United States
Environmental
Protection
Agency
Office of Air Quality
Planning and Standards
Technical Support Division
National Air Data Branch
Research Triangle Park, NC 27711
MARCH 1990
EPA-450/4-90-001
&EPA
AIR
NATIONAL AIR POLLUTANT
EMISSION ESTIMATES
1940 -1988
Jffl
-------
EPA-450/4-90-001
NATIONAL AIR POLLUTANT
EMISSION ESTIMATES
1940-1988
Technical Support Division
National Air Data Branch
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
MARCH 1990
-------
This report is published by the U.S. Environmental Protection Agency (EPA) to report informa-
tion of general interest in the field of air pollution. Copies are available free of charge to Federal
employees, current contractors and grantees, and nonprofit organizations - as supplies permit -
from the Library Services Office (MD-35), U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina 27711; or, for a fee, from the National Technical Information
Services, 5285 Port Royal Road, Springfield, Virginia 22161.
Publication No. EPA-450/4-90-001
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CONTENTS
LIST OF FIGURES iv
LIST OF TABLES v
1. SUMMARY 1
2. NATIONWIDE EMISSION TRENDS, 1940-1988 3
2.1 Paniculate (PM/TSP) 3
2.2 Sulfur Oxides (SOJ 4
2.3 Nitrogen Oxides (NOJ 4
2.4 Reactive Volatile Organic Compounds (VOC) 4
2.5 Carbon Monoxide (CO) 4
2.6 Lead (Pb) 5
3. METHODS 45
3.1 Transportation 46
3.1.1 Motor Vehicles 46
3.1.2 Aircraft 46
3.1.3 Railroads 47
3.1.4 Vessels 47
3.1.5 Non-highway Use of Motor Fuels 47
3.2 Fuel Combustion in Stationary Sources 47
3.2.1 Coal 47
3.2.2 Fuel Oil 47
3.2.3 Natural Gas 47
3.2.4 Other Fuels 48
3.3 Industrial Processes 48
3.3.1 Miscellaneous Industrial Processes for Lead 48
3.4 Solid Waste Disposal 48
3.5 Miscellaneous Sources 49
3.5.1 Forest Fires 49
3.5.2 Agricultural Burning 49
3.5.3 Coal Refuse Burning 49
3.5.4 Structural Fires 49
3.5.5 Non-industrial Organic Solvent Use 49
4 . ANALYSIS OF TRENDS 51
4.1 Paniculate (PM/TSP) 51
4.2 Sulfur Oxides (SOx) 55
4.3 Nitrogen Oxides (NOx) 56
4.4 Reactive Volatile Organic Compounds (VOC) 59
4.5 Carbon Monoxide (CO) 60
4.6 Lead 63
5 . REFERENCES 65
TECHNICAL REPORT DATA AND ABSTRACT 68
m
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LIST OF FIGURES
1. Trends in Emissions of Paniculate (PM/TSP), 1940-1988 6
2. Trends in Emissions of Sulfur Oxides, 1940-1988 7
3. Trends in Emissions of Nitrogen Oxides, 1940-1988 8
4. Trends in Emissions of Reactive VOCs, 1940-1988 9
5. Trends in Emissions of Carbon Monoxide, 1940-1988 10
6. Trends in Emissions of Lead, 1970-1988 11
7. Emissions of Paniculate (PM/TSP) by Source Category, 1940, 1970, and 1988 39
8. Emissions of Sulfur Oxides by Source Category, 1940, 1970, and 1988 40
9. Emissions of Nitrogen Oxides by Source Category, 1940,1970, and 1988 41
10. Emissions of Reactive VOCs by Source Category, 1940, 1970,1988 42
11. Emissions of Carbon Monoxide by Source Category, 1940,1970, 1988 43
12. Emissions of Lead by Source Category, 1970 and 1988 44
13. Theoretical Estimates of 1988 Nationwide Emissions of TSP, SOX, NOX, VOC
and CO with 1970 Level of Control 54
14. Emissions of Sulfur and Nitrogen Oxides from Electric Utility Coal Combustion .... 57
15. Emissions of Nitrogen Oxides from Highway Vehicles 58
16. Emissions of Reactive VOCs from Highway Vehicles 61
17. Emissions of Carbon Monoxide from Highway Vehicles 62
18. Theoretical Estimates of 1988 Nationwide Emissions of Lead with 1970 Level of
Control 64
IV
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LIST OF TABLES
1. Summary of Estimates of Nation wide Emissions 2
2. Summary of Estimated Emissions of Particualte, 1940-1970 12
3. Summary of Estimated Emissions of Sulfur Oxides, 1940-1970 13
4. Summary of Estimated Emissions of Nitrogen Oxides, 1940-1970 14
5. Summary of Estimated Emissions of Reactive VOCs, 1940-1970 15
6. Summary of Estimated Emissions of Carbon Monoxide, 1940-1970 16
7. Estimates of National Emissions of Paniculate, 1970-1988 17
8. Estimates of National Emissions of Sulfur Oxide, 1970-1988 18
9. Esitmates of National Emissions of NOX, 1970-1988 19
10. Estimates of National Emissions of Reactive VOCs, 1970-1988 20
11. Estimates of National Emissions of CO, 1970-1988 21
12. Estimates of National Emissions of Lead, 1970-1988 22
13. Emissions of Paniculate (PM/TSP) from Transportation 23
14. Emissions of Sulfur Oxides from Transportation 24
15. Emissions of Nitrogen Oxides from Transportation 25
16. Emissions of Reactive VOCs from Transportation 26
17. Emissions of Carbon Monoxide from Transportation 27
18. Emissions of Paniculate (PM/TSP) from Fuel Combustion 28
19. Emissions of Sulfur Oxides from Fuel Combustion 29
20. Emissions of Nitrogen Oxides from Fuel Combustion 30
21. Emissions of Reactive VOCs from Fuel Combustion 31
22. Emissions of Carbon Monoxide from Fuel Combustion 32
23. Emissions of Paniculate (PM/TSP) from Industrial Processes 33
24. Emissions of Sulfur Oxides from Industrial Processes 34
25. Emissions of Nitrogen Oxides from Industrial Processes 35
26. Emissions of Reactive VOCs from Industrial Processes 36
27. Emissions of Carbon Monoxide from Industrial Processes 37
28. Emissions of Lead from Industrial Processes 38
29. 1988 National Emission Estimates with 1970 Level of Control 53
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NATIONAL AIR POLLUTANT EMISSION ESTIMATES
1940-1988
1. SUMMARY
The primary objective of this publication is to provide current estimates of nationwide
emissions for six major air pollutants: paniculate with TSP as the indicator pollutant (PM/TSP),
sulfur oxides (SOJ, nitrogen oxides (NO,), reactive volatile organic compounds (VOC), carbon
monoxide (CO) and lead (Pb). Estimates are presented for 1940,1950,1960, and 1970 to give an
historical perspective of national air pollutant emissions, and for 1975 through 1988 as an indication
of recent trends. These data entirely replace those published earlier for 1940-1970 and 1975-1987
in the Environmental Protection Agency report National Air Pollutant Emission Estimates,
1940-1987 (EPA-450/4-88-022). Because of modifications in methodology and use of more refined
emission factors, data from this report should not be compared with data in the earlier report.
