals may not sum due to independent rounding.
and non-residential wood (EPA 1998).
"Other Fuels" category (EPA 1998).
B-3
-------
Table B-4: CO Emissions from Stationary Sources (Gg)
Sector/Fuel Type
Electric Utilities
Coal
Fuel Oil
Natural gas
Wood
Internal Combustion
Industrial
Coal
Fuel Oil
Natural gas
Wood
Otter Fuels'
Internal Combustion
Commercial/Institutional
Coal
Fuel Oil
Natural gas
Wood
Otfw Fuels'
Residential
Goaf
Fuel OH"
Natural Gas"
Wood
Other Fuels'
Total
NA (Not Available)
1990
329
,» in
213
18
46
NA
52
798
I 95
67
205
NA
253
177
205
13
16
40
NA
136
3,668
NA
NA
NA
3,430
238
4,999
1991
317
212
17
46
NA
41
835
92
54
257
NA
242
189
196
13
16
40
NA
128
3,965
NA
NA
NA
3,711
255
5,313
1992
318
214
14
47
NA
43
867
92
58
272
NA
239
205
204
13
16
46
NA
128
4,195
NA
NA
NA
3,930
265
5,583
1993
329
224
15
45
NA
46
946
92
60
292
NA
259
243
207
14
16
48
NA
129
3,586
NA
NA
NA
3,337
249
5,068
1994
335
224
13
48
NA
50
944
91
60
306
NA
260
228
212
13
16
49
NA
134
3,515
NA
NA
NA
3,272
243
5,007
* "Otter Fuels" include LPG, waste oil, coke oven gas, coke, and non-residential wood (EPA
* Coal, fuel oil, and natural gas emissions are included in the
1995
338
227
9
49
NA
52
958
88
64
313
NA
270
222
211
14
17
49
NA
132
3,876
NA
NA
NA
3,628
248
5,383
1998).
"Other Fuels" category (EPA 1998).
Note Totals may not sum due to independent rounding.
B-4 inventory of U.S.
:°iJ
Greenhouse
Gas Emissions
•
1996 1997
357 368
225 230
10 11
69 71
NA NA
53 56
972 1,007
90 91
65 66
316 329
NA NA
.
277 288
224 233
227 235
14 14
17 17
49 51
NA NA
148 152
3,867 2,759
NA NA
NA NA
NA NA
3,622 2,520
244 239
5,424 4,369
"
•
1
,
,
1
,
1
and Sinks: 1990-1997
-------
Table B-5: NMVOC Emissions from Stationary Sources (Gg)
Sector/Fuel Type
Electric Utilities
Coal
Fuel Oil
Natural gas
Wood
Internal Combustion
Industrial
Coal
Fuel Oil
Natural gas
Wood
Other Fuels2
Internal Combustion
Commercial/Institutional
Coal
Fuel Oil
Natural gas
Wood
Other Fuels3
Residential
Coalb
Fuel Oil"
Natural Gasb
Wood
Other Fuels3
Total
1990 1991
43
25
5
2
NA
11
165
7
11
52
NA
46
49
18
1
3
7
NA
8
686
NA
NA
NA
651
35
912
40
25
5
2
NA
9
177
5
10
54
NA
47
61
18
1
2
8
NA
7
739
NA
NA
NA
704
35
975
1992
40
25
4
2
NA
9
169
7
• 11
47
NA
45
60
20
1
3
9
NA
7
782
NA
NA
NA
746
36
1,011
1993
41
26
4
2
NA
9
169
5
11
46
NA
46
60
22
1
3
10
NA
8
670
NA
NA
NA
633
36
901
1994 1995 1996
41
26
4
2
NA
9
178
7
11
57
NA
45
58
21
1
3
10
NA
8
657
NA
NA
NA
621
36
898
40
26
2
2
NA
9
187
5
11
66
NA
45
59
21
1
3
10
NA
8
726
NA
NA
NA
689
37
973
44
25
3
7
NA
9
189
5
11
66
NA
46
60
21
1
3
10
NA
8
724
NA
NA
NA
687
37
978
1997
46
26
3
7
NA
9
197
5
11
70
NA
48
62
22
1
3
10
NA
8
515
NA
NA
NA
478
37
780
NA (Not Available)
3 "Other Fuels" include LPG, waste oil, coke oven gas, coke,
b Coal, fuel oil, and natural gas emissions are Included in the
Note: Totals may not sum due to independent rounding.
and non-residential wood (EPA 1998).
"Other Fuels" category (EPA 1998).
B-5
-------
t!
1'
•• i *• i
-------
Annex C
Methodology for Estimating Emissions of CH4, N20, and Criteria Pollutants from
Mobile Sources
Estimates of CH4 and N20 Emissions
Greenhouse gas emissions from mobile sources are reported by transport mode (e.g., road, rail, air, and water),
vehicle type, and fuel type. EPA does not systematically track emissions of CH4 and N2O as in EPA (1998a); therefore,
estimates of these gases were developed using a methodology similar to that outlined in the Revised 1996 IPCC
Guidelines (IPCC/UNEP/OECD/IEA 1997).
Step 1: Determine Vehicle Miles Traveled or Fuel Consumption by Vehicle Type, Fuel Type, and
Model Year
Activity data were obtained from a number of U.S. government agency publications. Depending on the category,
these basic activity data included such information as fuel consumption, fuel deliveries, and vehicle miles traveled
(VMT). The activity data for highway vehicles included estimates of VMT by vehicle type and model year from EPA
(1998a) and the MOBILESa emissions model (EPA 1997).
National VMT data for gasoline and diesel highway vehicles are presented in Table C-l and Table C-2,
respectively. Total VMT for each highway category (i.e., gasoline passenger cars, light-duty gasoline trucks, heavy-
duty gasoline vehicles, diesel passenger cars, light-duty diesel trucks, heavy-duty diesel vehicles, and motorcycles) were
distributed across 25 model years based on the temporally fixed age distribution of VMT by the U.S. vehicle fleet in
1990 (see Table C-3) as specified in MOBILESa. Activity data for gasoline passenger cars and light-duty trucks in
California were developed separately due to the different emission control technologies deployed in that state relative
to the rest of the country. Unlike the rest of the United States, beginning in model year 1994, a fraction of the computed
California VMT for gasoline passenger cars and light-duty trucks was attributed to low emission vehicles (LEVs).
LEVs have not yet been widely deployed in other states. Based upon U.S. Department of Transportation statistics for
1994, it was assumed that 8.7 percent of national VMT occurred in California.
Activity data for non-highway vehicles were based on annual fuel consumption statistics by transportation mode
and fuel type. Consumption data for distillate and residual fuel oil by ships and boats (i.e., vessel bunkering),
construction equipment, farm equipment, and locomotives were obtained from EIA (1998). In the case of ships and
boats, the EIA (1998) vessel bunkering data was reduced by the amount of fuel used for international bunkers.5 Data
on the consumption of jet fuel in aircraft were obtained directly from EIA, as described under CO2 from Fossil Fuel
Combustion, and were reduced by the amount allocated to international bunker fuels using data from DOT/BTS (1998).
Data on aviation gasoline consumed in aircraft were also taken directly from EIA as above. Data on the consumption
of motor gasoline by ships and boats, construction equipment, farm equipment, and locomotives data were drawn from
FHWA (1997). For these vehicles, 1996 fuel consumption data were used as a proxy because 1997 data were
unavailable. The activity data used for non-highway vehicles are included in Table C-4.
Step 2: Allocate VMT Data to Control Technology Type for Highway Vehicles
For highway sources, VMT by vehicle type for each model year were distributed across various control
technblogies as shown in Table C-5, Table C-6, Table C-7, Table C-8, and Table C-9. Again, California gasoline-fueled
passenger cars and light-duty trucks were treated separately due to that state's distinct mobile source emission
standards—including the introduction of Low Emission Vehicles (LEVs) in 1994—compared with the rest of the United
' See International Bunker Fuels.
C-1
-------
States, "Tlie1 categories "Tier 0" and "Tier 1" have been substituted for the early three-way catalyst and advanced three-
way catalyst categories, respectively, as defined in the Revised 1996 IPCC Guidelines. Tier 0, tier 1, and LEV are
actually U.S. emission regulations, rather than control technologies; however, each does correspond to particular
combinations of control technologies and engine design. Tier 1 and its predecessor Tier 0 both apply to vehicles
equipped with three-way catalysts. The introduction of "early three-way catalysts," and "advance three-way catalysts"
as described in the Revised 1996 IPCC Guidelines, roughly correspond to the introduction of Tier 0 and Tier 1
' {EPA 199§). ' ......... : ' ' ' ' ..... ":
Step 3: Determine the Amount of CH4 and N20 Emitted by Vehicle, Fuel, and Control Technology Type
111' I!' Ill in .''/i '" i! i'JJ'i \,ll ' , "', i '" ' ''I I' •' '• ' ' ' " ' , ill" ! | fi,,' ' "' •
Emissions of CH4 from mobile source combustion and N2O from non-highway vehicles were calculated by
multiply ing emission factors in IPCC/UNEP/OECD/IEA (1997) by activity data for each vehicle type as described in
Step 1 (see Table C-10 and Table C-l 1). The CH4 emission factors for highway sources were derived from EPA's
MOBlOSSa mobile source emissions model (EPA 1997). The MOBILESa model uses information on ambient
temperature, diurnal temperature range, altitude, vehicle speeds, national vehicle registration distributions, gasoline
volatility, emission control technologies, fuel composition, and the presence or absence of vehicle
inspection/maintenance programs in order to produce these factors.
^missions of N2O— in contrast to CH4, CO, NOX, and NMVOCs — have not been extensively studied and are
: Currently not well characterized. The limited number of studies that have been performed on highway vehicle emissions
of NjO have shown that emissions are generally greater from vehicles with catalytic converter systems than those
Without Such controls, and greater from aged than from new catalysts. These systems control tailpipe emissions of NOX
(i.e., NO and NO2) by catalytically reducing NOX to N2. Suboptimal catalyst performance, caused by as yet poorly
undersfoocj factors, results in incomplete reduction and the conversion of some ]SfOx to N2O rather than to N2.
Fortunately, newer vehicles with catalyst and engine designs meeting the more recent Tier 1 and LEV standards have
shown reduced emission rates of both NOX and N2O.
In order to better characterize the process by which N2O is formed by catalytic controls and to develop a more
accurate national emission estimate, the EPA's Office of Mobile Sources — at its National Vehicle and Fuel Emissions
Laboratory (NVFEL)— recently conducted a series of tests in order to measure emission rates of N2O from used Tier
I and LEV gasoline-fueled passenger cars and light-duty trucks equipped with catalytic converters. These tests and a
review of the literature were used to develop the emission factors for nitrous oxide used in this inventory (EPA 1998b).
The following references were used in developing the N2O emission factors for gasoline-fueled highway passenger cars
presented in Table C- 1 0:
LEVs, Tests performed at NVFEL (EPA 1998b)6 '.
Tier I. Tests performed at NVFEL (EPA 1998b)
Tier 0. Smith an4 Carey (1982), Barton and Simpson (1994), and one car tested at NVFEL (EPA 1998b)
Oxidation Catalyst. Smith and Carey (1982), Urban and Garbe (1979)
ii" "'I , 'I '» . liJill'l «! : i, , ''i" •'„'.:• II '
Non-Catafyst. Prigent and deSoete (1989), Dasch (1992), and Urban and Garbe (1979)
Nitrous oxide emission factors for other types of gasoline-fueled vehicles — light-duty trucks, heavy-duty vehicles,
and motorcycles- — were estimated by adjusting the factors for gasoline passenger cars, as described above, by their
relative fuel economies. This adjustment was performed using the carbon dioxide emission rates in the Revised 1996
"iPCC Guidelines (IPCC/UNEP/OECD/IEA 1997) as a proxy for fuel economy (see Table C-10). Data from the
literature and tests performed at NVFEL support the conclusion that light-duty trucks have higher emission rates than
* It was jusumcd Ihsl LEVs would be operated using low-sulfur fuel (i.e., Indolene at 24 ppra sulfur). All other NVFEL tests were performed
aslng a Standard commercial fuel (CAAB at 285 ppm sulfur). Emission tests by NVFEL have consistently exhibited higher N2O emission rates
from higher sulfur fuels on Tier 1 and LEV vehicles.
IK f ~ I iT7" ! " : ! • t
C-2 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
passenger cars. However, the use of fuel-consumption ratios to determine emission factors is considered a temporary
measure only, to be replaced as soon as real data are available.
The resulting N2O emission factors employed for gasoline highway vehicles are lower than the U.S. default values
presented in the Revised 1996IPCC 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. The U.S. defaults in the
Guidelines were based on three studies that tested a total of five cars using European rather than U.S. test procedures.
Nitrous oxide emission factors for diesel highway vehicles were taken from the European default values found in the
Revised 1996 IPCC Guidelines (IPCC/UNEP/OECD/IEA 1997). There is little data addressing N2O emissions from
U.S. diesel-fueled vehicles, and in general, European countries have had more experience with diesel-fueled vehicles.
U.S. default values in the Revised 1996 IPCC Guidelines were used for non-highway vehicles.
Compared to regulated tailpipe emissions, there is relatively little data available to estimate emission factors for
nitrous oxide. Nitrous oxide is not a criteria pollutant, and measurements of it in automobile exhaust have not been
routinely collected. Further testing is needed to reduce the uncertainty in nitrous oxide emission factors for all classes
of vehicles, using realistic driving regimes, environmental conditions, and fuels.
Estimates of NOX, CO, and NMVOC Emissions
The emission estimates of NOX, CO, and NMVOCs for mobile sources were taken directly from the EPA's Draft
National Air Pollutant Emissions Trends, 1900 -1997 (EPA 1998a), This EPA report provides emission estimates for
these gases by sector and fuel type using a "top down" estimating procedure whereby emissions were calculated using
basic activity data, such as amount of fuel delivered or miles traveled, as indicators of emissions. Table C-12 through
Table C-14 provide complete emissions estimates for 1990 through 1997.
Table C-1: Vehicle Miles Traveled for Gasoline Highway Vehicles (109 Miles)
Year
1990
1991
1992
1993
1994
1995
1996
1997
Passenger
Cars3
1,492.61
1,512.72
1,574.56
1,602.28
1,562.48
1,605.74
1,443.59
1,475.85
Light-Duty Heavy-Duty Passenger Cars Light-Duty
Trucks3 Vehicles Motorcycles (CA)b Trucks (CA)b
462.31
468.92
472.90
493.20
581.83
597.92
806.21
824.31
43.32
43.60
43.39
45.96
49.67
51.04
51.66
52.89
9.57
9.20
9.55
9.89
10.25
10.52
9.87
10.10
129.86
131.61
136.99
139.40
135.94
139.70
125.59
128.40
40.22
40.80
41.14
42.91
50.62
52.02
70.14
71.71
' Excludes California
b California VMT for passenger cars and light-duty trucks was treated separately and estimated as 8.7 percent of national total.
Source: VMT data are the same as those used in EPA (1998a).
Table C-2: Vehicle Miles Traveled for Diesel Highway Vehicles (10s Miles)
Passenger Light-Duty Heavy-Duty
Year
Cars
Trucks
Vehicles
1990
1991
1992
1993
1994
1995
1996
1997
20.6
20.9
21.7
22.1
21.5
22.1
19.9
20.4
3.8
3.8
3.9
4.1
4.8
4.9
6.7
6.8
112.2
112.9
115.0
119.6
127.0
130.5
137.1
140.5
Source: VMT data are the same as those used in EPA (1998a).
C-3
-------
Table C-3: VMT Profile by Vehicle Age (years) and Vehicle/Fuel Type for Highway Vehicles (percent of VMT)
I i,.! I , ;;lf '"ill! ' • •i-f!', >" • "'•-; : ', . ; : .-. .1 :;': 1, • • II', . ;
Vehicle Age
:• 1
2,
3
4
I
6
7
8
9
10
11
12
, ' J3
14
IS
16
17
18
19
If"
22
23
24
25
LDGV
4.9%
7.9%
8.3%
8.2%
8.S
I'UI'll* I
8.1%
7.7%
5.6%
5.0%
5.1%
5.0%
5.4%
4.7%
3.7%
2.4%
1.9%
1.4%
1.5%
1.1%
0.8%
6.5%
0.4%
0.3%
1.0%
LDGT
6.3%
8.4%
8.4%
8.4%
8.4%
6.9%
5.9%
4.4%
3.6%
3.1%
3.0%
5.3%
4.7%
4.6%
3.6%
2.8%
1.7%
2.2%
1.7%
"' " 1.4%
0.9%
0.8%
0.8%
0.5%
2.5%
HDGV
2.3%
4.7%
4.7%
4.7%
4.7%
3.8%
3.3%
2.1%
2.6%
2.9%
3.4%
6.4%
5.4%
5.8%
5.1%
3.8%
4.3%
4.1%
3.5%
2.9%
2.1%
2.2%
2.2%
1.4%
11.7%
LDDV
4.9%
7.9%
8.3%
8.2%
8.4%
8.1%
7.7%
5.6%
5.0%
5.1%
5.0%
5.4%
4.7%
3.7%
2.4%
1.9%
1.4%
1.5%
1.1%
0.8%
0.6%
0.5%
0.4%
0.3%
1.0%
LDDT
6.3%
8.4%
8.4%
8.4%
8.4%
6.9%
5.9%
4.4%
3.6%
3.1%
3.0%
5.3%
4.7%
4.6%
3.6%
2.8%
1.7%
2.2%
1.7%
1.4%
0.9%
0.8%
0.8%
0.5%
2.5%
HDDV
3.4%
6.7%
6.7%
6.7%
6.7%
7.3%
6.1%
4.0%
4.1%
5.1%
5.3%
6.6%
5.5%
5.7%
4.5%
1.9%
2.3%
2.8%
2.4%
1.6%
1.1%
0.9%
0.7%
0.5%
1.6%
MC
14.4%
16.8%
13.5%
ib.9%
8.8%
7.0%
5.6%
4.5%
3.6%
2.9%
2.3%
9.7%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
0.0%
LDGV (sjasoftie passenger cars, also referred to as light-duty gas vehicles)
LDGT (iaM-duty gas trucks)
HDGV (heavy-duty gas vehicles)
LDDV (diesel passenger cars, also referred to as light-duly diesel vehicles)
LDDT (tip-duly dtesel trucks)
HODV (heavy-duty diesel vehicles)
MC (motorcycles)
Table C-4: Fuel Consumption for Non-Highway Vehicles by Fuel Type (U.S. gallons)
Vehicle Type/Year
Aircraft*
1990
1991
1992
1993
1994
1995
1996
1997
Ships and Boats"
1990
1991
1992
1993
1994
1995
1996
1997
Residual
-
,
-
-
-
-
-
. ..
1,666,165,227
1,486,167,178
2,347,064,583
2,758,924,466
2,499,868,472
2,994,692,916
2,280,373,162
1,005,997,126
Diesel
-
-
-
-
-
-
.
-
1,943,259,570
1,806,653,451
1,820,275,621
1,661,285,902
1,746,597,258
1,636,189,216
1,952,357,254
1.917.777.070
Jet Fuel
19,138,571,644
18,362,671,260
17,978,360,318
18,099,464,134
18,885,264,653
18,397,377,217
19,296,093,738
19,123,384,372
-
-
-
-
'".
-
-
-
Other
374,401,818
346,945,685
341,953,660
319,448,684
317,309,701
329,315,519
310,795,109
330,286,644
1,300,400,000
1,709,700,000
1,316,170,000
873,687,000
896,700,000
1,060,394,000
993,671,000
993,671,000
C-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Vehicle Type/Year
Construction Equipment0
1990
1991
1992
1993
1994
1995
1996
1997
Farm Equipment11
1990
1991
1992
1993
1994
1995
1996
1997
Locomotives
1990
1991
1992
1993
1994
1995
1996
1997
Residual
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
25,422
6,845
8,343
4,065
5,956
6,498
9,309
3,431
Diesel
2,508,300,000
2,447,400,000
2,287,642,000
2,323,183,000
2,437,142,000
2,273,162,000
2,386,973,000
2,385,236,000
3,164,200,000
3,144,200,000
3,274,811,000
3,077,122,000
3,062,436,000
3,093,224,000
3,225,029,000
3,206,359,000
3,210,111,000
3,026,292,000
3,217,231,000
2,906,998,000
3,063,441,000
3,191,023,000
3,266,861,000
3,067,400,000
Jet Fuel Other
- 1,523,600,000
- 1,384,900,000
- 1,492,200,000
- 1,270,386,667
- 1,312,161,667
- 1,351,642,667
- 1,365,550,667
- 1,365,550,667
812,800,000
776,200,000
805,500,000
845,320,000
911,996,000
926,732,000
918,085,000
918,085,000
-
-
-
-
-
-
-
-
- Not applicable
" Other fuel aviation gasoline.
b Other fuel motor gasoline.
0 Construction Equipment includes snowmobiles. Other fuel is motor gasoline.
a Other fuel is motor gasoline.
Table C-5: Control Technology Assignments for Gasoline Passenger Cars (percentage of VMT)4
Model Years
1973-1974
1975
1976-1977
1978-1979
1980
1981
1982
1983
1984-1993
1994
1995
1996
1997
Non-catalyst
100%
20%
15%
10%
5%
Oxidation
80%
85%
90%
88%
15%
'14%
12%
TierO
7%
85%
86%
88%
100%
60%
20%
TieM
40%
80%
100%
100%
* Excluding California VMT
C-5
-------
Table C-6: Control Technology Assignments for Gasoline Light-Duty Trucks (percentage of VMT)*
Model Years
1973-1974
1975
J976
1977-1978
1979-1980
1981
1982
1983
1984
|985
1986
1987-1993
1994
1995
1996
1997
Non-catalyst
100%
30%
20%
25%
20%
1 ' !
Oxidation
70%
80%
75%
80%
95%
90%
80%
70%
60%
50%
5%
TierO
5%
10%
20%
30%
40%
50%
95%
60%
20%
Tierl
40%
80%
100%
100%
'Excluding California VMT
Table C-7: Control Technology Assignments for California Gasoline Passenger Cars and Light-Duty Trucks
(percentage of VMT)
Model Years Non-catalyst Oxidation
1973-1974
197:5-1979
1980-1981
1982
1983
1984-1991
1992
1994
1995
1996
1997
TierO
Tierl
LEV
100%
100%
15%
14%
12%
88%
100%
60%
20%
40%
80%
90%
85%
80%
75%
10"0/o
15%
20%
25%
Table C-8: Control Technology Assignments for Gasoline Heavy-Duty Vehicles (percentage of VMT)
Model Years Uncontrolled Non-catalyst Oxidation
TierO
s1981
198f2-1984
1985-1986
]987
1988-1989
1990-1997
95%
95%
70%
60%
45%
5%
5%
15%
25%
30%
15%
15%
25%
C-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
J,, 'i •„ i|l|||i;||i;ii,n,irt,i,,
ii 'i!,l.,il,'|. Jnimlll ' ll .hi,, III i
-------
Table C-9: Control Technology Assignments for Diesel Highway VMT
Vehicle Type/Control Technology Model Years
Diesel Passenger Cars and Light-Duty Trucks
Uncontrolled
. Moderate control
Advanced control
Heavy-Duty Diesel Vehicles
Uncontrolled
. Moderate control
Advanced control
Motorcycles
Uncontrolled
Non-catalyst controls
1966-1982
1983-1995
1996-1997
1966-1972
1983-1995
1996-1997
1966-1995
1996-1997
Table C-10: Emission Factors (g/km) for CH4 and N20 and "Fuel Economy"
(g C02/km)c for Highway Mobile Sources
Vehicle Type/Control Technology
Gasoline Passenger Cars
Low Emission Vehicles3
TieM
TierO
Oxidation Catalyst
Non-Catalyst
Uncontrolled
Gasoline Light-Duty Trucks
Low Emission Vehicles3
TieM
TierO
Oxidation Catalyst
Non-Catalyst
Uncontrolled
Gasoline Heavy-Duty Vehicles
TierO
Oxidation Catalyst"
Non-Catalyst Control
Uncontrolled
Diesel Passenger Cars
Advanced
Moderate
Uncontrolled
Diesel Light Trucks
Advanced
Moderate
Uncontrolled
Diesel Heavy-Duty Vehicles
Advanced
Moderate
Uncontrolled
Motorcycles
Non-Catalyst Control
Uncontrolled
N20
0.0176
0.0288
0.0507
0.0322
0.0103
0.0103
0.0249
0.0400
0.0846
0.0418
0.0117
0.0118
0.1729
0.0870
0.0256
0.0269
0.0100
0.0100
0.0100
0.0200
0.0200
0.0200
0.0300
0.0300
0.0300
0.0042
0.0054
CH,
0.025
0.030
0.040
0.070
0.120
0.135
0.030
0.035
0.070
0.090
0.140
0.135
0.075
0.090
0.125
0.270
0.01
0.01
0.01
0.01
0.01
0.01
0.04
0.05
0.06
0.13
0.26
g COj/km
280
285
298
383
531
506
396
396
498
498
601
579
1,017
1,036
1,320
1,320
237
248
319
330
331
415
987
1,011
1,097
219
266
* Applied to California VMT only.
b Methane emission factor assumed based on light-duty trucks oxidation catalyst value.
c The carbon emission factor (g C02/km) was used as a proxy for fuel economy because of the greater number of significant figures compared to the
km/L values presented in (IPCC/UNEP/OECD/IEA1997).
NA (Not Available)
C-7
-------
1:: ' '.', „ . ^ ,
Table C-11: Emission Factors for CH4 and N20 Emissions from Non-Highway Mobile Sources (g/kg fuel)
VehicleJype/Fuel Type N,0 CH4
Ships and Boats
Residual 0.08 0.23
Distillate ', 0.08 0.23
Gasojne , 0.08 0.23
Locomotives
Residual 0.08 0.25
Diesel 0.08 0.25
Coal 0.08 0.25
Farm Equipment
Gas/Tractor 0.08 0.45
Other Gas 0.08 0.45
Diesel/Tractor 0.08 0.45
: Othetpesel ; „ 0.08 0.45
Construction
Gas Construction 0.08 0.18
Diesi Construction 0.08 0.18
Other Ngn-Htghway
* Gas Snowmobile 0.08 0.18
I" Gas Sinan Utility 0.08 0.18
Gas OP Utility 0.08 0.18
Diesel HD Utility 0.08 0.18
Aircraft
Jet Fuel 0.1 0.087
Aviation Gasoline 0.04 2.64
TableC-12: NO, Emissions from Mobile Sources, 1990-1997 (Gg)
Fuel Type/Vehicle Type 1990 1991 1992 1993 1994
Gasoline Highway 4,356 4,654 4,788 4,913 5,063
Passenger Cars 2,910 3,133 3,268 3,327 3,230
! Light-Duty Trucks 1,140 1,215 1,230 1,289 1,503
! Heavy-Duty Vehicles 296 296 280 286 318
::,, Motorcycles 11 10 11 11 11
Diesel Highway 2,031 2,035 1,962 1,900 1,897
Passenger Cars 35 34 35 36 35
Light-Duty Trucks 67779
Heavy-Duty Vehicles 1,989 1,995 1,920 1,857 1,854
Non-Highway 3,844 3,869 3,910 3,936 3,989
Ships and Boats 253 265 259 250 254
Locomotives 843 842 858 857 859
Farm Equipment 894 905 918 931 943
: Construction Equipment 1,015 1,026 1,039 1,054 1,071
Alrcratf 143 141 142 142 146
*; Other* ; 697 690 695 703 716
Tola! 10,231 10,558 10,659 10,749 10,949
1995
4,804
3,112
1,378
301
12
1,839
35
9
1,795
4,089
264
898
955
1,094
150
729
10,732
i
ii
'
. Ii '
Ii
;,
I
1996
4,770
2,691
1,769
!' 298
11
1,803
! ' 31
11
1,760
4,063
: 265
836
965
1,110
151
736
10,636
1997
4,629
2,597
1,725
296
11
1,753
31
11
1,711
4,137
273
861
962
1,120
161
759
10,519
* Ateattestimates Include opy emissions related to Lit) cycles, and therefore do not include cruise altitude emissions.
* "Glrter" includes gasoline powered recreational, industrial, lawn and garden, light commercial, logging, airport service, other equipment;
powered recreational, industrial, lawn and garden, light construction, airport service.
Note; Totals may not sum due to Independent rounding.
[ • , •; ;
C-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
,;,',
i'
il
ii
and diesel
-------
Table C-13: CO Emissions from Mobile Sources, 1990-1997 (Gg)
Fuel Type/Vehicle Type 1990 1991 1992
Gasoline Highway 51,332 55,104 53,077
Passenger Gars 33,746 36,369 35,554
Light-Duty Trucks 12,534 13,621 13,215
Heavy-Duty Vehicles 4,863 4,953 4,145
Motorcycles 190 161 163
Diesel Highway 1,147 1,210 1,227
Passenger Cars 28 27 28
Light-Duty Trucks 556
Heavy-Duty Vehicles 1,115 1,177 1,193
Non-Highway 13,949 13,942 14,199
Ships and Boats 1,619 1,644 1,659
Locomotives 110 109 113
Farm Equipment 355 317 344
Construction Equipment 936 932 957
Aircraft3 820 806 818
Other" 10,110 10,134 10,308
Total 66,429 70,256 68,503
1993 1994
53,375 54,778
35,357 33,850
13,786 15,739
4,061 5,013
172 177
1,240 1,316
30 29
6 7
1,205 1,280
14,359 14,560
1,672 1,684
108 104
354 324
991 1,042
821 830
10,413 10,577
68,974 70,655
1995
47,767
30,391
13,453
3,741
182
1,318
30
7
1,281
14,761
1,678
103
298
1,072
855
10,755
63,846
1996
46,965
25,894
17,483
3,416
171
1,354
27
10
1,318
14,886
1,689
102
302
1,079
861
10,854
63,205
1997
44,225
24,356
16,659
3,039
171
1,368
27
10
1,332
15,201
1,704
105
298
1,080
918
11,096
60,794
3 Aircraft estimates include only emissions related to LTD cycles, and therefore do not include cruise altitude emissions.
b "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.
Note: Totals may not sum due to independent rounding.
Table C-14: NMVOCs Emissions from Mobile Sources, 1990-1997 (Gg)
Fuel Type/Vehicle Type 1990 1991 1992
Gasoline Highway 5,444 5,607 5,220
Passenger Cars 3,524 3,658 3,447
Light-Duty Trucks 1,471 1,531 1,440
Heavy-Duty Vehicles 392 384 303
Motorcycles 56 33 30
Diesel Highway 283 290 288
Passenger Cars 11 11 12
Light-Duty Trucks 233
Heavy-Duty Vehicles 269 276 274
Non-Highway 2,225 2,237 2,266
Ships and Boats 563 571 576
Locomotives 48 47 49
Farm Equipment 135 131 131
Construction Equipment 197 198 202
Aircraft3 163 161 162
Other* 1,120 1,129 1,146
Total 7,952 8,133 7,774
1993 1994
5,248 5,507
3,427 3,367
1,494 1,731
296 375
31 33
288 300
12 12
3 4
273 284
2,282 2,303
580 584
47 45
130 126
207 213
160 159
1,160 1,175
7,819 8,110
1995
4,883
3,071
1,478
297
37
290
12
4
274
2,182
439
45
123
219
161
1,196
7,354
1996
4,743
2,576
1,869
266
33
238
11
5
223
2,175
464
44
121
219
161
1,167
7,156
1997
4,528
2,467
1,785
243
33
217
11
5
201
2,205
468
45
116
219
170
1,186
6,949
a Aircraft estimates include only emissions related to LTO cycles, and therefore do not include cruise altitude emissions.
" "Other" includes gasoline powered recreational, industrial, lawn and garden, light commercial, logging, airport service, other equipment; and diesel
powered recreational, industn'al, lawn and garden, light construction, airport service.
Note: Totals may not sum due to independent rounding.
C-9
-------
-------
Annex D
Methodology for Estimating Methane Emissions from Coal Mining
The methodology for estimating methane emissions from coal mining consists of two distinct steps. The first step
addresses emissions from underground mines. For these mines, emissions were estimated on a mine-by-mine basis and
then were summed to determine total emissions. The second step of the analysis involved estimating methane emissions
for surface mines and post-mining activities. In contrast to the methodology for underground mines, which used mine-
specific data, the methodology for estimating emissions from surface mines and post-mining activities consists of
multiplying basin-specific coal production by basin-specific emissions factors.
Step 1: Estimate Methane Liberated and Methane Emitted from Underground Mines
Underground mines liberate methane from ventilation systems and from degasification systems. Some mines
recover and use methane liberated from degasification systems, thereby reducing methane emissions to the atmosphere.
Total methane emitted from underground mines equals methane liberated from ventilation systems, plus methane
liberated from degasification systems, minus methane recovered and used.
Step 1.1 Estimate Methane Liberated from Ventilation Systems
All coal mines with detectable methane emissions7 use ventilation systems to ensure that methane levels remain
within safe concentrations. Many coal mines do not have detectable methane emissions, while others emit several
million cubic feet per day (MMCFD) from their ventilation systems. On a quarterly basis, the U.S. Mine Safety and-
Health Administration (MSHA) measures methane emissions levels at underground mines. MSHA maintains a database
of measurement data from all underground mines with detectable levels of methane in their ventilation air. Based on
the four quarterly measurements, MSHA estimates average daily methane liberated at each of the underground mines
with detectable emissions.
