INVENTORY OF
U.S. GREENHOUSE GAS EMISSIONS AND SINKS:
- - f . i "-,-"
1990-1993
U.S. ENVIRONMENTAL PROTECTION AGENCY
pFFICE OF POLICY, PLANNING AND EVALUATION
WASHINGTON, D.C., U.S.A.
SEPTEMBER 1994
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This document has undergone U.S. Environmental Protection Agency internal review, interagency
review, and public review. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use. .
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ACKNOWLEDGEMENTS
The U.S. Environmental Protection Agency, Office of Policy, Planning and Evaluation would like to thank those
who contributed to the writing of this report, in particular, Craig Ebert, Barbara Braatz, Froilan Rosqueta, Melissa
Lavinson, Doug Keinath, My Ton, Mary DePasquale, Jeff Fiedler, Michael Gibbs, Jonathan Woodbury, and
Pradeep Hathiramani of ICF Consulting Group working as consultants to the U.S. EPA for the project. Other
Agencies and EPA Offices contributed greatly to data collection'and review, including: EPA's Office of Programs,
Office of Air Quality Planning and Standards, and the Air and Energy Engineering Research Laboratory; the
Energy Information Administration of the Department of Energy; and the Department of Agriculture.
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TABLE OF CONTENTS
EXECUTIVE SUMMARY :....,... ...... ES-1-
mTRODUCTION. .-., .........:. '. ; v.:........... ..... 1
PART I. EMISSIONS FROM ENERGY ,..-...'. ....; 9
A. EMISSIONS FROM FOSSIL FUEL CONSUMPTION...., 10
1. Carbon Dioxide Emissions from Fossil Fuel Consumption. :..... 10,
2. Other Greenhouse Gas Emissions from Stationary Fossil Fuel Combustion ........-, 15
3. Other Greenhouse Gas Emissions from Mobile Combustion 19
B. FOSSIL FUEL PRODUCTION, TRANSMISSION, STORAGE, AND DISTRIBUTION....; 21
1. Emissions from Coal Mining ,..., ; 21
2. Emissions from Natural Gas Production, Processing, Transport, and Distribution 22
3. Emissions from Oil Production, Crude Oil Transportation, Refining, and Storage 23
C., EMISSIONS FROM BIOMASS AND BIOMASS-BASED FUEL CONSUMPTION ........;................ 25
1. Emissions from Wood .". 25
2. Emissions fromEthanol :........ : . ;...,.... 25
PART H. INDUSTRIAL PROCESSES :..... .." .......I. ... 27
A. NON-FERROUS METALS .'. .'; . ...... .-. 27
1, Aluminum Production ': ,. ; 27
B. INORGANIC CHEMICALS ,... ...' ;........,......:...... .. 29
1. Nitric Acid Production.. .". ;.. 29
2. Carbon Dioxide Manufacture ;.. 29
C- ORGANIC CHEMICALS :..:..,....'....,...:., .:. ... 30
1. Adipic.Acid Productiop ;. ..,.....-. 30
D,. NON-METALLIC MINERAL PRODUCTS....... 31
1. Cement Production '. 31
2. Lime Manufacture ....: ....33
3. Limestone Use .: :.......,.... 34
4. Soda Ash Manufacture and Consumption ];. 36
E. OTHER EMISSIONS .' .................;.. '. 37
1. Emissions of HFCs and PFCs ... ...: ......'......,. ,...... -., .'. ; 37
2. NOx, NMVOCs, and CO ..'. '. .....:....: ..;... ,..;........ 41
' ':". i ' ' . " . . ' ./ '
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PART HI. EMISSIONS FROM SOLVENT USE 43
PART IV. EMISSIONS FROM AGRICULTURE .. 45
A. METHANE EMISSIONS FROM ENTERIC FERMENTATION IN DOMESTIC LIVESTOCK 45
1. Methane Emissions from Cattle 47
2. Methane Emissions from Other Domestic Animals 50
B. METHANE EMISSIONS FROM MANURE MANAGEMENT 50
C. METHANE EMISSIONS FROM RICE CULTIVATION 1 54
D. EMISSIONS FROM AGRICULTURAL SOIL MANAGEMENT '. 57
E. EMISSIONS FROM FIELD BURNING OF AGRICULTURAL WASTES 59
PART V. EMISSIONS FROM LAND-USE CHANGE AND FOREST MANAGEMENT 63
PART VI. EMISSIONS FROM WASTE , v. 69
A. LANDFILLS ...69
B. WASTEWATER ... .' 71
C. WASTE COMBUSTION 72
REFERENCES , - - R-l
ANNEX A ESTIMATING EMISSIONS OF CO2 FROM FOSSIL ENERGY CONSUMPTION A-l
ANNEX B EMISSIONS FROM MOBILE COMBUSTION , B-l
ANNEX C ESTIMATION OF 1990 METHANE EMISSIONS FROM ENTERIC FERMENTATION IN
CATTLE AND FROM ANIMAL MANURE MANAGEMENT C-l
ANNEX D IPCC REPORTING TABLES , D-l
ANNEXE SULFUR DIOXIDE: EFFECTS ON RADIATIVE FORCING AND SOURCES OF ;
EMISSIONS E-l
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LIST OF BOXES, TABLES, AND FIGURES
BOXES
Executive Summary
Box ES-1. The Global Warming Potential Concept
Box ES-2. Emissions of CFCs and Related Compounds.
Box ES-3. Sulfur Dioxide: Effects of Radiative Forcing and Sources of Emissions.
...ES-2
,ES-13
.ES-15
Introduction
Box 1. Greenhouse Gases and Photochemically Important Gases.
Box 2. The Global Warming Potential Concept..,........;
Parti.
Box I-1. About Energy Data and Estimating Carbon Emissions ,
.13
TABLES
Executive Summary
Table ES-1. Recent Trends in U.S. Greenhouse- Gas Emissions: 1990-1993 .
Table ES-2. .Sources of Carbon Dioxide Emissions: 1990
Table ES-3. Sources of Methane Emissions: 1990 ......, :
Table ES-4. Sources of Nitrous Oxide Emissions: 1990 ;..,
Table ES-5. Emissions of HFCs andPFCs: 1990........ ;
Table ES-6. Emissions of CO, NO , andNMVOCs: 1990.............................
..'...."ES-3
......ES-4
.ES-8
....ES-11
....ES-14;
....ES-14:
Introduction
Table 1.' Summary of U.S. Greenhouse Gas Emissions: 1990-1993
in
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Parti.
Table 1-1. U.S. CO2 Emissions from Energy Consumption by Sector and Fuel Type: 1990-1993 11
Table 1-2. Key Assumptions for Estimating Carbon Dioxide Emissions 14
Table 1-3. U.S. Greenhouse Gas Emissions from Stationary Combustion: 1990-1992 16
Table 1-4. U.S. Greenhouse Gas Emissions from Stationary Combustion by Sector and Fuel Source: 1990 .. 17
Table I-5-. Ratio of CH4 to NMVOCs Released During Combustion 18
Table 1-6. U.S. Greenhouse Gas Emissions from Mobile Combustion: 1990-1992 ~ 19
Table 1-7. U.S. Greenhouse Gas Emissions from Mobile Combustion by Vehicle Type: 1990 20
Table 1-8. Methane Emissions from U.S. Natural Gas Systems 23
Table 1-9. NOx,-NMVOCs, and CO Emissions from Oil and Gas Activities: 1990-1992 24
Table 1-10. CO2 Emissions from Wood Consumption by Sector: 1990-1992 ...25
Table 1-11. U.S. CO2 Emissions from Ethanol by Region: 1990 ...26
PartIL
Table II-l. U.S. Greenhouse Gas Emissions from Industrial Processes: 1990 28
Table II-2. Carbon Dioxide Emissions from U.S. Cement Production 32
Table II-3. Carbon Dioxide Emissions from U.S. Lime Production 34
Table II-4. Carbon Dioxide Emissions from Limestone Consumption 35
Table H-5. Emissions of HFCs and PFCs: 1990 38
Table II-6. Emissions of ODSs and Related Compounds: 1990.. 40
Table II-7. U.S. Emissions of NOx, CO, and NMVOCs from Industrial Processes: 1990 ..41
Table 11-8. U.S. Emissions of NOx, CO, and NMVOCs from Industrial Processes: 1991-1992 42
PartllL
Table III-l. Emissions of NMVOCs, NOx, and CO from Solvent Use: 1990-1992 43
Table III-2. U.S. Emissions of NMVOCs, NOx, and CO by Category: 1990 44
Part IK
Table IV-1. Methane Emissions from U.S. Cattle in 1990, by Animal Type 48
Table IV-2. Methane Emissions from U.S. Cattle in 1990, by Region 49
IV
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Table IV-3. Methane Emissions from U.S. Cattle: 199M993 , 49
Table IV-4. Methane Emissions from Other Animals.. ... .., .........................,;. ....50
Table IV-5. Range of Methane Emissions Estimates from Manure Management: 1990 .;........53
Table IV-6. Methane Emissions from Manure Management: 1991-1993 ..........:. ....:....... ,.......;.. 54
Table IV-7. Area Harvested and Flooding Season Lengths for Rice-Producing States 56
Table IV-8. Methane Emissions from Rice Cultivation in the U.S. ..............;......;....57
Table IV-9i Fertilizer Consumption and N2O Emissions in the U.S.: 1990-1993 ..-.;... .59
Table IV-10. Key Assumptions for Estimating Emissions from Crop Waste Burning ............i .61
Table IV-11. Trace Gas Emissions from Field Burning of Agricultural Crop Wastes: 1990-1992 ..................62
PartV. . '_^
Table V-l. Regional Carbon Flux Estimates;.... : .........;.... 66
Part VI. ' ''/ '-''--. .. , ' '''-.-.' '.:' -"'..
Table VI-1. U.S. Methane Emissions from Landfills: 1990-1992 ..."..... ........ ..70
Table VK2. Summary of U.S..Landfill Emission Rate Estimates., ........!......... ...71
Table VI-3. U.S. NMVOC, CO, and NOx Emissions from Waste Incineration: 19904992 .......:.. ..:.72
Table VT-4. U.S.. NMVOC, CO, and NOx Emissions from Waste Incineration by Source: 1990 ...73
FIGURES
Executive Summary
Figure ES-1. Total U.S. Greenhouse Gas Emissions: 1990 ....; '. ES-4
Figure ES-2. Types of Energy Consumed in the U.S.: 1990 ..: ...........;.:..... ES-5
Figure ES-3. Carbon Dioxide Emissions by End Use Sector: 1990 ....:..... ... '....... ES-6
Figure ES-4. Carbon Dioxide Emissions from Energy by Primary User and Fuel Type: 1990 ES-6
Figure ES-5. Sources of Methane Emissions: 1990'....?....' ES-8 ' -
Figure ES-6. Sources of Agricultural Methane Emissions: 1990 ...ES-9
Figure ES-7. Sources of Nitrous Oxide Emissions: 1990 .......,.:... ES-11
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Parti.
Figure 1-1.
Figure 1-2.
Figure 1-3.
Types of Energy Consumed in the U.S.: 1990 '.., : 10
Carbon Dioxide Emissions from Fossil Fuel Combustion by End Use Sector: 1990 12
Carbon Dioxide Emissions from Fossil Fuel Combustion by Sector and Fuel Type: 1990............. 12
PartV.
Figure V-l. Regions and States for the U.S. Inventory.
.66
VI
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EXECUTIVE SUMMARY
Central to any study of climate change is the
development of and participation in an emission
inventory process that identifies and quantifies a
country's primary sources and,sinks of greenhouse
gases.1 This process is important because: (1) it
provides a basis for the Ongoing development of a
comprehensive and detailed methodology for estimat-
ing sources and sinks of greenhouse gases,.and (2) it
provides a common and consistent mechanism that
enables all signatory countries to the United Nations'
Framework Convention on Climate Change (PCCC) to
estimate emissions and to compare the relative contri-
bution of different emission sources and greenhouse
gases to'climate change.: Moreover, systematically and
consistently estimating emissions at the national and
international levels is a prerequisite for evaluating the
cost-effectiveness and feasibility of pursuing possible
mitigation strategies and adopting emission-reduction
technologies. '-
This document provides information on green-
house gas sources and sinks, and estimates of emis-
sions and removals for th'e.United States for 1990-
1993, as well as the methods used to calculate these
estimates, and the uncertainties associated with them.
Although estimates are provided for all four years, the
1990 estimates are considered the base year, since
under the Framework Convention on Climate Change,
countries are to submit inventories of greenhouse gas
emissions for the year 1990. "
The emission estimates presented here were
calculated using the IPCC Draft Guidelines for Na-
tional Greenhouse Gas Inventories (IPCC/OECD,
1994) to ensure that the emission inventories submitted
to the FCCC are consistent and comparable across
sectors and between nations. In order to fully comply
with the./PCC Draft Guidelines, the United States has
provided a copy .'of the IPCC reporting tables in Annex
D of this report. These tables include the data used to
calculate emission estimates using the IPCC Draft
Guidelines. The United States has followed thes.e
guidelines, except where more detailed data or method-
ologies were available for major U.S. sources of
emissions. In such cases, the United States expanded
on the IPCC guidelines to provide a more comprehen-
sive and accurate account of U.S. emissions. These
instances have been documented, and explanations
have been provided for diverging from the IPCC .
Guidelines (IPCC/OECD, 1994). ; '.
The Greenhouse Gases and Photochemically
Important Gases
Naturally occurring greenhouse gases include
water vapor, carbon dioxide (CO2), methane (CH4),
nitrous oxide (N2O), and ozone (O3).2 Chlorofluoro-
carbons (CFCs) (a family of human-made compounds),
its substitute hydrofluofocarbons (HFCs), and other
compounds such as perfluorinated carbons (PFCs), are
also greenhouse gases. In addition, other photochemi-
cally important gases such as carbon monoxide
(CO),-oxides of nitrogen (NOx), and nonmethane
volatile organic compounds (NMVOCs) are not ?
greenhouse gases, but contribute indirectly to the
greenhouse effect (see Box ES-1. for explanation).
These are commonly referred to as "tropospheric ozone
precursors" because they influence the rate at which
ozone and other gases are created and destroyed in the
atmosphere. For convenience, all gases discussed in
this summary are generically referred to as "green-
house gases" (unless otherwise noted), although the
reader should keep these distinctions in mind. In
addition, emissions .of sulfur dioxide (SO2) are re-
ported. Sulfur gases, primarily sulfur dioxide, are
believed to contribute negatively to the greenhouse
effect. -
Recent Trends of U.S. Greenhouse Gas
Emissions
Although CQ2, CH4, and N2O occur naturally in
the atmosphere, then" recent atmospheric buildup
appears to be largely the result of anthropogenic
activities. This growth has altered the composition of
the Earth's atmosphere, and may affect future global
climate. Since 1800, atmospheric concentrations of '
carbon dioxide have increased by more than 25 per-
cent, methane concentrations have more than doubled,
and nitrous oxide concentrations have risen approxi-
mately 8. percent (IPCC, 1992). And, from the 1950s
until the mid-1980s, the use of CFCs increased by
nearly 10 percent per year. Now that CFCs are being
phased out under the;Montreal Protocol on Substances
that Deplete the Ozone Layer (Montreal Protocol), the
use of CFC substitutes is expected to grow significantly.
ES-1
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The current U.S. greenhouse gas inventory for
1990-93 is summarized in Table ES-1. For the 1990
base year, total U.S. emissions were 1,444 MMTCE.
To be consistent with the IPCC-recommended guide-
lines, this estimate excludes emissions of 22.6
MMTCE from international transport. Changes in CO2
emissions from fossil fiiel consumption had the greatest
impact on U.S. emissions from 1990 to 1993. While
U.S. emissions of CO2 in 1991 were approximately 1.2
percent lower than 1990 emission levels, in 1992 they
were about 1.5 percent over 1991 levels, thus returning
emissions to about 1990 levels. This trend is largely
attributable to changes in total energy consumption
resulting from the economic slowdown in the U.S.
economy and the subsequent recovery. Based on
preliminary data for 1993, the upward trend since 1991
has continued, with 1993 CO2 emissions from fossil
fuel combustion approximately 2.4 percent greater than
1990.
CH4, N2O, and HFCs and PFCs represent a much
smaller portion of total emissions than CO2. Overall,
emissions of these gases remained relatively constant
from 1990 to 1992. Methane emissions from coal
mining declined slightly due to small decreases in coal
production and increases in coalbed methane recovery.
N2O emissions remained relatively constant, while
HFC emissions increased slightly, due to increased
production of HCFC-22, which increased by-product
emissions of HFC-23. Emissions of PFCs have
remained constant over the period.
U.S. emissions were partly offset by an uptake of
carbon in U.S. forests of 119 MMTCE. This increase
was due to intensified forest management practices and
the regeneration of forest land previously cleared for
cropland and pasture.
Figure ES-1 illustrates the relative contribution
of the primary greenhouse gases to total U.S. emissions
in 1990. Due largely to fossil fuel consumption, CO2
emissions accounted for the largest share of U. S.
emissions 85 percent.. These emissions were par-
tially offset by the sequestration that occurred on
forested lands. Methane accounted for 11 percent of
total emissions, including contributions from landfills
and agricultural activities, among others. The other
gases were less important, withN2O emissions.corn-
Box ES-1. The Global Warming Potential (GWP) Concept'
As mentioned, gases can contribute to the green-
house effect both directly and indirectly. Direct effects
occur when the gas itself is a greenhouse gas; indirect
radiative forcing occurs when chemical transformation of
the original gas produces a gas or gases that are green-
house gases, or when a gas influences the atmospheric
lifetimes of other gases. The concept of Global Warming
Potential (GWP) has been developed to compare the
ability of each greenhouse gas to trap heat in the atmo-
sphere relative to another gas. Carbon dioxide was
chosen as the "reference" gas to be consistent with the
1993 U.S. Climate Change Action Plan. All gases in this
report are presented in units of million metric tonnes of
carbon-equivalent, or MMTCE. Carbon comprises 12/44
of carbon dioxide by weight.
The Global Warming Potential (GWP) of a
greenhouse gas is the ratio of global warming, or radia-
tive forcing (both direct and indirect), from one kilogram
of a greenhouse gas to one kilogram of carbon dioxide
over a period of time. While any time period can be
selected, the 100-year GWPs recommended by the IPCC
are used in this report.
Gas
Carbon dioxide
Methane
Nitrous oxide
HFC-134a
HFC-23
HFC-152a
PFCs
GWP
(100 Years)
1
11/22*
270
1,200
10,000
150
5,400
* The direct GWP for methane is 11. The U.S. has
accounted for both the direct and indirect effects of
methane on radiative forcing. The indirect effects of
methane are considered comparable in magnitude to the
direct effects, therefore a GWP of 22 has been used
(IPCC, 1992). Using a GWP of 22 for methane is also
consistent with the GWP used in the U.S. Climate
Change Action Plan, and follows the suggestion of the
INC 9th Session that requests that indirect effects be
included where applicable. The magnitude of the indirect
effects of other gases are either zero or uncertain.
ES-2
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; b
Table ES-1: Recent Trends in U.S. Greenhouse Gas Emissionsr 1990 - 1993
(Million Metric Tonnes)
Gas/Source
Greenhouse Gases
Carbon Dioxide (CO.,)
Fossil Fuel Combustion
Other
Total
Forests (sink)
Net Total
Methane (CH^
Landfills
Agriculture
Coal Mining
Oil and Gas Systems
Other"
Total
Nitrous Oxide (N2O)
Agriculture
Fossil Fuel Consumption
Industrial Processes
Total
HFCsandPFCs
Photochemicallv Important Gases
Carbon Monoxide (CO)
Nitrogen Oxides (NOx)
NMVOCs
NET U.S. EMISSIONS
Emissions
(Full Molecular Weight)
1-990 1991 1992 1993
4,895 4,835 4,908 5,013
62 61 62
4,956 ' 4,896 4,970
(436) (433) (429)
4,520 4,463 4,541 ' ' -
10.0 10.1 10.2 10.3
8.6 8.5 , 8.6 8.8
4.4 4.2 4.0 '
3.2 '3.3 3.3,
0.8 0.8 ' . 0.8
27.0 , 26.9 27.0
0.2 0.2 0.2
0.1 0.1 0.1 - -
0.1 , 0.1 0.1 , -,
0.4' 0.4 0.4
+ + - +-
-
82V7 81.4 - 78.1 '
21.4 21.2 21
19.1 1S.7 17.9
Emissions
(Direct and Indirect Effects;
Carbon-Equivalent)
1990 1991 1992 1993
" -
1,335 1,319 1,339 1,367
17 17 17
1,352 1,336 1,356
(119) (118) (117)'
1,233 1,218 1,239
60 61 61 62 '
52 51 52 53
26 , - 26 24
19 20 20
5 , ," 5 5
162 162 161, .
14 14 ' 14.
9 10 " 10
7 7 7
30 '32 32 " -
19.2 19.6 20
-
-
- - -
1,444 13432 1,452
+ Total of these gases does not exceed 0.01 million metric tonnes.
Note: Totals presented in the summary tables in this chapter may not equal the sum of the individual source categories
due to rounding. - -
Since 1990, overall emissions of carbon dioxide have increased, while emissions of other greenhouse and photochemi-
cally important gases iiave remained relatively constant.
ES-3
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prising about 2 percent of total U.S. emissions, HFCs
accounting for slightly over 1 percent, and PFCs about
0.3 percent. The emissions of the photochemically
important gases CO, NOx, NMVOCs, and SO2 are not
included in Figure ES-1 because there is no agreed
upon method to estimate their contribution to climate
change. These gases only affect radiative forcing
indirectly. Also, any gases covered under the
Montreal Protocol are not included in this figure
because their use is being phased out, and the IPCC
Guidelines (IPCC/OECD, 1994) recommend excluding
gases covered by the Montreal Protocol.
The following sections present the anthropogenic
sources of greenhouse gas emissions, briefly discuss
the emission pathways, summarize the emission
estimates, and explain the relative importance of
emissions from each source category.
Figure ES-1
Total U.S. Greenhouse Gas Emissions: 1990
1500
1000
500
1444
-119
O02 CO2
Eraluiom Soto
CH4 N2O
Gas Types
HFC/
PFC
Nat
Emissions
|ซOO2 ปCH4 m N2O ซHFC/PFC|
Largely because of fossil fuel consumption, CO2 emissions accounted for
ihe largest share of U.S. emissions In 1990.
CARBON DIOXIDE EMISSIONS
The global carbon cycle is made up of large
carbon flows and reservoirs. Hundreds of billions of
tons of carbon in the form of CO2 are absorbed by
oceans, trees, soil, and vegetative cover and are emitted
to the atmosphere annually through natural processes.
When in equilibrium, carbon flows between the various
reservoirs roughly balance each other. Since the
Industrial Revolution, however, atmospheric concen-
trations of carbon dioxide have risen more than 25
percent, principally because of the combustion of fossil
fuels (IPCC, 1992). While the combustion of fossil
fuels accounts for 99 percent of total U.S. CO2 emis-
sions, CO2 emissions also result directly from indus-
trial processes. Changes in land use and forestry
activities both emit carbon dioxide (e.g., as a result of
forest clearing) and can act as a sink for CO2 (e.g., as a
result of improved forest management activities).
Table ES-2 summarizes U.S. emissions and
uptake of carbon dioxide, while the remainder of this
section presents detailed information on the various
anthropogenic sources and sinks of carbon dioxide in
the United States.
The Energy Sector
Approximately 88 percent of U.S. energy is
produced through the combustion of fossil fuels. The
remaining 12 percent comes from renewable or other
energy sources such as hydropower, biomass, and
Table ES-2. Sources of CO2 Emissions by
Source: 1990
(Million Metric Tonnes)
cฐ2
Emissions
Source/Sink (Molecular
Basis)
Fossil Fuel Consumption
Residential
Commercial
Industrial
Transportation
U.S. Territories
Total
Fuel Production and
Processing
Cement Production
Lime Production
Limestone Consumption
Soda Ash Production and
Consumption
Carbon Dioxide
Manufacture
Total - All Sources
Sinks
Forestry and Land Use
Total Net Emissions
927
757
1,673
1,505.
31
4,895
6.6
32.7
11.9
5.1
4.1
(L2
4,956
(436)
4,520
C02
Emissions
(Carbon-
Equivalent)
252.7
206.4
456.4
410.5
2J--
1,335
1.8
- 8.9
3.2
1.4
1.1
01
1,352
(119)
1,233
Note: The totals provided here do not reflect emissions from
bunker fuels used in international transport activities. The
INC 9th Session instructed countries to report these emis-
sions separately,, and not include them in national totals,, U-S,.
emissions from bunker fuels were approximately 22.6
MMTCEinl990.
ES-4
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nuclear energy (see Figure ES-2). As they burn, fossil
fuels emit carbon dioxide due to oxidation of the
carbon contained in the fuel. The amount of carbon in
fossil fuels'varies significantly by fuel type. For
.example, coal contains the highest amount .of carbon
per unit of energy, while petroleum has about 20
percent less carbon than coal, and natural gas has about
45 percent less. The inventory includes carbon dioxide
emissions from all fossil fuel consumption and oil and
gas production and storage. Carbon dioxide emissions
from biomass and biomass-based fuel consumption are
reported on page 25, but are not included in the na-
tional total. This approach is consistent with the IPCC
Draft Guidelines (IPCC/OECD, 1994).
" . Figure ES-2
. Types of Energy Consumed in the U.S.: 1990
Nuclear, Renewables, Other
(12%or9.31QBtu)
Petroleum
'(41% or 33.55 Btu)
Coal(23%or19.00QBtu)
Natural Gas
.(24% or 19.28 Btu)
1 QBtu =-1 quadrillion Btu = 1X10E15 Btu
Approximately .88 percent of U.S. energy is produced through the
combustion of fossil fuels.
Fossil Fuel Consumption. In 1990, the United
States emitted a total of 1,335 MMTCE from fossil fuel
.combustion. (Bunker fuels, or fuels used in interna-
tional transport, accounted for an-additional 22.6
MMTCE.) The energy-related activities producing
these emissions included heating in residential and,
commercial buildings, the generation of electricity,
steam production for industrial processes, and gasoline
consumption .in automobiles and other vehicles.
Petroleum products across all sectors of the economy
accounted for about 44 percent of total U.S. energy- .
related carbon dioxide emissions; coal, 36 percent; and
natural gas, 20 percent.
Industrial Sector
Trie industrial sector accounts for 34 percent of
U.S. emissions from fossil fuel consumption, making it
the largest end-use source of CO2 emissions (see Figure
ES-3). About two-thirds of these emissions result from
the direct consumption of fossil fuels in order to meet
industrial demand for steam and process heat. The
remaining one-third of industrial energy needs is met
by electricity for such uses as motors, electric furnaces
and ovens, and lighting.
The industrial sector is also the largest user of
nonenergy applications of fossil fuels, which often
store carbon. Fossil fuels used for producing fertiliz-
ers, plastics, asphalt, or lubricants can store carbon in
products for very long periods. Asphalt used in road
construction, for example, stores carbon indefinitely.
Similarly, the fossil fuels used in the manufacture of
materials like plastics also store carbon, releasing this
carbon only if the product is incinerated. --..
Transportation Sector
The transportation sector is also a major source
of CO2, accounting for about 31 percent of U.S.
emissions. Virtually all of the energy consumed in this
sector comes from petroleum-based products. Nearly
two-thirds of the emissions are the result of gasoline
consumption in automobiles and other vehicles, with
other uses, including diesel fuel for the trucking
industry and jet fuel for aircraft, accounting for the
remainder.
Residential and Commercial Sectors ;
The residential and commercial sectors account
for about 19 and 16 percent, respectively, of CO2
emissions from fuel consumption. Both sectors rely
heavily on electricity for meeting energy needs, with
about two-thirds to three-quarters of their emissions
attributable to electricity consumption. End-use
applications include lighting,_ heating, cooling, and
pperating appliances. The remaining emissions are
largely due to the consumption of natural gas and oil,
primarily for meeting heating and cooking needs.
Electric Utilities
The U.S. reljes on electricity to meet a signifi-
cant portion of its energy requirements. In fact, as the .
largest consumers of fossil fuels, electric utilities are
collectively the largest producers of U.S. CO2 emis-
sions (see Figure ES-4). Electric utilities generate
electricity for such uses as lighting, heating, electric
motors, and air conditioning. Some of this electricity
is generated with the lowest CO2-ernitting energy
technologies, particularly nonfossil options, such as
nuclear energy, hydropower, or geothermal energy.
However, electric utilities rely on coal for 55 percent of
their total energy requirements and account for about
85 percent of all coal consumed in the United States.
ES-5-
-------
Figure ES-3
Carbon Dioxide Emissions by End Use Sector: 1990
Trปoปportซ!on(3t%)
Residential (19%)
Commerfcal (16%)
tndiKWH (34%)
in Ihis graph, emissions generated by electric utilities are allocated to each
ood-uso sector according to each sector's share of electricity consumption;..
Figure ES-4
Carbon Dioxide Emissions from Fossil Fuel Combustion by
Sector and Fuel Type: 1990
(MMT Carbon Equivalent)
500
Commercial Residential Industrial Transportation
Energy Sectors
| a Coal Natural Gas ป Petroleum |
| however, when the emissions attributable to electric utilities are pulled out
of the various end-use sectors, as depicted in this graph, the reliance of the
] U.S. economy on electricity to meet its needs is evident.
Fuel Production and Processing. CO2 is
produced via flaring activities at natural gas systems -
and oil wells. Typically, the methane that is trapped in
a natural gas system or oil well is flared to relieve the
pressure building in the system or to dispose of small
quantities of gas that are not commercially marketable.
As a result, the carbon contained in the methane
becomes oxidized and forms carbon dioxide. In 1990,
the amount of CO2 from the flared gas was approxi-
mately 1.8 MMTCE, or about 0.1 percent of total U.S.
CO2 emissions.
Blomass and Biomass-Based Fuel Consump-
tion. Biomass fuel is used primarily by the industrial
sector in the form of fuelwood and wood waste.
Biomass-based fuel use, such as ethanol from corn or
woody crops, occurs mainly in the transportation
sector. Ethanol and ethanol blends, such as gasohol,
are typically used to fuel public transport vehicles,
such as buses or centrally fueled fleet vehicles.
Biomass, ethanol, and ethanol-blend fuels do
release carbon dioxide. However, in the long run, the
carbon dioxide they emit does not increase total
atmospheric carbon dioxide because the biomass
resources are consumed on a sustainable basis. For
example, fuelwood burned one year but regrown the
next only recycles carbon, rather than creating a net
increase hi total atmospheric carbon. As a result,
carbon dioxide emissions from biomass have been
estimated separately from fossil fuel-based emissions
and, as recommended in the IPCC Draft Guidelines,
are not included in national totals.
For 1990, CO2 emissions from biomass con-
sumption were approximately 48 MMTCE, with the
industrial sector accounting for 73 percent of the
emissions and the residential sector, 25 percent.
Carbon dioxide emissions from ethanol use in the
United States are generally declining, due to a combi-
nation of low gasoline prices and limited ethanol
supply. In 1990, total U.S. CO2 emissions from
ethanol were estimated to be 1.2 MMTCE, and wefe
emitted mostly in the South and Midwest, where the
majority of ethanol is produced and consumed.
Industrial Processes
Emissions are often produced as a by-product of
various nonenergy-related activities. For example, in
the industrial sector raw materials are chemically
transformed from one state to another. This transfor-
mation often releases such greenhouse gases as carbon
dioxide. The production processes that emit CO2
include cement production, lime production, limestone
consumption (e.g., in iron and steel making), soda ash
production and use, and carbon dioxide manufacture.
Total carbon dioxide emissions from these sources
were approximately 15 MMTCE in 1990, accounting
for 1 percent of total U.S. CO2 emissions.
Cement Production (8.9 MMTCE). Carbon
dioxide is produced primarily during the production of
clinker, an intermediate product from which finished
Portland and masonry cement are made. Specifically,
carbon dioxide is created when calcium carbonate
(CaCO3) is heated in a cement kiln to form lime and
carbon dioxide. This lime combines with other materi-
als to produce clinker, while the carbon dioxide is
released into the atmosphere.
Lime Production (3.2 MMTCE). Lime is used
in steel making, construction, pulp and paper manufac-
turing, and water and sewage treatment. It is manufac-
ES-6.
-------
tured by heating limestone (mostly calcium carbonate)
in a kiln, creating calcium oxide (quicklime) and
carbon dioxide, which is normally emitted to the
atmosphere.
Limestone Consumption (1,4 MMTCE). Lime-
stone is a basic raw material used by a wide variety of
industries, including the construction, agriculture,
chemical, and metallurgical industries. For example,
limestone can be used as a purifier in refining metals,
such as iron. In this case, limestone heated in a blast
furnace reacts with impurities in the iron ore" and fuels,
generating carbon dioxide as'a by-product. It is also
used in flue gas desulfurization systems to remove '
sulfur dioxide from the exhaust gases. .
Soda Ash Production and Consumption (1.1
MMTCE). Commercial soda ash (sodium carbonate)
is used in many consumer products, such as glass, soap
and detergents, paper, textiles, and food. During the
manufacturing of these products, natural sources of
sodium carbonate are heated and transformed into a
crude soda ash, in which carbon dioxide is generated as
a by-product. In addition, carbon dioxide is released
when the soda ash is consumed. Of the.two .states that
produce natural soda ash, only Wyoming has net
emissions of carbon dioxide, because producers in
California recover the CO2 and use it in other stages of
production. U.S. CO2 emissions from soda ash produc-
tion were approximately 0.4 MMTCE in 1990, while
U.S. soda ash consumption generated about 0.7
MMTCE.
Carbon Dioxide Manufacture (0.3 MMTCE),
; Carbon dioxide is used in many segments of the
economy, including food processing, beverage manu-
facturing, chemical processing, crude oil products; and
a host of industrial and miscellaneous applications.
For the most part, carbon_dioxide used in these applica-
tions will eventually be released into the atmosphere.
Forests and Land Use Change
When humans use and alter the biosphere
through changes in land use-and forest-management
activities, they alter the natural balance of trace gas
emissions and uptake. These activities include clearing
an area of forest to create cropland or pasture, restock-
ing a logged forest, draining a wetland, or allowing a
pasture to revert to a grassland or forest. Forests,
which cover about 737 million acres of U.S. land
(USFS, 1990), are a potentially important terrestrial
sink for carbon dioxide. Because approximately half
the dry Weight of wood is carbon, as trees add mass to
trunks, limbs, and roots, more carbon is stored in the
trees than is released.to the atmosphere through/
respiration and decay. Soils and other types of vegeta-
tive cover also provide a potential sink for carbon.
In the United States improved forest-manage-
ment practices and the regeneration of previously
cleared forest area haye actually increased the amount
of carbon stored on U.S. lands. This uptake of carbon
is an ongoing result of land-use changes in previous ,.
decades. For example, because of improved agricul-
tural 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 between 1920 and 1950,
and were allowed to revert to forest land or were
actively reforested,: The regeneration of forest land
greatly increases carbon storage in both standing
biomass and soils, and the impacts of these land-use
changes are still affecting forest carbon fluxes in the
East. In addition to land-use changes in the early part
,of this century, forest carbon fluxes in the East are
affected by a trend toward managed growth on private
land in recent decades, resulting in a near doubling of
the biomass density in eastern forests since the early
1950s. More recently, the 1970s and 1980s saw a
resurgence of federally sponsored tree-planting pro-
grams (e.g., the Forestry Incentive Program) and soil
conservation programs (e.g., the Conservation Reserve
Program), which have focused on reforesting previ-
ously harvested lands, improving timber-management
activities, combatting soil erosion, and converting
marginal cropland^ forests. -.
As a result of these activities, the net CO2 flux,
from standing biomass and vegetative cover in 1990
was estimated to have been an uptake (sequestration)
of 119 MMTCE: The Northeast, North Central, and
South Central regions of the United States accounted-
for 99 percent of the uptake of carbon, largely due to
high growth rates that are the result of! intensified forest
management practices and the regeneration of forest
land previously cleared for cropland and pasture.
Western states are responsible for a small net-release of
carbon, reflecting mature forests with a near balance
between growth, mortality, and removals.
ES-7
-------
There are considerable uncertainties associated
with the estimates provided for the net carbon flux
from U.S. forests, however. Four major uncertainties
are presented briefly below:
The impacts afforest management activities
on soil carbon are quite uncertain. Since
forest soils contain over 50 percent of the total
stored forest carbon in the U.S., this difference
can have a large impact on flux estimates.
However, because of uncertainties associated
with soil carbon flux, this component is not
included in the U.S. estimate at this time.
* The U.S. has assumed that harvested timber
effectively results in immediate carbon emis-
sions. This assumption is consistent with the
methodology recommended by the IPCC
(IPCC/OECD, 1994), however, studies that
model the product pools in the U.S. estimate a
net accumulation of carbon in forest product
pools in 1990. This suggests that the esti-
mates of carbon sequestration presented here
may be too low.
The current estimate does not include forest
land in Alaska and Hawaii or reserved timber
land. However, forests in these states are
believed to be in equilibrium, so their inclu-
sion would not significantly affect the flux
estimates presented here.
Forest management activities may also result
influxes of other greenhouse and photochemi-
cally important gases. Dry soils are an
important sink for CH4 and source of N2O, and
both a source and a sink for CO, and vegeta-
tion is a source of several NMHCs
(nonmethane hydrocarbons, a subset of
NMVOCs). However, the effects of forestry
activities on these gases are highly uncertain,
and are therefore not included in the U.S.
inventory at this time.
METHANE EMISSIONS
Atmospheric methane (CH4) is second only to
CO2 as an anthropogenic source of the greenhouse
effect. Methane's overall contribution to global
warming is large because it is 22 times more effective
at trapping heat in the atmosphere than carbon dioxide
over a 100-year time horizon when both the direct and
indirect effects are accounted for. Furthermore,
methane's concentration in the atmosphere has more
than doubled over the last two centuries. Scientists
have concluded that these atmospheric increases are
largely due to increasing emissions from anthropogenic
sources, such as landfills, agricultural activities, coal
mining, fossil fuel combustion, the production and
processing of natural gas and oil, and wastewater
treatment (see Table ES-3 and Figure ES-5).
Table ES-3. Sources of Methane
1990
Emissions:
(Million Metric Tpnnes)
CH4 CH4
(Molecular (Carbon-
Source Basis) Equivalent;
GWP=11)
Landfills 10.0 30.0
Agriculture 8.6 25.8
Coal Mining 4.4 13.2
Oil and Natural
Gas Systems 3.2 9.7
Fossil Fuel
Combustion 0.6 2.0
Wastewater
Treatment 0.2 0.4
Total 27.0 81.1
CH4
(Carbon-
Equivalent;
GWP=22)
60.0
51.6
26.4
19.4
3.9
0.9
162.2
Figure ES-5
Sources of Methane Emissions: 1990
Oil and Gas
Fossil Fuel " Processes (12%) Coa|M|n|
Combustion (2%)
Landfills (37%)
Wastewater (1%)
Agriculture (32%)
Landfills and agriculture are the largest sources of atmospheric methane
in the United States.,
ES-8
-------
Landfills
Landfills are the largest single anthropogenic
source of methane'emissions, in the United States.
There are an estimated 6,000 landfills in the United
States, with.1,300 of the largest landfills accounting for
about half of the emissions.
In an environment where the oxygen content is
low or nonexistent, organic materials, such as yard
waste, household waste, food waste, and paper, are
decomposed by bacteria to produce methane, carbon
dioxide, and stabilized organic materials (materials that
cannot be decomposed further). Methane emissions
from landfills are affected by such factors as waste. .
composition, moisture, and landfill size.-
Methane emissions from U.S. landfills in 1990
were 60 MMTCE, or about 37 percent of total U.S.
methane emissions. Emissions from U.S. municipal
solid waste landfills, which received over 70'percent of
the total solid waste generated in the United.States,
accounted for about 90 to 95 percent of total landfill
emissions, while industrial landfills accounted for the
remaining 5 to 10 percent. Currently, about 10 percent
of the methane emitted is recovered for use/as an
energy source. .'"'
Agriculture
The agricultural sector accounted for approxi-
mately 32 percent of total U.S. methane emissions in
1990, with enteric fermentation in domestic livestock
and manure management together accounting for the
majority (see Figure ES-6). Other agricultural activi-
ties contributing to methane emissions include rice
cultivation and field, burning of agricultural crop
wastes. Several other agricultural activities, such as
irrigation and tillage practices, may contribute to
methane emissions, but emissions from these sources
are uncertain and are believed to.be small; therefore,
the United States has not included'them in the current
inventory. Details on the emission pathways included
in the inventory are presented below.
Enteric Fermentation in Domestic Livestock
(34.9 MMTCE). In 1990, enteric fermentation was the
source of about 22 percent of total U.S. methane
emissions, and about 68 percent of methane emissions
from the agricultural sector. During animal digestion,
methane is produced through enteric fermentation, a
process in which microbes .that reside 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 a significant amount of
methane-producing' fermentation occurs/ Nonruminant
domestic animals, such as pigs and horses, have much .
.lower methane emissions than ruminants because much
less methane-producing fermentation takes place in
their digestive systems. The amount of methane
produced and excreted by an individual animal also
depends upon the amount and type of feed it consumes.
Figure ES-6 ,
Methane Emissions from Agriculture by Source: 1990
Agricultural Waste
. . Burning (1%)
Enteric Fermentatii
. (68%) ,
Manure Management
(26%)
Rice Cultivation (5%)
Manure Management (13.7MMTCE). The
decomposition of organic material in animal manure in
an anaerobic environment produces methane. The
most important factor affecting the amount of methane
produced is how the manure is managed, since certain
types of storage and treatment systems promote an
oxygen-free environment. In particular, liquid systems
(e.g., lagoons, ponds, tanks, or pits) tend to produce a .
significant quantity of methane. However, when
.manure is handled as a solid or when it is deposited on
pastures and rangelands, it tends to decompose aerobi-
cally arid produce little or no methane. Higher tem-
peratures and moist climate conditions also promote '
methane production.
Emissions from manure management were about
8 percent of total U.S. methane emissions in 1990, and
about 27 percent of methane emissions from the
agricultural sector. Liquid-based manure management
systems accounted for over 80 percent of total emis-
sions from animal wastes.
ES-9
-------
Rice Cultivation (2.6 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 in the soils develop, and methane
is produced through anaerobic decomposition of soil
organic matter. Methane is released primarily through
the rice plants, which act as conduits from the soil to
the atmosphere.
Rice cultivation is a very small source of meth-
ane in the United States. In 1990, methane emissions
from this source were less than 2 percent of total U.S.
methane emissions, and about 5 percent of U.S.
methane emissions from agricultural sources.
Field Burning of Agricultural Wastes (0.5
MMTCE). Large quantities of agricultural crop wastes
are produced from farming systems. Disposal systems
for these wastes include plowing them back into the
field; composting, landfilling, or burning them in the
field; using them as a biomass fuel; or selling them in
supplemental feed markets. Burning crop'residues
releases a number of greenhouse gases, including
carbon dioxide, methane, carbon monoxide, nitrous
oxide, and oxides of nitrogen. Crop residue burning is ,
not considered to be a net source of carbon dioxide
emissions because the carbon dioxide released during
burning is reabsorbed by crop regrowth during the next
growing season. However, burning is a net source of
emissions for the other gases. Because this practice is
not common in the United States, it was responsible for
only 0.3 percent of total U.S. methane emissions in
1990, and 0.9 percent of emissions from the agricul-
tural sector.
Coal Mining
Coal mining and post-mining activities, such as
coal processing, transportation, and consumption, are
the third largest source of methane emissions in the
United States. Estimates of methane emissions from
coal mining for 1990 were 26.4 MMTCE, which
accounted for about 16 percent of total U.S. methane
emissions.
Produced millions of years ago during the
formation of coal, methane is trapped within coal
seams and surrounding rock strata. When coal is
mined,-methane is released to the atmosphere. The
amount of methane released from a coal mine depends
primarily upon the depth and type of coal, with deeper
mines generally emitting more methane (U.S. EPA,
1993a). Methane from surface mines is emitted
directly to the atmosphere as the rock strata overlying
the coal seam are removed.
Methane is hazardous in underground mines
because it is explosive at concentrations of 5 to 15
percent in air. Therefore, all underground mines are
required to remove methane by circulating large
quantities of air through the mine and venting this air
into the atmosphere. At some mines, more advanced
methane-recovery systems may be used to supplement
the ventilation systems and ensure mine safety. The
practice of using the recovered methane as an energy
source has been increasing in recent years.
Oil and Natural Gas Production and Processing
Methane is also a major component of natural
gas. Any leakage or emission during the production,
processing, transmission, and distribution of natural
gas emits methane directly to the atmosphere. Because
natural gas is often found in conjunction with oil,
leakage during the production of commercial quantities
of gas from oil wells is also a source of emissions.
Emissions vary greatly from facility to facility and are
largely a function of operation and maintenance
procedures and equipment :condition. Fugitive emis-
sions'can occur at all stages of extraction, processing,
and distribution. In 1990, emissions from the U.S.
natural gas system were estimated to be 17.8 MMTCE,
accounting for approximately 11 percent of total U.S.
methane emissions for 1990. . .
Methane is also released as a result of oil produc-
tion and processing activities, such as crude oil produc-
tion, crude oil refining, transportation, and storage,
when1 commercial gas production is not warranted due
to the small quantities present. Emissions from these
activities are generally released as a result of syste'm
leaks, disruptions, or routine maintenance. For 1990,
methane emissions from oil production and processing
facilities were 1.6 MMTCE, accounting for about one
percent of total U.S. methane emissions.
ES-10
-------
Other Sources
; Mfethane is also produced from several other
sources in the United States, including energy-related
, combustion activities, wastewater treatment, industrial
processes, and changes in land use. The sources
included in the U.S. inventory are fossil fuel combus-
tion and wastewater treatment, which accounted for
approximately 4.8 MMTCE in 1990, or about 3 percent
of,total U.S. methane emissions. Additional anthropo-
genic sources of methane in the United States, such as
land use changes and- ammonia, coke, iron, and steel
production are not included because, little information
on methane emissions from these sources is currently
available.
NITROUS OXIDE EMISSIONS
Nitrous oxide (N2O) is a chemically and
radiatively active greenhouse gas that is produced
naturally from a wide variety of biological sources in
soil and water. While actual emissions of N2O are
much smaller than CO2 emissions, N2O is approxi-
mately 270 times more powerful than C02 at trapping
heat in the atmosphere over a 100-year time horizon.
- Over the past two centuries, human activities
have raised atmospheric concentrations of nitrous .
oxide by approximately 8 percent. The main anthropo-
genic activities producing N2O are soil management
and fertilizer use for agriculture, fossil fuel combus-
tion, adipic acid production, nitric acid production, and.
agricultural waste burning. The relative share of each
of these activities to total U.S. nitrous oxide emissions
is shown in Figure ES-7, and U.S. nitrous oxide
emissions by source category for 199,0 are p'rovided in
Table ES-4. ' ;,
Figure ES-7
Sources of Nitrous Oxide Emissions: 1990
Agricultural Waste
- Burning (1%)
Agricultural Soils (44%)
Fossil Fuel
Consumption (31%)
Adipio Acid Production '
. (14%) ~ :
Nitric Acid Production
' ' (10%)
Agricultural Soil Management and Fertilizer
'Use. ' v . ' /' : ; ''".',
The primary sources of anthropogenic nitrous ..
oxide emissions in the United States are fertilizer use
and soil management activities. Synthetic nitrogen
fertilizers and organic fertilizers add nitrogen to soils,
and thereby increase emissions of nitrous_oxide.