Reporting of emissions on a nationwide basis, while useful as a general indicator of trends
in emissions, has definite limitations. National totals or averages are not the best guide for estimating
trends for particular localities. Yet, it is important that some criteria be established for reporting
national progress in the control of air pollutant emissions. The emission estimates presented in this
document represent calculated estimates based on standard emissions-estimating procedures. Since
these data are estimates and do not represent the results of any program for the measurement of
actual emissions, their accuracy is limited. Similarly, these emission estimates would not necessarily
be in agreement with emission estimates derived through a different emissions-estimating proce-
dure. The principal objective of compiling these data is to identify probable overall changes in
emissions on a national scale. It should be recognized that these estimated national trends in
emissions are not meant to be representative of local trends in emissions or air quality.
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2 . NATIONWIDE EMISSION TRENDS, 1940-1988
Table 1 presents a summary of total national emission estimates for 1940-1988. Figures 1
through 6 depict how total emissions and emissions from major source categories have changed
over time for each pollutant. Tables 2 through 12 present more detailed summaries for each year
according to five major categories of sources: transportation, stationary source fuel combustion,
industrial processes, solid waste disposal, and miscellaneous sources. Detailed breakdowns of
emissions for 1970 through 1988 are given in Tables 13 through 17 for transportation, Tables 18
through 22 for stationary source fuel combustion, and in Tables 23 through 28 for industrial pro-
cesses.
The Standard Industrial Classifications (SIC) are shown for each process category in the
industrial process tables. These estimates do not represent the complete emissions for all SIC
categories—only those particular industrial processes shown.
In all tables, data are reported in metric units, either as teragrams (1012 grams) or gigagrams
(109 grams) per year. One teragram equals 106 metric tons and approximately 1.1 x 106 short tons
(2000 Ibs.). One gigagram equals 103 metric tons and approximately 1.1 x 103 short tons.
Figures 7 through 12 show how the relative contribution of the major source categories to
the total emissions of each pollutant have changed with time. The major factors influencing these
changes for each pollutant are discussed briefly below. A more detailed discussion appears in
Chapter 4.
2.1 Participate (PM/TSP)
Emissions of paniculate (PM/TSP) result primarily from sources of fugitive dust. Fugitive
paniculate emissions (emissions from uncontrolled sources such as storage piles, material
loading, etc.) are incompletely accounted for in the emission totals. Rough estimates of industrial
process fugitive emissions are included for some industries. Area source fugitive dust emissions
(unpaved roads, construction activities, etc.) are not included at all; based on data in the National
Emissions Data System (NEDS), the 1986 paniculate emissions from these sources were esti-
mated to be 25.6 million metric tons (28.2 million short tons) or about 76% of the total national
emissions of PM/TSP in 1986. Similarly, natural sources of paniculate emissions such as wind
erosion or dust, are not included. (An exception is forest fires, some of which result from natural
causes). In total, these fugitive emissions may amount to a considerable portion of total par-
ticulate emissions. The controls applied to these sources have so far been minimal. Due to the
lack of adequate emission factors and emission inventory techniques for these sources, fugitive
paniculate emissions have not been included in most emission inventories. As additional data
become available, it is expected that estimates of fugitive paniculate emissions will be included
in future emission inventories. It should be noted, however, that a major portion of the fugitive
paniculate emissions are relatively large particles that are not readily captured by paniculate
air quality monitors. Similarly, these large particles do not effectively enter into the human
respiratory system.
In 1940 and 1950, emissions from transportation (coal combustion by railroads) and
miscellaneous sources (forest fires) were significant. Emissions from fuel combustion and
industrial processes did not change substantially from 1940 to 1970. Since 1970, emissions
from these categories have been substantially reduced as a result of the installation of air pollution
control equipment. Particulate emissions from transportation decreased substantially from 1940
to 1960 as the result of the obsolescence of coal-burning railroad locomotives. From 1960 to
1988, paniculate from transportation increased due to increased travel by highway motor
vehicles. Miscellaneous source emissions decreased substantially from 1940 to 1970, primarily
due to a major reduction in the acreage burned by forest wildfires. Solid waste emissions
increased from 1940 to 1970, but declined substantially to 1988 as the result of air pollution
regulations prohibiting or limiting the burning of solid waste.