For the years 1990 through 1996, EPA obtained MSHA emissions data for a large but incomplete subset of all
mines with detectable emissions. This subset includes mines emitting at least 0.1 MMCFD for some years and at least
0.5 MMCFD for other years, as shown in Table D-l. Well over 90 percent of all ventilation emissions are concentrated
in these subsets. For 1997, EPA obtained the complete MSHA database for all 586 mines with detectable methane
emissions. These mines were assumed to account for 100 percent of methane liberated from underground mines.
Using this complete 1997 database, the portion of total emissions accounted for by mines emitting more and less than
0.1 MMCFD or 0.5 MMCFD was estimated (see Table D-l). These proportions were then applied to the years 1990 through
1996 to account for the less than 10 percent of ventilation emissions not accounted for by mines without MSHA data.
Average daily methane emissions were multiplied by 365 days per year to determine annual emissions for each
mine. Total ventilation emissions for a particular year was estimated by summing emissions from individual mines.
7 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.
D-1
-------
Table D-1: Mine-Specific Data Used to Estimate Ventilation Emissions
Ilil!
-------
Step 2.1: Define the Geographic Resolution of the Analysis and Collect Coal Production Data
The first step in estimating methane emissions from surface mining and post-mining activities was to define the
geographic resolution of the analysis and to collect coal production data at that level of resolution. The U.S. analysis
was conducted by coal basin as defined in Table D-2. Table D-2 presents coal basin definitions by basin and by state.
The Energy Information Agency (EIA) Coal Industry Annual reports state- and county-specific underground and
surface coal production by year. To calculate production by basin, the state level data were grouped into coal basins
using the basin definitions listed in Table D-2. For two states—West Virginia and Kentucky—county-level production
data was used for the basin assignments because coal production occurred from geologically distinct coal basins within
these states. Table D-3 presents the coal production data aggregated by basin.
Step 2.2: Estimate Emissions Factors for Each Emissions Type
Emission factors for surface mined coal were developed from the in situ methane content of the surface coal in
each basin. Based on an analysis presented in EPA (1993), surface mining emission factors were estimated to be from
1 to 3 times the average in situ methane content in the basin. For this analysis, the surface mining emission factor was
determined to be twice the in situ methane content in the basin. Furthermore, the post-mining emission factors used
were estimated to be 25 to 40 percent of the average in situ methane content in the basin. For this analysis, the post-
mining emission factor was determined to be 32.5 percent of the in situ methane content in the basin. Table D-4
presents the average in situ content for each basin, along with the resulting emission factor estimates.
Step 2.3: Estimate Methane Emitted
The total amount of methane emitted was calculated by multiplying the coal production in each basin by the
appropriate emission factors.
Total annual methane emissions is equal to the sum of underground mine emissions plus surface mine emissions
plus post-mining emissions. Table D-5 and Table D-6 present estimates of methane liberated, methane used, and
methane emissions for 1990 through 1997. Table D-7 provides methane emissions by state.
D-3
-------
VI T
Table D-2: Coal Basin Definitions by Basin and by State
Basin
States
Northern Appalachian Basin
Central Appalachian Basin
Warrior Basin
;: llnolslasln
South West and Rockies Basin
North Great Plains Basin
West Inferior Basin
Northwest Basin
Maryland, Ohio, Pennsylvania, West VA North
Kentucky East, Tennessee, Virginia, West VA South
Alabama
Illinois, Indiana, Kentucky West
Arizona, California, Colorado, New Mexico, Utah
Montana, North Dakota, Wyoming
Arkansas, Iowa, Kansas, Louisiana, Missouri, Oklahoma, Texas
Alaska, Washington
State
Basin
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Illinois
Indiana
Iowa
Kansas
Kentucky East
Kentucky West
Louisiana
Maryland
Missouri
Montana
New Mexico
North Dakota
Ohio
Oklahoma
Pennsylvania.
Tennessee
Texas
Virginia
Washington
West Virginia South
West Virginia North
Wyoming _
Warrior Basin
Northwest Basin
South West And Rockies Basin
West interior Basin
South West And Rockies Basin
South West And Rockies Basin
Illinois Basin
Illinois Basin
West Interior Basin
West Interior Basin
Central Appalachian Basin
Illinois Basin
West Interior Basin
Northern Appalachian Basin
West Interior Basin
North Great Plains Basin
South West And Rockies Basin
North Great Plains Basin
Northern Appalachian Basin
West Interior Basin
Northern Appalachian Basin
Central Appalachian Basin
West Interior Basin
South West And Rockies Basin
Central Appalachian Basin
Northwest Basin
Central Appalachian Basin
Northern Appalachian Basin
North Great Plains Basin
D-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table D-3: Annual Coal Production (thousand short tons)
Underground Coal Production
Basin
Northern Appalachia
Central Appalachia
Warrior
Illinois
S. West/Rockies
N. Great Plains
West Interior
Northwest
Total
1990 1991
103,865 103,450
198,412 181,873
17,531 17,062
69,167 69,947
32,754 31,568
1,722 2,418
105 26
0 0
423,556 406,344
1992 1993
105,220 77,032
177,777 164,845
15,944 15,557
73,154 55,967
31,670 35,409
2,511 2,146
59 100
0 0
406,335 351,056
1994
100,122
170,893
14,471
69,050
41,681
2,738
147
0
399,102
1995
98,103
166,495
17,605
69,009
42,994
2,018
25
0
396,249
1996
106,729
171,845
18,217
67,046
43,088
2,788
137
0
409,850
1997
112,135
177,720
18,505
64,728
44,503
2,854
212
0
420,657
Surface Coal Production
Basin
Northern Appalachia
Central Appalachia
Warrior
Illinois
S. WesVRockies
N. Great Plains
West Interior
Northwest
Total
1990 1991
60,761 51,124
94,343 91,785
11,413 10,104
72,000 63,483
43,863 42,985
249,356 259,194
64,310 61,889
6,707 6,579
602,753 587,143
1992 1993
50,512 48,641
95,163 94,433
9,775 9,211
58,814 50,535
46,052 48,765
258,281 275,873
63,562 60,574
6,785 6,340
588,944 594,372
1994
44,960
106,129
8,795
51,868
49,119
308,279
58,791
6,460
634,401
1995
39,372
106,250
7,036
40,376
46,643
331,367
59,116
6,566
636,726
1996
39,788
108,869
6,420
44,754
43,814
343,404
60,912
6,046
654,007
1997
40,179
113,275
5,963
46,862
48,374
349,612
59,061
5,945
669,271
Total Coal Production
Basin
Northern Appalachia
Central Appalachia
Warrior
Illinois
S. West/Rockies
N. Great Plains
West Interior
Northwest
Total
1990 1991
164,626 154,574
292,755 273,658
28,944 27,166
141,167 133,430
76,617 74,553
251,078 261,612
64,415 61,915
6,707 6,579
1,026,309 993,487
1992 1993
155,732 125,673
272,940 259,278
25,719 24,768
131,968 106,502
77,722 84,174
260,792 278,019
63,621 60,674
6,785 6,340
995,279 945,428
1994
145,082
277,022
23,266
120,918
90,800
311,017
58,938
6,460
1,033,503
1995
137,475
272,745
24,641
109,385
89,637
333,385
59,141
6,566
1,032,975
1996
146,517
280,714
24,637
111,800
86,902
346,192
61,049
6,046
1,063,857
1997
152,314
290,995
24,468
111,590
92,877
352,466
59,273
5,945
1,0829,928
Source: EIA (1990-97), Coal Industry Annual. U.S. Department of Energy, Washington, D.C., Table 3.
Note: Totals may not sum due to independent rounding.
Table D-4: Coal Surface and Post-Mining Methane Emission Factors (ft3 per short ton)
Basin
Northern Appalachia
Central Appalachia
Warrior
Illinois
S. West/Rockies
N. Great Plains
West Interior
Northwest
Surface Average
in situ Content
49.3
49.3
49.3
39.0
15.3
3.2
3.2
3.2
Underground Average
in situ Content
171.7
330.7
318.0
57.20
225.8
41.67
41.67
41.67
Surface Mine
Factors
98.6
98.6
98.6
78.0
30.6
6.4
6.4
6.4
Post-Mining
Surface Factors
16.0
16.0
16.0
12.7
5.0
1.0
1.0
1.0
Post Mining
Underground
16.0
16.0
16.0
12.7
5.0
1.0
1.0
1.0
Source: EPA (1993), Anthropogenic Methane Emissions in the United States: Estimates for 1990, Report to Congress, U.S. Environmental Protection
Agency, Air and Radiation, April.
D-5
-------
Table D-5: Underground Coal Mining Methane Emissions (billion cubic feet)
Activity
Ventilation Output
Adjustment Factor for Mine Data'
Ventilation Liberated
Degasif!c,atiqn System Liberated
Total Underground 'Liberated
Recovered & Used
Total
1990
112
97.8%
114
57
171
(15)
156
1991
NA
NA
NA
NA
164
(15)
149
1992
NA
NA
NA
NA
162
(19)
142
1993
95
97.8%
97
49
146
(24)
121
1994
96
97.8%
98
50
149
(29)
119
1995
102
91.4%
111
50
161
(3D
130
1996
90
'91.4%
99
51
150
(35)
115
1997
96
100.0%
96
57
153
(42)
112
1 Refer to Table 0-1
Note: Totals may not sum due to Independent rounding.
Table D-6: Total Coal Mining Methane Emissions (billion cubic feet)
Activity
Underground Mining
Surface Mining
Post-Mining (Underground)
Post-Mining (Surface)
Total
1990
156
25
33
4
218
1991
149
23
31
4
207
1992
142
23
30
4
200
1993
121
23
27
4
175
1994
119
24
30
4
177
1995
130
22
30
4
185
1996
115
23
: 31
: 4
172
1997
112
24
31
4
171
Hole; Totals may not sum due to Independent rounding.
Table D-7: Total Coal Mining Methane Emissions by State (million cubic feet)
State
Alabama
Alaska
Arizona
Arkansas
Galorrfa
Colorado
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maryland
Missouri
Montana
New Mexico
North Dakota
Ohio
Oklahoma
Pennsylvania
Tennessee
Texas
Utah
Virginia
Washington
West Virginia
Wyoming
Total
1990
33,650
13
402
0
2
10,117
10,643
3,149
3
5
21,229
24
510
20
280
905
217
4,710
13
22,573
800
415
4,562
45,883
37
56,636
1,382
218,180
1993
27,000
12
433
0
0
7,038
8,737
2,623
1
3
19,823
23
245
5
267
1,186
238
4,110
14
26,437
350
406
4,512
30,454
35
39,477
1,578
175,007
1994
30,713
12
464
0
0
9,029
10,624
2,791
0
2
21,037
26
256
6
310
1,223
240
4,377
52
24,026
338
389
3,696
26,782
36
38,565
1,782
176,781
1995
39,945
13
425
0
0
8,541
11,106
2,106
0
2
19,103
28
259
4
294
980
224
3,900
14
27,086
366
392
3,541
19,898
36
44,894
1,977
185,134
1996
30,808
11
371
0
0
5,795
10,890
2,480
0
2
18,292
24
287
5
283
856
222
3,992
14
26,567
418
410
4,061
19,857
34
44,380
2,090
172,149
1997
26,722
11
417
0
0
9,057
8,571
3,088
0
3
20,089
26
296
3
305
961
220
4,313
132
30,339
390
397
4,807
16,990
33
41,454
2,122
170,746
Note: Tht""emission estimates provided above are inclusive of emissions from underground mines, surface mines and post-mining activities. The
following states have neither underground nor surface mining and thus report no emissions as a result of coal mining: Connecticut, Delaware, Florida,
Georgia, Hawaii, Wato, Maine, Massachusetts, Michigan, Minnesota, Mississippi, Nebraska, Nevada, New Hampshire, New Jersey, New York, North
Carolina. Oregon, Rhode Islam), South Carolina, South Dakota, Vermont, and Wisconsin. Emission estimates are not given for 1991 and 1992 because
underground mine data was not available for those years.
D-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Annex E
Methodology for Estimating Methane Emissions from Natural Gas Systems
The following steps were used to estimate methane emissions from natural gas systems.
Step 1: Calculate Emission Estimates for Base Year 1992 Using GRI/EPA Study
The first step in estimating methane emissions from natural gas systems was to develop a detailed base year
estimate of emissions. The study by GRI/EPA (1996) divides the industry into four stages to construct a detailed
emissions inventory for the year 1992. These stages include: field production, processing, transmission and storage
(both underground and liquefied gas storage), and distribution. This study produced emission factors and activity data
for over 100 different emission sources within the natural gas system. Emissions for 1992 were estimated by
multiplying activity levels by emission factors for each system component and then summing by stage. Since
publication, EPA has updated activity data for some of the components in the system. Table E-l displays the 1992
GRI/EPA activity levels and emission factors for venting and flaring from the field production stage, and the current
EPA activity levels and emission factors. The data in Table E-l is a representative sample of data used to calculate
emissions from all stages.
Step 2: Collect Aggregate Statistics on Main Driver Variables
As detailed data on each of the over 100 sources were not available for the period 1990 through 1997, activity
levels were estimated using aggregate statistics on key drivers, including: number of producing wells (IPAA 1997),
number of gas plants (AGA 1990, 1991,1992, 1993,1994, 1995,1996,1997), miles of transmission pipeline (AGA,
1990,1991,1992,1993,1994,1995,1996,1997), miles of distribution pipeline (AGA 1990,1991,1992,1993,1994,
1995,1996,1997), miles of distribution services (AGA 1990,1991,1992,1993,1994,1995,1996,1997), and energy
consumption (EIA 1997a). Data on the distribution of gas mains by material type was not available for certain years
from AGA. For those years, the average distribution by type was held constant. Table E-2 provides the activity levels
of some of the key drivers in the natural gas analysis.
Step 3: Estimate Emission Factor Changes Over Time
For the period 1990 through 1995, the emission factors were held constant, based on 1992 values. An assumed
improvement in technology and practices was estimated to reduce emission factors by 5 percent by the year 2020. This
assumption, annualized, amounts to a 0.2 and 0.4 percent decline in the 1996 and 1997 emission factors, respectively.
Step 4: Estimate Emissions for Each Source
Emissions were estimated by multiplying the activity levels by emission factors. Table E-3 provides emission
estimates for venting and flaring emissions from the field production stage.
E-1
-------
Table E-1: 1992 Data and Emissions (Wig) for Venting and Flaring from Natural Gas Field Production Stage
Activity
Drilling and Well Completion
Completion Flaring
Normal Operations
Pneumatic Device Vents
Chemical Injection Pumps
Kimray Pumps
Dehydrator Vents
Compressor Exhaust Vented
Gas Engines
Routine Maintenance
Well Workovers
Gas Wells
Well Clean Ups(LP Gas Wells)
Blowdowns
Vessel BD
Pipeline BD
Compressor BD
Compressor Starts
Upsets
Pressure Relief Valves
ESD
Mishaps
GRI/EPA Values
Activity Data Emission Factor
844 compl/yr
249,111 controllers
16,971 active pumps
11, 050,000 MMscf/yr
12,400,000 MMscf/yr
27,460 MMHPhr
9,392 w.o./yr
1 14,1 39 LP gas wells
255,996 vessels
340,000 miles (gath)
17,112 compressors
17,112 compressors
529,440 PRV
1,115 platforms
340,000 miles
733 scf/comp
345 scfd/device
248 scfd/pump
368 scf/MMsef
276 scf/MMscf
0.24 scf/HPhr
2,454 scfy/w.o.
49,570 scfy/LP well
78 scfy/vessel
309 scfy/mile
3,774 scfy/comp
8,443 scfy/comp
34.0 scfy/PRV
256,888 scfy/plat
669 scfy/mile
Emissions
11.9
602,291
29,501
78,024
65,608
126,536
443
108,631
383
2,017
1,240
2,774
346
5,499
4,367
EPA Adjusted 'Values
Activity Data Emission Factor
400 compl/yr
249,111 controllers
16,971 active pumps
7,380,194 MMscf/yr
8,200,215 MMscf/yr
27,460 MMHPhr
9,392 w.o./yr
1 14,1 39 LP gas wells
242,306 vessels
340,200 miles (gath)
17,112 compressors
17,112 compressors
529,440 PRV
1,372 platforms
340,200 miles
733 scf/comp
345 scfd/device
248 scfd/pump
992 scf/MMscf
276 scf/MMscf
0.24 scf/HPhr
2,454 scfy/w.o.
49,570 scfy/LP well
78 scfy/vessel
309 scfy/mile
3,774 scfy/comp
8,443 scfy/comp
34.0 scfy/PRV
256,888 scfy/plat
669 scfy/mile
Emissions
5.63
602,291
- 29,502
140,566
43,387
126,535
443
108,631
363
2,018
1,240
2,774
346
6,767
4,370
E-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table E-2: Activity Factors for Key Drivers
Variable
Transmission Pipelines Length
Wells
GSAM Appalachia Wells a
GSAM N Central Associated Wells a
GSAM N Central Non-Associated Wells a
GSAM Rest of US Wells3
GSAM Rest of US Associated Wells a
Appalch. + N. Central Non-Assoc. + Rest of US
Platforms
Gulf of Mexico Off-shore Platforms
Rest of U.S. (offshore platforms)
N. Central Non-Assoc. + Rest of US Wells
Gas Plants
•Number of Gas Plants
Distribution Services
Steel - Unprotected
Steel - Protected
Plastic
Copper
Total
Distribution Mains
Steel - Unprotected
Steel - Protected
Cast Iron
Plastic
Total
Unit
miles
# wells
# wells
# wells
# wells
# wells
# wells
# platforms
# platforms
# platforms
# gas plants
# of services
# of services
# of services
# of services
# of services
miles
miles
miles
miles
miles
1930
280,100
120,162
3,862
3,105
145,100
256,918
268,367
3,798
24
148,205
761
5,500,993
19,916,202
16,269,414
228,240
41,914,849
91,267
491,120
52,644
202,269
837,300
1991
281,600
121,586
3,890
3,684
147,271
262,441
272,541
3,834
24
150,955
734
5,473,625
20,352,983
17,654,006
233,246
43,713,860
90,813
492,887
52,100
221,600
857,400
1992
284,500
123,685
3,852
4,317
152,897
253,587
280,899
3,800
24
157,214
732
5,446,393
20,352,983
17,681,238
233,246
43,713,860
90,361
496,839
51,800
244,300
883,300
1993
269,600
124,708
3,771
4,885
156,568
249,265
286,161
3,731
24
161,453
726
5,419,161
20,512,366
18,231,903
235,073
44,398,503
89,909
501,480
50,086
266,826
908,300
1994
268,300
122,021
3,708
5,813
160,011
248,582
287,845
3,806
23
165,824
725
5,392,065
20,968,447
19,772,041
240,299
46,372,852
89,460
497,051
48,542
284,247
919,300
1995
264,900
123,092
3,694
6,323
164,750
245,338
294,165
3,868
23
171,073
675
5,365,105
21,106,562
20,270,203
241,882
46,983,752
89,012
499,488
48,100
294,400
931,000
1996
257,000
122,700
3,459
7,073
173,928
246,598
303,701
3,846
24
181,001
623
5,388,279
21,302,429
20,970,924
244,127
47,905,759
88,567
468,833
47,100
329,700
934,200
1997
257,000
122,700
3,459
7,073
173,928
246,598
303,701
3,846
23
181,001
615
5,388,279
21,302,429
20,970,924
244,127
47,905,759
88,567
468,833
47,100
329,700
934,200
1 GSAM is the Gas Systems Analysis Model (GSAM 1997) of the Federal Energy Technology Center of the U.S. Department of Energy. It is a supply, demand and transportation model.
E-3
-------
Table E-3: CH4 Emission Estimates for Venting and Flaring from the Field Production Stage (Mg)
Activity
Drilling and Well Completion
Completion Flaring
Normal Operations
Pneumatic Device Venfs
Chemical Injection Pumps
Kimray Pumps
Dflhydratar Vents
Compressor Exhaust Vented
Gas Engines
Routine Maintenance
WeiiWorkovers
Gas Wells
Well Clean Ups(LP Gas Wells)
Slowdowns
Vessel BD
Pipeline BD
Compressor BD
Compressor Starts
Upsets
Pressure Relief Valves
ESD
Mishaps
* :
1
F
1990
5.4
567,778
36,449
134,247
41,436
119,284
531
101,118
256
1,710
1,548
3,462
326
6,764
925
1991
5.5
578,313
37,323
136,380
42,095
121,498
540
102,725
261
1,729
1,573
3,518
332
6,827
936
E-4 Inventory of U.S. Greenhouse Gas Emissions
1992 1993 1994 1995
5.6 5.7 5.8 5.9
602,291 618,531 635,276 655,386
39,053 40,277 41,668 43,111
140,566 143,211 144,040 147,191
43,387 44,203 44,459 45,432
126,535 129,947 133,465 137,690
556 567 570 582
105,878 107,870 108,494 110,868
271 278 284 292
1,772 1,772 1,818 1,852
1,627 1,662 1,687 1,730
3,640 3,718 3,773 3,871
346 355 365 376
6,767 6,646 6,773 6,882
959 974 984 1,003
and Sinks: 1990-1997
1996 1997
6.1 6.1
691,999 691,999
45,664 45,664
151,565 151,565
46,782 46,782
145,382 145,382
I
600 600
114,162 114,162
306 306
1,908 1,908
1,802 1,802
4,031 4,031
397 397
6,834 6,829
! 1,033 1,033
I
i
ii
i
j
i
II
I!
i
ii
i
i
i
i
I
ii
!
i
i
ii
i
i
-------
Annex F
Methodology for Estimating Methane Emissions from Petroleum Systems
The methodology for estimating methane emissions from petroleum systems is being updated. EPA anticipates
that current methodology understates emissions, and that the new methodology will be incorporated into future
inventories. The following steps, however, were used to estimate methane emissions from petroleum systems for this
report.
Stepl: Production Field Operations
The American Petroleum Institute (API) publishes active oil well data in reports such as the API Basic Petroleum
Data Book. To estimate activity data, the percentage of oil wells that were not associated with natural gas production
(an average of 56.4 percent from 1990 through 1997) was multiplied by the total number of wells in the United States.
This number was then multiplied by per well emission factors for fugitive emissions and routine maintenance from
Tilkicioglu & Winters (1989). Table F-l displays the activity data, emission factors, and emissions estimates used.
Step 2: Crude Oil Storage
Methane emissions from storage were calculated as a function of annual U.S. crude stocks less strategic petroleum
stocks for each year, obtained from annual editions of the Petroleum Supply Annual published by the Energy
Information Administration (EAI1991,1992,1993,1994,1995,1996,1997,1998). These stocks were multiplied by
emission factors from Tilkicioglu & Winters (1989) to estimate emissions. Table F-2 displays the activity data,
emission factors, and emissions estimates used.
Step 3: Refining
Methane emissions from refinery operations were based on U.S. refinery working storage capacity. The EIA
reports this data every two years. The data was last reported in 1997 for the 1996 estimates. Consequently, 1997 data
for total U.S. refinery working storage capacity were not available. These estimates were derived using the average of
the percent difference each year from 1990 through 1996 (EIA 1990, 1991, 1992, 1993, 1994, 1995, 1997). This
capacity was multiplied by an emission factor from Tilkicioglu & Winters (1989) to estimate emissions. Table F-3
provides the activity data, emission factors, and emissions estimates used.
Step 4: Tanker Operations
Methane emissions from the transportation of petroleum on marine vessels were estimated using activity data on
crude oil imports, U.S. crude oil production, Alaskan crude oil production, and Alaskan refinery crude oil capacity.
All activity data, excluding the Alaskan refinery crude oil capacity estimates, were taken from annual editions of the
Petroleum Supply Annual (EIA. 1991,1992,1993,1994,1995,1996,1997,1998). The capacity estimates are reported
every two years but were not reported for 1997. The data were derived using the average of the percent difference in
Alaskan refinery crude oil capacity each year from 1990 through 1996 (EIA 1990,1991,1992,1993,1994,1995,1997).
Tilkicioglu & Winters (1989) identified three sources of emissions in the transportation of petroleum. These are
emissions from loading Alaskan crude oil onto tankers, emissions from crude oil transfers to terminals, and ballast
emissions.
Step 4.1: Loading Alaskan Crude Oil onto Tankers
The net amount of crude oil transported by tankers was determined by subtracting Alaskan refinery capacity from
Alaskan crude oil production. This net amount was multiplied by an emission factor from Tilkicioglu & Winters (1989)
to estimate emissions. The activity data and emissions estimates are shown in Table F-4.
F-1
-------
I
Step 4.2: Crude Oil Transfers to Terminals
I" . ,;i /I . " ' ' ,"•'.•!•
Methane emissions from crude oil transfers were taken from the total domestic crude oil transferred to terminals.
I ' ,"'!! :i, injl! •' , ' , nP ; " • .; li'i '!' " 'In |1"1"v: ' • , ; I ' : '•' •
Tins amount was assumed to be 10 percent of total domestic crude oil production less Alaskan crude oil production.
To estimate emissions, this transferred amount was multiplied by an emission factor from Tilkicioglu & Winters (1989).
The activity data and emissions estimates are shown in Table F-5.
Step 4.3: Ballast Emissions
Ballast emissions are emitted from crude oil transported on marine vessels. This amount was calculated from the
sum of Alaskan crude oil on tankers, the amount of crude oil transferred to terminals, and all crude oil imports less
Canadian imports. Ballast volume was assumed to be 17 percent of this sum (Tilkicioglu & Winters 1989). This
amount was then multiplied by an emission factor to estimate emissions. The activity data and emissions estimates are
shown in Table F-6.
],
Total emissions from tanker operations are shown in Table F-7.
Step 5: Venting and Flaring
I,
Methane emissions from venting and flaring were based on 1990 emissions estimates from EPA (1993) and were
held constant through 1997 due to the lack of data available to assess the change in emissions.
(' !' '; , ' s, '
F-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table F-1: CH4 Emissions from Petroleum Production Field Operations
Variable
Total Oil Wells
% Not Assoc. w/ Natural Gas
Oil Wells in Analysis
Emission Factors
Fugitive
Routine Maintenance
Emissions
Fugitive
Routine Maintenance
Units
%
1990
587,762
55.6%
1991
610,204
56.4%
326,982 343,873
kg/well/yr
kg/well/yr
mill kg/yr
mill kg/yr
72
0.15
23.5
0.05
24.8
0.05
1992
1993
594,189 583,879
56.7%
56.7%
336,749 330,843
24.3
0.05
23.9
0.05
1994
581,657
56.6%
329,366
23.7
0.05
1995
574,483
56.7%
325,451
23.4
0.05
1996
574,419
56.5%
324,362
23.4
0.05
1997
573,504
56.5%
323,883
23.3
0.05
Table F-2: CH4 Emissions from Petroleum Storage
Variable
Total Crude Stocks
Strategic Petroleum Stocks
Crude Oil Storage
Emission Factors
Breathing
Working
Fugitive
Emissions
Breathing
Working
Fugitive
Total Emissions
Units
1000barrels/yr
1000barrels/yr
1000barrels/yr
kg CIVbrl/yr
kg CHVbrl/yr
kg CH/brl/yr
kg/yr
kg/yr
kg/yr
mill, kg/yr
1990
908,387
585,692
322,695
0.002612
0.002912
4.99x1 0'5
842,892
939,602
16,118
1.80
1991
893,102
568,508
324,594
847,853
945,131
16,213
1.81
1992
892,864
574,724
318,140
830,994
926,339
15,891
1.77
1993
922,465
587,080
335,385
876,039
976,552
16,752
1.87
1994
928,915
591,670
337,245
880,897
981,968
16,845
1.88
1995
894,968
591,640
303,328
792,305
883,210
15,151
1.69
1996
849,669
566,000
283,669
740,955
825,969
14,169
1997
868,11
563,429
304,609
795,862
887,176
15,219
1.58 1.70
Table F-3: CH4 Emissions from Petroleum Refining
Variable ( Jan 1)
Refinery Storage Capacity
Storage Emission Factor
Emissions
Units
1000barrels/yr
Mg CHvWyr
mill, kg/yr
1990
174,490
5.9 X10'5
10.29
1991
171,366
10.10
1992
167,736
9.89
1993 1994 1995
170,823 164,364 161,
1996
1997
305 158,435 155,929
10.07 9.69 9.51
9.34
9.19
F-3
-------
Taile F«4: CHt Enii«siinsfra'nj Pettofeiira Traispirtatlott: toaidlig /tefcai Creite 01 otto Tankers (Barrels/day)*
Variable
1990
1991
1992
1993
1994
1995
1996
1997
Alaskan Crude
Alaskan Refinery Crude Capacity
NetTankered
Conversion Factor (gal oiV barrel oil)
Emission factor (Ibs/gallon)
Emissions @ Loading AK (Ibs/day)
Methane Content of Gas (%)
Emissions @ Loading AK (mill kg/yr)
1,773,452 1,798,216 1,718,690 1,582,175 1,558,762 1,484.000 1,393,000 1,296,000
229,850 239,540 222,500 256,300 261,000 275,152 283,350 293,989
1,543,602 1,558,676 1,496,190 1,325,875 1,297,762 1.208,848 1,109,650 1,002,011
42
0.001
64,831 65,464 62,840 55,687 54,506 50,772 46,605 42,084
20.80%
2.23 2.26 2.17 1.92 1.88 1.75 1.61 1.45'
' Unless otherwise noted
Table F-5: CH4 Emissions from Petroleum Transportation: Crude Oil Transfers to Terminals (Barrels/day)*
Variable
US Crude Production
AK Crude Production
US Crude - AK Crude
1 0% transported to terminals
Conversion Factor (gal oil/ barrel oil)
Emission factor (Ibs/gallon)
Emissions from Transfers (Ibs/day)
Methane Content of Gas (%)
Emissions from Transfers (mill koyyr)
1990
7,355,307
1,773,452
5,581,855
558,185
42
0.001
23,444
20.80%
0.81
1991
7,416,545
1,798,216
5,618,329
561,833
23,597
0.81
1992
7,190,773
1,718,690
5,472,082
547,208
22,983
0.79
6
1
1993
,846,666
,582,175
5,264,490
526,449
22,111
0.76
1994
6,661,578
1
5
,558,762
,102,816
510,282
21,432
0.74
1995
6,560,000
1,484,000
5,076,000
507,600
21,319
0.73
1996
6,465,000
1,393,000
5,072,000
507,200
21,302
0.73
1997
6,452,000
1,296,000
5,156,000
515,600
21,655
0.75
Table F-6: CH4 Emissions from Petroleum Transportation: Ballast Emissions (Barrels/day)4
Variable
Crude Imports (less Canadian)
Alaskan Crude (NetTankered)
10% Crude Prod. Transported to terminals
Conversion Factor (gal oil/ barrel oil)
Emission factor (lbs/1000 gallons)
Crude Oil Unloaded
Ballast Volume (17% of Crude Unloaded)
Ballast Emissions (Ibs/day)
Methane Content of Gas (%)
Ballast Emissions (mill kg/yr)
* Unless otherwise noted
1990
5,251,701
1,543,602
558,185
42
1.4
7,353,489
1,250,093
73,505
20.80%
2.53
1991
5,038,786
1,558,676
561,833
7,159,296
1,217,080
71,564
2.47
1992
5,300,616
1,496,190
547,208
7,344,015
1,248,483
73,411
2.53
1993
5,886,921
1,325,875
526,449
7,739,245
1,315,672
77,361
2.67
1994
6,079,773
1,297,762
510,282
7,887,816
1,340,929
78,847
. 2.72
1995
6,125,482
1,208,848
507,600
7,841,930
1,333,128
78,388
2.70
1996
6,909,429
1,109,650
507,200
8,526,279
1,449,467
85,229
2.94
1997
7,787,604
1,002,011
515,600
9,305,215
1,581,887
93,015
3.20
F-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table F-7: Total CH4 Emissions from Petroleum Transportation
Year
1990
1991
1992
1993
1994
1995
1996
1997
Million kg/yr
5.6
5.5
5.5
5.4
5.3
5.2
5.3
5.4
F-5
-------
lEii;11 i in—'T
-------
Annex G
Methodology for Estimating Methane Emissions from Enteric Fermentation
The following steps were used to estimate methane emissions from enteric fermentation in livestock.
Step 1: Collect Livestock Population Data
All livestock population data, except for horses, was taken from U.S. Department of Agriculture (USDA)
statistical reports. For each animal category, the USDA publishes monthly, annual, and multi-year livestock population
and production estimates. Multi-year reports include revision to earlier published data. Recent reports were obtained
from the USDA Economics and Statistics System website, at , while historical
data were downloaded from the USDA-National Agricultural Statistics Service (NASS) website at
.
The Food and Agriculture Organization (FAO) publish horse population data. These data were accessed from
the FAOSTAT database at . Table G-1 summarizes the published population data by animal type.
Step 2: Estimate Emission Factors for Dairy Cows
Regional dairy cow emission factors from the 1993 Report to Congress (EPA 1993) were used as the starting point
for the analysis. These emission factors were used to calibrate a model of methane emissions from dairy cows. The
model applies revised regional emission factors that reflect changes in milk production per cow over time. Increases
in milk production per cow, in theory, require increases in feed intake, which lead to higher methane emissions per cow.