Nitrous oxide emissions in 1990 due to consumption of
synthetic and organic fertilizers were 13.5 MMTCE, or
approximately 44 percent of total U.S. nitrous oxide
emissions. "
Other agricultural soil management practices,
such as irrigation, tillage practices, or the fallowing of
land, can also affect N,O fluxes to and from the soil.
- . Z - -
However, because there is much uncertainty about the
direction and magnitude of the effects of these other
practices, only the emissions from fertilizer use and'
field burning of agricultural wastes are included in the
U.S. inventory at this time.
Table ES-4. Sources of N2O
1990
.(Million
Source
V,
Agricultural Soil
Management and
Fertilizer Use .
Fossil Fuel
Consumption
Adipic Acid
Production
Nitric Acid
Production
Agricultural Waste
Burning
Total
Emissions:
Metric Tonnes) ,
N2O
(Molecular
Basis)
0.2 "
0.13
0.06
-
0.04
0.01
0.41
N2O
(Carbon-
Equivalent;
GWP=270)
13.5
'9.4
4.1
2.9
ฐ-4 '
30.3
ES-n
-------
Fossil Fuel Combustion
Nitrous oxide is a product of the reaction that
occurs between nitrogen and oxygen during fossil fuel
combustion. Both mobile and stationary sources emit
nitrous oxide. Emissions from mobile sources are
more significant and are better understood than those
from stationary sources. The amount of nitrous oxide
emitted varies, depending upon fuel, technology type,
and pollution control device. Emissions also vary with
the size and vintage of the combustion technology, as
well as maintenance and operation practices.
For example, catalytic converters installed to
reduce air pollution resulting from motor vehicles have
been proven to promote the formation of nitrous oxide.
As catalytic converter-equipped vehicles have in-
creased in the U.S. motor vehicle fleet, emissions of
nitrous oxide from this source have also increased
(EIA, 1994g). Mobile emissions totalled 6.8 MMTCE
in 1990 (22.4 percent of total N2O emissions), with
road transport accounting for approximately 95 percent
of these N2O emissions. Nitrous oxide emissions from
stationary sources were 2.6 MMTCE in 1990.
Adipic Acid Production
Nitrous oxide is emitted as a by-product of the
production of adipic acid. Ninety percent of all adipic
acid produced in the United States is used to produce
nylon 6,6. It is also used to produce some low-tem-
perature lubricants, and to provide foods with a
"tangy" flavor. In 1990, U.S. adipic acid production
generated 4.1 MMTCE of nitrous oxide, or 13.7
percent of total U.S. N2O emissions.
Nitric Acid Production
Production of nitric acid is another industrial
source of N2O emissions. Nitric acid is a raw material
used primarily to make synthetic commercial fertilizer,
and is also a major component in the production of
adipic acid and explosives. Virtually all of the nitric
acid that is manufactured commercially in the United
States is obtained by the oxidation of ammonia.
During this process, N2O is formed and emitted to the
atmosphere. Nitrous oxide emissions from this source
were about 2.9 MMTCE in 1990, accounting for about
9.7 percent of total U.S. N2O emissions.
Other Sources of N2O
Other activities that emit N2O include the
burning of agricultural crop residues and changes in
land use. Emissions from agricultural crop residue
burning are extremely small relative to overall U.S. ,
N2O emissions. Nitrous oxide emissions in 1990,from
this source were approximately 0.4 MMTCE, or about
1.2 percent of total U.S. nitrous oxide emissions.
Forestry activities may also result in fluxes of
nitrous oxide, since dry soils are a source of N2O
emissions. However, the effects of forestry activities,
on fluxes of these gases are highly uncertain; therefore,
they are not included in the inventory at this time.
Similarly, the U.S. inventory does not account for
several land-use changes because of uncertainties in
their effects on trace gas fluxes, as well as poorly
quantified land-use change statistics. These land-use
changes include loss and reclamation of freshwater
wetland areas, conversion of grasslands to pasture and
cropland, and conversion of managed lands to grasslands.
EMISSIONS OF HFCS AND PFCS
Partially halogenated compounds (HFCs) and
perfluorinated compounds (PFCs) were introduced as
alternatives to the ozone-depleting substances (ODSs)
being phased out under the Montreal Protocol and
Clean Air Act Amendments of 1990 '(see Box ES-2).
Because HFCs and PFCs are not directly harmful to the
stratospheric ozone layer, they are not controlled by the
Montreal Protocol. However, these compounds are
powerful greenhouse gases and are, therefore, consid-
ered under the Framework Convention on Climate
Change. For example, HFC-134a has an estimated
direct GWP of 1,200, which makes the compound
1,200 times more heat absorbent than an equivalent
amount by weight of CO2 in the atmosphere. There-
fore, emission estimates for these gases have been
included in the U.S. inventory and are provided in
Table ES-5.
ซ
In 1990, the use of CFC and HCFC substitutes
was minimal. Thus, emissions of HFCs and PFCs
were quite small, and were largely the result of by-
product emissions from other production processes.
For example, HFC-23 is a by-product emitted during
the production of HCFC-22, and PFCs (CF4 and C2F0)
ES-12
-------
are emitted during aluminum smelting. While the use
of such ozone-depleting substances as methyl chloro-
form, CFC-12, arid HCFC-22 is declining, consump-
tion of HFCs is increasing markedly. Emissions of
HFCs and PFCs should continue to rise as their use as
replacements increases..
Box ES-2. Emissions of CFCs and Related Compounds
Chlorofluorocarbons (CFCs) and other halogenated fluorocarbpns were emitted into the atmosphere for the first
time this century. This family of man-made compounds includes Chlorofluorocarbons, halons, methyl chloroform,
carbon tetrachloride, methyl bromide, and partially halogenated fluorocarbons (HCFCs). These substances are used in a
variety of industrial applications, including foam production and refrigeration, air conditioning, solvent cleaning, :
sterilization, fire extinguishing, paints, coatings, other chemical intermediates, and miscellaneous uses (e.g., aerosols,
propellants, and other products). . :
Because these compounds have been shown to deplete stratospheric ozone, they are typically referred to as ozone-
depleting substances. In addition, they are important greenhouse gases because they block infrared radiation that would
otherwise escape into space (IPCC, 1990). ; . _ .
Recognizing the harmful effects of these compounds on the atmosphere, in 1987 many governments signed the
Montreal Protocol on Substances that Deplete the Ozone Layer to limit the production and consumption of a number of
GFCs and other halogenated compounds. As of June 1994, 133 countries had signed the Montreal Protocol. The United
States furthered its commitment to phase out these substances by signing and ratifying the Copenhagen Amendments to
the Montreal Protocol in 1992. Under these amendments, the United States committed to eliminating the production of
all halons.by January 1,1994, and all CFCs by January.''!, 1996. ; - .
The IPCC Guidelines do not include reporting emissions of CFGs and related compounds because their use is
being phased out under the Montreal Protocol. The United States believes that no inventory is complete without these
emissions; therefore, emission estimates for several Class I and Class II ozone-depleting substances are provided in the "
table below. Compounds are classified as "Class I" or "Class II" substances based on their ozone-depletion potential,
and must adhere to a distinct set of phase-out requirements under the Montreal Protocol. Class I compounds are the
primary ozone-depleting substances in use today; Class II compounds include partially halogenated chlorine compounds
(known as HCFCs), 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 about one-tenth to one-hundredth the threat to stratospheric ozone compared to CFCs. Also, it should be noted
that the effects of these compounds on radiative forcing are not provided here. Although CFCs and related compounds
have very large direct GWPs, their indirect effects are believed to be negative and, therefore, could significantly reduce
the magnitude of their direct .effects (IPCC, 1992). Given the uncertainties surrounding the net effect of these gases, they
are reported here on a full molecular basis only, <
U.S. Emissions of Ozone-Depleting Substances and Related Compounds: 1990
(Million Metric Tonnes; Molecular Basis)
Compound
ClassIODSs
CFC-11
CFC-12 '..'
CFC-113
CFC-I14 .
CFC-115 \ ',
Carbon Tetrachloride
Methyl Chloroform
Halon-1211
Halon-4301
Class nODSs
HCFC-22
HCFG-141b
HCFC- 124
Emissions
0.06
0.1
0.05 ^
0.005 ^
0.003
0.03
: 0.3
0.001
0.001
0.08
0.002 ,
0.003
Source: Estimates prepared by ICF Consulting Group for U.S. EPA, Office of Air and Radiation.
ES-13
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table ES-5. Emissions of HFCs' and PFCs:
1990
, (Million Ivletric Tonnes)
Compound
Molecular
Basis
GWPa Carbon-
Equivalent
HFCs
HFC-23
HFC-I34a
HFC-152a
PFCs
Total PFCs
0.00552
0.0005
0.0003
0.003
10,000
1,200
150
5,400
15.05
0.16
0.01
3.98
* The GWP for HFC-23 was obtained from U.S. EPA's
Office of Air and Radiation and is based on unpub-
lished data from DuPont Chemical Company and
others. The GWPs for the other compounds are from
1PCC, 1992,
Source: U.S. EPA, 1994b
In 1990, the use of substitutes for ODSs was minimal.
Thus, emissions of HFCs were quite small, and were
largely the result of by-product emissions from the
production of HCFC-22. PFC emission were the result
of aluminum smelting activities.
EMISSIONS OF CRITERIA POLLUTANTS
Carbon monoxide (CO), nitrogen oxides (NOx),
nonmethane volatile organic compounds (NMVOCs),
and sulfur dioxide (SO2) are commonly referred to in
the United States as "criteria pollutants".3 Carbon
monoxide is created when carbon-containing fuels are
burned incompletely; oxides of nitrogen, NO andNO2,
are created from lightning, biomass fires, fossil-fuel
combustion, and in the stratosphere from nitrous oxide;
nonmethane VOCs include compounds such as pro-
pane, butane, and ethane, and are emitted primarily
from transportation and industrial processes, as well as
biomass burning, and nonindustrial consumption of
organic solvents (U.S. EPA, 1990a); sulfur dioxide can
result from the combustion of fossil fuels, industrial
processing (particularly in the metals industry), waste
incineration, and biomass burning (U.S. EPA, 1993b).
Because of their contribution to the formation of
urban smog, they are regulated under the 1970 Clean
Air Act and successive amendments. These gases also
have an impact on global climate, although their
impact is limited because their radiative effects are
indirect (i.e., they do not directly act as greenhouse
gases but react with other chemical compounds in the
atmosphere). It should be noted, however, that sulfur
dioxide emitted into the atmosphere affects the Earth's
radiative budget negatively; therefore, it is discussed
separately from the other criteria pollutants hi Box ES-3.
The most important of the indirect effects of the
criteria pollutants CO, NOx, and NMVOCs 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, carbon monoxide interacts with the hydroxyl
radical (OH) the major atmospheric sink for meth-
ane to form carbon dioxide. Therefore, increased
atmospheric concentrations of CO limit the number of
OH compounds available to .destroy methane, thus
increasing the atmospheric lifetime of methane.
Table ES-6.
Emissions
NMVOCs:
(Million Metric
Source
Fossil Fuel
Combustion
Industrial
Processes
Fossil Fuel
Production,
Distribution,
and Storage
Waste
Incineration
Agricultural
Waste Burning
Solvent Use
Total
CO
73.65
4.35
0.39
1.53
2.76 .
0.002
82.67
ofCO,NOx,and
1990
Tonnes)
NOt NMVOCs
20.36 8:94
0.72 3.49
0.09 0.67
0.07 0.29
0.12 -
0.002 5.74
21.36 19.13
, ... ',....
ES-14
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Box ES-3. Sulfur Dioxide,: Effects on Radiative Forcing and Sources of Emissions
Sulfur dioxide emitted into the atmosphere through natural and anthropogenic processes affects the
Earth's radiative budget through photochemical transformation into sulfate particles that (i) scatter sunlight
back to space, thereby reducing the radiation reaching the Earth's surface; (ii) possibly increase the .number
of cloud condensation nuclei, thereby potentially altering the physical characteristics of clouds, and (iii)
affect atmospheric chemical composition, e.g. stratospheric O3, by providing surfaces for heterogeneous
chemical processes. As a result of these activities., the effect of these gases on radiative forcing may be
negative (IPCC, 1992). Therefore, since their effects are uncertain and opposite from the other criteria
pollutants, emissions of SO2 have been presented separately below.
Emissions of Sulfur Dioxide: 1990
(Million Metric Tonnes)
Source
Fossil Fuel Combustion
Industrial Processes
Solvent .Use
Waste Incineration.
Fossil Fuel Productions
Distribution and Storage
Total
Emissions
22.69
1.91
0.001
0.04
0.51
25.15
Source:' U.S. EPA,1993b
The major source of SO2 emissions in the U.S. is the burning of sulfur containing fuels, mainly coal.
Metal smelting and other industrial processes also release significant quantities of SO2. As a result, the
largest contributor to overall U.S. emissions of SQ2 are electric utilities, accounting for about 70 percent. .
Coal combustion accounted for approximately 96 percent of SO2 emissions from electric utilities. The
second largest source is industrial fuel combustion, which produced about 14 percent of 1990 SO2 emissions.
Sulfur dioxide is important for reasons other .than its effect on radiative forcing. It is a major con-
tributor 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 S02 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, as well as cause the acidification of lakes and streams and damage trees. As a result of these harm-
ful effects, the U.S. has regulated the emissions of SO2 in ihe_ Clean Air Act of 1970 and in its amendments
of 1990. The U.S. EPA has also developed a strategy to control these emissions via four programs: (!) the
National Ambient Air Quality Program, which protects air quality and public health on the local level; (2)
the New Source Performance Standards, which set emission limits for;new sources; (3),the New Source
Review/Prevention of Significant Deterioration Program, which protects air quality from deteriorating,
especially in clean areas; and (4) the Acid Rain Program, which addressees regional environmental prob-
lems often associated with long-range transport of SO2 and other pollutants. .
ES-15
-------
These criteria pollutants are generated through a
variety of anthropogenic activities, including, fossil fuel
combustion, solid waste incineration, oil and gas
production and processing, industrial processes and
solvent use, and agricultural crop waste burning. Table
ES-6 summarizes U.S. emissions from these sources
for 1990. The United States has annually'published
estimates of criteria pollutants since 1970. Table ES-6
clearly shows that fuel consumption accounted for the
majority of emissions of these gases. In fact, motor
vehicles that burn fossil fuels comprise the single
largest source of CO emissions in the United States,
contributing about two-thirds of all U.S. CO emissions
in 1990. Motor vehicles also emit about one-third of
total U.S. NOx and NMVOC emissions.' Industrial
processes, such as the manufacture of chemical and
allied products, metals processing, and industrial uses
of solvents are also major sources of CO, NOx, and
NMVOCs.
A "sink" is a process that destroys or absorbs
greenhouse gases. The carbon cycle is com-
posed of reservoirs of carbon (e.g., the oceans,
atmosphere, and biota), and of flows of carbon to
and from these reservoirs. "Sinks" of carbon
dioxide include absorption of atmospheric
carbon dioxide by terrestrial biota (such as trees)
and oceanic biota. The primary anthropogenic
"sink" of carbon is tree planting and other forest
management activities. The U.S. has estimated
the enhancement of forests as a carbon sink.
Ozone exists in the stratosphere and troposphere.
In the stratosphere (about 20 - 50 km above the
Earth's surface), ozone provides a protective
layer shielding the Earth from ultraviolet radia-
tion and subsequent harmful health effects on
humans and the environment. In the troposphere
(from the Earth's surface to about 10 km above),
ozone is a chemical oxidarit and a major compo-
nent of photochemical smog. Most ozone is
found in the stratosphere, with some transport
occurring to the troposphere (through the tropo-
pause, i.e., the transition zone separating the
stratosphere and the troposphere) (IPCC, 1992).
The term "criteria pollutant" refers to those
compounds for which attainment criteria have
been established under the Clean Air Act Amend-
ments ofl970. CO, NOx, NMVOCs, and SO2 all
have air quality standards for which air quality
criteria have been issued.
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INTRODUCTION
Overview
" The Earth absorbs radiation -from the Sun, ' .'.
primarily at the surface, and reradiates this energy to
space. A portion of this reradiated energy is absorbed
or "trapped" by gases in the atmosphere. This
"trapped" energy warms the Earth's .surface and
atmosphere, creating what is known as the "greenhouse
effect." Without the natural heat-trapping properties of
these atmospheric gases, the Earth's temperature would
average about 55ฐ F lower than today.
Naturally occurring greenhouse gases include
water vapor, carbon dioxide (C02), methane (CH4),
nitrous oxide (N2O), and ozone
Chlorofluoro-
carbons (CFCs) and partially halogenated fluorocar-
bons (HCFCs), a family of human-made compounds,
their substitutes hydrofluorocarbons (MFCs), and other
compounds such as perfluorinated carbons (PFCs), are
also greenhouse gases. In addition, there are photo-;
chemically important gases such as carbon monoxide
(CO), oxides of nitrogen (NOx), and nonmethane
volatile organic compounds (NMVOCs) that, although
not greenhouse gases, contribute indirectly to the .
greenhouse effect. These are commonly referred to as
tropospheric ozone precursors because they influence
the rate at which ozone and other gases are created and
destroyed in the atmosphere. Box 1 contains a brief
description of these gases, their sources, and their roles
. in the atmosphere.2 In addition, emissions of sulfur
dioxide (SO2) are provided in Annex E of this report.
.Sulfur gases, primarily sulfur dioxide, are believed to
contribute negatively to the greenhouse effect. There-
fore, the U.S. -has discussed these emissions separately.
Although CO2,CH4, and N2O occur naturally in
the atmosphere, their recent atmospheric buildup
appears to be largely the result of anthropogenic
activities.. This buildup has altered the composition of
the Earth's atmosphere, and possibly will affect future
global climate. Since 1800, atmospheric concentra-
tions of carbon dioxide have increased more than 25
percent, methane concentrations have more than
doubled, and nitrbus oxide concentrations have risen
.approximately 8 percent (IPCC, 1992). And, from the
1950s until.the mid-1980s, when international concern
over CFCs grew, the use of these gases increased -
nearly 10 percent per year. The consumption of CFCs
is declining quickly, however, as these gases are, ,
phased out under the Montreal Protocol. Use of CFC
substitutes, in contrast, is expected to grow significantly.
The Inventory Process
Central to any study of climate; change is the
development of an emissions inventory that identifies
and quantifies a country's primary sources and sinks of
greenhouse gases. Developing and participating in the
inventory process is important for two reasons: (1) it
provides a basis for the ongoing development of a
comprehensive and detailed methodology forestimat-
ing sources and sinks of greenhouse gases, and (2) it
provides a common and consistent mechanism through
which all signatory countries to the United Nations'
Framework Convention on Climate Change (FCCC)
can estimate emissions and compare the relative
contribution of different emission sources and green-
house gases to climate change. Moreover, systemati-
cally and consistently estimating emissions at the
national and international levels is a prerequisite for
1 Ozone exists in the stratosphere and troposphere. In the stratosphere (about 20 - 50 km above the Earth's, surface),
ozone provides a protective layer shielding the Earth from ultraviolet radiation and subsequent harmful health" effects on -'."
humans and the environment. In the troposphere (from the Earth's surface:to about 10 km above), ozone is a chemical
oxidant and major component of photochemical smog. Most ozone is found in the stratosphere, with some transport
occurring to the troposphere (through the tropopause, i.e., the transition zone separating the stratosphere and the troposphere)
(IPCC,. 1992).
2 For convenience, all gases discussed in this inventory are generically referred to as "greenhouse gases," although the
reader should keep in mind the distinction between actual greenhouse gases and photochemically important trace gases. :
1
-------
Box 1. Greenhouse Gases and Photochemically Important Gases
Carbon Dioxide (CO>J. The combustion of liquid, solid,
and gaseous fossil fuels is the major anthropogenic source of
carbon dioxide emissions. Some other non-energy production
processes (e.g., cement production) also emit notable quantities
Of carbon dioxide. CO,'emissions are also a product of forest
clearing and biomass burning. Atmospheric concentrations of
carbon dioxide have been increasing at a rate of approximately
0.5 percent per year (IPCfi, 1992), although recent measure-
ments suggest that this rate of growth may be moderating (Kerr,
1994).
Ifl nature, carbon dioxide is cycled between various
atmospheric, oceanic, land biotic, and marine biotic reservoirs.
The largest fluxes occur between the atmosphere and terrestrial
biota, and between the atmosphere and surface water of the
oceans. While there is a small net addition pf CO2 to the
atmosphere (/.*., a net source of CO2) from equatorial regions,
oceanic and terrestrial biota in the Northern Hemisphere, and to
a lesser extent in the Southern Hemisphere, act as a net sink of
COj (i.e., remove more CO2 from the atmosphere than they
release) (IPCC, 1992).
Methane (CHJ. Methane is.produced through anaerobic
decomposition of organic matter in biological systems.
Agricultural processes such as wetland rice cultivation, enteric
fermentation in animals, and the decomposition of animal '
wastes emit methane, as does the decomposition of municipal
solid wastes. Methane is also emitted during the production and
distribution of natural gas and oil, and is released as a by-
product of coal production and incomplete fuel combustion.
The atmospheric concentration of methane, which has been
shown to be increasing at a rate of about 0.6 percent per year,
may be stabilizing (Steele et ai., 1992).
The major sink for methane is its interaction with the
hydroxyl radical (OH) in the troposphere. This interaction
results in the chemical destruction of the methane compound, as
the hydrogen molecules in methane combine with the oxygen in
OH to form water vapor (H3O) and CH3. After a number of
other chemical interactions, the remaining CHj turns into CO
which itself reacts with OH to produce carbon dioxide (CO2)
and hydrogen (H).
fjalogenated Fluorocarbons, HFCs, andPFCs.
Htlogenated fluorocarbons are human-made compounds that
include: chlorofluorocarbons (CFCs), halons, methyl chloro-
form, carbon tetrachlpride, methyl bromide, and
hydrochlorofluorocarbons (HCFCs). All of these compounds
not only enhance the greenhouse effect, but also contribute to
Stratospheric ozone depletion. Under the Montreal Protocol and
the Copenhagen Amendments, which control the production and
consumption of these chemicals, the U.S. phased out the
production and use of all halons by January 1,1994 and will
phase out CFCs, HCFCs, and other ozone-depleting substances
by January 1,1996. Perflubrinated carbons (PFCs) and
hydrafluorocarbons (HFCs), a family of CFC and HCFC
replacements not covered under the Montreal Protocol, are also
powerful greenhouse gases.
Nitrous Oxide (N^O). Anthropogenic sources of nitrous
oxide emissions include soil cultivation practices, especially the
use of commercial and organic fertilizers, fossil fuel combus-
tion, adipic (nylon) and nitric acid production, and biomass
burning.
Ozone (OJ. Ozone is both produced and destroyed in
the atmosphere through natural processes. Approximately 90
percent resides in the stratosphere, where it controls the
absorption of solar ultraviolet radiation; the remaining 10
percent is found in the troposphere and could play a significant
greenhouse role. Though ozone is not emitted directly by
human activity, anthropogenic emissions of several gases
influence its concentration in the stratosphere and troposphere.
Chlorine and bromine-containing chemicals, such as CFCs,
deplete stratospheric ozone. However, as previously stated,
under the Montreal Protocol and Copenhagen Amendments, the
U.S. phased out the production and use of all halons by January
1, 1994 and will phase out CFCs and other ozone-depleting
substances by January 1, 1996.
mcreased emissions of carbon monoxide, nonmethane
volatile organic compounds, and oxides of nitrogen have
contributed to the increased production of tropospheric ozone
(otherwise known as urban smog). Emissions of these gases,
known as criteria pollutants, are regulated under the Clean Air
Act of 1970 and subsequent amendments.
Photochetnicaily Important Gases
Carbon Monoxide (CO). Carbon monoxide is created
when carbon-containing fuels are burned incompletely.
Carbon monoxide elevates concentrations of methane and
tropospheric ozone through chemical reactions with
atmospheric constituents (e.g., the hydroxyl radical) that
would otherwise assist in destroying methane and ozone.
It eventually oxidizes to C0r
Oxides of Nitrogen (NOJ. Oxides of nitrogen, NO and
NO2, are created from lightning, biomass burning (both
natural and anthropogenic fires), fossil fuel combustion,
i i, ir r,;,:"Hi'"*1 '::." :iff JK!^;ปw^ jivv n, > *, ., ,*, ป ,n'v
and in the stratosphere from nitrous oxide. They play an
important role in climate change processes due to their
contribution to the formation of ozone.
Nonmethane Volatile Organic Compounds (NMVOCs).
Nonmethane VOCs include compounds such as propane,
butane, and ethane. Volatile organic compounds
participate along with nitrogen oxides in the formation of
ground-level ozone and other photochemical oxidants.
VOCs are emitted primarily from transportation and
industrial processes, as well as biomass burning and non-
industrial consumption of organic solvents (U.S. EPA,
1990a).
-------
evaluating the cost-effectiveness and feasibility of
pursuing possible mitigation strategies and implement-
ing" emission reduction technologies. . -
This report presents estimates by the United States -.
Governmentof U.S. greenhouse gas emissions and
sinks for 1990-1993. A summary of these estimates is
provided in Table 1 by gas and source category. The
remainder of this document discusses the methods and
data used to calculate these emission estimates. The
emission estimates in Table 1 are presented On both a
full molecular basis and on a carbon-equivalent basis in
order to show the relative contribution of each gas to .
total radiative forcing (see Box 2 for an explanation of
how the relative contribution of each gas was calcu-
lated).
The U.S. views this submission as an
opportunity to fulfill its commitment under Article 4-1
of the FCCC, which came into force on March 21,
1994, following ratification. As decided at the Ninth
Session of the International Negotiating Committee
(INC), emission estimates are to be estimated and
presented in.accordance with the IPCC Draft
Guidelines for National Greenhouse Gas Inventories
(IPCC/OECD, 1994) to ensure that the emission
inventories submitted to the FCCC are consistent and
comparable across sectors and among nations. The
information provided in this inventory is presented in
accordance with the IPCC Draft Guidelines for
National Greenhouse Gas Inventories (IPCC/OECD, .
1994), unless otherwise noted.
Methodology and Data
Emissions of greenhouse gases from various
sources are estimated using methodologies that are
consistent with Volumes 1-3 of IPCC Draft Guidelines
for National Greenhouse Gas Inventories (IPCC/
OECD, 1994).3 To the extent possible, the present U.S.
inventory relies directly on published activity and
emission factor data.4 Inventory emission estimates
from energy consumption and-production activities are
-based primarily on the latest official information from
the Energy Information Administration of the Depart-
ment of Energy (DOE/EIA). Emission estimates for
oxides of nitrogen, carbon monoxide, and nonmethane ,
. volatile organic compounds are based directly on
Box 2. The Global Warming Potential (GWP) Concept
As mentioned, gases can contribute to the green-
house effect both directly and indirectly. Direct effects,
occur when the gas itself is a greenhouse gas; indirect
radiative forcing occurs when chemical transformation of
the original gas produces a gas or gases that are green-
house gases, or when a gas influences the atmospheric
lifetimes of other gases. The concept of Global Warming
Potential (GWP) has been developed to compare the
ability of each greenhouse gas to trap heat in the atmo-
sphere relative to another gas. Carbon dioxide was
chosen as the "reference" gas to be consistent with the
1993 U.S. Climate Change Action Plan. All gases in this
report are presented in units of million metric tonnes of .
carbon-equivalent, or MMTCE." Carbon comprises 12/44
of carbon dioxide by weight.
The Global Warming Potential (GWP) of a
greenhouse gas is the ratio oT global warming, or radia-
tive forcing (both direct and indirect), from one kilogram
of a greenhouse gas to one kilogram of carbon dioxide
over a period of time. While any time period can be
selected, the 100-year GWPs recommended by the IPCC
are used in this report.
Gas
Carbon dioxide
Methane
Nitrous oxide
HFC-134a
HFC-23
HFC-152a
PFCs
GWP
(100 Years)
1
11/22*
.270
1,200
10,000
150
. 5,400
* The direct GWP for methane is 11. The U.S. has
accounted for both the direct and indirect effects of
methane on radiative forcing: The indirect effects of
methane are considered comparable in magnitude to the
direct effects, therefore a GWP of 22 has been used
(IPCC, 1992). Using a GWP of 22 for methane is also
consistent with the GWP used in the U.S. Climate
Change Action Plan, and follows the suggestion of the
INC 9th Session that requests that indirect effects be
included where applicable. The magnitude of the indirect
effects of other gases are either zero Or uncertain-.
-------
|'| , , ' ',! ., , , i I i, I . 1
i ' !" " 1 A 1 f , ( !
Table 1: Summary of U.S. Greenhouse Gas Emissions: 1990 - 1993
(Million Metric Tonnes)
Gas/Source
QmmkQuse_Qases
Carbon Dioxide (CO2)
Fossil Fuel Combustion
Other
Total
Forests (sink)
Net Total
Methane (CH4)
Landfills
Agriculture
Coal Mining
Oil and Gas Systems
Other
Total
Nitrous Oxide (N2O)
Agriculture
Fossil Fuel Consumption
Industrial Processes
Total
HFCs and PFCs
Carbon Monoxide (CO)
Nitrogen Oxides (NO%)
NMVOCs
NET U.S. EMISSIONS
Emissions
(Full Molecular Weight)
1990 1991 1992 1993
4,895 4,835 4,908 5,013
62 61 62
4,956 4,896 4,970
(436) (433) (429)
4,520 4,463 4,541
10.0 10.1 10.2 10.3
8.6 8.5 8.6 8.8
4.4 4.2 4.0
3.2 3.3 3.3 .
0.8 0.8 0.8
27.0 26.9 27.0
0.2 0.2 0.2
0.1 0.1 0.1
0.1 0.1 0.1
0.4 0.4 0.4
82.7 81.4 78.1
. 21.4 21.2 21
19.1 18.7 17.9
Emissions
(Direct and Indirect Effects;
Carbon-Equivalent)
1990 1991 1992 1993
1,335 1,319 1,339 1,367
17 17 17
1,352 1,336 1,356
(119) (118) (117)
1,233 1,218 1,239 '."-'
60 61 61 62
52 51 .52 53
26 26 24
19 20 20
5 5 5
162 162 161
14 14 14 -
,9 10 10
77 7
30 32 32
19.2 19.6 20
. .
-
1,444 1,432 1,452
-
+ Total of tliese gases does not exceed 0.01 million metric tonnes.
Note; The "Totals" presented in the summary tables hi this chapter may not equal the sum of the individual source categories due to
rounding, ' i ' ] '.';'.. ; ...'.,. , '.' , ... :' ",' "
Changes in CO, emissions from fossil fuel consumption had the greatest impact on U.S. emissions from 1990 to 1993. U.!3
emissions of CO3 in 1991 were. 1,319 MMTCE, about 1.2 percent lower than 1990 emission levels. Emissions for 1992 were; 1,339
MMTCE, an increase of about 1.5 percent over 1991 levels, offsetting the decrease in 1991 and returning emissions to about 1990
levels. Based on preliminary data for 1993, the upward trend since 1991 has continued, with 1993 C62 emissions from fossil fuel about
2,4 percent greater than 1990. This trend is largely attributable to changes in total energy consumption resulting from the economic
Slowdown in the U.S. economy and the subsequent recovery.
CH4, NjO, and HFCs and PFCs represent a much smaller portion of total emissions than CO,. Overall, emissions of these gases
remained relatively constant over the period from 1990 to 1992. Methane emissions from coal mining declined slightly due to small
decreases -in coal production and increases in coalbed methane recovery. N?O emissions remained relatively constant, while HFC
emissions increased slightly, due to increased production of HCFC-22, which increased by-product emissions of HFC-23. PFC emis-
sions remained constant pver the period. '.....
-------
available U.S. Environmental Protection Agency (U.S.
EPA)'emissions.data. These estimates are supple-
mented by calculations using the best available activity
data from other agencies. Complete documentation of
emission estimations can be found in the sources
, referenced throughout, the text. In these supplementary
calculations, attempts were made to adhere-as closely
as possible to IPCC methods. In many cases, the IPCC
default methodologies have been followed. However,
for emission sources considered to be major sources in
the U.S., the IPCC default methodologies were ex-
panded and more comprehensive-methods used. These
instances, including energy consumption, forest sinks,
and some methane sources are documented in the text,
along with the reasons for diverging from 'the IPCC
default methodologies.5
The majority of 1990 U.S. methane emission
estimates presented in this inventory were taken
directly from the U.S. EPA report, Anthropogenic
Methane Emissions in the United States, Estimates for
1990: Report to Congress (U.S. EPA, 1993a). That
U.S. EPA report provided 1990 U.S. methane emis-
sions for a variety of domestic sources, including
naturalgas systems, coal mining, landfills, domesti-
cated livestock, manure management, rice cultivation,
fuel combustion, and production and refining of
petroleum liquids. The methodologies used to" arrive at
the emissions estimates in U.S. EPA (1993a) are
conceptually similar to IPCC methodologies. Where ~
the methodologies differ, information is provided in the
text and/or annexes to ensure that the estimates pre-
sented are reproducible. Estimates for 1991, 1992, and
1993 have been developed using these same method-
ologies unless otherwise noted.
Emission estimates for NOx, CO, and NMVOCs
were taken directly, except where noted, from the U.S.
EPA report, National Air Pollutant Emission Trends
1900 - 1992 (U.S. EPA, 1993b), which is an annual
U.S. EPA publication that provides the latest estimates
of regional arid national emissions for criteria pollut-
ants.6 Emissions of these pollutants are estimated by
the U.S. EPA based on statistical mformation about
each source category, emission factor, and control
efficiency. While the U.S. EPA's estimation method-
ologies are conceptually similar to the IPCC-recom-
mended methodologies and are discussed in detail
below, the large number of sources EPA used in
developing the estimates makes it difficult to reproduce
the information from EPA (1993b) in this inventory
document In these instances, the sources containing
the detailed documentation of the methods used are
referenced for the interested reader. .
Organization of the Inventory
In accordance with the IPCC guidelines for.
reporting contained in the IPCC Draft Guidelines for
National Greenhouse Gas Inventories (IPCC/OECD,
1994), this inventory is organized into six parts. These
six parts correspond to the six major source categories
below. In addition, annexes provide additional data on
calculations which are not included in the main text.
(Note: while the list below follows the IPCC's list of
"recommended.source categories, emission sources that
are riot applicable to the U.S. are not included).
I. Part I covers emissions from all energy activities,
including:
A. Fuel Combustion Activities:
1. Iridustry
3" Discussions of inventory methods can also be found in Estimation of Greenhouse Gas Emissions'and Sinks: Final .
Report from the OECD Experts Meeting, 18-21 February 1991 (August 1991). That report documents baseline inventory
methodologies for a variety of source categories, which have subsequently been" further refined based on recommendations
provided at an IPCC-sponsored experts workshop held in Geneva, Switzerland in December 1991 and at an OECD/
Netherlands-sponsored workshop in Amersfoort, Netherlands in February 1993. The proceedings* from these meetings, the
Final Report (OECD, 1991), as well as several other international meetings, form the basis for the current IPCC Draft
'Guidelines.
4 Depending on the emission source category, activity data can;include fuel consumption or deliveries, vehicle-miles
travelled, raw material processed, etc.; emission factors are factors that relate the quantity of emissions to the activity.
5 In order to, folly comply with the IPCC Draft .Guidelines, the United States has provided a copy of the IPCC reporting
tables in Annex D. " .-.,-'_-.
6 Criteria pollutants include: carbon monoxide (CO), lead (Pb), niffbgen oxides (NOx), particulate matter less than ten
microns (PM-'lO), sulfur gases (especially SO2), total particulate matter (TP), and nonmethane vplatile organic compounds
(NMVOCs). ' , ' ' . "-' -.'" ' ' '
5
-------
2. Transportation
3. Residential
4. Commercial/Institutional
5. Electric Utilities
6. Biomass for energy
B. Fuel Production, Transmission, Storage, and
Distribution:
1. Crude oil and natural gas
2. Coal mining
II. Part II covers emissions from other industrial
production processes (nonenergy ISIC), including:
A. Chemicals
B. Non-Metallic Mineral Products
C. Other, including chlorofluorocarbons and
other substances
III. Part III covers emissions from solvent use
IV. Part IV covers emissions from agriculture,
including:
A. Enteric Fermentation (in domestic animals)
B. Manure Management (for domestic animals)
C. Rice Cultivation
D. Agricultural Soils
E. Agricultural Crop Waste Burning
V. Part V covers emissions resulting from land-use
change and forestry
VI. Part VI covers emissions from wastes and waste-
treatment processes, including:
A. Landfills
B. Wastewater Treatment
C. Waste Combustion
Uncertainty and Limitations of Emissions
Estimates
While the current U.S. emissions inventory
provides a solid foundation for the development of a
more detailed and comprehensive national inventory, it
has several strengths and weaknesses. First of all, this
report by itself does not provide a complete picture of
past or future emissions in the U.S.; it only p'rovides an
inventory- of U.S. emissions for the years 1990 - 1993.
However, the U.S. believes that common and consis-
tent inventories taken over a period of time can and
will contribute to understanding future emission trends.
The U.S. plans to update this comprehensive inventory
of greenhouse gas emissions and sinks on an annual
basis and to use the information gained to track
progress of commitments made under the U.S. Climate
Change Action Plan. The methodologies used to
estimate emissions will be periodically updated as
methods and information improve, and as further
guidance is received from the IPCC and the INC. In
order to maintain consistency as methodologies change
over time, the U.S. will also include, as appendices to
future updates, estimates of emissions using the
methods described in this,document.
Secondly, there are uncertainties associated with
the emissions estimates. Some of the current estimates,
such as those for CO2 emissions from energy-related
activities and cement processing, are considered
accurate. For other categories of emissions, however, a
lack of data or an incomplete understanding of how
. emissions are generated limit the scope or accuracy of
the inventory. For certain categories, emission esti-
mates are given as a specific range to reflect the
associated uncertainty. Where applicable, specific
factors affecting the accuracy of the estimates are also
discussed in detail.
Finally, while the IPCC methodologies provided
in the three volume IPCC/OECD report, IPCC Draft
Guidelines for National Greenhouse Gas Inventories,
represent baseline methodologies for a variety of
source categories, many of these methodologies are
still being refined. The current U.S. inventory uses the
IPCC methodologies where possible, and supplements
with other available methodologies and data where
needed. The U.S. realizes that not only are the meth-
odologies still evolving, but that additional efforts are
necessary to improve methodologies and data collec-
tion procedures. Specific areas requiring further.
research include:
Completing estimates for various source
categories. Quantitative estimates of some of
the sources and sinks of greenhouse gas
emissions are not available at this time. In
particular, emissions from some land-use
activities and industrial processes are not
included in the inventory either because data
are incomplete or because methodologies do
not exist for estimating emissions from these
source categories.
Understanding the relationship between
emissions and sources. This is a crucial step
in completing and refining existing method-
ologies and in developing methodologies for
emission source categories where none
-------
currently exist. For example, a great deal of
uncertainty exists in how nitrous oxide,
emissions are produced from energy-related
activities and fertilizer consumption. As a
consequence, the quality of emission factors
and activity data for these categories are
particularly weak.
Improving the accuracy of emissions factors.
A substantial amount of research is underway
that could improve the accuracy of emission
factors used to calculate estimates for a variety
of sources. For example, the accuracy of
current emission factors .used to estimate
emissions from surface coal mining is limited
by a lack of available data. Emission factors
for methane from landfills are also currently
undergoing revision. To more accurately
assess methane emissions from landfills,
researchers are working to determine the
relationship between moisture, climate, and
waste composition and methane generation
rates. Emission factors used to estimate
greenhouse gas emissions from biomass
burning and land use are also being revised.
Providing appropriate activity data. Although
methodologies exist for estimating emissions
for some source categories, problems arise in
obtaining data that are compatible with
methodology requirements.' For example, the
ability to estimate emissions from oil and gas
systems is constrained by a lack of informa-"
tion on compressor type, amount of leakage,
and emission control technology. In the
agricultural sector, estimating emissions of
animal wastes using the IPCC methodology is
arduous because of the complexity of the data
required. Obtaining information on animal
weights, waste management systems, and
feeding practices by animal type is difficult.
Efforts need to be made to collect activity data
appropriate for use in the IPCC methodologies.
The uncertainties and limitations associated with
calculating greenhouse gas emissions are both qualita-
tive and quantitative. Emissions calculated for the U.S.
inventory reflect current best estimates; in some cases,
however, estimates are based on approximate method-
ologies and incomplete data.' Efforts need to be made
to improve existing methodologies and data collection
activities, so that methodologies and data are consistent
with one another and so that they allow both the U.S.
and other countries to estimate emissions with greater
ease, certainty, and consistency.
-------
fit'1 iป 'i.'iii !!ป"' ' ,!;",
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PARTI. EMISSIONS FROM ENERGY
Total US Emissions by Source: 1990
(MMT Carbon Equivalent)
1396
1444
Energy Industry Agriculture Forestry Wastes Net Total
Source
U.S. Carbon Dioxide Emissions by Source: 1990
(1%) Other
\
Energy-related activities are title most significant
contributor to U.S. greenhouse gas emissions, account-
ing for 1,396 MMTCE, or 89 percent of U.S. emissions
in 1990. Emissions from fossil fuel combustion
comprise the vast majority of these energy-related
emissions, with releases of CO2 from fossil fuel
combustion accounting for 1,335 MMTCE. Activities
associated with the production, transmission, storage,
and distribution of fossil fuels also emit greenhouse
gases. These are primarily fugitive emissions from
natural gas systems, oil production and refining, and
coal mining. The main gas emitted through these
activities is methane, while smaller quantities of
NMVOCs,,CO2, and CO can also be emitted. These
gases represent a much smaller portion of total energy
emissions than CO2, but are nonetheless important.
About 30 percent of the nation's CH4 emissions and 31
percent of N2O emissions come from energy-related
activities. Additionally, the majority of criteria pollut-
ants are emitted from energy activities, which account
for 96, 90, and 50 percent of NOx, CO, and NMVOC
emissions, respectively.
The combustion of biomass and biomass-based
fuels also emits greenhouse gases, although CO2
emissions from these activities are not included in the
U.S. total because biomass resources in the U.S. are
used on a sustainable basis/ That is, the carbon
released when biomass is consumed is recycled as U.S.
forests regenerate, causing no additional CO2 to be
added to the atmosphere.'
U.S. emissions of CO2 from energy decreased
over one percent in 1991 compared to 1990 levels,
declining from 1,335 MMTCE to 1,319 MMTCE.
Emissions for 1992 were 1,339 MMTCE, offsetting the
decrease in 1991 and returning emissions to about
1990 levels. Based on preliminary data for 1993, the
upward trend since 1991 has continued, with 1993 CO2
emissions from fossil fuel combustion at 1,367
MMTCE, or about 2.4 percent greater than 1990. This
trend is largely attributable to changes in total energy
consumption resulting from the economic slowdown in
the U.S. economy and the subsequent recovery. Meth-
ane emissions from coal mining did decline slightly
over this period due to small decreases in coal produc-
tion and increases in coalbed methane recovery.
Emissions of the criteria pollutants CO, NOx, and
NMVOCs declined, continuing a downward trend in
these gases over the past several years.
1 Any emissions related to land use changes are discussed in Part V of this document.
-------
A. EMISSIONS FROM FOSSIL FUEL
CONSUMPTION
1. Carbon Dioxide Emissions from Fossil Fuel
Consumption
Tlte majority of energy in the United States,
approximately 88 per cent, is produced through the
combustion of fossil fuels such as coal, natural gas,
and petroleum. The remaining 12 percent consists of
renewable or other energy sources such as
hydropower, biomass, and nuclear energy.
Carbon Dioxide Emissions by End Use Sector: 1990
TrwwfK>(tปiJon(J1%)
Residential (19%)
Commerlcal (16%)
Indutlio! (MS)
! In this graph, emissions generated by electric utilities are allocated to each
end-usa sector according to each sector's share of electricity consumption. ;
In 1990 the U.S. emitted a total of 1,335
MMTCE as CO2 from fossil fuel combustion, or
about 99 percent of total U.S. emissions ofCO2 and
85 percent of all greenhouse gas emissions (fuels for
international transport accounted for an additional
22.6 MMTCE, which is not included in the U.S.
estimates)2. These emissions were produced from a
variety of fossil fuel combustion activities, including
heating in residential and commercial buildings,
energy combustion to generate electricity, steam
production for industrial processes, and gasoline
consumption in automobiles and other vehicles.
As fossil fuels are combusted, the carbon stored
in the fuels is emitted as carbon dioxide and smaller
amounts of other gases, including CO, CH4, and
NMVOCs. These other gases are emitted as a by-
product of incomplete fuel combustion. The amount of
carbon in the fuel varies significantly by fuel type. For
example, coal contains the highest amount of carbon
per unit of useful energy. Petroleum has about 80
percent of the carbon per unit of energy as compared to
coal, and natural gas has only about 55 percent. Petro-
leum supplies the largest share of U.S. energy needs,
accounting for over 40 percent of total energy consump-
tion (see Figure 1-1). As a result, uses of petroleum
released approximately 581 MMTCE in 1990, or 43
percent of all CO2 emissions from energy consumption
(see Table 1-1). The other fossil fuels, coal and natural
gas, accounted for 36 and 21 percent, respectively.
Figure l-,1
Types of Energy Consumed in the U.S.: 1990
Nuclear, Renewablas, Other
(12%or9.31QBtu)
Petroleum
(41% or 33.55 Btu)
Coal (23% or 19.00 QBtu)
Natural Gas
(24% or 19.28 Btu)
1 QBtu = 1 quadrillion Btu = 1X10E15 Btu
Approximately 88 percent of U.S. energy is produced through the
combustion of fossil fuels.
U.S. emissions of CO2 from energy were esti-
mated to be 1,335 MMTCE in 1990, declining to 1,319
MMTCE in 1991. 1992 emissions increased to 1,339
MMTCE, Based on preliminary data for 1993, CO2
emissions from fossil fuel combustion were 1,367
MMTCE,= or about 2.4 percent greater than 1990 (see
Table 1-1). This trend is largely due to the economic
recession and subsequent recoveiy.
Industrial Sector
The industrial sector accounts for 34 percent of
U.S. emissions from fossil fuel consumption, making it
the largest end-use source of CO2 emissions (see Figure
1-2). About two-thirds of these emissions result from
the direct consumption of fossil fuels in order to meet
industrial demand for steam and process heat. The
remaining one-third of industrial energy needs is met
by electricity for such uses as motors, electric furnaces
and ovens, and lighting.
The industrial sector is also the largest user of
non-energy applications of fossil fuels, which often
store carbon. Fossil fuels used for producing fertiliz-
ers, plastics, asphalt, or lubricants can store carbon in
products for very long periods. Asphalt used in road
construction, for example, stores carbon indefinitely.
1 There is international disagreement as to which countries are responsible for emissions produced from international
transport activities (fuels used in international transport are typically referred to as bunker fuels). The IPCC recommends
that countries account separately for bunker fuel emissions and exclude them from national totals until an internationally
recognized method is developed to allocate these emissions to specific countries. These emissions are therefore reported
separately in the U.S. inventory and not included in the national total.
10
-------
Table 1-1. U.S. CO2 Emissions from Energy Consumption by Sector and Fuel Type: 1990 - 1993
(Million Tonnes of Carbon-Equivalent)
Sector
Residential
Coal
Petroleum
Gas
Total Residential
Commercial
Coal
Petroleum
Gas
Total Commercial
Industrial
Coal
Petroleum
Gas
Total Industrial
Transportation
Coal
Petroleum
Gas
Total Transportation
U.S. Territories
Coal
Petroleum
Gas
Total Territories
All Sectors
Coal
Petroleum
Gas
Total
1990
140.3
' 3.3.1
79.4
252.7
128.3
26.3 ..
, 51.8 .