-------
2.2 Sulfur Oxides (SOX)
Emissions of sulfur oxides occur mostly from stationary source fuel combustion and to
some extent, from industrial processes. Emissions of sulfur oxides from the combustion of coal
by railroad locomotives were significant in 1940 and 1950. Emissions from solid waste disposal
and miscellaneous sources have always been minor. Emissions from stationary source fuel
combustion increased greatly from 1940 to 1970. From 1970 to 1988, emissions from fuel
combustion have decreased slightly. During this time period, fuel combustion, particularly of
sulfur-bearing coal, continued to increase, but the average sulfur contents of fuels decreased
and an increasing number of pollution control systems (flue gas desulfurization) were installed.
Emissions from industrial processes increased from 1940 to 1970 reflecting increased industrial
production. From 1970 to 1987, industrial process emissions decreased primarily due to control
measures by primary non-ferrous smelters and sulfuric acid plants. Increased industrial activity
in refining, metals, minerals, and chemicals led to a slight increase (6 percent) in emissions from
1987 to 1988.
2.3 Nitrogen Oxides (NOX)
Emissions of nitrogen oxides are produced largely by stationary source fuel combustion
and by transportation sources. Emissions have steadily increased over the period from 1940 to
1970 as the result of increased fuel combustion. From 1970 to 1988, the size of the increase
was reduced somewhat by controls installed on highway motor vehicles and to a lesser extent
by controls on coal-fired electric utility boilers. From 1978-1983, NOX emissions decreased
slightly. Since then, NOX emissions have increased, but remain below the 1978peak. Emissions
of nitrogen oxides by industrial processes increased from 1940 to 1970, but have remained about
constant since then.
2.4 Reactive Volatile Organic Compounds (VOC)
The largest sources of reactive VOC emissions are transportation sources and industrial
processes. Miscellaneous sources, primarily forest wildfires and non-industrial consumption
of organic solvents, also contribute significantly to total VOC emissions. Emissions from
stationary source fuel combustion and solid waste disposal are relatively small. Transportation
source emissions increased greatly from 1940 to 1970, primarily as the result of increased travel
by highway motor vehicles. Since 1970, air pollution controls installed on motor vehicles have
been effective in reducing VOC emissions. Industrial process emissions have increased through
the late 70's, generally reflecting increased levels of industrial production. Controls installed
on industrial processes since 1970 have had a modest effect in preventing additional increases
in VOC emissions. Since 1979, VOC emissions from industrial processes have decreased. This
reflects both the installation of controls and a lower level of industrial output during 1980-1983.
However, during 1987-1988 industrial activity increased which led to a slight increase in
emissions (2 percent). Emissions from stationary source combustion declined from 1940 through
the mid-1970's and then increased to 1984, reflecting primarily the trend in residential wood
combustion.
2.5 Carbon Monoxide (CO)
Transportation sources are the largest emitters of carbon monoxide. Major increases in
emissions occurred from 1940 to 1970 as the result of increased motor vehicle travel. From
1970 to 1988, transportation emissions decreased as the result of highway vehicle emission
controls, despite continued increases in highway vehicle travel. Emissions from stationary
source fuel combustion have declined from 1940 through the mid-1970's and then increased
slightly in 1987.
-------
Prior to 1970, residential coal and wood combustion contributed significantly to CO
emissions. However, as residential use of coal has been replaced by other fuels, residential
emissions have declined. Beginning in the late 1970's, residential combustion of wood has
increased, however, and as a result CO emissions from residential fuel combustion increased.
Carbon monoxide emissions from industrial processes increased from 1940 to 1950 but have
declined somewhat since then. The decline is due largely to the obsolescence of a few high-
polluting industrial processes such as carbon black manufacture by the channel process and
limited installation of control equipment on other processes. These factors have been significant
enough to offset growth in industrial production which would otherwise have caused a net
increase in emissions. However, due to increased industrial activity in 1988 emissions from
1987 to 1988 increased slightly (4 percent). Carbon monoxide emissions from solid waste
disposal increased from 1940 to 1970, but have subsequently declined as the result of airpollution
control efforts. Substantial emissions of carbon monoxide from forest fires occurred in 1940.
In later years, these emissions have been much smaller due to improved fire prevention efforts
and more effective suppression of wildfires.
2.6 Lead(Pb)
The primary sources of lead emissions are transportation (gasoline engines) and industrial
processes. This report does not include estimates of lead emissions for 1940, 1950 or 1960
because of missing data, especially for transportation sources. In the early 1970's, the trans-
portation emissions varied based on the amount of gasoline consumed and the average lead
content. From 1975 to 1987, transportation emissions decreased as a result of the conversion
to unleaded gasoline. A major reduction occurred between 1984 and 1986 due to EPA rule-
making which required petroleum refiners to lower the lead content of leaded gasoline in 1985.
Emissions from industrial processes have declined from 1970 to 1987 as the result of installation
of air pollution control equipment. However, due to increased industrial activity in 1988
emissions from 1987 to 1988 increased slightly (5 percent).