Table G-2 presents the emission factors per head by region used for dairy cows and milk production. The regional,
definitions are from EPA (1993).
Step 3: Estimate Methane Emissions from Dairy Cattle
Dairy cow emissions for each state were estimated by multiplying the published state populations by the regional
emission factors, as calculated in Step 2. Dairy replacement emissions were estimated by multiplying national
replacement populations by a national emission factor. The USDA reported the number of replacements 12 to 24
months old as "milk heifers." It is assumed that the number of dairy cow replacements 0 to 12 months old was
equivalent to the number 12 to 24 months old replacements.
Step 4: Estimate Methane Emissions from Beef Cattle
Beef cattle methane emissions were estimated by multiplying published cattle populations by emission factors.
Emissions from beef cows and replacements were estimated using state population data and regional emission
developed in EPA (1993), as shown in Table G-3. Emissions from slaughter cattle and bulls were estimated using
national data and emission factors. The emission factors for slaughter animals represent their entire life, from birth to
slaughter. Consequently, the emission factors were multiplied by the national data on total steer and heifer slaughters
rather than live populations of calves, heifers, and steers grown for slaughter. Slaughter population numbers were taken
from and USDA datasets. The Weanling and Yearling mix was unchanged from earlier estimates derived from
discussions with industry representatives.
Step 5: Estimate Methane Emissions from Other Livestock
Methane emissions from sheep, goats, swine, and horses were estimated by multiplying published national
population estimates by the national emission factor for each year.
A summary of emissions is provided in Table G-4. Emission factors, national average or regional, are shown by
animal type in Table G-5.
G-1
-------
'I1!! I'!":1 , !| ilm !|""''"' I
"1
Table G-1: Livestock Population (thousand head)
'MI lilii ,. ,: i '.'ill.!1
Animal Type
Dairy
Cows
Replacements 0-1 2
Replacements 12-24
Beef ; ;' ; .::
Cows
Replacements 0-1 2
Replacements 12-24
Slaughter-Weanlings
Slaughtsr-Yeaiflngs
..I MC " . ...r
"Other
Sheep
;:; Goats,.,
Horses
Hogs
ir ' ni1"'
Table 6-2: Dairy Cow
, :i , iliilliii;i | . ,,| ..„..,.„, ,
Region
: it " •.. i :"!".. . • '»
1990 1991 1992 1993 1994 1995
10,007 9,883 9,714 9,679 9,514 9,494
4,135 4,097 4,116 4,088 4,072 4,021
4,135 4,097 4,116 4,088 4,072 4,021
32,677 32,960 33,453 34,132 35,325 35,628
5,141 5,321 5,621 5,896 6,133 6,087
5,141 5,321 5,621 5,896 6,133 6,087
5,199 5,160 5,150 5,198 5,408 5,612
20,794 20,639 20,600 20,794 21,632 22,450
2,180 2,198 2,220 2,239 2,304 2,395
11,356 11,174 10,797 10,201 9,742 8,886
2,545 2,475 2,645 2,605 2,595 2,495
5215 5650 5650 5850 5900 6000
54,014 56,478 58,532 57,999 60,018 59,792
:; : ' ,"
CH4 Emission Factors and Milk Production Per Cow
,liili|,,il|.|il,| , ;.. •,,,,• , ,- , ,, i , „ ,"• ,,i i1 i ' in' , in,
1990 1991 1992 1993 1994
j
• i
1996
9,409
3,902
3,902
35,414 :
5,839
5,839
5,580
22,322
2,346
8,454
2,495
6,000 "
56,716
I
I
• i
1995
1997
9,304
3,828
3,828
34,486
5,678
5,678
5,692
22,767
2,320
7,607
2,295
6,150
58,671
1996
1997
Dairy Cow Emission Factors (kg/head)
North Atlantic
Sout!|Mantic
North Central
South Central
1 West!;1' ' ' '.
Milk Production (kg/year)
North Atlantic
South Atlantic
North Central
South Central
West
116.2 118.8 121.3 121.0 122.3
127.7 128.7 132.3 132.2 134.5
105.0 105.7 107.8 107.6 109.8
116.2 116.1 117.9 119.2 121.1
130.4 129.4 132.7 132.3 135,6
6,574 6,811 7,090 7,055 7,185
6,214 6,300 6,622 6,608 6,813
6,334 6,413 6,640 6,627 6,862
5,696 5,687 5,849 5,971 6,148
8,339 8,255 8,573 8,530 8,874
124.7
134.4 '
111.2
122.2
134.8 '
' I!
7,424
6,792
6,987
6,248
8,789
124.8
132.9
110^0
120.9
137.3
7,440
6,673
6,881
6,128
9,047
125.8
136.5
111.8
120.5
139.4
7,542
6,990
7,080
6,098
9,260
Table G-3: CH4 Emission Factors Beef Cows and Replacements (kg/head/yr)
Jlr1 ' '„ Si',! 'I' i!|ii|r i • . i , ' ' ' ! II n,
Region Replacements (0-12) Replacements (12-24) Mature Cows
North Atlantic
South Atlantic
North Central
South Central
West ""
!!„• • j sj
19.2 63.8 61.5
22.7 67.5 70.0
20.4 60.8 59.5
23.6 67.7 70.9
22.7 64.8 69.1
EI ! . . • , i.,i;
I
;
G-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table G-4: Methane Emissions from Livestock Enteric Fermentation (Tg)
Animal Type
Dairy
Cows
Replacements 0-1 2
Replacements 1 2-24
Beef
Cows
Replacements 0-1 2
Replacements 12-24
Slaughter-Weanlings
Slaughter-Yearlings
Bulls
Other
Sheep
Goats
Horses
Hogs
Total
Table G-5: Enteric
Animal Type
Dairy
Cows
Replacements 0-1 2
Replacements 1 2-24
Beef
Cows
Replacements 0-1 2
Replacements 12-24
Slaughter-Weanlings
Slaughter-Yearlings
Bulls
Other
Sheep
Goats
Horses
Hogs
1990 1991
1.47
1.15
0.08
0.24
3.95
2.18
0.11
0.33
0.12
0.98
0.22
0.28
0.09
0.01
0.09
0.08
5.70
1.46
1.14
0.08
0.24
3.98
2.20
0.12
0.35
0.12
0.98
0.22
0.29
0.09
0.01
0.10
0.08
5.73
1992 1993
1.47
1.15
0.08
0.24
4.04
2.23
0.13
0.37
0.12
0.97
0.22
0.29
0.09
0.01
0.10
0.09
5.80
Fermentation CH4 Emission
1
1
0
0
4
2
0
0
0
0
0
0
.47
.15
.08
.24
.12
.28
.13
.38
.12
.98
.22
.29
0.08
0.01
0
.11
0.09
5.88
1994
1.47
1.15
0.08
0.24
4.27
' 2.36
0.14
0.40
0.12
1.02
0.23
0.29
0.08
0.01
0.11
0.09
6.03
1995
1
1
0
0
4
.47
.16
.08
.24
.34
2.38
0
.14
0.40
0
1
0
.13
.06
.24
0.28
0
0
0
0
6
.07
.01
.11
.09
.10
1996
1.46
1.15
0.08
0.23
4.29
2.36
0.13
0.38
0.13
1.06
0.23
0.27
0.07
0.01
0.11
0.09
6.02
1997
1
1
.45
.15
0.08
0.23
4
2
0
0
0
1
0
0
0
.24
.30
.13
.37
.13
.08
.23
.27
.06
0.01
0
.11
0.09
5.96
Factors
kg/head/year
regional
19.6
58.8
regional
regional
regional
23.1
47.3
100.0
8.0
5.0
18.0
1.5
G-3
-------
-------
Annex H
Methodology for Estimating Methane Emissions from Manure Management
The following steps were used to estimate methane emissions from the management of livestock manure.
Step 1: Collect Livestock Population Data
All livestock population data, except for horses, were taken from U.S. Department of Agriculture (USDA)
statistical reports. For each animal category, the USDA publishes monthly, annual, and multi-year livestock population
and production estimates. Multi-year reports include revisions to earlier published data. Recent reports were obtained
from the USDA Economics and Statistics System website, at , while historical
data were downloaded from the USDA National Agricultural Statistics Service (NASS) website at
.
Dairy cow and swine population data by farm size for each state, used in Step 2, were found in the 1992 Census
of Agriculture published by the U.S. Department of Commerce (DOC). This census is conducted every five years. Data
from the census were obtained from the USDA NASS website at .
The Food and Agriculture Organization (FAO) publishes horse population data. These data weree accessed from
the FAOSTAT database at . Table H-l summarizes the published population data by animal type.
Step 2: Estimate State Methane Conversion Factors for Dairy Cows and Swine
Data from EPA (1993) were used for assessing dairy and swine manure management practices by farm size.
Based on this assessment, an average methane conversion factor (MCF) was assigned to each farm size category for
dairy and swine farms, indicating the portion of the methane producing potential realized. Because larger farms tend
to use liquid manure management systems, which produce more methane, the MCFs applied to them were higher for
smaller farm sizes.
Using the dairy cow and swine populations by farm size in the DOC Census of Agriculture for each state,
weighted average dairy and swine MCFs were calculated for each state. The MCF value for each state reflected the
distribution of animals among farm sizes within the state. Table H-2 provides estimated MCF values.
Step 3: Estimate Methane Emissions from Swine
For each state, the total swine population was multiplied by volatile solids (VS) production rates to determine total
VS production. Estimated state level emissions were calculated as the product of total VS production multiplied by the
maximum methane production potential for swine manure (B0), and the state MCF. Total U.S. emissions are the sum
of the state level emissions. The VS production rate and maximum methane production potential are shown in Table
H-3.
Step 4: Estimate Methane Emissions from Dairy Cattle
Methane emissions from dairy cow manure were estimated using the same method as emissions from swine (Step
3), but with an added analysis to estimate changes in manure production associated with changes in feed intake, or dry
matter intake (DMi). It is assumed that manure and VS production will change linearly with changes in dry matter
intake (DMi).
Changes in DMi were calculated reflecting changes in feed intake associated with changes in milk production per
cow per year. To estimate the changes in feed intake, a simplified emission factor model was used for dairy cow enteric
fermentation emissions (see Annex G). This model estimates the change in DMi over time relative to 1990, which was
used to calculate VS production by dairy cows by state, as summarized in the following equation: (Dairy cow
population) x (VS produced per cow) x (DMi scaling factor). Methane emissions were then calculated as follows: (VS
H-1
-------
produced) x (Maximum methane production potential for dairy cow manure) x (State-specific MCF). Total emissions
were finally calculated as the sum of the state level emissions. The 1990 VS production rate and maximum methane
production potential are shown in Table H-3.
Step 5: Estimate Methane Emissions for Other Animals
The 1990 methane emissions for the other animal types were estimated using the detailed method described above
for dairy cows and swine (EPA 1993). This process was not repeated for subsequent years for these other animal types.
Instead, national populations of each of the animal types were used to scale the 1990 emissions estimates to the period
1991 through 1997.
Emission estimates are summarized in Table H-4.
ill!1'1 I '' '' Pi isi'ir!"' '"''', , i , II
Table H-1: Livestock Population (1000 head)
Animal Type
Dairy Cattle
Dairy Cows
Dairy Heifers
Swine
peefCafife
Feedto^ Steers
; FeedtotHetfers
Feedtot Cow/Other
NOFBuiis
NQF Calves
?? NOF Ipe^s '"
>• I NOF Seers
NOF cows
Sheep
' ;i Ewes>1yr
Rams/V\feth>lyr
Ewes<1yr
Rams/Weth<1yr
Sheep on Feed
'Goals
Poultry
Hens>lyr
Pullets laying
Pu!lets>3mo
Pullets <3mo
Chickens
Broilers
Other ilost)
Other {Sold}
Turkeys
Horses
1990
14,143
10,007
4,135
54,014
86^065
„. I-252
3,753
88
2,180
23,909
','.'. ,'1.740
7,554
32,589
11,356
7,961
369
1,491
381
1,154
2,545
Ijd^OS?
119,551
153,916
34,222
38,945
6,546
1,172,830
6,971
41,672
128]384
5,650
1991
13,980
9,883
4,097
56,478
87,266
7,927
4,144
98
2,198
23,854
8,828
7,356
32,860
11,174
7,799
361
1,464
373
1,177
2,475
1,767,513
117,178
162,943
34,272
42,344
6,857
1,227,430
7,278
39,707
129,505
5,650
1992
13,830
9,714
4,116
58,532
88,546
7,404
3,884
92
2,220
24,118
9,261
8,208
33,359
10,797
7,556
350
1,432
366
1,093
2,645
1,832,308
121,103
163,397
34,710
45,160
7,113
1,280,498
7,025
41,538
131,764
5,850
1993
13,767
9,679
4,088
57,999
90,317
7,838
4,094
95
2,239
24,209
9,727
8,081
34,033
10,201
7,140
331
1,349
348
1,032
2,605
1,895,851
131,688
158,938
33,833
47,941
7,240
1,338,862
6,992
39,606
130,750
5,900
1994
13,686
9,614
4,072
60,018
92,754
8,063
4,088
93
2,304
24,692
10,179
8,108
35,227
9,742
6,775
314
1,277
332
1,044
2,595
1,971,404
134,876
163,628
32,808
44,875
7,319
1,403,508
12,744
40,272
131,375
6,000
1995
13,514
9,493
4,021
59,792
94,364
7,635
3,934
97
2,395
25,184
10,790
8,796
35,531
8,886
6,184
282
1,167
296
957
2,495
2,031,455
133,767
164,526
32,813
45,494
7,641
1,465,134
8,152
40,917
133,012
6,000
1996
13,310
9,408
3,902
56,716
93,683
7^822
4,063
96
2,346
24,644
10,800
8,594
35,318
8,454
5,875
269
1,107
282
921
2,495
2,091,364
137,944
165,304
31,316
44,611
7,243
1,519,640
8,124
39,588
137,595
6,050
1997
13,133
9,304
3,828
58,671
91,997
7,925
4,126
97
2,320
24,355
10,751
8,035
34,389
7.607
5,317
244
1,011
258
777
2,295
2,140,362
140,686
170,398
34,174
50,693
7,544
1,552,052
9,972
38,198
136,645
6,150
if!"1!!'
H-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table H-2: Dairy Cow and Swine CH4 Conversion Factors
State Dairy Cow
AK 0.35
AL 0.23
AR 0.45
AZ 0.09
CA 0.44
CO 0.31
CT 0.19
DE 0.21
FL 0.41
GA 0.27
HI 0.40
IA 0.04
ID 0.23
IL 0.07
IN 0.06
KS 0.09,
KY 0.06
LA 0.19
MA 0.13
MD 0.15
ME • 0.10
Ml 0.12
MN 0.04
MO 0.07
MS 0.17
Table H-3: Dairy Cow
Description
Typical Animal Mass (kg)
Swine
0.35
0.28
0.59
0.68
0.44
0.46
0.01
0.29
0.23
0.35
0.40
0.38
0.27
0.42
0.43
0.33
0.30
0.30
0.40
0.42
0.01
0.42
0.38
0.33
0.35
and Swine
State
MT
NG
ND
NE
NH
NJ
NM
NV
NY
OH
OK
OR
PA
Rl
SC
SD
TN
TX
UT
VA
VT
WA
Wl
WV
WY
Constants
Dairy Cow
0.16
0.20
0.05
0.08
0.12
0.13
0.42
0.36
0.11
0.07
0.13
0.25
0.06
0.07
0.29
0.06
0.14
0.31
0.21
0.17
0.11
0.29
0.05
0.11
0.12
kgVS/daypeMOOOkgmass
Maximum methane generation potential (Bn) m3 methane/kg VS
Swine
0.39
0.65
0.22
0.34
0.36
0.26
0.47
0.50
0.22
0.30
0.31
0.35
0.35
0.59
0.40
0.26
0.28
0.30
0.34
0.34
0.09
0.29
0.27
0.11
0.20
Dairy Cow Swine
640 150
10 8.5
0.24 0.47
Source
ASAE1995
ASAE1995
EPA 1992
H-3
-------
Table H-4: CH4 Emissions from Livestock Manure Management (Tg)
Animal Type
Dairy Cattle
Dairy Cows
Dairy Heifers
Swine
Bee! Cattle
Feedlot Steers
Feedlot Heifers
Feedlot Cow/Other
NOF Bulls
NOF Calves
NOFfefers
NOF Steers
NOF Cows
Sheep
Ewes > 1 yr
Rams/Weth > 1 yr
Ewes < 1 yr
Rams^VVeth < 1 yr
Sheep on Feed
Goals
Poultry
Hens > 1 yr
Pullets laying
Pullets > 3 mo
Pullets < 3 mo
Chickens
Broilers
Other (Lost)
Other(Sold)
Turkeys
Horses
r
t
H-4 Inventory of
1990
0.75
0.58
0.17
t"37
ot2o
0^03
0.02
0.00
0.01
0.02
0.02
0.01
aio
0.004
0.003
0.000
0.000
o.dbo
d.dbo
0.001
0.26
bibs
0.06
0.01
0.01
0.00
If I . ,''!* I
d.bo
0.01
0.03
0.03
•. < , 3
V
•>!
1991
0.75
0.59
0.16
1.44
0.20
0.03
0.02
0.00
0.01
0.02
0.02
0.01
0.10
0.004
0.003
0.000
0.000
0.000
o.doo
0.001
0.27
0:05
0.06
0.01
0.01
0.00
0.10
0.00
0.01
0.03
0.03
U.S. Greenhouse Gas
1992
0.76
0.60
0.17
1.51
0.21
0.03
0.02
0.00
0.01
0.02
0.02
0.02
0.10
0.004
0.003
0.000
0.000
0.000
o.odo
0.001
0.28
0.06
0.06
0.01
0.01
0.00
0.11
0.00
0.01
0.03
0.03
1993
0.77
0.61
0.16
1.51
0.21
0.03
0.02
0.00
0.01
0.02
0.02
0.02
0.10
0.003
0.003
0.000
0.000
0.000
0.000
0.001
0.28
0.06
0.06
0.01
0.01
0.00
0.11
0.00
0.01
0.03
0.03
Emissions and
1994
0.79
0.63
0.16
1.58
0.22
0.03
0.02
0.00
0.01
0.02
0.02
0.02
0.11
0.003
0.003
0.000
0.000
0.000
0.000
0.001
0.29
0.06
0.06
0.01
0.01
0.00
0.12
0.00
0.01
0.03
0.03
1995
0.79
0.63
0.16
1.60
0.22
0.03
0.02
0.00
0.01
0.02
0.02
0.02
0.11
0.003
0.002
0.000
0.000
0.000
0.000
0.001
0.30
0.06
0.06
0.01
0.01
0.00
0.12
o.od
0.01
0.03
0.03
1996
0.79
0.64
0.16
1.55
0.23
0.03
0.02
0.00
0.01
0.02
0.02
0.02
0,11
0.003
0.002
0.000
0.000
0.000
0.000
0.001
0.30
0.06
0.06
0.01
0.01
0.00
0.13
'" 0.00
0.01
0.03
0.03
1997
0.81
0.65
0.15
1.62
0.23
0.03
0.02
0.00
0.01
0.02
0.02
0.02
0.11
0.003
0.002
0.000
0.000
0.000
0.000
0.001
0.31
0.06
0.06
0.01
0.01
0.00
0.13
o.od
0.01
0.03
0.03
', :
,i .,."
1 '
;,;
Sinks: 1990-1997
-------
Annex I
Methodology for Estimating Methane Emissions from Landfills
Landfill methane is produced from a complex process of waste decomposition and subsequent fermentation under
anaerobic conditions. The total amount of methane produced in a landfill from a given amount of waste and the rate
at which it is produced depends upon the characteristics of the waste, the climate, and operating practices at the landfill.
To estimate the amount of methane produced in a landfill in a given year the following information is needed: quantity
of waste in the landfill, the waste characteristics, the residence time of the waste in the landfill, and landfill management
practices.
The amount of methane emitted from a landfill is less than the amount of methane produced in a landfill. If no
measures are taken to extract the methane, a portion of the methane will oxidize as it travels through the top layer of
the landfill cover. The portion of the methane that oxidizes turns primarily to carbon dioxide (CO2). If the methane
is extracted and combusted (e.g., flared or used for energy), then that portion of the methane produced in the landfill
will not be emitted as methane, but again would be converted to CO2. In general, the CO2 emitted is of biogenic origin
and primarily results from the decomposition—either aerobic or anaerobic—of organic matter such as food or yard
wastes.8
To take into account the inter-related processes of methane production in the landfill and methane emission, this
analysis relied on a simulation of the population of landfills and waste disposal. A starting population of landfills was
initialized with characteristics from the latest survey of municipal solid waste (MSW) landfills (EPA 1988). Using
actual national waste disposal data, waste was simulated to be placed in these landfills each year from 1990 to 1997.
If landfills reached their design capacity, they were simulated to have closed. New landfills were simulated to open only
if annual disposal capacity was less than total waste disposal. Of note is that closed landfills continue to produce and
emit methane for many years. This analysis tracks these closed landfills throughout the analysis period, and includes
their estimated methane production and emissions.
The age of the waste in each landfill was tracked explicitly. This tracking allowed the annual methane production
in each landfill to be estimated. Methane produced in industrial landfills was also estimated. It was assumed to be 7
percent of the total methane produced in MSW landfills. Finally, methane recovered and combusted and methane
oxidized were subtracted to estimate final methane emissions.
Using this approach, landfill population and waste disposal characteristics were simulated over time explicitly,
thereby allowing the time-dependent nature of methane production to be modeled. However, the characteristics used
to initialize the landfill population in the model were relatively old and may not represent the current set of operating
landfills adequately. There is also uncertainty in the methane production equation developed in EPA (1993), as well
as in the estimate of methane oxidation (10 percent).
Step 1: Estimate Municipal Solid Waste in Place Contributing to Methane Emissions
The landfill population model was initialized to define the population of landfills at the beginning of 1990. Waste
was simulated to be placed into these landfills for the years 1990 through 1997 using data on the total waste landfilled
from BioCycle (1998). The annual acceptance rates of the landfills were used to apportion the total waste by landfill.
More waste was preferentially disposed in "Large" landfills (see Table 1-3), reflecting the trend toward fewer and more
centralized disposal facilities. The model updates the landfill characteristics each year, calculating the total waste in
place and the full time profile of waste disposal. This time profile was used to estimate the portion of the waste that
contributes to methane emissions. Table 1-1 shows the amount of waste landfilled each year and the total estimated
waste in place contributing to methane emissions.
Emissions and sinks of biogenic carbon are accounted for in the Land-Use Change and Forestry chapter.
1-1
-------
Step 2: Estimate Landfill Methane Production
if,!:1 *\ , S ' ' !, i . ' il "' '
Emissions for each landfill were estimated by applying the emissions model (EPA 1993) to the landfill waste in
place contributing to methane production. Total emissions were then calculated as the sum of emissions from all
landfills.
Step 3: Estimate Industrial Landfill Methane Production
!/,,"! . ,!,:j ;: li| ' ,;< ' , : ;••'... . 'I ,':'
Industrial landfills receive waste from factories, processing plants, and other manufacturing activities. Because
there were no data available on methane generation at industrial landfills, the approach used was to assume that
industrjal methane production equaled about 7 percent of MSW landfill methane production (EiPA 1993), as shown
below in Table 1-2.
i"1- • , ;: /ji . {-.'• , .. ji
Step 4: Estimate Methane Recovery
To estimate landfill gas (LFG) recovered per year, data on current and planned LFG recovery projects in the
United States were obtained from Governmental Advisory Associates (GAA 1994). The GAA report, considered to
be the most comprehensive source of information on gas recovery in the United States, has estimates for gas recovery
in 1990 and 1992, Their data set showed that 1.20 and 1.44 teragrams (Tg) of methane were recovered nationally by
municipal solid waste lanSfills in 1990 and 1992, respectively. In addition, a number of landfills were believed to
rccov
-------
Table 1-2: CH4 Emissions from Landfills (Tg)
Activity
MSW Generation
Large Landfills
Medium Landfills
Small Landfills
Industrial Generation
Potential Emissions
Recovery
Oxidation
Net Emissions
1990
11.6
4.53
5.79
1.27
0.73
12.3
(1.50)
(1.09)
9.82
1991
11.8
4.62
5.91
1.30
0.75
12.6
(1.50)
(1.12)
10.0
1992
12.2
4.76
6.07
1.33
0.77
12.9
(1.80)
(1.12)
10.1
1993
12.5
4.91
6.23
1.36
0.79
13.3
(1.80)
(1.16)
10.4
1994
12.8
5.11
6.36
1.39
0.81
13.7
(1.80)
(1.19)
10.8
1995
13.2
5.29
6.53
1.41
0.83
14.1
(1.80)
(1.23)
11.1
1996
13.5
5.45
6.62
1.42
0.85
14.3
(1.80)
(1.26)
11.4
1997
13.8
5.64
6.70
1.44
0.87
14.7
(1.80)
(1.20)
11.6
Note: Totals may not sum due to independent rounding.
Table 1-3: Municipal Solid Waste Landfill Size Definitions (Tg)
Description
Waste in Place
Small Landfills
Medium Landfills
Large Landfills
<0.4
0.4 - 2.0
>2.0
1-3
-------
•" "III-
-------
Annex J
Global Warming Potential Values
Table J-1: Global Warming Potentials and Atmospheric Lifetimes (years)
Gas
Carbon dioxide (CO.,)
Methane (CH4)b
Nitrous oxide (N20)
HFC-23
HFC-125
HFC-134a
HFC-143a
HFC-152a
HFC-227ea
HFC-236fa
HFC-4310mee
CF4
C2F6
C4F10
C6F14
SFR
Atmospheric Lifetime
50-200
12+3
120
264
32.6
14.6
48.3
1.5
36.5
209
17.1
50,000
10,000
2,600
3,200
3,200
GWPa
1
21
310
11,700
2,800
1,300
3,800
140
2,900
6,300
1,300
6,500
9,200
7,000
7,400
23,900
Source: (IPCC1996)
MOO year time horizon
b The methane SWP 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.
J-1
-------
1:1
-------
Annex K
Ozone Depleting Substance Emissions
Ozone is present in both the stratosphere9, where it shields the Earth from harmful levels of ultraviolet radiation,
and at lower concentrations in the troposphere10, where it is the main component of anthropogenic photochemical
"smog". Chlorofluorocarbons (CFCs) and other compounds that contain chlorine or bromine have been found to
destroy ozone in the stratosphere, and are commonly referred to as ozone-depleting substances (ODSs). If left
unchecked, ozone depletion could result in a dangerous increase of ultraviolet radiation reaching the earth's surface.
In 1987, nations around the world signed the Montreal Protocol on Substances that Deplete the Ozone Layer. This
landmark agreement created an international framework for limiting, and ultimately eliminating, the use and emission
of most ozone depleting substances, which are used in a variety of industrial applications, including refrigeration and
air conditioning, foam blowing, fire extinguishing, aerosol propellants, sterilization, and solvent cleaning.
In the United States, the Clean Air Act Amendments of 1990 provide the legal instrument for implementation of the
Montreal Protocol controls. The Clean Air Act classifies ozone depleting substances as either Class I or Class n, depending
upon the ozone depletion potential (ODP) of the compound.11 The production of CFCs, halons, carbon tetrachloride, and
methyl chloroform, all Class I substances, has already ended in the United States. However, because stocks of these chemicals
remain available and in use, they will continue to be emitted for many years from applications such as refrigeration and air
conditioning equipment, fire extinguishing systems, and metered dose inhalers. As a result, emissions of Class I compounds
will continue, in ever decreasing amounts, into the early part of the next century. Class II substances, which are comprised
of hydrochlorofluorocarbons (HCFCs), are being phased-out at a later date because of their lower ozone depletion potentials.
These compounds are serving as interim replacements for Class I compounds in many industrial applications. The use and
emissions of HCFCs in the United States is anticipated to increase over the next several years. Under current controls, the
production of all HCFCs in the United States will end by the year 2030.
In addition to contributing to ozone depletion, CFCs, halons, carbon tetrachloride, methyl chloroform, and HCFCs are
also significant greenhouse gases. The total impact of ozone depleting substances on global warming is not clear, however,
because ozone is also a greenhouse gas. The depletion of ozone in the stratosphere by ODSs has an indirect negative radiative
forcing, while most ODSs have a positive direct radiative forcing effect. The IPCC has prepared both direct GWPs and net
(i.e., combined direct and indirect effects) GWP ranges for some of the most common ozone depleting substances (IPCC
1996). Direct GWPs account for the direct global warming impact of the emitted gas. Net GWP ranges account for both the
direct impact of the emitted gas and the indirect effects resulting from the destruction of ozone.
Although the IPCC emission inventory guidelines do not include reporting emissions of ozone depleting
substances, the United States believes that no inventory is complete without the inclusion of these emissions. Emission
estimates for several ozone depleting substances are provided in Table K-l.
The stratosphere is the layer from the top of the troposphere up to about 50 kilometers. Approximately 90 percent of atmospheric ozone lies
within the stratosphere. The greatest concentration of ozone occurs in the middle of the stratosphere, in a region commonly called the
ozone-layer.
The troposphere is the layer from the ground up to about 11 kilometers near the poles and 16 kilometers in equatorial regions (i.e., the lowest
layer of the atmosphere, where humans live). It contains roughly 80 percent of the mass of all gases in the atmosphere and is the site for weather
processes including most of the water vapor and clouds.
11 Substances with an ozone depletion potential of 0.2 or greater are classified as Class I. All other substances that may deplete stratospheric
ozone but which do not have an ODP of 0.2 or greater, are classified as Class n.
K-1
-------
Table K-1: Emissions of Ozone Depleting Substances (Mg)
Compound
Class)
CFd-1i
CFC-12
CFC-113
CFC-114
CFC-115
Carjjqn Tetrachloride
Meliyl Chloroform
Haton-1211
Halors-1301
Class il
HCFC-22
HCfif}.-j23
HCFC-124
HCFC-l4lb
HCFC5-142b
HCFC-225ca/cb
1990
53,500
112,600
26,350
4,700
4,200
32,300
158,300
1,000
1,800
79,789
+-
+
+
+
+
1991
48,300
103,500
20,550
3,600
4,000
31,000
154,700
1,100
1,800
79,540
+
+
+
+
+
1992
45,100
80,500
17,100
3,000
3,800
21,700
108,300
1,000
1,700
79,545
285
429
+
3,526
+
1993
45,400
79,300
17,100
3,000
3,600
18,600
92,850
1,100
1,700
71,224
570
2,575
1,909
9,055
+
1994
36,600
57,600
8,550
1,600
3,300
15,500
77,350
1,000
1,400
71,386
844
4,768
6,529
14,879
+
1995
'36,200
51,800
8,550
1,600
3,000
4,700
46,40d
1,100
1,400
74,229
1,094
5,195
11,608
21,058
565
1996
"' 26,600
35,500
+
300
3,200
+
+
: 1,100
1,400
s
' 77,472
" 1,335
" 5,558
" 14,270
" 27,543
579
1997
25,100
23,100
+
100
2,900
+
+
1,100
1,300
79,620
1,555
5,894
12,113 '
"28,31 5
593
Source: EPA estimates
+ Does not exceed 10 Mg
Methodology and Data Sources
Emissions of ozone depleting substances were estimated using two simulation models: the Atmospheric and
Health Effects Framework (AHEF) and EPA's Vintaging Model.
The Atmospheric and Health Effects Framework model contains estimates of U.S. domestic use of each of the
ozone depleting substances. These estimates were based upon data that industry reports to EPA and other published
material. The annual consumption of each compound was divided into various end-uses based upon historical trends
and research into specific industrial applications. These end-uses include refrigerants, foam blowing agents, solvents,
aerosol propellants, sterilants, and fire extinguishing agents.
With the exception of aerosols, solvents, and certain foam blowing agents, emissions of ozone depleting
substances are not instantaneous, but instead occur gradually over time (i.e., emissions in a given year are the result of
both QDS use in that year and use in previous years). Each end-use has a certain release profile, which gives the
percentage of the compound that is released to the atmosphere each year until all releases have occurred. In
refrigeration equipment, for example, the initial charge is released or leaked slowly over the lifetime of the equipment,
which could be 20 or more years. In addition, not all of the refrigerant is ultimately emitted—some will be recovered
when the equipment is retired from operation.
The AHEF model was used to estimate emissions of ODSs that were in use prior to the controls implemented
under the Montreal Protocol. This included CFCs, halons, carbon tetrachloride, methyl chloroform, and HCFC-22.
Certain HCFCs, such as HCFC-123, HCFC-124, HCFC-141b, HCFC-142b, HCFC-225ca and HClFC-225cb, have also
entered the market as interim substitutes for ODSs. Emissions estimates for these compounds were taken from EPA's
Vintaging Model.
K-2 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
I il, |, ,,!,,,|,| I,,' ,«„! Jill!: I
-------
The Vintaging Model was used to estimate the use and emissions of various ODS substitutes, including HCFCs.