206.4
210,3
112.8
133.3
456.4
0.6
400.0
9.9
410.5
0.1
9.0
0.0
9.1
-
479.6
581.1
274.4
1,335.1
1991
139.5
33.0
83.2
255.7
127.5
' 24.8
54.3
206.6
205.9
99.4
138.5
443.8
0.6
391.9
9.2
401.7
0.2
10.6
0.0
10.8
473.7
559.7 '
285.1
1,318.5
1992
141.1'
31.6
8.5.0
257.7
129.0
, 22.3
55.2
206.5
205.6
108.8
143.2
457.7
0.6
397.8
9.0
407.5
0.2
9.2
0.0
9.4
476.5
569.8
"292.4
1,338.6
1993
147.5
..32.8
' 88.2
268.4
134.9 .
22.9
56.2
214.0
'
212.5
105.9
145.3
463.8
0.6
401.9
9.2
411.7
0.2
9.2
0.0
9.4
495.7
572.7
298.9
1,367.3
Source: Based on Energy consumption estimates from EIA, (1994b &1994h) and carbon coefficients from EIA
(1994g) and IPCC (IPCC/OECD, 1994). For complete references see Annex A.
1 1
-------
Similarly, the fossil fuels used in the manufacture of
materials like plastics also store carbon, releasing this
carbon only if the product is incinerated.
Figure 1-2
Carbon Dioxide Emissions from Fossil Fuel Combustion by
End-Use Sector: 1990
(MMT Carbon Equivalent)
Ctxanwddt RwWซnttil lodoitital
Sectors
Transportation
Note; U,S, Tanftories comprise less than 1% of emissions.
Transportation Sector
The transportation sector is also a major source
of CO2> accounting for about 31 percent of U.S.
emissions. Virtually all of the energy consumed in this
sector comes from petroleum-based products. Nearly
two-thirds of the emissions are the result of gasoline
consumption in automobiles and other .vehicles, with
other uses, including diesel fuel for the trucking
industry and jet fuel for aircraft, accounting for the
remainder.
Residential and Commercial Sectors
The residential and commercial sectors account
for about 19 and 16 percent, respectively, of CO2
emissions from fuel consumption. Both sectors are
heavily reliant on electricity for meeting energy needs,
with about two-thirds of their emissions attributable to
electricity consumption. End-use applications include
lighting, heating, cooling, and operating appliances.
The remaining emissions are largely due to the con-
sumption of natural gas and oil, primarily for meeting
heating and cooking needs.
Electric Utilities
As noted above, the U.S. relies on electricity to
meet a significant portion of its energy requirements.
In fact, as the largest consumers of U.S. energy (about
36 percent of total energy), electric utilities are collec-
tively the largest producers of U.S. CO2 emissions (see
Figure 1-3). This sector generates electricity for such
uses as lighting, heating, electric motors, and air
conditioning. Some of this electricity is generated with
the lowest CO2-emitting energy technologies, particu-
larly nonfossil options, such as nuclear energy, hydro-
power, or geothermal energy. However, electric
utilities rely on coal for 55 percent of their total energy
requirements and account for about 85 percent of .all
coal consumed in the United States.
Figure 1-3
Carbon Dioxide Emissions from Fossil Fuel Combustion by
Sector and Fuel Type: 1990
(MMT Carbon Equivalent)
36%
Commercial Residential Industrial Transportation Utllll
Energy Sectors
| ป Coal * Nalural'Gas ซ Petroleum"] ,
Note: U.S. Territories comprise less than 1 % of emissions.
Methodology Used to Estimate Emissions
The methodology used by the U.S. for estimating
CO2 emissions from fossil fuel combustion is concep-
tually similar to, the approach recommended by the
IPCC for countries that intend to develop detailed,
sectoral-based emission estimates (see Greenhouse Gas
Inventory Reference Manual; IPCC, 1994; Vol. 3). A
detailed description of the U.S. methodology is pre-
sented in Annex A,-and is characterized by the follow-
ing five steps:
1. Determine fuel consumption by fuel type and
sector. Fuel consumption data were obtained
directly from the Energy Information Admin-
istration (EIA) of the U.S. Department of
Enefgy (DOE), which is responsible for the
collection of all U.S. energy data. By aggre-
gating consumption data by sector (e.g.,
commercial, industrial, etc.), primary fuel
types (e.g., coal, oil, gas), and secondary fuel
categories (e.g., gasoline, distillate fuel, etc.),
EIA estimates total U.S. energy consumption
for a particular year.3 A discussion of the data
sources and comparison of different method-
ological approaches can be found in Box 1-1.
3 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 about 9 MMTCE of emissions in 1990.
12
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Box l-l. About Emergy Data and Estimating Carbon Emissions
When fuels are burned, the carbon con-
tained within them combines with atmospheric
oxygen to form carbon dioxide. In theory, if the
carbon content, of the fuel and the combusted
quantity is known, the resulting volume of carbon
dioxide can be estimated with a high degree of
certainty. Therefore, energy-related carbon
dioxide emissions can be estimated with a fairly
high degree of precision using available energy
data.
1. Data Availability
In the U.S., the organization responsible for
reporting and maintaining annual energy statistics
is the Energy Information Administration (EIA),
an agency of the U.S. Department of Energy (U.S.
DOE). EIA reports consumption statistics for the
50 U.S. states (e.g, the State Energy Data Report)
and U.S. territories as well as international
statistics. EIA is also responsible for reporting
U.S. data to the IEA and U.N.
2. Data format
For consistency of reporting, the IPCC has
recommended 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 categories are estimated from energy
production data (accounting for 'imports, exports,
stock changes, and losses). The resulting quanti-
ties are referred to as "apparent consumption."
The data collected in the U.S. by EIA are
more of the "bottom up" nature, i.e., they are
collected through EIA surveys at the point of
delivery or use and aggregated to determine
national totals. In other words, the EIA data
reflect the reported consumption quantities of
fuel categories and types.
For reporting to IEA, EIA converts the
data for the 50 states into IEA fuel categories
and units, calculates "apparent consumption, "
and adjusts for production, imports, exports, and
stock changes in U.S. territories and islands.
The "converted" data are then submitted to the
IEA, along with the conversion factors used and
other relevant information.
Both of the above approaches have advan-
tages and disadvantages. For example* while the
"top down " approach more accurately captures
fuel flow (and therefore the carbon flow) in most
countries, the "bottom.'up" allows for more
detailed information by end-use sectors and fuel
types.
3. Estimating Carbon Emissions
Theoretically, both approaches should
yield similar carbon emissions results. But, in
reality, in most countries' estimates will vary
depending on the approach used to estimate
consumption totals, the definition and interpreta-
tion of data sources, the carbon coefficients
used, and the assumptions regarding both the
quantity of carbon stored in products and
combustion efficiency. Both approaches are
believed to produce highly accurate results in the
U.S.
Carbon emissions estimates from the
"bottom up" approach are presented in this
chapter and total 1,335 MMTCE. The "top
down " approach results in carbon emissions of
1,320 MMTCE. A comparison of these two
approaches is provided in Annex A.
13
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2. Determine the total carbon content of all fuels.
Total carbon is estimated by multiplying the
amount of fuel consumed by the amount of
carbon in each fuel. This total carbon estimate
defines the maximum amount of carbon that
could potentially be released to the atmo-
sphere if all of the carbon were converted to
CO2. For 1990 the potential emissions were
estimated to be 1,427 MMTCE. The carbon
emission coefficients used by the U.S. are
presented in Table 1-2.
3. Estimate the amount of carbon stored in
products. Non-fuel uses of fossil fuels can
result in storage of some or all of the carbon
contained in the energy for some period of
time, depending on the end-use. For example,
asphalt made from petroleum can sequester up
to 100 percent of the carbon for extended
periods of time, while other products, such as
lubricants or plastics, lose or emit some
carbon when they are used and/or are burned
as waste after utilization. The amount of
carbon sequestered or stored in nori-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 occur in the industrial and
transportation sectors, and for 1990 were
estimated to be about 66 MMTCE.
Table 1-2. Key Assumptions for Estimating Carbon Dioxide Emissions
Fuel Type
Petroleum
Gasoline
LPG
Jet Fuel
Distillate Fuel
Residual Fuel
Asphalt and Road Oil
Lubricants
Petrochemical Feed
Aviation Gas
Kerosene
Petroleum Coke
Special Naphtha
Waxes and Misc.
Petroleum Other
Coal
Residential/Commercial
Industrial
Coking
Other
Utility
Natural Gas
Flare
Natural Gas
Carbon
Coefficients
(kg C/106 Btu)
19.41
17.16
19.74
19.95
21.49
20.62
20.24
19.37
18.87
19.72
27.85
19.86
19.81
a
26.05
25.46
25.47
25.57
14.9.2
14.47
Stored C
(%)
. 80*
.
100*
50
80
'
100
-
75
75
--
100*
Combustion
Efficiency
(%)
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
99.5
Sources: Carbon coefficients from EIA (1994g). Stored carbon from Marland & Pippen (1990) and Rypinski (1994).
Combustion efficiency for coal from Bechtel (1993) and for oil and gas from IPCC (IPCC/OECD, 1994; Vol. 2.).
* Only the portion used as a feedstock is included in the carbdn stored calculation.
See Table A-1A in Annex A.
14
-------
'4. Adjust for carbon that does not oxidize during
combustion. Because combustion processes
are not 1;00 percent efficient, some of the
carbon contained in fuels will not be emitted
to the atmosphere. The estimated amount of
carbon not oxidized due to inefficiencies
during the combustion process range from
approximately 1 percent for oil and coal to 0.5
percent for gas (see Table 1-2 for the assump-
tions used by the U.S.),
5. Subtract emissions from bunker fuels. Ac-
cording to the IPCC guidelines, emissions .
from international transport activities, or
bunker fuels, should not be included in
national totals. This recommendation is due to
international disagreement as to which coun-
tries are responsible for these emissions.
These emissions were about 22.6 MMTCE hi
1990.
Uncertainty in the Carbon Dioxide Emission
Estimates "
Uncertainties exist for all of the emission esti-
mates provided in this report. For estimates of CO2
from energy consumption, in, principle the amount of
CO2 emitted is directly related to the amount of fuel
consumed, the fraction of the fuel that is oxidized, and
the carbon content of the'fuel. Therefore, a careful
accounting of fossil fuel consumption by energy type,
carbon content of fossil fuels consumed, and consump-
tion of products with long-term carbon storage would
yield an accurate estimate of CO2 emissions.
There are uncertainties, however, over the levels
of detail, data sources, carbon content of fuels and
products, and combustion efficiency. For example,
given the same energy 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 (such as in the
production of napthas, lubricants, etc.) can create
situations where the carbon is not emitted to the
atmosphere (e.g., plastics, asphalt) or is emitted at a
much delayed rate. The proportions of fuels used in
these non-fuel production processes and their carbon
content can also vary. Additionally, inefficiencies in
the combustion process, which can result in ash or soot
remaining unoxidized for long periods, can vary.
These factors all contribute to the uncertainty in the
CO2 estimates. For the U.S., however, these uncertain-
ties, are believed to be relatively small.4
2. Other Greenhouse Gas Emissions from
Stationary Fossil Fuel Combustion
Stationary combustion encompasses all fuel
combustion activities except transportation (i.e.,
mobile combustion). Other than CO2, gases from
stationary combustion include the greenhouse gases
methane and nitrous oxide and the photochemically
important gases such as oxides of nitrogen, carbon
monoxide, and non-methane volatile organic
compounds, which are all products of incomplete
combustion. The amount of emissions varies
depending upon fuel, technology type, arid pollution
control policies. Emissions also vary with size and
vintage of the combustion technology as well as
maintenance and operational practices.
Stationary combustion is a significant source of
oxides of nitrogen and carbon monoxide emissions.'
1990 emissions ofNOxfrom stationary combustion
represented 50 percent of national NOx emissions,
while CO emissions from stationary combustion
contributed 7percent to the national CO total.
NMVOCs emissions from stationary combustion are a
minor source, accounting for about 4 percent of the
national total Emissions of these criteria pollutants
have declined from much higher levels in the past due
to a combination of technological advances and more
stringent emissions requirements. From 1990 -1992,
emissions ofNOx remained relatively constant, while
emissions of CO and NMVOCs showed a slight
decline (see Table 1-3). Stationary combustion is
believed to be a small source of methane and nitrous
oxide. Methane emissions from stationary
combustion in 1990 accounted for about 1.5 percent
of total U.S. methane emissions, while nitrous oxide
emissions from stationary combustion accounted for
about 8.5 percent of all N2O emissions.
4 U.S. CO emission estimates from fossil fuel consumption are considered accurate within one or two percent. See, for
example, Marland and Pippin, 1990 or EIA,'1993d.
15
-------
Table 1-3. U.S. Greenhouse Gas Emissions from Stationary Combustion: 1990-1992
(Thousand Metric Tonnes)
Year
1990
1991
1992
N0x
10,695
10,730
10,635
NMVOCs
685
678
639
CO
6,128
6,004
5,603
CH4
424 -
414
386
N2O
35
35,
35
Sources: 1. Criteria pollutant emission estimates are from U.S. EPA (1993b).
2. Methane emissions are based on NMVOC emissions from U.S. EPA (1993b)
and emission factors from U.S. EPA (1993a).
3. N2O emissions are based on IPCC/OECD emission factors for uncontrolled
stationary combustion, wood fuel combustion, and U.S. fossil fuel and wood
fuel energy consumption data. (IPCC/OECD, 1994; Vol. 2)
N2O and NOX emissions from stationary source
combustion are closely related to air-fuel mixes and
combustion temperatures, as well as pollution control
equipment. CO emissions from stationary combustion
are generally a function of the efficiency ofcombus-
tion and emission controls. CO emissions are highest
when there is less oxygen in the air-fuel mixtures than
necessary for complete combustion. This is likely to
occur during combustion stopping and stalling, or
switching of fuels (for example, the switching of coal
grades at a coal-burning utility plant). Methane and
NMVOC emissions from stationary combustion are
believed to be a function of the methane content of the
fuel and post-combustion controls.
Methane emission estimates from stationary
sources are highly uncertain, primarily due to major
uncertainties in emissions from wood combustion (i.e.,
fireplaces and wood stoves). The largest source of
N2O emissions comes from utility coal combustion,
accounting for about 37 percent of total N2O emissions
from stationary combustion in 1990. It is important to
note, however, that bom of these gases are currently
not regulated in the U.S., and therefore, their emission
processes are not as well understood as emission
processes for some criteria pollutants. The estimates
of methane and nitrous oxide emissions presented here
are based on broad indicators of emissions (i.e.,
aggregate emissions ratios of CH4 emitted to total
NMVOCs and rate per amount of fuel used, respec-
tively), rather than specific emission processes (i.e.,
rate by combustion technology and type of emission
control).
Greenhouse gas emissions from energy-related
stationary combustion activities have been grouped
into four sectors:
Industrial
Cpmmercial/Institutional.
Residential
Electric Utilities
The major fuel source categories included in this
section are: coal, fuel oil, natural gas, wood, other fuels
(which encompasses bagasse, LPG, coke, and coke
oven gas), and internal combustion (which includes
emissions from internal combustion engines that are
not used in transportation). A summary of the emis-
sions from stationary combustion sources in 1990 is
provided in Table 1-4.
Emissions estimates for NOx, CO, and NMVOCs
in this section were taken directly from the U.S. EPA's
National Air Pollutant Emissions Trends: 1900 - 1992
(U.S. EPA, 1993b). U.S. EPA (1993b) estimates
emissions of NOx, NMVOCs, and CO by sector and
fuel source using a "bottom-up" estimating procedure,
i.e., the emissions were calculated either for individual
sources (e.g., industrial boilers) or for many sources
combined, using basic activity data (such as fuel
consumption or deliveries, etc.) as indicators of
emissions. The national activity data used to calculate
the individual source categories were obtained from
many different sources. Depending on the source
category, these basic activity data may include fuel
consumption or deliveries of fuel, tons of refuse
16
-------
Table 1-4. U.S. Greenhouse Emissions from Stationary Combustion
by Sector and Fuel Source: 1990
(Thousand Metric Tonnes)
Source Category
Electric Utilities
Coal
Fuel Oil
Natural Gas
Wood
Other Fuelsb
Internal Combustion
Total Utilities
Industrial
Coal
Fuel Oil
Natural Gas
Wood
Other Fuelsb
Internal Combustion
Total Industrial
Commercial-Institutional
Coal
Fuel Oil
Natural Gas
Wood
Other Fuelsb
Internal Combustion
Total Commercial
Residential
Goal6
Fuel Oil6
Natural Gase
.Wood
Other Fuelsb
Internal Combustion
Total Residential
Stationary Combustion Total
N0x
6,083
190
507
NA
NA
45
6,825
556
271
1,745 .
NA
117 '
, 517
3,206
, 35
90
149
NA
10
NA1
"284
NA
NA
NA
60
319
NA
379
10,695
NMVOCs
24
' 5
2
.NA
NA
1 '
32
6
15
190
NA
33
14
258
1 '
4
6
NA
4
NA
15
NA
NA
NA
367
14
NA
381
685
CO
211
18
46
NA
NA
10
285
78 .
42
284
NA
156
89
649
14
15
45'
NA
. 47
NA
121
NA
NA
NA
4,930
143
NA
5,073
6,128
CH4ฐ
13
+
NA -
NA
NA
. +
13
3
1
NA
' NA
3
1
9
- 1
+
NA
NA
+
NA
1
NA
NA
NA
. 367
1
, NA
369 '
424C
N2O
13
1
+
+
NA
NA
14 .
-
4
5
1
7 -
NA
NA
16
+
1
+
+
NA
~ NA
. ' 1
'+'
1
+
3 .
NA
NA
4
35"
Source: NO , NMVOCs, and CO data are from U.S. EPA (1993b). CH4 emissions were calculated from EPA (1993b) data using CH4 to
NMVOCs ratios from U.S. EPA (1993a) (see text). NO emissions were calculated from EIA data and IPCC emission factors.
(EIA, 1994b, 1994h, 1994; IPCC/OECD, 1994; Vol. 1) ' .
Notes: 1. Technically, of this group only CH4 and N2O are greenhouse gases. See Box 1.
2. Components may not sum to totals due to independent rounding. , . .
"+" Denotes negligible; "NA" denotes not available. ,
a. Calculated using the midpoint of CH4 to NMVOC.ratios from U.S. EPA (1993a).
b. Other fuels include: LPG, waste oil, coke oven gas, coke, and wood (except in the residential sector, where Wood has been
dissaggregated) (U.S. EPA, 1993b). .
c. This figure includes total CH4 emissions from natural gas stationary sources as reported in U.S. EPA (1993a). This estimate
(16-63 thousand metric tonnes, with a mean estimate of 32) was not disaggregated by sector in the EPA report. Therefore,
32 thousand metric tonnes has been added to the total at the bottom of the CH4 column. See Table 1-5 for data used in
methane emission estimates. .
d. Includes emission estimates from wood fuel combustion. . - .
e. Coal, fuel oil, and natural gas emissions of NOX, NMVOCs, CO, and CH4 are included in "Other Fuels" (U.S. EPA, 1993b).
17
-------
burned, raw material processed, etc. Activity data are
used in conjunction with emission factors, which relate
the quantity of emissions to the activity. The basic
"bottom-up" calculation procedure for most source
categories presented in EPA (1993b) is represented by
the following equation:
where E
p
s
A
EF
C
emissions
pollutant
source category
activity level
emissions factor
percent control efficiency
Emission factors are generally available from the
U.S. EPA's Compilation of Air Pollutant Emission
Factors, AP-42 (U.S. EPA, 1985), often referred to as
AP-42 emission factors. The U.S. currently derives the
overall control efficiency of a source category from its
Aerometric Information Retrieval System AIRS
database (U.S. EPA, 1992). 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 the IPCC (IPCC/
OECD, 1994; Vol. 1).
Methane emissions from stationary combustion
of coal, fuel oil, and wood Were calculated using
reported NMVOC emissions for each activity from
U.S. EPA (1993b), and published emission ratios of
CH< to NMVOCs (U.S. EPA, 1993a) for these activities
The emission ratios used are provided in Table 1-5.
Estimates of methane emissions from natural gas
consumption came from U.S. EPA (1993a). The total
emission estimate of 16 to 63 thousand metric tonnes
of methane (0.1 to 0.4 MMTCE) is compiled by sector
(utility, industrial, commercial, and residential) and
technology type (boiler and non-boiler). The U.S. EPA
(1993a) reported 300 thousand to 1.4 million metric
tonnes (1.8 to 8.4 MMTCE) as the range of methane
emissions from all stationary sources.
The estimates of methane emissions from
stationary sources, other than gas-fired sources, are
subject to considerable uncertainty due to the lack of
accurate data regarding the technology type and the
pollution control equipment in each of the other source
categories (e.g., coal, fuel oil, and especially wood).5
As a result, estimates are based on broad estimates of
Table 1-5. Ratio of CH4 to NMVOCs
Released During Combustion
Activity
(Source Category)
Coal Combustion
Fuel Oil Combustion
Wood Combustion
(Industrial Use)
Wood Combustion
(Residential Use)
Other
Ratio of CH4 to NMVOCs
(Low - High)
0.05 to 1.00
0.05 to 0.10
0.2
2
0.1
Source: U.S. EPA (1993a); except for "Other", where the upper
end of the fuel oil category was used as an approximation.
Notes: Emissions from wood-fired equipment are based on U.S.
EPA (1985). For industrial wood combustion, the mean
methane to NMVOC ratio is based on wood combustion
in boilers. For residential wood combustion, the mean
ratio is based on available emission factors for residential
wood stoves.
the percentage of methane emissions relative to
NMVOC emissions a methodology that results in ,
very imprecise estimates. The estimates for gas-fired
stationary combustion are more precise due to the
greater level of disaggregation by sector and technology.
Nitrous oxide emissions were estimated using
IPCC-recommended emission factors and U.S. fossil
fuel and wood fuel consumption data. Estimates were
obtained by multiplying the appropriate emission
factors (by sectors and fuel types) by the appropriate
U.S. energy data. The emission factors used were: 4.3
g N2O/GJ6 of energy input for wood in all sectors; 0.1 g
N2O/GJ for gas use and 0.6 g N2O/GJ for oil use in all
sectors; and for coal use, 0.8 g N2O/GJ for the utility
sector and 1.4 g N2O/GJ for the industrial, commercial,
and residential sectors.
Estimating emissions other than carbon dioxide
from stationary combustion can be time consuming and
complex. Moreover, the amount of gases emitted from
these activities are not thought to be major contributors
to climate change, the uncertainties associated with
the emission estimates of these gases, especially
methane and nitrous oxide estimates, are also much
higher than the uncertainty associated with estimates of
CO2 from fossil fuel combustion. Uncertainties in the
methane estimates are due primarily to the fact that
* Methane emissions from gas-fired sources were extensively researched and documented in U.S. EPA (1993a).
4 GJ = Gigajoule = one billion joules. One joule = 0.9478 Btu.
18
il
-------
they are based on simple ratios of methane to emitted
NMVOCs and are derived from a limited number of
emissions tests. Uncertainties in the nitrous oxide
estimates are due to the fact that emissions were
estimated based on a limited set of emission factors.
For the other gases, the uncertainties are partly due to
assumptions concerning combustion technology types,
age of equipment, and the emission factors used.
3. Other Greenhouse Gas Emissions from Mobile
Combustion
Mobile sources emit the greenhouse gases
methane and nitrous oxide, and photochemically
important gases, including carbon monoxide,
nitrogen oxides, and nonmethane volatile organic
compounds. Emissions of these trace gases are
produced by the incomplete combustion of the fossil
fuels used to power vehicles.
Fossil fueled motor vehicles comprise the single
largest source of CO emissions in the U.S. For the
period 1990-1992, CO emissions from mobile sources
contributed about 80 percent of all U.S. CO emissions
(see Table 1-6). Motor vehicles also emit about 45
percent of total U.S. anthropogenic NOx and NMVOC
emissions. Mobile emissions are also a small but
significant source of methane and nitrous oxide in
the U.S., Road transport accounts for the majority of
mobile source emissions. For the period 1990-1992,
emissions of the criteria pollutants as a whole show a
declining trend, while methane and nitrous oxide
emissions have increased slightly.
As in combustion in stationary sources, N2O and
N.Ox emissions are closely related to ahyfuel mixes and
combustion temperatures, as well as pollution control
equipment. CO emissions from mobile combustion are
a function of the efficiency of combustion and post-
combustion emission controls. CO emissions are
highest when air-fuel mixtures have less oxygen than
required for complete combustion. This occurs espe-
cially in idle, low speed and cold start conditions.
Methane-and NMVOC emissions from motor vehicles
are a function of the methane content of motor fuel, the
amount of hydrocarbons passing unburnt through the
engine, and any post-combustion control of hydrocar-
bon emissions, such as catalytic converters.
Emissions from mobile sources are estimated by
major transport activity, (i.e., road, air, rail, and ships),
where several major fuel types, including gasoline,
diesel fuel, jet fuel, aviation fuel, natural gas, liquified
petroleum gas (LPG), and residual fuel oil are
considered. Road transport accounts for the majority
of mobile source fuel consumption, and hence, the
majority of mobile source emissions. Table 1-7
summarizes emissions from mobile sources by
transport activity, vehicle type, and fuel type for 1990.7
Estimating emissions from mobile combustion,
as with stationary combustion, can be time consuming
and complex. Because of many factors, including type
of fuel, type of technology, extent of emission control
equipment, age of equipment, and operating and
maintenance practices, emission estimates for mobile
combustion vary significantly. However, compared to
stationary sources, more detailed data are available on
activity levels and emission factors by vehicle type. A
brief description of the methodology used for each gas
is provided below.
NOx, NMVOCs, and CO
Emissions estimates for NOx, NMVOCs, and CO
(U.S. criteria pollutants) in this section were taken
directly from EPA (1993b), except for emissions from
Table 1-6. U.S. Greenhouse Gas Emissions from Mobile Combustion: 1990-1992
(Thousand Metric Tonnes)
Year
1990
1991
1992
NO3
9,668
9,514
9,367
.NMVOCs
8,252
8,047
7,461
CO
67,520
66,269
63,460
CH4
221
242
247
N2O
92
103
105
7 Annex B contains a description of the methodology and data sources used for these gases. Estimates of carbon dioxide
emissions from mobile combustion are provided earlier in the section titled "Carbon Dioxide Emissions from Fossil Fuel
Consumption." These GO2 estimates are not provided at the level of detail indicated in Table 1-7 for gases other than CO2
' because fuel consumption data for each of these categories, which would be needed to complete calculations, are not readily
available. .
19
-------
bunker fuels (fuels delivered to marine vessels, includ-
ing warships and fishing vessels, and aircraft for
international transport), which were calculated based
on U.S. EPA data. The U.S. EPA provided emission
estimates for eight categories of highway vehicles8,
aircraft landing and take-off cycles9, and seven catego-
ries of off-highway vehicles1?.
CH4 and N2O
Emission estimates ofmethane and nitrous oxide
from mobile sources historically have not been calcu-
lated by the U.S. Emission estimates for these gases
were calculated using the IPCC-recommended method-
ologies and emission factors. 'Activity data used were
derived from U.S. EPA (1992b), Brezinski, et al.
(1992); Carlson (1994); and Nizich (1994).
Table 1-7. U.S. Greenhouse Gas Emissions from Mobile Combustion by Vehicle Type: 1990
(Thousand Metric Tonnes)
Source Category
Gasoline Highway Vehicles
Passenger Cars
Light-Duty Trucks (all)
Heavy-Duty Vehicles
Motorcycles
Total Gasoline
Diesel Highway Vehicles*
Passenger Cars
Light-Duty Trucks
Heavy-Duty Vehicles
Total Diesel
Other Mobile Sources
Aircraft
Locomotives
Vessels (Marine)
Farm Equipment
Construction Equipment
Other Off-Highway
Total Other Mobile Sources
Transportation Total
NOx
3,206
1,064
180
NA
4,450
39
26
2,574
2,639
126
843
175
210
859
366
2,579
9,668
NMVOCs
4,198
1,521
217
NA
5,935
13
11
370
394
174
38
35
47
139
1,489
1,923
8,252
CO
37,661
12,431
2,677
NA
52,769
30
21
1,419
1,470
876
111
1,147
217
837
10,092
13,280
67,520
CH/ '
116
50
18
4
187
+
+
14
14
6
2
3
6
2
b
20
221ฐ
N2O"
68
13
+
+
82
+
+
5
5
+
1
1
1
1
" b '
5
92ฐ.
Source: NOS, NMVOCs, and CO emissions data are from U.S. EPA (1993b) (except for bunker fuels); CH4 and N2O emissions
were calculated with data provided by the U.S. EPA (Brezinski, et al. (1992); Carlson (1994); Nizich (1994)).
Notes: "*" Denotes negligible (i.e., <0.5 Thousand MT).
a. Average of high and low estimates reported for diesel vehicles.
b. For CH4 and N2O,"Other Off-Highway" is included with "Construction Equipment."
a Estimates carry an error range of ฑ 50 percent, of which these numbers are the midpoints.
!
, .
These categories include: gasoline powered automobiles, diesel powered automobiles, 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.
* Currently, emissions factors are not available for aircraft flying above 3000 feet. These emissions may be significant
and do affect atmospheric chemistry, but insufficient information to calculate these emissions is available at this time.
19 These categories include: gasoline and diesel farm tractors, other gasoline and diesel farm machinery, gasoline and
diesel construction equipment, snowmobiles, small gasoline utility engines, heavy duty gasoline and diesel general utility-
engines, and motorcycles.
' , II . , *. . :: . '" .' .' : -'I
20
-------
B. FOSSIL FUEL PRODUCTION,
TRANSMISSION, STORAGE, AND
DISTRIBUTION
Emissions of greenhouse gases and photochemi-
cally important gases are released as a result of energy
production, transmission, storage, and distribution
activities. These emissions are primarily methane,
although smaller quantities of carbon dioxide, non-
methane volatile organic compounds, and carbon
monoxide can be emitted. This section presents
estimates of emissions from the following source
categories:
Coal mining, including emissions from
underground mines, surface mines, and post-
mining activities;
Natural gas systems, including production,
processing, transportation, and distribution;
and
Crude oil production, transportation, refining,
and storage.
Collectively, these sources accounted for about
30 percent of total U.S. methane emissions in 1990.
Methane emissions from coal mining accounted for the
majority of these emissions, or about 16 percent of
total U.S. methane emissions. Natural gas systems .
accounted for about 11 percent of total U.S. methane
emissions. Crude oil production, transportation refin-
ing, and storage accounted for about one percent total
U.S. methane emissions. Criteria pollutant emissions
from fuel activities contributed only a small portion of
total U.S. emissions of these gases in 1990.
1. Emissions from Coal Mining
The most significant emissions from coal
mining are methane. Emissions from coal mining
are currently the third largest source of methane
emissions in the U.S., behind landfills and domestic
livestock. Estimates of methane emissions from coal
mining for 1990 were about 26.4 MMTCE.
The amount of methane released during coal
mining is primarily a function of coal rank and
depth, although other factors such as moisture also
affect the amount of methane released. In most
underground coal mines, methane is removed by
circulating large quantities of air through the mine
and venting this air (typically containing a .
concentration ofl percent methane or less) into the
Methane Emissions from Energy Activities by Source: 1990
Coal Mining (53%)
Fossil Fuel
Combustion (8%)
Oil and Gas
Processes (39%)
atmosphere. In some mines, however, more advanced
methane recovery systems may be used to supplement
the ventilation systems and ensure mine safety. In
addition to emissions from these activities, a portion
of the CH4 emitted from coal mining comes from
post-mining activities such as coal processing,
transportation, and consumption.
The process of coal formation, commonly called
coalification, inherently generates methane and other
by-products. The degree of coalification (defined by
the rank, i.e., quality, of the coal) determines the
quantity of methane generated. Once generated, the
amount of methane stored in coal is controlled by the
pressure and temperature of the coal seam and other,
less well-defined characteristics of the coal. The
methane will remain stored in the coal until the pres-
sure on the coal is reduced. This can occur through
erosion of the overlying strata or through coal mining.
Once the methane has been released, it flows through
the coal toward a pressure sink (such as a coal mine)
and methane is released into the atmosphere (U.S.
EPA, 1990b).
The U.S. EPA estimated that methane emissions
from coal mining in 1990 ranged from 3,400,000 to
5,400,000 metric tonnes of CH4 (20.4 to 32.4 MMTCE),
with a central estimate of 4,400,000 metric tonnes
(26.4 MMTCE). Based on the same methodologies,
1991 and 1992 emissions from methane are estimated
to be about 25.5 and 24-3 MMTCE, respectively;-
These estimates were based on detailed analysis
from coal mine methane emissions in 1990, and then
adjusted for any differences in coal production between
1990 and subsequent years. Emissions were estimated
for each major coal mining source, including both
21
-------
ventilation and degasification systems at underground
mines and surface mines as well as post mining opera-
tions. The analysis of the 1990 emissions is based on
actual data from methane ventilation systems where
available; where data were not available, various
estimation procedures were employed.
The emission estimates for underground mines
included:
measured methane emissions in the ventilated
air from gassy underground mines;
estimated ventilation emissions from mines for
which measurements were not available; and
ป estimated emissions from degasification
systems.
Emissions from surface mines were estimated
using reported methane contents for the surface coals
mined in each U.S. coal basin. Post-mining emissions
from both underground mines and surface mines were
estimated to be between 25 to 40 percent of the in-situ
methane content of the coal mined in each basin. A
more detailed discussion of emissions from each stage
of the coal extraction process can be found in U.S. EPA
(1993a).
The key uncertainties in these estimates arise
from emissions for which measurements are not
available. This is the case for emissions from mine
degasification systems at underground mines, from
surface mining, and in some cases from ventilation
systems. In addition, there is some uncertainty as to
the exact number of mines that have degasification
systems in place.
Due to a combination of instrument error and
sampling and aggregation errors, measured estimates
of emissions from ventilation systems may have an
uncertainty range of ฑ20 percent. For degasification
systems, it was assumed that, based on previous
experience with degasification systems, mines recover
40 to 65 percent of their total emissions. To the extent
that the degasification strategy varies by mine or coal
basin, emissions could be over- or underestimated
within this range. Estimates for surface mining are
considerably less certain as there are no direct emission
measurements, and these may range from 1 to 3 (and
possibly as much as five) times the amount of methane
contained in the coal.
2. Emissions from Natural Gas Production,
Processing, Transport, and Distribution
The only significant emissions from natural gas
production, processing, transport and distribution are
methane. Methane emissions from the U.S. natural
gas systems account for about 11 percent of total -U.S
methane emissions. 1990 emissions from the U.S.
natural gas system were estimated to be between 13.1
and 25.6 MMTCE, with a central estimate of about
17.8MMTCE.
Methane Emissions from Energy Activities by Source: 1990
Coal Mining (53%)
Fossil Fuel
Combustion (8%)
Oil and Gas
Processes (39%)
Emissions from the U.S. natural gas systems,
one of the most efficient natural gas systems in the
world, are estimated to range from about 0.8 to 1.5
percent of the marketed gas. Like emissions from oil
and gas production and distribution activities, these
emissions are generally process related: fugitive
emissions occur in all the stages of extraction,
'processing, and distribution. Fugitive emissions
across all production stages are estimated to account
for about 38 percent of 1990 U.S. natural gas systems
emissions. Together with emissions from gas-fired
engines and engine exhausts, these emissions account
for about 75 percent of total estimated emissions, with
the remaining 25 percent accounted for by system
upsets and maintenance activities.
According to EPA (1993 a), 1990 emissions from
the U.S. natural gas system are estimated to be between
2,180 and 4,260 thousand metric tonnes of CH4 (13.1
, to 25.6 MMTCE), with a central estimate of about
3,000 thousand metric tonnes (17.8 MMTCE). This is
less than 1 percent of the 1990 total marketed natural
gas in the U.S. in the same year (see Table 1-8).
22
-------
Table 1-8. Methane Emissions from U.S. Natural Gas Systems
Source of Emissions
(stages)
Field Production
Processing
Storage and Injection/Withdrawal
Transmission
Distribution
Engine Exhaust
Total1
1990 Emissions (103 MX) Average % of 1990
Low High Marketed Production
690 '
40
10
590
170
270
2,180
1,820 .
270 _
60
2,060
750
640
4,260
0.29
0.02
0.01
0.28
0.09
0.11
0.80
Source: US. EPA (1993a).
Note: 1. The uncertainty in the total is estimated assuming that some of the uncertainty for each source is
independent. Consequently, the range for the total is narrower than the sum of the ranges for the individual
sources.
Methane emissions from natural gas systems
were estimated using the following general approach:
one or more "model facilities" were defined
for each stage of the natural gas system, that
is, each stage from production through stor-
age, to define the representative facility or
facilities,in each stage of the production and
distribution process;
an emission type, based on detailed data and
known emission processes, was estimated for
each manufacturing facility;
emission factors for each model facility were
determined based on an appropriate measure
of the facility's activity, such as throughput in .
cubic feet per year or miles of pipeline;
average emission factors were determined for
each stage by averaging the emission factors
estimated for each of the model facilities in
that stage; and,
national emissions were estimated by multi-
plying the average emission factor for each
stage by the total applicable size of the
national system (such .as cubic feet of through-
put or miles of pipeline).
The major source of uncertainty in these esti-
mates arises from extrapolating measurement data from
a small number of "model" facilities and applying
these to the industry as a whole. Subjective uncer-
tainty ranges for the emission factors derived from
these measurements Were assigned based on the
amount of information available. In some cases these
ranges span an order of magnitude. The industry
activity levels are typically subject to less uncertainty,
and for this analysis are assumed to be ฑ25 percent.
The uncertainty surrounding national estimates does
not reflect uncertainty about the simple summation of
sector uncertainties, because in many cases the uncer-
tainties are independent and uncorrelated. Taking this
into account, the overall uncertainty is about -25
percent and +45 percent of the mean estimate of about
2.97 million metric tonnes (17.8 MMTCE) for 1990.
3. Emissions from Oil and Gas Production, and
Crude Oil Transportation, Refining, and
Storage
Greenhouse gases are emitted from crude oil
and natural gas production, and crude oil refining,
transportation, and storage. These emissions are
primarily methane, although smaller quantities of
carbon dioxide, non-methane volatile organic
compounds, and carbon monoxide can be emitted.
Natural gas venting and flaring occurs at oil
wells where there are no markets to sell gas or the
market value of the gas is well below the additional
development and transportation costs of the gas,
when gas handling facilities are under construction,
or when the volume of gas that is produced is very
low. Other emissions from oil production,
transportation, refining, and storage are generally
released by the processes themselves. These can be
system leaks, disruptions, or routine maintenance
releases. For 1990 methane emissions from these
activities ranged from 0.6 to 3.72 MMTCE, with a
point estimate of 1.6 MMTCE, accounting for about
one per cent of total U.S. methane emissions.
23
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CO2 Emissions from Oil Production and
Processing Activities
CO2 emissions from oil production and process-
ing come from the natural gas that is flared at the
production site, which releases CO2 as a by-product of
the combustion process. Bams and Edmonds (1990)
note that of the total reported U.S. venting and flaring,
approximately 20 percent is actually vented, with the
remaining 80 percent flared. According to the Natural
Gas Annual 1992 (EIA 1993d), published by the U.S.
Department of Energy's Energy Information Adminis-
tration, the total amount of natural gas vented or flared
is 4,261 million cubic meters for 1990, 4,813 million
cubic meters for 1991, and 4,746 million cubic meters
for 1992.
The amount of CO2 resulting from the flared gas
was estimated to be 6.56 million metric tonnes (1.79
MMTCE) for 1990, 7.4 million metric tonnes (2.02
MMTCE) for 1991, and 7.3 million metric tonnes (1.99
MMTCE) for 1992. These estimates were prepared
using a conversion factor of 525 g C per m3 as deter-
mined by Marland and Rotty (1984), and an assumed
flaring efficiency of 100 percent. The assumed uncer-
tainty range is =t25 percent. The 20 percent vented as
methane is accounted for in the section below.
Methane Emissions from Oil Production and
Processing Activities
Methane emissions from oil production and
processing were estimated in EPA (1993a) by deter-
mining representative emissions from major activities.
These include
* fugitive emissions in the production field,
routine maintenance emissions in the
production field,
crude oil storage facility emissions, and
emissions from crude oil storage facilities,
refineries, marine vessel operations, and
venting and flaring.
These total emissions, based on model facilities,
are estimated to be between 100,000 and 620,000
metric tonnes of CH4 (0.6 to 3.72 MMTCE) per year.
The uncertainty surrounding the estimates for
production-related activities are higher than for other
sectors of the oil and natural gas system due to a
general lack of emissions data. This is particularly true
of venting and flaring data, the largest component of
emissions, which in many cases is based on "balance"
estimates of unaccounted-for-gas. The overall uncer-
tainty range is estimated to be 1/4 to 4 times the
estimated value.
NOx, NMVOCs, and CO Emissions from Oil
and Gas Production Activities
Criteria pollutant emissions from oil and gas
production, storage, and transportation contribute only
a relatively small portion to the overall U.S. emissions
of these gases. Emissions of these gases were rela-
tively stable for the 1990 - 1992 period (see Table 1-9).
Due to the diverse nature of the various types of
emissions and the fact that some emissions occur
periodically or unexpectedly, precise measurements are
not practical in many cases. As a result, the uncertain-
ties associated with the emission estimates in this
section vary, ranging anywhere from 25 to 50 percent.
Table 1-9. NOx, NMVOCs, and CO Emissions
from Oil and Gas Activities: 1990 -1992
(Thousand Metric Tonnes)
Year
1990
1991
1992
N0x
92
93
85
NMVOCs
668
676
648
CO
393
397
365
Source: U.S. EPA (1993b).
The U.S. EPA (1993b) provided emission
estimates fpr NOx, NMVOCs, and CO from petroleum
refining, petroleum product storage and transfer, and
petroleum marketing operations. Included are gaso-
line, crude oil and distillate fuel oil storage and transfer
operations, gasoline bulk terminal and bulk plants
operations, and retail gasoline service stations opera-
tions. Emission estimates were determined using
industry-published production data and applying
average emission factors.
24
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Table 1-10. CO2 Emissions from Wood Consumption by Sector: 1990 - 1992
(Million Metric Tonnes)
Sector
Electric Utility
Industrial
Residential
Commercial
Total
1990
1.0
124.8
46.4
2.4
174.6
1991
0.8
122.1
49.0
2.4
174.3
1992
0.9
127.3
51.6
2.4
182.2
Source: Consumption estimates (in trillion Btu) are from EIA (19941).
Notes: Components may not sum to totals because of rounding.
1. Consumption estimates in trillion Btu were converted to short tons based on an
average'energy content of 14 million Btu per short ton of dry wood (1994i).
2. Estimates carry an error range of ฑ25 percent.
3. According to EIA, commercial wood energy use is typically not reported because
there are no accurate data sources to provide reliable estimates (EIA, 1994i).
However, EIA's 1986 Nonresidential Building Energy Consumption Survey
estimates that commercial sector use is about 20 to 40 trillion Btu. An average of
30 trillion Btu is used here.
C. EMISSIONS FROM BIOMASS AND
BIOMASS-BASED FUEL CONSUMPTION
/. Emissions from Wood
The combustion of biomass fuels (such as
wood, charcoal, and wood waste) and biomass-based
fuels (such as ethanolfrom corn or woody crops)
produce carbon dioxide. However, the carbon dioxide
emitted from biomass consumption in the long run
does not increase total atmospheric carbon dioxide if
this consumption is done on a sustainable basis (i.e.,
annual emissions ofCO2 due to consumption of
biomass fuel, as well as CO2 emissions associated
with harvest, transport, and processing of the
biomass, are completely offset by the annual uptake
ofCO2from regrowing biomass). As a result, carbon
dioxide emissions from biomass have been estimated
separately from fossil fuel-based emissions and are
not included in the U.S. totals.
For 1990, CO2 emissions from woody biomass
were about 48 MMTCE. The U.S. industrial sector
accounted for the largest share (73 percent) ofCO2
emissions from biomass consumption, while the
residential sector accounted for 25 percent of the
emissions from biomass use. The electric utility
sector accounted for the smallest portion of emissions
from biomass, just slightly over one half of one
percent. This sectoral distribution was largely
unchanged for 1991 and 1992 (Table 1-10).
Emissions estimates were calculated based on the
methodology recommended by the IPCC. Emissions
were estimated by first converting U.S. consumption
data (in trillions of Btus) reported in Estimates of U.S.
Biomass Energy Consumption 1992 (EIA, 1994i) to
tonnes of dry matter using EIA assumptions (for 1990,
U.S. biofuel consumption totals 2,359 trillion Btus).
Next, the carbon content of the dry fuel was estimated
based on IPCC default values of 45 to 50 percent
carbon in dry biomass. The estimated amounts of
carbon released from combustion were also estimated
using IPCC-proyided default values of 87 percent
combustion efficiency. This is probably an underesti-
mate of the efficiency of wood combustion processes
in the U.S. The IPCC assumption has been used,
however, since better data are not yet available.
2. Emissions from Ethanol
Biomass-based fuel use in the U.S. consists
mainly ofethanol use in the transportation sector.
Ethanol is mostly produced from corn grown in the
25
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U.S. Midwest, and used primarily in the Midwest and
South. Ethanol can be used directly, or mixed with
gasoline as a supplement or an octane enhancer. The
most common form is a 90 percent gasoline, 10
percent ethanol blend known as gasohol. Ethanol
and ethanol blends are used to fuel public transport
vehicles such as buses, or centrally-fueled fleet
vehicles. Ethanol and ethanol blends are believed to
burn "cleaner" than gasoline flower in NOx and
other hydrocarbons), and are being tested in urban
areas with poor air quality. However, because
ethanol is a hydrocarbon fuel, its combustion releases
carbon dioxide.
Carbon dioxide emissions from ethanol use in
the U.S. are generally declining, due to a combination
of low gasoline prices and limited ethanol supply. In
1990, total U.S. CO2 emissions were 1.2 MMTCE,
mostly from the South and Midwest (see table 1-11).
These emissions are not included in the U.S. total
since the corn from which the ethanol is derived is
produced on a sustainable basis.
Table 1-11. U.S. CO2 Emissions from Ethanol
by Region: 1990
(Million Metric Tonnes)
Region
Northeast
South
Midwest
West
Total
1990
0.1
1.6
2.4
0.4
4.4
Source: EIA (1994i).
Emissions from ethanol were estimated using
EIA (1994i). In 1990, the U.S. consumed an estimated
750 million gallons (or 63 trillion Btus) of ethanol,
mostly in the transportation sector (EIA .1994i), Using
an ethanol carbon coefficient of 19 milligrams C/Btu
(OTA, 1991), 1990 emissions of CO2 from the use of
ethanol were calculated to be 4.4 million metric tonnes
(1.2 MMTCE).
26
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PARTII. INDUSTRIAL PROCESSES
Total US Emissions by Source: 1990
- (MMT Carbon Equivalent)
1396
1444
41
65
-61
Energy Industry Agriculture Forestry Wastes Net Total
; Source
Emissions are often produced as a by-product of-
various non-energy related activities. That is, these
emissions are produced directly from the process itself
and are not a result of energy consumed during the
process. For example, in the industrial sector raw "
materials are chemically transformed from one state to
another. This transformation often results in the
release of greenhouse gases such as carbon dioxide.
The production processes addressed in this section
include: adipic acid production, carbon dioxide manu-
facture, cement production, lime production, limestone
use (e.g., for iron and steel making, flue gas desulfur-
ization, and glass manufacturing), nitric acid produc-
tion, soda ash production and use, and aluminum
production. Total carbon dioxide emissions from
industrial processes were approximately 55 million
metric tonnes in 1990 (15 MMTCE), accounting for
1.1 percent of total U.S. CO2 emissions. Nitrous oxide
emissions from adipic acid and nitric acid production
were about 96 thousand metric tonnes (7.1 MMTCE)
-in 1990, or 23.4 percent of total U.S. N2O emissions.