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TABLE 2
1940-1970 SUMMARY OF ESTIMATED
EMISSIONS OF PARTICULATE (PM/TSP)
(TERAGRAMS/YEAR)
Source Category
1940
1950
1960
1970
Transportation
Highway Vehicles
Aircraft
Railroads
Vessels
Other-Off Highway
Transportation Total
Stationary Source Fuel Combustion
Electric Utilities
Industrial
Commercial-Institutional
Residential
Fuel Combustion Total
Industrial Processes
Iron and Steel Mills
Primary Metal Smelting
Secondary Metals
Mineral Products
Chemicals
Petroleum Refining
Wood Products
Food and Agriculture
Mining Operations
Industrial Processes Total
Solid Waste Disposal
Incineration
Open Burning
Solid Waste Total
Miscellaneous
Forest Fires
Other Burning
Misc. Total
Total of All Sources
0.2
0.0
2.4
0.1
0.0
2.7
1.3
3.3
0.4
2.5
7.5
3.0
0.6
0.2
2.0
0.3
0.0
0.5
0.8
1.3
8.7
0.3
0.2
0.5
2.9
0.8
3.7
23.1
0.3
0.0
1.7
0.1
0.0
2.1
2.0
2.8
0.5
1.7
7.0
3.5
0.6
0.3
2.9
0.4
0.0
0.8
0.8
3.4
12.7
0.3
0.3
0.6
1.7
0.8
2.5
24.9
0.6
0.0
0.1
0.0
0.0
0.7
2.8
1.8
0.1
1.0
5.7
1.7
0.5
0.2
3.8
0.3
0.1
0.9
0.9
4.1
12.5
0.4
0.5
0.9
1.0
0.8
1.8
21.6
0.9
0.1
0.1
0.0
0.1
1.2
2.3
1.6
0.1
0.6
4.6
1.2
0.6
0.2
2.9
0.2
0.1
0.7
0.8
3.9
10.5
0.4
0.7
1.1
0.7
0.4
1.1
18.5
12
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TABLE 3
1940-1970 SUMMARY OF ESTIMATED
EMISSIONS OF SULFUR OXIDES
(TERAGRAMS/YEAR)
Source Category 1940 1950 1960 1970
Transportation
Highway Vehicles
Aircraft
Railroads
Vessels
Other-Off Highway
Transportation Total
Stationary Source Fuel Combustion
Electric Utilities
Industrial
Commercial-Institutional
Residential
Fuel Combustion Total
Industrial Processes
Primary Metal Smelting
Pulp Mills
Chemicals
Petroleum Refining
Iron and Steel
Secondary Metals
Mineral Products
Natural Gas Processing
Industrial Processes Total
Solid Waste Disposal
Incineration
Open Burning
Solid Waste Total
Miscellaneous
Forest Fires
Other Burning
Misc. Total
Total of All Sources
0.0
0.0
2.7
0.2
0.0
2.9
2.2
5.5
1.0
2.3
11.0
2.5
0.0
0.2
0.2
0.5
0.0
0.3
0.0
3.7
0.0
0.0
0.0
0.0
0.5
0.5
17.6
0.1
0.0
2.0
0.2
0.0
2.3
4.1
5.2
1.7
1.9
12.9
2.8
0.0
0.4
0.3
0.6
0.0
0.5
0.0
4.6
0.0
0.0
0.0
0.0
0.5
0.5
19.8
0.1
0.0
0.2
0.1
0.0
0.4
8.4
3.5
1.0
1.1
14.0
3.0
0.1
0.4
0.6
0.6
0.0
0.5
0.1
5.3
0.0
0.0
0.0
0.0
0.5
0.5
19.7
0.3
0.0
0.1
0.2
0.1
0.6
15.8
4.1
0.9
0.5
21.3
3.7
0.2
0.5
0.7
0.7
0.0
0.6
0.1
6.4
0.0
0.0
0.0
0.0
0.1
0.1
28.3
13
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TABLE 4
1940-1970 SUMMARY OF ESTIMATED
EMISSIONS OF NITROGEN OXIDES
(TERAGRAMS/YEAR)
Source Category
1940
1950
1960
1970
Transportation
Highway Vehicles
Aircraft
Railroads
Vessels
Other-Off Highway
Transportation Total
Stationary Source Fuel Combustion
Electric Utilities
Industrial
Commercial-Institutional
Residential
Fuel Combustion Total
Industrial Processes
Petroleum Refining
Chemicals
Iron and Steel Mills
Pulp Mills
Mineral Products
Industrial Processes Total
Solid Waste Disposal
Incineration
Open Burning
Solid Waste Total
Miscellaneous
Forest Fires
Other Burning
Misc. Total
Total of All Sources
1.4
0.0
0.6
0.1
0.2
2.3
0.6
2.3
0.2
0.3
3.4
0.1
0.0
0.0
0.0
0.1
0.2
0.0
0.1
0.1
0.7
0.2
0.9
6.9
2.2
0.0
0.9
0.1
0.4
3.6
1.2
2.9
0.3
0.3
4.7
0.1
0.0
0.1
0.0
0.1
0.3
0.1
0.1
0.2
0.4
0.2
0.6
9.4
3.8
0.0
0.7
0.1
0.5
5.1
2.3
3.7
0.3
0.4
6.7
0.2
0.1
0.1
0.0
0.1
0.5
0.1
0.2
0.3
0.2
0.2
0.4
13.0
6.3
0.1
0.6
0.1
0.8
8.0
4.4
3.9
0.3
0.4
9.1
0.2
0.2
0.1
0.0
0.2
0.7
0.1
0.3
0.4
0.2
0.1
0.3
18.5
14
-------
TABLE 5
1940-1970 SUMMARY OF ESTIMATED
EMISSIONS OF REACTIVE VOCS
(TERAGRAMS/YEAR)
Source Category 1940 1950 1960 1970
Transportation
Highway Vehicles
Aircraft
Railroads
Vessels
Other-Off Highway
Transportation Total
Stationary Source Fuel Combustion
Electric Utilities
Industrial
Commercial-Institutional
Residential
Fuel Combustion Total
Industrial Processes
Chemicals
Petroleum Refining
Iron and Steel Mills
Mineral Products
Food and Agriculture
Industrial Organic Solvent Use
Petroleum Product Production
and Marketing
Industrial Processes Total
Solid Waste Disposal
Incineration
Open Burning
Solid Waste Total
Miscellaneous
Forest Fires
Other Burning
Misc. Organic Solvent Use
Misc. Total
Total of All Sources
4.0
0.0
0.5
0.0
0.2
4.7
0.0
0.1
0.0
1.7
1.8
0.8
0.4
0.3
0.0
0.1
1.0
0.7
3.3
0.4
0.5
0.9
3.1
0.6
0.8
4.5
15.2
5.7
0.1
0.5
0.1
0.4
6.8
0.0
0.1
0.0
1.2
1.3
1.2
0.5
0.4
0.0
0.1
2.1
1.1
5.4
0.4
0.6
1.0
1.7
0.6
1.3
3.6
18.1
8.3
0.2
0.2
0.2
0.5
9.4
0.0
0.1
0.0
0.7
0.8
1.1
0.7
0.3
0.0
0.2
2.4
1.6
6.3
0.5
0.9
1.4
0.9
0.5
1.7
3.1
21.0
9.1
0.3
0.2
0.3
0.5
10.3
0.0
0.1
0.0
0.4
0.6
1.6
0.7
0.4
0.0
0.2
4.0
2.1
8.9
0.5
1.3
1.8
0.7
0.3
2.3
3.3
25.0
15
-------
TABLE 6
1940-1970 SUMMARY OF ESTIMATED