The name refers to the fact that the model tracks the use and emissions of various compounds by the annual "vintages"
of new equipment that enter service in each end-use. The Vintaging Model is a "bottom-up" model. Information was
collected regarding the sales of equipment that use ODS substitutes and the amount of the chemical required by each
unit of equipment. Emissions for each end-use were estimated by applying annual leak rates and release profiles, as
in the AHEF. By aggregating the data for more than 40 different end-uses, the model produces estimates of annual use
and emissions of each compound.
Uncertainties
Uncertainties exist with regard to the levels of chemical production, equipment sales, equipment characteristics,
and end-use emissions profiles that are used by these models.
K-3
-------
-------
Annex L
Sulfur Dioxide Emissions
Sulfur dioxide (SO2) emitted into the atmosphere through natural and anthropogenic processes affects the Earth's
radiative budget through photochemical transformation into sulfate aerosols that can (1) scatter sunlight back to space,
thereby reducing the radiation reaching the Earth's surface; (2) affect cloud formation; and (3) affect atmospheric
chemical composition (e.g., stratospheric ozone, by providing surfaces for heterogeneous chemical reactions). The
overall effect of SO2 derived aerosols on radiative forcing is believed to be negative (IPCC 1996). However, because
SO2 is short-lived and unevenly distributed through the atmosphere, its radiative forcing impacts are highly uncertain.
Sulfur dioxide emissions have been provided below in Table L-l.
The major source of SO2 emissions in the United States was the burning of sulfur containing fuels, mainly coal.
Metal smelting and other industrial processes also released significant quantities of SO2. As a result, the largest
contributors to overall U.S. emissions of SO2 were electric utilities, accounting for 64 percent in 1997 (see Table L-2).
Coal.combustion accounted for approximately 96 percent of SO2 emissions from electric utilities in the same year. The
second largest source was industrial fuel combustion, which produced 17 percent of 1997 SO2 emissions. Overall,
sulfur dioxide emissions in the United States decreased by 16 percent from 1990 to 1997. Seventy-six percent of this
decline came from reductions from electric utilities, primarily due to increased consumption of low sulfur coal from
surface mines in western states.
Sulfur dioxide is important for reasons other than its effect on radiative forcing. It is a major contributor to the
formation of urban smog and acid rain. As a contributor to urban smog, high concentrations of SO2 can cause
significant increases in acute and chronic respiratory diseases. In addition, once SO2 is emitted, it is chemically
transformed in the atmosphere and returns to earth as the primary contributor to acid deposition, or acid rain. Acid rain
has been found to accelerate the decay of building materials and paints, and to cause the acidification of lakes and
streams and damage trees. As a result of these harmful effects, the United States has regulated the emissions of SO2
under the Clean Air Act. The EPA has also developed a strategy to control these emissions via four programs: (1) the
National Ambient Air Quality Standards program,12 (2) New Source Performance Standards,13 (3) the New Source
Review/Prevention of Significant Deterioration Program,14 and (4) the sulfur dioxide allowance program.15
References
EPA (1998) National Air Pollutant Emissions Trends Report, 1900-1997, U.S. Environmental Protection Agency,
Office of Air Quality Planning and Standards, Research Triangle Park, NC.
• [42 U.S.C § 7409, CAA § 109]
1 [42 U.S.C § 7411, CAA § 111]
1 [42 U.S.C § 7473, CAA § 163]
1 [42 U.S.C § 7651, CAA § 401]
L-1
-------
in.! , •. * iH:. ;l«i
it,',' ' . 'I" I''',*
Table L-1: S02 Emissions (G
Sector/Source
Energy
Stationary Sources
Mobfe Sources " :
0| a& Gas Activities
Industrial Processes
Chemical Manufacturing
Metals Processing
Storage and Transport
Other Industrial Processes
Miscellaneous*
Solvent USB
Decreasing
Grapfte Arts
Dry Cleaning
Surface Coating
Otberjndustrial
Non-Industrial
Agriculture
Agricultural Burning
Waste
Waste Combustion
Landls
Wastewater Treatment
Miscellaneous Waste
Toiat : : :.. ' :: :.:.
9)
1990
20,526
18,407
1,728
390
1,306
269
658
6
362
11
+
+
+
NA
+
+
NA
NA
NA
38
38
+
+
+
21,871
1991
20,031
17,959
1,729
343
1,187
254
555
9
360
10
+
+
+
NA
+
+
NA
NA
NA
40
39
+
+
1
21,259
1992
19,851
17,684
1,791
377
1,186
252
558
8
360
9
+
+
+
+
+
+
NA
NA
NA
40
39
+
+
1
21,077
1993
19,514
17,459
1,708
347
1,159
244
547
4
355
8
1
+
+
NA
+
+
NA
NA
NA
65
56
+
+
8
20,738
1994
19,003
17,134
1,524
344
1,135
249
510
1
361
13
1
+
+
+
+
+
NA
NA
NA
54
48
,+
+
5
20,192
5, • • '
1995
16,583
14,724
1,525
334
1,116
260
481
2
365
8
1
_+
+
+
+
+
NA
NA
NA
43
42
+
1
+
17,742
IL
1
1996
16,804
15,253
1,217
334
1,125
260
481
2
371
12
II i
+
, +
+
+
'.. +
NA
NA
NA
43
_ ,42
+
1
+
17,973
1997
17,258
15,658
1,252
349
1,175
273
501
2
387
12
1
+
+
+
+
+
NA
NA
NA
45
44
+
1
+
18,478
Source:(EPA 1998)
* Miscellaneous Includes other combustion and fugitive dust categories.
+ Doss not exceed 0.5 Gg
NA (MAvallable)
Note: Totals may not sum due to independent rounding.
Table L-2: S02 Emissions from Electric Utilities (Gg)
L .' ! , * "I ,.
Fuel Type
Coal
Petroleum
Natural Gas
Misc, Internal Combuston
Total
;,„:,„
1990
13,807
580
1
45
14,432
: ,;; ,
1991
13,687
591
1
41
14,320
1992
13,448
495
1
42
13,986
1993
13,179
555
1
. . 45
13,779
',.
1994
12,985
474
1
48
13,507
1995
10,526
375
8
50
10,959
1996
11,010
395
2
52
11,460
I!
1997
11,368
440
4
55
11,868
Source; (EPA 1998}
Note: Totals may not sum due to Independent rounding.
L-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Annex M
Complete List of Sources
Chapter/Source
Gas(es)
Energy
Carbon Dioxide Emissions from Fossil Fuel Combustion
Stationary Sources (excluding C02)
Mobile Sources (excluding C02)
Coal Mining
Natural Gas Systems
Petroleum Systems
Natural Gas Flaring and Criteria Pollutant Emissions from Oil and Gas Activities
International Bunker Fuels
Wood Biomass and Ethanol Consumption
Non-Energy Use Carbon Stored
C02
CH4, N20, CO, NOX, NMVOC
CH4, N20, CO, NOX, NMVOC
CH4
CH4
CH4
C02, CO, NOX, NMVOC
C02, CH4, N20, CO, NOX, NMVOC
C02
CO, (sink)
Industrial Processes
Cement Manufacture
Lime Manufacture
Limestone and Dolomite Use
Soda Ash Manufacture and Consumption
Carbon Dioxide Consumption
Iron and Steel Production
Ammonia Manufacture
Ferroalloy Production
Petrochemical Production
Silicon Carbide Production
Adipic Acid Production
Nitric Acid Production
Substitution of Ozone Depleting Substances
Aluminum Production
HCFC-22 Production
Semiconductor Manufacture
Electrical Transmission and Distribution
Magnesium Production and Processing
Industrial Sources of Criteria Pollutants
C02
C02
C02
C02
C02
C02
C02
C02
CH4
CH4
N20
N20
HFCs, PFCsa
C02, CF4, C2F6
HFC-23
HFCs, PFCs, SF6b
SF6
SF6
CO, NO,, NMVOC
Solvent Use
CO, NO,, NMVOC
Agriculture
Enteric Fermentation
Manure Management
Rice Cultivation
Agricultural Soil Management
Agricultural Residue Burning
CH4
CH4, N20
CH4
N20
CH4, N,0. CO, NO,
Land-Use Change and Forestry
Changes in Forest Carbon Stocks
Changes in Non-Forest Soil Carbon Stocks
C02 (sink)
CO, (sink)
Waste
Landfills
Wastewater Treatment
Human Sewage
Waste Combustion
Waste Sources of Criteria Pollutants
CH4
CH4
N20
N20
CO, NO,, NMVOC
9 In 1997, included HFC-23, HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-227ea, HFC-236fa, HFC-4310mee, C
-------
-------
Annex N
IPCC Reporting Tables
This annex contains a series of tables which summarize the emissions data discussed in the body of this report
for the year 1997. The data in these tables conform with guidelines established by the IPCC
(IPCC/UNEP/OECD/IEA 1997; vol. 1) for consistent international reporting of greenhouse gas emissions
inventories. The format of these tables does not always correspond directly with the calculations discussed in the
body of the report. In these instances, the data have been reorganized to conform to IPCC reporting guidelines.^
As a result, slight differences may exist between the figures presented in the IPCC tables and those in the body of
the report. These differences are merely an artifact of variations in reporting structures; total U.S. emissions are
unaffected.
Title of Inventory
Contact Name
Title
Organisation
Address
Phone
Fax
E-Mail
Is uncertainty addressed?
Related documents filed with IPCC
Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
Wiley Barbour
Senior Analyst
U.S. Environmental Protection Agency
Climate Policy and Programs Division (2175)
401 M Street, SW
Washington, DC 20460
(202) 260-6972
(202) 260-6405
barbour.wiley@epa.gov
Yes
Yes
An additional table has been added (Table 2, sheet 3) that addresses emissions of HFCs and PFCs by individual gas. The standard IPCC
reporting format for these gases is not sufficiently detailed. It was not possible to disaggreggate by gas the emissions of halocarbons and SF6
from certain source categories or portions of source categories. In these cases, aggregate Global Warming Potential weighted emissions are
reported in million metric tons of carbon equivalents (MMTCE).
N-1
-------
TABLE 1 SECTORAL REPORT FOE EHERBY (1997)
(Sheet 1 of 3)
SECTORAL REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(Gg)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
Total Energy
A Fuel Combustion Activities (Reference Approach)
A Fuel Combustion Activities (Sectoral Approach)
1 Energy Industries
a Public Electricity and Heat Production
b Petroleum Refining [a]
c Manufacture of Solid Fuels and Other Energy Industries [a]
2 Manufacturing Industries and Construction
a Iron and Steel
b Non-Ferrous Metals
c Chemicals
d Pulp, Paper and Print
e Food Processing, Beverages and Tobacco
f Other (please specify)
CO,
5,390,398
5,415,400
5,375,164
1,951,908
1,951,908
IE
IE
1,125,447
-
-
-
-
-
NA
CH4
10,025
NE
633
24
24
IE
IE
151
-
-
-
-
-
NA
N,0
256
NE
256
27
27
IE
IE
18
-
-
-
-
-
NA
NO,
20,352
NE
20,248
5,605
5,605
IE
IE
2,967
-
-
-
-
-
NA
CO
65,493
NE
65,163
368
368
IE
IE
1,007
-
-
-
-
-
NA
NMVOC
8,217
NE
7,730
46
46
IE
IE
197
-
-
-
-
-
NA
S0?
17,258
NE
16,909
11,868
11,868
IE
IE
3,053
-
-
-
-
-
NA
[a] Included under "Manufacturing Industries and Construction"
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
si!
N-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
ili
-------
TABLE 1 SECTORAL REPORT FOR ENERGY (1997)
(Sheet 2 of 3)
SECTORAL REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(Gg)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
3 Transport
a Civil Aviation
b Road Transportation
c Railways
d Navigation
e Miscellaneous Non-Highway
Pipeline Transport
4 Other Sectors
a Commercial/Institutional
b Residential
c Agriculture/Forestry/Fishing
5 Other (U.S. Territories)
B Fugitive Emissions from Fuels
1 Solid Fuels
a Coal Mining
b Solid Fuel Transformation
c Other (please specify)
2 Oil and Natural Gas
a Oil
b Natural Gas
c Venting and Flaring
C02
1,634,556
137,569
1,271,038
32,371
56,402
137,175
IE
616,927
238,591
378,335
IE
46,326
15,235
NE
NE
NE
NE
15,235
NE
NE
15,235
CH4
242.4
IE
222.0
IE
IE
20.4
IE
215.2
24.2
191.0
IE
NE
9,391.7
3,274.1
3,274.1
IE
NE
6,117.6
270.7
5,846.9
IE
N20
207.40
IE
197.93
IE
IE
9.47
IE
4.13
0.88
3.25
IE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NO,
10,519
IE
6,382
IE
IE
4,137
IE
1,157
379
779
IE
NE
104
NE
NE
NE
NE
104
-
-
-
CO
60,794
IE
45,593
IE
IE
15,201
IE
2,994
235
2,759
IE
NE
330
NE
NE
NE
NE
330
-
-
-
NMVOC
6,949
IE
4,744
IE
IE
2,205
IE
538
22
515
IE
NE
488
NE
NE
NE
NE
488
-
-
-
S02
1,252
IE
290
IE
IE
962
IE
737
-
-
-
NE
349
NE
NE
NE
NE
349
-
-
-
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-3
-------
TABIM SECTORAL REPO'RTFim ENEB6Y (1997)
(Sheet 3 of 3)
SECTORAL REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(Gg)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
Memo Items [a]
International Bunkers
Aviation
Marine
CO? Emissions from Biomass [b]
C02
97,542
50,974
46,568
216,561
CH4
1.8
1.4
0.4
ai --
N,0
2.76
1.62
1.15
N0t
1,448
202
1,246
CO
111
84
27
NMVOC
46
13
33
SO,
NE
NE
NE
[a] Not included in energy totals.
[b] C02 emission from biomass are estimated from energy production industries, industrial, transportation, residential, and commercial sectors. Estimates of
non-COz emissions are incorporated in sectoral estimates under heading A.1.
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
TABLE 2 SECTORAL REPORT FOR INDUSTRIAL PROCESSES (1997)
(Sheet 1 of 3)
SECTORAL REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(Gg)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
Total Industrial Processes
A Mineral Products
1 Cement Production
2 Lime Production
3 Limestone and Dolomite Use
4 Soda Ash Production and Use
5 Asphalt Roofing
6 Road Paving with Asphalt
7 Other
Glass Production
Concrete Pumice Stone
B Chemical Industry
1 Ammonia Production [b]
2 Nitric Acid Production
3 Adipic Acid Production
4 Carbide Production
5 Petrochemicals
C Metal Production
1 Iron and Steel Production [b]
2 Ferroalloys Production [b]
3 Aluminum Production [b]
4 SF6 Used in Aluminum and Magnesium Foundries
5 Other
C02
65,155
63,926
37,459
14,223
7,810
4,434
NE
NE
NE
NE
NE
IE
26,122
NO
NO
NE
NE
IE
86,080
1,789
5,296
NA
NA
CH4
75.4
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
75.4
NE
NE
NE
0.8
74.6
NE
NE
NE
NE
NA
NA
N20
91.77
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
91.77
NE
45.27
46.49
' NE
NE
NE
NE
NE
NE
NA
NA
NO,
781
IE
IE
IE
IE
IE
IE
IE
IE
IE
IE
151
-
-
-
-
-
93
-
-
-
NA
NA
CO
7,689
IE
IE
IE
IE
IE
IE
IE
IE
IE
IE
1,168
-
-
-
-
-
2,237
-
-
-
NA
NA
NMVOC
2,622
IE
IE
IE
IE
IE
IE
IE
IE
IE
IE
415
-
-
-
-
-
66
-
-
-
NA
NA
S02
1,175
IE
IE
IE
IE
IE
IE
IE
IE
IE
IE
273
-
-
-
-
-
501
-
-
-
NA
NA
HFCs
P
[a]
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
NA
A
[a]
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
NA
PFCs
P
[a]
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
[a]
NE
NE
[a]
NA
NA
A
[a]
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
[a]
NE
NE
[a]
NA
NA
SF,[c]
P
2.723
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
0.460
NE
NE
NE
0.460
NA
A
1.534
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
0.460
NE
NE
NE
0.460
NA
[a] Emissions of HFCs and PFCs are documented by gas in Table 2 Sheet 3.
[b] C02 emissions from ammonia, iron & steel production, ferroallyos production, and aluminum production are included in this table for informational purposes only. These estimates are not included in the
national total, however, in order to prevent double counting. Emissions from these sources are included under non-energy use of fossil fuels in the IPCC Energy Sector.
[c] Totals for actual SF6 exclude emissions from Semiconductor Manufacture, which are provided in Table 2 Sheet 3.
"A" Actual emissions based on Tier 2 Approach.
"P" Potential emissions based on Tier 1 Approach.
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-5
-------
TABLE 2 SECTORAL REPORT FOE INDUSTRIAL PROCESSES (1997)
(Sheet 2 of 3)
SECTORAL REPORT FOR NATION
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
D Other Production
1 Pulp and Paper
2 Food and Drink
3 Carbon Dioxide
E Production of Halocarbons & SFE
1 By-product Emissions
2 Fugitive Emissions
3 Other
F Consumption of Halocarbons & SF6
1 Refrigeration and Air Conditioning Equipment
2 Foam Blowing
3 Fire Extinguishers
4 Aerosols
5 Solvents
6 Electrical Transmission and Distribution
G Other
1 Storage and Transport
2 Other Industrial Processes
3 Miscellaneous
C0?
1,229
NE
NE
1,229
NE
NE
NE
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
CH,
NE
NE
NE
NE
NE
NE
NE
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
M GREENHOUSE GAS INVENTORIES
Gg)
N?0
NE
NE
NE
NE
NE
NE
NE
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NO,
IE
IE
IE
IE
IE
IE
IE
NA
NA
NA
NA
NA
NA
NA
NA
538
6
382
150
CO
IE
IE
IE
IE
IE
IE
IE
NA
NA
NA
NA
NA
NA
NA
NA
4,285
24
601
3,660
NMVOC
IE
IE
IE
IE
IE
IE
IE
NA
NA
NA
NA
NA
NA
NA
NA
2,141
1,249
416
476
SO,
IE
IE
IE
IE
IE
IE
IE
NA
NA
NA
NA
NA
NA
NA
NA
401
2
387
12
HFCs
P
NA
NA
NA
NA
fa]
NA
NE
NA
fal
-
-
-
-
NA
NA
NA
NA
NA
A
NA
NA
NA
NA
fa]
fa]
NE
NA
fal
-
-
-
-
NA
NA
NA
NA
NA
PFCs
P
NA
NA
NA
NA
fa]
NE
NE
NA
fa]
-
-
-
-
NA
NA
NA
NA
NA
A
NA
NA
NA
NA
fa]
NE
NE
NA
fa]
-
-
-
-
NA
NA
NA
NA
NA
SF6
P
NA
NA
NA
NA
NE
NE
NE
NA
2.263
NE
NE
NE
NE
NE
2.263
NA
NA
NA
NA
A
NA
NA
NA
NA
NE
NE
NE
NA
1.074
NE
NE
NE
NE
NE
1.074
NA
NA
NA
NA
[a] Emissions of HFCs and PFCs are documented by gas in Table 2 Sheet 3.
"A" Actual emissions based on Tier 2 Approach.
"P" Potential emissions based on Tier 1 Approach.
Note: Totals may not equal sum ot components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
TABLE 2 SECTORAL REPORT FOR INDUSTRIAL PROCESSES (1997)
(Sheet 3 of 3)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
Total HFCs and PFCs
C 3 Aluminum Production
D 4 Semiconductor Manufacture [a]
E 1 By-Product Emissions (HCFC-22 Production)
F Consumption of Halocarbons & SF6
1 Refrigeration and Air Conditioning Equipment
2 Foam Blowing
3 Fire Extinguishers
4 Aerosols
5 Solvents
Sectoral Report for National Greenhouse Gas Inventories
(MMTCE)
Aggre-
gate
P
NA
NA
NA
NA
25.7
-
-
-
-
-
Aggre-
gate
A
NA
[b]
1.3
[b]
[b,c] 4.0
-
-
-
-
-
(Gg)
HFC-
23
A
2.613
NO
IE
2.570
0.043
-
-
-
-
-
HFC-
125
A
3.572
NO
NO
NO
3.572
-
-
-
-
-
HFC-
134a
A
17.960
NO
NO
NO
17.960
-
-
-
-
•
HFC-
143a
A
0.427
NO
NO
NO
0.427
-
-
-
-
-
HFC-
236fa
A
0.175
NO
NO
NO
0.175
-
-
-
-
-
HFC-
4310mee
A
1.479
NO
NO
NO
1.479
-
-
-
-
-
CF<
A
1.434
1.434
IE
NO
NE
NE
NE
NE
NE
NE
C2F6
A
0.143
0.143
IE
NO
NE
NE
NE
NE
NE
NE
C4F10
A
NE
NE
NO
NO
0.105
-
-
-
-
-
CeFu
A
NE
NE
NO
NO
0.012
-
-
-
-
-
"A" Actual emissions based on Tier 2 Approach.
"P1 Potential emissions based on Tier 1 Approach.
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
[a] Includes gases such as HFC-23, CF4, C2F6, SF6, C3F8, and NF3.
[b] Does not include emissions where estimates for individual gases were available for reporting.
[c] Includes HFC-152a, HFC-227ea, and PFC/PFPEs. PFC/PFPEs are a proxy for many diverse PFCs and perfluoropolyethers (PFPEs) that are employed in solvent
applications. The GWP and atmospheric lifetime of this aggregate category is based upon that of C6F14.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-7
-------
TABLE 3 SECTORAL REPORT FOR SOLVENT AMD OTHER PRODiCT USE (1997)
(Sheet 1 of 1)
StUIUKRL HtrUHl t-UK HAIIUNflL UHt
(Gg)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
Tola) Solvent and Other Product Use
A Paint Application
B Decreasing and Dry Cleaning
C Chemical Products, Manufacture and Processing
Graphic Arts
D Other Industrial
D Nonindustrial
UtrtUUSt tifl
NO,
3
2
0
IE
0
0
sirtvtmun
CO
6
1
1
IE
3
0
ts
NMVOC
5,882
2,713
801
IE
Q7Q
O/O
51
1,943
SO,
1
0
0
IE
0
NA
_
'--"-- " * - -_ _ ^ i". j U"_±:" " -:"'"_ " : '"_. /. __
. . ,
_ _ _. _ . _ . _ _ _ _ _..
ill
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
. i ill
-------
TABLE 4 SECTORAL REPORT FOR AGRICULTURE (1997)
(Sheet 1 of 2)
SECTORAL REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(6g)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
Total Agriculture
A Enteric Fermentation
1 Cattle
2 Buffalo
3 Sheep
4 Goats
5 Camels and Llamas
6 Horses
7 Mules and Asses
8 Swine
9 Poultry
10 Other
B Manure Management
1 Cattle
2 Buffalo
3 Sheep
4 Goats
5 Camels and Llamas
6 Horses
7 Mules and Asses
8 Swine
9 Poultry
CH4
9,448.6
5,962.6
5,691.6
NE
88.0
60.9
NE
11.5
NE
110.7
NE
NA
2,970.5
1,023.0
NE
2.5
0.8
NE
31.3
NE
1,605.2
307.7
N20
913.56
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
35.83
15.40
NE
0.25
0.05
NE
0.61
NE
0.79
18.74
NO,
37
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
CO
843
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NMVOC
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-9
-------
TABLE 4 SECTORAL REPORT FOR ASRICiLTORE (1997)
(Sheet 2 of 2)
SECTORAL REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(GO)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
B Manure Management (cant..)
10 Anaerobic
11 Liquid Systems
12 Solid Storage and Dry Lot
13 Other
C Rice Cultivation
1 Irrigated
2 Rainfed
3 Deep Water
4 Other
D Agricultural Soils
E Prescribed Burning of Savannas
F Field Burning of Agricultural Residues
1 Cereals
2 Pulse
3 Tuber and Root
4 SugarCane
5 Other
G Other
CH<
IE
IE
IE
NA
475.4
475.4
NO
NO
NA
NE
NO
40.1
29.1
10.1
NE
1.0
NA
NA
N,0
IE
IE
IE
NA
NE
NE
NO
NO
NA
876.17
NO
1.56
0.70
0.85
NE
0.02
NA
NA
NO,
NE
NE
NE
NA
NE
NE
NO
NO
NA
NE
NO
37
16
20
NE
0
NA
NA
CO
NE
NE
NE
NA
NE
NE
NO
NO
NA
NE
NO
843
610
212
NE
20
NA
NA
NMVOC
NE
NE
NE
NA
NE
NE
NO
NO
NA
NE
NO
NE
NE
NE
NE
NE
NA
NA
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
TABLE 5 SECTORAL REPORT FOR LAND-USE CHANGE AND FORESTRY (1997)
(Sheet 1 of 1)
SECTORAL REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(Qg)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
Total Land-Use Change and Forestry
A Changes in Forest and Other Woody Biomass Stocks
1 Tropical Forests
2 Temperate Forests
3 Boreal Forests
4 Grasslands/Tundra
5 Other (General Forest Flux)
5 Other (Forest Products Flux)
5 Other (Landfill Carbon)
B Forest and Grassland Conversion
1 Tropical Forests
2 Temperate Forests
3 Boreal Forests
4 Grasslands/Tundra
5 Other
C Abandonment of Managed Lands
1 Tropical Forests
2 Temperate Forests
3 Boreal Forests
4 Grasslands/Tundra
5 Other
D C02 Emissions and Removals from Soil
E Other
C02 Emissions
[a] NA
[a] NA
NE
NA
NA
NE
NA
NA
NA
[a] NE
NE
NE
NE
NE
NA
[a] NE
NE
NE
NE
NE
NA
[a] NE
NA
CO, Removals
[a] -764,683
[a] -764,683
NE
IE
IE
NE
-627,917
-65,523
-71,243
[a] NE
NE
NE
NE
NE
NA
[a] NE
NE
NE
NE
NE
NA
[a] NE
NA
CH4
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
NE
NE
NE
NE
NE
NA
NE
NA
N20
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
NE
NE
NE
NE
NE
NA
NE
NA
NO,
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
NE
NE
NE
NE
NE
NA
NE
NA
CO
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NE
NA
NE
NE
NE
NE
NE
NA
NE
NA
[a] Please do not provide an estimate of both C02 emissions and C02 removals. You should estimate "net" emissions of C02 and place a single number in either the C02 emissions
or C02 removals column, as appropriate. Please note that for the purposes of reporting, the signs for uptake are always (-) and for emissions (+).
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-11
-------
TABLE 6 SECTORAL REPORT FOR WASTE (1997]
(Sheet 1 of t)
SECTORAL REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(Gfl)
GREENHOUSE GAS SOURCE AND SINK CATEGORIES
Tola! Waste
A Solid Waste Disposal on Land
1 Managed Waste Disposal on Land
2 Unmanaged Waste Disposal Sites
3 Other
B Wastewaler Handling
1 Industrial Wastewater
2 Domestic and Commercial Wastewater
3 Other
C Waste Incineration
D Other
Transport, Storage, and Disposal Facility
Other Waste
Human sewage
COJa]
IE
IE
IE
NE
NA
NE
NE
NE
NA
IE
NE
NE
NE
NE
CH4
11,807.7
11,646.4
11,646.4
NE
NA
161.3
NE
161.3
NA
NE
NE
NE
NE
IE
N,0
28.19
NE
NE
NE
NA
[b]
NE
[b]
NA
0.83
27.36
NE
NE
27.36
NO,
94
1
1
NE
NA
0
0
0
NA
92
1
0
1
NE
CO
1,127
2
2
NE
NA
0
0
0
NA
1,124
1
0
1
NE
NMVOC
407
21
21
NE
NA
61
12
49
NA
246
79
43
36
NE
SO,
45
0
0
NE
NA
1
0
0
NA
44
0
0
0
NE
[a] Note that C02 from waste disposal and incineration should only be included if it stems from non-biological or inorganic waste sources.
[b] Emissions from the human sewage portion of this source category is included under section D.
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-12 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
TABLE 7A SUMMARY REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES (1997)
(Sheet 1 of 3)
SUMMARY REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(Gg)
GREENHOUSE GAS SOURCE AND SINK
CATEGORIES
Total National Emissions and Removals
1 Energy
A Fuel Combustion (Sectoral Approach)
1 Energy Industries
2 Manufacturing Industries & Construction
3 Transport
4 Other Sectors
5 Other (U.S. Territories)
B Fugitive Emissions from Fuels
1 Solid Fuels
2 Oil and Natural Gas
2 Industrial Processes
A Mineral Products
B Chemical Industry
C Metal Production
D Other Production
E Production of Halocarbons and SF6
F Consumption of Halocarbons and SF6
G Storage/Other/Miscellaneous
C02
Emissions
5,455,553
5,390,398
5,375,164
1,951,908
1,125,447
1,634,556
616,927
46,326
15,235
NE
15,235
65,155
63,926
IE
IE
1,229
NE
NA
NA
CO.,
Removals
-764,683
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
CH4
31,356.8
10,025.1
633.4
24.4
151.4
242.4
215.2
NE
9,391.7
3,274.1
6,117.6
75.4
NE
75.4
NE
NE
NE
NA
NA
N20
1,289.77
256.24
256.24
26.79
17.92
207.40
4.13
NE
91.77
NE
91.77
NE
NE
NE
NA
NA
NOX
21,267
20,352
20,248
5,605
2,967
10,519
1,157
NE
104
104
781
IE
151
93
IE
IE
NA
538
CO
75,158
65,493
65,163
368
1,007
60,794
2,994
NE
330
330
7,689
IE
1,168
2,237
IE
IE
NA
4,285
NMVOC
17,129
8,217
7,730
46
197
6,949
538
NE
488
488
2,622
IE
415
66
IE
IE
NA
2,141
S02
18,478
17,258
16,909
11,868
3,053
1,252
737
NE
349
349
1,175
IE
273
501
IE
IE
NA
401
MFCs
P
[a]
> > i
>,
^
X
- '
i y
„
^
rai
NE
NE
NE
NA
fa]
fa]
NA
A
fa]
V
v«r
> \
* ;
*&
XN
*U ;
V, *
\
fai
NE
NE
NE
NA
fa]
fa]
NA
PFCs
P
fa]
-"*«
>s ^
x* '
. * x •
s^>v
>>
fal
NE
NE
fal
NA
NE
fa]
NA
A
fa]
UJ '
«%*
X
V. ^
\. t
% "\
-;< ^
... t;
fai
NE
NE
fa]
NA
NE
fal
NA
SF6
P
2.723
\ ^ i
V> '
« n
* ^
v\.
\;
;•" •»*
i1*
\l
* ^
2.723
NE
NE
0.460
NA
NE
2.263
NA
A
1.534
ij * )
t r
i^<
,'v/i
v "* ^
•''
^ *
•5^1
1.534
NE
NE
0.460
NA
NE
1.074
NA
[a] Emissions of HFCs and PFCs are documented by gas in Table 2 Sheet 3.
"A" Actual emissions based on Tier 2 Approach.
"P" Potential emissions based on Tier 1 Approach.
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-13
-------
TABIE 7A S1MIAIY REPORT FOR NOTIONAL BREENHOtSE BAS INVEUTORIES (1997)
(Sheet 2 of 3]
SUMMARY REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(Gg)
GREENHOUSE GAS SOURCE AND SINK
CATEGORIES
3 Solvent and Other Product Use
4 Agriculture
A Enteric Fermentation
B Manure Management
C Rice Cultivation
D Agricultural Soils
E Prescribed Burning of Savannas
F Field Burning of Agricultural Residues
G Other
5 Land-Use Change & Forestry
A Changes in Forest and Other Woody Biomass Stocks
B Forest and Grassland Conversion
C Abandonment of Managed Lands
D C02 Emissions and Removals from Soil
E Other
6 Waste
A Solid Waste Disposal on Land
B Wastewater Handling
C Waste Incineration
D Other
7 Other
C02
Emissions
NE
NE
NE
NE
NE
[a] NE
NO
NE
NA
[a] NA
[a] NA
[a] NE
[a] NE
[a] NE
. NA
IE
IE
NE
IE
NE
NA
COZ
Removals
NE
NE
NE
NE
NE
[a] NE
NO
NE
NA
[a] -764,683
[a] -764,683
[a] NE
[a] NE
[a] NE
NA
IE
IE
NE
NE
NE
NA
CH4
NE
9,448.6
5,962.6
2,970.5
475.4
NE
NO
40.1
NA
NE
NE
NE
NE
NE
NA
11,807.7
11,646.4
161.3
NE
NE
NA
N20
NE
913.56
NE
35.83
NE
876.17
NO
1.56
NA
NE
NE
NE
NE
NE
NA
28.19
NE
[b]
0.83
27.36
NA
HO,
3
37
NE
NE
NE
NE
NO
37
NA
NE
NE
NE
NE
NE
NA
94
1
0
92
1
NA
CO
6
843
NE
NE
NE
NE
NO
843
NA
NE
NE
NE
NE
NE
NA
1,127
2
0
1,124
1
NA
NMVOC
5,882
NE
NE
NE
NE
NE
NO
NE
NA
NE
NE
NE
NE
NE
NE
407
21
61
246
79
NA
SOj
1
NE
NE
NE
NE
NE
NO
NE
NA
NE
NE
NE
NE
NE
NE
45
0
1
44
0
NA
MFCs
P
,i|.:
A
.