Emissions of HFCs and PFCs were about 19.2
MMTCE. Table II-1 contains a summary of non-
energy related greenhouse gas emissions from indus-
, trial processes in the U.S.
Greenhouse gases are emitted from a number of
industrial processes not covered in this section. For
example, ammonia production is believed to be an
industrial source of methane, nitrous oxide, and
NMVOC emissions. However, emissions for these
sources have not been estimated at this time due to a.
lack of information on the emission processes, the
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.
The emission estimates presented here generally
follow the draft IPCC-recommended guidelines,
although the only processes for which the IPCC -
provides a specific methodology for estimating emis-
sions are cement, adipic acid, and nitric acid produc-
tion. The IPCC has not provided specific details (e.g.,
default emission factors) to calculate emissions from
the other sources, but recommends a basic approach
that can be followed for each source category, i.e.,.
multiplying production data for each process by an
emission factor per unit of production. The methods
used to estimate emissions in this section generally
follow this basic approach. Most of the emission
factors used below were derived using calculations that
assume precise, efficient chemical reactions. As a
result, uncertainties in the emission coefficients can be
attributed to impurities contained in the raw materials
or to inefficiencies in the chemical reactions associated
with each production process. Additional sources of
uncertainty specific to an individual source category
are discussed in the appropriate section.
A. NON-FERROUS METALS
1. Aluminum Production
The production of aluminum results in emis-
sions of several greenhouse gases, including carbon
dioxide (CO) and two perfluorocarbons (PFCs), CF4
and Cff Carbon dioxide is emitted as carbon
contained in the anode and cathode of the electrolytic
production cell is oxidized during the reduction of
alumina to aluminum. Emissions of CO., from
aluminum production in the U.S. were 2 MMTCE in
1990, or about 0.15 percent of total U.S. CO2 emissions.
The aluminum production industry is thought
to be the largest source ofCF4 and Cfff Emissions
of these two perfluorocarbons also occur during the
reduction of alumina in the primary smelting process.
As with emissions of carbon dioxide, the carbon is
27
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Table II-l. U.S. Greenhouse Gas Emissions from Industrial Processes: 1990
Source
Emissions
Full Molecular Weight
(103 metric tonnes)
MMTCE
CARBON DIOXIDE (CO2)
Cement Production
Lime Production
Limestone Use
Soda Ash Production and Use
Carbon Dioxide Manufacture
TOTAL
32,700
11,900
5,100
4,100
1,200
55,000
8.9
3.2
1.4
1.1
0.3
15.0
NITROUS OXIDE (N,O)
Adipic Acid Production
Nitric Acid Production
TOTAL
56
40
96
4.1
2.9
7.1
MFCs and PFCs
HFC-23
HFC-134a
HFC-152a
PFCs (CF4 and C2F6)
TOTAL
5.5
0.5
0.3
3.0
15.05
0.16
0.01
4.0
19.2
Note: Totals may not add to the sum of the individual source categories due to independent rounding.
present in the anode and cathode material; the
fluorine is present in the molten cryolite in which the
reduction of alumina occurs. Total U.S. emissions in
1990 ranged from roughly 1,200 to 3,700 metric tons
ofCF4 (L 7 to 5.2 MMTCE). Emissions ofC2F6 are
estimated to be an order of magnitude lower, ranging
from 120 to 370 metric tons (0.17 to 0.52 MMTCE).
Carbon dioxide is emitted during the aluminum
production process when alumina (aluminum oxide) is
reduced to aluminum. The reduction of the alumina
occurs through electrolysis in a molten bath of natural
or synthetic cryolite. The reduction cells contain a
carbon lining that serves as the cathode. Carbon is also
contained in the anode, which can be a carbon mass of
paste, coke briquettes, or prebaked carbon blocks.
During reduction, some of this carbon is oxidized and
released to the atmosphere as carbon dioxide.
Approximately 1.5 to 2.2 tons of carbon dioxide
are emitted for each ton of aluminum produced
(Abrahamson, 1992). U.S. primary aluminum produc-
tion in 1990 was 4,048 thousand metric tonnes (Bureau
of Mines,. 1993a). Using the midpoint of the emission
factor range, CO2 emissions from aluminum production
are estimated to have been 7.5 million metric tonnes of
CO2 (2 MMTCE), or 0.15 percent of total U.S. CO2
emissions in 1990. Aluminum production in 1991 and
-------
1992 was 4,121 thousand metric tonnes and 4,042
thousand metric tonnes, respectively, generating 7.6
million metric tonnes of CO2 (2.1 MMTCE) in 1991
and 7.5 million metric tonnes of CO2 (2 MMTCE) in
1992. The CO2 emissions from this source are already
accounted for in the non-fuel use portion of CO2
emissions from fossil fuel consumption, which was
estimated in Part 1A of the inventory (i.e., the carbon
contained in the anode is considered a non-fuel use of
petroleum coke). Thus, to avoid double-counting, CO2
emissions from aluminum production are not included
in the industrial process emission totals.
Aluminum production is also thought to be the
largest source of two PFCs, CF4 and C2F6. Emissions
of these two potent greenhouse gases occur during the
reduction of alumina in the primary smelting process.
Emission estimates and a description of the estimation
methodology are provided in the section on HFCs and
PFCs.
B. INORGANIC CHEMICALS
1. Nitric Acid Production
Industrial Nitrous Oxide Emissions by Source: 1990
Adipic Acid Production
Nitric Acid Production
(42%)
The production of nitric acid (HNO^ produces
nitrous oxide (N2O) as a by-product via the oxidation
of ammonia. Nitric acid is a raw material used
primarily to make synthetic commercial fertilizer. It
is also a major component in the production ofadipic
acid (a feedstock for nylon) and explosives. In 1990,
this inorganic chemical ranked thirteenth in total
production of all chemicals in the United States.
Nitric acid plants are in operation in all regions
of the U.S., with a total annual operating capacity of
10.3 million metric tons (SRI, 1993). Nitrous oxide
emissions from this source were about 3 MMTCE in
1990, accounting for nearly 10 percent of total U.S.
N2O emissions. Nitric acid grew slightly from 1991 to
1993, resulting in N2O emissions of 2.9 MMTCE in
1991, 3.0 MMTCE in 1992, and 3.1 MMTCE in 1993.
Nitric acid is an inorganic compound used
primarily as a feedstock for nitrate fertilizer produc-
tion. It is also a raw material used in the production of
adipic acid and explosives. Relatively small quantities
of nitric acid are employed for stainless steel pickling,
metal etching, rocket propellants, and nuclear-fuel
processing. Virtually all of the nitric acid produced in
the U.S. is manufactured by the catalytic oxidation of
ammonia .(U.S. EPA, 1985). During this reaction,
nitrous oxide is fprmed 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 nitrous oxide.
Nitric acid production in the U.S. was approxi-
mately 7.26 million metric tonnes in 1990 (C&EN,
1992). Off-gas measurements at one nitric acid
production facility showed N2O emission rates to be
approximately 2-9 g N2O per kg of nitric acid produced
(Reimer et al, 1992). Using the midpoint of the range
of emission factors, nitrous oxide emissions from nitric
acid production were about 40 thousand metric tonnes
(3 MMTCE). Nitric acid production was 7.19 million
metric tonnes in 1991, 7.30 million metric tonnes in
1992, and 7.74 million metric tonnes in 1993 (C&EN,
1993, 1994). This results in annual nitrous oxide
emissions of 39.5, 40.2, and 42.6 thousand metric
tonnes, respectively.
These emission estimates are highly uncertain
because of insufficient information on manufacturing
processes and emission controls. Although no abate-
ment techniques are specifically directed at removing
nitrous oxide, existing control measures for other
pollutants will have some effect on the nitrous oxide
contained in the gas stream. While the emissioli
coefficients used here do account for these other
abatement systems, there may be some variation
between different production facilities depending on
the existing level of pollution control at a given plant.
2.
Carbon Dioxide Manufacture
Carbon dioxide is used in many segments of the
economy, including food processing, beverage manu-
facturing, chemical processing, crude oil products,
and a host of industrial and miscellaneous applica-
29
-------
tfons. For the most part, carbon dioxide used in these
applications will eventually be released into the
atmosphere.
Industrial Carbon Dioxide Emissions by Source: 1990
Carbon Dioxida
Minufactura (2%)
SซiปAihPtod and
Uu(7%)
Cement Production
i.. (59%)
Carbon dioxide emissions from this source are
estimated to be about 0.33 MMTCE in 1990, or less
than 0.1 percent of total U.S. CO2 emissions. Carbon
dioxide demand is expected to expand five percent
annually through 1995, with the greatest opportuni-
ties in chemical manufacturing, enhanced oil recov-
ery, and various industrial applications (Freedonia
Group, 1991). As a result, carbon dioxide emissions
are estimated to have been 0.34 MMTCE in 1991,
0.36 MMTCE in 1992, and 0.38 MMTCE in 1993.
Carbon dioxide is used for a variety of industrial
and miscellaneous applications, including food pro-
cessing, chemical production, carbonated beverages,
and enhanced oil recovery. Carbon dioxide used for
enhanced oil recovery is injected into the ground to
increase reservoir pressure, and is therefore considered
sequestered1. For the most part, however, carbon
dioxide used in these applications will eventually enter
the atmosphere.
With the exception of a few natural wells, carbon
dioxide is produced as a by-product from the produc-
tion of other chemicals (e.g., ammonia), or obtained by
separation from crude oil or natural gas. Depending on
the raw materials that are used, the by-product carbon
dioxide 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 use). For example,
ammonia is manufactured using natural gas and
naphtha as feedstocks. Carbon dioxide emissions from
this process are included in the portion of carbon for
non-fuel use that is not sequestered (see Part I).
Carbon dioxide emissions were calculated by
estimating the fraction of manufactured carbon dioxide
that is not accounted for in these other emission
sources. Carbon dioxide consumption for uses other
than enhanced oil recovery was estimated to be 4.4
million short tons in 1990 (Freedonia Group, 1991).
Carbon dioxide wells, natural gas wells, and fermenta-
tion account for approximately 30 percent of total
production capacity in the U.S. Assuming that the
remaining carbon dioxide is accounted for in emission
estimates from other source categories, CO2 emissions
from this source are estimated to be about 1.2 million
metric tonnes (0.33 MMTCE) in 1990. Because
carbon dioxide demand is expected to expand five
percent annually through 1995 (Freedonia Group,
1991), carbon dioxide emissions were estimated to
have risen to 1.26 million metric tonnes (0.34
MMTCE) in 1991, 1.32 million metric tonnes (0.36
MMTCE) in 1992, and 1.4 million metric tonnes (0.38
MMTCE) in 1993. These estimates are highly uncer-
tain due to the limited information on CO2 production
and use in the U.S.
C. ORGANIC CHEMICALS
1. Adipic Acid Production
Adipic acid production has been identified as a
significant anthropogenic source of atmospheric
nitrous oxide (N2O). Adipic acid is a major compo-
nent used in nylon production, as well as production
of some low-temperature lubricants. It is also used to
provide foods with a "tangy" flavor. The U.S. ac-
counts for approximately one-third of the total
annual global production ofadipic acid (Thiemens &
Trogler, 1991). Based on 1990 U.S. adipic acid
production of 735 thousand metric tonnes (C&EN,
1992), nitrous oxide emissions from this source are
estimated to be 4.1 MMTCE, or 13.7 percent of total
, . , . i, , . ,,., . . ,
1 It is unclear to what extent the CO2 used for enhanced oil recovery will be re-released. For example, the carbon
dioxide used for EOR is likely to show up at the wellhead after a few years of injection (Hangebrauk et al., 1992). This CO2,
however, is typically recovered and reinjected into the well. More research is required to determine the amount of carbon
dioxide that may potentially escape. For the purposes of this analysis, it is assumed that all of the CO2 remains sequestered.
30
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U.S. N2O emissions. Adipic acid production in the
U.S. rose to 771 thousand metric tonnes in1991 and
fell to 708 thousand metric tonnes in 1992 and 1993.
Annual N2O emissions for those years were 4.3, 4.0,
and'4.0 MMTCE, respectively.
Industrial Nitrous Oxide Emissions by Source: 1990
Adipic Acid Production
(58%)
Nitric Acid Production
(42%)
Adipic acid is a white crystalline solid used in
the manufacture of synthetic fibers, coatings, plastics,
urethane foams, elastomers, and synthetic lubricants.
Commercially, it is the most important of the aliphatic
dicarboxylic acids, which are used to manufacture
polyesters. Ninety percent of all adipic acid produced
in the United States is used in the production of nylon
6,6. /
Adipic acid is produced through a two-stage
process. The second stage involves the oxidation of
ketone-alcohol with nitric acid. Nitrous oxide is ,
generated as a by-product of this reaction and enters
the waste gas stream. In the U.S., this waste gas is
treated to remove NOx and other regulated pollutants
(and, in some cases, N2O as well) and is then released
into the atmosphere. There are currently four plants in
the U.S. that produce adipic acid. In 1990, two of
these plants had emission control measures that de-
stroyed about 98 percent of the nitrous oxide before it
was released into the atmosphere (Radian, 1992). By
1996, all adipic acid production plants will have
nitrous oxide emission controls,in place as a result of a
voluntary agreement among producers.
Since emissions of N2O in the U.S. are not
regulated, very little emissions data exist However,
based on the overall reaction stoichiometry for adipic
acid, it is estimated that approximately 0.3 kg of
nitrous oxide is generated for every kilogram of adipic
acid produced (Radian, 1992). Based on 1990 U.S.
adipic acid production of 735 thousand metric tonnes ,
(C&EN, 1992) and existing levels of pollution control,
nitrous oxide emissions from this source are estimated
to be 56.2 thousand metric tonnes N2O (4.1 MMTCE).
Adipic acid production in the U.S. was 771
thousand metric tonnes in 1991 and 708 thousand
metric tonnes in 1992 and 1993 (C&EN, 1993, 1994)..,
Using the methodology described above, nitrous oxide
emissions from this source were estimated to be 59
thousand metric tonnes (4.3 MMTCE) in 1991 and 54
thousand metric tonnes (4.0 MMTCE) in 1992 and
1993.
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 cases, however, these data are confiden-
tial. As a result, plant-specific production figures were
estimated by disaggregating total adipic acid produc-
tion using existing plant capacities (SRI, 1990). This
creates a significant degree of uncertainty in the adipic
acid production data used to derive the emission
estimates. The most accurate N2O emissions estimates
would be derived from actual production figures, if
these data were reported by each plant.
D. NON-METALLIC MINERAL
PRODUCTS.
1. Cement Production
Industrial Carbon Dioxide Emissions by Source: 1990
Carbon Dioxide
Consun7ptSon(9%) Manufacture (2%)
Soda Ash Prod, and
Use (7%)
iement Production
(59%)
Carbon dioxide emitted during the cement
production process represents the most significant
non-energy source of industrial carbon dioxide
31
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emissions. Cement i$ produced in most states (and in
Puerto Rico) and is used in all of them. Carbon
dioxide is created when calcium carbonate (CaCO) is
heated in a cement kiln to form lime (calcium oxide
or CaO) and carbon dioxide. This lime is combined
with other materials to produce clinker (an intermedi-
ate product from which finishedportland and ma-
sonry cement are made), while the carbon dioxide is
released into the atmosphere.
Carbon dioxide emissions from cement produc-
tion were estimated to be approximately 8.9 MMTCE
in 1990, or 0.7 percent of total U.S. CO2 emissions
(Table H-2). Carbon dioxide emissions for 1991 and
1992 were estimated to be 8.7 MMTCE and 8.8
MMTCE, respectively.
Table H-2. Carbon Dioxide Emissions from U.S.
Cement Production
Clinker
Masonry
TOTAL
Production
(103 metric tonnes)
1990 1991 1992
64,356 62,918 63,415
2,911 2,591 2,806
67,267 65,509 66,221
CO,, Emissions
(103 metric tonnes)
1990 1991 1992
32,626 31,897 32,149
65 58 63
32,700 31,955 32,212
Source: Production data taken from the Bureau of Mines (1992a)
Carbon dioxide is produced during the produc-
tion of clinker, an intermediate product from which
finished portland and masonry cement are made. The
quantity of carbon dioxide released during cement
production is directly proportional to the lime content
of die clinker.
During cement production, calcium carbonate
(CaCO,) from limestone, chalk, or other calcium-rich
materials are heated in cement kilns to form lime
(CaO) and carbon dioxide:
CaCO.*CaO + CO,
This process is known as calcination or
calcining. The lime is then combined with silica-
containing materials (provided to the kiln as clays or
shales) to form dicalcium or tricalcium silicates, two of
the four major compounds in cement clinker (Griffin,
1987). i(| ' ^ " \ _" ' ^ /' "
Carbon dioxide emissions were estimated by
applying an emission factor, in tonnes of CO2 released
per tonne of clinker produced, to the total amount of
clinker produced. The emission factor used in this
analysis is the product of the fraction of lime used in
the cement clinker and a constant reflecting the mass of
CO2 released per unit of lime. The emission factor was
calculated as follows:
EF
clinker
= fraction CaO X
/44.01g/mo/eCO2\
\56.08 g/mole CaO/
This analysis assumes an average lime fraction for
clinker of 64.6 percent, which yields an emission factor
of 0.507 tonnes of carbon dioxide per tonne of clinker
produced.
Clinker production in the U.S. (including Puerto
Rico) was reported as 64.4 million metric tonnes (or 71
million short tons) in 1990 (Bureau of Mines, 1992a).
Using the emissions factor derived above, carbon
dioxide emissions from cement manufacturing were
estimated to be 32.6 million metric tonnes (8.9
MMTCE)." ";' '"'!, ,'', r ' ' .'. , " '" .'.' ''"''
Masonry cement requires additional lime over
and above the lime used in the clinker. During the
production of masonry cement, non-plasticizer addi-
tives such as lime, slag, and shale are added to the
cement, increasing its weight by 5 percent. Lime
accounts fqr approximately 60 percent of the added
substances. An emission factor for this additional lime
can be calculated as follows:
EF
fraction of weight added \ x ( padded 6]
mas ~ \1 + fraction of weight added / \ substance /
y /44.01 g/mole CO2\
\56.08 g/mole CaO/
0.05
1+ 0,05
= 0.0224
x 0.60 x 0.785
32"
1 , '.i 'fliiitiii:,! ii.i at ..-li;,: 'i
.<-"! 'iiliiillili-ll I
-------
Thus, 0.0224 tonnes of additional carbon dioxide
are emitted for every tonne of masonry cement pro-
duced. Masonry cement production in the U.S. was
reported to be 2.9 million metric tonnes (3.2-million
short tons) in 1990 (Bureau of Mines, 1992a), resulting
in additional CO2 emissions of 65,200 metric tonnes.
Therefore, total emissions from cement production are
approximately 32.7 million metric tonnes (8.9
MMTCE).
Carbon dioxide emissions from cement produc-
tion for 1991 and 1992 were also estimated using the
methodology described above. Carbon dioxide emis-
sions from cement production were estimated to be 8.7
MMTCE in 1991 and 8.8 MMTCE in 1992. The
uncertainties contained in these estimates are primarily
due to uncertainties in the lime content of clinker and
in the amount of lime added to masonry cement. For
example, the lime content of clinker varies from 64 to
66 percent.
Some amount of CO2 is reabsorbed when the
cement is used for construction. As cement reacts with
water, alkaline substances such as calcium hydroxide
are formed. During the curing process, these com-
pounds may react with CO2 in the atmosphere to create
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 included here.
Industrial Carbon Dioxide Emissions by Source: 1990
2.
Lime Manufacture
Lime is a manufactured product with many
chemical, industrial, and environmental uses. In
1990, lime ranked fifth in total production of all
chemicals in the United States. Its major uses are in
steelmaking, construction, pulp and paper manufac-
turing, and water and sewage treatment Lime is
manufactured by heating limestone (mostly calcium
carbonate CaCOJ in a kiln, creating calcium oxide
(quicklime) and carbon dioxide. The carbon dioxide
is driven off as a gas and is normally emitted to the
atmosphere.
Lime production in the U.S. was 17,481 thou-
sand short tons in 1990 (Bureau of Mines, 1992b),
resulting in net CO2 emissions of 3.2 MMTCE, or
0.24 percent of total U.S. CO2 emissions. Carbon
dioxide emissions were estimated to be 3.2 MMTCE
in 1991 and 3.3 MMTCE in 1992.
Limestone
Consumption (9%)
Carbon Dioxide
Manufacture (2%)
Soda Ash Prod, and
Use (7%)
Lime Production
(21%)
Cement Production
(59%)
Lime is an important chemical with a variety of
industrial, chemical, and environmental applications in ,
the U.S. Lime production involves three main pro-
cesses: stone preparation, calcination, and hydration.
Carbon dioxide is generated during the calcination
stage, when limestone (calcium carbonate or a combi-
nation of calcium and magnesium carbonate) or other
calcium carbonate materials are roasted at high tem-
peratures. This process is usually performed in either a
rotary or vertical kiln, although there are a few other
miscellaneous designs. Carbon dioxide is produced as
a by-product of this process, just as CO2 is released
during clinker production (see previous section on
cement production). The carbon dioxide is driven off
as a gas and normally exits the system with the stack
gas. The mass of CO2 released per unit of lime pro-
duced can be calculated based on their molecular
weights:
44.01 g/mole CO2 -*- 56.08 g/mole CaO = 0.785
Lime production in the U.S. was 17,481 thou-
sand short tons in 1.990 (Bureau of Mines, 1992b),
This results in potential carbon dioxide emissions of
12.45 million metric tonnes. Some of the CO2 gener-
ated during the production process, however, is recov-
ered for use in sugar refining and precipitated calcium
carbonate (PCC) production. Lime production by
these producers was 911 thousand short tons, generat-
ing 650 thousand metric tonnes of carbon dioxide.
Approximately 80 percent of this CO2 is recovered and
not emitted, resulting in net CO2 emissions of about
11.9 million metric tonnes (3.2 MMTCE) from U.S.
lime production in 1990. Using this methodology, CO2
emissions were estimated to be approximately 11.7
million metric tonnes (3.2 MMTCE) in 1991 and about
12.1 million metric tonnes (3.3 MMTCE) in 1992 (see
Table II-3).
33 .
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Table II-3. Carbon Dioxide Emissions from U.S. Lime Production
Potential CO2
Emissions from
All Lime Producers
Recovered CO2 from
Sugar & PCC Manufacturers
NET EMISSIONS
Production
(103 metric tonnes)
1990 1991 1992
15,859 15,694 16,227
826 964 1,023
CO2 Emissions
(103 metric tonnes)
1990
12,445
519
11,927
1991 1992
12,317 12,734
605 642
11,711 12,092
Source: Production data taken from Bureau of Mines (1992b)
Note; Totals may not add due to independent rounding.
The term "lime" is actually a general term that
includes various chemical and physical'forms of this
commodity. Uncertainties in the emission estimate can
be attributed to slight differences in the chemical
composition of these products. For example, although
much care is taken 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 limestone used as a
raw material, a rigid specification of lime material is
impossible. As a result, few plants manufacture lime
with exactly the same properties.
A portion of the carbon dioxide emitted during
lime production will actually be reabsorbed when the
lime is consumed. In most processes that use lime
(e.g., water softening), carbon dioxide reacts with the
lime to create calcium carbonate. This is not necessar-
ily true about lime consumption in the steel industry,
however, which is the largest consumer of lime. A
detailed accounting of lime use in the U.S. and further
research into the associated processes are required to
quantify the amount of carbon dioxide that will be
reabsorbed. As more information becomes available,
this emission estimate \\ill be adjusted accordingly.
3.
Limestone Use
Limestone is a basic raw material used by a
wide variety of industries, including the construction,
agriculture, chemical, and metallurgical industries.
For example, limestone can be used as a flux or
purifier in rejining metals such as iron. In this case,
limestone heated in a blastfurnace reacts with
Industrial Carbon Dioxide Emissions by Source: 1990
Limestone
Consumption (9%)
Carbon Dioxide
Manufacture (2%)
Soda Ash Prod, and
Use (7%)
Cement Production
(59%)
impurities in the iron ore and fuels, generating
carbon dioxide as a by-product. Limestone is also
used for glass manufacturing and for SO2 removal
from stack gases in utility and industrial plants.
In 1990, approximately 10.5 million metric
tonnes of limestone and 0.9 million metric tons of
dolomite were used as flux stone in the chemical and
metallurgical industries, in flue gas desulfurization
systems, and for glass manufacturing. Assuming that
all of the carbon is released into the atmosphere, this
results in total carbon dioxide emissions of 1.4
MMTCE, or 0.1percent of total U.S. CO2 emissions
that year. Carbon dioxide emissions were estimated
to be 1.3 MMTCE in 1990 and 1.4 MMTCE in 1992.
Limestone is widely distributed throughout the
world in deposits of varying sizes and degrees of
purity. Deposits of limestone occur in nearly every
state, usually in tremendous amounts. Great quantities
34
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of limestone are extracted for commercial use. For
example, limestone can be used as a flux or purifier in
metallurgical furnaces, as a sorbent in flue gas desulfu-
rization (FGD) systems in utilities and industrial
plants, or as a raw material in glass manufacturing.
Limestone is heated during these processes, generating
carbon dioxide as a by-product. Carbon emissions can
be calculated by multiplying the amount of limestone
consumed by the carbon content of the limestone
(which is approximately 12 percent for calcite, 13
percent for dolomite).2
The U.S. Bureau of Mines reports that approxi-
mately 5,213 thousand metric tonnes of limestone and
838 thousand metric tonnes of dolomite were used as
flux stone in the chemical and metallurgical industries
in 1991 (Bureau of Mines, 1993b).3 Additionally, 386
thousand metric tonnes of limestone were used for
glass manufacturing (Bureau of Mines, 1993b) and
4,500 thousand metric tonnes of limestone were used
in FGD systems (DOE/EIA Form EIA-767). Assum-
ing that all of the carbon is released into the atmo-
sphere, these applications result in total carbon emis-
sions of 1.3 million metric tonnes, or 4.8 million metric
tonnes of CO2. Using the same methodology described
above, CO2 emissions were estimated to be about 5.1
million metric tonnes (1.4 MMTCE) in 199.0; about 4.8
million metric tonnes (1.3 MMTCE) in 1991, and
approximately 5 million metric tonnes (1.4 MMTCE)
in 1992 (see Table II-4).
Uncertainties in this estimate are due to varia-
tions in the chemical composition of limestone. In
addition to calcite, limestone may contain smaller
amounts of magnesia, silica, and sulfur. The exact
specifications for limestone or dolomite used as flux
stone vary with the pyrometallurgical process, the kind
of ore processed, and the final use of the slag. Simi-
larly, the quality of the limestone used for glass manu-
facturing will depend on the type of glass being
manufactured. Uncertainties also exist in the activity .
data. Much of the limestone consumed in the U.S. is
reported as "other unspecified uses." Furthermore,
some of the limestone reported as "limestone" is
actually dolomite (which has a higher carbon content
than limestone).
Table II-4. CO. Emissions from Limestone Consumption in the U.S.
Flux Stone
Limestone
Dolomite
Glass Making
SO2 Removal
TOTAL
Consumption
(103 metric tonnes)
1990a 1991 1992a
5,776 5,213 5,490
929 838 883
428 386 407
4303 4499 4465
CO2 Emissions
(103 metric tonnes)
1990 1991
2,541 2,294
444 400
188 170
1,893 1,979
5,067 4,844
1992
2,416
422
179
1,964
4,981
a Although the U.S. Bureau of Mines reports production of total crushed stone annually, limestone and dolomite production are
provided for odd-numbered years only. Limestone production for 1990 and 1992 were estimated by assuming that limestone
and dolomite accounted for the same percentage of total crushed stone in those years as they did in 1991.
Note: Totals may not add to the sum of the individual source categories due to independent rounding.
2 Limestone (CaCO3) and dolomite (CaMg(CO3)2) are collectively referred to as limestone by the industry, .and
intermediate varieties are seldom distinguished. . ' '
3 Of the 723 million tons of limestone consumed in the U.S. in 1991, 218.8 million tons or 30.3 percent were reported as
"Other unspecified uses" and only 4 million tons were reported as "Flux stone." The Bureau of Mines recommends that
when analyzing the industry, however, the quantity reported as unspecified should be distributed among the various reported
uses. For example, limestone used as flux stone accounts for 0.8 percent of specified limestone uses. Assuming the same
percentage of unspecified limestone use was actually used as flux stone, total limestone used would be (0.008 x 218.8) + 4 =
5.75 million tons. A similar calculation was used for dolomite and the other end-uses.
35
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4. Soda Ash Manufacture and Consumption
Industrial Carbon Dioxide Emissions by Source: 1990
Carbon Dioxide
Mซniifซctuiป (2%)
\ ซ^ Cement Production
(59%)
Commercial soda ash (sodium carbonate) is
used in many familiar consumer products such as
glass, soap and detergents, paper, textiles, and food.
Internationally, ttvo types of soda ash are produced --
natural and synthetic. The U.S. produces only
natural soda ash. During the production process,
natural sources of sodium carbonate are heated and
transformed into a crude soda ash that requires
further refining. Carbon dioxide is generated as a
byproduct of this reaction, and is eventually emitted
into the atmosphere, fn addition, carbon dioxide is
released when soda ash is consumed.
Of the two states that produce natural soda ash,
only Wyoming has net emissions of carbon dioxide.
Because a different production process is used in
California, those soda ash producers never actually
release the carbon dioxide into the atmosphere.
Instead, the CO2 is recovered and used in other stages
of production. U.S. carbon dioxide emissions from
soda ash production are estimated to be approxi-
mately 0.39 MMTCE in 1990. Carbon dioxide
emissions from soda ash production were 0.39
MMTCE in 1991, 0.40 MMTCE in 1992, and 0.38
MMTCE in 1993.
Soda ash consumption in the U.S. generated
about 0.74 MMTCE of carbon dioxide in 1990.
Annual soda ash consumption in the U.S. decreased
Slightly in 1991 and 1992, but recovered in 1993.
Carbon dioxide emissions from soda ash consump-
tion were 0. 71 MMTCE in 1990 and 1992, and 0. 74
MMTCE in 1993. Together, soda ash production and
use accounted for almost 0.1 percent of total U.S. CO2
emissions in 1990.
strongly alkaline. Commercial soda ash is used as a
raw material in a variety of industrial processes. It is
used primarily as an alkali, either in glass manufactur-
ing or simply as a material which reacts with and
neutralizes acids or acidic substances. About 75
percent~of world production is synthetic ash made from
sodium chloride; the remaining 25 percent is produced
from natural sodium carbonate-bearing deposits. The
U.S. produces only natural soda ash.
During the production process, trona (the princi-
pal ore from which natural soda ash is made) is cal-
cined in a rotary kiln and chemically transformed into a
crude soda ash that requires further processing. Car-
bon dioxide and water are generated as a by-product of
the calcination process. CO2 emissions from the
calcination of trona can be estimated based on the
following chemical reaction:
2(Na3H(CO3)22H2O) > 3Na2CO3 + 5H2O + CO2
[trona]
[soda ash]
Soda ash (sodium carbonate, NajCO,,) is a white
crystalline solid that is readily soluble in water and is
Based on this formula, it takes approximately
10.27 metric tonnes of trona to generate 1 metric tonne
of CO2. According to the U.S. Bureau of Mines, 14.7
million metric tonnes of trona were mined in 1990 for
soda ash production (Bureau of Mines, 1993c). This
results in CO2 emissions of approximately 1.4 million
metric tonnes (0.39 MMTCE). Trona production from
1991 to 1993 was 14.7, 14.9, and 14.5 million metric
tonnes, respectively. Using the methodology described
above, carbon dioxide emissions from soda ash produc-
tion in these years were 1.43 million metric tonnes
(0.39 MMTCE) in 1991, 1.45 million metric tonnes
(0.40 MMTCE) in 1992, and 1.41 million metric
tonnes (0.38 MMTCE) in 1 993 .
An alternative method of natural soda ash
production uses sodium carbonate-bearing brines. To
extract the sodium carbonate, the complex brines are
first treated, with carbon dioxide in,carbonation towers
to convert the sodium carbonate into sodium bicarbon-
ate, which will precipitate under these conditions. 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.
Glass manufacture represented about 49 percent
of domestic soda ash consumption, with smaller
amounts used for chemical manufacture, soap and
detergents, flue gas desulfurization, and other miscella-
36
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neous uses. In each of these applications, a mole of
carbon is released for every mole of soda ash used.
Thus, approximately 0.113 tonnes of carbon (or 0.415
tonnes of carbon dioxide) is released for every tonne of
soda ash consumed.
In 1990, U.S. consumption of soda ash was
reported as 6.5 million metric tonnes (Bureau of
Mines, 1993c), which generates about 2.7 million
metric tonnes (0.74 MMTCE) of carbon dioxide.
Annual soda consumption in the U.S. was 6.3 million
metric tonnes in 1991 and 1992, and 6.5 thousand
metric tonnes in 1993. As a result, carbon dioxide ,
emissions from soda ash consumption were estimated
to be 2.6 million metric tonnes (0.71 MMTCE) in 1991
and 1992, and 2.7 million metric tonnes (0.74
MMTCE) in 1993.
E. OTHER EMISSIONS
1. Emissions of HFCs and PFCs
Partially halogenated compounds (HFCs) and
perfluorinated compounds (PFCs) are used primarily
as alternatives to the ozone depleting substances
(ODSs) being phased out under the Montreal Proto-
col and Clean Air Act Amendments of 1990. ODSs,
which include chlorofluorpcarbons (CFCs) and
partially halogenated fluorocarbons (HCFCs,) are
used in a variety of industrial applications, including
refrigeration, solvent cleaning, foam, production,
sterilization, and fire extinguishing. Although the
ODS replacements (Le., HFCs and PFCs) are not
harmful to the stratospheric ozone layer, they are
powerful greenhouse gases (for example, HFC-134a
is 1,200 times more heat absorbent than an equivalent
amount ofCO2 by weight in the atmosphere).
Emissions of HFCs and PFCs: 1990
(1%)hFC/PFC
(10%) CH4
CO2 (87%)
Note: Carbon Dioxide Emissions include Sources and Sinks.
In 1990, HFCs and PFCs were not used widely
as commercial chemicals. However, these gases were
emitted as by-products from other industrial produc-
tion processes. For example, HFC-23 was emitted as,
a by-product of HCFC-22 production, and CF4 and
C2F6 (two PFCs) were released during aluminum
smelting. Emissions of these gases totaled approxi-
mately 19 MMTCE in 1990. The manufacture and
emissions of HFCs and PFCs are expected to rise as
their use as ODS replacements increases.
Partially halogenated compounds (HFCs) and
perfluorinated compounds (PFCs) were introduced as
alternatives to the ozone depleting substances (ODSs)
being phased out under the Montreal Protocol and
Clean Air Act Amendments of 1990 (see discussion on
ODSs below). ODSs, which include chlorofluorocar-
bons (CFCs), partially halogenated fluorocarbons
(HCFCs), and related compounds, are used in several
major end use sectors, including refrigeration, air
conditioning, solvent cleaning, foam production,
sterilization, fire extinguishing, paints, Coatings, and
other chemical intermediates, and miscellaneous uses
(e.g., aerosols, propellants, and other products).
Because HFCs and PFCs are not harmful to the strato-
spheric ozone layer, they are not controlled by the
Montreal Protocol. However, HFCs and PFCS are
powerful greenhouse gases and are, therefore, covered
under thePCCC (for example, HFC-134a has an
estimated direct GWP of 1,200, which makes HFC-
134a 1,200 times more heat absorbent than an equiva-
lent amount by weight of CO2 in the atmosphere). As a
result, emission estimates for these gases have been
included in the U.S. inventory and are provided in
Table II-5,
Because the use of CFC and HCFC substitutes
was minimal in 1990, emissions of HFCs and PFCs
were largely the result of by-product emissions from -
other production processes, and not the result of their
use as CFC alternatives. For example, HFC-23 is a by-
product emitted during HCFC-22 production, and
PFCs (CF4 and C2Fg) are emitted during aluminum
smelting. Emissions of HFCs and PFCs should con-
tinue to rise, however, as their use as ODS replace-
ments increases.
Partially halogenated compounds (HFCs)
Emission estimates were developed using a
computer model that estimates ODS emissions based
on:
37
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a vintaging framework that generates results
using information on the stock of equipment
in each end use, chemical use per piece of
equipment, equipment lifetimes, and emission
rates from each piece of equipment, and
substitution scenarios that describe when
chemicals will replace ODSs as they ate
phased out under the Copenhagen Amend-
ments to the Montreal Protocol. The scenarios
are based on estimated market penetration and
the number of years it may take to fully
implement a substitute.
Table II-5. Emissions of HFCs and PFCs: 1990
(Million Metric Tonnes)
Compound Molecular GWP Carbon-
BasisEquivalent"
HFCs
HFC-23
HFC-134a
HFC-152a
PFCs
Total PFCs
0.00552 10,000
0.0005 1,200
0.0003 150
0.003
5400
15.05
O'.l 6
0.01
3.98
The GWP for HFC-23 was obtained from U.S. EPA's
Office of Air and Radiation and is based on unpublished
data from DuPont Chemical Company and others. The
GWPs for the other compounds are from IPCC (1992).
Source: U.S. EPA, 1994b
Because HFCs were not used widely as commer-
cial chemicals in 1990, emissions of these compounds
were relatively small. Emissions of HFC-134a were
estimated to be approximately 500 metric tonnes (0.16
MMTCE) in 1990. Emissions of HFC-152a (a compo-
nent of the refrigerant blend R-500) were estimated to
be approximately 300 metric tonnes (0.01 MMTCE).
HFCs continue to be evaluated and introduced on the .
market as refrigerants, solvents, fire extinguishing
agents, sterilizers, and foam,blowing agents.
HFC-23 is currently emitted as a by-product of
HCFC-22 production. Even after HCFC-22 is phased
out under the Montreal Protocol, production of HCFC-
22 as a polymer precursor will continue. By-product
emissions of HFC-23 are assumed to be 4 percent of
HCFC-22 production. HCFC-22 production was
estimated to be about 138 thousand metric tonnes in
1990, resulting in 5.5 thousand metric tonnes of HFC-
23 (15.05 MMTCE).
Perfluorocarbons (PFCs)
The aluminum production industry is thought to
be the largest source of two PFCs CF4 and C2F6.
Emissions of these two potent greenhouse gases occur
during the reduction of alumina in the primary smelt-
ing process.4 Aluminum is produced by the electro-
lytic reduction of alumina (A12O3) in the Hall-Heroult
reduction process, whereby alumina is dissolved in
molten cryolite (Na3AlF6), which acts as the electrolyte
and is the reaction medium. PFCs are formed during
disruptions of the production process known as anode
effects (AE), which are characterized by a sharp rise in
voltage across the production vessel. The PFCs can be
produced through two mechanisms: direct reaction of
fluorine with the carbon anode; and electrochemical
formation. In both cases the fluorine originates from
dissociation of the molten cryolite.
Because CF4 and C2F6 are inert, and therefore
pose no health or local environmental problems, there
has been little study of the processes by which emis-
sions occur and the important factors controlling the
magnitude of emissions. In general, however, the
magnitude of emissions for a given level of production
depends on the frequency and duration of the anode
effects during that production period. The more
frequent and long-lasting the anode effects, the greater
the emissions.
The methodology used to estimate emissions of
PFCs from aluminum production first calculates a per
unit production emissions factor as a function of
several important operating variables, including
average anode effect frequency and duration. Total
annual emissions are then calculated based on reported
annual production levels. The five components of the
per unit production emissions factor are:
the amount of CF4 and C2F6 emitted during
every minute of an anode effect, per kAmp of
current;
the average duration of anode effects, ex-
pressed in anode effect minutes per effect;
Perfluorocarbons are not emitted during the smelting of recycled aluminum.
38
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the average frequency of anode effects,
expressed in anode effects per day;
the current efficiency for aluminum smelting
(no units); arid,
the current required to produce a metric ton of
aluminum, assuming 100 percent efficiency.
Using currently available data for the U.S., this
methodology yields a range in the emissions factor of
0.3 to 0.9 kg CF4 per metric ton of aluminum produced
EPA, 1993c). The emissions factor for C2F6 is esti-
mated to be an order of magnitude lower, and therefore
ranges from 0.03 to 0.09 kg C2F6 per metric ton of
aluminum produced. Based on 1990 aluminum
production of 4.048 million metric tons, total U.S.
emissions of PFCs in 1990 were estimated to be 1,200
to 3,700 metric tons of CF4 (1.7 to 5.2 MMTCE) and
120 to 370 metric tons of C2F6 (0.17 to 0.52 MMTCE).
U.S. aluminum production in 1991 and 1992 varied '
less than 2 percent from the 1990 level, resulting in
minor fluctuations in emissions estimates of CF4 and
C2F6 (relative to the current uncertainty in these
emissions estimates).
Because there has been relatively little study of
emissions from this source, considerable uncertainty
remains hi several of the values used in the estimates
presented here. In particular, the value for emissions
per AE minute per kAmp is based on a single measure-
ment study which may not be representative of the
industry as a whole (U.S. EPA, 1993c). For example,
this emissions factor may vary by smelter technology
type, among other factors. The average duration of
anode effects, according to preliminary results of
ongoing research, may in fact be considerably shorter
than the current values used. The average frequency of,
anode effects and the current efficiency are well
documented, although they may change over time as
operating efficiencies improve. Because recent studies
indicate that the values for the important variables used
in developing the emission coefficient may actually be
lower than previously thought, the estimates presented
here are likely to be conservatively high.
Emissions ofCFCs and Related Compounds
Chlorofluorocarbons (CFCs) and other haloge-
nated fluorocarbons, which were emitted into the
atmosphere for the first time this century, are a family
of man-made compounds used in a variety of industrial
applications, including foam blowing, refrigeration,
and solvent cleaning. These compounds, which
contain chlorine and bromine, have been shown to
deplete stratospheric ozone, and thus are typically
referred to as ozone-depleting substances, or ODSs. In
addition, they are important greenhouse gases because
they block infrared radiation that would otherwise
escape into space (EIA, 1993d). Unlike other green-
house gases, however, these compounds do not occur
naturally in the atmosphere. CFCs and other haloge-
nated fluorocarbons include the following substances:
Chlorofluorocarbons, halons, methyl chloroform,
carbon tetrachloride, methyl bromide, and partially
halogenated fluorocarbons (HCFCs).
Many governments, recognizing the harmful
effects of these compounds on the atmosphere, signed
the Montreal Protocol on Substances that Deplete the
Ozone Layer in 1987 to limit the production and
consumption of a number of CFCs and other haloge-
nated compounds5. The U.S. furthered its commitment
to phase-out these substances by signing and ratifying
the Copenhagen Amendments to the Montreal Protocol
in 1992. Under these amendments, the U.S. committed
to eliminating the production of all halons by January
1, 1994 and all CFCs by January 1, 1996.
Under the Clean Air Act (CAA), which devel-
oped the U.S. phaseout schedule for the Montreal
Protocol, ODSs were categorized based on their ozone
depletion potential.' Compounds are classified as
"Class I" or "Class II" substances, and must adhere to a
distinct set of phase-out requirements.
Class I ODSs include fully halogenated CFCs,
halons, tetrachlorocarbon (commonly known
as carbon tetrachloride), and 1,1,1
trichloroethane (a.k.a. methyl chloroform).
Fully halogenated compounds have no hydro-
gen atoms in their makeup and are so called
because they contain chlorine, fluorine, or
bromine atoms (elements'belonging to the
halogen family). Of the elements in the
halogen family, chlorine and bromine are
thought to be ozone-depleting agents, while
fluorine is believed to be a potent greenhouse
gas. Halon compounds contain bromine atoms
instead of chlorine atoms, while methyl .
There are currently 133 countries thathave signed the Montreal Protocol.
39
-------
chloroform is actually a partially halogenated
compound (the only one to be included in this
Class). These compounds are the primary
ODSs in use today.
Class II ODSs Include partially halogenated
chlorine compounds (known as HCFCs),
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
about one-tenth to one-hundredth the threat to
stratospheric ozone compared to CFCs.
Although HCFCs pose less of a threat to the
earth's stratospheric ozone layer, they are still
powerful greenhouse gases, with GWPs
several orders of magnitude larger than CO2
(for example, HCFC-22 has an estimated
direct GWP of 1600, which makes HCFC-22
1600 times more heat absorbent than an
equivalent amount by weight of CO2 in the
atmosphere).
The production and use of Class I and Class II
substances in the U.S. are being phased out in accor-
dance with the Montreal Protocol and the 1990 Clean
Air Act. Under these measures, the production of Class
I substances in the U.S. will cease by January 1996,
while the production of Class II substances will be
gradually phased out by January 2015. Another group
of partially-halogenated compounds that do not contain
chlorine, known as HFCs, are being developed as long-
term replacements for Class I and Class II substances.
Although the IPCC emission inventory guide-
lines do not include reporting emissions of CFCs and
related compounds, the U.S. believes that no inventory
is complete without the inclusion of these emissions;
therefore, emission estimates for several Class I and
Class II ozone-depleting substances are provided in
Table H-6. It should be noted that the use of these
compounds is declining as the U.S. fulfills its obliga-
tions under the Montreal Protocol. Also, the effects of
these compounds on radiative forcing are not provided
here. Although CFCs and related compounds have
very large direct GWPs, their indirect effects are
believed to be negative, possibly equal in magnitude to
their direct effects. Given the uncertainties surround-
ing the net effect of these gases, they are reported here
on a full molecular basis only.
Table II-6. U.S. Emissions of ODSs and Related
Compounds for 1990
(Million Metric Tonnes; Molecular Basis)
Compound
Class I
CFC-11
CFC-12
CFC-113
CFC-114
CFC-11 5
Carbon Tetrachloride
Methyl Chloroform
Halon-1211
Halon-1301
Class II
HCFC-22
HCFC-141b
HCFC-124
Emissions
0.06
0.1
0.05
0.005
0.003
0.03
0.3
0.001
0.001
0.08
0.002
0.03
Emissions of ODSs were estimated by the U.S.
EPA using the Atmospheric and Health Effects Frame-
work (AHEF) model. The EPA model starts with
global production forecasts for each compound and
estimates U.S. consumption based on forecasted
regional shares. These data are further subdivided by
end-use.
With the exception of solvents, emissions from
ODSs and related compounds are not instantaneous,
occurring gradually over time, i.e., emissions in a
given year are the result of both ODS and related
compound use in that year and their 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.
i " .'.' ' : "
The emission estimates provided here account
for ODS use in both the current year and in previous
years. Uncertainties exist over the levels of produc-
tion, data sources, and emissions profiles that are used
by the model to estimate yearly emissions for each
compound.
Methyl chloroform, CFC-12, and HCFC-22 were
three of the most prevalent ODS emissions in 1990,
1991, and 1992. In .1990, an estimated 316 thousand
40
-------
metric tonnes of methyl chloroform were emitted into
the atmosphere, along with an estimated 112 thousand
metric tonnes of CFC-12, and 82 thousand metric
tonnes of HCFC-22. In contrast, emissions of HCF-
134a, a replacement compound, were O.5., 0.9, and 1.2
thousand metric tonnes from 1990 through 1992.
However, while the use of methyl chloroform, CFC-12,
and HCFC-22 is declining, the use of HFC-134a, a
CFC substitute, is showing a marked increase.