EMISSIONS OF CARBON MONOXIDE
(TERAGRAMS/YEAR)
Source Category 1940 1950 1960 1970
Transportation
Highway Vehicles
Aircraft
Railroads
Vessels
Other-Off Highway
Transportation Total
Stationary Source Fuel Combustion
Electric Utilities
Industrial
Commercial-Institutional
Residential
Fuel Combustion Total
Industrial Processes
Chemicals
Petroleum Refining
Iron and Steel Mills
Primary Metal Smelting
Secondary Metals
Pulp Mills
Industrial Processes Total
Solid Waste Disposal
Incineration
Open Burning
Solid Waste Total
Miscellaneous
Forest Fires
Other Burning
Misc. Total
Total of All Sources
22.6
0.0
3.7
0.2
3.4
29.9
0.0
0.4
0.1
15.8
16.3
3.8
0.2
1.5
0.0
1.0
0.1
6.6
2.0
1.3
3.3
22.8
3.7
26.5
82.6
34.2
0.8
2.8
0.2
6.7
44.7
0.1
0.5
0.1
10.9
11.6
5.3
2.4
1.1
0.1
1.4
0.2
10.5
2.5
1.8
4.3
12.8
3.7
16.5
87.6
47.7
1.6
0.3
0.6
8.0
58.2
0.1
0.6
0.0
6.4
7.1
3.6
2.8
1.3
0.3
1.0
0.3
9.3
2.5
2.6
5.1
6.7
3.3
10.0
89.7
65.3
0.9
0.3
1.2
6.8
74.4
0.2
0.7
0.1
3.5
4.5
3.1
2.0
1.6
0.6
1.1
0.6
8.9
2.7
3.7
6.4
5.1
2.1
7.2
101.4
16
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3. METHODS
The preparation of an emission inventory involves many steps to achieve the desired result,
which is to estimate the amount of emissions for selected pollutants in a defined geographical area
over a specific period of time. Ideally, nationwide emission estimates should result from a sum-
mation of county, State, and Regional data in which each component is reported separately. The
National Emissions Data System (NEDS) uses this procedure. The methods used to prepare data
for this publication are as similar as possible to those used for NEDS data preparation. To develop
the NEDS point source file, a complex calculation procedure must be used which includes data
from (1) state-by-state emissions calculation, (2) reporting of emissions for individual sources and
(3) summation of these individual emissions totals to produce national totals. Because point source
data is compiled from this variety of sources, there is a much greater chance for errors or omissions
to occur in the NEDS data.
In addition to the NEDS point source file, there is a NEDS area source file. The NEDS area
source file contains estimates of emissions from sources not included in the NEDS point source
file. The sources covered by the NEDS area source file include the following: small (< 100 T/Y)
combustion sources, transportation, and other miscellaneous categories. Because of the basic
similarity of techniques, discrepancies between national totals reported herein and those given in
NEDS reports are due largely to incomplete data reporting and errors in the NEDS data. An
additional difference between the detailed NEDS reports and this publication is that the NEDS
reports include some fugitive dust categories not covered by this report.
Fugitive particulate emissions (emissions from unconfined sources such as storage piles,
material loading, etc.) are incompletely accounted for in the emission totals. Rough estimates of
industrial process fugitive emissions are included for some industries. Area source fugitive dust
emissions (unpaved roads, construction activities, etc.) are not included at all. Similarly, natural
sources of particulate, such as wind erosion or dust, are not included. (An exception to the previous
statement is forest fires, some of which result from natural causes). In total, these fugitive emissions
may amount to a considerable portion of total particulate emissions. The controls applied to these
sources have, to date, been minimal. Due to the lack of adequate emission factors and emission
inventory techniques for these sources, fugitive particulate emissions have not been included in
most emission inventories. As additional data become available, it is expected that estimates of
fugitive particulate emissions will be included in future emission inventories. It should be noted,
however, that a major portion of the fugitive particulate emissions are relatively large particles that
are not readily captured by particulate air quality monitors. Similarly, these large particles do not
effectively enter into the human respiratory system. The quality of NEDS data over time has
improved so that the differences between NEDS emission reports for 1977 and later years and
national emission totals determined by the procedure used for this publication are not as great as
in earlier NEDS reports. Moreover, historical NEDS data are not revised to account for updated
emission factors, errors or omissions in the data. As a result, annual NEDS publications do not
represent a consistent trend in estimated emissions.