PFCs
P
A
l-
SF,
P
"?•-:
A
IF
; f
[a] Please do not provide an estimate of both C02 emissions and C02 removals. You should estimate "net" emissions of C02 and place a single number in either the C02 emissions
or C02 removals column, as appropriate. Please note that for the purposes of reporting, the signs for uptake are always (-) and for emissions (+).
[b] Emissions from the human sewage portion of this source category is included under section 6.D.
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
Ml
I!
-------
TABLE 7A SUMMARY REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES (1997)
(Sheet 3 of 3)
SUMMARY REPORT FOR NATIONAL GREENHOUSE GAS INVENTORIES
(Gg)
GREENHOUSE GAS SOURCE AND SINK
CATEGORIES
»
Memo Items [a]
International Bunkers
Aviation
Marine
C02 Emissions from Biomass
C02
Emissions
97,542
50,974
46,568
216,561
C02
Removals
NE
NE
NE
SfiT!"!fS%';
CH4
1.8
1.4
0.4
:?;;;'":';".
NZ0
2.76
1.62
1.15
_ >v..v ;!,.,;*;
NO,
1,448
202
1,246
'iwtn
CO
111
84
27
L'Hifey
NMVOC
46
13
33
'?,'•;«? '" ~'
SOZ
NE
NE
NE
'• "• -..*<*,}
HFCs
P
®!K}
te-.i'v
*v/.
^;r "
*~>i
:4TC
A
•sT
^'5 'J
£>•?.;'
•&&s
M'i
PFCs
P
rf^
•M
s? \
, ,
"
A
$0-$
Sr-f
$>i
4\^
SF6
P
!§•••
_;-?" ^
1
A
Sl
&aFS
«•,*;.!
," ',>
[a] Not included in totals.
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-15
-------
T1BIE 7B sWOif SUMMARY RIPMT FOR NATIOfAt GBEERHOOSE 6AS litENTOftJlS (1997)
SHORT SUMMARY REPORT FOB NATIONAL GREENHOUSE GAS INVENTORIES
(Gg)
GREENHOUSE GAS SOURCE AND SINK
CATEGORIES
Total National Emissions and Removals
1 Energy
Reference Approach [b]
Sectoral Approach [b]
A Fuel Combustion
8 Fugitive Emissions from Fuels
2 Industrial Processes
3 Solvent and Other Product Use
4 Agriculture
5 Land-Use Change
6 Waste
& Forestry
7 Other
Memo Items:
International Bunkers
Aviation
Marine
C02 Emissions from Biomass
C02
Emissions
5,455,553
5,415,400
5,390,398
5,375,164
15,235
65,155
NE
NE
[c] NA
IE
NA
97,542
50,974
46,568
216,561
COZ
Removals
-764,683
NA
NA
NA
NA
NE
NE
[c] -764,683
IE
NA
NE
NE
NE
CH<
31,356.8
10,025.1
633.4
9,391.7
75.4
NE
9,448.6
NE
11,807.7
NA
1.8
1.4
0.4
"- "*" * -
N20
1,289.77
256.24
256.24
91.77
NE
913.56
NE
28.19
NA
2.76
1.62
1.15
NO,
21,267
20,352
20,248
104
781
3
37
NE
94
NA
1,448
202
1,246
CO
75,158
65,493
65,163
330
7,689
6
843
NE
1,127
NA
111
84
27
NMVOC
17,129
8,217
7,730
488
2,622
5,882
NE
NE
407
NA
46
13
33
-•-•-- "•>-'-?-
S02
18,478
17,258
16,909
349
1,175
1
NE
NE
45
NA
NE
NE
NE
HFCs
P
M
l«l
•
A
W
~f :
M
.' :*
* "
PFCs
P
[a|
w-
_f -™ _-=tf
W
-'--
":-, -
:_.- -'-••
A
W
£V*
• _---vx
W
--*
--_ _ \
y
:.'^V
'.-'-•
SFS
P
2.723
_** : i: . '
~^"t
:: V -" r
2.723
! V?
" .4ii»-
~*rf* -~1^K-~
: • -'-•
*!™vKJ'
r V::~.; '=MT
A
1.534
WE*
= ^ =-- -=
—i*:1;^
1.534
;y*-
--_.-;- -'-
~~~.'-.
-i*f^^-*
--^ftfq^=-"
,:_>:,:. si.
-*.- • - -
-1
[a] Emissions of HFCs and PFCs are documented by gas in Table 2 Sheet 3.
[b] For verification purposes, countries are asked to report the results of their calculations using the Reference Approach and explain any differences with the Sectoral Approach. Do not include the results
of both the Reference Approach and the Sectoral Approach in national totals.
[c] Please do not provide an estimate of both C02 emissions and C02 removals. You should estimate "net" emissions of C02 and place a single number in either the C02 emissions
or C02 removals column, as appropriate. Please note that for the purposes of reporting, the signs for uptake are always (-} and for emissions (+).
Note: Totals may not equal sum of components due to independent rounding.
- Value is included in an aggregate figure, but not estimated separately.
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
N-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
TABLE 8A OVERVIEW TABLE FOR NATIONAL GREENHOUSE GAS INVENTORIES (1997)
(Sheet 1 of 6)
OVERVIEW TABLE
GREENHOUSE GAS SOURCE
AND SINK CATEGORIES
Total National Emissions
and Removals
1 Energy
A
C02
Estimate
Quality
CH4
Estimate
Quality
N20
Estimate
Quality
NOX
Estimate
Quality
CO
Estimate
Quality
NMVOC
Estimate
Quality
S02
Estimate
Quality
Fuel Combustion Activities
Reference Approach
Sectoral Approach
1 Energy Industries
2 Manufacturing Industries
& Construction
3 Transport
4 Other Sectors
5 Other (U.S. Territories)
B
Fugitive Emissions from Fuels
1 Solid Fuels
2 Oil and Natural Gas
2 Industrial Processes
A
B
C
U
b
Mineral Products
Chemical Industry
Metal Production
Other Production
Production of Halocarbons & SF6
ALL
ALL
ALL
ALL
ALL
ALL
ALL
NE
PART [a]
ALL
ALL
IE
NA
NO
H
H
H
H
H
H
M
M
H
M
I "'
ALL
ALL
ALL
ALL
ALL
NE
PART [b]
ALL
NE
PART [c
NE
NA
NO
k
M
M
M
M
L
M
L
M
'. ^
ALL
ALL
ALL
PART
ALL
NE
NE
NE
NE
ALL
NE
NA
NO
L
L
L
L
L
H
'' N i
ALL
ALL
ALL
ALL
ALL
NE
NE
ALL
IE
ALL
ALL
IE
IE
•* < 4
M
M
M
H
M
M
M
M
/ *•
ALL
ALL
ALL
ALL
ALL
NE
NE
ALL
IE
ALL
ALL
IE
IE
M
M
M
H
M
M
M
M
N> 1 *
ALL
ALL
ALL
ALL
ALL
NE
NE
ALL
IE
ALL
ALL
IE
IE
> V-
L
L
L
L
L
L
M
M
>
ALL
ALL
ALL
ALL
IE
NE
NE
ALL
IE
ALL
ALL
IE
IE
^
M
M
M
M
M
M
M
Quality:
H = High Confidence in Estimation
M = Medium Confidence in Estimation
L = Low Confidence in Estimation
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
PART (Partly estimated)
ALL (Full estimate of all possible sources)
[a] Estimate excludes geologic carbon dioxide deposits released during petroleum and natural gas production.
[b] Does not include abandoned coal mines.
[c] Not all potential sources were included. See sources excluded annex.
[d] Only HCFC-22 production included.
Disaggregation:
1 = Total emissions estimated
2 = Sectoral split
3 = Subsectoral split
Documentation:
H = High (all background information included)
M = Medium (some background information included)
L = Low. (only emission estimates included)
N-17
-------
TABtfSA OfEKVlEWTABLE FOR MAttOlAl GREEIBQOSE GAS IIVEMTORlES
(Sheet 2 of 6)
Quality:
H = High Confidence in Estimation
M = Medium Confidence in Estimation
L = Low Confidence in Estimation
OVERVIEW TABLE
GREENHOUSE GAS SOURCE
AND SINK CATEGORIES
Total National Emissions
and Removals
MFCs
Estimate
1 Energy
A
Qusftty
PFCS
Estimate
Dually
SF,
Estimate
Dually
Documen-
tation
galion
Fuel Combustion Activities
Reference Approach
Sectoral Approach
1 Energy Industries
2 Manufacturing Industries
& Construction
3 Transport
4 Other Sectors
5 Other (U.S. Territories)
B
Fugitive Emissions from Fuels
1 Solid Fuels
2 Oil and Natural Gas
2 Industrial Processes
A
B
C
D
E
Mineral Products
Chemical Industry
Metal Production
Other Production
Production of Halocarbons & SF6
i i
NO
NO
NO
NO
NO
NO
NO
NO
NE
NE
NE
NA
PART [d]
H
NO
NO
NO
NO
NO
NO
NO
NO
NE
NE
ALL
NA
NE
H
NO
NO
NO
NO
NO
NO
NO
NO
NE
NE
ALL
NA
NE
M
H
H
H
H
H
H
H
H
H
H
H
M
M
1
3
1
1
2
1
1
3
3
V,
f]
3
2
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
PART (Partly estimated)
ALL (Full estimate of all possible sources)
[a] Estimate excludes geologic carbon dioxide deposits released during petroleum and natural gas production.
[b] Does not include abandoned coal mines.
[c] Not all potential sources were included. See sources excluded annex.
[d] Only HCFC-22 production included.
Disaggregate:
1 = Total emissions estimated
2 = Sectoral split
3 = Subsectoral split
Documentation;
H = High (all background information included)
M = Medium (some background information included)
L = Low (only emission estimates included)
N-18 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
TABLE 8A OVERVIEW TABLE FOR NATIONAL GREENHOUSE GAS INVENTORIES (1997)
(Sheet 3 of 6)
OVERVIEW TABLE
GREENHOUSE GAS SOURCE
AND SINK CATEGORIES
C02
Estimate
Quality
CH4
Estimate | Quality
N20
Estimate
Quality
NOX
Estimate | Quality
CO
Estimate
Quality
NMVOC
Estimate
Quality
S02
Estimate
Quality
Industrial Processes (cont...)
F
Q
Consumption of Halocarbons & SF6
Potential [a]
Actual [b]
Storage/Other/Miscellaneous
3 Solvent and Other
Product Use
4 Agriculture
A
B
C
D
E
F
G
Enteric Fermentation
Manure Management
Rice Cultivation
Agricultural Soils
Prescribed Burning of
Savannas
Field Burning of
Agricultural Residues
Other
5 Land-Use Change &
Forestry
A
B
Changes in Forest and
Other Woody Biomass Stocks
Forest and Grassland
Conversion
NA
NA
NA
NE
NE
NE
NE
NE
NO
NE
NA
PART [c]
NE
M
NA
NA
NA
NE
ALL
ALL
ALL
NE
NO
ALL
NA
NE
NE
M
M
L
L
NA
NA
NA
NE
NE
ALL
NE
ALL
NO
ALL
NA
NE
NE
L
L
L
NA
NA
ALL
ALL
NE
NE
NE
NE
NO
ALL
NA
NE
NE
M
M
L
NA
NA
ALL
ALL
NE
NE
NE
NE
NO
ALL
NA
NE
NE
M
M
L
NA
NA
ALL
ALL
NE
NE
NE
NE
NO
NE
NA
NE
NE
L
M
NA
NA
ALL
ALL
NE
NE
NE
NE
NO
NE
NA
NE
NE
M
M
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
PART (Partly estimated)
ALL (Full estimate of all possible sources)
[a] Potential emissions based on Tier 1 Approach.
[b] Actual emissions based on Tier 2 Approach.
[c] Estimate does not include Alaska, Hawaii, or U.S. Territories.
Quality:
H = High Confidence in Estimation
M = Medium Confidence in Estimation
L = Low Confidence in Estimation
Disaggregation:
1 = Total emissions estimated
2 = Sectoral split
3 = Subsectoral split
Documentation:
H = High (all background information included)
M = Medium (some background information included)
L = Low (only emission estimates included)
N-19
-------
TABLE 8A OVERVIEW TABLE FOR NATIOMAL GiREEiHOtSE 6AS lltfEHTORJES (1997)
(Sheet 4 of 6)
OVERVIEW TABLE
GREENHOUSE GAS SOURCE
AND SINK CATEGORIES
MFCs
Estimate
duty
PFCs
Estimate | Dually
SF»
Estimate
QuaMy
Documen-
tation
Disaggre-
gate
Industrial Processes (coot.)
F Consumption of Halocarbons & SF6
Potential [a]
Actual [b]
6 Storage/Otrter/Misceilaneous
3 Solvent and Other
Product Use
4 Agriculture
A Enteric Fermentation
B Manure Management
C Rice Cultivation
D Agricultural Soils
E Prescribed Burning of
Savannas
F Field Burning of
Agricultural Residues
G Other
5 Land-Use Change &
Forestry
A Changes in Forest and
Other Woody Biomass Stocks
B Forest and Grassland
Conversion
ALL
ALL
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
M
M
ALL
ALL
NA
NA
NA
NA
NA
NA
NA
NO
NA
NA
NA
M
M
ALL
ALL
NA
NA
NA
NA
NA
NA
NA
NO
NA
NA
NA
M
M
M
M
M
M
H
H
H
H
H
M
2
2
2
3
3
3
3
3
3
2
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
PART (Partly estimated)
ALL (Full estimate of all possible sources)
[a] Potential emissions based on Tier 1 Approach.
' [bj Actual emissions based on Tier 2 Approach.
[c] Estimate does not include Alaska, Hawaii, or U.S. Territories.
Quality:
H = High Confidence in Estimation
M = Medium Confidence in Estimation
L = Low Confidence in Estimation
Disaggregation:
1 = Total emissions estimated
2 = Sectoral split
3 = Subsectoral split
Documentation:
H = High (all background information included)
M = Medium (some background information included)
L = Low (only emission estimates included)
N-20 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
TABLE 8A OVERVIEW TABLE FOR NATIONAL GREENHOUSE GAS INVENTORIES (1997)
(Sheet 5 of 6)
OVERVIEW TABLE
GREENHOUSE GAS SOURCE
AND SINK CATEGORIES
5 Land-Use Change &
Forestry (cont....)
C Abandonment of
Managed Lands
D C02 Emissions and
Removals from Soil
E Other
6 Waste
A Solid Waste Disposal on Land
B Wastewater Handling
C Waste Incineration
D Other
7 Other
Memo Items:
International Bunkers
Aviation
Marine
COZ Emissions from Biomass
C02
Estimate
NE
PART
f«l
NA
IE
NE
IE
NE
NA
ALL
ALL
ALL
Quality
L
M
M
M
CH<
Estimate
NE
NE
NA
ALL
PART [b]
NE
NE
NA
NE
NE
••
Quality
M
L
V \^
'V .»
N20
Estimate
NE
NE
NA
NE
PART [c]
ALL
ALL
NA
NE
NE
" * »
Quality
L
L
L
js?;."
NO,
Estimate
NE
NE
NA
ALL
ALL
ALL
ALL
NA
IE
IE
- Vi:W
*!' "->,i'S- %%'
Quality
L
L
L
L
rasro
CO
Estimate
NE
NE
NA
ALL
ALL
ALL
ALL
NA
IE
IE
fP ii';:^
Quality
L
L
L
L
c5fe:^
NMVOC
Estimate
NE
NE
NA
ALL
ALL
ALL
ALL
NA
IE
IE
*"• ^M
Quality
L
L
L
L
::- &*•'
S02
Estimate
NE
NE
NA
ALL
ALL
ALL
ALL
NA
IE
IE
" "• '^
Quality
L
L
L
L
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
PART (Partly estimated)
ALL (Full estimate of all possible sources)
[a] Non-forest soils are not included in this estimate.
[b] Estimate does not include emissions from industrial wastewater.
[c] Includes emissions from human sewage only
Quality:
H = High Confidence in Estimation
M = Medium Confidence in. Estimation
L = Low Confidence in Estimation
Disaggregation:
1 = Total emissions estimated
2 = Sectoral split
3 = Subsectoral split
Documentation:
H = High (all background information included)
M = Medium (some background information included)
L = Low (only emission estimates included)
N-21
-------
TABLE 8A OVEIVIEW TABLE FOR NATIONAL GIEENHOISE GAS INVENTORIES (1997)
(Sheet 6 of 6)
OVERVIEW TABLE
GREENHOUSE GAS SOURCE
AND SINK CATEGORIES
5 Land-Use Change &
Forestry (cont...)
C Abandonment of
Managed Lands
D C02 Emissions and
Removals from Soil
• E Other
6 Waste
A Solid Waste Disposal on Land
B Wastewater Handling
C Waste Incineration
D Other
7 Other
Memo Items:
International Bunkers
Aviation
Marine
C02 Emissions from Biomass
HFCs
Estimate
NA
NA
NA
NO
NO
NO
NO
NA
NO
NO
: ' ;
Quay
PFCs
Estimate
NA
NA
NA
NO
NO
NO
NO
NA
NO
NO
Dually
SF8
Estimate
NA
NA
NA
NO
NO
NO
NO
NA
NO
NO
Quay
Documen-
tation
H
H
H
H
H
H
H
H
Disaggre-
gate
2
2
2
1
1
1
1
2
"0" (Estimate for source is insignificant or close to zero)
NA (Not applicable to source category)
NE (Not estimated)
NO (Not occurring in the United States)
IE (Estimated but included elsewhere)
PART (Partly estimated)
ALL (Full estimate of all possible sources)
[a] Non-forest soils are not included in this estimate.
[b] Estimate does not include emissions from industrial wastewater.
[c] Includes emissions from human sewage only
Quality:
H = High Confidence in Estimation
M = Medium Confidence in Estimation
L = Low Confidence in Estimation
Disaggregate
1 = Total emissions estimated
2 = Sectoral split
3 = Subsectoral split
Documentation:
H = High (all background information included)
M = Medium (some background information included)
L = Low (only emission estimates included)
N-22 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Annex O
IPCC Reference Approach for Estimating C02 Emissions from Fossil Fuel
Combustion
It is possible to estimate carbon emissions from fossil fuel consumption using alternative methodologies and
different data sources than those described in Annex A. For example, the IPCC requires countries in addition to their
"bottom-up" sectoral methodology to complete a "top-down" Reference Approach for estimating carbon dioxide
emissions from fossil fuel combustion. Section 1.3 ofthe Revised 1996 IPCCGuidelines for National Greenhouse Gas
Inventories: Reporting Instructions states, "If a detailed, Sectoral Approach for energy has been used for the estimation
of CO2 from fuel combustion you are still asked to complete...the Reference Approach...for verification purposes"
(IPCC/UNEP/OECD/IEA 1997). This reference method 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. The basic principle is 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. The following discussion provides the detailed calculations for estimating CO2
emissions from fossil fuel combustion from the United States using the IPCC-recommended Reference Approach.
Step 1: Collect and Assemble Data in Proper Format
To ensure the comparability of national inventories, the IPCC has recommended that countries report energy data
using the International Energy Agency (IEA) reporting convention. National energy statistics were collected in physical
units from several DOE/EIA documents in order to obtain the necessary data on production, imports, exports, and stock
changes.17 These data are presented in Table O-l.
The carbon content of fuel varies with the fuel's heat content. Therefore, for an accurate estimation of CO2
emissions, fuel statistics should be provided on an energy content basis (e.g., BTU's or joules). Because detailed fuel
production statistics are typically provided in physical units (as in Table O-l), they were converted to units of energy
before carbon emissions were calculated. Fuel statistics were converted to their energy equivalents by using conversion
factors provided by DOE/EIA. These factors and their data sources are displayed in Table O-2. The resulting fuel data
are provided in Table O-3.
Step 2: Estimate Apparent Fuel Consumption
The next step of the IPCC Reference Approach is to estimate "apparent consumption" of fuels within the country.
This requires a balance of primary fuels produced, plus imports, minus exports, and adjusting for stock changes. In this
way, carbon enters an economy through energy production and imports (and decreases in fuel stocks) and is transferred
out of the country through exports (and increases in fuel stocks). Thus, apparent consumption of primary fuels
(including crude oil, natural gas liquids, anthracite, bituminous, subbituminous and lignite coal, and natural gas) can
be calculated as follows:
Production + Imports - Exports - Stock Change
17 For the United States, national aggregate energy statistics typically exclude data on the U.S. territories. As a result, national statistics were
adjusted to include U.S. territories data. The territories include Puerto Rico, U.S. Virgin Islands, Guam, American Samoa, Wake Island, and
U.S. Pacific Islands. Consumption data were used for the territories because they are thought to be more reliable than production, import,
export, and stock change data.
0-1
-------
Flows of secondary fuels (e.g., gasoline, residual fuel, coke) should be added to primary apparent consumption.
The production of secondary fuels, however, should be ignored in the calculations of apparent consumption since the
carbon contained in these fuels is already accounted for in the supply of primary fuels from which they were derived
(e.g., the estimate for apparent consumption of crude oil already contains the carbon from which gasoline would be
refined). Flows of secondary fuels should therefore be calculated as follows:
I ;'• ; ii ' t
|j :" ' Imports - Exports - Stock Change
| ' j j '1,1 • '•; )• ,.
frlote that this calculation can result in negative numbers for apparent consumption. This is a perfectly acceptable
result since it merely indicates a net export or stock increase in the country of that fuel when domestic production is not
considered.
TJie IPCC Reference Approach calls for estimating apparent fuel consumption before converting to a common
energy link. However, certain primary fuels in the United States (e.g., natural gas and steam coal) have separate
conversion factors for production, imports, exports, and stock changes. In these cases, it is not appropriate to multiply
apparent consumption by a single conversion factor since each of its components have different heat contents.
Therefore, United States fuel statistics were converted to their heat equivalents before estimating apparent consumption.
The energy value of bunker fuels used for international transport activities was subtracted before computing energy
totals.1* Results are provided in Table O-3.
I
Step 3: Estimate Carbon Emissions
ii1:,,;, ' i1'1 si1 i1" I
Once apparent consumption is estimated, the remaining calculations are virtually identical to those for the
"bottom-up" Sectoral Approach (see Annex A). That is:
• Potential carbon emissions were estimated using fuel-specific carbon coefficients (see Table O-4).19
* The carbon sequestered in non-energy uses of fossil fuels (e.g., plastics or asphalt) was then estimated and
subtracted from the total amount of carbon (see Table O-5).
• Finally, to obtain actual carbon emissions, net carbon emissions were adjusted for any carbon that
remained unoxidized as a result of incomplete combustion (e.g., carbon contained in ash or soot).20
IT"
Step 4: Convert to CO, Emissions
I'"r •(•' .-'••" r.ti i!!: • • '<• •„ " • F
Because the IPCC reporting guidelines recommend that countries report greenhouse gas emissions on a full
molecular weight basis, the final step in estimating CO2 emissions from fossil fuel consumption was converting from
units ojf carbon to units of CO2. Actual carbon emissions were multiplied by the molecular-to-atomic weight ratio of
C0a to carbon (44/12) to obtain total carbon dioxide emitted from fossil fuel combustion in teragrams (Tg). The results
are contained in Table O-6,
Bunker fueU refer to quantities of fuels used for international transportation. The IPCC methodology accounts for these fuels as part of the
energy balance of the country in which they were delivered to end-users. Carbon dioxide emissions from the combustion of these fuels were
'csttnuKcfl separately and were not included in U.S. national totals. This is done to ensure that all fuel is accounted for in the methodology and so
thai the IPCC Is able to prepare global emission estimates.
" Carbon coefficients from EIA were used wherever possible. Because EIA did not provide coefficients for coal, the IPCC-recommended
emission" factors were used in the top-down calculations for these fuels. See notes in Table O-4 for more specific source information.
For the portion of carbon that is unoxidized during coal combustion, the EPCC suggests a global average value of 2 percent. However,
Because combustion technologies in the United States are more efficient, the United States inventory uses 1 percent in its calculations for
petroleum and coal and 0.5 percent for natural gas. ,
!,;" • ' i'1 :i • ' • ' ,' ' ]'
0-2 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Comparison Between Sectoral and Reference Approaches
These two alternative approaches can both produce reliable estimates that are comparable within a few percent.
The major difference between methodologies employed by each approach lies in the energy data used to derive carbon
emissions (i.e., the actual reported consumption for the Sectoral Approach versus apparent consumption derived for the
Reference Approach). In theory, both approaches should yield identical results. In practice, however, slight
discrepancies occur. For the United States, these differences are discussed below.
Differences in Total Amount of Energy Consumed
Table O-7 and Table O-921 summarize the differences between the Reference and Sectoral approaches in
estimating total energy consumption in the United States. Although theoretically the two methods should arrive at the
same estimate for U.S. energy consumption, the Reference Approach provides an energy total that is 0.4 percent lower
than the Sectoral Approach for 1997. The greatest difference lies in the higher estimate of petroleum consumption with
the Sectoral Approach (1.0 percent).
There are several potential sources for the discrepancies in consumption estimates:
• Product Definitions. The fuel categories in the Reference Approach are different from those used in the
Sectoral Approach, particularly for petroleum. For example, the Reference Approach estimates apparent
consumption for crude oil. Crude oil is not typically consumed directly, but refined into other products.
As a result, the United States does not focus on estimating the energy content of crude oil, but rather
estimating the energy content of the various products resulting from crude oil refining. The United States
does not believe that estimating apparent consumption for crude oil, and the resulting energy content of the
crude oil, is the most reliable method for the United States to estimate its energy consumption. Other
differences in product definitions include using sector-specific coal statistics in the Sectoral Approach (i.e.,
residential, commercial, industrial coking, industrial other, and transportation coal), while the Reference
Approach characterizes coal by rank (i.e. anthracite, bituminous, etc.). Also, the liquefied petroleum gas
(LPG) statistics used in the bottom-up calculations are actually a composite category composed of natural
gas liquids (NGL) and LPG.
• Heat Equivalents. It can be difficult to obtain heat equivalents for certain fuel types, particularly for
categories such as "crude oil" where the key statistics are derived from thousands of producers in the
United States and abroad. For heat equivalents by coal rank, it was necessary to refer back to EIA's State
Energy Data Report 1992 (1994) because this information is no longer published.
• Possible inconsistencies in U.S. Energy Data. The United States has not focused its energy data collection
efforts on obtaining the type of aggregated information used in the Reference Approach. Rather, the
United States believes that its emphasis on collection of detailed energy consumption data is a more
accurate methodology for the United States to obtain reliable energy data. Therefore, top-down statistics
used in the Reference Approach may not be as accurately collected as bottom-up statistics applied to the
Sectoral Approach.
• Balancing Item. The Reference Approach uses apparent consumption estimates while the Sectoral
Approach uses reported consumption estimates. While these numbers should be equal, there always seems
to be a slight difference that is often accounted for in energy statistics as a "balancing item."
Differences in Estimated C02 Emissions
Given these differences in energy consumption data, the next step for each methodology involved estimating
emissions of CO2. Table O-8 summarizes the differences between the two methods in estimated carbon emissions for
1997. Although complete data and calculations are not presented, comparison tables are also presented for 1996
emissions in Table O-10.
Although complete energy consumption data and calculations are not presented, comparison tables are also presented for 1996.
0-3
-------
1
AS shown previously, the Sectoral Approach resulted in a 0.4 percent higher estimate of energy consumption in
the United States than the Reference Approach, but the resulting emissions estimate for the Reference Approach is 0.8
percent higher. While both methods' estimates of natural gas emissions are almost exactly the same, coal and petroleum
emission estimates from the Reference Approach are higher than the Sectoral Approach. Potential reasons for these
patterns may include:
« "", Product Definitions. Coal data is aggregated differently in each methodology, as noted above, with United
! States coal cjsta typically collected in the format used for the Sectoral Approach. This results in more
: accurate estimates than in the Reference Approach. Also, the Reference Approach relies on a "crude oil"
: category for determining petroleum-related emissions. Given the many sources of crude oil in the United
- States, it is not an easy matter to track potential differences in carbon content between different sources of
Crude, particularly' since information on the carbon content of crude oil is not regularly collected.
1 Carbon Coefficients. The Reference Approach relies on several default carbon coefficients provided by
IPCC (iPCCTtlNEP/OECD/IEA 1907), while the Sectoral Approach uses category-specific coefficients
• that are likely to be more accurate. Also, as noted above, the carbon coefficient for crude oil is not an easy
I! value to obtain given the many sources and grades of crude oil consumed in the United States.
;;;• ;;" ; ;'| ;• _ •!, • ^ '; '' • •]••
Although the two approaches produce similar results, the United States believes that the "bottom-up" Sectoral
Approach provides a more accurate assessment of CO2 emissions at the fuel level. This improvement in accuracy is
largely a result of the data collection techniques used in the United States, where there has been more emphasis on
^btainiiig the detailed products-based information used in the Sectoral Approach than obtaining the aggregated energy
'flow data used in the Reference Approach. The United States believes that it is valuable to understand both methods.
Ik1', ' !ii lll:il' '' ' „ " ' ii : ''
References
• i i, : . '.:.",,! • > . , i •. ,
EIA (1998a) Annual Energy Review 1997, DOE/EIA- 0384(97)-annual, Energy Information Administration, U.S.
Department of Energy, Washington, DC.
EJA (199Sb) Coal Industry Annual-1997, DOE/EIA 0584(97)-annual, Energy Information Administration, U.S.
Department of Energy, Washington, DC.
i1, jjii"" • ' >i| .' ' , , • '., ''i , , 'i ,,: , | . :' . .
&A (1998c) Emissions of Greenhouse "Gases in the United States 1997, DOE/EIA 0573(97)-annual, Energy
Information Administration, U.S. Department of Energy, Washington, DC.
IflA (I998d) Moi'thly Energy Review, DOE/EIA 0035(98)-monthly, Energy Information Administration, U.S.
Department of Energy, Washington, DC. November.
I HA (1998e) Petroleum Supply Annual-1997, DOE/EIA 0340(97)-annual, Energy Information Administration,
U.S. Department of Energy, Washington, DC, Volume I.
EJ(A (1994J State Energy Data Report 1992, DOE/EIA 0214(92)-annual, Energy Information Administration, U.S.
Department of Energy, Washington, DC.
I: I" i1 ! . •• ' :Vi ""''it\ •:,:.' , • . :'. l! ,. .. I
IPCCAJNEP/OECD/IE A (1997) Revised 1996IPCC Guidelines for National Greenhouse Gas Inventories, Paris:
Intergovernmental Panel on Climate Change, United Nations Environment Programme, Organization for Economic Co-
Opcration and Development, International Energy Agency.
0-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 0-1: 1997 U.S. Energy Statistics (physical units)
Fuel Category (Units)
Solid Fuels (1000 Short Tons)
Gas Fuels (Million Cubic Feet)
Liquid Fuels (Thousand Barrels)
Fuel Type
Anthracite Coal
Bituminous Coal
Sub-bituminous Coal
Lignite
Coke
Unspecified Coal
• Natural Gas
Crude Oil
Nat Gas Liquids and LRGs
Other Liquids
Motor Gasoline
Aviation Gasoline
Kerosene
Jet Fuel
Distillate Fuel
Residual Fuel
Naptha for petrochemical feedstocks
Petroleum Coke
Other Oil for petrochemical feedstocks
Special Napthas
Lubricants
Waxes
AsphalVRoad Oil
Still Gas
Misc. Products
Production
4,692
653,828
345,071
86,341
19,152,427
2,354,831
663,266
78,471
Imports
[1]
[1]
[1]
[1]
1,565
7,487
2,972,368
3,002,299
74,831
224,060
112,837
41
570
33,109
83,102
70,829
18,681
386
69,086
2,709
4,026
441
11,862
-
101
Exports
[1]
[1]
[1]
[1]
832
83,545
157,463
39,308
20,882
9,265
49,878
-
138
12,763
55,507
43,782
-
111,615
.
7,849
11,275
993
2,879
.
125
Stock
Change Bunkers
[1]
[1]
[1]
[1]
(29)
(10,817)
(26,906)
18,450
2,617
5,576
9,367
(575)
273
4,178 128,123
11,698 13,637
(5,458) 83,221
35
772
281
215
(80)
1,619
.
618
U.S.
Territories
480
2,791
27,547
12,949
19,371
27,912
.
20,005
[1] Included in Unspecified Coal
Data Sources: Solid Fuels - EIA Coal Industry Annual 1997; Gas Fuels - EIA Annual Energy Review 1997; Liquid Fuels - EIA Petroleum Supply Annual 1997
0-5
-------
Table 0-2: Comen-ston Factors to Energy Orate (heat equivalents)
Fuel Category (Units)
Fuel Type
Stock
Production Imports Exports Change Bunters Territories
Solid Fuels (Mllitm Btu/Sbort Ton) Anthracite Coal
Bituminous Coal
Sub-bituminous Coal
Lignite
Coke
Unspecified
Natural Gas (BTU/Cubic Foot)
Liquid Fuels (Million Btu/Barrel) Crude Oil
Nat Gas Liquids and LRGs
Other Liquids
Motor Gasoline
Aviation Gasoline
Kerosene
Jet Fuel
Distillate Fuel
Residual Oil
Naptha for petrochemical feedstocks
Petroleum Coke
Other Oil for petrochemical feedstocks
Special Napthas
Lubricants
Waxes
Asphalt/Road Oil
Still Gas
Misc. Products
22.573
23.89
17.14
12.866
24.8
25.000
1,027 1,022
5.800 5.935
3.777 3.777
5.825 5.825
5.253
5.048
5.67
5.67
5.825
6.287
5.248
6.024
5.825
5.248
6.065
5.537
6.636
6.000
5.796
24.8
26.174
1,011
5.800
3.777
5.825
5.253
5.048
5.67
5.67
5.825
6.287
5.248
6.024
5.825
5.248
6.065
5.537
6.636
6.000
5.796
24.8
21.287
1,027
5.800
3.777
5.825
5.253
5.048
5.67
5.67
5.825
6.287
5.248
6.024
5.825
5.248
6.065
5.537
6.636
6.000
5.796
5.800
3.777
5.825
5.253
5.048
5.67
5.67
5.825
6.287
5.248
6.024
5.825
5.248
6.065
5.537
6.636
6.000
5.796
--.