2. NOx, NMVOCs, and CO
In addition to the main greenhouse gases ad-
dressed above, many industrial processes generate
emissions of criteria air pollutants. Total U.S.- emis-
sions of NOx, NMVOCs, and CO from non-energy
industrial processes in 1990 are reported by detailed
source category in Table II-7. Emissions for 1991 and
1992 are summarized in Table II-8. The emission
Table II-7. U.S. Emissions of NOx, CO and NMVOCs from Industrial Processes: 1990
(Thousand metric tonnes)
Source Category
CHEMICAL AND ALLIED PRODUCT MANUFACTURING
Organic Chemical Manufacturing
Inorganic Chemical Manufacturing
Polymer & Resin Manufacturing
Agricultural Chemical Manufacturing
Paint, Varnish, Lacquer, Enamel Manufacturing
Pharmaceutical Manufacturing
Other Chemical Manufacturing
METALS PROCESSING
Nonferrous Metals Processing
Ferrous Metals Processing
Metals Processing NEC
OTHER INDUSTRIAL PROCESSES
Agriculture, Food, & Kindred Products
Textiles, Leather, & Apparel Products
Wood, Pulp & Paper, and Publishing Products
Rubber and Miscellaneous Plastic Products
Mineral Products
Machinery Products ,
Electronic Equipment
Transportation Equipment
Miscellaneous Industrial Processes
STORAGE AND TRANSPORT . .
Bulk Terminal & Plants
Service Stations
. Organic Chemical Storage & Transport
Inorganic Chemical Storage & Transport
Bulk Materials Storage
TOTAL3
a . Totals may not add due to independent rounding.-
Source: U.S EPA, 1993b
N0x
38
17
21
251
.
34
24
48
1
5
0
70
0
196
2
1
0
6
2-
0
1
715
CO
259
86
17
15
~
0
1339
622
1265
0
0
0
596
0
39
0
11
0
5
0
87
o .
5
4,346
NMVOC
621
34
284
23 ..
10
230
405
18
47 '
0
230
9
40
42
13
3
0
0
96
597
645
- 141
0
0
3,488
41
-------
estimates in this section were taken directly from the
U.S. EPA's National Air Pollutant Emissions Trends,
1900 - 1992 (U.S. EPA, 1993b). This EPA report
provided emission estimates of these gases by sector,
using a "top down" estimating procedure: the emis-
sions were calculated either for individual sources or
for many sources combined, using basic activity data
(e.g,, the amount of raw material processed) as an
indicator of emissions. National activity data were
collected for individual source categories from various
agencies. Depending on the source category, these
basic activity data may include data on production, fuel
deliveries, raw material processed, etc.
Activity data are used in conjunction with
emission factors, which relate the quantity of emissions
to the activity. Emission factors are generally available
from the U.S. EPA's Compilation of Air Pollutant
Emission Factors, AP-42 (U.S. EPA, 1985). The EPA
currently derives the overall emission control effi-
ciency of a source category from a variety of sources,
including published reports, the 1985 NAPAP (Na-
tional Acid Precipitation and Assessment Program)
emissions inventory, or other EPA data bases.
Table II-8. U.S. Emissions of NOx, CO, and NMVOC from Industrial Processes: 1091-1992
(Thousand metric tonnes)
Source
Chemical & Allied Product Manufacturing
Metals Processing
Other Industrial Processes
Storage and Transport
TOTAL8
NO
1991
363
72
270
3.
708
1992
364
71
273
3
710
CO
1991
1,729
1,807
645
93
4,275
1992
1,699
1,794
655
91
4,239
NMVOC
1991
1,613
63
431
1,387
3,494
1992
1,595
64
431
1,295
3,385
a Totals may not add due to independent rounding. .
Source: U.S EPA, 1993b
42
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PART HI. EMISSIONS FROM SOLVENT USE
MMVOCs from Solvents
(70%) Othei
Solvents (30%)
The use of solvents and other chemical
products can result in emissions of various green-
house and photochemically important trace gases.
Nonmethane VOCs, commonly referred to as
"hydrocarbons," are the primary gases emitted ,
from most processes employing organic or petro-
leum-based solvents, along with small amounts of
carbon monoxide (CO) and oxides of nitrogen
Emissions from solvent use in the U.S. consist
mainly of VOCs, along with trace amounts of CO
and NOx. VOC emissions from solvent use showed
a slight decline from 1990 to 1991, while emissions
of CO and NOx remained relatively stable for the
period 1990 - 1992 (Table III-l). Surface coatings
accounted for the majority of emissions from
solvent use (over 40 percent), while "non indus-
trial" uses accounted for about 30 percent of the
emissions during the same period. Emissions from
dry cleaning accounted for slightly over three
percent of the yearly emissions from solvents use.
VOC emissions from solvent use accounted for
about 30 percent of 1990 overall VOC emissions..
Although a comparatively minor source category
in.the U.S., emissions from solvent use have been
reported separately by the U.S. to be consistent with
the reporting guidelines recommended by the IPCC. :
These guidelines identify solvent use as one of the
major source categories for which countries should
report emissions. In the U.S. 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 use
include: .
v Degreasing
Graphic arts
Surface coating
Other industrial uses of solvents (i.e.,
electronics, etc.)
Dry cleaning
Non-industrial uses (i.e., uses of paint
thinner, etc.) .
Table III-l. Emissions of VOC, NOx, and CO from Solvent Use: 1990 - 1992
(Thousand Metric Tonnes)
Gas
VOCs
N0x
CO
1990
5,740
2
2
1991
5,499
2
2
1992
5,498 - '.
3
2
Source: EPA (1993a).
43
-------
Table III-2 contains detailed 1990 emission
estimates from solvents by the major source categories.
Estimates of emissions from solvents came from
U.S. EPA (1993a), which estimated emissions based on
a "bottom up" process. This process involves aggre-
gating solvent use data based on information relating to
solvent uses from different sectors such as degreasing,
graphic arts, etc. Emission factors for each consump-
tion category are then applied to the data to estimate
emissions. For example, emissions from surface
coatings are mostly due to solvent evaporation as the
coatings solidify. By applying the appropriate solvent
emission factors to the type or types of solvents used
for surface coatings, an estimate of emissions can be
obtained.
Table III-2. U.S. Emissions of VOCs, NOx, and CO by Category: 1990
(Thousand Metric Tonnes)
Source
Degreasing
Graphic Arts
Surface Coating
Other Industrial
Dry Cleaning
Non-Industrial
Total
VOCs
682
621
' 2,375
149
190
1,723
5,740
N0x
+
+
2
+
NA
NA
2
CO
1
+
1
+
NA
NA
2
Source: EPA (1993a).
Note: "+" Denotes less than 453.5 metric tonnes (500 short tons).
44'.
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PART IV. EMISSIONS FROM AGRICULTURE
Total US Emissions by Source: 1990
(MMT Carbon Equivalent)
1396
1444
1000
Energy Industry Agriculture Forestry Wastes NetYotal
Source
Agricultural activities contribute directly to
emissions of greenhouse gases through a variety of
different processes. This part of the U.S. inventory
presents emission estimates for five types of agricul-
tural activities: management of domestic livestock,
management of domestic livestock and poultry manure,
cultivation of rice, fertilizer use, and field burning of
agricultural crop wastes. Several other agricultural
activities, such as irrigation and tillage practices, may
contribute to greenhouse gas emissions, but emissions
from these sources are uncertain and are believed to be
insignificant.1 Agriculture-related land-use change
activities, such as conversion of grassland to cultivated
land, are discussed in part V of this inventory.
In 1990, agricultural activities were responsible
for emissions of 65 MMTCE, or approximately 5
percent of total U.S. emissions. Methane (CH4) is the
most significant gas emitted by agricultural activities,
accounting for 52 MMTCE. Domestic livestock,
manure management, rice cultivation, and field burning
of agricultural crop wastes are all sources of methane.
In 1990, domestic livestock and manure management
together were responsible for 94 percent of methane
emissions from agricultural activities, and about 30
percent of total methane emissions from all anthropo-
genic activities in the U.S. Of all domestic animal
types, beef and dairy cattle are by far the largest
emitters of methane. Management of cattle and their
manure account for about 75 percent of U.S. methane
emissions from all agricultural activities. Rice cultiva-
tion and agricultural waste burning are minor sources
of methane, having released about 5 and 1 percent of
U-.S. methane emissions from agriculture, respectively.
In addition to methane, agricultural activities are
a source nitrous oxide (N2O), carbon monoxide (CO),
and nitrogen oxides (NOx). Fertilizer use is a major
contributor to nitrous oxide emissions, responsible for
about 44 percent of total U.S. emissions. Agricultural
crop waste burning is a source of nitrous oxide, carbon
monoxide, and nitrogen oxides, in addition to methane.
However, as with methane, agricultural crop waste
burning accounts for less than 1 percent of total U.S.
emissions of each gas.
A. METHANE EMISSIONS FROM
ENTERIC FERMENTATION IN DOMESTIC
LIVESTOCK
Methane Emissions from Agriculture by Source: 1990
Agricultural Waste
Burning (1%)
Manure Management
(26%)
Rice Cultivation (5%)
I Enteric Fermentation
Methane is a natural by-product of animal
digestion. During digestion, methane is produced
through a process referred to as enteric fermentation
in which microbes that reside in animal digestive
systems break down feed consumed by the animal
Ruminants, which include cattle, buffalo, sheep, and
goats, have the highest methane emissions among all
animal types because of their unique digestive system.
Ruminants possess a rumen, or large "fore-stomach,"
in which a significant amount of methane-producing
fermentation occurs. Non-ruminant domestic ani-
mals, such as pigs and horses, have much lower
methane emissions than ruminants because much
less methane-producing fermentation takes place in
their digestive systems. The amount of methane
produced and excreted by an individual animal
depends upon its digestive system (i.e., whether or not
it possesses a rumen), and the amount and type of
feed it consumes.
1 Irrigation associated with rice cultivation is included in this inventory.
V 45
-------
Enteric fermentation in domestic livestock is a
major source of methane in the U.S. Emissions in
1990 are estimated to have been approximately 28 to
42 MMTCE. This represents about 22 percent of
total U.S. methane emissions, and about 68 percent of
methane emissions from the agriculture sector.
Of all domestic livestock, cattle are by far the
largest source of methane. In 1990, cattle accounted
for 95 percent of total emissions from enteric fermen-
tation in domestic livestock; of total cattle emissions,
beef cattle accounted for 73 percent, and dairy cattle
the rest. The North Central and South Central states
each account for roughly 35 percent of emissions
from beef cattle, primarily due to the large beef cattle
populations managed in those states. The North
Central, West, and North Atlantic states each account
for roughly 43, 20, and 18 percent of emissions from
dairy cattle. Tliese regional contributions are also
largely a reflection of the large dairy cattle popula-
tions in those states.
Emissions from enteric fermentation in domes-
tic livestock increased by about 0.8 percent per year
between 1990 and 1992, and by about 1 percent in
1993. This increase is primarily due to increasing
beef cattle populations. Methane emissions from
enteric fermentation in the U.S. ranged from 28 to 42
MMTCE in 1991,28 to 43 MMTCE in 1992, and 29
to 43 MMTCE in 1993.
Methane is produced during the normal digestive
processes of animals. During digestion, feed con-
sumed by the animal is fermented by microbes resident
in the digestive system. This microbial fermentation
process, referred to as enteric fermentation, produces
methane as a by-product, which is exhaled or eructated
by the animal. The amount of methane produced and
excreted by an individual animal is dependent prima-
rily upon the animal's digestive system, and the
amount and type of feed it consumes.
Among animal types, the ruminant animals (i.e.,
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 consumed feed into soluble products that can be
utilized by the animal. The microbial fermentation that
occurs in the rumen enables ruminants to digest coarse
plant material that non-ruminant animals cannot digest.
Ruminant animals have the highest methane emissions ,
among all animal types because a significant amount of
methane-producing fermentation occurs within the
rumen.
Non-ruminant domestic animals, such as pigs,
horses, mules, rabbits, and guinea pigs, also produce
methane through enteric fermentation, although this
microbial fermentation occurs in the large intestine.
The non-ruminants have much lower methane emis-
sions than ruminants because much less methane-
producing fermentation takes place in their digestive
systems.
In addition to the type ofidigestive system that an
animal possesses, its feed intake also affects the
amount of methane produced and excreted. In general,
the higher the feed intake, the higher the methane
emissions. Feed intake is positively related to animal
size, growth rate, and production (i.e., milk production,
wool growth, pregnancy, or work). Therefore, feed
intake varies among animal types as well as among
different management practices for individual animal
types.
This section presents estimates of methane
emissions resulting from enteric fermentation in
domestic livestock. The emission estimates were
obtained or derived from U.S. EPA (1993a). Only
animals managed by humans for production of animal
products, including meat, milk, hides and fiber, and
draft power are included.2 Although methane emis-
sions from non-ruminants are significantly less than
those for ruminants, both animal types are included in
order to produce a complete inventory.
U.S. EPA (1993a) contains estimates of methane
emissions from domestic livestock in the U.S. for the
year 1990. To derive these estimates, U.S. EPA
developed emission factors for representative animal
types and then multiplied the emission factors by
applicable animal populations. The resultant emissions
by animal type were then summed over all animal
a Wild animals also produce methane emissions. The principal wild animals that contribute to U.S. emissions are wild
ruminant animals such as antelope, caribou, deer, elk, and moose. Termites have also been identified as a potentially
Important source of methane emissions and are generally examined separately from other wild animals. These sources are
not included the U.S. inventory because they are not considered anthropogenic.
46
-------
types to estimate total annual methane emissions. The
emission estimates for 1990 presented here were taken
directly from U.S. EPA (1993a); emission estimates for
1991, 1992, and 1993 were derived using the emission
factors in U.S. EPA (1993a) and 1991, 1992, and 1993
animal population statistics from the U.S. Department
of Agriculture (USDA) National Agricultural Statistics
Service and the.USDA Economic Research Service.
The principal uncertainty in estimates of methane
emissions from livestock digestion results from the
large diversity of animal management practices found
in the U.S., all of which cannot be precisely character-
ized and evaluated. Also, the methodological assump-
tions used to derive emission factors are only as
accurate as the experimental data upon which they are
based. Nevertheless, significant scientific literature
exists that describes the quantity of methane produced
by individual ruminant animals, particularly cattle.
Also, cattle production systems in the U.S are well
characterized compared to other livestock management
systems in the U.S.
For these reasons, it is possible to estimate
methane emissions from cattle in the U.S. using fairly
detailed analyses of feeding practices and production
characteristics. Also, due to their large population,
large size, and particular digestive characteristics,
cattle account for the majority of methane emissions
from livestock in the U.S. Therefore, estimates of
emissions from cattle presented below are based on a
detailed analysis that accounts for regional differences
in sizes, ages, feeding systems, and management
systems among cattle subgroups.
Methane emissions from other animals account
for a very small fraction of total methane emissions
from livestock in the U.S. Also, the variability in
emission factors for each of these other animal types
(e.g., variability by age, production system, and
feeding practice within each animal type) is much
smaller than for cattle. Therefore, emissions from each
, of these other animal types are derived using a more
simple analysis that is based on average emission
factors representative of entire populations of each
animal type.
1.
Methane Emissions from Cattle
In order to derive emission factors representative
of the diverse types of cattle found in the U.S., U.S.
EPA (1993 a) applied a mechanistic model of rumen
digestion and animal production (Baldwin et al., 1987)
to 32 different diets and 9 different cattle types.3 The
cattle types (listed in Table IV-1) were defined to
represent the different sizes, ages, feeding systems, and
management systems that are typically found in the
U.S. Representative diets were defined for each
category of animal, reflecting the diverse feeds and
forages consumed by different types of cattle in
different regions of the U.S. Using the mechanistic
model, an emission factor was derived for each combi-
nation of animal type and representative diet. Based
upon the extent to which each diet is used in each of
five regions of the U.S., regional average emission
factors for each of the 9 cattle types were derived.4
These emission factors were then multiplied by the
applicable animal populations in each region, and the
results were summed over all cattle types and all
regions to produce the total emissions estimate for U.S.
cattle.
The methodology employed in U.S. EPA (1993a)
is a detailed version of the draft Tier 2 methodology
recommended by the IPCC (IPCC/OECD, 1994). This
greater level of detail used in the analysis is possible
because of in-depth scientific understanding of cattle
digestion processes typical of the U.S., as well as the
availability of extensive data on U.S. cattle production ,
systems.
National weighted-average emission factors, and
national populations, for each of the nine animal types
analyzed by U.S. EPA (1993a) are presented in Table
IV-1. The regional data from which these numbers
were derived, as well as.a more detailed discussion of
the methodology used to derive the emission factors,
are presented in Annex C. Total methane emissions
from the U.S. cattle herd in 1990 are estimated to be
5.54 million metric tonnes CH4 (33.2 MMTCE).
Methane emissions from beef cattle account for about
73 percent of this total, and dairy cattle the rest.
Regional variability in methane emissions from
3 The basic model of Baldwin et al. (1987) was revised somewhat to allow for evaluations of a greater range of animal
types and diets. See U.S. EPA (1993a) for more detail.
, 4 Feed intake of bulls does not vary significantly by region, so only a national emissions factor was derived for this
cattle type.
47.
-------
cattle is largely a reflection of the uneven distribution
of cattle populations across the U.S. (see Table IV-2).
The North Central and South Central states each
account for roughly 35 percent of emissions from beef
cattle, primarily due to the large beef cattle populations
managed in those states. The North Central, West, and
North Atlantic states, which support large dairy herds,
each account for roughly 43, 20, and 18 percent of
emissions from dairy cattle. The North Central states
account for approximately 40 percent of total methane
emissions from all cattle.
There are a variety of factors that make the 1990
emissions estimate uncertain. First, animal population
and production statistics, particularly for range fed
cattle, are uncertain. Second, the diets analyzed using
the rumen digestion model are broad representations of
the types of feed consumed within each region, so the
full diversity of feeding strategies is not represented.
And last, the rumen digestion model is itself uncertain
since it was validated using uncertain experimental
data. Together, these sources of uncertainty result in
an overall uncertainty of about ฑ 20 percent in the
emission estimate (U.S. EPA, 1993a). Applying this
uncertainty range to the national emission estimate
results in low and high estimates of 4.40 and 6.65
million metric tonnes CH4 (26 to 40 MMTCE). .
Table IV-1. Methane Emissions from U.S. Cattle in 1990, By Animal Type
Animal Type
Dairy Cattle
Replacements 0-12 months8
Replacements 12-24 months3
Mature Cows
Subtotal
Beef Cattle
Replacements 0-12 monthsa
Replacements 12-24 months"
Mature Cows
Weanling System Steers/Heifersb
Yearling System Steers/Heifersc
Bulls
Subtotal
Total Cattle
Emission Factor
(kg/head/yr)
19.6
58.8
114.6
80.4
22.3
65.0
66.7
23.1
47.3
100.0
47.5
Population
(103 head)
4,205
4,205
10,130
18,540
5,535
5,535
33,478
5,260
21,040
2,200
85,398
103,938
Emissions
(106 metric tonnes)
0.082
0.247
1.161
1.490
0.124
0.360
2.234
0.122
0.994
0.220
4.054
5.544
a A portion of the offspring are retained to replace mature cows that die or are removed from the herd
(culled) each year. Those that are retained are called "replacements."
b In "weanling systems," calves are moved directly from weaning to confined feeding programs. This system
represents a very fast movement of cattle through to marketing. Weanling system cattle are marketed at about
420 days of age (14 months).
c "Yearling systems" represent a relatively slow movement of cattle through to marketing. These systems include
a wintering over, followed by a summer of grazing on pasture. Yearling system cattle, are marketed at 565 days
of age (18.8 months).
Source: U.S. EPA, 1993a.
-------
Table IV-2. Methane Emissions from U.S. Cattle in 1990, By Region
Region
North Atlantic
South Atlantic
North Central
South Central
West -
National Total
Dairy Cattle Emissions
(106 metric tonnes)
0.267
0.111
0.644
0.166
0.303
1.490
Beef Cattle Emissions
(106 metric tonnes)
0.031
"0.315
1.442
1.402
0.865
4.054
Total Regional Emissions
(106 metric tonnes)
0.298
0.426
2.086 '
1.568,
1.168
5.544
Source: U.S. EPA, 1993a.
Emission estimates for 1991, 1992, and 1993
were derived using the nationally weighted-average
emission factors for each cattle type from U.S. EPA
(1993a) and national populations from the USDA
(1994a, 1994b, 1994d). The following factors should
be considered when assessing these emission estimates:
1
Because all estimates were done nationally
(rather than regionally), regional shifts in
animal populations were not considered.
There continues to be a shift in dairy cows
away from the North Central U.S. and toward
the West. This shift, which would affect
emissions since emission factors vary region-
ally, is not reflected in these estimates.
Emission factors for mature dairy cattle were
increased to reflect higher feed intakes in
1991, 1992, and 1993, relative to 1990. The
higher feed intakes were implemented to
increase milk production per cow.
The mix of Weanling and Yearling slaughters
was kept~constant. Although we believe that
there has been a shift toward more Weanling
slaughters, this change has not been quantified.
Total methane emissions from the U.S. cattle
herd in 1991, 1992, and 1993 are estimated to be S.59
million metric tonnes CH4 (33.5 MMTCE), 5.63
million metric tonnes CH4 (33.8 MMTCE), and 5.70
million metric tonnes CH4 (34.2 MMTCE), respec-
tively (see Table IV-3). Assuming an uncertainty ,
range of ฑ 20 percent, emission estimates for 1991,
1992, and 1993 are between 4.5 and 6.7 million metric
tonnes CH4 (27 and 40 MMTCE), between 4.5 and 6.8
million metric tonnes CH4 (27 and 41 MMTCE), and
between 4.6 and 6.8 million metric tonnes CH4 (27 and
41 MMTCE), respectively. The growth in emissions,
0.7 percent per year between 1990 and 1992 and 1.2
percent per year between 1992 and 1993, is due
primarily to increasing beef cattle populations. The
higher emissions per head for dairy cattle in 1991-
1993, relative .to 1990, was largely offset by smaller
populations, resulting in relatively flat dairy emissions
for the four-year period.
Table IV-3. Methane Emissions from U.S. Cattle: 1991-1993 (106 metric tonnes)
Cattle.Type
Dairy
Beef
Total Cattle
1991
1.51
4.08
5.59
1992
1.50
4.13
5.63
1993
1.50
4.20
5.70
Sources: Emission factors from U.S. EPA (1993a). Cattle populations from USDA (1994a,
1994b, 1994d).
' 49
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2. Methane Emissions from Other
Domestic Animals
Methane emissions from other domestic animals
(i.e., sheep, goats, pigs, and horses) were estimated by
U.S. EPA (1993a) using emission factors from Crutzen
et al. (1986) and population data from FAO (1991) and
USDA (1994b, 1994e).5 These emission factors are
representative of typical animal sizes, feed intakes, and
feed characteristics in developed countries. The
methodology and emission factors employed in U.S.
EPA (1993a) are the same as those recommended by
the IPCC (IPCC/OECD, 1994).
In 1990, total methane emissions from other
animals are estimated to be 275 thousand metric tonnes
CH4 (1.7 MMTCE) (Table FV-4). The uncertainty in
tin's estimate is probably greater than that for the cattle
emissions estimate because a less detailed analysis was
performed. However, since cattle account for over 95
percent of the emissions from all domestic livestock,
the uncertainty in the cattle estimates drive the overall
uncertainty for all livestock. Therefore, the same
uncertainty range that was applied to cattle (20 per-
cent) has been applied to other animals (U.S. EPA,
I993a). This results in low and high estimates of 200
and 350 thousand metric tonnes CH4 (1.2 to
2.1 MMTCE).
Enteric fermentation emissions from other
animals changed little from 1990 to 1993. This is a
reflection of very slight fluctuations in other animal
populations and the small magnitude of the emission
source. The emission factors, populations, and total
emission estimates for each of the inventory years are
presented in Table IV-4.
B. METHANE EMISSIONS FROM
. MANURE MANAGEMENT
Methane Emissions from Agriculture by Source: 1990
Agricultural-Waste
Burning (1%)
Manure Management
(26%)
:
Enteric Fermei
Rice Cultivation (5%)
When animal manure decomposes in an
anaerobic environment, decomposition of the organic
material in the manure produces methane. The way
in which manure is managed is the most important
factor affecting the amount of methane produced,
since certain types of storage and treatment systems
promote an oxygen-free environment. In particular,
liquid systems, e.g., lagoons, ponds, tanks, or pits,
tend to produce a significant quantity of methane.
When manure is handled as a solid or when it is
deposited on pastures and rangelands, it tends to
decompose aerobically and produce little or no
methane. JUigher temperatures and moist climatic
conditions also promote methane production.
Table IV-4. Methane Emissions from Other Animals
Animal
Sheep
Goats
Pigs
Horses
Total
Emission
Factor
(kg/head/yr)
8
5
1.5
1.8
Population (103 head)
1990 1991 1992 1993
11,364 11,000 10,750 10,013
1,900 1,900 1,900 1,900
53,852 54,477 57,684 58,116
5,215 5,215 5,215 5,215
--
Emissions (106 metric tonnes)
1990 1991 1992 1993
0.09 0.09 0.09 0.08
0.01 0.01 0.01 0.01
0.08 0.08 0.09 0.09
0.09 0.09 0.09 0.09
0.27 0.27 0.28 0.27
Sources: Emission factors from Crutzen et al. (1986). Populations from FAO (1991) and USDA (1994b, 1994e).
5 Population data for goats and horses were not realdily available for 1991 and 1992. These emissions are small and
were assumed to be constant.
50
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In 1990, emissions from manure management
are estimated to have been approximately 10 to 22
MMTCE. this represents about 8 percent of total
U.S. methane emissions, and about 26 percent of
methane emissions from the agriculture sector.
Liquid-based manure systems account for over 80
percent of the total emissions from manure manage-
ment. Of the animal manure types included in the
analysis, swine manure is the highest emitter, respon-
sible for about 49 percent of total emissions. Dairy
cattle manure accounts for about 32 percent of the
U.S. total.
Emissions from manure management decreased
by 6.4percent in 1991. This decrease is the result of
numerous factors, including changes in total animal
populations, manure production rates, distribution of
waste systems, and distribution of animal types.
Methane emissions increased by 2 percent in 1992
and 3.5 percent in 1993. These increases reflect
changes in animal populations, including higher beef
and swine populations and a redistribution of dairy
cattle towards lagoon management systems (which
are characterized by higher methane emission rates).
Animal manure is primarily composed of organic
material and water. When animal waste decomposes in
an anaerobic environment (i.e., in the absence of
oxygen), the organic material in the waste is broken
down by methanogenic bacteria that are present in the
waste. Methane, .carbon dioxide, and stabilized organic
material are produced as end products.
The principal factors that affect the amount of
methane produced during decomposition axe the way in
which the manure is managed and the climatic environ-
ment in which the manure decomposes. Methane
production will only occur under anaerobic conditions.
Therefore, when manure is stored or treated in systems
that promote an oxygen-free environment (e.g., as a
liquid in lagoons, ponds, tanks, or pits), the manure
tends to produce a significant quantity of methane.
When manure is handled as a solid (e.g., in stacks or
pits) or when it is deposited on pastures and range-
lands, it tends to decompose aerobically and produce
little or no methane. Air temperature and moisture also
affect the amount of methane produced since they
influence the growth of the bacteria responsible for
methane formation. Methane production generally
increases with rising temperature. Also, for non-liquid
based manure systems, moist conditions (which are a -
function of rainfall and humidity) favor methane
production.
The composition of the manure also affects the
amount of methane produced. Manure composition
depends on the composition and digestibility of the
animal diet. The greater the energy content and
digestibility of the feed, the greater the amount of
methane that potentially could be produced by the
resulting manure. For example, feedlot cattle fed a
high energy grain diet produce a highly biodegradable
manure with a high methane-producing capacity.
Range cattle feeding on a low energy forage diet
produce a less biodegradable manure with only half the
methane-producing capacity of feedlot cattle manure.
However, as described above, in either case the amount
of methane that is actually produced and emitted to the
atmosphere depends largely on the way that the manure
is managed.
Like those from enteric fermentation, estimates
of methane emissions from manure management were
obtained or derived from U.S. EPA (1993a). The 1990
emission'estimates were taken directly from U.S. EPA
(1993a); emission estimates for 1991, 1992, and 1993
were derived using the emission factors in U.S. EPA
(1993a) and animal population statistics from the
USDA. As with enteric fermentation emissions, only
animals managed by humans for production of animal
products, including meat, milk, hides and fiber, and
draft power, are included.
The methodology employed in U.S. EPA (1993a)
to derive 1990 methane emission estimates for manure
management in the U.S. is based on the approach
developed by Safley et al. (1992a), and is consistent
with the draft Tier 2 methodology recommended by the
IPCC (IPCC/OECD, 1994). This methodology con-
sists of the following steps:
51
-------
(1) Estimate annual methane emissions for each animal type z and manure system/ in each state k:
Annual methane emis-
sions for each animal
type ; and manure
management system/ in
each state k
number of animals of type i in state k x typical animal mass of
animal i x average annual volatile solids6 production per unit of
animal mass for animal / x the methane producing capacity7 of
the manure of animal / x the methane conversion factor8 of the
manure system/ in the state k x the percent of animal /'s manure
managed in manure system/ in state k
(2) Estimate total annual methane emissions for animal i by summing annual emissions over all applicable
manure management systems/ and states k.
(3) Estimate total annual methane emissions from all animals by summing over all animal types i.
The data used to derive the estimate of emissions
from animal manure (Le.} animal populations, sizes,
and volatile solids production; maximum methane
producing capacities; methane conversion factors; and
manure system usages) are presented in Annex C.
These data were obtained from the U.S. Census of
Agriculture, the U.S. Department of Agriculture,
livestock manure management experts throughout the
U.S., and the scientific literature. Specific sources for
the data are also noted in Annex C. Some of the
animal populations used by U.S. EPA in these calcula-
tions are estimates as of 1987, since this was the last
year for which detailed data could be obtained. There-
fore, the 1990 emissions estimate is based on changes
in animal production and population between 1987 and
1990 for several animal types.
Based on these data, total 1990 methane emis-
sions from manure management are estimated to be 2.3
million metric tonnes CH4 (14 MMTCE). Liquid-
based manure systems account for over 80 percent of
the total emissions (Table IV-5). Of the animal manure
types included in the analysis, swine manure is the
highest emitter, responsible for about 50 percent of
total emissions. Dairy cattle manure accounts for
about 30 percent of the U.S. total.
Uncertainties in these point estimates result from
assumptions concerning several factors used in the
calculations. In particular, the methane conversion
factors (MCFs) are based on dry manure, and therefore
they may be underestimates for dry, open air systems
(i.e., pasture, range, drylots, solid storage, and pad-
docks) in regions of the U.S. with significant rainfall.
Also, the methane-producing potential of liquid/slurry
and pit storage manure systems may be greater than
assumed in this analysis. To account for these uncer-
tainties, U.S. EPA developed low and high emission
estimates by varying the MCFs for different manure
management systems! (A discussion of the derivation
of the low and high estimates is provided in Annex C.)
The resultant range in emissions is 1.7 to 3.6 million
metric tonnes CHA(10 to 22 MMTCE) (see Table IV-5).
Emission estimates for 1991, 1992, and 1993
were derived using the methodology described above
and state populations from the National Agricultural
Statistics Service of the USDA. However, several
changes were made to the 1990 assumptions before
they were used to estimate 1991-1993 methane emis-
sions, including:
a change in the distribution of waste systems
utilized for a limited number of states (based
on interviews with persons familiar with
manure management practices in their respec-
tive states), and
* Volatile solids (VS) are defined as the organic fraction of the total solids in manure that will oxidize and be driven off
as a gas at a temperature of 600ฐC. Total solids are defined as the material that remains after evaportion of water at a
temperature between 103ฐ and 105ฐC. ' ,
1 The methane producing capacity of the manure for a particular animal type is the maximum amount of methane that
can be produced per kilogram of volatile solids, and varies by animal type and diet.
8 The methane conversion factor is the extent to which the maximum methane producing potential is realized for a given
manure management system and climate.
52
-------
an increase in the Volatile Solids (VS) produc-
tion figure for dairy cows from 10.0 to 10.9
kg/day/1000 kg animal mass to reflect increas-
ing feed intake ofxlairy cows.
Emissions from manure management decreased
to 2.13 million metric tonnes (12.8 MMTCE) in 1991.
This decrease is the result of numerous factors
(including changes in total animal populations,
distribution of waste systems, and distribution of
animal types) and cannot be attributed to a single
animal type or management technique. For example,
while the population and feed intake of dairy cattle
increased, the distribution of waste systems utilized in
some states shifted away from the higher methane-
generating practices. Although these changes should
have opposite effects on methane emissions, the net
effect was a decrease in total -dairy emissions.
Methane emissions increased to 2.18 million
metric tonnes (13.1 MMTCE) in 1992 and 2.25 million
metric tonnes (13.5 MMTCE) in 1993. This increase is
Table FV-5. Range of Methane Emission Estimates from Manure Management: 1990
MANURE MANAGEMENT
Solid Systems
Pasture/Range
Drylot
Solid Storage
Other Solid Systems2
Total Solid Systems'1
Liquid Systems
Liquid/Slurry Storage
Pit Storage
Anaerobic Lagoon
Total Liquid Systemsd
Totald
Low
(106 metric tonnes)
SYSTEM
.
0.09
0.02
O.01
0.15
0.26
. 0.19
0.21
1.04
1.44
1.70
Point Estimate
(106 metric tonnes)
0.12
0.03
<0.01
0.26
0.41
0.21
0.23
1.42
1.87
2.28
High
(106 metric tonnes)
0.59
0.15
0.02
0.54
1.30
0.42
0.46
1.42
2.30
3.60
ANIMAL TYPE '
Beef
Dairy
' . Swine
Poultry6
Other0
Total"
0.13
0.56
0.85
0.14
0.02
1.70
0.17
0.73
1.12
0.23
0.02
2.28
-. 0.67
1.04
1.43
0.38
0.09
3.60
a Other solid systems include litter, deep pit stacking, and paddocks.
b Includes broilers, layers, turkeys, and ducks.
c Includes sheep, goats, horses, mules, and donkeys.
d Totals may not add due to rounding.
53
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Table IV-6. Methane Emissions from Manure Management: 1991 - 1993
Dairy
Beef
Swine
Other
1991
Population Emissions
(103 head) (10s metric tonnes)
14,376 0.71
89,746 0.18
54,477 1.00
0.24
2.13
1992
Population Emissions
(103 head) . (10* metric tonnes)
14,104 0.70
90,857 0.19
57,684 1.05
0.24
2.18
1993
Population Emissions
(103 head) (10s metric tonnes)
14,062 0.71
91,929 0.19
57,798 1.11
0.24
2.25
due primarily to changes in animal populations, most
notably in New Mexico and California, both of which
rely on liquid-based management systems. These
results are summarized in Table IV-6.
C. METHANE EMISSIONS FROM RICE
CULTIVATION
Mothana Emissions from Agriculture by Source: 1990
Agricultural Waste
Burning (1%)
Manure Management
(26%)
EniafK Fermentation
(68%)
Rice Cultivation (5%)
Most of the world's rice, and all of the rice in
the U.S., is grown on flooded fields. Wlien fields are
flooded, anaerobic conditions in the soils develop,
and methane is produced through anaerobic decom-
position of soil organic matter. Methane is released
primarily through the rice plants, which act as
conduits from the soil to the atmosphere.
Rice cultivation is a very small source of
methane in the U.S. In 1990, methane emissions
front this source are estimated to have been approxi-
mately 0.65 to 4.5MMTCE. This represents less than
1 percent of total U.S. methane emissions from all
sources, and about 4 percent of U.S. methane emis-
sions from agricultural sources. Seven states grow
rice: Arkansas, California, Florida, Louisiana,
Mississippi, Missouri, and Texas. Emissions from
Arkansas account for about 35 percent of the total,
primarily because it has the largest rice area har-
vested. Louisiana, which has a longer growing
season, has the second highest level of emissions,
accounting for about 25 percent of the national total.
Emission estimates increased by about 5
percent between 1990 and 1991, stayed flat between
1991 and 1992, and increased by 2 percent between
1992 and 1993. This is a reflection of the relatively
large areas harvested for most states in 1992. How-
ever, the areas harvested fluctuated inconsistently
from year to year, so the four years of emission
estimates do not suggest a meaningful trend.
Most of the world's rice is grown on flooded
fields. When fields are flooded, aerobic decomposition
of organic material gradually depletes the oxygen
present hi the soils and floodwater, and anaerobic
conditions in the soils develop. Methane is produced
through anaerobic decomposition of soil organic matter
by methanogenic bacteria! However, not all of the
methane that is produced is released into the atmo-
sphere. As much as 60 to 90 percent of title produced
methane is oxidized by aerobic methanotrophic bacte-
ria in the soils (Holzapfel-Pschorn et al., 1985; Sass et
al., 1990). Some of the methane is also leached away
as dissolved methane in floodwater that percolates
from the field. The remaining non-oxidized methane is
transported from the submerged soil to the atmosphere
54
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primarily by diffusive transport through the rice plants.
Some methane also escapes from the soil via diffusion
and bubbling through the 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 1 meter), the lower stems and roots of the
rice plants are dead, thereby effectively blocking the
primary CH4 transport pathway to the atmosphere.
Therefore, while deepwater rice growing areas are
believed to emit methane, the quantities released are
likely to be significantly less than areas with more
shallow, typical flooding depths. Also, some flooded
, fields are drained periodically during the growing
season, either intentionally or accidental!}'. If water is
drained and soils are allowed to dry sufficiently,
methane emissions decrease or stop entirely. This is
due to soil aeration, which not-only causes existing soil
methane to oxidize but also inhibits further methane
production in the soils.
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. Several studies have indicated
that some types of nitrogen fertilizer inhibit methane
generation, while organic fertilizers enhance methane
emissions. However, while it is generally acknowl-
edged that these factors influence methane emissions,
the extent of the influence of these factors individually
or in combination has not been well quantified.
Methane emissions from rice cultivation in the
U.S. were derived using the draft methodology recom-
mended by the IPCC (IPCC/OECD, 1994). This
method utilizes a daily emission factor, which is
multiplied by the harvested area flooded and the
number of days of flooding during the growing season.
Agricultural statisticians in each of the seven states in
the U.S. that produce rice were contacted to determine
water management practices and flooding season
lengths in each state. All rice growing areas in the
U.S. are continually flooded; none are either upland or
deepwater. Because flooding season lengths varied
considerably among states, the IPCC/OECD (1994)
method was applied to each of the seven states sepa-
rately, and results were summed over all states.
Daily methane emission factors were taken from
results of field studies performed in California (Cice-
rone et al., 1983); Texas (Sass et al., 1990, 1991a?
1991b, 1992), and Louisiana (Lindau et al., 1991;
Lindau and Bollich, 1993). A range based on. the
endpoints of the emission rates measured in these
studies - 0.1065 to 0.5639 g/m2/day - was applied to
the areas and season lengths in each state.9 Since these
measurements were taken in rice growing areas of the
U.S., they are representative of rice soil temperatures,
and water and fertilizer management practices typical
of the U.S.
The climatic conditions of southwest Louisiana,
Texas, and Florida allow for a second or "ratoon" rice
crop in those areas. This second crop rice is produced
from regrowth on the stubble after the first crop has
been harvested. The emission estimates presented here
account for this additional harvested area.
Rice, fields for the second crop typically remain
flooded for a shorter period of time than for the first
crop. Recent studies indicate, however, that the
methane emission rate of the second 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 & 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.
To avoid unrepresentative results based upon
fluctuations in economic or climatic conditions, a
three-year average (centered on 1990) for the area
harvested in each state (USDA, 1991; USDA, 1993)
was used to estimate 1990 emissions. Also, since the
9 Two measurements from these studies were excluded when determining the emission coefficient range.- A low seasonal"
average flux of 0.0595 g/m2/day in Sass et al. (1990) was excluded because this site experienced a mid-season accidental
drainage of floodwater, after which methane emissions declined substantially and did not recover for about two weeks. Also,
the high seasonal average flux of 2.041 g/m2/day in Lindau and Bollich (1993) was excluded since this emission rate is -
anomalously high, compared to other flux measurements in the U.S., as well as in Europe and Asia (see IPCC/OECD, 1994).
55
-------
number of days that the rice fields remain permanently
flooded varies considerably with planting system and
cultivar type, a range for the flooding season length
was adopted for each state. Tfie harvested areas and
flooding season lengths for each state are presented in
Table IV-7. Arkansas and Louisiana have the largest
harvested areas, approximately 40 and 20 percent of
the U.S. total, respectively. California, Louisiana, and
Florida have the longest flooding season lengths, 138,
105, and 105 days, respectively.
Total methane emissions for the U.S. in 1990 are
estimated to have been 109-749 thousand metric tonnes
of CH4 (0.65 to 4.5 MMTCE) in 1990 (Table IV-8).
Emissions from Arkansas account for over 35" percent
of tliis total, primarily because it has the largest rice
area harvested. Louisiana, because of its relatively
large rice area and long growing season, has the second
highest level of emissions, accounting for about 25
percent of the national total.
Using the same methodology described above,
methane emissions from rice cultivation were esti-
mated to be 114-784 thousand metric tonnes (0.68-4.7
MMTCE) in 1991, 114-783 thousand metric tonnes
(0.68-4.7 MMTCE) in 1992, and 116-799 thousand
metric tonnes (0.70-4.8 MMTCE) in 1993 (see Table
IV-8). To be consistent with the draft IPCC/OECD
guidelines, three-year averages of areas harvested were
used for each emission estimate (the 1993 emission
estimate, however, was based on a two-year average).
The small increase in total emissions in 1991 and 1992
compared to 1990 (about 5 percent) is a reflection of
the relatively large areas harvested for most states in
1992. However, the areas harvested fluctuated incon-
sistently from year to year, so the three years of
emission estimates do not suggest a meaningful trend.
Table IV-7. Area Harvested and Flooding Season Length for Rice-Producing States
" ' "
State
Arkansas
California
Florida*
primary
ratoon
Louisiana*
primary
ratoon
Mississippi
Missouri
Texas*
primary
ratoon
Total
Area Harvested (ha)
1989
461,352
165,925
5,585
2,792
196,277
58,883
95,103,
31,971
136,787
54,715
1,209,389
1990
485,633
159,854
4,978
2,489
220,558
66,168
101,174
32,376
142,857
57,143
1,273,248
1991
509,915
141,643
8,580
4,290
206,394
62,940
89,033
37,232
138,810
56,700
1,255,536
1992
558,478
159,450
8,944
4,472
250,911
55,484
111,291
45,326
142,048
56,819
1,393,221
1993
497,774
176,851
8,903
4,452
214,488
46,484
99,150
37,637
120,599
48,240
1,254,577
Flooding Season
Length (days)
low
75
123
90
90
75
80
60
. high
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.
56
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Table IV-8. CH4 Emissions from Rice Cultivation in the U.S.
State
Arkansas
California
Florida
Louisiana
Mississippi
Missouri
Texas
Total
Annual Emissions (103 metrie tonnes)3
1990
low
38.8
20.4
0.9
25.9
7.6
2.9
12.5
109.0
hi
273.8
*. 134-4
6.5.
183.0
44.0
19.1
88.3
749.1
1991
low
41.4
20.1
1.1
27.6
8.0
3.3
12.7
114.1
hi
292.1
132.6
7.6
194.5
46.5
21.6
89.4
784.3
1992
low
41.7
20.9
1.3
26.7
8.0
3.4
12.0
114.0
hi
294.4
137.5
8.9
188.7
46.2
22.6
84.7
782.9
1993b
low
42.2 '
22.0
1.3
27.2
8.4
3.5
11.8
116.4
hi
297.8
145.1
9.0
192.0
48.7
23.4
82.9
798.9
a Emission Factor: 0.1065-0.5639 (gCH4/m2/day)
b Emission estimates for 1993 are based on two-year averages for harvested area (i.e., 1992 and 1993).
D. EMISSIONS FROM AGRICULTURAL SOIL
MANAGEMENT
Nitrous Oxide Emissions from
Agriculture by Source: 1990
(3%) Agricultural
Waste Burning
Agricultural Soils
(97%)
Various agricultural soil management practices
contribute to greenhouse gas emissions. The use of
synthetic and organic fertilizers adds nitrogen to soils,
thereby increasing natural emissions of nitrous oxide.
Other agricultural soil management practices such as
irrigation, tillage practices, or the fallowing of land
can also affect trace gas fluxes to and from the soil
since soils are both a source and a sink for carbon
dioxide and carbon monoxide, a sink for methane,
and a source of nitrous oxide. However, there is
much uncertainty about the direction and magnitude
of the effects of these other practices, so only the
emissions from fertilizer use are included in the
inventory at this time.
Fertilizer use is the most significant source of
nitrous oxide in the U.S. Nitrous oxide emissions in
1990 due to consumption of synthetic fertilizers (both
multi-nutrient and nitrogen) and organic fertilizers
were about 13.5 MMTCE. This represents approxi-
mately 44 percent of total U.S. nitrous oxide emis-
sions, and about 97 percent of nitrous oxide emis-
sions from all agricultural sources. Approximately
55 percent of the fertilizer was consumed in the
Midwest.
Due to an increase in fertilizer consumption
between 1990 and 1993, emissions increased by about
3.6 percent over the period. .
Nitrous oxide is produced naturally in soils
through the microbial processes of denitrification and
nitrification.10 A number of anthropogenic activities
57
-------
add nitrogen to soils, thereby increasing the amount of
nitrogen available for nitrification and denitrification, ,
and ultimately the amount of N2O emitted. These
activities include application of fertilizers, acid deposi-
tion, and cultivation of nitrogen-fixing crops. This
section discusses emissions of N2O due to the use of
fertilizers. Synthetic nitrogen fertilizers, synthetic
multi-nutrient fertilizers, and organic fertilizers are
included in the emission estimates. Emissions due to
atmospheric deposition and nitrogen-fixing crops are
not included for two reasons: these emission sources
are highly uncertain, and activity data are not readily
available.
Research has shown that a number of factors
affect nitrification and denitrification rates in soils,
including: water content, which regulates oxygen
supply; temperature, an important factor in microbial
activity; nitrogen concentration, in particular nitrate
and ammonium concentration; available organic carbon
for microbial activity; and soil pH. These conditions
vary greatly by soil type, crop type, management
regime, and fertilizer application. Moreover, the
interaction of these conditions and their combined
effect on the processes leading to nitrous oxide emis-
sions are not fully understood*
Scientific knowledge regarding nitrous oxide
production and emissions from fertilized soils is
limited. Significant uncertainties exist regarding the
agricultural practices, soil properties, climatic condi-
tions, and biogenic processes that determine how much
fertilizer nitrogen various crops absorb, how much
remains in soils after fertilizer application, and in what
ways the remaining nitrogen either evolves into nitrous
oxide or into gaseous nitrogen and other nitrogen
compounds.
A major difficulty in estimating the magnitude of
emissions from this source has been the relative lack of
emissions measurement data across a suitably wide
variety of controlled conditions, making it difficult to
develop statistically valid estimates of emission factors.
Previous attempts have been made to develop emission
factors for different fertilizer and crop types for the
purposes of developing national emissions inventories.
However, the accuracy of these emission factors has
been questioned. For example, while some studies
indicate that N2O emission rates are higher for ammo-
nium-based fertilizers than for nitrate, other studies
show no particular trend in N2O emissions related to
fertilizer types (see Eichner (1990) and Bouwman
(1990) for reviews of the literature). Therefore, it is
possible that fertilizer type is not the most important
factor in determining emissions. One study suggests
thatN2O emissions from the nitrification of fertilizers
may be more closely related to soil properties than to
the type of fertilizer applied (Byrnes et al., 1990).
Until a sufficient number of studies are conducted to
develop statistically valid emission factors, the IPCC
recommends that countries assume that 1 percent of the
nitrogen applied as fertilizer is released into the
atmosphere (IPCC/OECD, 1994).