Because it is impossible to test every pollutant source individually, particularly area sources,
an estimating procedure must be used. In order to do this, however, one must either estimate the
emissions directly or estimate the magnitude of other variables that can then be related to emissions.
These indicators include fuel consumption, vehicle miles, population, sales, tons of refuse burned,
raw materials processed, etc., which are then multiplied by appropriate emission factors to obtain
emission estimates. The limitations and applicability of emission factors should be noted. In general,
emission factors are not precise indicators of emissions from a single source; rather, they are
quantitative estimates of the average rate of pollutants released as a result of some activity. They
are most valid when applied to a large number of sources and processes. If their limitations are
45
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recognized, emission factors are extremely useful in estimating emission levels. A detailed dis-
cussion of emission factors and related information is contained in Reference 2. The emission factor
thus relates quantity of pollutants emitted to indicators such as those noted above, and is a practical
approach for estimating emissions from various source categories.
A basic discussion of trends is meaningful only when there is a common basis for evaluation.
It was necessary, therefore, to quantify emissions using the same criteria for each year. This meant
using the same estimation techniques, using equal or equivalent data sources, covering the same
pollutant sources, and using compatible estimates of pollutant control levels from year to year.
Estimates for previous years were updated using current emission factors and including the most
recent information available. The criteria used in calculating emissions was the same for all years.
The methodology used in generation of emission estimates for individual source categories
follows.
3.1 Transportation
3.1.1 Motor Vehicles
Emission estimates from gasoline and diesel-powered motor vehicles were based upon
vehicle-mile tabulations and emission factors. Eight vehicle categories are considered; light
duty gasoline (mostly passenger cars), light duty diesel passenger cars, light duty gasoline
trucks (trucks less than 6000 pounds in weight), light duty gasoline trucks 6000 to 8500
pounds in weight, light duty diesel trucks, heavy duty gasoline trucks and buses, and heavy
duty diesel trucks and buses, and motorcycles. The emission factors used are based on the
latest available data from Reference 3. The MOBILE 4 model, developed by the EPA Office
of Mobile Sources was used to calculate emission factors for each year. The emission factors
are weighted to consider the approximate amount of motor vehicle travel in low altitude
areas, high altitude areas, and California to obtain overall national average emission factors.
For each area a representative average annual temperature, together with national averages
for motor vehicle model year distributions and hot/cold start vehicle operation percentages
were used to calculate the emission factors. Average speed is taken into account according
to the published distribution of vehicle-miles travelled (VMT) as published in Reference 4.
The published VMT are divided into three road categories corresponding to roads with
assumed average speeds of 55 miles per hour for interstates and other primary highways,
45 miles per hour for other rural roads, and 19.6 miles per hour for other urban streets. For
1940 and 1950, average speeds were assumed to be 45, 35 and 19.6 miles per hour for these
roadway classifications.
Lead emission estimates from gasoline-powered-motor vehicles, were based on
highway gasoline consumption, lead content of gasoline, percent unleaded gasoline, and
emission factors. The gasoline consumption is based on highway gasoline usage as published
in Reference 4. The lead content of gasoline was obtained from Reference 13 for 1970 and
Reference 2 for 1975-88. The percent unleaded gasoline is obtained from Reference 6. The
emission factor was also obtained from Reference 2.
3.1.2 Aircraft
Aircraft emissions are based on emission factors and aircraft activity statistics reported
by the Federal Aviation Administration.5 Emissions are based on the number of landing-
takeoff (LTO) cycles. Any emissions in cruise mode, which is defined to be above 3000
46
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feet (1000 meters) are ignored. Average emission factors for each year, which take into
account the national mix of aircraft types for general aviation, military, and commercial
aircraft, are used to compute the emissions.
3.1.3 Railroads
The Department of Energy reports consumption of diesel fuel and residual fuel oil by
railroads.34 Average emission factors applicable to diesel fuel consumption were used to
calculate emissions. The average sulfur content of each fuel was used to estimate SOX
emissions. Coal consumption by railroads was obtained from References 7 and 13.
3.1.4 Vessels
Vessel use of diesel fuel, residual oil, and coal is reported by the Department of
Energy.34'7 Gasoline use is based on national boat and motor registrations, coupled with a
use factor (gallons/motor/year) from Reference 8 and marine gasoline sales as reported in
Reference 4. Emission factors from AP-422 are used to compute emissions. Since AP-42
does not contain an emission factor for coal use by vessels, an average emission factor for
coal combustion in boilers was used.
3.1.5 Non-highway Use of Motor Fuels
Gasoline and diesel fuel are also consumed by off-highway vehicles. The fuel use is
divided into seven categories; farm tractors, other farm machinery, construction equipment,
industrial machinery, small general utility engines such as lawn mowers and snowthrowers,
snowmobiles, and motorcycles. Fuel use is estimated for each category from estimated
equipment population and an annual use factor of gallons/unit/year8, together with reported
off-highway diesel fuel deliveries given in Reference 34 and off-highway gasoline sales
reported in Reference 4.
3.2 Fuel Combustion in Stationary Sources
3.2.1 Coal
Bituminous coal, lignite, and anthracite coal use is reported by the Department of
Energy.7'31 Most coal is consumed by electric utilities. Average emission factors and the
sulfur content of each type of coal were used to estimate emissions. The degree of particulate
control was based on a report by Midwest Research Institute9 together with data from
NEDS10. Sulfur content data for electric utilities are available from the Department of
Energy11. Sulfur contents for other categories are based on coal shipments data reported in
Reference 7 and average sulfur contents of coal shipped from each production district as
reported in Reference 13 or 24. For electric utilities, SO2 emissions are adjusted to account
for flue gas desulfurization controls, based on data reported in Reference 25.