21.287«H
5.800
3.777
5.825
5.253
5.048
5.67
5.67
5.825
6.287
5.248
6.024
5.825
5.248
6.065
5.537
6.636;
6.000
5.796-
Data Sources: Coal and lignite production - EIA State Energy Data Report 1992; Coke - EIA Monthly Energy Review, November 1998; Unspecified Solid Fuels - EIA Monthly Energy Review, November 1998; Natural
Gas - EIA Monthly Energy Review, November 1998; Crude Oil - EIA Monthly Energy Review, November 1998; Natural Gas Liquids and LRGs - EIA Petroleum Supply Annual 1997; all other Liquid Fuels- EIA
Monthly Energy Review, November 1998
0-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 0-3: 1997 Apparent Consumption of Fossil Fuels (TBtu)
Fuel Category
Solid Fuels
Gas Fuels
Liquid Fuels
Total
Fuel Type
Anthracite Coal
Bituminous Coal
Sub-bituminous Coal
Lignite
Coke
Unspecified
Natural Gas
Crude Oil
Nat Gas Liquids and LRGs
Other Liquids
Motor Gasoline
Aviation Gasoline
Kerosene
Jet Fuel
Distillate Fuel
Residual Oil
Naptha for petrochemical feedstocks
Petroleum Coke
Other Oil for petrochemical feedstocks
Special Napthas
Lubricants
Waxes
Asphalt/Road Oil
Still Gas
Misc. Products
Production
105.9
15,620.0
5,914.5
1,110.9
-
-
19,669.5
13,658.0
2,505.2
457.1
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
59,041.1
Imports
38.8
187.2
3,037.8
17,818.6
282.6
1,305.1
592.7
0.2
3.2
187.7
484.1
445.3
98.0
2.3
402.4
14.2
24.4
2.4
78.7
-
0.6
25,006.6
Exports
20.6
2,186.7
159.2
228.0
78.9
54.0
262.0
-
0.8
72.4
323.3
275.3
-
672.4
-
41.2
68.4
5.5
19.1
-
0.7
4,468.4
Stock
Change
(0.7)
(230.3)
(27.6)
107.0
9.9
32.5
49.2
(2.9)
1.5
23.7
68.1
(34.3)
0.2
16.6
4.5
1.5
1.3
(0.4)
10.7
-
3.6
34.1
U.S.
Bunkers Territories
.
-
-
-
-
10.2
•
-
10.5
-
144.7
-
73.4
726.5
79.4 112.8
523.2 175.5
-
-
.
-
-
-
.
.
115.9
988.2 643.2
Apparent
Consumption
105.9
15,620.0
5,914.5
1,110.9
18.9
(1,759.1)
22,575.7
31,141.7
2,709.6
1,675.8
426.2
3.1
74.3
(634.8)
126.0
(143.4)
97.9
(686.7)
397.9
(28.4)
(45.3)
(2.6)
48.9
0.0
112.2
78,859.3
Note: Totals may not sum due to independent rounding.
0-7
-------
Table 0-4: 1997 Potential Carfioti Emissions
==--- n - . -
j is; 3^
Fuel Category Fuel Type
Apparent Consumption (QBtu)
Carbon Coefficients Potential Carbon Emissions
(MMTCE/QBIu) (MMTCE)
Solid Fuels
Gas Fuels
Liquid Fuels
Total
Anthracite Coal
Bituminous Coal
Sub-bituminous Coal
Lignite
Coke
Unspecified
Natural Gas
Crude Oil
Nat Gas Liquids and LRGs
Other Liquids
Motor Gasoline
Aviation Gasoline
Kerosene
Jet Fuel
Distillate Fuel
Residual Oil
Naptha for petrochemical feedstocks
Petroleum Coke
Other Oil for petrochemical feedstocks
Special Napthas
Lubricants
Waxes
Asphalt/Road Oil
Still Gas
Misc. Products
0,106
15.620
5.915
1.111
0.019
(1.759)
22.576
31.142
2.710
1.676
0.426
0.003
0.074
(0.635)
0.126
(0.143)
0.098
(0.687)
0.398
(0.028)
(0.045)
(0.003)
0.049
0.000
0.112
26.86
25.86
26.26
27.66
25.56
25.74
14.47
20.23
16.99
20.23
19.38
18.87
19.72
19.33
19.95
21.49
18.14
27.85
19.95
19.86
20.24
19.81
20.62
17.51
19.81
2.8
403.9
155.3
30.7
0.5
(45.3)
326.7
630.0
46.0
33.9
8.3
0.1
1.5
(12.3)
2.5
(3-D
1.8
(19.1)
7.9
(0.6)
(0.9)
(0.1)
1.0
0.0
2.2
1,573.9
Data Sources: Coal and Lignite - Revised 1996IPCC Guidelines Reference Manual, Table 1-1; Coke - EIA Monthly Energy Review, November 1998 Table C1; Unspecified Solid Fuels -£IA Monthly Energy Review,
November 1998 Table C1 (U.S. Average); Natural Gas and Liquid Fuels - EIA Emissions of Greenhouse Gases in the United States 1997. -: -_ -
Note: Totals may not sum due to independent rounding.
0-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Table 0-5: 1997 Non-Energy Carbon Stored in Products
Consumption for Non-
Energy Use (TBlu) Carbon Coefficients
Fuel Type (MMTCE/QBtu)
Coal
Natural Gas
Asphalts Road Oil
LP6
Lubricants
Pentanes Plus
Petrochemical Feedstocks
Petroleum Coke
Special Naptha
Waxes/Misc.
Misc. U.S. Territories Petroleum
Total
27.7
391.4
1223.6
1651.3
354.'4
295.4
[1]
179.0
72.3
[1]
[1]
25.55
14.47
20.62
16.86
20.24
18.24
[1]
27.85
19.86
[1]
[1]
Carbon Carbon Sequestered
Content Fraction (MMTCE)
(MMTCE) Sequestered
0.7
5.7
25.2
27.8
7.2
5.4
[1]
5.0
1.4
[1]
m
0.75
1.00
1.00
0.80
0.50
0.80
[1]
0.50
0
[1]
[11
0.5
5.7
25.2
22.3
3.6
4.3
15.9
2.5
0.0
3.4
0.2
83.6
[1] Values for Misc. U.S. Territories Petroleum, Petrochemical Feedstocks and Waxes/Misc. are not shown because these categories are aggregates of numerous smaller components.
Note: Totals may not sum due to independent rounding.
Table 0-6: Reference Approach C02 Emissions from Fossil Fuel Consumption (MMTCE unless otherwise noted)
Fuel Category
Coal
Petroleum
Natural Gas
Total
Potential Carbon
Emissions
548.0
699.2
326.7
1,573.9
Carbon
Sequestered
0.5
77.4
5.7
83.6
Net Carbon
Emissions
547.5
621.7
321.0
1,490.2
Fraction Oxidized
(percent)
99.0%
99.0%
99.5%
-
C02 Emissions
(MMTCE)
542.0
615.5
319.4
1,476.9
C02 Emissions
(Tg)
1,987.4
2,256.9
1,171.1
5,415.4
Note: Totals may not sum due to independent rounding.
Table 0-7: 1997 Energy Consumption in the United States: Sectoral vs. Reference Approaches (TBtu)
Approach
Sectoral3
Reference (Apparent)'
Difference
Coal
20,931.8
91 mi 1
0.4%
Natural Gas
22,575.3
22,575.7
0.0%
Petroleum
35,632.8
35,272.4
-1.0%
Total
79,140.0
78,859.3
-0.4%
a Includes U.S. territories
Note: Totals may not sum due to independent rounding.
0-9
-------
Table 0-8: 1937 C02 Eraissfci^froin FossifFuel Corotoistfenly Esttaating Approach5
.[Approach
Coal
Natural Gas
Petroleum
Sectoral1
Reference1
533,3
542.0
319.4
319.4
613.3
615.5
Difference
1.6%
0.0%
0.4%
1 Includes U.S. territories
Note: Totals may not sum due to independent rounding.
Total
1,465.9
1,476.9
0.8%
Table 0-9: 1996 Energy Consumption in the United States: Sectoral vs. Reference Approaches (TBtu)
Approach
Sectoral'
Reference (Apparent)'
Difference
Coal
20,459
20,334
-0.6%
Natural Gas
22,552
22,547
0.0%
Petroleum
35,170
34,642
-1.5%
Total
78,181
77,523
-0.8%
* Includes U.S. territories
Note: Totals may not sum due to independent rounding.
Table 0-10: 1996 C02 Emissions from Fossil Fuel Combustion by Estimating Approach (MMTCE)
Approach
Coal
Natural Gas
Petroleum
Total
Sectoral3
Reference3
521.1
524.7
319.3
319.3
607.2
605.6
1,447.7
1,449.5
Difference
0.7%
0.0%
-0.3%
0.1%
a Includes U.S. territories
Note: Totals may not sum due to independent rounding.
0-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
-------
Annex P
Sources of Greenhouse Gas Emissions Excluded
Although this report is intended to be a comprehensive assessment of anthropogenic22 sources and sinks of
greenhouse gas emissions for the United States, certain sources have been identified yet excluded from the estimates
presented for various reasons. Before discussing these sources, however, it is important to note that processes or
activities that are not anthropogenic in origin or do not result in a net source or sink of greenhouse gas emissions are
intentionally excluded from a national inventory of anthropogenic greenhouse gas emissions. In general, processes or
activities that are not anthropogenic are considered natural (i.e., not directly influenced by human activity) in origin and,
as an example, would include the following:
• Volcanic eruptions
• CO2 exchange (i.e., uptake or release) by oceans
• Natural forest fires23
• CH4 emissions from wetlands not affected by human induced land-use changes
Some processes or activities may be anthropogenic in origin but do no't result in net emissions of greenhouse
gases, such as the respiration of CO2 by people or domesticated animals. Given a source category that is both
anthropogenic and results in net greenhouse gas emissions, reasons for excluding a source related to an anthropogenic
activity include one or more of the following:
• There is insufficient scientific understanding to develop a reliable method for estimating emissions at a
national level.
• Although an estimating method has been developed, data were not adequately available to calculate
emissions.
• Emissions were implicitly accounted for within another source category (e.g., CO2 from Fossil Fuel
Combustion).
It is also important to note that the United States believes the exclusion of the sources discussed below introduces
only a minor bias in its overall estimate of U.S. greenhouse gas emissions.
CH4, N20, and Criteria Pollutant Emissions from the Combustion of Jet Fuel
The combustion of jet fuel by aircraft results in emissions of CH4, N2O, CO, NOX, and NMVOCs. The emissions
per mass of fuel combusted during landing/take-off (LTO) operations differ from those during aircraft cruising.
Accurate estimation of these emissions requires a detailed accounting of LTO cycles and fuel consumption during
cruising by aircraft model (e.g., Boeing 747-400). Sufficient data for separately calculating near ground-level emissions
during landing and take-off and cruise altitude emissions by aircraft model were not available for this report, (see
Revised 1996IPCC Guidelines for National Greenhouse Gas Inventories: Reference Manual, pp. 1.93 - 1.96)
22 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/1EA 1997).
23 In some cases forest fires that are started either intentionally or unintentionally are viewed as mimicking natural burning processes which have
been suppressed by other human forest management activities. The United States does not consider forest fires within its national boundaries to
be a net source of greenhouse emissions.
P-1
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Emissions from Bunker Fuels and Fossil Fuels Combusted Abroad by the U.S. Military
Emissions from fpssi| fuels combusted in military vehicles (i.e., ships, aircraft, and ground vehicles) may or may
not be included in U.S.. energy statistics. Domestic fuel sales to the military are captured in US. energy statistics;
however, fuels purchased abroad for base operations and refueling of vehicles are not. It is not clear to what degree
fuels purchased domestically are exported by the military to bases abroad.
Fuels combusted by military ships and aircraft while engaged in international transport or operations in
International waters or airspace (i.e., flying or cruising in international airspace or waters) that is purchased domestically
is Srjelu|led in U.S. energy statistics. Therefore, the United States may under report international bunker fuel emissions,
and mo§t likely over reports CO2 emissions from transportation-related fossil fuel combustion by a similar amount. At
this time, fuel consumption statistics from the Department of Defense are not adequately detailed to correct for this
" ' ' "
C02 from Burning in Coal Deposits and Waste Piles
Coal is periodically burned in deposits and waste piles. It has been estimated that the burning of coal in deposits
and wastepilcs would represent less than,! .3 percent of total U.S. coal consumption (averaged over ten-years). Because
there is currently no known source of data on the quantity of coal burned in waste piles and there is uncertainty as to
the fraction of coal oxidized during such burnings, these CO2 emissions are not currently estimated. Further research
i would {jo required to develop accurate emission factors and activity data for these emissions to be estimated, (see
Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories: Reference Manual, p. 1.112- 1.113)
Fossil C02 from Petroleum and Natural Gas Wells, C02 Separated from Natural Gas, and
C0? from Enhanced Oil Recovery (EOR)
Petroleum and natural gas well drilling, petroleum and natural gas production, and natural gas
processing- — including removal of CO2 — may result in emissions of CO2 that was at one time stored in underground
' formations. . ..... , . , . \ .
I!' « , , ' ' if :! ' ? ! , , , , ..... S3; i " ", pi, ,
Carbon dioxide and other gases are naturally present in raw natural gas, in proportions that vary depending on
the geochcmical circumstances that caused the formation of the gas. After the heavier gases are removed, small
amounjs of carbon dioxide may be allowed to remain in the natural gas. If the amount of CO2 sufficiently lowers the
heating value of the natural gas, it is typically extracted by amine scrubbing and, in most cases, emitted into the
atmosphere. These emissions can be estimated by calculating the difference between the average carbon dioxide content
of raw natural gas ami the carbon dioxide content of pipeline gas. The Energy Information Administration (EIA)
estimates that annual CO2 emissions from scrubbing are about 4 million metric tons of carbon. Because of imprecision
in the reporting of U.S. natural gas production and processing, emissions estimates from energy production sources may
be doupie-counted or under-reported, and thus are uncertain.
Carbon dioxide is also injected into underground deposits to increase crude oil reservoir pressure in a field
technique known as enhanced oil recovery (EOR). It is thought that much of the injected CO2 may be effectively and
permanently sequestered, but the fraction of injected CO2 that is re-released remains uncertain. The fraction re-released
varies from well to well depending upon the field geology and the gas capture/re-injection technology employed at the
wellheXL Over time, carbon dioxide may also seep into the producing well and mix with the oil and natural gas present
there. If the gas portion of this mixture has a sufficiently high energy content, it may be collected and sent to a natural
gas plant; if not, it may be vented or flared. The EIA estimates that the amount of CO? used for EOR is on the order
of 12 million metric tons, of which emissions would be some fraction yet to be defined. This figure is based on the
difference between O.S. Department of Commerce sales figures for industrial CO2 (17 million metric tons) minus the
Sec the Defense Energy Support Center (formerly the Defense Fuel Supply Center), Fact Book 1997.
|l«tpi//www,desc,dla,mil/main/pulicati.htm]
P-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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5 million metric tons reported by the Freedonia Group that is used for purposes other than EOR. Further research into
EOR is required before the resulting CO2 emissions can be adequately quantified. (See the discussion of the Carbon
Dioxide Consumption source category in the Industrial Processes chapter).
Carbon Sequestration in Underground Injection Wells
Organic hazardous wastes are injected into underground wells. Depending on the source of these organic
substances (e.g., derived from fossil fuels) the carbon in them may or may not be included in U.S. CO2 emission
estimates. Sequestration of carbon containing substances in underground injection wells may be an unidentified sink.
Further research is required if this potential sink is to be quantified.
CH4 from Abandoned Coal Mines
Abandoned coal mines are a source of CH4 emissions. In general, many of the same factors that affect emissions
from operating coal mines will affect emissions from abandoned mines such as the permeability and gassiness of the
coal, the mine's depth, geologic characteristics, and whether it has been flooded. A few gas developers have recovered
methane from abandoned mine workings; therefore, emissions from this source may be significant. Further research
and methodological development is needed if these emissions are to be estimated.
C02 from "Unaccounted for" Natural Gas
There is a discrepancy between the amount of natural gas sold by producers and that reported as purchased by
consumers. This discrepancy, known as "unaccounted for" or unmetered natural gas, was assumed to be the sum of
leakage, measurement errors, data collection problems, undetected non-reporting, undetected over reporting, and
undetected under reporting. Historically, the amount of gas sold by producers has always exceeded that reportedly
purchased by consumers; therefore, some portion of unaccounted for natural gas was assumed to be a source of CO2
emissions. (It was assumed that consumers were underreporting their usage of natural gas.) In DOE/EIA's energy
statistics for 1996, however, reported consumption of natural gas exceeded the amount sold by producers. Therefore,
the historical explanation given for this discrepancy has lost credibility and unaccounted for natural gas is no longer
used to calculate CO2 emissions.
C02 from Shale Oil Production
Oil shale is shale saturated with kerogen.25 It can be thought of as the geological predecessor to crude oil. Carbon
dioxide is released as a by-product of the process of producing petroleum products from shale oil. As of now, it is not
cost-effective to mine and process shale oil into usable petroleum products. The only identified large-scale oil shale
processing facility in the U.S. was operated by Unocal during the years 1985 to 1990. There have been no known
emissions from shale oil processing in the United States since 1990 when the Unocal facility closed.
CH4 from the Production of Carbides other than Silicon Carbide
Methane may be emitted from the production of carbides because the petroleum coke used in the process contains
volatile organic compounds which form methane during thermal decomposition. Methane emissions from the
production of silicon carbide were estimated and accounted for, but emissions from the production of calcium carbide
and other carbides were not. Further research is needed to estimate CH4 emissions from the production of calcium
carbide and other carbides other than silicon carbide, (see Revised 1996IPCC Guidelines for National Greenhouse Gas
Inventories: Reference Manual, pp. 2.20 - 2.21)
Kerogen is fossilized insoluble organic material found in sedimentary rocks, usually shales, which can be converted to petroleum products by
distillation.
P-3
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C02 from Calcium Carbide and Silicon Carbide Production
Carbon dioxide is formed by the oxidation of petroleum coke in the production of both calcium carbide and silicon
carbide. These CO2 emissions are implicitly accounted for with emissions from the combustion of petroleum coke in
the Energy chapter. There Is currently not sufficient data on coke consumption to estimate emissions from these sources
explicitly, (see Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories: Reference Manual, pp. 2.20 -
C02 from Graphite Consumption in Ferroalloy and Steel Production
The CO2 emissions from the three reducing agents used in ferroalloy and steel production — coke, wood (or
biomjiss), and graphite — are accounted for as follows:
• Emissions resulting from the use of coke are accounted for in the Energy chapter under fossil fuel
cpmbustion.
• : Estimating emissions from the use of wood or other biomass materials is unnecessary because these
emissions should be accounted for in Land-Use Change and Forestry chapter if the biomass is harvested on
|| '" an unsustainable, oasis. ^ ^ [ ..... i |
• The CO2 emissions from the use of graphite, which is produced from petroleum by-products, may be
accounted for in the Energy chapter (further analysis is required to determine if these emissions are being
properly estimated) The CO2 emissions from the use of natural graphite, however, have not been
accounted for in the estimate.
Emissions from graphite electrode consumption — versus its use as a reducing agent — in ferroalloy and steel
production may at present only be accounted for in part under fossil fuel combustion if the graphite used was derived
from a fossil fuel substrate (versus natural graphite ore). Further research into the source and total consumption of
graphite for these purposes is required to explicitly estimate emissions, (see Iron and Steel Production and Ferroalloy
Production in the Industrial Processes chapter)
N20 from Caprofactam Production
Caprolactam is a widely used chemical intermediate, primarily to produce nylon-6. All processes for producing
caprolaetam involve the catalytic oxidation of ammonia, with N2O being produced as a by-product. Caprolactam
production could be a significant source of N2O — it has been identified as such in the Netherlands.. More research is
required to determine this source's significance because there is currently insufficient information available on
Caprolactam production to estimate emissions in the United States, (see Revised 1996 IPCC Guidelines for National
Greenhouse Gas Inventories: Reference Manual, pp. 2.22 - 2.23)
i. • • , li' :..j'.\ ' :: I. .
N20 from Cracking of Certain Oil Fractions
In order to improve the gasoline yield in crude oil refining, certain oil fractions are processed in a catcracker.
Because crude oil contains some nitrogen, N2O emissions may result from this cracking process. There is currently
insufficient data to develop a methodology for estimating these emissions, (see Revised 1996 IPCC Guidelines for
National Greenhouse Gas Inventories: Reference Manual, p. 2.23)
CH4 from Coke Production
Coke production may result in CH4 emissions. Detailed coke production statistics were not available for the
purposes of estimating CH4 emissions from this minor source, (see Petrochemical Production in the Industrial Processes
chapter and the Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories: Reference Manual, p. 2.23)
P-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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C02 from Metal Production
Coke is used as a reducing agent in the production of some metals from their ores, including magnesium,
chromium, lead, nickel, silicon, tin, titanium, and zinc. Carbon dioxide may be emitted during the metal's production
from the oxidization of this coke and, in some cases, from the carbonate ores themselves (e.g., some magnesium ores
contain carbonate). The CO2 emissions from coke oxidation are accounted for in the Energy chapter under Fossil Fuel
Combustion. The CO2 emissions from the carbonate ores are not presently accounted for, but their quantities are
thought to be minor, (see Revised 1996IPCC Guidelines for National Greenhouse Gas Inventories: Reference Manual,
p. 2.37 - 2.38)
N20 from Acrylonitrile Production
Nitrous oxide may be emitted during acrylonitrileproduction. No methodology was available for estimating these
emissions, and therefore further research is needed if these emissions are to be included, (see Revised 1996 IPCC
Guidelines for National Greenhouse Gas Inventories: Reference Manual, p. 2.22)
SF6 from Aluminum Fluxing and Degassing
Occasionally, sulfur hexafluoride (SF6) is used by the aluminum industry as a fluxing and degassing agent in
experimental and specialized casting operations. In these cases it is normally mixed with argon, nitrogen, and/or
chlorine and blown through molten aluminum; however, this practice is not used by primary aluminum production firms
in the United States and is not believed to be extensively used by secondary casting firms. Where it does occur, the
concentration of SF6 in the mixture is small and a portion of the SF6 is decomposed in the process (Waite and Bernard
1990, Corns 1990). It has been estimated that 230 Mg of SF6 were used by the aluminum industry in the United States
and Canada (Maiss and Brenninkmeijer 1998); however, this estimate is highly uncertain.
Miscellaneous SF6 Uses
Sulfur hexafluoride may be used in gas-filled athletic shoes, in foam insulation, for dry etching, in laser systems,
as an atmospheric tracer gas, for indoor air quality testing, for laboratory hood testing, for chromatography, in tandem
accelerators, in sound-insulating windows, in tennis balls, in loudspeakers, in shock absorbers, and for certain
biomedical applications. Data need to be gathered and methodologies developed if these emissions are to be estimated.
A preliminary global assessment of aggregate emissions from these applications can be found in Maiss, M. and C.A.M.
Brenninkmeijer (1998).
CO, from Solvent Incineration
CO2 may be released during the incineration of solvents. Although emissions from this source are believed to
be minor, data need to be gathered and methodologies developed if these emissions are to be estimated.
CO, from Non-Forest Soils
Non-forest soils emit CO2 from decaying organic matter and carbonate minerals—the latter may be naturally
present or mined and later applied to soils as a means to adjust their acidity. Soil conditions, climate, and land-use
practices interact to affect the CO2 emission rates from non-forest soils. The U.S. Forest Service has developed a model
to estimate CO2 emissions from forest soils, but no such model has been adequately developed for non-forest soils.
Further research and methodological development is needed if these emissions are to be accurately estimated, (see
Changes in Non-Forest Carbon Stocks in the Land-Use Change and Forestry chapter)
P-5
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CH4 from Land-Use Changes Including Wetlands Creation or Destruction
Wetlands are a known source of CH4 emissions. When wetlands are destroyed, CH4 emissions may be reduced.
Conversely, when wetlands are created (e.g., during the construction of hydroelectric plants), CH4 emissions may
increase. Grasslands and forest lands may also be weak sinks for CH4 due to the presence of methanotrophic bacteria
that use CH4 as an energy source (i.e., they oxidize CH4 to CO2). Currently, an adequate scientific basis for estimating
these emissions and sinks does not exist, and therefore further research and methodological development is required.
Ill1' ' ':! ' ' li ' i II "
CH4 from Septic Tanks and Drainfields
Methane is produced during thebiodegradation of organics in septic tanks if other suitable electron-acceptors (i.e.,
oxygen, nitrate, or sulfate) besides CO2 are unavailable. Such conditions are called methanogenic. There were
insufficient data and methodological developments available to estimate emissions from this source.
; ' ' . ! i. i • . • • • ' i . •
N20 from Wastewater Treatment
As a result of nitrification and denitrification processes, N2O may be produced and emitted from both domestic
and industrial wastcwater treatmentplants. Nitrogen-containing compounds are found in wastewater due to the presence
of both human excrement and other nitrogen-containing constituents (e.g. garbage, industrial wastes, dead animals, etc.).
The portion of emitted N26 which originates from human excrement is currently estimated under the Human Sewage
soureeeategory—based upon average dietary assumptions. The portion of emitted N2O which originates from other
nitrogen-containing constituents is not currently estimated. Further research and methodological development is needed
if these emissions are to be accurately estimated.
I"1 ' i ,„! »!' ; ' ' , ,„ ||
CH4 from Industrial Wastewater
Methane may be produced during the biodegradation of organics in wastewater treatment if other suitable
electron-acceptors (i.e. oxygen, nitrate, or sulfate) besides CO2 are unavailable. Such conditions are called
methanogenic. Methane produced from domestic wastewater treatment plants is accounted for in the Waste chapter.
These emissions are estimated by assuming an average 5-day biological oxygen demand (BOD5) per capita contribution
in conjunction with the approximation that 15 percent of wastewater* s BOD5 is removed under methanogenic
conditions. This method itself needs refinement. It is not clear if industrial wastewater sent to domestic wastewater
treatment plants, which may contain biodegradable material, are accounted for in the average BC)D5 per capita method
when this wastewater is sent to domestic wastewater treatment plants. Additionally, CH4 emissions from methanogenic
processes at industrial wastewater treatment plants are not currently estimated. Further researcfi and methodological
development is needed if these emissions are to be accurately estimated, (see Wastewater Treatment in the Waste
chapter)
P-6 inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Annex Q
Constants, Units, and Conversions
Metric Prefixes
Although most activity data for the U.S. is gathered in customary U.S. units, these units are converted into metric
units per international reporting guidelines. The following table provides a guide for determining the magnitude of
metric units.
Table Q-1: Guide to Metric Unit Prefixes
Prefix/Symbol
atto (a)
femto (f)
pico (p)
nano (n)
micro (p )
mill! (m)
centi (c)
dec! (d)
deca (da)
hecto (h)
kilo (k)
mega (M)
giga (G)
tera (T)
peta (P)
exa (E)
Factor
10-18
10'15
10'12
10'9
10'6
io-3
io-2
1C'1
10
102
103
106
109
1012
1015
1018
Unit Conversions
1 kilogram
1 pound
1 short ton
1 metric ton
1 cubic meter
1 cubic foot
1 U.S. gallon
1 barrel (bbl)
1 barrel (bbl)
1 liter
2.205 pounds
0.454 kilograms
2,000 pounds
1,000 kilograms
= 0.9072 metric tons
= 1.1023 short tons
35.315 cubic feet
0.02832 cubic meters
3.785412 liters
0.159 cubic meters
42 U.S. gallons
0.1 cubic meters
1 foot = 0.3048 meters
1 meter = 3.28 feet
1 mile = 1.609 kilometers
1 kilometer = 0.622 miles
1 acre = 43,560 square feet = 0.4047 hectares
1 square mile = 2.589988 square kilometers
= 4,047 square meters
To convert degrees Fahrenheit to degrees Celsius, subtract 32 and multiply by 5/9
To convert degrees Celsius to Kelvin, add 273.15 to the number of Celsius degrees
Q-1
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. ., ; v
Density Conversions26
Methane 1 cubic meter = 0.67606 kilograms
Carbon dioxide 1 cubic meter = 1.85387 kilograms
Natural gas liquids ' 1 metric ton = 11.6 barrels = 1,844.2 liters
Unfinished oils 1 metric ton = 7.46 barrels = 1,186.04 liters
Alcohol 1 metric ton = 7.94 barrels = 1,262.36 liters
Liquefied petroleum gas 1 metric ton = 11.6 barrels = 1,844.2 liters
Aviation gasoline 1 metric ton = 8.9 barrels = 1,415.0 liters
Naphtha Jet fuel 1 metric ton = 8.27 barrels = 1,314.82 liters
Kerosene Jet fuel 1 metric ton = 7.93 barrels = 1,260.72 liters
Motor gasoline 1 metric ton = 8.53 barrels = 1,356.16 liters
Kerosene 1 metric ton = 7.73 barrels = 1,228.97 liters
Naphtha' 1 metric ton = 8.22 barrels = 1,306.87 liters
Distillate 1 metric ton = 7.46 barrels = 1,186.04 liters
Residua! oil 1 metric ton = 6.66 barrels = 1,058!85 liters
.Lubricants 1 metric ton = 7.06 barrels = 1,122.45 liters
feitumerj 1 metric ton = 6.06 barrels = 963.46 liters
Waxes 1 metric ton = 7.87 barrels = 1,251.23 liters
Petroteln coke 1 metric ton = 5.51 barrels = 876.02 liters
Petrochemical feedstocks 1 metric ton = 7.46 barrels = 1,186.04 liters
Special naphtha 1 metric ton = 8.53 barrels = 1,356.16 liters
Miscellaneous products 1 metric ton = 8.00 barrels = 1,271.90 liters
Energy Conversions
' ' !i." ' •. i'»;, ,• 'i-' i i'
Converting Various Energy Units to Joules
The common energy unit used in international reports of greenhouse gas emissions is the joule. A joule is the
energy required to push with a force of one Newton for one meter. A terajoule (TJ) is one trillion (1012) joules. A
kritish thermal unit (fitu, the customary U.S. energy unit) is the quantity of heat required to raise the temperature of
one pound of water one degree Fahrenheit at or near 39.2 Fahrenheit.
1TJ= 2,388x10" calories
!' 23.88 metric tons of crude oil equivalent
947.8 million Btus
277,800 kfiowatt-hours
Converting Various Physical Units to Energy Units
I . ' ' !.; ' ,. ,' ' •• . ' . • I
Data on the production and consumption of fuels are first gathered in physical units. These units must be
converged to their energy equivalents. The values in the following table of conversion factors can be used as default
factors, if local data are not available. See Appendix A of EIA's Annual Energy Review 1997 (EIA 1998) for more
detailed information on the energy content of various fuels.
Reference: EIA(1998a)
Q-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Table Q-2: Conversion Factors to Energy Units (heat equivalents)
Fuel Type (Units)
Factor
Solid Fuels (Million Btu/Short ton)
Anthracite coal 22.573
Bituminous coal 23.89
Sub-bituminous coal 17.14
Lignite 12.866
Coke 24.8
Natural Gas (Btu/Cubic toot) 1,027
Liquid Fuels (Million Btu/Barrel)
Crude oil 5.800
Natural gas liquids and LRGs 3.777
Other liquids 5.825
Motor gasoline 5.253
Aviation gasoline 5.048
Kerosene 5.670
Jet fuel, kerosene-type 5.670
Distillate fuel 5.825
Residual oil 6.287
Naphtha for petrochemicals 5.248
Petroleum coke 6.024
Other oil for petrochemicals 5.825
Special naphthas 5.248
Lubricants 6.065
Waxes 5.537
Asphalt 6.636
Still gas 6.000
Misc. products 5.796
Note: For petroleum and natural gas, Annual Energy Review 1997 (EIA 1998b). For coal ranks, Sfafe Energy Data Report 1992 (EIA 1993). All values
are given in higher heating values (gross calorific values).
References
EIA (1998a) Emissions of Greenhouse Gases in the United States, DOE/EIA-0573(97), Energy Information
Administration, U.S. Department of Energy. Washington, D.C. October.
EIA (1998b) Annual Energy Review, DOE/EIA-0384(97), Energy Information Administration, U.S. Department
of Energy. Washington, D.C. July.
EIA (1993) State Energy Data Report 1992, DOE/EIA-0214(93), Energy Information Administration, U.S.