Nitrous oxide emissions from fertilizer use in
1990 were estimated using this draft IPCC methodol-
ogy, although with a slightly higher emission coeffi-
cient. The emission coefficient used (1.17 percent)
was based on research done by the U.S. Department of
Agriculture (CAST, 1992). The amount of fertilizer
consumed (synthetic nitrogen, multiple-nutrient, and
organic fertilizer, measured in mass units of nitrogen)
was multiplied by this emission coefficient. Fertilizer
data for the U.S. were obtained from the Tennessee-
Valley Authority's National Fertilizer and Environmen-
tal Research Center (TVA, 1993).11 Because agricul-
tural activities fluctuate from year to year due to
economic, climatic, and other variables, the IPCC
recommends that an average of three years of fertilizer
consumption (centered on 1990) should be used. Total
1990 N2O emissions from fertilizer use are estimated to
be 183 thousand metric tonnes N2O (13.5 MMTCE)
(see Table rV-9):
N2O Emissions
= Fertilizer Consumption (tonnes
. N) x 0.0117 x 44/28
= 9,966 thousand metric tonnes N
x 0.0117 x 44/28
= 183 thousand metric tonnes
N20 ..
10 Denitrification is the process by which nitrates or nitrites are reduced by bacteria and which results in the escape of
nitrogen into the air. Nitrification is the process by which bacteria and other microorganisms oxidize ammonium salts to
nitrities, and further oxidize nitrites to nitrates.
11 Fertilizer consumption data may be underestimates since they do, not include organic fertilizers that do not enter the
comrnerical market.
58
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Table IV-9. Fertilizer Consumption and NO Emissions in the U.S.
Annual Fertilizer
Consumption1 (103 tonnes N)
3-year Average Fertilizer
Consumption2 (103 tonne's N)
N2O Emissions (103 tonnes N2O)3
1989
9,609.5
1990
^
1.0,048.1
9,965.7
183.2
1991
10,239,4
10,223.9
188.0
1992
10,384.1
10,309.1
189.5
1993'
10,303.7
10,343.9
190.2
1 Includes synthetic multiple nutrient fertilizers, synthetic nitrogen fertilizers, and organic fertilizers.
2 Since 1994 data are not available, the 1993-centered average is the average of 1992 and 1993 consumption.
3 Based on an emission coefficient of 1.17 percent.
Source: Fertilizer consumption data from TVA, 1993
Approximately 55 percent of the synthetic
nitrogen, multiple-nutrient, and organic fertilizer
consumed in 1990 (measured on a mass of nitrogen
basis) was consumed in the Midwest (TVA, 1993).
The methodology described above was also used
to estimate N2O emissions from fertilizer use in 1991,
1992, and 1993(see Table IV-9).12 Fertilizer consump-
tion increased 4 percent from 1989 to 1990, and then
leveled off to an average annual rate of increase of 2
percent between 1990 and 1992. Consumption then
declined by about 1 percent between 1992 and 1993.
Based on the consumption statistics, nitrous oxide
emissions in 1991, 1992, and 1993 are estimated to be
approximately 188 thousand metric tonnes (13.8
MMTCE), 190 thousand metric tonnes. (14.0
MMTCE), and 1.90 thousand metric tonnes (14.0
MMTCE), respectively.
These estimates are highly uncertain due to the
large degree of uncertainty associated with the emis-
sion factor. A survey of the current scientific literature
on field N2O flux provides a rather broad range for the
emission coefficient ~ greater than 0.001 and less than
0.1 (CAST, 1992). Also, the emission coefficient used
(1.17 percent) is probably too low for organic fertiliz-
ers, and as mentioned earlier, organic fertilizer con-
sumption may be underestimated since the statistics
only include fertilizers that enter the commercial "
market. Uncertainty is also introduced due to the
variable nitrogen content of organic fertilizers. Nitro-
gen content varies by type of organic fertilizer as well
as within individual types, and average values are used
to estimate total organic fertilizer N consumed. Fur-
ther research is required to constrain these uncertainties
and develop more accurate estimates of N2O emissions
from fertilizer.
E. EMISSIONS FROM FIELD BURNING OF
AGRICULTURAL WASTES
In some parts of the U.S., agricultural crop
wastes are burned in the field to clear remaining
straw and stubble after harvest and to prepare the
field for the next cropping cycle. When crop residues
are burned, a number of greenhouse gases are
released, including carbon dioxide, methane, carbon
monoxide, nitrous oxide, and oxides of nitrogen.
However, crop residue burning is not thought to be a
net source of carbon dioxide because the carbon
dioxide released during burning is reabsorbed by crop
regrowth during the next growing season.
Field burning of crop residues is not a common
method of agricultural waste disposal in the U.S., so
emissions from this source are minor. Emissions in
1990 from this source are estimated to have been
approximately 80 thousand metric tonnes of methane
(0.5 MMTCE), 2,760 thousand metric tonnes of
carbon monoxide, 5 thousand metric tonnes of
nitrous oxide (0.4 MMTCE), and 115 thousand metric
tonnes of nitrogen oxides. These estimates are highly
uncertain because data on the amounts of residues
burned each year are not available. The emission
estimates represent approximately 0.3, 3.3,1.2, and
0.5 percent of total U.S. emissions of methane,
carbon monoxide, nitrous oxide, and nitrogen oxides,
respectively. Cereal crops (e.g., wheat, corn, and
sorghum) account for about 75 percent of the carbon
gases released and 50 percent of the nitrogen gases
released.
12 Fertilizer consumption data are not yet available for 1994, so only 1992 and 1993 consumption data were used to
estimate 1993 emissions.
- 59
-------
Emissions increased on average by about 10
percent between 1990 and 1991, decreased by about 3
percent between 1991 and 1992, and then increased
by about 3 percent between 1992 and 1993. These
fluctuations reflect average annual fluctuations in
crop production.
Large quantities of agricultural crop wastes are
produced from farming systems. There are a variety of
ways to dispose of these wastes. 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 biomass fuel
or sold in supplemental feed markets. This section
addresses field burning of agricultural crop wastes.
Field burning of crop wastes is not thought to be a net
source of CO2 because the carbon released to the
atmosphere during burning is reabsorbed during the
next growing season. Crop residue burning is, how-
ever, a net source of CH4, CO, N2O, and 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 at., 1988), although this process is highly
uncertain and will not be accounted for in this section.
The methodology for estimating greenhouse gas
emissions from field burning of agricultural wastes is
based on the amount of carbon burned, emission ratios
of CH,, and CO to CO2 measured in the smoke of
biomass fires, and emission ratios of N2O and NOX to
the nitrogen content of the fuel. The methodology is
the same as the draft methodology of the IPCC (IPCC/
OECD, 1994).
The first step in estimating emissions from
agricultural waste burning is to estimate the amounts of
carbon and nitrogen released during burning:
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 Effi-
ciency x Nitrogen Content of
the Residue x Combustion
Efficiency
To avoid unrepresentative results based upon
fluctuations in economic or climatic conditions, a
three-year average (centered on 1990) for crop produc-
tion (USDA, 1991; USDA, 1993) was used to estimate
1990 emissions. Estimates of the amounts of crop
residues burned in situ, or in the field, are not readily
available. Therefore, the default value recommended
by the IPCC for developed countries, 10 percent, was
used. However, this default value, based on Crutzen
and Andreae (1990), may be an overestimate for the
U.S. because open burning is banned in many states.
Emissions of carbon as CH4 and CO are calcu-
lated by multiplying the amount of carbon released by
the appropriate emission ratio (i.e., CH4/C or CO/C).
Similarly, N2O and NOX emissions are calculated by
multiplying the amount of nitrogen released by the
appropriate emission ratio (i.e., N2O/N or NOX/N). The
specific values used in this inventory and the results
are presented in Tables IV-10 and IV-11. Field burn-
ing of agricultural wastes was estimated to release
approximately 80 thousand metric tonnes CH4 (0.5
MMTCE), 2,760 thousand metric tonnes CO, 5 thou-
sand metric tonnes N2O (0.4 MMTCE), and 115
thousand metric tonnes NOx in 1990. Cereal crops
account for about 75 percent of the carbon released and
50 percent of the nitrogen released.
Using the same methodology described above,
trace gas emissions for 1991, 1992, and 1993 were
estimated using production data from the USDA
(1994c). The data and results are contained in Tables
IV-10 and IV-11. Emissions increased by 7 to 12
percent from 1990 to 1991, decreased by about 3
percent between 1991 'and 1992, and then increased by
2 to 4 percent from 1992 to 1903. These fluctuations
reflect average changes in production: three-year
production averages for most crops increased from
1990 to 1991, and then declined between 1991 and
1992.' "' "" "''":"'''''': ;
'* Burning Efficiency is defined as the fraction of dry biomass exposed to burning that actually Burns. Combustion
Efficiency is defined as the fraction of carbon in the fire that is oxidized completely to CO2. In the draft methodology
recommended by the IPCC, the "burning efficiency" is assumed to be contained in the "fraction of residues burned" factor.
However, the number used here to estimate the "fraction of residues burned'* does not account for the fraction of exposed
residue mat does not burn. Therefore, a "burning efficiency factor" is added to the calculations.
! ' . ' ; i ' ' (
60 .! , '''.' ;','. ,'
-------
Table IV-10. Key Assumptions for Estimating Emissions from Crop Waste Burning
Crop
Cereals
Wheat
Barley
Maize
Oats
Rye
Rice
Milletb
Sorghum
Pulse
Soya
Beans
Peas
Lentils
Production 3-yr.
1990
61,273
9,367
194,192
4,715
284
7,077
183
15,017
' 52,945
1,359
204
56
1991
65,104
9,757
210,755
4,334
270
7,457
180
17,291
55,342
1,342
172
62
avg. (103 tonnes)
1992
62,071
9,598
197,293
3,602
271
7,457
180 '
17,245
54,277
1,183
, 185
79
1993a
66,147
9,342
200,996
3,636
283
7,615
180
15,440
54,383 '
1,008
169
81 .
Res/Crop
Ratio
1.3
1.2
1.0
1.3
1.6"
1.4
1.4
8.0
2.1
2.1
1.5
2.1
Res Dry
Burned Matter
(%) (%)
10%
10%
10%
10%
10%
10%
10%
10%
10%
10%
10%
10%
91.1%
' 90.4%
88.0%
. 90.6%
90.0%
90.0%
88.5%
90.0%
89'.3%
88.7%
90.2%
89.3%
Fraction
Carbon
0.4853
0.4567
0.4709
0.4853
0.4853
0.4144
0.4853
0.4853
0.45
0.45
0.45
0.45
Fraction
Nitrogen
0.004
0.006
0.0081
0.007
.0.007
0.0067
0.007*
0.0085*
0.023*
0.023*
0.023*
0.023*
Tuber and Root . ,
Sugarbeet
Artichoke0
Peanut
Potatoes
Other
Sugarcane
24,448
59
1,893
17,995
534
.26,555
25,661
56
1,937
18,826
544'
26,838
25,323
54
1,896
19,087
532
27,560
25,192
52
1,762
19,159
543
27,618.
0.3
0.8
1.0
0.4
0.4
0.8
10%'
10%
10%
10%
10%
10%
90.0% ' .
90.0%.
\ 90.1%
86.7%
86.7%
90.0%
0.4072
0.4226
0.4226
0.4226
0.4226
0.4695
0.0228
0.011
0.011
0.011
0.011
0.003 .
a Crop production for 1993 are two-year averages (i.e., 1992 and 1993).
b Because millet is such a small commodity relative to other crops, the USDA no longer tracks its production.
These production estimates were taken from the FAO (1993).
c The USDA provided artichoke production for California only. Total artichoke production was estimated by
assuming that California accounted for 90% of the entire market.
Sources: Data on annual crop production were taken from USDA (1991, 1993, 1994c). Residue/crop ratios, dry matter
contents, and carbon contents were taken from Strehler and Stutzle (1987) and University of California (1977).
Nitrogen contents were also taken from Strehler and Stutzle (1987) except where indicated by an asterisk (*).
These data were taken from-Barnard (1990), The percent of produced residue that is burned is based on Crutzen
and Andreae (1990).
61
-------
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62
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PART V. EMISSIONS FROM LAND-USE CHANGE AND
FOREST MANAGEMENT
Total US Emissions by Source: 1990
' (MMT Carbon Equivalent)
1396 '
1444
.;
Energy Industry Agriculture Forestry Wastes Net Total
i Source
The biosphere emits and absorbs a wide variety
of carbon and nitrogen trace gases, including carbon
dioxide (CO), methane (CH^, carbon monoxide
(CO), nitrous oxide (N2O), oxides of nitrogen (NOJ,
and nonmethane hydrocarbons (NMHC).1 When
humans use and alter the biosphere through land-use
change and forest management activities, such as
clearing an area of forest to create cropland, restock-
ing a logged forest, draining a wetland, or allowing a
pasture to revert to a grassland, the natural balance
, of these trace gas emissions and uptake is altered and
their atmospheric concentrations adjust. Globally,
the most important human activity that affects the .
biosphere is deforestation, particularly the clearing of
tropical forests for agricultural use. Deforestation is
estimated to be responsible for about 20 percent of the
current annual global emissions of CO2 from anthro-
pogenic activities (IPCC, 1992).
In the U.S., however, forest management
activities and the regeneration of previously cleared
forest area are believed to be the primary activities
responsible for current greenhouse gas fluxes from
land-use change and forest management, as the
amount of forest land changed by only about 0.1
percent per year between 1977 and 1992. The net
CO2 flux in 1990 due to these activities is estimated to
have been an uptake (sequestration) of 119 MMTCE.
This carbon uptake represents an offset of about 9
percent of the CO2 emissions from energy-related
activities. The Northeast, North Central, and South
Central regions of the U.S. account for 98 percent of
the uptake of carbon, largely due to high growth rates
that are the result of intensified forest management
practices and the regeneration of forest land previ-
ously cleared for cropland and pasture. Western
states are responsible for a small net release of
carbon, reflecting mature forests with a near balance
between growth, mortality, and removals.
Relative to 1990, net flux rates for 1991 and
1992 are estimated to have declined slightly, to 118
and 117 MMTCE, respectively. This declining trend
in sequestration is due to maturation of existing
forests and associated slowing of carbon accumula-
tion rates. A flux estimate has not yet been derived
for the year 1993 since the last U.S. forest inventory
was completed in 1992.
The U.S. land area is roughly 2,263 million
acres, of which 33 percent, or 737 million acres, is
forest land (Powell etal., 1993). The amount of forest
land has remained fairly constant, over recent decades,
declining by approximately 5 million acres between
1977 and 1987 (USDA Forest Service, 1982; Waddell
et al., 1989), and increasing by about 0.5 million acres
between 1987 and 1992 (Powell etal., 1993). These
changes represent fluctuations of well under 1 percent
of the forest land area, or on average, about 0.1 percent
per- year. Other major land uses in the U.S. include
range and pasture lands (36 percent), cropland (18
percent), urban uses (3 percent), and other lands (10
percent) (Daugherty, 1991).2 Urban lands are the
fastest growing land use.
Given that U.S. forest land area changed by only
about 0.1 percent per year over the last 15 years, the"
major influences on the 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
'ป Nonmethane hydrocarbons (NMHCs) are a subset of nonmethane volatile organic compounds.
2 Other lands include farmsteads, transportation uses, marshes, swamps, deserts, tundra, and miscellaneous other lands.
63
-------
stored in the biomass3 and soils of forest ecosystems.
For example, intensified 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 will, over decades,
result in increased storage in biomass and soils (i.e., in
general, forests contain more biomass and soil carbon
than cropland).
Forests are complex ecosystems with several
interrelated components, each of which acts as a
carbon storage pool, including:
trees (i.e., living trees, standing dead trees,
foots, stems, branches, and foliage);
soil;
the forest floor (i.e., woody debris and tree
litter); and,
understory vegetation (i.e., shrubs and
bushes).
As a result of biological processes (e.g., growth
and mortality) and anthropogenic activities (e.g.,
harvesting, thinning, and other removals), carbon is
continuously cycled through these ecosystem compo-
nents, 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 in living trees. As these trees age, they con-
tinue to accumulate 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 will release carbon to
the atmosphere and also increase soil carbon. The net
change in forest carbon is the change in the total net
amount of carbon stored in each of these pools (i.e., in
each ecosystem component) over time.
The net change in forest carbon, however, is not
likely to be equivalent to the net flux between forests
and the atmosphere. Because most of the timber that is
harvested and removed from U.S. forests is used in
wood products, removals may not always result in an
immediate flux of carbon to the atmosphere. Harvest- .
ing in effect transfers carbon from one of the "forest
pools" to a "product pool." Once in a product pool, the
carbon is emitted over time as CO2 through either
combustion or decay,4 although the exact rate of
emission varies considerably between different product
pools and may in fact result in effective long-term
carbon storage. For example, if timber is harvested
and subsequently used as lumber in a house, it may be
many decades or even centuries before the lumber is
allowed to decay and carbon is released to the atmo-
sphere. If timber is harvested for energy use, subse-
quent combustion results in an immediate release of
carbon., Paper production may result in emissions over
years or decades.
The U.S. forest carbon flux estimates for 1990,
1991, and 1992 presented in this inventory are based
on a total accounting of biomass carbon stored in all
forest ecosystems and the tracking of changes in the
total biomass carbon stored on forest lands. The
tracking of soil carbon, as well as carbon in product
pools, have not been included at this time due to
methodological uncertainties and inadequate data. The
forest carbon in trees, understory vegetation, and the
forest floor is tracked by utilizing dynamic forest
resource survey data collected by the U.S. Forest
Service (UjSFS). These resource data include estimates
of timber volume by species, size class, and other
categories, which are combined with information from
the research literature to derive estimates of the total
carbon stored in forest biomass.
The net flux is the difference in total carbon
storage between two years for which forest survey data
are available (and therefore for which carbon invento-
ries can be derived) divided by the number of years
between the surveys. If carbon storage decreases, then
the difference is a net emission to the atmosphere; if
carbon storage increases, then the difference is a net
sequestration of carbon on land.
The inventory methodology applied here differs
somewhat from that recommended by the IPCC (IPCC/
OECD, 1994). Instead of directly inventorying carbon
stocks and changes in stocks over time, the draft IPCC
3 Biomass is a shorthand term for organic material. The amount of biomass in a given land area includes all the living
and dead organic material, both above and below the ground surface.
4 Actually, if timber undergoes combustion, some small portion of the carbon - as much as 10 percent of the total carbon
released - will be released as CO and CH4 rather than CO2. In addition, if timber products are placed in landfills, about 50
percent of the carbon that eventually decomposes is oxidized to CO2 and about 50 percent is released as CH4. However,
eventually both CO and CH4 oxidize to CO2 in the atmosphere.
64 ..
-------
methodology uses average annual statistics on land-use
change and management activities, and applies carbon
density and flux data to these activity estimates to
derive total flux estimates. The IPCC has adopted this
type of methodology because the majority of the
world's .countries do not have the detailed forest
inventory statistics available in the U.S. and used in
preparing this inventory.
Theoretically, the two methods should result in
similar flux estimates. However, the U.S. inventory
methodology explicitly tracks changes in forest carbon
through time using direct measurement of timber
volume and forest ecology studies, while the IPCC
methodology is an indirect approach using average
annual activity data and theoretically or experimentally
derived carbon data. Although there are large uncer-
tainties associated with the inventory estimates, the
methodology employed here is likely to have resulted
in a more accurate flux estimate than if the basic IPCC
methodology had been employed.
The estimates of the 1990, 1991, and 1992 forest
carbon flux presented here were derived from Birdsey
and Heath (1993) and Birdsey (1994). These estimates
are based on national compilations of forest inventory
statistics for 1977 (USFS, 1982), 1987 (Waddell et al,
1989), and 1992 (Powell et al., 1993). These statistics
measure the changes in timber volume over time due to
timber growth, harvest, and mortality. Although the
estimates cover only timberland, which is a subset of
the forest land base, they capture the most productive
and intensively managed forest lands.5 Birdsey and
Heath (1993) and Birdsey (1994) calculated total
stored biomass carbon in each of the ecosystem
components in the years 1987 and 1992 using the
timber inventory data and number of conversion
factors from the research literature.6 The 1990 flux
was derived by subtracting the biomass carbon storage
estimated for 1992 from that for 1987, and dividing by
5. Therefore, the 1990 flux is actually an average
annual flux for the period 1987-1992. Flux estimates
for 1991 and 1992 were derived using exponential
interpolation between a flux for 1982 (from the 1977
and 1987 storage estimates) and the 1990 flux.
-The 1990 carbon flux from U.S. forests is
estimated to have been a net sequestration of carbon
from the atmosphere to the biosphere of 119 MMTCE.
This is equivalent to approximately 436 million metric
tonnes CO2. Carbon sequestration rates are estimated
to have declined slightly in 1991 and 1992, to 118 and
117 MMTCE, respectively. Also, because 1992 is the
last year for which a forest inventory has been com-
piled, a flux estimate for 1993 is not yet available.
- There is considerable regional variation in the
carbon flux estimates for 1990, reflecting different
underlying trends in the forest resource base through-
out the United States. A regional breakdown of carbon
flux estimates from forest land is presented in Table V-
1. This table also shows the contribution of each of the
forest ecosystem components to the total flux.
All of the net uptake of carbon in U.S. forest
land in 1990 occurred in the Eastern regions (see Table
V-l and Figure V-l .)7 This is primarily due to forest
regeneration on areas previously cleared for cropland
and pasture and the use of intensified forest manage-
ment practices. All of these Eastern regions have
significant net carbon uptakes, except for the Southeast
states where harvesting activity has increased recently.
In Western states, i.e., the Rocky Mountain and Pacific
Coast regions, carbon flux is slightly negative since
forest growth, mortality, and harvesting are in near
balance.
5 Forest land in the U.S. includes all land that is at least 10 percent stocked with trees of any size. Timberlands are the
most productive of these forest lands, 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 Timberlands are 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 a statute or regulation, or Other Forest Land, which includes unreserved and reserved unproductive forest land. While
this inventory does not quantify the carbon flux on Productive Reserved or Other Forest Lands, this missing flux is assumed
to be relatively minor because trees on these lands grow slowly and the standing stock of trees is not managed intensively.
6 Birdsey and Heath (1993) and Birdsey (1994) also include soil carbon in their calculations, but this component of
forest carbon has nqt been included in the U.S. inventory at this time because of significant associated uncertainties.
7 The East includes the Northeast, North Central, Southeast, and South Central regions.
65
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Table V-l: Regional Carbon Flux Estimates
Region"
Northeast
North Central
Southeast
South Central
Rocky Mountains
Pacific Coast
U.S. Total
Carbon Flux by Ecosystem Component, 1990
(106 tonnes C)
Forest Floor Understory
10 1
7 <1
<1 0
2 1
2 >-l
-1 0
21 2
Trees
37
29
1
35
-4
--2
96
Total Carbon
Flux, 1990 ' .
(106 tonnes C)
48
36
2
38
-2
-3
119
Sources: Birdsey and Heath (1993), Birdsey (1994)
Note: A positive flux indicates uptake; a negative flux indicates emissions.
1 _ , 1 ' '
a. Regions are defined in Figure V-l.
T ; "'
Figure V-l. Regions and States for the U.S. Inventory
ROCKY MOUNTAINS
1NTERMOUNTAIN GREAT PLAINS ^^R CENTRAL
PACIFIC
COAST \ V \
PACIFIC
SOUTHWEST S. \
SOUTH
Source: Waddell et al (1989)
66
-------
The uptake of carbon due to forest regeneration
is an ongoing result of land-use changes in previous
decades. The rate of clearing forest land for crop
cultivation and pasture slowed greatly in the late 19th
century and by 1920 had all but ceased. The reduced
need for cropland and pasture resulted from improved
agricultural productivity and the reduced use of draft
animals following the widespread use of tractors. As
farminglexpanded in the Midwest and West, large areas
of previously cultivated land in the Eastern states were
brought out of crop production, primarily between
1920 and 1950, and allowed to revert to forest land.
The regeneration of forest land greatly increases
carbon storage in standing biomass, and the impacts of
these land-use changes are still affecting carbon fluxes
from Eastern forests. In addition to land-use changes
in the early part of this century, carbon fluxes from
Eastern forests are affected by a trend towards man-
aged growth on private land since World War Two,
resulting in a near doubling of forest biomass density
in Eastern forests since the early 1950s.
The Southeast states are an exception to these
Eastern forest trends, with increases in timber removals
and decreases in growth rates resulting in a small net
uptake of carbon compared to other Eastern regions.
The Southeast accounted for 25 percent of timber
removals in 1991, up from 20 percent in 1976, largely
in response to the removal of forest land from commer-
cial harvesting in the West. Moreover, the rate of
timber growth in the Southeast has diminished, reflect-
ing maturing forests, and timber mortality in the
Southeast increased 3 percent between 1986 and 1991.
The Rocky Mountain and Pacific Coast states
have relatively little impact on the U.S. net carbon
flux. This reflects a near balance between growth,
mortality, and removals, associated with mature forests ,
with low growth, and a decline in timber removals
from 1987 to 1992 of 5 percent and 10 percent, respec-
tively, in these two regions.
Within regions where there has been an increase
in carbon storage, and thus a net uptake of carbon, the
majority, of the carbon flux is accounted for by in-
creased storage in the trees (see Table V-l). Addi-
tional carbon is stored in the understory vegetation and
the forest floor. These, trends reflect the growth of new
and existing forests due to ongoing forest regeneration
and intensified forest management. However, the
declining uptake rates for the 1990-1993 period
indicate that growth rates are slowing on average. This
is a reflection of maturing forests in which carbon
accumulation rates have begun to lessen.
There are. considerable uncertainties associated
with the estimates of the net carbon flux from U.S.
forests. Four major uncertainties are discussed briefly
below, as well as areas needing further research and
analysis.
First, the impacts of forest management activities
on soil carbon are quite uncertain, particularly after
harvest Research indicating a 20 percent loss of soil
carbon after harvest (Moore et al., 1981) has been used
by Birdsey and Heath (1993) and Birdsey (1994),
whereas results showing little or no net change in soil
carbon following harvest (Johnson, 1992) and during
regeneration have been used in other studies (e.g.,
Turner et al., 1993). Since forest soils contain over 50
percent of the total stored forest carbon in the U.S., this
difference can have a large impact on flux estimates.
However, because of uncertainties associated with soil
carbon flux, this component is not included, in the
inventory at this time.
Second, Birdsey and Heath (1993) and Birdsey
(1994) assume that harvested timber effectively results
in immediate carbon emissions (i.e., they do not model
time-dependent emissions from the product pools).
This assumption is consistent with the methodology
recommended by the IPCC (IPCC/OECD, 1994) and
will result in an accurate assessment of net emissions if
the amount of material in product pools, and the
distribution of this material among different pools,
have not changed over the past 100 years or so. How-
ever,, other studies that model the product pools in the
U.S. estimate a net accumulation of carbon in product
pools in 1990. This is because more timber carbon was
transferred to wood products than was released to the
atmosphere due to the decay or combustion of material
stored in product pools (Turner et al., 1993). Turner et
al. estimate that the net accumulation of carbon in the "
product pools is 36 million metric tonnes C in 1990.
This would indicate that less carbon was actually
emitted to the atmosphere as a result of timber remov-
als than the current inventory estimate accounts for,
and that the total net flux would be a larger uptake of
carbon in 1990-1992. However, estimates of the net
annual accumulation of carbon in product pools are
highly uncertain due to scientific uncertainties associ-
ated with decay rates as well as a lack of accurate
historical carbon pool statistics. Therefore, this result-
is not included in the inventory estimate.
67
-------
Third, the current inventory estimate does not
include forest land in Alaska and Hawaii or reserved
timberland. Inclusion of Alaska and Hawaii would
significantly increase the storage estimates in both
studies, but is not likely to significantly alter the flux
estimates because forests in these states are believed to
be in relative equilibrium, i.e., neither accumulating or
emitting significant quantities of carbon. Reserved
timberlands are not managed or harvested, and there-
fore are not likely to contribute greatly to total flux
estimates.
Finally, forest management activities may also
result in fluxes of other greenhouse and radiatively
important gases since dry soils are an important sink
for CH4, a source of N2O, and both a source and a sink
for CO, and vegetation is a source of several NMHCs.
However, the effects of forestry activities on fluxes of
these gases are highly uncertain, and, therefore, are not
included in the inventory at this time. Similarly, there
are several land-use changes that are not accounted for
in the inventory due to uncertainties in their effects on
trace gas fluxes as well as poorly quantified land-use
change statistics. These land-use changes include loss
and reclamation of freshwater wetland areas, conver-
sion of grasslands to pasture and cropland, and conver-
sion of managed lands to grasslands and other
unmanaged, non-forest dryland types.
68
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PART VI. EMISSIONS FROM WASTE
Total US Emissions by Source: 1990
(MMT Carbon Equivalent)
1396
1444
Energy Industry Agriculture forestry Wastes Net Total
Source
Anaerobic decomposition of organic materials in
landfills by bacteria can result in emissions of methane,
carbon dioxide, and other greenhouse and photochemi-
cally important gases. Currently, methane emissions
from landfills are the largest single anthropogenic
source of methane in the U.S., contributing about 37
percent'of total U.S. methane emissions. Other anaero-
bic decomposition processes, such as wastewater
streams with high organic material content from
municipal and industrial processes, can also emit large
quantities of methane. In addition, the combustion of
waste, both in incinerators and by open burning, is also
a source Of many greenhouse and photochemically
important gases. This section covers methane emis-
sions from U.S. landfills, wastewater streams, and
criteria pollutant emissions from waste incineration.
A. LANDFILLS
Methane Emissions from Wastes by Source: 1990
(1%) Wastewater
Organic landfill materials such as yard waste,
household garbage, food waste, and paper can
decompose and produce methane. This decomposi-
tion process is a natural mechanism through which
microorganisms derive energy for growth. Methane
production typically begins one or two years after
waste placement in a landfill and may last from 10 to
60 years. Methane emissions from landfills are the
largest single anthropogenic source of methane in the
U.S. In 1990, methane emissions from U.S. landfills
ranged between 49 and 71MMTCE, or about 37
percent of total U.S. methane emissions. Emissions
from U.S. municipal solid waste landfills, which
received over 70 percent of the total solid waste
generated in the U.S., account for about 90 to 95
percent of the total landfill emissions, while industrial
landfills account for the remaining 5 to 10 percent.
There are an estimated 6,000 landfills in the U.S.,
with 1,300 of the largest landfills accounting for
about half of the emissions. Currently, about 10
percent of the methane is recovered for use as an
energy source. Emissions of methane from landfills
over the period 1990 -1992 have been relatively
constant (Table VI-1).
Organic waste first decomposes aerobically (in
the presence of oxygen) and is then attacked by
anaerobic bacteria which convert organic material to
simpler forms like cellulose, amino acids, sugars, and
fats. These simple substances are further broken down
through fermentation into gases and short-chain
organic compounds which form the substrates for
methanogenic bacteria. Methane producing bacteria
then convert these fermentation products into stabilized
organic materials and a biogas consisting of approxi-
mately 50 percent carbon dioxide and 50 percent
methane by volume. The percentage of carbon dioxide
in the biogas released from a landfill may be smaller
because some CO2 dissolves in landfill water
(Bingemer and Crutzen, 1987).
Landfills in the U.S. are classified by size,
ranging from class 1 to class 7. Class 1 landfills are
the smallest in size and are also the most common type
of landfills. However, class 1 landfills account for less
than five percent of the total waste landfilled to date.
On the other hand, there are 19 class 7 landfills in the
69
-------
Table VI-1. U.S. Methane Emissions from Landfills: 1990 - 1992
(Thousand Tonnes of CH4)
Source
Large Municipal Landfills
Medium Municipal Landfills
Small Municipal Landfills
Industrial Landfills
Totala'b
Number
152
1,137
4,744
NA
6,033-=
1990
2,600-4,200
3,300-6,000
900-1,500
600-900
8,100-ll,800d
1991
NA
NA
'NA
NA
10,100
1992
NA
NA
NA
NA
10,200
Source: U.S. EPA (1993a)
Note: a. The uncertainly in the total is estimated assuming t$at some of the uncertainty for each
source is independent. Consequently, the uncertainty range for the total is more narrow
than the sum of the ranges for the individual sources
b. The total does not include an additional 1,500 thousand tonnes of methane recovered from
landfills that was flared or used as an energy source.
c. Excluding industrial landfills. Also, this table does not include the 3000 class 1 landfills
that, because of their very small size, are believed to produce negligible amounts of methane.
d. Equivalent to 48.6-70.8 MMTCE.
U.S. which account for over 25 percent of the total
waste. Because of their different sizes and characteris-
tics, landfills generate different rates of methane
emissions. Table VI-2 contains a summary of the
landfill class sizes and the associated emissions factors
used to estimate landfill emissions.
Estimates of methane emissions from landfills
are from U.S. EPA (19?3a). The U.S. EPA employed a
statistical model relating measured methane recovery
rates from landfills with recovery systems to the
physical characteristics of landfills to estimate U.S.
emissions.1
Some landfills practice flaring of recovered
landfill gas, which converts the methane portion of the
gas to carbon dioxide. While landfill gas contains
roughly equal amounts of methane and carbon dioxide,
landfill carbon dioxide emissions are small compared
to emissions from other sources discussed. Moreover,
carbon dioxide from landfills is believed to come
mainly from organic materials. Since these materials
are assumed to absorb a similar amount of carbon
during the growing cycle, the net contribution of
landfills to the global carbon dioxide budget is as-
sumed to be zero.* The same is not true for the meth-
ane that may be produced since the methane is typi-
cally only produced as a by-product of the landfilling
process.
The total methane emissions from landfills
reported above do not include an estimated 1,500
thousand metric tonnes (9 MMTCE) of methane
1 ' !, 'I, ! - , ' "''i'UH'l!1 I'1:! ",'' ^ . , 'I11 ,' ' ' ,. , .,":,,, ' .'. . . , " "k :" " J , J. L'1
annually recovered by landfills with recovery systems.
Currently, this recovered methane is either flared or
used as an energy source, resulting in carbon dioxide
emissions. Assuming that the 9 MMTCE of recovered
methane is flared or combusted for other purposes,
potential carbon dioxide emissions of 4,125,000 metric
1 TTic IPCC Draft Guidelines for National Inventories (IPCC/OECD,
similar to U.S. EPA (1993a) but simpler in execution.
2 In some instances landfills may be a long-term sink for carbon if the
research is necessary to determine the extent to which landfills may be acting
1994) presents a methodology conceptually
organic material does not degrade. Further
as longer term carbon sinks.
70
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Table VI-2. Summary of U.S. Landfill Emission Rate Estimates
Landfill
Class/size # in Class
1
2
3
4
5
6
7
3,000
4,744
425
712
106
27
19
Methane
Low
+
1.1
5.4
13.5
37.0
72.5
253.7
Emissions (m3
Mean
+
1.6 -
,7.6
19.9
42.7
85.8
322.6
per minute)
High
+
2.0
9.8
26.3
48.4
99.2
361.6
. Source: U.S. EPA (1993a).
Note: "+" denotes negligible.
tonnes (1.125 MMTCE) were produced using the
carbon dioxide to methane molecular ratio of 44/16.
Although estimated here, this quantity of carbon
dioxide emissions is not included in the U.S. emissions
total because, as described earlier, these emissions
were likely to have occurred naturally if the materials
in the landfills had been allowed to decompose aerobically.
There are a number of reasons why the estimates
of landfill emissions are uncertain. Currently, there are
limited measurements of landfill emissions on which to
base an analysis. Landfill gas recovery data are being
used as a surrogate in existing analyses. In general, the
statistical model used in the U.S. EPA (1993a) analysis
may not accurately capture the relationship between
emissions and various physical characteristics of U.S.
landfills. To the degree that emission data and inputs
for the model are not representative of landfills as a
whole, error may be introduced. Additional factors
that increase uncertainty are the accuracy of data on
landfill size and waste characteristics, waste manage-
ment practices, and the oxidation rate of methane as it
passes through the soil cover of a landfill.
B. WASTEWATER
Wastewater can be treated using aerobic and/or
anaerobic technologies, or if untreated, can degrade
under either aerobic or anaerobic conditions. Meth-
ane is produced when organic material in treated and
untreated wastewater degrades anaerobically, i.e.,
Methane Emissions from Wastes by Source: 1990
(1%) Wastewater
without the presence of oxygen. Based on available
data, methane emissions from municipal wastewater
in the U.S. are about 0.9 MMTCE, or about one half
.of one percent of total U.S. methane emissions.
Estimates for 1991 and 1992 are assumed to be about
the same as 1990 levels. At this time, data are not
sufficient to estimate methane emissions from indus-
trial wastewater streams in the U.S.
Highly organic wastewater streams such as waste
streams from food processing or pulp and paper plants
' rapidly deplete available oxygen in the water stream as
their organic matter decomposes. The organic content,
otherwise known as "loading" of these wastewater
streams, is expressed in terms of biochemical oxygen
demand, or "BOD." BOD represents the amounts of
71
-------
oxygen taken up by the organic matter in the wastewa-
ter during decomposition. Under the same conditions,
wastewater with higher BOD concentrations will
produce more methane than wastewater with relatively
lower BOD concentrations. Most industrial wastewa-
ter has a low BOD content, while food processing
facilities such as fruit, sugar, meat processing plants,
and breweries can produce untreated waste streams
with high BOD content.
Although IPCC-recommended methodologies for
estimating municipal and industrial wastewater meth-
ane emissions exist, the data required by these method-
ologies are not easily obtained, especially industrial
wastewater data.. Estimates of municipal wastewater
methane for the U.S. provided in this section are taken
from U.S. EPA (1994a). That report's methodologies,
which are similar to the proposed IPCC methodologies,
are based on BOD loading in the wastewater flow in
the U.S.
'The following equation was developed by the U.S. to estimate methane emissions from municipal
wastewater:
kgCH4
= (Population)
kg BOD 5
capita/day I.
v /
365 days
yr
\ /
0.22 kg CH4
kg BOD 5
\
[ Fraction
Anaerobically
I Digested
\ ' ป
Based on available data, U.S. EPA (1994a)
estimated methane emissions from municipal wastewa-
ter in the U.S. to be about 150,000 metric tonnes (0.9
MMTCE), or about one half of one percent of total
U.S. methane emissions. Because of the lack of data,
more detailed estimates are not yet available for 1991
and 1992. For these years, methane emissions from
municipal wastewater in the U.S. are assumed to be at
about the same levels as 1990. Insufficient data are
available to estimate emissions from industrial waste-
water.
There is uncertainty in this estimate due to a lack
of data characterizing wastewater management prac-
tices, the quantities of wastewater that are subject to
anaerobic conditions, the extent to which methane is
emitted under anaerobic conditions, and flaring or
utilization practices.
C. WASTE COMBUSTION
Like other types of combustion, waste combus-
tion, whether in incinerators or out in the open, can
be a source of carbon dioxide, NO^ CO and
NMVOCs. Waste combustion is also a source of
methane and nitrous oxide, but emissions pathways
are still highly uncertain.
The criteria pollutants from waste incineration
(such as emissions from municipal solid waste
(MSW) incineration plants) constitute only a small
fraction of total U.S. criteria pollutant emissions for
1990-1992. #ฃ emissions of VOCs, CO, andNO^
from waste incineration remained relatively un-
changed for the period 19^0 - 1992 (Table Vt-3).
Open burning contributes the majority of criteria
pollutant emissions from waste combustion: about 82
percent of VOCs, 61 percent ofNO^ and 50 percent
of CO emissions. Detailed 1990 emissions are
provided in fable VI-4.
Table VI-3. U.S. VOC, CO, and NOx Emissions
from Waste Incineration: 1990 - 1992
(Thousand Metric Tonnes)
Source
VOCs
CO
N0x
1990
290
1528
74
1991
283
1,491
74
1992
290
1528
74
Source: U.S. EPA (1993b).
72
-------
Criteria pollutants from waste combustion are
inventoried annually by the U.S. EPA. Emissions of
criteria pollutants from waste incineration were
reported in National Air Pollutant Emission Trends,
1900 - 1992, (EPA, 1993b). The U.S. EPA estimated
emissions from waste combustion by applying activity
emission factors (such as MSW incineration or open
burning) to collected or estimated local and regional
activities to obtain local and regional emissions, which
were then aggregated to obtain national emissions.
Presently, net carbon dioxide emissions from
waste incineration are not included in this inventory .
because a large fraction of the carbon in combusted
waste (for example, food waste) is quickly recycled,
typically on an annual basis as" crops re-grow or trees
are replanted. Combusted wastes can also contain
plastics or other fossil-fuel based products that contrib-
ute to net carbon dioxide emissions. - At this time,
however, carbon emissions from the incineration of
fossil-based products are not estimated.
Table YI-4. U.S. VOCs, CO, and NOx Emissions from Waste Incineration by Source: 1990
(Thousand Metric Tonnes)
Source
Municipal Waste Incineration
Open Burning
Total
VOCs
52
239
290
CO
770
758
1,528
NO
X
29 ,
45
74'
Source: U.S. EPA (1993b).
73
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REFERENCES
Abrahamson, D. 1992. "Aluminum and Global Warming." Nature, 356: 484.
American Iron and Steel Institute (AISI). 1993.. Annual Statistical Report: American Iron and Steel Institute,
1992. AISI, Washington, DC.
Anderson, I.C., J.S. Levine, M.A. Poth and P.J. Riggan. 1988. "Enhanced Biogenic Emissions of Nitric Oxide
and Nitrous Oxide Following Surface Biomass Burning." Journal of Geophysical Research 93: 3893-3898.
ASAE (American Society of Agricultural Engineers). 1988. Manure Production and Characteristics. ASAE
Data: ASAE D3 84.1. American Society of Agricultural Engineers. St. Joseph, ML
Baldwin, R.L., J. France, D.E. Beever, M. Gill, and J.H.M. Thornley. 1987. "Metabolism of the Lactating Cow.
III. Properties of Mechanistic Models Suitable for Evaluation of Energetic Relationships and Factors Involved in
the Partition of Nutrients." Journal of Dairy Research 54:133-145.
Baldwin, R.L., J.H.M. Thornley, and D.E. Beever. 1987. Metabolism of the lactating cow. II. Digestive elements
of a mechanistic model. Journal of Dairy Research 54:107-131.
Barnard, G.W. 1990. "Use of Agricultural Residues as Fuel." In: Pasztor, J. and L. A. Kristoferson (eds.).
Bioenergy and the Environment. Westview Press, Inc., Boulder, Colorado, pp. 85-112. :
Bechtel. 1993. A Modified EPRI Class II Estimate for Low NOx Burner Technology Retrofit. Prepared for Radian
Corporation by Bechtel Power, Gaithersburg, Maryland. April, 1993.
Bingemer, H. and P. Crutzen. 1987. "The Production of Methane from Solid Wastes." Journal of Geophysical
Research 92: 2181-2187.^
BioCycle, 1992. "1992 Nationwide Survey: The State of Garbage." May 1992.
Birdsey, RA. 1994. Correspondence from Richard Birdsey of the U.S. Forest Service to Bill Hohenstein of
USEPA regarding a carbon storage estimate for 1992 based on 1992 Forest Statistics. January 12, 1994.
Birdsey, Richard A. and L.S. Heath. 1993. Carbon Sequestration Impacts of Alternative Forestry Scenarios.
USDA Forest Service. Prepared for the Environmental Protection Agency. April, 1993.
R-l
-------
Birdsey, Richard A. 1992. Carbon Storage and Accumulation in the United States Forest Ecosystems. USDA
Forest Service. General Technical Report WO-59.
Bouwman, A.F. 1990. "Exchange of Greenhouse Gases between Terrestrial Ecosystems and the Atmosphere."
In: Bouwman, A.F., ed. Soils and the Greenhouse Effect. John Wiley & Sons, Chichester. pp.61-127.
Brezinski, D., T. Newell, and L. Schultz. 1992. Personal communications between My Ton (ICF Inc.) and David
Brezinski and Terry Newell of the U.S. EPA National Vehicle and Fuel Emissions Laboratory, Ann Arbor, ML;
and Laurel Schultz of the U.S. EPA Office of Air Quality Planning and StoncfardK Research Triangle Park, NC.
(The information collected was compiled in spreadsheets. Hardcopy versions o? these spreadsheets are included
in the docket.)
Bureau of Census. 1987. Census of Agriculture. United States Department of Commerce. U.S. Government
Printing Office. Washington, DC 20402.
. " , ' ,''. ', :' II 'i ..*!'.' ',' ,:,
Bureau of Mines. 1992a. Cement: Annual Report 1990. U.S. Department of the Interior, Bureau of Mines.
Washington, DC. April, 1992.
Bureau of Mines. 1992b. Lime: Annual Report 1991. U.S. Department of the Interior, Bureau of Mines.
Washington, DC. November, 1992.
Bureau of Mines. 1993a. Aluminum, Bauxite, and Alumina: Annual Report 1991. U.S. Department of the
Interior, Bureau of Mines. Washington, DC. January, 1993.
' if- is- f iii'vv, :'(;. . 'i :..- ,. i,; :. . >,;'"-' .':>;,';'. *'ฃ'':: >"i\
Bureau of Mines. 1993b. Crushed Stone: Annual Report 1991. U.S. Department of the Interior, Bureau of Mines.
Washington, DC. March, 1993.
Bureau of Mines. 1993c. Soda Ash: Annual Report 1992. U.S. Department of the Interior, Bureau of Mines.
Washington, DC. August, 1993. .
Byrnes, B.H., C.B. Christianson, L.S. Holt, and E.R. Austin. 1990. "Nitrous Oxide Emissions from the
Nitrification of Nitrogen Fertilizers." In: Bouwman, A.F., ed. Soils and the Greenhouse Effect. John Wiley &
Sons, Chichester. pp.489-495.
. , ' ' ' v ' ';;' ' '.' :: : ,
Carlson. 1994. Telefax communication between Doug Keinath of ICF, Inc. and Patty Carlson of E.H. Pechan and
Associates, Inc. regarding transportation activity data. Three faxes dated March 22, 1994; March 23, 1994; and
April 5, 1994.
R-2
-------
Carter, T. A. 1989. Personal communication with Dr. Thomas A. Carter. Extension Professor of Poultry Science.
Poultry Science Department. North Carolina State University. Box 7608. Raleigh, NC 27695-7608.
CAST (Council for Agricultural Science and'Technology). 1992. Preparing U.S. Agriculture for Global Climate
Change. Task Force Report No. 119." Waggoner, P.E., Chair. CAST, Ames, Iowa. June, 1992.
C&EN. 1994. "Top 50 Chemicals Production Rose Modestly Last Year." Chemical & Engineering News, .vol.
72, number 15, p. 13. April 11, 1994
C&EN. 1993. "Top 50 Chemicals Production Recovered Last Year." Chemical &Engineering News, vol. 71,
number 15, p. 11. April 12, 1993 . . .
C&EN. 1992. "Production of Top 50 Chemicals Stagnates in 1991." Chemical and Engineering News. 70(15):
17. April 13, 1992.
CF Resources. 1991. 1991 Cattle Industry Reference Guide. Englewood, Colorado.
Chen, Y.R. 1983. "Kinetic Analysis of Anaerobic Digestion in Swine Wastes." in WJ. Jewell (ed.). Energy,
Agriculture and Waste Management, pp. 307-316. Ann Arbor.Science. Ann Arbor, MI.
Cicerone R.J., J.D. Shelter, and C.C. Delwiche. 1983. "Seasonal Variation of Methane Flux from a California
Rice Paddy." Journal of Geophysical Research, 88: 11,022 - 11,024.