3.2.2 Fuel Oil
Distillate oil, residual oil, and kerosene are consumed by stationary sources nation-
wide. Consumption by user category is reported by the Department of Energy.34 Average
emission factors and the sulfur content of each fuel were used to estimate emissions.
3.2.3 Natural Gas
Natural gas consumption data are reported by the Department of Energy.12 Average
emission factors from AP-42 were used to calculate the emission estimates.
47
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3.2.4 Other Fuels
Consumption of wood has been estimated by the Department of Energy.27'35 Con-
sumption of bagasse is based on data reported in NEDS.10 Sales of liquified petroleum gas
(LPG) are reported in Reference 6. Estimated consumption of coke and coke-oven gas are
based on References 11 and 26. Average emission factors from NEDS were used to calculate
emissions.
Lead emissions from the combustion of waste oil were based on information obtained
from Reference 32. The amount of waste oil burned has been assumed to remain constant
and the emissions have been changed as a result of a decrease in the lead content of the
waste oil.
3.3 Industrial Processes
In addition to fuel combustion, certain other industrial processes generate and emit varying
quantities of pollutants into the air. The lack of published national data on production, type of
equipment, and controls, as well as an absence of emission factors, makes it impossible to include
estimates of emissions from all industrial process sources.
Production data for industries that produce the great majority of emissions were obtained
from publicly available reports. Generally, the Minerals Yearbook,13 published by the Bureau
of Mines, and Current Industrial Reports,4 published by the Bureau of the Census, provide
adequate data for most industries. Average emission factors were applied to production data
to obtain emissions. Control efficiencies applicable to various processes were estimated on the
basis of published reports9 and from NEDS data.10
For the purposes of this report, petroleum product storage and marketing operations
(gasoline, crude oil, and distillate fuel oil storage and transfer, gasoline bulk terminals and bulk
plants, retail gasoline service stations) are included as industrial processes. Also included as
industrial processes are industrial surface coating and degreasing operations, graphic arts
(printing and publishing), and dry cleaning operations. All of these processes involve the use
of organic solvents. Emissions from the consumption of organic solvents are estimated based
on data reported in Reference 15. It is assumed that all solvents consumed are eventually released
as air pollution, except for industrial surface coating operations. Estimates of the level of control
for surface coating operations have been derived from References 10 and 28. In addition, the
methodology given in Reference 15 has been updated to be consistent with similar procedures
used for estimating organic solvent emissions in the National Emissions Data System (NEDS).29
3.3.1 Miscellaneous Industrial Processes for Lead
Lead emissions from miscellaneous industrial processes include the major source of
lead alkyl production as well as other minor sources such as type metal production, can
soldering, cable covering, and other minor sources. The lead alkyl production is based on
information from Reference 33. The production information for the other minor sources is
from Reference 13.
3.4 Solid Waste Disposal
A study conducted in 1968 on solid waste collection and disposal practices1" was the basis
for estimating emissions from solid waste disposal. Results of this study indicate that the average
collection rate of solid waste is about 5.5 pounds per capita per day in the United States. It has
been stated that a conservative estimate of the total generation rate is 10 pounds per capita per
day. The results of this survey were updated based on data reported in NEDS and used to
estimate, by disposal method, the quantities of solid waste generated. Average emission factors
were applied to these totals to obtain estimates of total emissions from the disposal of solid
wastes.
48
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3.5 Miscellaneous Sources
3.5.1 Forest Fires
The Forest Service of the Department of Agriculture publishes information on the
number of forest fires and the acreage burned.17 Estimates of the amount of material burned
per acre are made to estimate the total amount of material burned. Similar estimates are
made to account for managed burning of forest areas. Average emission factors were applied
to the quantities of materials burned to calculate emissions.
3.5.2 Agricultural Burning
A study18 was conducted by EPA to obtain from local agricultural and pollution control
agencies estimates of the number of acres and estimated quantity of material burned per acre
in agricultural burning operations. These data have been updated and used to estimate
agricultural burning emissions, based on average emission factors.
3.5.3 Coal Refuse Burning
Estimates of the number of burning coal-refuse piles existing in the United States are
made in reports by the Bureau of Mines.9 Their publication presents a detailed discussion
of the nature, origin, and extent of this source of pollution. Rough estimates of the quantity
of emissions were obtained using this information by applying average emission factors for
coal combustion. It was assumed that the number of burning refuse piles decreased to a
negligible amount by 1975.
3.5.4 Structural Fires
The United States Department of Commerce publishes information on the number
and types of structures damaged by fire in their statistical abstracts.20 Emissions were
estimated by applying average emission factors for wood combustion to these totals.
3.5.5 Non-industrial Organic Solvent Use
This category includes non-industrial sales of surface coatings (primarily for archi-
tectural coating, solvent evaporation from consumer products (aerosols, space deodorants,
polishes, toiletries, etc.), use of volatile organic compounds as general cleaning solvents,
paint removers, and liquefaction of asphalt paving compounds, and other undefined end
uses. Total national organic solvent use is estimated from chemical production reports of
References 21 and 33, together with estimates of the portion of total production for use as
solvent for each chemical.5>29 It is assumed that all solvent production is equal to the amount
necessary to make up for solvent lost through evaporation.