Department of Energy. Washington, D.C. December.
Q-3
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if "I
Hi"'1..
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Annex R
Abbreviations
AFEAS Alternative Fluorocarbon Environmental Acceptability Study
MPFCO American Association of Plant Food Control Officials
ASAE American Society of Agricultural Engineers
BEA Bureau of Economic Analysis, U.S. Department of Commerce
BOD5 Biochemical oxygen demand over a 5-day period
BTS Bureau of Transportation Statistics, U.S. Department of Transportation
Btu British thermal unit
CAAA Clean Air Act Amendments of 1990
C&EN Chemical and Engineering News
CFC Chlorofluorocarbon
CMA Chemical Manufacturers Association
CMOP Coalbed Methane Outreach Program
CVD Chemical vapor deposition
DIG Dissolved inorganic carbon
DOC U.S. Department of Commerce
DOD U.S. Department of Defense
DOE U.S. Department of Energy
DOT U.S. Department of Transportation
EIA Energy Information Administration, U.S. Department of Energy
EPA U.S. Environmental Protection Agency
FAA Federal Aviation Administration
FAO Food and Agricultural Organization
FCCC Framework Convention on Climate Change
FHWA Federal Highway Administration
GAA Governmental Advisory Associates
GHG Greenhouse gas
GRI Gas Research Institute
GSAM Gas Systems Analysis Model
GWP Global warming potential
HBFC Hydrobromofluorocarbon
HCFC Hydrochlorofluorocarbon
HDGV Heavy duty gas vehicle
HDDV Heavy duty diesel vehicle
HFC Hydrofluorocarbon
HFE Hydrofluoroethers
ICAO International Civil Aviation Organization
IEA International Energy Association
ILENR Illinois Department of Energy and Natural Resources
IMO International Maritime Organization
IPAA Independent Petroleum Association of America
IPCC Intergovernmental Panel on Climate Change
LDDT Light duty diesel truck
LDDV Light duty diesel vehicle
LDGV Light duty gas vehicle
LDGT Light duty gas truck
LFG Landfill gas
LPG Liquefied petroleum gas(es)
MC Motorcycle
MMTCE Million metric tons of carbon equivalent
MSW Municipal solid waste
NIAR Norwegian Institute for Air Research
NMVOCs Nonmethane volatile organic compounds
R-1
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NO, Nitrogen Oxides
fiVFEL National Vehicle Fuel Emissions Laboratory
OAQPS EPA Office of Air Quality Planning and Standards
QOS Ozone depleting substances
OECD Organization of Economic Co-operation and Development
QMS EPA Office of Mobile Sources
ORNL Oak Ridge National Laboratory
OSHA Occupational Safety and Health Administration
OTA Office of technology Assessment
PFC Perfluorocarbon
PFPE Perfluoro(K)lyether
pprnv Parts per mllltorif 1 0°) by volume
ppbv Parts per billion flO9) by volume
pptv Parts per trillion (1O12) by volume
SAE Society of Automotive Engineers
SNG Synthetic natural gas
TBtu Trillion Btu
TJ Terajoule
TSDF Hazardous waste treatment, storage, and disposal facility
TVA Tennessee Valley Authority
U.S. United States
USDA United St^tjs Department of Agriculture
USFS United Sta|s Forest Service
USGS United States Geological Survey
UNEP United Nations Environmental Programme
UKFCCC United Nations Framework Convention on Climate Change
VAIP EPA's Voluntar^ Aluminum Industrial Partnership
VMT Vehicle miles traveled
WMO World Meteorological Organization
R-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Annex S
Chemical Symbols
Table S-1: Guide to Chemical Symbols
Symbol
Name
Al
Br 3
C
CH4
C2H6
C3H8
CF4
C2F6
c-CF
CF3I
CFCI3
CF2CI2
CF3CI
CCI3CF3
C2F4CI2
C2F5CI
CHF2C1
C2F3HCI2
C2F4HCI
C2FH3CI2
C3F5HCI2
CCI4
CHCICCI2
CCI2CCI2
CH3CI
CH3CCI3
CH2CI2
CHCI3
CHF3
CH2F2
CH3F
C2HF5
C2H2F4
CH2FCF3
C2H3F3
C2H3F3
C2H4F2
C3HF7
C3H2F6
C3H3F5
CH2Br2
CH2BrCI
Aluminum
Aluminum Oxide
Bromine
Carbon
Methane
Ethane
Propane
Perfluoromethane
Perfluoroethane, hexafluoroethane
Perfluoropropane
Perfluorocyclobutane
Perfluoropentane
Perfluorohexane
Trifluoroiodomethane
Trichlorofluoromethane (CFC-11)
Dichlorodifluoromethane (CFC-12)
Chlorotrifluoromethane (CFC-13)
Trichlorotrifluoroethane (CFC-113) *
CFC-113a*
Dichlorotetrafluoroethane (CFC-114)
Chloropentaf luoroethane (CFC-115)
Chlorodifluoromethane (HCFC-22)
HCFC-123
HCFC-124
HCFC-141b
HCFC-142b
HCFC-225ca/cb
Carbon tetrachloride
Trichloroethylene
Perchloroethylene.tetrachloroethene
Methylchloride
Methylchloroform
Methylenechloride
Chloroform, trichloromethane
HFC-23
HFC-32
HFC-41
HFC-125
HFC-134
HFC-134a
HFC-143*
HFC-143a*
HFC-152a
HFC-227ea
HFC-236fa
HFC-245ca
HFC-43-10mee
Dibromomethane
Dibromochloromethane
S-1
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CHBr,
CF3Br(CBrF3)
CO
COj
CaCOj
•''CaMg(06j)i
CaO
Cl
F
Fe i .....
FeA
FeS!
H,H,
HjO
HA
OH
N,N2
NH,
NIV
HMO,
NO
NOz
NO,
Na
o,
s
SO,
Si
SIC
SiO,
Tribromomettiane
Metiiyiromide
Bromodichloromethane (Halon 1211)
Bromqfrifluoromettiane (Halon 1301)
Carbon monoxide
Carbon dioxide
Calcium carbonate, Limestone
Dolomite
Calcium oxide, Lime
atomic Chlorine
Fluorine
lron_
Ferric oxide
Ferrosilicon
atomic Hydrogen, molecular Hydrogen
Water
Hydrogen peroxide
Hydroxyi
atomic Nitrogen, molecular Nitrogen
Ammonia
tmmonium ion
rtric Acid
Nitrogen trifluoride
Nitrous oxide
Nitric oxide
Nitrogen dioxide
Nitrate radical
Sodium
Sodium caroonate, soda ash
Synthetic cryolite
atomic Oxygen, molecular Oxygen
Ozone
atomic Sulfur
Sulfuric acid
Sulfur hexafluoride
Sulfur dioxide
Silicon
Silicon carbide
Quartz
* Distingtisomers.
S-2 Inventory of U.S. Greenhouse Gas Emissions anci Sinks: 1990-1997
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Annex T
Glossary
Abiotic.7 Nonliving. Compare biotic.
Absorption of radiation.1 The uptake of radiation by a solid body, liquid or gas. The absorbed energy may be
transferred or re-emitted.
Acid deposition.6 A complex chemical and atmospheric process whereby recombined emissions of sulfur and nitrogen
compounds are redeposited on earth in wet or dry form. See acid rain.
Acid rain.6 Rainwater that has an acidity content greater than the postulated natural pH of about 5.6. It is formed when
sulfur dioxides and nitrogen oxides, as gases or fine particles in the atmosphere, combine with water vapor and
precipitate as sulfuric acid or nitric acid in rain, snow, or fog. The dry forms are acidic gases or particulates.
See acid deposition.
Acid solution.7 Any water solution that has more hydrogen ions (H+) than hydroxide ions (OH-); any water solution
with a pH less than 7. See basic solution, neutral solution.
Acidic.7 See acid solution.
Adiabatic process.9 A thermodynamic change of state of a system such that no heat or mass is transferred across the
boundaries of the system. In an adiabatic process, expansion always results in cooling, and compression in
warming.
Aerosol.1&9 Particulate matter, solid or liquid, larger than a molecule but small enough to remain suspended in the
atmosphere. Natural sources include salt particles from sea spray, dust and clay particles as a result of
weathering of rocks, both of which are carried upward by the wind. Aerosols can also originate as a result of
human activities and are often considered pollutants. Aerosols are important in the atmosphere as nuclei for the
condensation of water droplets and ice crystals, as participants in various chemical cycles, and as absorbers and
scatters of solar radiation, thereby influencing the radiation budget of the Earth's climate system. See climate,
paniculate matter.
Afforestation.2 Planting of new forests on lands that have not been recently forested.
Air carrier8 An operator (e.g., airline) in the commercial system of air transportation consisting of aircraft that hold
certificates of, Public Convenience and Necessity, issued by the Department of Transportation, to conduct
scheduled or non-scheduled flights within the country or abroad.
Air pollutant. See air pollution.
Air pollution.7 One or more chemicals or substances in high enough concentrations in the air to harm humans, other
animals, vegetation, or materials. Such chemicals or physical conditions (such as excess heat or noise)-are called
air pollutants.
Albedo.9 The fraction of the total solar radiation incident on a body that is reflected by it.
Alkalinity.6 Having the properties of a base with a pH of more than 7. A common alkaline is baking soda.
Alternative energy.6 Energy derived from nontraditional sources (e.g., compressed natural gas, solar, hydroelectric,
wind).
Anaerobic.6 A life or process that occurs in, or is not destroyed by, the absence of oxygen.
Anaerobic decomposition.2 The breakdown of molecules into simpler molecules or atoms by microorganisms that
can survive in the partial or complete absence of oxygen.
Anaerobic lagoon.2 A liquid-based manure management system, characterized by waste residing in water to a depth
of at least six feet for a period ranging between 30 and 200 days. Bacteria produce methane in the absence of
oxygen while breaking down waste.
Anaerobic organism.7 Organism that does not need oxygen to stay alive. See aerobic organism.
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Antarctic "Ozone Ho le." 6 Refers to the seasonal depletion of stratospheric ozone in a large area over Antarctica. See
'
er.
Anthracite. 2 A hard, black, lustrous coal containing a high percentage of fixed carbon and a low percentage of volatile
matter. Often referred to as hard coal.
Anthropogenic.2 Human made. In the context of greenhouse gases, emissions that are produced as the result of human
activities.
Arable land. 7 Land that can be cultivated to grow crops.
Aromatic.* Applied to a group of hydrocarbons and their derivatives characterized by the presence of the benzene ring.
Ash. 6 Jhs mineral cgntenf of a product remaining after complete combustion.
Asphalt. 2 A dark-brown-to-black cement-like material containing bitumen as the predominant constituent. It is
obtained by petroleum processing. The definition includes crude asphalt as well as the following finished
products: cements, fluxes, the asphalt content of emulsions (exclusive of water), and petroleum distillates
Ijended with asphalt to make cutback asphalt.
Atmosphere. ' The mixture of gases surrounding the Earth. The Earth's atmosphere consists of about 79. 1 percent
nitrogen (by volume), 20.9 percent oxygen, 0.036 percent carbon dioxide and trace amounts of other gases. The
atmosphere can be divided into a number of layers according to its mixing or chemical characteristics, generally
'cle'te'rniirjed by its thermal properties (temperature). The layer nearest the Earth is the frap_Qj/7/!ere, which reaches
up to an altitude of about 8 kilometers (about 5 miles) in the polar regions and up to 17 kilometers (nearly 1 1
miles) above the equator. The stratosphere, which reaches to an altitude of about 50 kilometers (3 Imiles) lies
atop the troposphere. Themesosphere, which extends from 80 to 90 kilometers atop the stratosphere, and finally,
tfte thermosphere,or ionosphere, gradually diminishes and forms a fuzzy border with outer space. There is
relatively little mixing of gases between layers.
Atmospheric lifetime. See lifetime.
Atomic weight.6 TKe average weight (or mass) of all the isotopes of an element, as determined from the proportions
; in which they are present in a given element, compared with the mass of the 12 isotope of carbon (taken as
precisely 12.000), that is the official international standard; measured in daltons.
Atoms, 7 Minute particles that are the basic building blocks of all chemical elements and thus all matter.
Aviation Gasoline. 8 All special grades of gasoline for use in aviation reciprocating engines, as given in the American
Society for Testing and Materials (ASTM) specification D 9 10. Includes all refinery products within the gasoline
range that are to be marketed straight or in blends as aviation gasoline without further processing (any refinery
Operation except mechanical blending). Also included are finished components in the gasoline range, which will
be used for blending or compounding into aviation gasoline.
Bacteria. 7 One-celled organisms. Many act as decomposers that break down dead organic matter into substances that
dissolve in water and are used as nutrients by plants.
Barrel (bbl).* A liquid-volume measure equal to 42 United States gallons at 60 degrees Fahrenheit; used in expressing
quantities of petroleum-based products.
Basic solution. 7 Water solution with more hydroxide ions (OH-) than hydrogen ions (H+); water solutions with pH
greater than 7. See acid solution, alkalinity, acid.
Biodegradable. 7 Material that can be broken down into simpler substances (elements and compounds) by bacteria or
other decomposers. Paper and most organic wastes such as animal manure are biodegradable. See
lfionbiodegraaa"ble.
Biofucl. 3*7 Gas or liquid fuel made from plant material (biomass). Includes wood, wood waste, wood liquors, peat,
railroad ties, wood sludge, spent sulfite liquors, agricultural waste, straw, tires, fish oils, tall oil, sludge waste,
Saste alcohol, municipal solid waste, landfill gases, other waste, and ethanol blended into motor gasoline.
Biogcochemical cycle. 7 Natural processes that recycle nutrients in various chemical forms from the environment, to
organisms, and then back to the environment. Examples are the carbon, oxygen, nitrogen, phosphorus, and
hydrologic cycles.
Biological oxygen demand (BOD). 7 Amount of dissolved oxygen needed by aerobic decomposers to break down the
organic materials in a given volume of water at a certain temperature over a specified time period. See BODS.
T-2 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
„„ ., ....,„,, , „ , ,..,,, i.
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Biomass.7 Total dry weight of all living organisms that can be supported at each tropic level in a food chain. Also,
materials that are biological in origin, including organic material (both living and dead) from above and below
ground, for example, trees, crops, grasses, tree litter, roots, and animals and animal waste.
Biomass energy.' Energy produced by combusting biomass materials such as wood. The carbon dioxide emitted from
burning biomass will not increase total atmospheric carbon dioxide if this consumption is done on a sustainable
basis (i.e., if in a given period of time, regrowth of biomass takes up as much carbon dioxide as is released from
biomass combustion). Biomass energy is often suggested as a replacement for fossil fuel combustion.
Biosphere.2&7 The living and dead organisms found near the earth's surface in parts of the lithosphere, atmosphere,
and hydrosphere. The part of the global carbon cycle that includes living organisms and biogenic organic matter.
Biotic.7 Living. Living organisms make up the biotic parts of ecosystems. See abiotic.
Bitumen.7 Gooey, black, high-sulfur, heavy oil extracted from tar sand and then upgraded to synthetic fuel oil. See
tar sand.
Bituminous coal.2 A dense, black, soft coal, often with well-defined bands of bright and dull material. The most
common coal, with moisture content usually less than 20 percent. Used for generating electricity, making coke,
and space heating.
BODS.2 The biochemical oxygen demand of wastewater during decomposition occurring over a 5-day period. A
measure of the organic content of wastewater. See biological oxygen demand.
British thermal unit (Btu).3 The quantity of heat required to raise the temperature of one pound of water one degree
of Fahrenheit at or near 39.2 degrees Fahrenheit.
Bunker fuel.2 Fuel supplied to ships and aircraft for international transportation, irrespective of the flag of the carrier,
consisting primarily of residual and distillate fuel oil for ships and jet fuel for aircraft.
Bus.6&8 A rubber-tired, self-propelled, manually steered vehicle that is generally designed to transport 30 individuals
or more. Bus types include intercity, school and transit.
Carbon black.2 An amorphous form of carbon, produced commercially by thermal or oxidative decomposition of
hydrocarbons and used principally in rubber goods, pigments, and printer's ink.
Carbon cycle.2 All carbon reservoirs and exchanges of carbon from reservoir to reservoir by various chemical,
physical, geological, and biological processes. Usually thought of as a series of the four main reservoirs of
carbon interconnected by pathways of exchange. The four reservoirs, regions of the Earth in which carbon
behaves in a systematic manner, are the atmosphere, terrestrial biosphere (usually includes freshwater systems),
oceans, and sediments (includes fossil fuels). Each of these global reservoirs may be subdivided into smaller
pools, ranging in size from individual communities or ecosystems to the total of all living organisms (biota).
Carbon dioxide.2 A colorless, odorless, non-poisonous gas that is a normal part of the ambient air. Carbon dioxide
is a product of fossil fuel combustion. Although carbon dioxide does not directly impair human health, it is a
greenhouse gas that traps terrestrial (i.e., infrared) radiation and contributes to the potential for global warming.
See global warming.
Carbon equivalent (CE).' A metric measure used to compare the emissions of the different greenhouse gases based
upon their global warming potential (GWP). Greenhouse gas emissions in the United States are most commonly
expressed as "million metric tons of carbon equivalents" (MMTCE). Global warming potentials are used to
convert greenhouse gases to carbon dioxide equivalents. See global warming potential, greenhouse gas.
Carbon flux.9 The rate of exchange of carbon between pools (i.e., reservoirs).
Carbon intensity. The relative amount of carbon emitted per unit of energy or fuels consumed.
Carbon pool.9 The reservoir containing carbon as a principal element in the geochemical cycle.
Carbon sequestration.' The uptake and storage of carbon. Trees and plants, for example, absorb carbon dioxide,
' release the oxygen and store the carbon. Fossil fuels were at one time biomass and continue to store the carbon
until burned. See carbon sinks.
Carbon sinks.' Carbon reservoirs and conditions that take-in and store more carbon (i.e., carbon sequestration) than
they release. Carbon sinks can serve to partially offset greenhouse gas emissions. Forests and oceans are large
carbon sinks. See carbon sequestration.
T-3
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Carbon tetrachloride (CC14).'' A compound consisting of one carbon atom and four chlorine atoms. It is an ozone
depleting substance. Carbon tetrachloride was widely used as a raw material in many industrial applications,
including the production of chlorofluorocarbons, and as a solvent. Solvent use was ended in the United States
when it was discovered to be carcinogenic. See ozone depleting substance.
Chemical reaction.i Interaction between chemicals in which there is a change in the chemical composition of the
elements or compounds involved.
I,,,!; ; ;'!!r i, ji , ,, , , • , {' I- • ;.,.,
Chlorofluorocarbons (CFCs). Organic compounds made up of atoms of carbon, chlorine, and fluorine. An example
Ss CFC-12 (CC12F2), used as a refrigerant in refrigerators and air conditioners and as a foam blowing agent.
paseous CFCs can deplete the ozone layer when they slowly rise into the stratosphere, are broken down by
strong ultraviolet radiation, release chlorine atoms, and then react with ozone molecules. See Ozone Depleting
Substance.
I ;.:: ! > .('• i141 . . • • •• i' , iiif ' ' •• 'I ' '* j
Climate. The average weather, usually taken over a 30 year time period, for a particular region and time period.
Climate is not the same as weather, but rather, it is the average pattern of weather for a particular region.
Weather describes the short-term state of the atmosphere. Climatic elements include precipitation, temperature,
humidity, sunshine, wind velocity, phenomena such as fog, frost, and hail-storms, and other measures of the
feather. See weather.
Climate change.' The term "climate change" is sometimes used to refer to all forms of climatic inconsistency, but
because the Earth's climate is never static, the term is more properly used to imply a significant change from one
climatic condition to another. In some cases, "climate change" has been used synonymously with the term,
^global warming"; scientists however^ tend to use the term in the wider sense to also include natural changes in
fclimate. See global warming, greenhouse effect, enhanced greenhouse effect, radiative forcing.
Climate feedback.' An atmospheric, oceanic, terrestrial, or other process that is activated by direct climate change
induced by changes in radiative forcing. Climate feedbacks may increase (positive feedback) or diminish
(negative feedback) the magnitude of the direct climate change.
Climate lag.' The delay that occurs in climate change as a result of some factor that changes very slowly. For
example, the effects of releasing more carbon dioxide into the atmosphere may not be known for some time
because a large fraction is dissolved in the ocean and only released to the atmosphere many years later.
Climate sensitivity.' The equilibrium response of the climate to a change in radiative forcing; for example, a doubling
of the carbon dioxide concentration. See radiative forcing.
Climate system (or Earth system).' The atmosphere, the oceans, the biosphere, the cryosphere, and the geosphere,
together make up the climate system.
ti" i ir« .'.•"» i-1 ' •, "i
Coal. A black or brownish black solid, combustible substance formed by the partial decomposition of vegetable
matter without access to air. The rank of coal, which includes anthracite, bituminous coal, subbituminous coal,
and lignite, is based on fixed carbon, volatile matter, and heating value. Coal rank indicates the progressive
Alteration, or coalification, from lignite to anthracite. See anthracite, bituminous coal, subbituminous coal,
lignite.
Coal coke.: A hard, porous product made from baking bituminous coal in ovens at temperatures as high as 2,000
degrees Fahrenheit. It is used both as a fuel and as a reducing agent in smelting iron ore in a blast furnace.
Coal gasification.7 Conversion of solid coal to synthetic natural gas (SNG) or a gaseous mixture that can be burned
as a fuel.
Coal liquefaction.7 Conversion of solid coal to a liquid fuel such as synthetic crude oil or methanol.
Coalbed methane.2 Methane that is produced from coalbeds in the same manner as natural gas produced from other
Strata. Methane is the principal component of natural gas.
Co-control benefit.I0 It is the additional benefit derived from an environmental policy that is designed to control one
type of pollution, while reducing the emissions of other pollutants as well. For example, a policy to reduce
carbon dioxide emissions might reduce the combustion of coal, but when coal combustion is reduced, so too are
the emissions of particulates and sulfur dioxide. The benefits associated with reductions in emissions of
parliculates and sulfur dioxide are the co-control benefits of reductions in carbon dioxide.
Cogeneration.7 Production of two useful forms of energy such as high-temperature heat and electricity from the same
process.
T-4 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Combustion.2 Chemical oxidation accompanied by the generation of light and heat.
Commercial sector.8 An area consisting of non-housing units such as non-manufacturing business establishments
(e.g., wholesale and retail businesses), health and educational institutions, and government offices.
Compost.7 Partially decomposed organic plant and animal matter that can be used as a soil conditioner or fertilizer.
Composting.7 Partial breakdown of organic plant and animal matter by aerobic bacteria to produce a material that can
be used as a soil conditioner or fertilizer. See compost.
Compound.7 Combination of two or more different chemical elements held together by chemical bonds. See element.
See inorganic compound, organic compound.
Concentration.7 Amountof a chemical in a particular volume or weight of air, water, soil, or other medium. Seeparts
per billion, parts per million.
Conference Of Parties (COP).10 The supreme body of the United Nations Framework Convention on Climate Change
(UNFCCC). It comprises more than 170 nations that have ratified the Convention. Its first session was held in
Berlin, Germany, in 1995 and is expected to continue meeting on a yearly basis. The COP's role is to promote
and review the implementation of the Convention. It will periodically review existing commitments in light of
the Convention's objective, new scientific findings, and the effectiveness of national climate change programs.
See United Nations Framework Convention on Climate Change.
Conifer.7 See coniferous trees.
Coniferous trees.7 Cone-bearing trees, mostly evergreens, that have needle-shaped or scale-like leaves. They produce
wood known commercially as softwood. See deciduous trees.
Criteria pollutant.2 A pollutant determined to be hazardous to human health and regulated under EPA's National
Ambient Air Quality Standards. The 1970 amendments to the Clean Air Act require EPA to describe the health
and welfare impacts of a pollutant as the "criteria" for inclusion in the regulatory regime. In this report,
emissions of the criteria pollutants CO, NOX, NMVOCs, and SO2 are reported because they are thought to be
precursors to greenhouse gas formation.
Crop residue.2 Organic residue remaining after the harvesting and processing of a crop.
Crop rotation.7 Planting the same field or areas of fields with different crops from year to year to reduce depletion
of soil nutrients. A plant such as corn, tobacco, or cotton, which remove large amounts of nitrogen from the soil,
is planted one year. The next year a legume such as soybeans, which add nitrogen to the soil, is planted.
Crude oil.2 A mixture of hydrocarbons that exist in liquid phase in underground reservoirs and remain liquid at
atmospheric pressure after passing through surface separating facilities. See petroleum.
Deciduous trees.7 Trees such as oaks and maples that lose their leaves during part of the year. See coniferous trees.
Decomposition.9 The breakdown of matter by bacteria and fungi. It changes the chemical composition and physical
appearance of the materials.
Deforestation.' Those practices or processes that result in the conversion of forested lands for non-forest uses. This
is often cited as one of the major causes of the enhanced greenhouse effect for two reasons: 1) the burning or
decomposition of the wood releases carbon dioxide; and 2) trees that once removed carbon dioxide from the
atmosphere in the process of photosynthesis are no longer present.
Degradable.7 See biodegradable.
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Desertification.' The progressive destruction or degradation of existing vegetative cover to form a desert. This can
Ijccur due to overgrazing, deforestation, drought, and the burning of extensive areas. Once formed, deserts can
only support a sparse range of vegetation. Climatic effects associated with this phenomenon include increased
reflectivity of solar radiation, reduced atmospheric humidity, and greater atmospheric dust (aerosol) loading.
Distillate fuel oil.2 A general classification for the petroleum fractions produced in conventional distillation operations.
Included are products known as No. 1, No. 2, and No. 4 fuel oils and No. 1, No. 2, and No. 4 diesel fuels. Used
Jptimarily for space heating, on and off-highway diesel engine fuel (including railroad engine fuel and fuel for
Agricultural machinery), and electric power generation.
Economy.7 System of production, distribution, and consumption of economic goods.
Ecosystem.10 The complex system of plant, animal, fungal, and microorganism communities and their associated non-
Jiving environment interacting as an ecological unit. Ecosystems have no fixed boundaries; instead their
fJaramctefs are""set'lo the scientific, management, or policy question being examined. Depending upon the
purpose of analysis, a single lake, a watershed, or an entire region could be considered an ecosystem.
Electrons,7 Tiny particle moving around outside the nucleus of an atom. Each electron has one unit of negative charge
|-) and almost no mass.
Element.7 Chemicals such as hydrogen (H), iron (Fe), sodium (Na), carbon (C), nitrogen (N), or oxygen (0), whose
distinctly different atoms serve as the basic building blocks of all matter. There are 92 naturally occurring
y ements. Anoitier $ have been made in laboratories. Two or more elements combine to form compounds that
make up most of the world's matter. See compound.
Emission inventory. A list of air pollutants emitted into a community's, state's, nation's, or the Earth's atmosphere
|n amounts per some unit time (e.g. day or year) by type of source. An emission inventory has both political and
scientific applications.
Emissjqns, coefficient/factor.2 A unique value for scaling emissions to activity data in terms of a standard rate of
Emissions per unit of activity (e.g., grams of carbon dioxide emitted per barrel of fossil fuel consumed).
Emissions.2 Releases of gases to the atmosphere (e.g., the release of carbon dioxide during fuel combustion).
Emissions can be either intended or unintended releases. See fugitive emissions.
Energy conservation.7 Reduction or elimination of unnecessary energy use and waste. See energy-efficiency.
i • Hi?' , • • .jin11' "liriiii' • i: ' • * ',, I ' '
Energy intensity.5 Ratio between the consumption of energy to a given quantity of output; usually refers to the amount
of primary or final energy consumed per unit of gross domestic product.
Energy quality.7 Ability of a form of energy to do useful work. High-temperature heat and the chemical energy in
Fossil fuels and nuclear fuels are concentrated high quality energy. Low-quality energy such as low-temperature
heat is dispersed or diluted and cannot do much useful work.
Energy,3 The capacity for doing work as measured by the capability of doing work (potential energy) or the
conversion of this capability to motion (kinetic energy). Energy has several forms, some of which are easily
convertible and can be changed to another form useful for work. Most of the world's convertible energy comes
from fossil fuels that are burned to produce heat that is then used as a transfer medium to mechanical or other
means in order to accomplish tasks. In the United States, electrical energy is often measured in kilowatt-hours
KJfeWh), while heat energy is often measured in British thermal units (Btu).
Energy-efficiency. ^ The ratio of the useful output of services from an article of industrial equipment to the energy
use by such an article; for example, vehicle miles traveled per gallon of fuel (mpg).
Enhanced greenhouse effect.' The concept that the natural greenhouse effect has been enhanced by anthropogenic
emissions of greenhouse gases. Increased concentrations of carbon dioxide, methane, and nitrous oxide, CFCs,
MFCs, PFCs, SF6, HP3, and other photochemically important gases caused by human activities such as fossil fuel
consumption, trap more infra-red radiation, thereby exerting a warming influence on the climate. See greenhouse
gas, anthropogenic, greenhouse effect, climate.
Enhanced oil recovery.7 Removal of some of the heavy oil left in an oil well after primary and secondary recovery.
Sec primary oil recovery, secondary oil recovery.
T-6 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Enteric fermentation.2 A digestive process by which carbohydrates are broken down by microorganisms into simple
molecules for absorption into the bloodstream of an animal.
Environment.7 All external conditions that affect an organism or other specified system during its lifetime.
Ethanol (C2HSOH). 8 Otherwise known as ethyl alcohol, alcohol, or grain spirit. A clear, colorless, flammable
oxygenated hydrocarbon with a boiling point of 78.5 degrees Celsius in the anhydrous state. In transportation,
ethanol is used as a vehicle fuel by itself (E100), blended with gasoline (E85), or as a gasoline octane enhancer
and oxygenate (10 percent concentration).
Evapotranspiration.10 The loss of water from the soil by evaporation and by transpiration from the plants growing
in the soil, which rises with air temperature.
Exponential growth.7 Growth in which some quantity, such as population size, increases by a constant percentage
of the whole during each year or other time period; when the increase in quantity over time is plotted, this type
of growth yields a curve shaped like the letter J.
Feedlot.7 Confined outdoor or indoor space used to raise hundreds to thousands of domesticated livestock. See
rangeland.
Fertilization, carbon dioxide.' An expression (sometimes reduced to 'fertilization') used to denote increased plant
growth due to a higher carbon dioxide concentration.
Fertilizer. 7 Substance that adds inorganic or organic plant nutrients to soil and improves its ability to grow crops,
trees, or other vegetation. See organic fertilizer.
Flaring.9 The burning of waste gases through a flare stack or other device before releasing them to the air.
Fluidized bed combustion (FBC).7 Process for burning coal more efficiently, cleanly, and cheaply. A stream of hot
air is used to suspend a mixture of powdered coal and limestone during combustion. About 90 to 98 percent of
the sulfur dioxide produced during combustion is removed by reaction with limestone to produce solid calcium
sulfate.
Fluorocarbons. ' Carbon-fluorine compounds that often contain other elements such as hydrogen, chlorine, or
bromine. Common fluorocarbons include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs),
hydrofluorocarbons (MFCs), andperfluorocarbons (PFCs). See chlorofluorocarbons, hydrochlorofluorocarbons,
hydrofluorocarbons, perfluorocarbons.
Forcing mechanism.' A process that alters the energy balance of the climate system (i.e., changes the relative balance
between incoming solar radiation and outgoing infrared radiation from Earth). Such mechanisms include
changes in solar irradiance, volcanic eruptions, and enhancement of the natural greenhouse effect by emission
of carbon dioxide.
Forest.7 Terrestrial ecosystem (biome) with enough average annual precipitation (at least 76 centimeters or 30 inches)
to support growth of various species of trees and smaller forms of vegetation.
Fossil fuel. A general term for buried combustible geologic deposits of organic materials, formed from decayed plants
and animals that have been converted to crude oil, coal, natural gas, or heavy oils by exposure to heat and
pressure in the earth's crust over hundreds of millions of years. See coal, petroleum, crude oil, natural gas.
Fossil fuel combustion.' Burning of coal, oil (including gasoline), or natural gas. The burning needed to generate
energy release carbon dioxide by-products that can include unburned hydrocarbons, methane, and carbon
monoxide. Carbon monoxide, methane, and many of the unburned hydrocarbons slowly oxidize into carbon
dioxide in the atmosphere. Common sources of fossil fuel combustion include cars and electric utilities.
Freon. See chlorofluorocarbon.
Fugitive emissions.2 Unintended gas leaks from the processing, transmission, and/or transportation of fossil fuels,
CFCs from refrigeration leaks, SF6 from electrical power distributor, etc.
Gasohol.7 Vehicle fuel consisting of a mixture of gasoline and ethyl or methyl alcohol; typically 10 to 23 percent
ethanol by volume.
General Aviation.8 That portion of civil aviation, which encompasses all facets of aviation except air carriers. It
includes any air taxis, commuter air carriers, and air travel clubs, which do not hold Certificates of Public
Convenience and Necessity. See air carriers.
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General circulation model (GCM).' A global, three-dimensional computer model of the climate system which can
be used to simulate human-induced climate change. GCMs are highly complex and they represent the effects
of such factors as reflective and absorptive properties of atmospheric water vapor, greenhouse gas concentrations,
Clouds, annual and daily solar heating, ocean temperatures and ice boundaries. The most recent GCMs include
global representations of the atmosphere, oceans, and land surface.