Crutzen, P.J., I. Anselmann, and W. Seller. 1986. "Methane Production by Domestic Animals, Wild Ruminants,
and Other Herbivorous Fauna, and Humans." Tellus 38B: 271-284.
Crutzen, P.J. and M.O. Andreae. 1990. "Biomass Burning in the Tropics: Impact on Atmospheric Chemistry and
Biogeochemical Cycles." Science 250:1669-1678.
Daugherty, A.B. 1991. Major Uses of Land in the United States: 1987. U.S. Department of Agriculture,
Economic Research Service, AER No. 643. 35 pp.
Energy Information Administration (EIA). 1990-93a. Unpublished data from EIA-767, Steam and Electric Plant
Opperation and Design Report.
EIA. 1990-93b. Petroleum Supply Annual (Various Editions), DOE\EIA-0340, Energy Information
Administration, U.S. Department of Energy. .
R-3 .1 "
-------
EIA. 199 la. Estimates ofBiofeul Consumption in the United States During 1990. Energy Information
Administration, U.S. Department of Energy, Washington, DC.
EIA. 1991b. Natural Gas Annual 1990, Volume 1. Energy Information Agency, U.S. Department of Energy,
Washington, DC.
EIA. 1992a. Estimates of U.S. Biomass Energy Consumption 1992, DOE/EIA-0548(92), Energy Information
Administration, U.S. Department of Energy. May, 1994.
EIA. 1992c. "Full table presentation of Table 14." International Energy Annual 1991, DOE/EIA-0219(91),
Energy Information Administration, U.S. Department of Energy, December, 1992b.
EIA. 1993a. Annual Energy Review, 1992. Energy Information Administration, U.S. Department of Energy,
Washington, DC. June 1993.
EIA. 1993b. State Energy Data Report, 1991. Energy Information Administration, U.S. Department of Energy,
Washington, DC. May 1993.
EIA. 1993c. Ftiel Oil and Kerosene Sales 1992. Report DOE/EIA-0535(92)r Energy Information
Administration, U.S. Department of Energy, Washington, DC*. October 1993.
EIA. 1993d. Natural Gas Annual 1992: Volumes 1 & 2, DOE/EIA-0131(92)/1&2, Energy Information
Administration, U.S. Department of Energy, November, 1993.
EIA. 1994a Monthly Energy Review, DOE/EIA-003 5(94/03), Energy Information Administration, U.S.
Department of Energy, Washington, DC. March, 1994.
EIA. 1994b. State Energy Data Report 1992. Tables 12-17, Energy Information Administration, U.S. Department
of Energy-, Washington, DC. May, 1994.
EIA. 1994c. Quarterly Coal Report: October-December 1993, DOE/EIA-0121(4Q), Energy Information
Administration, U.S. Department of Energy. May, 1994.
EIA. 1994d. Natural Gas Monthly DOE/EIA-0130(94/5), Energy Information Administration, U.S. Department
of Energy. May, 1994. '
R-4
-------
EIA. 1994e. "Full table presentation of Table 14." International Energy Annual 1992. DOE/EIA-0219(92),
Energy Information Administration, U.S. Department of Energy, January, 1994.
EIA. 1994g. Emissions of'Greenhouse Gases in the United[States 1987'- 1992. DOE/EIA-0573. Energy
Information Administration, U.S. Department of Energy, In Press November, 1994.
EIA. 1994h, Annual Energy Review 1993. Energy Information Administration, U.S. Department of Energy,
Washington, DC. July 1994. ,
EIA. 1994L Estimates of U.S. Biomass Energy Consumption 1992. DOE/EIA-0548(92). Energy Information
Administration, U.S. Department of Energy, Washington, DC. May, 1994.
Eichner, M.J. 1990. "Nitrous Oxide Emissions from Fertilized Soils: Summary of Available Data." Journal of
Environmental Quality 19:272-280.
FAO (Food and Agricultural Organization). 1993. FAO Production Yearbook, 1992. Vol. 46. United Nations
Food and Agriculture Organization. Rome, Italy.
FAO. 1991. FAO Production Yearbook, 1990. Vol.44. United Nation Food and Agriculture Organization.
Rome, Italy.
Federal Aviation Administration (FAA). 1992. General Aviation Activity Survey:, Calendar Year 1992. Report
FAA-APO-93-10. Office of Aviation Policy, Plans, and Management Analysis; Federal Aviation Administration,
U.S. Department of Transportation; Washington, .DC. - '
FAA. 1990-92. Fuel Cost and Consumption. Monthly reports January 31, 1990 through December 31, 1992.
DAI-10, FAA, U.S.'Department of Transportation, Washington, DC.
Freedonia Group, Inc. 1991. Business Research Report B286: Carbon Dioxide. The Freedonia Group,
Incorporated. Cleveland, OH.
Ghosh, S. 1984. "Methane Production from Farm Waste." in M.M. El-Halwagi (ed.). Biogas Technology,
Transfer and Diffusion, pp. 372-380. .Elsevier. New York.
Griffin, R.C. 1987. CO, Release from Cement Production, 1950 - 1985. Institute for Energy Analysis, Oak Ridge
Associated Universities, Oak Ridge, TN.
R-5
-------
Hangebrauk, R.P., R.H. Borgwardt, and C.D. Geron. 1992. "Carbon Dioxide Sequestration." EPA, August 1992.
Hashimoto, A. G. 1992. Personal communication with Dr. Andrew Hashimoto. Professor and Department
Chairman. Bioresource Engineering Department. Oregon State University. Corvallis, OR. July 1992.
Hashimoto, A.G., V.H. Varel, and Y.R. Chen. 1981. "Ulitmate Methane Yield from Beef Manure; Effect of
Temperature, Ration Constituents, Anitbiotics and Manure Age." Agricultural Wastes. 3:241-256.
I!',! 1 ' ',,il' .'III!
Hill, D.T. 1984. "Methane Productivity of the Major Animal Types." Transactions of the ASAE. 27(2):530-540.
Hill, D.T. 1982. "Design of the Digestion System for Maximum Methane Production." Transactions of the ASAE^
2S(1);226-230.
Holzapfel-Pschom, A., R. Conrad, and W. Seiler. 1985. "Production, Oxidation, and Emissions of Methane in
Rice Paddies." FEMS Microbiology Ecology 31: 343-3 51.
ICF Consulting Group. Personal Communication with John Wasson. Estimate prepared for U.S. EPA, Office of
Air and Radiation, Washington, D.C.
!' II I
'
1
'
IPCC. 1992. Climate Change: The Supplementary Report to the IPCC Scientific Assessment. J.T. Houghton,
B.A. Callander, and S.K. Varney (eds.). World Meteorological Organization/United Nations Environment
Programme. New York, NY.
IPCC/ OECD. 1994. IPCC Guidelines for National Greenhouse'Gas Inventories, 3 volumes: Vol. 1, Reporting
Instructions; Vol. 2, Workbook; Vol. 3, Draft Reference Manual. Intergovernmental Panel on Climate Change,
Organization for Economic Co-Operation and Development. Paris, France.
Johnson, D.W.. 1992. "Effects of Forest Management on Soil Carbon Storage." Water, Air, and Soil Pollution
64:83-120.
.' ' I " ,
Kern, J.S., and M.G. Johnson. 1993. "Conservation Tillage Impacts on Natural Soils and Atmospheric Carbon
Levels." Soil Science Society of America Journal 57:200-210.
Kerr, R. 1994. "Did Pinatubo Send Climate-Warming Gases into a Dither?" Science, 263:18
Levine, J.S., W.R. Gofer, D.I. Sebacher, E.L. Winstead, S. Sebacher, and P.J. Boston. 1988. "The Effects of Fire
on Biogenic Soil Emissions of.Nitric Oxide and Nitrous Oxide." Global Biochemical Cycles 2: 445-449.
R-6
, , ,, i ^' ,
^;*1. ..... ill ..... !t "3! ..... lilS
-------
Lindau, C.W. and P.K, Bollich. 1993. "Methane Emissions from Louisiana First and Ratoon Crop Rice." Soil
Science 156:42-48.
Lindau, C.W., P.K. Bollich, R.D. DeLaune, W.H. Patrick, Jr., and V.J. Law. 1991. "Effect of Urea Fertilizer and
Environmental Factors on CH4 Emissions from a Louisiana, USA Rice Field." Plant Soil 136: 195-203.
Marland, G. and A, Pippin. 1990. ."United States Emissions of Carbon Dioxide to the Earth's Atmosphere by
Economic Activity." Energy Systems and Policy, 14(4); 323.
Marland, G. and R.M. Rotty. 1984. "Carbon Dioxide Emissions from Fossil Fuels: A Procedure for Estimation
and Results for 1950-1982." Tellus 36b:232-26l. '
Moore, B., R.D. Boone, I.E. Hobbie, R.A. Houghton, J.M. Melillo, G.R. Shaver, C.J. Vorosmarty, and G.M.
Woodwell. 1981. "A Simple Model for Analysis of the Role of Terrestrial Ecosystems in the Global Carbon
Cycle." In: Bolin, B. (ed.). Modelling the Global Carbon Budget. SCOPE 16. John Wiley and Sons, New York,
NY. pp. 365-385.
Morris, G.R. 1976. Anaerobic Fermentation of Animal Wastes: A Kinetic and Emiprical Design Fermentation.
M.S. Thesis. Cornell University. . .
NCDC (National Climatic Data Center). 1991. Historical Climatological Series Divisional Data. National
Oceanic and Atmospheric Administration. Ashville, NC.
Nizich, S.. 1994. Telefax communication between Doug Keinath of ICF, Inc. and Sharon Nizich of EPA
regarding transportation activity data. One fax dated March 14, 1994.
North, M. O. 1978. Commercial Chicken Production Manual. AVI. Westport, Connecticut.
OECD (Organization for Economic Co-Operation and Development). 1991. Estimation of Greenhouse Gas
Emissions and Sinks: Final Report from the OECD Experts Meeting, 18-21 February 1991. OECD, Washington,
DC.
ORNL (Oak Ridge National Laboratory). 1993. Transportation Energy Data Book, ORNL-6743, Edition 13.
ORNL, Oak Ridge, Tennessee. March, 1993.
ORNL. 1989. Estimate ofCO2 Emissions from Fossil Fuel Burning and Cement Manufacturing, Based on the
United Nations Energy Statistics and U.S. Bureau of Mines Cement Manufacturing Data. ORNL/CDIAC-25,
NDP-030. ORNL. Oak Ridge, Tennessee.
R-7
-------
OTA (Office of Technology Assessment. 1991. Changing by Degrees: Steps to Reduce Greenhouse Gases.
OTA-0-482. U.S. Government Printing Office. Washington, DC. February, 1991.
Powell, D.S., J.L. Faulkner, D.R. Darr, Z. Zhu, and D.W. MacCleery. 1993. Forest Statistics of the United States,
1992, USDA Forest Service. Report RM-234.
Radian. 1992. Nitrous Oxide Emissions from Adipic Acid Manufacturing - Final Report. Radian Corporation,
Rochester,NY " ' , "' ' \ ''"'"'i'' ' , '_""" ,'" ' " "''
Reimer, R.A., R.A. Parrett, and C.S. Slaten. 1992. Abatement of N2O Emissions Produced in Adipic Acid
Manufacture. Proceedings of the 5th International Workshop on Nitrous Oxide Emissions. Tsukuba, Japan. July
1-3, 1992. ' ' ' ' ! ' " '. """ ' ''
Rypinski. 1994. Memorandum from Arthur Rypinski of the Energy Information Administraion to Bill Hohenstein
of U.S. EPA regarding "Unpublished Data for Inventory," July 27, 1994.
Safley, L.M., M.E. Casada, J.W. Woodbury, and K.F. Roos. 1992a. Global Methane Emissions from Livestock
and Poultry Manure. EPA/400/1091/048. U.S. Environmental Protection Agency. Washington, D.C. February
1992. ' ' ""'
Safley, L.M., Jr. and P.W. Westerman. 1992b. "Performance of a-Low Temperature Lagoon Digester."
Bioresource Technology. 41:167-175.
Sass, R.L., F.M. Fisher, and Y.B. Wang. 1992. "Methane Emission from Rice Fields: The Effect of Floodwater
Management." Global Biogeological Cycles 6(3): 249-262.
Sass, R.L., F.M. Fisher, P.A. Harcombe, and F.T. Turner. 199 la. "Mitigation of Methane Emissions from Rice
Fields: Possible Adverse Effects of Incorporated Rice Straw." Global Biogeochemical Cycles 5: 275-287.
Sass, R.L., F.M. Fisher, F.T. Turner, and M.F. Jund. 1991b. "Methane Emissions from Rice Fields as Influenced
by Solar Radiation, Temperature, and Straw Incorporation." Global Biogeochemical Cycles 5: 335-350.
Sass, R.L., F.M. Fisher, P.A. Harcombe, and F.T. Turner. 1990. "Methane Production and Emissions in a Texas
Rice Field." Global Biogeochemical Cycles 4:47-68.
Schoeff, R.W. and D.J. Castaldo. 1991. "Market Data 1990." Feed Management 42:10-33.
R-8
-------
SRI (Stanford Research Institute). 1993. U.S. Directory of Chemical Producers. SRI International.
SRI. 1990. 1990 Directory of Chemical Producers, United States. SRI International, p. 444.
Strehler, A. and W. Stiitzle. 1987. "Biomass Residues." In: Hall, D.O. and R.R Overend (eds.). Biomass,
Regenerable Energy. John Wiley and Sons, Ltd. Chichester, UK.
Steele, L.R, E.J. Dlugokencky, P.M. Lang, P.P. Tans, R.C. Martin, and K.A. Masarie. 1992. "Slowing Down of
the Global Accumulation of Atmospheric Methane During the 1980's." Nature 358: 313-316.
Summers, R. and S. Bousfield. 1980. "Low Temperature Digestion of Siwne Manure," in Journal of the
Environmental Engineering Division, ASCE. 105(EEl):33-42.
Taiganides, E. P. and R. L. Stroshine. 1971. Impacts of farm animal production and processing on the total
environment, pp. 95-98. In: Livestock Waste Management and Pollution Abatement. The Proceedings ofthe-
International Symposium on Livestock Wastes, April 19-22, 1971, Columbus, Ohio. ASAE. St. Joseph, ML
Thiemens, Mark H. and William C. Trogler. 1991. "Nylon Production: An Unknown Source of Atmospheric
Nitrous Oxide. Science 251:932.
Turner, D.P., J.L. Lee, G.J. Koerper, and J.R. Barker (eds.). 1993. The.Forest Sector Carbon Budget of the United
States: Carbon Pools and Flux under Alternative Policy Options. EPA/600/3-93/093. U.S. EPA, Office of
Research and Development. May 1993.
TVA (Tennessee Valley Authority). 1993. Commercial Fertilizers, 1993. National Fertilizer and Environmental
Research Center, Tennessee Valley Authority, TN. December 1993.
University of California. 1977. Emission Factors From Burning of Agricultural Waste Collected in California.
USDA (U.S. Department of Agriculture). 1994a. Cattle. USDA, National Agricultural Statistics Service,
Agricultural Statistics Board. Washington, D.C. February 4,. 1994.
USDA. 1994b. Cattle and Sheep Outlook. USDA, Economic Research Service. Washington, D.C. February 14,
1994.
USDA. 1994c. Crop Production: 1993 Summary. USDA, National Agricultural Statistics Service, Agricultural
Statistics Board. Washington, D.C. January 1994.
R-9
-------
USDA. 1994d. Daily Outlook. USDA, Economic Research Service. Washington, D.C. February 23, 1994.
USDA. 1994e. Hog Outlook. USDA, Economic Research Service. Washington, D.C. January 13, 1994.
USDA. 1993. Crop Production: 1992 Summary. USDA, National Agricultural Statistics Service, Agricultural
Statistics Board, Washington, DC. January, 1993.
USDA. 1992a. Cattle. National Agricultural Statistics Service, USDA, Washington, D.C. February 1992.
USDA. 1992b. Cattle on Feed. National Agricultural Statistics Service, USDA, Washington, D.C. April 1992.
USDA. 1991. Crop Production: 1990 Summary. USDA, National Agricultural Statistics Service, Agricultural
Statistics Board, Washington, DC. January, 1991.
USDA. 1989a. Cattle. Released: February 8, 1989. Agricultural Statistics Board. ERS-NASS, USDA, P.O.
Box 1608, Rockville, MD 20850. 15pp.
I
USDA. 1989b. Cattle on Feed. Released: January 26, 1989. Agricultural Statistics Board. ERS-NASS, USDA,
P.O. Box 1608, Rockville, MD 20850. 14 pp.
USDA. 1989c. Hogs and Pigs. Released: January 6, 1989. Agricultural Statistics Board. ERS-NASS, USDA,
P.O. Box 1608, Rockville, MD 20850. 20 pp.
USDA. I989d. Layers and Egg Production,-1988 Summary. January, 1989. Agricultural Statistics Board. ERS-
NASS, USDA, P.O. Box 1608, Rockville, MD 20850. 40 pp.
USDA. 1989e. Poultry, Production and Value, 1988 Summary. April, 19891 Agricultural Statistics Board. ERS-
NASS, USDA, P.O. Box 1608, Rockville, MD 20850.
USDA. 1989f. Sheep and Goats. Released: February 8, 1989. Agricultural Statistics Board. ERS-NASS,
USDA, P.O. Box 1608, Rockville, MD 20850. 11 pp.
U.S.DOT (U.S. Department of Transportation). 1993. National Transportation Statistics, Annual Report. Report
DOT-VNTSC-BTS-93-1. Bureau of Transportation Statistics, U.S. Department^ Transportation, Washington,
DC. September 1993.
R-10
-------
U.S. EPA (U.S. Environmental Protection Agency). 1994a. International Anthropogenic Methane Emissions:
Estimates for 1990, Report to Congress. Office of Policy Planning and Evaluation, U.S. EPA, "Washington, DC.
U.S. EPA. 1994b. Memorandum from Jean Lupinacci of U.S. EPA's Office of Air and Radiation (EPA/OAR).
June 1994.
U.S. EPA, 1993a. Anthropogenic Methane Emissions in the United States, Estimates for 1990: Report to
Congress. Office of Air and Radiation, U.S. EPA, Washington, DC.
U.S. EPA. 1993b. National Air Pollutant Emission Trends, 1900-1992. U.S. EPA, Office of Air Quality
Planning and Standards. Research Triangle Park, NC. October 1993
U.S. EPA.-1993Q. Proceedings Workshop on Atmospheric Effects, Origins, and Options for Control of Two
Potent Greenhouse Gases: CF4 and Cf6. Sponsored by the Global Change Division, Office of Ah- and Radiation,
EPA, April 21-22, 1993.
U.S. EPA. 1992b. National Air Pollutant Emissions Estimates: 19QO -1991. U.S. EPA, Office of Air Quality
Planning and Standards, Research Triangle Park, NC.
U.S. EPA. 1990a. Policy Options for Stabilizing Global Climate. Office of Policy, Planning, and Evaluation,
U.S. EPA. Report No. 21P-2003.1.
U.S. EPA. 1990b. Methane Emissions from Coal Mining: Issues and Opportunities for Reduction. U.S. EPA,
Washington, DC.
U.S. EPA. 1985. Compilation of Air Pollutant Emission Factors, AP-42. U.S. EPA, Washington, DC.
USFS (USDA, Forest Service). 1990. An Analysis of the Timber Situation in the United States: 1989 - 2040: A
Technical Document Supporting the 1989 USDA Forest Service RPA Assessment. Forest Service, United States
Department of Agriculture. General Technical Report RM-199.
Waddell, Karen L., D.D. Oswald, and D.S. Powell. 1989, Forest Statistics of the United States, 1987. U.S.
Department of Agriculture, Forest Service. Resource Bulletin PNW-RB-168. 106 pp.
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11 i 11 in11,11 PI11iiini nil mini
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. ANNEX A ;
ESTIMATING EMISSIONS OF CO2 FROM
FOSSIL ENERGY CONSUMPTION
; The purpose of this annex is to provide detailed descriptions of two different methods for
estimating emissions of CO2 from fossil energy consumption and to. discuss their differences. This
annex is divided into three sections. The first section presents the methodology used to estimate
emissions in the main body of this report. This methodology is a detailed, end-use oriented
approach, often referred to as a "bottom-up" methodology, which relies on Obtaining fossil energy
consumption information at a very disaggregated level by specific .use of the energy within the
U.S. economy. This methodology is conceptually similar to the detailed technology-based
approach discussed in the IPCC emission inventory guidelines (IPCC/OEGD, 1994; Vol. 3). The
second section presents a methodology that relies on aggregated.data monitoring the flow of fossil
energy into and .out of the U.S. economy at the national level. This approach is often referred to
as a "top-down" methodology, and it is the default estimation methodology recommended by the
IPCC (IPCC/OECD, 1994; Vol. 3). In the third section, the two methods are compared and the
resulting differences briefly discussed.
I.
Estimating Carbon Dioxide Emissions Using the Bottom-up Methodology
. - The bottom-up methodology is characterized by the seven basic steps described below. ,
This discussion focuses on emission estimates for the year 1990,-with the relevant data presented
in Tables A-l through A-6. Relevant data sources and notations are referenced: in each table.
Emission estimates for 1991, 1992, and 1993 were calculated using the same bottom-up,.
methodology. \
7.
Determine energy consumption by energy type and sector.
The bottom-up methodology used by the U.S. for estimating CO2 emissions from fossil
energy consumption is conceptually similar to the approach recommended by the IPCC for
countries that .intend to develop detailed, sectoral-based emission estimates (IPCC, 1994; Vol. 3).
Basic consumption data by sector are presented in Rows A-E of Table A-l, with total U.S. fossil
fuel consumption by energy type presented in Row F of Table A-l. Fuel consumption data for
the bottom-up approach were obtained directly from the Energy Information Administration
(EIA) of the U.S. Department of Energy, which is responsible for the collection of all U.S. energy
data. All the ELA data were collected through surveys at the point of delivery or use, so they
reflect the reported consumption of fuel by sector and fuel type. Individual data elements came
from a Variety of sources within EIA Most information is from published reports, although some
data have-been drawn from unpublished energy studies and databases maintained by EIA. Exact
sources are indicated in footnotes provided in each table of this annex.
Sectoral ancTcategory totals are presented in the last column and last row of Table A-l.
By aggregating consumption data by sector (Le., residential, commercial, industrial, transportation,
and electric utilities), primary fuel type (e.g., bituminous coal, natural gas, and petroleum), and
secondary fuel category (e.g., gasoline, distillate fuel, etc.), one can estimate total U.S. energy
consumption for a particular year: The 1990 total energy consumption across all sectors and
energy types is 71,836 trillion Btu, as indicated in the last entry of Row F in Table A-l.
A-l
-------
There are differences between the consumption figures presented in Table A-l and those
recommended in the IPCC emission inventory methodology. First, all consumption data,in .the
U.S. inventory are presented using higher heating values (HHV) rather than the'lower heating
values (LHV) reflected in the IPCC emission inventory methodology. This convention is followed
because all data obtained from EIA were based on'HHV. Second, the energy data in Table A-l
do not include energy use from U.S. territories. The IPCC methodology, however, recommends
that countries report emissions according to the reporting format used by the International
Energy Agency (IEA). Since the IEA data for the U.S. include energy use in U.S. territories,
U.S. energy consumption data have been adjusted accordingly to ensure that emissions from these
territories are included in the U.S. total (see Step 5 for further discussion). Third, the
consumption figures in Table A-l include bunker fuels. The IPCC recommends that countries
estimate emissions from bunker fuels separately and exclude these emissions from national totals.
This adjustment is described below in Step 6. -
2.
Determine the total carbon content of all fuels.
Total carbon was estimated by multiplying energy consumption by a carbon coefficient that,
reflected the amount of carbon per unit of energy for each fuel. The resulting quantities are
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. Potential emissions by sector and
fuel type are given in Rows H-L of Table A-l, with total potential emissions provided in Row M.
The carbon coefficients used in the U.S. inventory are given in Row G of Table A-l and Table A-
1A. These carbon coefficients are estimates derived by EIA from detailed fuel information and
are similar to the carbon coefficients contained in the IPCCs default methodology, with
modifications reflecting fuel qualities specific to the .U.S.
ซ
3. Estimate the amount of carbon stored in products. ';
Depending on end use, non-fuel uses of fossil energy can result in storage of some or all
of the carbon contained in the energy product for some period of time. 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-fuel 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 after utilization. '
, ' ! ' ' , ' :' ' , '
The amount of carbon sequestered or stored in non-fuel uses of fossil fuel energy
products was based on data concerning -the end uses and ultimate fate of various energy products,
with all non-fuel use attributed to the industrial and transportation sectors. This non-fuel
consumption is presented in Rows A and B of Table A-2. Non-fuel consumption was then
multiplied by a carbon coefficient (Row C of Table A-2) to obtain the carbon content of the fuel,
or the maximum amount of carbon that could potentially be sequestered if all the carbon in the
fuel were stored in non-fuel products. Values for the total amount of carbon that could be stored
are given in Rows D and E of Table A-2. Carbon content was then multiplied by the fraction of
carbon actually sequestered in products (Row F of Table A-2), resulting in the final estimate of
carbon sequestration by sector and fuel type in Rows G-H of Table A-2. Total sequestered
carbon is provided in Row I of Table A-2. Assumptions of the proportion of carbon sequestered
were based on IPCC (1994; Vol. 3) and U.S. specific estimates by EIA. Subtracting carbon
A-2
-------
sequestered from potential emissions results in net potential carbon emissions (Row A of Table
A-3). ; . '.' ;. . .-.- - - - -
4. Adjust for carbon that does not oxidize during combustion.
Since combustion processes are not 100 percent efficient, some of the carbon contained in
fuels would not be emitted to the atmosphere. Rather, it remains stored as soot or other
byproducts of inefficient combustion. The estimated fraction of carbon not oxidized in U.S. .
energy conversion processes due to inefficiencies during the combustion process ranges from one
percent for oil and coal'to 0,5 percent for gas. Except for coal these assumptions are consistent
with the default values recommended by the IPCC. In the U.S. unoxidized carbon from coal
combustion was estimated to be no more than.one percent (Bechtel, 1993). Row B of Table A-3
presents fractions oxidized by fuel type. Row C of the same table gives the actual net emissions
once oxidation has been considered (but prior to adding emissions from territories or subtracting
emissions from bunker fuels).
5. . Account for fuel consumed in U.S. Territories
EIA's energy use data for the U.S. includes only the 50-U.S. states and the District of
Columbia. The data reported for the U.S. by international agencies, such as the International
Energy Agency (IEA), includes consumption in the U.S". territories. To account for this
difference, emission estimates for the U.S. territories were computed separately and added to
domestic emissions from fossil fuel combustion for energy. Energy consumption data from U.S.
territories are presented in Rows A-G of Table A-4. They are reported in thousands of barrels
. per day, except for coal, which is reported in thousands of short tons. To calculate territory
emissions, it was necessary to convert consumption in barrels per day and short tons to units of
.annual energy consumption by multiplying the physical units with appropriate conversion factors
from EIA (EIA, 1994b), which are presented in Row H. The resulting energy consumption by
territory is given in Rows I-N of Table A-4, with total copsumption in all territories provided in
Row O. v
The remaining calculations for territories followed the same procedure used for the
consumption of fuels in the fifty States, Le. estimation of carbon content and adjustment for the
fraction of carbon not oxidized (see Rows P-Y of Table A-4). Once these calculations were
completed, actual emissions from territories (Row Y) were added to actual emissions from the
fifty States (see Row D'of Table A-3). - . ; _ ,
.''"-" , " '
6. Subtract emissions from bunker fuels. ;'..''.
According to the decision reached at INC-9, emissions from international transport
activities, or bunker fuels, should not be included in national totals. There is international
disagreement as ,to which countries are responsible for these emissions, and until this issue is
resolved, countries are to report these emissions separately. EIA data include bunker fuels
(primarily residual oil) as part of consumption by the transportation sector. To compensate for
this, bunker fuel emissions were calculated separately and subtracted from total net emissions.
The calculations for bunker fuel emissions followed the same procedures used for consumption of
all fossil fuels in. the United States (Le., estimation of consumption, determination of carbon
A-3
-------
content, and adjustment for the fraction of carbon not oxidized). These calculations are
summarized in Table A-5. Total emissions from bunker fuels were then subtracted from actual
net emissions from domestic fuel consumption (see Row E of Table A-3). Bunker fuel emissions
were allocated to the transportation sector.
7. Summarize emission estimates. . -
Table A-6 summarizes actual CO2 emissions in the U.S. by major consuming .sector (i.e.,
residential, commercial, industrial, transportation, and electric utilities) and major fuel type (i.e.,
coal, natural gas, and oil). Adjustments for bunker fuels and carbon sequestered in products have
already been made. Emissions are expressed in terms of million metric tons of carbon equivalent
(MMTCE), except in the last column and row of Table A-6, which shows carbon dioxide
emissions on a full molecular weight basis (Column E and Row H).
Table A-7 summarizes U.S. carbon dioxide emissions by end-use sector. To determine
these estimates, emissions from the electric utility sector were distributed over the four end use
sectors according to their share of electricity consumed. Column A presents electricity
consumption by end-use sector, which was used to calculate the fraction of total electricity
consumed by each of the four end-use sectors (Column B). This fraction was then multiplied by
total emissions from the utility sector from Table A-6, Column D, resulting in the portion of
utility emissions attributable to each end-use sector (Column D). These end use emissions from
electricity consumption were then added to the non-utility emission estimates taken from Table
A-6 (Column E), resulting in emissions from each of the four end-use sectors (Column F).
II. Estimating Carbon Dioxide Emissions Using the Top-Down Methodology
I '. ' <
It is possible to estimate carbon emissions from fossil fuel consumption using alternative
methodologies and/or different data sources than those described above. For example, the IPCC
recommends a "top-down" (carbon balance) approach for estimating carbon dioxide emissions (see
Greenhouse Gas Inventory Workbook (IPCC/OECD, 1994; Vol. 3)). This method estimates fossil
fuel consumption by adjusting national aggregate production data for imports, exports, and stock
changes rather than relying on end-user surveys. The operating principle is that once carbon is
brought into a national economy, it is either saved in some way (e.g., stored in products, kept in
fuel stocks, or left unoxidized in ash) or released into the atmosphere. Accounting for actual
consumption of fuels at the sectoral or sub-natio.nal level is not required. The following
discussion provides the detailed calculations for estimating CO^ emissions for the U.S. using the
IPCC-recommended "top-down" methodology.
/, Collect and Assemble Data in Proper Format
To ensure the comparability of national inventories, the IPCC has recommended that
inventories report energy data using the International Energy Agency (IEA) reporting convention.
National energy statistics were collected from several DOE/EIA, documents in order to obtain the
A-4
-------
necessary data on production, imports, exports, and stock changes. These data are presented in ,
the appropriate format in Table A-8. '. _
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 basis, (e.g., Btu's or
joules). Because detailed fuel statistics are typically provided in physical units (as in Table A-8),
they must first be converted to units of energy before carbon emissions can be calculated. Fuel
statistics were converted to their energy equivalents by using conversion factors provided by
DOE/EIA (EIA, 1991d; EIA, 1993d). These factors are listed in Table A-9. The resulting fuel
statistics (in trillion Btu) are provided in Rows A-E of Table A-10.
2. Estimate Apparent Fuel Consumption -
The next step of the IPCC method 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, coking coal, steam coal, subbituminous coal, lignite, and natural gas) can be
calculated as follows: .. . . . ,
. Production + Imports ^Exports Stock Change
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:
* Imports , Exports Stock Change
Note 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:
The IPCC-jcecommended default methodology calls for estimating apparent fuel ;
consumption before converting to a common energy unit. However, certain primary fuels in the
U.S. (e.g., natural gas arid 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, U.S. fuel statistics were converted to their heat equivalents first, followed by the
estimation of apparent consumption. The results are provided in Row F of Table A-10.
1 For the U.S., national aggregate energy statistics typically exclude data on the U.S. territories. As a
result, national statistics were adjusted to include production, imports, exports, and stock changes within
the U.S. territories. ~ ."'''"
A-5
-------
3.
Estimate Carbon Emissions
Once apparent consumption is estimated, the remaining calculations are virtually identical
to those for the bottom-up approach (see Section I above). That is:
Potential carbon emissions are estimated using fuel-specific carbon emission factors (see
Table A-ll).2
ซ The carbon sequestered in non-fuel uses of fossil fuels (e.g., plastics or asphalt) is then
estimated and subtracted from the total amount of carbon (see Table A-12).
The carbon contained in bunker fuels is subtracted from the remaining amount of carbon
to obtain net carbon emissions (Rows C and D in Table A-13).3
Finally, to obtain actual carbon emissions, net carbon emissions are adjusted for any
carbon that remains unoxidized as a result of incomplete combustion (e.g., carbon
contained in ash or soot; see Rows E and F in Table A-13).4
4. Convert to CO2 Emissions
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 is converting from.units of carbon to units of CO2. Actual carbon emissions.
were multiplied by the molecular to atomic weight ratio of CO2 to carbon (44/12) to obtain total
carbon dioxide emitted from fossil fuel combustion. The results are contained in Row G of Table
A-13. . ,
III. Comparison Between The Two Methods
These two alternative methods can both produce reliable estimates that are comparable
within a few percent. The major difference between these methods lies in the energy data used
to derive carbon emissions (Le., actual reported consumption for the bottom-up methodology vs.
2 Carbon coefficients from ELA. were used wherever possible. Because EIA did not provide
coefficients for coking coal, steam coal, coke, and natural gas liquids, the IPCC-recommended emission
factors were used in the top-down calculations for these fuels.
3 Bunker fuels 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. Thus, CO2 emissions from the combustion of those fuels are attributed to the
country of delivery even though most of the actual emissions may occur outside its boundaries. This is
done to ensure that all fuel is accounted for hi the methodology. For informational purposes, the IPCC
methodology originally recommended that emissions from bunker fuels be estimated separately, but not
subtracted from the national total. However, at the 9th session of the INC, it was recommended that
countries report bunker fuel emissions separately and exclude these emissions from the national total.
* , . '"
4 For the portion of carbon that is unoxidized during coal combustion, the IPCC suggests a global
average value of 2 percent. However, because combustion technologies in the U.S. are more efficient, the
U.S. inventory uses 1 percent in its calculations.
A-6
-------
apparent consumption derived for the top-down methodology). In theory, both approaches
should yield the same results. In practice, however, slight discrepancies may occur. For the U.S.
these differences are discussed below.
1. Differences in Total Amount of Energy Consumed
The following table summarizes the differences between the two methods in estimating
total energy consumption in the U.S.
Energy Consumption in the U.S.: Bottom-Up Versus Top-Down Methodology
(Trillion Btu)
BottomTUpa
Top-Down3
Difference
Coal
18,943
18,882
+0.3%
Gas
. 19,348
19,297
: +0.3%
Oil
34,001
33,009
+2.9%
TOTALb
72,291
71,189
+7.5%
a. Includes U.S. territories. Totals may not equal sum of components due to independent rounding.
b. . Totals presented may not equal the sum of the individual source categories due to independent rounding. .
Although theoretically the two methods should arrive at the same estimate for U.S. energy
consumption, the bottom-up methodology provides an energy total that is about 1.5 percent
higher than.the top-down methodology. The greatest difference lies in the higher amount of-oil
consumption estimated using the bottom-up methodology. There are several potential sources for
these discrepancies: .
'. . Product Definitions: The fuel categories in the top-down approach are different
than the bottom-up categories, particularly for petroleum. For example, the top-
down approach estimates apparent consumption for crude oil. Crude oil is not
typically consumed directly, but refined into other products. As a result, the U.S.
does not focus on-estimating the energy content of crude oil, but rather estimating
the energy content of the various products from trie crude oil refining process.
: , The U.S. 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
U.S. for estimating energy consumption. Other differences in product definition
include using sector specific coal statistics in the bottom-up approach (ฃ&,
residential, commercial, industrial coking, industrial other, and transportation coal),
while the top-down method uses coking coal and steam coal (steam coal consists of
, both anthracite and bituminous coal). Also, the LPG used in the bottomrup
calculations is actually a combination of the NGL and LPG statistics used in the
' top-down methodology.
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 U.S. and abroad. Similarly, for the
top-down methodology, the U.S. used a weighted average for steam coal based on
the fraction of production that is anthracite and bituminous because the U.S. does
A-7
-------
not typically estimate the energy content of a "steam coal" category. However, this
overstates the bituminous fraction of~the steam coal because a portion of
bituminous production is also part of coking coal.
Possible inconsistencies in U.S. Energy Data: The U.S. has not focused its energy
data collection efforts on Obtaining the type of aggregated information used in the
top-down methodology. Rather, the U.S. believes that its emphasis on collection
of detailed energy consumption data is a more accurate methodology for the U.S.
to obtain reliable energy data.
Balancing Item: The top-down method uses apparent consumption estimates while
the bottom-up method 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."
Given these differences in energy consumption data, the next step for each methodology
involved estimating emissions of CO2. The following table summarizes the differences between
the two methods in potential carbon emissions.
Potential Carbon Emissions in the U.S.: Bottom-Up Versus Top-Down Methodology3
(MMT Carbon)
Bottom-Upb
Top-Downb
difference
Coal
485
491
-7.2%
Gas
280
279
+0.3%
Oil
671
654
+2.5%
TOTAL
1,436
1,424
0.8%
This comparison is based on potential carbon emissions rather than actual net emissions. The two methods are
identical from this point forward since the carbon sequestered calculation and the amount oxidized are the same
for both methods.
Includes U.S. territories.
As previously shown, the bottom-up methodology resulted in a 1.5 percent higher estimate
of energy consumption in the U.S. than the top-down methodology, but the resulting estimate of
carbon emissions was only 0.8 percent higher. Since natural gas figures were consistently higher
in the bottom-up methodology and the oil figures, showed only a small variation, the major source
of the difference was due to coal estimates, where the bottom-up method yielded coal
consumption that was slightly higher and emissions that were lower than in the top-down method.
Potential reasons for these patterns may include:
Product Definitions: Coal data is aggregated differently in each methodology, as
noted above, with U.S. coal data typically collected in the format used the bottom-
up methodology. This results in more accurate estimates than in the top-down
methodology. Also, the top-down methodology relies on a "crude oil" category for
determining petroleum-related emissions. Given the many sources of crude oil in
A-8
-------
the U.S., 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. . .
., Carbon Coefficients: The top-down methodology relies on several default carbon
coefficients provided by IPCC (IPCC\OECD,. 1994; Vol. 2), while the bottom-up .
methodology uses category specific coefficients that are likely to be more accurate.
For example, in the top-down methodology default coefficients are used for coking
coal, steam coal, coke and natural gas liquids. Also, as noted above, the carbon ,
coefficient for crude oil is not an easy value to obtain given the many sources of
.crude pilfer the U.S. . '.
Although the two estimates using different methodologies are fairly,close, the U.S.,
believes that the bottom-up methodology provides a more accurate assessment of CO2 emissions
for the U.S. This is largely a result of the data collection techniques used in the U.S., where
there has been more emphasis on obtaining the detailed, products-based information used in the '"
bottom-up methodology than obtaining the aggregated energy flow data used in the.top-down
methodology., However, the U.S. believes that it is important.to understand fully the reasons for
the differences between the two methods. At this time the U.S. is actively involved in evaluating
the reasons for these differences. The U.S. will continue to work with the IPCC/OECD
Greenhouse Gas Emission Inventory Programme as further/information becomes available.
A-9
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Table A-4: CO2 EMISSIONS FROM FOSSIL FUEL CONSUMPTION FOR ENERGY IN U.S. TERRITORIES -1990
Territory Consumption
Row
A
B
C
D
E
P
G
TERRITORY
American Samoa
Guam
Puerto Rico
U.S. Virgin Islands
Other U.S. Pacific Island
Wake Island
TOTAL
of Fossil Fuel for Energy
COAL
(1000 Short Tons)
Total
Coal
220.0
PETROLEUM
(1000 Barrels oerdav)
Distillate
Fuel Oil
2.6
4.8
21.5
4.5
1.1
0.3
34.8 ,
Jet Fuel &
Kerosene
0.7
5.1
12.4
4.7
0.4
7.4
30.7
LPG
0.0
0.2
2.4
7.7
0.0
10.3
Lubricants
0.0
0.0
0.3
0.0
0.0
0.3
Motor
Gasoline
0.3
2.3
45.7
3.9
0.5
52.7
Residual
Fuel Oil
0.2
36.8
16.0
0.0
53.0
Other
Petroleum
0.1
0.1
21.0
18.2
0.0
0.9
40.3
Total
Petroleum
3.7
12.7
140.1
55.0
2.0
8.6
222.1
TOTAL
NA
Conversion Factors (Btu/Short Ton and Million Btu/Barrel)
H
24.4
5.825
5.670
4.011
6.065
4.620
6.287
5.796
Territory Consumption of Fossil Fuel for Erterqy (trillion Btu)
1
O
K
L
M
N
O
American Samoa
Guam
Puerto Rico
U.S. Virgin Islands
Other U.S. Pacific Island
l/Vako Island
TOTAL
5.4
5.5
10.2
45,7
9.6
2.3
0.6
74.0
Carbon Coefficients (MMT/Quadrillion Btu)
P 1 25.14
19.95
1.4
10.6
25.7
9.7
0.8
15.3 '
63.5
19.74
0.0
0.3
3.5
11.3
0.0
0.0
15.1
17.16
0.0
0.0
0.7
0.0
0.0
0.0
Q.7
0.5
3.9
77.1
6.6
0.8
0.0
- 88.9
0.0
0.5
84.4
36.7
- o.o
0.0
121.6
0.2
0.2
44.4
38.5
0.0
1.9
85.3
20.24
19.41
21.49
20.31
' 7.7
25.6
281.5
112.4
4.0
17.9
449.0
454.4
Territory Emissions from the Consumption of Fossil Fuel for Enerqy (MMTCE)
Q
R
8
T
U
V
W
American Samoa
Guam
Puerto Rico
U.S. Virgin Islands
Other U.S. Pacific Island
Wake Island
TOTAL
0.1
0.1
0.2
0.9
0.2
0.0
0.0
1.5
S iFraction Oxidized
0.990
0.990
Actual Emissions from Territories (MMTCE)
Y I
0.1
1.5
0.0
0.2 -.
0.5
0.2
0.0
0.3
1.3
0.990
1.2
0.0
0.0
0.1
0.2
0.0
0.0
0.3
0.990
0.3
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.990
0.0
0.0
0.1
1.5
0.1
0.0
0.0
1.7
0.990
1.7
0.0
0.0
1.8
0.8
0.0
0.0
2.6
0.990
2.6
0.0
0.0
0.9
, 0.8
0.0
0.0
, 1.7
0,990
1.7
0.2
0.5
5.7
2.3
0.1
0.4
9.1
9.2
9.0 II 9.1
Sources: At( consumption data is from EIA (1992c). The thermal conversion factors for petroleum were taken
from Appendix D of the State Energy Data Report 1992 (El A, 1994b)." The thermal
conversion factor for coal was derived by El A as described in Rypinski (1994). Carbon coefficients
, are the same as used for U.S. energy emissions in Table A-1 (the coal coefficient is for bituminous coal).
Notes; 1. As defined by EIA, "Petroleum Other includes asphalt,-coke, aviation gasoline, .naphthas,
paraffin wax, petrochemical feedstocks, unfinished oils, white spirits, blending components,
and miscellaneous production. All territory consumption of "Other Petroleum" fell into the
"Miscellaneous Production" category. A conversion factor of 5.796 million Btu per barrel for this
category is given in Appendix D of the State Energy Data Report 1992 (EIA, 1994b). The carbon
coefficient for this category is the same as that given for "Miscellaneous Products," in Table A-1 -A.
2, "-" Indicates consumption is less than 50 barrels per day, and thus not reported.
3. NA= Not Applicable
4. -The conversion from barrels per day to trillion Btu is done as follows:
(1000 barrels/day)(365 days/year)(millionBtu/Barrel)(i trillionBtu/10"6 millionBtu)
-------
Table Ar5: EMISSIONS FROM BUNKER FUEL CONSUMPTION -1990
Bunker Fuel Consumption (1000 Barrels)
Re
h
I
)W TERRITORY
i TOTAL
FUEL
Jet Residual
Fuel Fuel Oil
NA 113880.0
Distillate Fuel Oil TOTAL
& Other Products
19345.0 . - '
Conversion Factors (Million Btu/Barrel)
II .' :'.
NA 6.287
Bunker Fuel Consumption (Trillion Btu)
. I Q HTOTAL
263.8 716.0
Carbon Coefficients (MMT/QBtu)
I R -I
19.74 21.49
5.825
. -.
112.7 1092.4
1 9.95
Emissions from Bunker Fuel Consumption (MMTCE)
I z HTOTAL
5.2 15.4
| AA ||Fraction Oxidized
0.990 0.990
2.2 || 22.8
-
0.990
Actual Emissions from Bunker Fuel Consumption (MMTCE)
I BB II 5.2 15.2
2,2 || 22.6 |
"--.-' '- ' '
Sources:. Residual and distillate fuel consumption are form ElA(1992c). Jet fuel consumption
is'from ORNL (1993). The barrels to Btu conversion factors are from EIA (1994b).
Carbon coefficients are the same as used in Table A-1.
-------
Table A-6: Summary of U.S. Emissions -1990
Row
A
B
C
D
E
F
Column A :
Sector
Residential
Commercial
Industrial
Transportation
Utilities
U.S. Territories
Coal
(MMTCE)
1.6'
2.4
68.3
0.0
407.3
0.1
G llTOTAL
479.6
H HTOTAL (MMTC02) I 1 758.7
B
Natural Gas
(MMTCE)
65.3
39.0
118.9
9.9
41.3
0.0
274.4
1006.1
CD E
Petroleum
(MMTCE)
24.0
18.0
103.5
399.9
26.6
9.0
Total
(MMTCE)
90.9
59.4
290.7
409.8
475.2
9.1
Total
(MMTC02)
333.2
217.8
1065.9
1502.6
1742.5
33.4
581.1
1335.1
2130.7
4895.4
4895.4
Sources: Tables A-1 through A-3
Note: Bunker Fuels account for emissions of 24.6 MMTCE and are already subtracted in the above table.
-------
Table A-7: END USE SECTOR EMISSIONS COMPARISON -1990
Column A
Sector
Residential
Commercial
Industrial
Transportation
U.S.Territories
Electricity
Consumption
(Bkwhrs)
924.0
839.0
946.0
4.0
0.0
B
Fraction
of Total
Consumption
0.3406
0.3093
0.3487
0.0015
0.0000
C
Utility
Emissions
(MMTCE)
475.2
475.2
475.2
475.2
475.2
D "
Emissions from
Electricity Consumption
(MMTCE)
161.9
147.0
165.7
0.7
0.0
E
Non-Electricity
Emissions
(MMTCE)
90.9
59.4
290.7
409.8
, . 9.1
F
Total Sector
Emissions
(MMTCE)
252.7
206.4
456.4
410.5
9.1
TOTAL
2713.0
1.0
475.2
859.9
1335.1
Sources: Electricity consumption by sector is from Tables 13-16 of State Energy Data Report,
1992(EIA, 1994b). All other information is taken from Tables A-1 and A-2.
-------
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-------
ANNEXE
EMISSIONS FROM MOBILE COMBUSTION
, Greenhouse gas emissions from mobile sources in this section are reported by transport
mode (i.e., road, rail, air),-vehicle type, and fuel type. The emissions estimates for NOX,
NMVOCs, and CO (U.S. criteria pollutants) in this section were taken directly from the U.S.
EPA's National Air Pollutant Emissions Trends, 1900 -1992 (U.S. EPA, 1993b). This EPA report
provides emission estimates for these gases by sector and fuel type using a "top down" estimating
procedure: the emissions were calculated either for individual sources or for many sources
combined using basic activity data (such as amount of fuel delivered, or miles travelled) as
indicators of emissions.
Estimates for methane and nitrous oxide emissions from mobile combustion were
calculated by multiplying the appropriate emission factors provided in OECD (1991) by the source
numbers of each activity level. National activity data for individual source categories were
obtained from a number of publications from U.S. agencies. Depending on the source category,
these basic activity data may include fuel consumption or deliveries, total vehicle miles travelled,
etc. Activity data used in conjunction with emission factors relate the quantity of emissions to the
activity.
Estimates of NMVOCs, NOX, and CO Emissions From Mobile Combustion
Estimates of NMVOCs, NOX, and CO emissions from gasoline and diesel-powered motor
vehicles reported by EPA (1993b) are based upon vehicle miles traveled (VMT) and emission
factors. For NMVOCs, NOX, and CO, emission factors were obtained from the MOBILE4 model,
a model used by the U.S. EPA as a tool for estimating exhaust and running loss emissions from
highway vehicles in nonattainment areas and urban air sheds. The emission factors developed by
the Organization for Economic Co-Operation and Development of the IPCC (OECD, 1991) were
derived from data used in this model. The MOBILE4 model requires information on ambient
temperature, vehicle speeds, gasoline volatility, and other variables for emission calculation.
Emissions of NMVOCs, NOX, and CO from aircraft reported by EPA (1993b) are based
on the number of take-offs and landings reported by the Federal Aviation Administration (FAA,
1990-92 and 1992) and AP-42 emission factors for various types of aircraft.4 Average emission
factors were calculated which take into account the national mix of different types of aircraft used
for general aviation, military, and commercial purposes.
Emissions from railroads are calculated by EPA based on diesel, coal, and residual fuel
consumption by railroads, as reported by the Energy Information Administration (EIA) of the
U.S. Department of Energy (U.S. DOE; EIA, 1993c). Average emission factors that are
applicable to .each type of fuel were used.
Emissions from vessels operating inside the U.S. boundaries are based on:
diesel, residual fuel, and coal consumption data reported by the
4 Emission occurring when aircraft are above 3,000 feet are not included in these estimates.
B-l
-------
U.S. Department of Energy (U.S. DOE)
, 'IP . , - ;j .,.'' ' J I II
marine gasoline sales data reported by U.S. Department of
Transportation (U.S. DOT)
national boat and motor registration and usage factors
"li" ' - ' '; :' ,'>,'' I II
AP-42 emission factors
Emissions from coal-fired vessels were based on an average emission factor for coal
combustion in boilers. Emissions from off-highway vehicles were calculated from estimated fuel
use (based on each equipment subcategory, population data, and an annual fuel use factor) along
with fuel deliveries of diesel and gasoline reported by the U.S. DOE and U.S. DOT.
Estimates of CH^ and N2O Emissions From Mobile Combustion
Estimates of CH4 and N2O emissions from gasoline vehicles (motorcycles excepted) were
determined by multiplying the appropriate emission factors provided in OECD (1991) by the
source numbers of each activity level (the distance traveled by each vehicle category and emission
control type). The source number of each activity level was determine'd* from:
v-i : , ' ' " ' , I ,W III II
travel fraction of each model year (the fraction of the vehicle miles
travelled or VMT attributed to a particular model year)
'': ; '" ...;- II i| i i 11 i, in
.,':.: '. :",, I; ll i1 ll I i i I" 1
distribution of control technology in each model year
V :, ' ' i'; vv . ' II ' I ' uill 'I
total vehicle miles travelled by each vehicle category.
Data were obtained from the U.S. EPA's National Vehicle and Fuel Emissions Laboratory
(Brezinski et al, 1992; Carlson, 1994; Nizich, 1994; U.S. EPA, 1992b) and the U.S. Department of
Transportation (FAA, 1990-1992; FAA, 1992; U.S. DOT, 1SJ93). Data for all gasoline vehicles are
presented in Table B-l. Given the uncertainty underlying these estimates, an arbitrary uncertainty
range of ฑ 50 percent was assigned to the resulting emission totals.
B-2
'I lili, ' ,., Jiilliiliglil , * ,,;,j hi ; !, > ฃ M 'iซ IL blH,, lilt' Ililll ' n./lLif i! i
-------
Table B-l. Gasoline Vehicle Data
Data Category
VMT (TO6 Miles)
3-Way Catalyst
Oxi-3-Way Catalyst
Oxi-Catalyst
Non-Catalyst
Uncontrolled
Passenger
Cars
1,503,000
45%
32%
18%
2%
4%
Light Duty
Trucks 1
323,000
36%
17%
14%
2%
31%
Light Duty
Trucks 2
157,000
30%
15%
' 14%
3%
39%
Heavy Duty
Vehicles
33,000
6%
0%
9%
35%
50%
Source: 1. VMT are from U.S. Department of Transportation, Federal Highway
Administration, and U.S. EPA (Brezinski, 1992).
2. Distribution of control technologies are calculated from U.S. EPA data (Brezinski,
1992). _
Because the travel fraction and control technology data for diesel vehicles and motorcycles
are currently not available from the U.S. EPA, emissions for these vehicle types were calculated
as a range by multiplying the total source activity level (i.e., the total vehicle miles travelled)
available from the U.S. EPA by the high (uncontrolled) and low (advanced) emission factors
provided for each category (OECD, 1991). The emission estimate reported in the inventory for
diesel vehicles and motorcycles is the midpoint of this range. The data used are included in Table
B-2. ' .'' '
Table B-2. Diesel Vehicle and Motorcycle Data
Vehicle Type
Diesel Passenger Cars
Light Duty Diesel
Heavy Duty Diesel
Motorcycles
Vehicle Miles Travelled (106 Miles)
12,000
4,000
106,000
11,000
Source: U.S. Department of Transportation, Federal Highway Administration and U.S. EPA
(Brezinski, 1.992).
Emissions from locomotives and off-highway vehicles were calculated using (1) emissions
factors from OECD (1991) and (2) estimated consumption by vehicle and fuel type (Brezinski, et.
ai; Carlson, 1994; Nizich, 1994; FAA, 1990-92 and 1992; and U.S. DOT, 1993). Emissions from
(marine) vessels were calculated using (1) U.S. EPA data on quantity and type of fuel used and
emissions factors provided for bunkers and boats (OECD, 1991). Emissions from aircraft were
B-3
-------
T.jfl
I ,i/n ..... . "?, ..... >;; , ...... i ;
II," liilji'"! ' ,\ ' aiillri'l ,:iiii ..... 1'iinlK', ..... I'l1'""1 I K ": ,'
': ,1'iric !l,. ' i!",*1.': -11 ....... '
II'' j" i Iปwi: 111 'i1' llllS'1'" .il'iwiii 11,:!"''!"!' ซi i:: ' v ''! !ป '.::' 'Ilii." > * I'M iili "in *, ''i.,'"'! Ii ; '' i","' -
estimated using (1) emission factors5 (OECD, 1991) and (2) fuel use by subcategory (U.S. DOT,
1992; FAA 1990-92 and 1992). The data used are included in Tables B-3 and B-4.
I i
Table B-3. Data for Bunkers, Boats, and Locomotives
Fuel Category
Bunkers
Boats
Locomotives
Fuel Quantity (U.S. Gallons)
Residual
4,686,100,000
1,562,000,000
28,000,000
Diesel
549,200,000
1,647,000,000
3,210,100,000
Other
NA
l,300,400,000a
+
Source: U.SI EPA (Brezinski, 1992).
Notes: a. Gaspjine.
*+* l)enotes insignificant; "NA" denotes not applicable.
N2O emission for jet and turboprop were not available from OECD.
B-4
-------
ANNEXC
ESTIMATION OF 1990 METHANE EMISSIONS FROM
ENTERIC FERMENTATION IN CATTLE AND
FROM ANIMAL MANURE MANAGEMENT
This annex presents a detailed explanation of the methodologies and data used to estimate
1990 methane emissions from enteric fermentation in cattle and from animal manure
management. This information is provided in order to enable the reader to verify the emission
estimates presented in Part 4 of the inventory. All of the information contained in this annex is
taken from U.S. EPA (1993a), to which the reader is referred for more detail.
Methane Emissions from Enteric Fermentation in Cattle
To estimate 1990 methane emissions from enteric fermentation in cattle, detailed analyses
of rumen digestion and animal production were performed using a mechanistic model of cattle
digestion. This model, originally described in Baldwin et al. (1987), explicitly models the
fermentation of feed within the rumen, and estimates the amount of methane formed and emitted
as a result. Since the original model of Baldwin et al. was developed for application to lactating
cows, it was revised to enable evaluations of a wider range of animal types, sizes, and stages of
maturity, as well as a wider range of diets.
To apply the model, representative cattle types and diets for five geographic regions of the
U.S. were defined. The cattle type categories represent the different sizes, ages, feeding systems,
and management systems that are typically found in the U.S. Representative diets were defined
for each category of cattle, reflecting the diversity of diets that are found in each of the five
.regions (Figure C-l). Each cattle type within each region was evaluated using the model,
resulting in emission factors (kilograms CH4/head/year) for each type in each region.
The following animal types were defined for the cattle population:
Dairy Animal Types
Replacement heifers 0-12 months of age1
Replacement heifers 12-24 months of age
Mature dairy cows (over 24 months of age)
Beef Animal Types
-Replacement heifers 0-12 months of age
Replacement heifers 12-24 months of age
Mature beef cows (over'24 months of age)
Weanling system heifers and steers2
1 "Replacements" are the offspring that are retained to replace mature cows that die or are removed
from the herd (culled) each year.
2 In "weanling systems", calves are moved directly from weaning to confined feeding programs. This
system represents a very fast movement of cattle through to marketing for slaughter. Weanling system
cattle are marketed at about 420 days of age (14 months).
C-l
-------
Figure C-l: Geographic Regions Used in the Analysis
West <
North:
Central
Ala Kk;i ond Hawaii
Source: US. EPA (1993a)
Yearling system heifers and steers3
Mature bulls
Due to their small number, mature dairy bulls were not evaluated. Dairy calves that are not kept
as replacements are generally fed for slaughter. Therefore, these animals were included in the
total for weanling and yearling system heifers and steers (i.e., heifers and steers grown for
slaughter). Tables C-l and C-2 summarize the size, age, and production characteristics used to
simulate each of the representative animal types.
.' ..;':'.' i. ' : '.''':; "'':. ,:.!;; :f jsp life ifXMi'fiaW if, W, lisii-i iiit' ",' * I ' i;~- i'' -fiv', \'
A total of 32 different diets were defined to represent the diverse feeds and forages
consumed by cattle in the U.S. Fourteen diets were defined for dairy cattle: six for dairy cows
and four each for replacement heifers 0-12 months and 12-24 months. Eighteen diets were
defined for beef cattle: three each for beef cows, replacements 6-12 months, weanling system
heifers and steers, and yearling system heifers and steers; four for replacements 12-24 months; and
two for beef bulls.
1
11 i i
n ii' i i
3 "Yearling systems" represent a relatively slow movement of cattle through to marketing for slaughter.
These systems include a wintering over, followed by a summer of grazing on pasture. Yearling system
cattle are marketed at 565 days of age (18.8 months). [
C-2
-------
Table C-l. Representative Animal Characteristics: Heifers and Cattle Fed for Slaughter
Animal Type
Initial
Weight
(kg)a
Final
Weight
(kg)
Initial Age
(days)
Final Age
(days)
Other
Replacement Heifers:
Dairy Replacement Heifers:
0-12 months
Dairy Replacement Heifers:
, 12-24 months
Beef Replacement Heifers:
0-12 months
Beef Replacement Heifers:
12-24 months-
170
285
165
270
285
460
270
390
165
365
165
365
365
730
365
730
-
Pregnant
Pregnant
Feedlot Fed Cattle for Slaughter:
Yearling Systemb
Weanling System0
170
170
480
480
165
165
565
422
fed to 26-27%
carcass fat
fed to 29-30%
carcass fat
a All weights reported as empty body weight.
b Includes 260 day stocker period principally on forages and a 140 day feedlot period with a high grain ration.
, c Includes a 257 day feeding period, initially at 30 to 50 p_ercent concentrate (125 days), followed by 132 days
of a high grain ration.
Source: U.S. EPA (1993a)
Table C-2. Representative Animal Characteristics: Dairy Cows and Beef Cows
Animal Type
Dairy Cows
Beef Cows
Beef Bulls
Initial and Final
Weight
.
-------
irl
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The regional emission factors for mature dairy cows were estimated by applying the cattle
digestion model to the average diet and the average annual milk production per head in each
region (Table C-4). For the other dairy cattle types and all of the beef cattle types, emission
factors were simulated for each of the defined diet types, and then using the diet percentages
assigned for each region, weighted average emission factors were calculated for each animal type
in each region. The statistics used in these simulations, .and the resultant regional emission factors
are summarized in Tables C-5 through C-ll.
Table C-4. Regional Estimates of Methane Emissions from Mature Dairy Cows
Statistics for the Average Animal Modeled
Peed consumed
per year (kg DM)
M-Ea consumed
per year (Meal)
Diet ME
(Meal/kg)
Average feed
digestibility (%)b
Methane emissions
per year (kg/cow)
Milk Production
per cow per year
(kg)
Methane emissions
per kg of milk
produced (g/kg)
N. Atlantic
5735
15,224
2.65
68
117.5
6710
17.5
S. Atlantic
5460
13,421
2.46
66
126.5
6110
20.7
N. Central
5805
15,012
2.59
66
109.4
6830
16.0
S. Central
5182
12,975
2.50
64
114.8
5570
20.6
West
6032
15,190
2.52
66
119.3
7190
16.6
a ME = metabolizable energy
b Digestibility is reported as simulated digestible energy divided by gross energy intake.
Note: Regional diets are weighted averages of the diets shown in Table C-3.
Source: U.S. EPA (1993a)
To estimate national emissions for each cattle type, the regional emission factors were
multiplied by regional populations of^each type (Tables C-12 and C-13). For all but the feedlot
cattle, the average 1990 regional populations were taken from published statistics (Schoeff and
Castaldo, 1991; USDA, 1992a). Emission factors for the feedlot fed cattle (i.e., for yearling
system and weanling system cattle) are based on the entire model simulation period, which is
greater than 365 days for both systems. Therefore, the yearling system and weanling system cattle
populations were derived from 1990 slaughter statistics (USDA, 1992b; CF Resources, 1991).
National emissions from the entire cattle population are estimated by summing the emission
estimates for all cattle types.4
4 The total number of cattle marketed for slaughter from feedlots in 1990 was estimated at 26.3
million. This figure was used to estimate emissions from feedlot fed cattle assuming that 80% of the cattle
were produced using the yearling system and 20% were produced using the weanling system. Using the
C-5
-------
Table C-5. Regional Estimates of Emissions from Dairy Replacement Heifers: 0-12 Months
Statistics for the Average Animal Modeled
Diet Description
Feed consumed per
year (kg DM)
MEC consumed
(Meal)
Diet ME (Meal/kg)
Average feed
digestibility (%)d
"Methane emissions
(kgted/yr)
Diet 1
Alfalfa hay
1116
2623
2.35
62
21.4
Diet 2
75% alfalfa
hay, 25%
concen.3
1080
2684
2.48
65
20.0
Diet 3
High quality
grass forage
(CP=18%)b
967
2613
2.70
67
20.1
Diet 4
Corn silage
with protein
to 14% CP
904
2432
2.69
69
14
Regional Distribution of Diets (%)c
North Atlantic
South Atlantic
North Central
South Central
West
25%
33%
25%
15%
50%
25%
60%
67%
50%
85%
25%
15%
25%
Emissions
.(kg/header)
19.5
20.5
18.9
20.3
20.7
a Concentrate of corn meal and soybean meal
b CP = crude protein
c ME = metabolizable energy
d Digestibility is reported as simulated digestible energy divided by gross energy intake.
e Regional distribution of diets shows the extent to which each of the four diets is used in each
region. The emissions estimates are the weighted average emissions using these percentages:
Source: U.S. EPA (1993a) ,
simulated lifetimes for the yearling system cattle (565 days) and the weanling system cattle (422 days), the
implied total annual average population of cattle needed to support this level of feedlot fed cattle
slaughter is estimated as 38.6 million as follows:
i'1"':; i - !:: : , '... lij-i ,,",!, , t- .Mi ''.I jU'-MEtt t.' '*: '."I ...... ', Jdiit;^1
(80% yearling 'system x 565days) + (20% weanling system x 422 days) , .. _ , ..
- - - - Hf_ , - r-s-^ - ............... J.. -. x 26.3milhon = 3S.6milhon
365 days
When added to the annual average populations tor the other cattle types, the total annual average U.S.
cattle population is estimated at 103.8 million, which is consistent with ..the January 1 and July 1
population estimates reported by USD A (1992"a) for 1990. This 'method' foTestimatmg the population and
emissions from feedlot fed cattle is appropriate because the population of feedlot fed cattle has been stable
in recent years.
C-6
-------
Table C-6. Regional Estimates of Emissions from
Dairy Replacement Heifers: 12-24 Months
Statistics for the Average Animal Modeled
Diet Description
Feed consumed per
year (kg DM)
ME0 consumed (Meal)
Diet ME (Meal/kg)
Average feed
digestibility (%)d
Methane emissions
(kg/head/yr)
Diet 1
Alfalfa hay
3184
7419
2.33
62
63.0
Diet 2
75% alfalfa
' hay, 25% .
concen."
3018
7437
2.46
64
57,3 .
Diet3
Grass forage
of declining
quality15
-.3172 '
7183
2.25
58
61.4
Diet 4
Corn silage
with protein
to 14% CPC
2540
6801
2.68
67
47.9
Regional Distribution of Diets (%/
North Atlantic
South Atlantic
North Central
South Central
West .
25%
25%
' 33% ,
20%
50%
10%
25% .
, 50%
45%
33%
80%
. 25%
25%
20%
33%
Emissions
(kg/head/yr)
58.4
58.7
57.4
61.7
- 61.2
a Concentrate of corn and cottonseed meal
b High quality grass forage for 100 days (ME=2.8 Meal/kg). Intermediate quality grass forage for 100
days (ME=2.5 Meal/kg). Lower quality grass forage for 165 days (ME=2.1 Meal/kg).
c CP = crude protein
d ME = metabolizable energy
e Digestibility is reported as simulated digestible energy divided by gross energy Jntake.
f Regional distribution of diets shows the extent to which each of the four diets is used in each region.
The emissions estimates are the weighted average emissions using these percentages.
Source: U.S. EPA (1993a)
C-7
-------
Table, C-7. Regional Estimates of Methane Emissions from Beef Cows
Statistics for the Average Animal Modeled
' I' ..' J.' . " . ' J !'!': ..". ;!', .:! !": f.\ I.'! ..' t. P. .v. . i a. .-, . < , , .
Diet Description
Feed consumed per
year (kg DM)
ME* consumed
(Meal)
Diet ME (Meal/kg)
Average feed
digestibility (%)e
Methane emissions
(kg/head/yr)
Dietl
Pasture for
7 mos; mixed
hay for
5 mos"
3029
7370
2.43
63
'63.4
Diet 2
Pasture of
varying
qualityb
' 3172
7731
2.44
63
71.7
Diet 3
Pasture with
4 mos of
supplement0
2700
7047
2.61 .
65
53.7
Regional Distribution of Diets (%)f
North Atlantic
South Atlantic
North Central
South Central
West
80%
20%
60%
10%
10%
80%
90%
80% :
20%
40%
10%
Emissions
(kg/head/yr)
60.5
70.0
59.5
70.9
69.1
a Seven months of pasture declining in quality as the seasons progress. Five months
of mixed hay, grass with some legumes.
b Pasture quality varies with the seasons.
c Pasture with four months of supplementation using a mixed forage (80 percent)
and concentrate (20 percent) supplement.
d ME = metabolizable energy
e Digestibility is reported as simulated digestible energy divided by gross energy
intake.
f Regional distribution of diets shows the extent to which each of the three diets is
used in each region. The emissions estimates are the weighted average emissions
using these percentages.
Source: U.S. EPA (1993a) - -
C-8
I1
-------
Table C-8. Regional Estimates of Emissions from Beef Replacements: 0-12 Months
Statistics for the Average Animal Modeled
Diet Description
Feed consumed per year
(kg DM)
ME0 consumed (Meal)
Diet ME (Meal/kg)
Average feed digestibility
(%)d
Methane emissions
(kg/head/yr)
Diet 1
Legume
pasture with
supplement3
984
2443
2.48
65
18.1
Diet 2
Very high
quality grass
(18% CP)b
1011
2614
2.58
68
27.2
Diet 3
Corn silage
.supplemented
to 14% CP
922 .
. 2454'
2.66
68
15.8
Regional Distribution of Diets (%)e
North Atlantic
South Atlantic
North Central
South Central
West
50%
50%
33%
40%
50%
20%
50%
33%
60%
50%
30%
33%
Emissions
(kg/head/yr)
19.2
22.7
20.4
23.6
22.7
a Concentrate = 25 percent of ration
b CP = Crude protein
c ME = metabolizable energy
d Digestibility is reported as simulated digestible energy divided by gross energy intake.
e Regional distribution of diets shows the extent to which each of the three diets is used in
each region. The emissions estimates are the weighted average emissions using these
percentages.
t ,
Source: U.S. EPA (1993a)
C-9
-------
Table C-9. Regional Estimates of Emissions from Beef Replacement Heifers: 12-24 Months
Statistics forJ:he Average Animal Modeled
Diet Description
Feed consumed per
year (kg DM)
MEC consumed (Meal)
Diet ME (Meal/kg)
Average feed
digestibility (%)f
Methane emissions
(kg/header)
Dietl
Varying
quality grass
forage3
2454
6356
2.59
67
66.9
Diet 2
Varying
quality grass
forageb
2675
6524
2.49
66
71.0
Diets
Varying
quality grass
with winter
supplement0
2359
5990
2.54
66
56.5
Diet 4
Varying
quality grass
with winter
supplement11
2305
6000
2.60
67
54.8
Regional Distribution of Diets (%)ซ
North Atlantic
South Atlantic
North Central
South Central
West
50%
80%
33%
50%
40%
33%
20%
33%
50%
10%
33%
33%
33%
Emissions
(kg/head/yr)
63.8
67.5
60.8
67.7
64.8
a 165 days of high quality grass followed by 200 days of intermediate quality grass.
b 120 days of high quality grass followed by 125 days of intermediate quality grass -- grass hay provided
for 120 days during winter
c 120 days of high quality grass followed by 125 days of intermediate quality grass - medium quality
alfalfa with a corn:soybean meal concentrate (25 percent) provided for 120 days during winter
d 120 days of high quality grass followed by 125 days of. intermediate quality grass -- corn silage
supplemented to 14 percent CP provided for 120 days- during winter
e ME = metabolizable energy
f Digestibility is reported as simulated digestible energy divided by gross energy intake.
g Regional distribution of diets shows the extent to which each of the three diets is used in each
region. The emissions estimates are the weighted average emissions using these percentages.
Source: U.S. EPA ( 1993a) :
C-10
-------
Table C-10. Regional Estimates of Emissions from Feedlot Fed Cattle: Yearling System
Statistics for the Average Animal Modeled
Diet Description
Feed consumed per year
(kg DM)
MEb consumed (Meal)
Diet ME (Meal/kg)
Average feed digestibility (%)ฐ
Methane emissions (kg/head/yr)
Adjustment for ionophores and
hormone implants
Methane emissions (kg/header)
Diet 1
Diet 2
Diet 3
All diets include forages during the stocker phase
followed by high grain diets during feedlot
feeding0
2865
7588
2.65
67
50.0
90%
45.0
2775
7383
2.66
67
54.1
90%
48.7
2755
7366
2.67
68
52.9
90%
47.6
Regional Distribution of Diets (%)d
Emissions
(kg/head/yr)
North Central
30%
20%
50%
47.0
South Central
100%
47.6
West
20%
50%
30%
47.6
a All three diets include a high quality mixed hay (legume and grass) for the first winter (90
days). The three diets then include:
Diet 1: mixed pasture (legume and grass) to 425 days of age; 50 percent alfalfa:50 percent
concentrate for 40 days; 10 percent alfalfa:90 percent concentrate for 100 days.
Diet 2: grass.pasture to 425 days of age; 50 percent alfalfa:50 percent concentrate for 40
days; 10 percent alfalfa:90 percent concentrate for 100 days.
Diet 3: grass pasture to 425 days -of age; 70 percent corn silage:30 percent concentrate for 40
days; 10 percent alfalfa:90 percent concentrate for 100 days.
b ME = metabolizable energy
c Digestibility is reported as simulated digestible energy divided by gross energy intake.
d . Regional distribution of diets shows the extent to which each of the four diets is used in each
region. The emissions estimates are the weighted average emissions using these percentages.
Only the three regions with feedlots are shown.
Source: U.S. EPA (1993a)
C-ll
-------
Table C-ll. Regional Estimates of Emissions from Feedlot Fed Cattle: Weanling System
Statistics'for'the Average Animal"'IvlotleO
y
Diet Description
Feed consumed per year (kg
DM)
ME* consumed (Meal)
Diet ME (Meal/kg)
Average feed digestibility (%)ฐ
Methane emissions (kg/header)
Adjustment for ionophores and
hormone implants
Methane emissions (kg/head/yr)
Diet 1
Diet 2
Diet 3
All diets include mixed rations with increasing
amounts of high grain concentrates"
1935
5232
2.70
68
31.2
85%
26.5
1763
5184
2.94
71
25.3 .
85%
21.5
1742
5059
2.90
71
25.4
85%
21.6
Regional Distribution of Diets (%)d
North Central
South Central
West
20%
50%
40%
20%
50%
30%
60%
30%
Emissions
(kg/head/yr)
22.6
24.0
23.5
a The following diets were simulated:
Diet 1: 60 percent alfalfa:40 percent concentrate for 125 days; '10 percent alfalfa:90 percent
concentrate for 132 days.
Diet 2: 50 percent alfalfa:50 percent concentrate for 125 days; 10 percent alfalfa:90 percent
concentrate for 132 days. .
Diet 3: 69 percent corn silage:31 percent concentrate for 125 days; 10 percent alfalfa:90
percent concentrate for 132 days.
b ME = metabolizable energy
c Digestibility is reported as simulated digestible energy divided by gross energy intake.
d Regional distribution of diets shows the extent to which each of the four diets is used in each
region. The emissions estimates are the weighted average emissions using these percentages.
Only the three regions with feedlots are shown.
Source: U.S. EPA (1993a)
CA2
-------
Table C-12. Methane Emissions From Enteric Fermentation in U.S. Dairy Cattle
Region/Animal Type
North Atlantic
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
South Atlantic
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
North Central
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
South Central
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
West
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
National Total
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
Total
Emissions Factor
(kg/head/yr)
19.5
58.4
117.5
20.5
58.7
126.5
18.9
57.4
109.4
20.3 -
61.7
114.8
20.7
61.2
119.3
19.6
58.8
114.6
80.4
Population
(000 Head)
712
712
1,795
268
268
710
1,987
1,987
4,497
405
405
1,156
833
833
1,972
4,205
4,205
10,130
18,540 .
Emissions
(Tg/yr) '
0.014
0.042
0.211
0.005
0.016 ,
0.090
0.038
0.114
0.492
0.008
0.025
0.133 .
0.017
0.051
0.235
0.082
0.247
1.161
1.490
Source: U.S. EPA (1993a)
Methane Emissions from Animal Manure Management
Estimates of 1990 methane emissions from animal manure management were derived using
the approach of Safley et al. (1992a). This approach is as follows:
(1) Estimate annual methane emissions for each animal type i and manure system; in each state
k:
Where
Nik
TAMj
VS:
MCFjk
WS%ijk
Nik x
Sj x Boi x MCFjk x
annual methane emissions for each animal type i and manure
management system j in each state k
number of animals of type z in state k
typical animal mass of animal i
average annual volatile solids production per unit of animal
mass for animal z
ma>dmum methane producing capacity of the manure of animal i
the methane conversion factor of the manure system j in th,e
state k
the percent of animal i's manure managed in manure system / in
state &
C-13
-------
;,: ''.' !-1<; , 'if yซ;; ,< :& L w si's i| i lie" H MM HBipiT r!f v>sm iwii ซi"?H sis s^rartrtiSiBPliWii I
> " ." I '"I" .". >. :( I. ((!; HI'!1!!" Ill IT I I" ' 111"! I in'" ' I I' 11 "ซ l"l""iritl Ill Ill I"1!1'1!"
(2) Estimate total annual methane emissions for animal z by summing annual emissions over all
applicable manure management systems / and states k.
'.:. ' * ; ;;..,.;; ' . : .,; .is-, :. >/ป v.i"^. .' .; if.';r M. I I in
(3) Estimate total annual methane emissions from all animals by summing over all animal types i.
Table C-13. Methane Emissions From Enteric Fermentation in U.S. Beef Cattle
Region/Animal Type
North Atlantic
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
South Atlantic
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
North Central
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
Weanling System Steers/Heifersb
Yearling System Steers/Heifers
South Central
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
Weanling System Steers/Heifers
Yearling System Steers/Heifers
West
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
Weanling System Steers/Heifers
Yearling System Steers/Heifers
Bulls: Nationally
National Total
Replacements 0-12 months
Replacements 12-24 months
Mature Cows
Weanling System Steers/Heifers
Yearling System Steers/Heifers
Bulls
Total11
Emissions Factor
(kg/head/yr)
19.2
63.8
61.5
22.7
67.5
70.0
20.4
6o:s
59.5
22.6
47.0
23.6
67.7
70.9
24.0
47.6
22.7
64.8
69.1
23.5 -
47.6
100.0
22.3
65.0
66.7
23.1
47.3
100.0
47.5
Population
(000 Head)0
87
87
337
594
594
3,418
1,546
1,546
10,592
2,963
1 1,852
2,079
2,079
12,359
1,164
4,656
1,229
1,229
6,772
1,133
4,532
2,200
5,535
5,535
33,478
5,260
21,040
2,200
85,398C
Emissions
(Tg/yr)
0.002
0.006
0.021
0.013
0.040
0.239
0.032
0.094
0.630
0.067
0.557
0.049
0.141
0.876
0.028
0.222
0.028
0.080
0.468
0.027
0.216
0.220
0.124
0.360
2.234
0.122
0.994
0.220
4.054
a Population for slaughter steers and heifers in each region is the number slaughtered annually.
h The emissions from Yearling and Weanling System steers and heifers are assigned to the regions in which
they are managed in feedlots.
c The national population is estimated using the average annual population of Yearling and Weanling System
cattle: 38.65 million. See text.
d Total may not add due to rounding.
Source: U.S. EPA (1993a)
C-14
i ill ill! i kin HI
-------
To implement this methodology, twenty types of animals were defined for the U.S., and
data were collected on the 1990 populations of each animal type in each state, their typical animal
mass, and their average annual volatile solids production per unit of animal mass. These data and
their sources are listed in Table C-14. The cattle populations and weights are equal to those used
in the previous section of this annex to estimate emissions from enteric fermentation.5
The maximum amount of methane that can be produced per kilogram of volatile solids, or
the maximum methane producing capacity of each animal's manure (B0), varies by animal type
and diet. Appropriate B0 values were chosen from the scientific literature depending on the
typical diet of each animal type. For animal types without BQ measurements, the BQ was
estimated based on similarities with other animals and the experience of the authors of Safley et
al. (1992a). Table C-15 lists the values selected for the analysis.
The extent to which the maximum methane producing capacity of each animal's manure is
realized, or the methane conversion factor (MCF), depends upon the management system and
climate conditions in which the manure is managed. Ten categories of manure management
systems were identified, for the U.S.., and based upon estimates in the scientific literature and
research sponsored by U.S. EPA, MCFs for each system were identified (Table C-16). The MCF
for each management system in each state was calculated by:
estimating the average monthly temperature in each climate division of each state;
estimating the MCF value for each month using the average temperature data and the
MCF values listed in Table C-16;
estimating the annual MCF by averaging the monthly division estimates; and
estimating the state-wide MCF by weighting the average MCF for each division by the
fraction of the state's dairy population represented in each division.
Table C-17 summarizes the resultant MCF estimates by management system for each state.
Livestock manure management.system usage in the U.S. was determined by obtaining
information from Extension Service personnel in each state. The U.S. was divided into eleven
geographic regions based on similarities of climate and livestock production. For states that did
not provide information, the regional average manure system usage was assumed. The results are
summarized in Table C-18.
5.Tables C-l and C-2 (in the enteric fermentation section) list weights on an empty body weight basis.
These values were converted to live weight for purposes of estimating emissions from animal manure
management.
6 The average temperature in each climate division of each state was calculated for the normal period
of 1951 to 1980 using the National Climatic Data Center time-bias corrected Historical Climatological
Series Divisional Data .(NCDC, 1991). . .
7 The dairy populations in each climate division were estimated using the dairy population in each
county (Bureau of the Census, 1987) and detailed county and climate division maps (NCDC, 1991). Using
the dairy population as a weighting factor may slightly over or underestimate the MCFs for other livestock
populations.
C-15
-------
Table C-14. y.S. Animal Populations, Average Size, and YS Production
Animal Type
Fccdlot Beef Cattle
Other Beef Cattle
Dairy Cattle
Swine
Poultry1
Other
Steers/Heifers
Calves
Heifers
Steers
Cows
Bulls
Total
Heifers
Cows
Total
Market
Breeding
Total
Layers
Broilers
Ducks
Turkeys
Sheep
Goats
Donkeys
Horses and Mules
Population"'1"
N,
10,088,000
36,040,000
5,535,0000
2,162,000
33,478,000
2,200,000
79,205,000
4,205,000
10,130,000
14,335,000
48,259,000
7,040,000
55,299,000
355,469,000
951,914,000
7,000,000
53,783,000
10,639,000
2,396,000
4,000
2,405,000
Typical
Animal
Mass
(TAM,)'
Kg
415
180
360
360
5.00
720
410
610
46
181
1.6
0.7
1.4
3.4
70
64
300
450 .
Manure per day.*1
(kg/day per 1000 kg mass)
Total
Manure
58
58
58
58
58
58
86
86
84
84
64
85
107
47
40
41
51
51
Volatile
Solids
vs,
7.2
7.2
7.2
7.2
7.2
7.2
10
10
-
8.5
8.5
12
17.
18.5
9.1
9.2
9.5
10
10
a Population data for swine, poultry, and sheep from USDA (1989a-f). Goat and horse population data
from Bureau of Census (1987). Population data for cattle are the same as those used to estimate
emissions from enteric fermentation in cattle in 1990. Population data as of January 1, 1988 for poultry,
and sheep and as of December 1, 1987 for swine, goats, and horses. Cattle populations represent an
average for 1990.
b Broiler/turkey populations estimated yearly based on number of flocks per year (North 1978; Carter
1989). _ .,
c Source: Taiganides and Stroshine (1971).
d Source: ASAE (1988). :
Source: U.S. EPA (1993a)
"ii,: * MIL ItMillJiillii HIlIK^^^^ ซl,ii!!Kll!
"!:" / .' i i! VII lii" -/"..iMfUifi IlillilililH^^^^^^^^^^ JiilSIIEll I
-------
Table C-15. Maximum Methane Producing Capacity Adopted For U.S. Estimates
Animal
Cattle:
Swine:
Poultry:
Sheep:
Goats:
Horses, Mules, and
Donkeys:
Source: U.S. EPA
Type, Category
Beef in Feedlots
Beef Not in Feedlots
Dairy
Breeder
Market
Layers
Broilers
Turkeys
Ducks
In Feedlots
Not in Feedlots
(1993a)
Maximum Potential
Emissions (BJ
0.33
0.17.
0.24
0.36
0.47
0.34
0.30
0.30
0.32
0.36
0.19
0.17
0.33
Reference
. Hashimoto et al. (1981)
Hashimoto et al. (1981)
Morris (1976)
Summers & Bousfield (1980)
Chen (1983)
Hill (1982 & 1984)
Safleyetal. (1992a)
Safley et al. (1992a)
Safley. et al. (1992a)
Safley etal. (1992a)
Safley et al, (1992a)
Safley et al. (1992a)
- Ghosh (1984)
Table C-16. Methane Conversion Factors for U.S. Livestock Manure Systems
MCFs based on
. laboratory measurement
Pasture, Range, Paddocks0
Liquid/Slurry"
Pit Storage < 30 daysa
Pit Storage > 30 days"
Drylotb
Solid Storage11
Daily Spread"
MCF measured by
long term field monitoring
MCF at 30ฐ
2%
65 %
33 %
65%
5%
2%
' 1 %
MCF at 20ฐC
r.5 %
35%
18%
35 %
1.5%
1.5 %
0.5 %
MCF at 10ฐC
1 %
10%
5 %
10 %
1 %
1 %
0.1 %
Average Annual MCF
Anaerobic Lagoonsc 90 %
MCFs estimated by Safley et al.
Average Annual ,MCF
Litter" . , 10 %
Dee,p Pit Stacking11 5 %
a Hashimoto (1992)
b Based on Hashimoto (1992).
c Safley et al. (1992a) and Safley and Westerman (1992b).
d Safley et al. (1992a)..
Source: U.S. EPA (1993a)
C-17
-------
Table C;17. Methane Conyersipn .Factors for ,1LJ,S{JLiyestQcJ^ Manure Systems
Pasture, Range
State & Paddocks
Alabama
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming
( )lher Systems: Pit Storage for
1.4%
1.4%
1.3%
1.2%
0.9%
0.9%
1.2%
1.5%
1.4% -
0.8%
1.1%
1.0%
0.9%
1.1%
1.2%
' 1.4%
0.8%
1.1%
0.9%
0.8%
0.8%
1.4%
1.1%
0.7%
1.0%
1.2%
0.8%
1.0%
1.2%
0.9%
1.3%
0.7%
1.0%
1.4%
1.1%
0.9%
1.0%
1.3%
0.8%
1.3%
1.4%
0.9%
0.8%
1.2%
1.0%
1.2%
0.8%
0.8%
less than 30
Liquid/Slurry, Pit Storage for more than 30
lagoons are assumed to have an
Source: U.S. EPA (1993a)
MCF of 90
Drylot
1.9%
1.9%
1.8%
1.4%
1.0%
1.0%
1.4%
2.4%
1.8%
0.8%
1.3%
1.2%
1.1%
1.5%
1.5%
2.1%
0.8%
1.2%
1.0%
0.9%
0.8%
1.9%
1.4%
0.8%
1.1%
1.4%
0.8%
1.1%
1.3%
0.9%
1.5%
0.7%
1.1%
1.9%
1.1%
1.0%
1.1%
1.7%
0.9%
1.6%
2.1%
- "1.0%.
0.8%
1.4%
1.0%
1.3%
0.8%
0.8%
days is assumed to
Solid
Storage
1.4%
1.4%
1.3%
1.2%
0.9%
0.9%
1.2%
1.5%
1.4%
0.8%
1.1%
1.0%
0.9%
1.1%
1.2%
1.4%
0.8%
1.1%
0.9%
0.8%
0.8%
1.4%
1.1%
0.7%
1.0%
1.2%
0.8%
1.0%
1.2%
0.9%
1.3%
0.7%
1.0%
1.4%
1.1%
0.9%
1.0%
1.3%
'' 0.8%
1.3%
1.4%
0.9%
0.8%
1.2%
. 1.0%
1.2%
0.8%
0.8%
have an MCF
days is assumed to have an MCF
percent; litter and
deep pit stacks
Daily
Spread
0.4%
0.4%
0.4%
0.3%
0.2%
0=2%
0.3%
0.6%
0.4%
0.2%
0:3%
0.3%
. 0.2%
0.3%
0.3%
0.5%
0.2%
0.3%
0.2%
0.2%
0.2%
0.4%
0.3%
0.2%
0.2%
0.3%
0'.2%
0.3%
0.3%
0.2% ''"'
0.3%
0.2%
0.2%
0.4%
0.2%
. ' ' 0.2%
0.2%
0.4%
0.2%
,0.3%
0.5%
0.2%
0.2%
0.3%
0.2%
0.3%
0.2%
0.2%
equal to 50 percent of the
Liquid/
Slurry
29.0%
28.9%
1 27.6%
21.9%
18.2%
18.5%
22.6%
38.6%
29.0%
15.5%
22.8%
- 21.5%
20.7%
24.7%
23.8%
32.5%
15.5%
21.0%
18.1%
17.0%
18.0%
29.3%
24:1%
15,8%
' 20.8%
, 22.1%
16.3%
20.6%
21.3%
1871'%'
24.5%
16.8%
20.2%
28.7%
16.2%
18.7%
18.7%
. 27.3%
19.1%
24.8%
31.7%
17.4%
16.6%
, 22.5%
15.5%
,21.4%
17.0%
15.9%
MCF fnr
equal to liquid/slurry. Anaerobic
an MCF of 10 percent.
C-18
-------
Table C-18. Livestock Manure System Usage for the U.S.
Animal
Non-Dairy Cattle
Dairy
Poultry1"
Sheep
Swine
Other Animals0
Anaerobic
Lagoons
<1%
11%
4%
0%
' 29%
0%
Liquid/Slurry
and Pit
Storage
<1%
21%
3%
0%
44%
. 0%
Daily
Spread
0%
41%
0%
0%
0%
0%
Solid
Storage
& Drylot
10%
' 18%
0%
0%
20%
0%
Pasture,
Range'&
Paddock
89%
0% -
<1%
. 92%
0%
89%
Litter, "
Deep Pit Stacks
and Other
0%
8%
93%
8%
7% '
11%
Note: Totals may not add due to rounding. ,
a Includes liquid/slurry storage and pit storage.
b Includes chickens, turkeys, and ducks. .
c Includes goats, horses, mules, and donkeys.
Source: Safley et
al. (1992a).
Point estimates of emissions were calculated using the previously described data.
Emissions were estimated for each animal type by summing annual emissions over all applicable
manure management systems and states. Total annual methane emissions from all animals were
estimated by summing over all animal types.
Uncertainties in the point estimates result from uncertainties in the data used to make
these estimates, in particular: -
The estimated MCF values for pasture, range, drylots, solid storage, and paddocks are
based on dry manure. This may underestimate the MCFs for regions with significant
rainfall. Because a large fraction of animal manure is managed in these systems, total
emissions may be underestimated.
The methane producing potential of liquid/slurry and pit storage manure systems may be
greater than assumed. These systems are widespread, so total emissions may be
underestimated.
The greatest uncertainty results from the MCF assumptions. Therefore, "high" and "low"
case emission estimates were defined based on varying the MCFs used for the various manure
management systems in the base case:
High Case. The MCFs for liquid/slurry, pit storage, litter, and deep pit stacking systems
were assumed to be double the base case. The MCFs for solid systems (except litter and
deep stack pits) were assumed to be five times the base case. The MCFs for anaerobic
lagoons were the same as the base case.
ซ Low Case. The MCFs for'each of the major solid systems (pasture/range, solid storage,
and drylots) were assumed to be 80 percent of the base case. The MCFs for liquid/slurry
and pit storage were assumed to be 90 percent of the. base case. The MCFs for litter and
deep pits were assumed to be half the base case. The MCFs for anaerobic lagoons,
C-19
-------
estimated using a lagoon methanogenesis model prepared for U.S. EPA8, were 40 to 100
percent of the base case.
' ;'' : .'-. '; V; . ; '; ' I ! IP in1 i
These assumptions are summarized in Table C-19.
. i
Table C-19. Base, High, and Low Case Emission Estimate Assumptions
Management System
Pasture, Range, Paddock, Drylot, Daily Spread
Liquid/Slurry, Pit Storage
Utter, Deep Pits
Anaerobic Lagoons
MCF
High Case
Five Times
Base Case
Two Times
Base Case
Two Times
Base Case
Same as
Base Case
Low Case
80 percent of
Base Case
90 percent of
Base Case
50 percent of
Base Case
Model Estimates
40 to 100 percent
of Base Case
Source: U.S. EPA (1993a)
8 The model estimates methane production based on loading rates, lagoon characteristics, and climate.
The model estimates are "conservative" because the model focuses, on the amount of methane that can be
recovered reliably for use as an energy source.
C-20
I!
-------
ANNEXD
IPCC REPORTING TABLES:
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ANNEXE
SULFUR DIOXIDE: EFFECTS ON
RADIATIVE FORCING AND SOURCES OF EMISSIONS
Sulfur dioxide emitted into the atmosphere through natural and anthropogenic processes
affects the Earth's radiative budget through photochemical transformation into sulfate particles
that (i) scatter sunlight back to space, thereby reducing the radiation reaching the Earth's surface;
(ii) possibly increase the number of cloud condensation nuclei, thereby potentially altering the
physical characteristics of clouds, and (iii) affect atmospheric chemical composition, e.g.
stratospheric O3, by providing surfaces for heterogeneous chemical processes. As a result of
these activities, the effect of these gases on radiative forcing may be negative (IPCC, 1992).
Therefore, since their effects are uncertain and opposite from the other criteria pollutants,
emissions of SO2 have been presented separately below in Table E-l.
Table E-l. Emissions of Sulfur Dioxide: 1990
(Million Metric Tonnes)
Source
Fossil Fuel Combustion
Electric Utilities
Industrial
Gommercial
Residential
Transportation
Industrial Processes
Metals Processing
Chemical and Allied Manufacturing
Asphalt Manufacturing
Agriculture, Food, Kindred Prod.
Wood, Pulp, Paper, and Publishing
Mineral Products
Solvent Use
Waste Incineration
Fossil Fuel Production, Distribution
and Storage
Total
Emissions
22.69
17.49
3.42
0.45
0.20
1.21
1.91
1.001
0.467
0.001
0.003
0.151
0.283 ,
0.001
0.04
0.51
25.15
Source: U.S. EPA, 1993b
Note: Total may not add to the sum of the individual source categories due to
independent rounding.
The major source of SO2 emissions in the U.S. is the burning of sulfur containing fuels,
mainly coal. Metal smelting and other industrial processes also release significant quantities of
SO2- As a result, the largest contributor to overall U.S. emissions of SO2 are electric utilities,
E-l
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accounting for about 70 percent. Coal combustion accounted for approximately 96 percent of
SO2 emissions from electric utilities. The second largest source is industrial fuel combustion,
which produced about 14 percent of 1990 SO2 emissions. Table E-2 provides SO2 emissions
disaggregated by fuel source.
Table E-2. Emissions of SQ2 from Fossil Fuel Combustion
by Fuel Source: 1990
i(!Vimipfl, Metric Tonnes^ '_ ^
Fuel Source
Coal
Fuel Oil
Natural Gas
Wood3
Internal Combustion
Other Fuelsb
Total
Emissions
19.01
3.14
0.38
0.01
0.04
0.10
22.69
Source: ' U.S. EPA' (1993b)'' ''' '"'"_ \\"'_""'''"''"'"' "'_" "" :''i'''.;.",'. ',.' ^
Notes: Totgl may not add to the sum of the independent source categories
due to independent rounding
a. Residential sector only.
b. Other fuels include: LPG, waste oil, coke oven gas, coke, and wood
from sectors other than the residential sector.
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, as well as cause the acidification of
lakes and streams |nd damage trees. As a result of these harmful effects, the U.S. has regulated
the emissions of SO2 in the Clean Air Act of 1970 and in the amendments of 1990. The U.S. -
EPA has also developed a strategy to control these emissions via four programs: (1) the National
Ambient Air Quality Program, which protects air quality and public health on the local level; (2)
New Source Performance Standards, which set emission limits for new sources; (3) the New
Source Review/Prevention of Significant Deterioration Program, which protects air quality from
deteriorating, especially in clean areas; and (4) the Acid Rain Program, which addressees regional
environmental problems often associated with long-range transport of SO2 and other pollutants.
; ' ". . : : . .' '"' Ji", II I i ill
E-2
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