Geosphere.' The soils, sediments, and rock layers of the Earth's crust, both continental and beneath the ocean floors.
Geothcnnal energy.7 Heat transferred from the earth's molten core to under-ground deposits of dry steam (steam with
"po water droplets), wet steam (a mixture of steam and water droplets), hot water, or rocks lying fairly close to
the earth's surface. . " ^
Global! Warming Potential (G\VP).' The index used to translate the level of emissions of various gases into a
common meaSffre in order to compare the relative radiative forcing of different gases without directly calculating
the changes in atmospheric concentrations. GWPs are calculated as the ratio of the radiative forcing that would
result from the emissions of one kilogram of a greenhouse gas to that from the emission of one kilogram of
carbon dioxide over a period of time (usually 100 years). Gases involved in complex atmospheric chemical
processes have not been assigned GWPs. See lifetime.
Globa| warming. "*" The progressive gradual rise of the earth's surface temperature thought to be caused by the
'greenhouse effect and responsible for changes in global climate patterns. See enhanced greenhouse effect,
"greenhouse effect, climate change.
Grassland.7 Terrestrial ecosystem (biome) found in regions where moderate annual average precipitation (25 to 76
centimeters or Io to 30 inches) is enough to support the growth of grass and small plants but not enough to
Support large stands of trees.
Greenhouse effect. ^ Trapping and build-up of heat in the atmosphere (troposphere) near the earth's surface. Some
of the heat flowing back toward space from the earth's surface is absorbed by water vapor, carbon dioxide, ozone,
I and several other gases in the atmosphere and then reradiated back toward the earth's surface. If the atmospheric
"Concentrations of these greenhouse gases rise, the average temperature of the lower atmosphere will gradually
increase. Sec enhanced greenhouse effect, climate change, global warming.
Greenhouse gas (CfHG).1" Any gas that absorbs infrared radiation in the atmosphere. Greenhouse gases include, but
are not limited to, water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O),
hydrochlorofluorocarbons (HCFCs), ozone (O3), hydrofluorocarbons (MFCs), perfluorocarbons (PFCs), and
Sulfur hexafluoride (SF6). See carbon dioxide, methane, nitrous oxide, hydrochlorofluorocarbon, ozone,
[hydrofluorocarbon,perfluorocarbon, sulfur hexafluoride.
Halocarbons.1 Chemicals consisting of carbon, sometimes hydrogen, and either chlorine, fluorine, bromine or iodine.
Halotis.'" Compounds, also known as bromofluorocarbons, that contain bromine, fluorine, and carbon. They are
generally used as fire extinguishing agents and cause ozone depletion. Bromine is many times more effective
at destroying stratospheric ozone than chlorine. See ozone depleting substance.
Heat Content. * The amount of heat per unit mass released upon complete combustion.
Heat.1 Form of kinetic energy that flows from one body to another when there is a temperature difference between
the two bodies'! Heat always flows spontaneously from a hot sample of matter to a colder sample of matter. This
is one way to state the second law of thermodynamics. See temperature.
Higher heating value.5 Quantity of heat liberated by the complete combustion of a unit volume or weight of a fuel
assuming that the produced water vapor is completely condensed and the heat is recovered; also known as gross
calorific value. See lower heating value.
Histosol.9 Wet organic soils, such as peats and mucks.
Hydrocarbons.' Substances containing only hydrogen and carbon. Fossil fuels are made up of hydrocarbons. Some
hydrocarbon compounds are major air pollutants.
Hydrochlorofluorocarbons (HCFCs).' Compounds containing hydrogen, fluorine, chlorine, and carbon atoms.
Although ozone depleting substances, they are less potent at destroying stratospheric ozone than
chlorofluorocarbons (CFCs). They have been introduced as temporary replacements for CFCs and are also
greenhouse gases. See ozone depleting substance.
T-8 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Hydroelectric power plant.7 Structure in which the energy of fading or flowing water spins a turbine generator to
produce electricity.
Hydrofluorocarbons (HFCs).' Compounds containing only hydrogen, fluorine, and carbon atoms. They were
introduced as alternatives to ozone depleting substances in serving many industrial, commercial, and personal
needs. HFCs are emitted as by-products of industrial processes and are also used in manufacturing. They do
not significantly deplete the stratospheric ozone layer, but they are powerful greenhouse gases with global
warming potentials ranging from 140 (HFC-152a) to 11,700 (HFC-23).
Hydrologic cycle. The process of evaporation, vertical and horizontal transport of vapor, condensation, precipitation,
and the flow of water from continents to oceans. It is a major factor in determining climate through its influence
on surface vegetation, the clouds, snow and ice, and soil moisture. The hydrologic cycle is responsible for 25
to 30 percent of the mid-latitudes' heat transport from the equatorial to polar regions.
Hydropower.7 Electrical energy produced by falling or flowing water. See hydroelectric power plant.
Hydrosphere.7 'All the earth's liquid water (oceans, smaller bodies of fresh water, and underground aquifers), frozen
water (polar ice caps, floating ice, and frozen upper layer of soil known as permafrost), and small amounts of
water vapor in the atmosphere.
Industrial sector.8 Construction, manufacturing, agricultural and mining establishments.
Infrared radiation. ' The heat energy that is emitted from all solids, liquids, and gases. In the context of the
greenhouse issue, the term refers to the heat energy emitted by the Earth's surface and its atmosphere.
Greenhouse gases strongly absorb this radiation in the Earth's atmosphere, and re-radiate some of it back towards
the surface, creating the greenhouse effect.
Inorganic compound.7 Combination of two or more elements other than those used to form organic compounds. See
organic compound.
Inorganic fertilizer.7 See synthetic fertilizer.
Intergovernmental Panel on Climate Change (IPCC).' The IPCC was established jointly by the United Nations
Environment Programme and the World Meteorological Organization in 1988. The purpose of the IPCC is to
assess information in the scientific and technical literature related to all significant components of the issue of
climate change. The IPCC draws upon hundreds of the world's expert scientists as authors and thousands as
expert reviewers. Leading experts on climate change and environmental, social, and economic sciences from
some 60 nations have helped the IPCC to prepare periodic assessments of the scientific underpinnings for
understanding global climate change and its consequences. With its capacity for reporting on climate change,
its consequences, and the viability of adaptation and mitigation measures, the IPCC is also looked to as the
official advisory body to the world's governments on the state of the science of the climate change issue. For
example, the IPCC organized the development of internationally accepted methods for conducting national
greenhouse gas emission inventories.
Irreversibilities.I0 Changes that, once set in motion, cannot be reversed, at least on human time scales.
Jet fuel8 Includes both naphtha-type and kerosene-type fuels meeting standards for use in aircraft turbine engines.
Although most jet fuel is used in aircraft, some is used for other purposes such as generating electricity.
Joule.' The energy required to push with a force of one Newton for one meter.
Kerogen.7 Solid, waxy mixture of hydrocarbons found in oil shale, with a fine grained sedimentary rock. When the
rock is heated to high temperatures, the kerogen is vaporized. The vapor is condensed and then sent to a refinery
to produce gasoline, heating oil, and other products. See oil shale, shale oil.
Kerosene.2 A petroleum distillate that has a maximum distillation temperature of 401 degrees Fahrenheit at the 10
percent recovery point, a final boiling point of 572 degrees Fahrenheit, and a minimum flash point of 100 degrees
Fahrenheit. Used in space heaters, cookstoves, and water heaters, and suitable for use as an illurriinant when
burned in wick lamps.
Kyoto Protocol.10 This is an international agreement struck by 159 nations attending the Third Conference of Parties
(COP) to the United Nations Framework Convention on Climate Change (held in December of 1997 in Kyoto
Japan) to reduce worldwide emissions of greenhouse gases. If ratified and put into force, individual countries
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Save committed to reduce their greenhouse gas emissions by a specified amount. See Framework Convention
"on Climate Change, Conference of Parties.
Landfill.7 Land waste disposal site in which waste is generally spread in thin layers, compacted, and covered with a
fresh layer of soil each day.
Lifetime (atmospheric).' The lifetime of a greenhouse gas refers to the approximate amount of time it would take for
the anthropogenic increment to an atmospheric pollutant concentration to return to its natural level (assuming
emissions cease) as a result of either being converted to another chemical compound or being taken out of the
'atmosphere via a sink. This time depends on the pollutant's sources and sinks as well as its reactivity. The
lifetime of a pollutant is often considered in conjunction with the mixing of pollutants in the atmosphere; a long
lifetime will allow tfie pollutant to mix throughout the atmosphere. Average lifetimes can vary from about a
Week (e.g., sulfate aerosols) to more than a century (e.g., CFCs, carbon dioxide). See residence'time.
Light-duty vehicles.8 Automobiles and light trucks combined.
Lignite.! A brownish-black coal of low rank with high inherent moisture and volatile matter content, used almost
exclusively for electric power generation. Also referred to as brown coal.
! Liquefied natural gas (LNG).7 Natural gas converted to liquid form by cooling to a very low temperature.
Liquefied petroleum gas (LPG). * Ethane, ethylene, propane, propylene, normal butane, butylene, and isobutane
produced at refineries or natural gas processing plants, including plants that fractionate new natural gas plant
liquids.
Litter.* Undecompbsed plant residues on the soil surface. See decomposition.
Longwave radiation.9 The radiation emitted in the spectral wavelength greater than 4 micrometers corresponding to
the radiation emitted from the Earth and atmosphere. It is sometimes referred to as terrestrial radiation or infrared
radiation, although somewhat imprecisely. See infrared radiation.
Low Emission Vehicle (LEV).8 A vehicle meeting the low-emission vehicle standards.
Lower heating value.5 Quantity of heat liberated by the complete combustion of a unit volume or weight of a fuel
assuming that the produced water remains as a vapor and the heat of the vapor is not recovered; also known as
net calorific value. See higher heating value.
Lubricant.2 A substance used to reduce friction between bearing surfaces or as aprocess material, either incorporated
into other materials used as aids in manufacturing processes or as carriers of other materials. Petroleum
lubricants may be produced either from distillates or residues. Other substances may be added to impart or
Improve Useful properties. Does not include by-products of lubricating oil from solvent extraction or tars derived
from de-asphalting. Lubricants include all grades of lubricating oils from spindle oil to cylinder oil and those
Used in greases! Lubricant categories are paraffinic and naphthenic.
Manure.T Dung and urine of animals that can be used as a form of organic fertilizer.
Mass balance. '* The application of the principle of the conservation of matter.
Mauna Loa. * An intermittently active volcano 13,680 feet (4,170 meters) high in Hawaii.
Methane (CH4).' A hydrocarbon that is a greenhouse gas with a global warming potential most recently estimated at
21. Methane is produced through anaerobic (without oxygen) decomposition of waste in landfills, animal
digestion, decomposition of animal wastes, production and distribution of natural gas and petroleum, coal
production, and incomplete fossil fuel combustion. The atmospheric concentration of methane as been shown
tp be increasing at a rate of about 0.6 percent per year and the concentration of about 1.7 per million by volume
(ppmv) is more than twice its pre-industrial value. However, the rate of increase of methane in the atmosphere
may be stabilizing.
Mcthanol (CH3OH).8 A colorless poisonous liquid with essentially no odor and little taste. It is the simplest alcohol
With a boiling point of 64.7 degrees Celsius. In transportation, methanol is used as a vehicle fuel by itself
(M100), or blended with gasoline (M85).
Methanotrophic.7 Having the biological capacity to oxidize methane to CO2 and water by metabolism under aerobic
conditions. See aerobic.
T-10 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Methyl bromide (CH3Br). " An effective pesticide; used to fumigate soil and many agricultural products. Because
it contains bromine, it depletes stratospheric ozone when released to the atmosphere. See ozone depleting
substance.
Metric ton.' Common international measurement for the quantity of greenhouse gas emissions. A metric ton is equal
to 1000 kilograms, 2204.6 pounds, or 1.1023 short tons.
Mineral.7 Any naturally occurring inorganic substance found in the earth's crust as a crystalline solid.
Model year.8 Refers to the "sales" model year; for example, vehicles sold during the period from October 1 to the next
September 31 is considered one model year.
Molecule.7 Chemical combination of two or more atoms of the same chemical element (such as O2) or different
chemical elements (such as H2O).
Montreal Protocol on Substances that Deplete the Ozone Layer. " The Montreal Protocol and its amendments
control the phaseout of ozone depleting substances production and use. Under the Protocol, several international
organizations report on the science of ozone depletion, implement projects to help move away from ozone
depleting substances, and provide a forum for policy discussions. In the United States, the Protocol is
implemented under the rubric of the Clean Air Act Amendments of 1990. See ozone depleting substance, ozone
layer,
Motor gasoline.2 A complex mixture of relatively volatile hydrocarbons, with or without small quantities of additives,
obtained by blending appropriate refinery streams to form a fuel suitable for use in spark-ignition engines. Motor
gasoline includes both leaded and unleaded grades of finished gasoline, blending components, and gasohol.
Municipal solid waste (MSW).2 Residential solid waste and some non-hazardous commercial, institutional, and
industrial wastes. This material is generally sent to municipal landfills for disposal. See landfill.
Naphtha.2 A generic term applied to a petroleum fraction with an approximate boiling range between 122 and 400
degrees Fahrenheit.
Natural gas.7 Underground deposits of gases consisting of 50 to 90 percent methane (CH4) and small amounts of
heavier gaseous hydrocarbon compounds such as propane (C3H4) and butane (C4H10).
Natural gas liquids (NGLs).2 Those hydrocarbons in natural gas that are separated as liquids from the gas. Includes
natural gas plant liquids and lease condensate.
Nitrogen cycle.7 Cyclic movement of nitrogen in different chemical forms from the environment, to organisms, and
then back to the environment.
Nitrogen fixation.7 Conversion of atmospheric nitrogen gas into forms useful to plants and other organisms by
lightning, bacteria, and blue-green algae; it is part of the nitrogen cycle.
Nitrogen oxides (NOX).' Gases consisting of one molecule of nitrogen and varying numbers of oxygen molecules.
Nitrogen oxides are produced, for example, by the combustion of fossil fuels in vehicles and electric power
plants. In the atmosphere, nitrogen oxides can contribute to formation of photochemical ozone (smog), impair
visibility, and have health consequences; they are considered pollutants.
Nitrous oxide (N2O).' A powerful greenhouse gas with a global warming potential most recently evaluated at 310.
Major sources of nitrous oxide include soil cultivation practices, especially the use of commercial and organic
fertilizers, fossil fuel combustion, nitric acid production, and biomass burning.
Noiibiodegradable. 7 Substance that cannot be broken down in the environment by natural processes. See
biodegradable.
Nonlinearities.10 Occur when changes in one variable cause a more than proportionate impact on another variable.
Non-methane volatile organic compounds (NMVOCs).2 Organic compounds, other than methane, that participate
in atmospheric photochemical reactions.
Non-point source.7 Large land area such as crop fields and urban areas that discharge pollutant into surface and
underground water over a large area. See point source.
Nuclear electric power.3 Electricity generated by an electric power plant whose turbines are driven by steam
generated in a reactor by heat from the fissioning of nuclear fuel.
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.
Nuclear energy.1 Energy released when atomic nuclei undergo a nuclear reaction such as the spontaneous emission
Qf radioactivity, nuclear fission, or nuclear fusion.
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Oil shale. Underground formation of a fine-grained sedimentary rock containing varying amounts of kerogen, a solid,
w'axy mixture of hydrocarbon compounds. Heating the rock to high temperatures converts the kerogen to a
yapor, which can be condensed to form a slow flowing heavy oil called shale oil. See kerogen, shale oil.
(311. See crude oil, petroleum.
Ore.7 lylineral deposit containing a high enough concentration of at least one metallic element to permit the metal to
be extracted and sold at a profit.
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Organic compound.7 Molecule that contains atoms of the element carbon, usually combined with itself and with
Horns of one or more other element such as hydrogen, oxygen, nitrogen, sulfur, phosphorus, chlorine, or fluorine.
See inorganic compound.
Organic fertilizer.7 Organic material such as manure or compost, applied to cropland as a source of plant nutrients.
Oxidize.* To chemically transform a substance by combining it with oxygen.
Oxygen cycle. 7 Cyclic movement of oxygen in different chemical forms from the environment, to organisms, and then
back to the environment.
Ozonel * A colorless gas witlra pungent odor, having the molecular form of O3, found in two layers of the atmosphere,
tfee stratosphere an
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Petroleum.2 A generic term applied to oil and oilproducts in all forms, such as crude oil, lease condensate, unfinished
oils, petroleum products, natural gas plant liquids, and non-hydrocarbon compounds blended into finished
petroleum products. See crude oil.
Photosynthesis.7 Complex process that takes place in living green plant cells. Radiant energy from the sun is used
to combine carbon dioxide (CO2) and water (H2O) to produce oxygen (O2) and simple nutrient molecules, such
as glucose (C6HI2O6).
Photovoltaic and solar thermal energy.2 Energy radiated by the sun as electromagnetic waves (electromagnetic
radiation) that is converted into electricity by means of solar (i.e., photovoltaic) cells or useable heat by
concentrating (i.e., focusing) collectors.
Point source.7 A single identifiable source that discharges pollutants into the environment. Examples are smokestack,
sewer, ditch, or pipe. See non-point source.
Pollution.7 A change in the physical, chemical, or biological characteristics of the air, water, or soil that can affect the
health, survival, or activities of humans in an unwanted way. Some expand the term to include harmful effects
on all forms of life.
Polyvinyl chloride (PVC).2 A polymer of vinyl chloride. It is tasteless, odorless and insoluble in most organic
solvents. A member of the family vinyl resin, used in soft flexible films for food packaging and in molded rigid
products, such as pipes, fibers, upholstery, and bristles.
Population.7 Group of individual organisms of the same species living within a particular area.
Prescribed burning.7 Deliberate setting and careful control of surface fires in forests to help prevent more destructive
fires and to kill off unwanted plants that compete with commercial species for plant nutrients; may also be used
on grasslands.
Primary oil recovery.7 Pumping out the crude oil that flows by gravity into the bottom of an oil well. See enhanced
oil recovery, secondary oil recovery.
Quad.8 Quad stands for quadrillion, which is, 1015.
Radiation.' Energy emitted in the form of electromagnetic waves. Radiation has differing characteristics depending
upon the wavelength. Because the radiation from the Sun is relatively energetic, it has a short wavelength (e.g.,
ultraviolet, visible, and near infrared) while energy re-radiated from the Earth's surface and the atmosphere has
a longer wavelength (e.g., infrared radiation) because the Earth is cooler than the Sun. See ultraviolet radiation,
infrared radiation, solar radiation, longwave radiation, terrestrial radiation.
Radiative forcing.' A change in the balance between incoming solar radiation and outgoing infrared (i.e., thermal)
radiation. Without any radiative forcing, solar radiation coining to the Earth would continue to be approximately
equal to the infrared radiation emitted from the Earth. The addition of greenhouse gases to the atmosphere traps
an increased fraction of the infrared radiation, reradiating it back toward the surface of the Earth and thereby
creates a warming influence.
Rail.8 Includes "heavy" and "light" transit rail. Heavy transit rail is characterized by exclusive rights-of-way, multi-
car trains, high speed rapid acceleration, sophisticated signaling, and high platform loading. Also known as
subway, elevated railway, or metropolitan railway (metro). Light transit rail may be on exclusive or shared rights
of way, high or low platform, multi-car trains or single cars, automated or manually operated. In generic usage,
light rail includes streetcars, trolley cars, and tramways.
Rangeland.7 Land, mostly grasslands, whose plants can provide food (i.e., forage) for grazing or browsing animals.
Seefeedlot.
Recycling.7 Collecting and reprocessing a resource so it can be used again. An example is collecting aluminum cans,
melting them down, and using the aluminum to make new cans or other aluminum products.
Reforestation.2 Replanting of forests on lands that have recently been harvested.
Renewable energy.2 Energy obtained from sources that are essentially inexhaustible, unlike, for example, the fossil
fuels, of which there is a finite supply. Renewable sources of energy include wood, waste, geothermal, wind,
photovoltaic, and solar thermal energy. See hydropower, photovoltaic.
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Residence time. Average time spent in a reservoir by an individual atom or molecule. Also, this term is used to define
the age of a molecule when it leaves the reservoir. With respect to greenhouse gases, residence time usually
infers to how long a particular molecule remains in the atmosphere. See lifetime.
Residential sector. 3 An area or portion consisting only of housing units.
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Residual fuel oil.* The heavier oils that remain after the distillate fuel oils and lighter hydrocarbons are distilled away
In refinery operations and that conform to ASTM Specifications D396 and D975. Included are No. 5, a residual
fuel oil of medium viscosity; Navy Special, for use in steam-powered vessels in government service and in shore
power plants; and No. 6, which includes Bunker C fuel oil and is used for commercial and industrial heating,
electricity generation, and to power ships. Imports of residual fuel oil include imported crude oil burned as fuel.
Secondary oil recovery. 7 Injection of water into an oil well after primary oil recovery to force out some of the
remaining thicker crude oil. See enhanced oil recovery, primary oil recovery.
Sector, Division, most commonly used to denote type of energy consumer (e.g., residential) or according to the
Intergovenimental Panel on Climate Change, the type of greenhouse gas emitter (e.g. industrial process). See
Jntergovernmentai Panel on Climate Change.
Septic tank. 7 Underground tank for treatment of wastewater from a home in rural and suburban areas. Bacteria in the
|JinI< decompose organic wastes and the sludge settles to the bottom of the tank. The effluent flows out of the
tank into the ground through a field of drainpipes.
Sewage treatment (primary). 7 Mechanical treatment of sewage in which large solids are filtered out by screens and
Suspended solids settle out as sludge in a sedimentation tank.
Shale oil. 7 Slow- flowing, dark brown, heavy oil obtained when kerogen in oil shale is vaporized at high temperatures
and then condensed? Shale oil can be refined to yield gasoline, heating oil, and other petroleum products. See
Herogen, oil shale.
Short ton. ' Common measurement for a ton in the United States. A short ton is equal to 2,000 Ibs. or 0.907 metric
, • , ,:. , .
Sink. ' A reservoir that uptakes a pollutant from another part of its cycle. Soil and trees tend to act as natural sinks for
carbon.
Sludge. 7 Gooey solid mixture of bacteria and virus laden organic matter, toxic metals, synthetic organic chemicals,
and solid chemicals removed from wastewater at a sewage treatment plant.
Soil. 7 Complex mixture of inorganic minerals (i.e., mostly clay, silt, and sand), decaying organic matter, water, air,
and living organisms.
Soil carbon. * A major component of the terrestrial biosphere pool in the carbon cycle. The amount of carbon in the
Soil is a function of the historical vegetative cover and productivity, which in turn is dependent in part upon
climatic variables.
Solar energy. 7 Direct radiant energy from the sun. It also includes indirect forms of energy such as wind, falling or
flowing water (hydropower), ocean thermal gradients, and biomass, which are produced when direct solar energy
interact with the earth. See solar radiation.
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Solar radiation, ' Energy from the Sun. Also referred to as short-wave radiation. Of importance to the climate system,
solar radiation includes ultra-violet radiation, visible radiation, and infrared radiation.
Source/ Any process or activity that releases a greenhouse gas, an aerosol, or a precursor of a greenhouse gas into
the atmosphere.
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Special naphtha.2 All finished products within the naphtha boiling range that are used as paint thinners, cleaners, or
solvents. Those products are refined to a specified flash point.
Still gas. 2 Any form or mixture of gases produced in refineries by distillation, cracking, reforming, and other
p'rbeess"e"S. Principal constituents are methane, ethane, ethylene, normal butane, butylene, propane, propylene,
etc. Used as a refinery fuel and as a petrochemical feedstock.
Stratosphere. 7 Second layer of the atmosphere, extending from about 19 to 48 kilometers (12 to 30 miles) above the
earth's surfaeej It contains small amounts of gaseous ozone (O3), which filters out about 99 percent of the
incoming harmful ultraviolet (UV) radiation. Most commercial airline flights operate at a cruising altitude in
the lower stratosphere. See ozone layer, ultraviolet radiation.
T-14 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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Stratospheric ozone. See ozone layer.
Strip mining.7 Cutting deep trenches to remove minerals such as coal and phosphate found near the earth's surface
in flat or rolling terrain. See surface mining.
Subbituminous coal.2 A dull, black coal of rank intermediate between lignite and bituminous coal.
Sulfur cycle.7 Cyclic movement of sulfur in different chemical forms from the environment, to organisms, and then
back to the environment.
Sulfur dioxide (SO2).' A compound composed of one sulfur and two oxygen molecules. Sulfur dioxide emitted into
the atmosphere through natural and anthropogenic processes is changed in a complex series of chemical reactions
in the atmosphere to sulfate aerosols. These aerosols are believed to result in negative radiative forcing (i.e.,
tending to cool the Earth's surface) and do result in acid deposition (e.g., acid rain). See aerosols, radiative
forcing, acid deposition, acid rain.
Sulfur hexafluoride (SF6).' A colorless gas soluble in alcohol and ether, slightly soluble in water. A very powerful
greenhouse gas used primarily in electrical transmission and distribution systems and as a dielectric in
electronics. The global warming potential of SF6 is 23,900. See Global Warming Potential.
Surface mining.7 Removal of soil, sub-soil, and other strata and then extracting a mineral deposit found fairly close
to the earth's surface. See strip mining.
Synthetic fertilizer.7 Commercially prepared mixtures of plant nutrients such as nitrates, phosphates, and potassium
applied to the soil to restore fertility and increase crop yields. See organic fertilizer.
Synthetic natural gas (SNG).3 A manufactured product chemically similar in most respects to natural gas, resulting
from the conversion or reforming of petroleum hydrocarbons. It may easily be substituted for, or interchanged
with, pipeline quality natural gas.
Tailings.7 Rock and other waste materials removed as impurities when minerals are mined and mineral deposits are
processed. These materials are usually dumped on the ground or into ponds.
Tar sand.7 Swamp-like deposit of a mixture of fine clay, sand, water, and variable amounts of tar-like heavy oil
known as bitumen. Bitumen can be extracted from tar sand by heating. It can then be purified and upgraded to
synthetic crude oil. See bitumen.
Temperature.7 Measure of the average speed of motion of the atoms or molecules in a substance or combination of
substances at a given moment. See heat.
Terrestrial.7 Pertaining to land.
Terrestrial radiation.9 The total infrared radiation emitted by the Earth and its atmosphere in the temperature range
of approximately 200 to 300 Kelvin. Terrestrial radiation provides a major part of the potential energy changes
necessary to drive the atmospheric wind system and is responsible for maintaining the surface air temperature
within limits of livability.
Trace gas.' Any one of the less common gases found in the Earth's atmosphere. Nitrogen, oxygen, and argon make
up more than 99 percent of the Earth's atmosphere. Other gases, such as carbon dioxide, water vapor, methane,
oxides of nitrogen, ozone, and ammonia, are considered trace gases. Although relatively unimportant in terms
of their absolute volume, they have significant effects on the Earth's weather and climate.
Transportation sector.8 Consists of private and public passenger and freight transportation, as well as government
transportation, including military operations.
Troposphere.1&7 The lowest layer of the atmosphere and contains about 95 percent of the mass of air in the Earth's
atmosphere. The troposphere extends from the Earth's surface up to about 10 to 15 kilometers. All weather
processes take place in the troposphere. Ozone that is formed in the troposphere plays a significant role in both
the greenhouse gas effect and urban smog. See ozone precursor, stratosphere, atmosphere.
Tropospheric ozone precursor. See ozone precursor.
Tropospheric ozone.' See ozone.
Ultraviolet radiation (UV)." A portion of the electromagnetic spectrum with wavelengths shorted than visible light.
The sun produces UV, which is commonly split into three bands of decreasing wavelength. Shorter wavelength
radiation has a greater potential to cause biological damage on living organisms. The longer wavelength
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ultraviolet band, UVA, is not absorbed by ozone in the atmosphere. UVB is mostly absorbed by ozone, although
E reaches the Earth. The shortest wavelength band, UVC, is completely absorbed by ozone and normal
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jn in the atmosphere.
oils.* All oils requiring further refinery processing, except those requiring only mechanical blending.
Includes naphtha and lighter oils, kerosene and light gas oils, heavy gas oils, and residuum.
United Nations Framework Convention on Climate Change (UNFCCC).' The international treaty unveiled at the
United Nations Conference on Environment and Development (UNCED) in June 1992. The UNFCCC commits
signatory countries to stabilize anthropogenic (i.e. human-induced) greenhouse gas emissions to "levels that
§6'uld prevent dangerous anthropogenic interference with the climate system". The UNFCCC also requires that
all signatory parties develop and update national inventories of anthropogenic emissions of all greenhouse gases
flptoiherwise controlled by the Montreal Protocol. Out of 155 countries that have ratified this accord, the United
States was the first industrialized nation to do so.
Vehicle miles traveled (VMT).8 One vehicle traveling the distance of one mile. Thus, total vehicle miles is the total
mileage traveled by all vehicles.
Volatile organic compounds (VOCs).6 Organic compounds that evaporate readily into the atmosphere at normal
temperatures. VOCs contribute significantly to photochemical smog production and certain health problems.
fjee non-methane volatile organic compounds.
Wastewatcr.2 Water that has been used and contains dissolved or suspended waste materials. See sewage treatment.
Water vapor.' The most abundant greenhouse gas; it is the water present in the atmosphere" in gaseous form. Water
vapor is an important part of the natural greenhouse effect. While humans are not significantly increasing its
: concentration, it contributes to the enhanced greenhouse effect because the warming influence of greenhouse
"';" gl>scs leads to a positive water vapor feedback. In addition to its role as a natural greenhouse gas, water vapor
pays an important role in regulating the temperature of the planet because clouds form when excess water vapor
in the atmosphere condenses to form ice and water droplets and precipitation.
i. ' , *, , ,,,,, „ „„, | , , ,„ „„, . „. ,„ , „ ,,„ „,, ,, || , , ,,„
Waxes.2 Solid or semisolid materials derived from petroleum distillates or residues. Light-colored, more or less
translucent crystalline masses, slightly greasy to the touch, consisting of a mixture of solid hydrocarbons in
which the paraffin series predominates! Included are all marketable waxes, whether crude scale or fully refined.
Used primarily as industrial coating for surface protection.
Weather.' Weather is the specific condition of the atmosphere at a particular place and time. It is measured in terms
of such things as wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. In most
places, weather can change from hour-to-hour, day-to-day, and season-to-season. Climate is the average of
weather over time and space. A simple way of remembering the difference is that climate is what you expect
(e.g. cold winters) and 'weather' is what you get (e.g. a blizzard). See climate.
Wetland.7 Land that stays flooded all or part of the year with fresh or salt water.
Wetlands.1 Areas regularly saturated by surface or groundwater and subsequently characterized by a prevalence of
vegetation adapted for life in saturated-soil conditions.
Wood energy.2 Wood and wood products used as fuel, including roundwood (i.e., cordwood), limbwood, wood chips,
bark, sawdust, forest residues, and charcoal.
References
1 U.S. Environmental Protection Agency, Global Warming website, http://www.epa.gov/globalwarming. February
'
, , , ., . ....
1 Energy Information Administration, Emissions of Greenhouse Gases in the United States 1997, DOE/EIA-
0573(97), U.S. Department of Energy, Washington, DC. October 1998. [See http://www.eia.doe.gov]
} Energy Information Administration, Annual Energy Review 1997, DOE/EIA-0387(97), U.S. Department of
Energy^ Washington, DC, July 1998.
* United Nations Framework Convention on Climate Change. [See http://www.unfccc.de]
T-16 Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-1997
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5 Intergovernmental Panel on Climate Change, Climate Change 1995: The Science of Climate Change, Cambridge
University Press: New York, 1996
6 Cooper's Comprehensive Environmental Desk Reference, Arthur R. Cooper, Sr., Van Nostrand Reinhold: New
York, 1996.
7 Miller, G. Tyler, Jr., Living in the Environment, An Introduction to Environment Science, sixth edition, 1990.
8 Davis, Stacy, Transportation Energy Data Book, Oak Ridge National Laboratory, U.S. Department of Energy,
Edition 17, 1997.
9 Carbon Dioxide Information Analysis Center, website at http ://cdiac.esd.ornl.gov. Oak Ridge National
Laboratory, U.S. Department of Energy, February 26, 1999.
10 Resources for the Future, Weathervane website, http://www.weathervane.rff.org/glossarv/index.html.
February 26, 1999.
11 U.S. Environmental Protection Agency, Ozone Depletion Glossary, http://www.epa.gov/ozone/defns.html.
February 26, 1999.
T-17
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Produced millions of years ago during the formation of coal, methane
trapped within coal seams and surrounding rock strata is released when
coal is mined.
The decomposition of organic animal waste in an anaerobic environment
produces methane. Liquid manure management systems tend to encourage
anaerobic conditions and produce significant quantities of methane.
Burning crop residue releases methane. Agricultural residue burning is
considered to be a net source of methane emissions because, unlike CO2,
methane released during burning is not reabsorbed by crop regrowth
during the next growing season.
Methane emissions from the components of petroleum systems (including
crude oil production, crude oil refining, transportation, and distribution
(generally occur as a result of system leaks, disruptions, and routine
maintenance.
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