49
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4. ANALYSIS OF TRENDS
National trends in air pollutant emissions are a function of a number of factors. Air pollution
control measures and economic conditions have the strongest impact on total emissions. National
emission trends do not provide any insight into the distribution or concentration of air pollution
sources within the United States. Therefore, local emission trends do not necessarily coincide with
national emission trends. Based on the national implementation of control measures for some
classes of sources, such as highway motor vehicles, it is reasonable to infer that for most localities,
the national trend in emissions reasonably approximates local trends in emissions for the same class
of sources.
In addition to the fact that national emission trends do not measure local changes in emission
densities, national emission trends may not be consistent with air quality trends because of the
impact of meteorological factors on air quality data. Also, the estimates for PM, SO,, and NOX
emissions include more substances than are routinely measured by ambient air monitoring equip-
ment. For example, high-volume air samplers collect only suspended paniculate approximately
0.3 to 100 micro-meters in diameter, but paniculate emission inventories include both suspended
and settled paniculate generated by man's activities. Likewise, sulfur dioxide (SO2) and nitrogen
dioxide (NO2) ambient air monitors measure only those two compounds while oxides of sulfur
(SOX) and nitrogen (NOX) are included in the emission estimates. In each case, the substance
measured by the ambient air monitor is the most prevalent constituent of its pollutant class or is
acknowledged to be its most representative indicator. In this report, emissions of sulfur oxides are
reported as the equivalent weight of SO2, which is the predominant sulfur oxide species. Some
emissions of sulfur trioxide (SO3) are also included, expressed at the equivalent weight of SO2.
Similarly, nitrogen oxides include predominantly nitric oxide (NO) and nitrogen dioxide (NO2).
Other nitrogen oxides are probably emitted in small amounts. In this report all nitrogen oxide
emissions are expressed as the equivalent weight of NO2. Estimates of oxidant emissions are not
provided because most oxidant species are secondary pollutants generated by photochemical
reactions in the atmosphere. Emission estimates of VOC, a major ingredient in oxidant-producing
reactions, were developed from current emission factors.2' Generally excluded from VOC estimates
were emissions of methane, ethane, methyl chloroform, and other compounds which are considered
to be of negligible photochemical reactivity. Organic species were identified based on Reference
22. If no data were available for a source category, the total non-methane hydrocarbon or the total
hydrocarbon emission factor from Reference 2 was used. Highway vehicle emissions were estimated
as non-methane VOC's.3
The following sections discuss the most important factors influencing the emission trends for
each pollutant.
4.1 Particulate (PM/TSP)
1940-1970
The estimated paniculate emissions for 1940,1950 and 1960 are 10 to 30 percent higher
than in 1970. Even though industrial production levels and the quantities of fuels consumed
were lower than the post-1970 period, the general lack of air pollution controls before 1970
resulted in relatively large paniculate emissions. Also, for the years 1940 and 1950, paniculate
emissions from coal combustion by railroads and from forest wildfires were significant.
A large portion of the paniculate emissions from stationary source fuel combustion, result
from the combustion of coal. In 1940, coal was consumed largely in the industrial and residential
sectors. Residential coal use has declined substantially since 1940, resulting in a corresponding
reduction in emissions. Industrial coal use has also declined, but not to the same extent. The
degree of control employed by industrial coal consumers has increased, however, so that overall
industrial coal combustion emissions decreased by 1970 to only about 40 percent of the estimated
51
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1940 level. On the other hand, coal combustion by electric utilities has increased greatly, from
an estimated 51 million tons in 1940 to 321 million tons in 1970. This increased consumption
resulted in increased emissions from 1940 to 1950. Since then, paniculate emissions from
electric utilities have decreased, despite continued increases in coal consumption. Installation
of improved control equipment is responsible for this reduction.
Particulate emissions from industrial processes increased from 1940 to 1950, reflecting
increased industrial production. From 1950 to 1970, industrial output continued to grow, but
installation of pollution control equipment helped to offset the increase in industrial production.
As a result, from 1950 to 1960 industrial process emissions stayed about the same, and decreased
slightly from 1960 to 1970.
1970-1988
Since 1970, paniculate emissions have decreased substantially as the result of air pollution
control efforts. The extent of the reduction is most evident from the data in Table 29 which
shows theoretical 1988 national emission estimates, assuming that pollutant control levels did
not change since 1970. Figure 13 illustrates this difference. Overall, paniculate emissions
would have increased by about 20 percent from 1970 to 1988 with no change in the degree of
control from 1970. In reality, as shown in Table 1, paniculate emissions decreased about 63
percent from 1970 to 1988. Thus, 1988's actual paniculate emissions were about a third of
what they might have been without the additional control put in place since 1970.
A large portion of the paniculate emissions from stationary source fuel combustion result
from the combustion of coal. In 1970, a larger portion of coal was consumed in the industrial
and residential sectors. Residential coal use has declined substantially since 1970, resulting in
a corresponding reduction in emissions. Industrial coal use has declined, but not to the same
extent. The degree of control employed by industrial coal consumers has increased, however,
so that overall industrial coal combustion emissions have decreased by 1988 to only about 7
percent of the estimated 1970 level. On the other hand, coal combustion by electric utilities has
increased greatly, from an estimated 321 million tons in 1970 to 757.6 million tons in 1988.
However, paniculate emissions from electric utilities have decreased, despite continued
increases in coal consumption. Installation of improved control equipment is responsible for
this reduction. New facilities constructed in the 1970's were required to meet New Source
Performance Standards (NSPS) requirements to achieve a high degree of control. From Tables
2 and 29, it can be seen that if the 1970 level of control had remained in effect in 1988, electric
utility emissions would have more than doubled, from 2.3 teragrams to 5.3 teragrams. Estimated
actual 1988 emissions from electric utilities were 0.4 teragrams, a decrease of 83 percent from
1970.
Particulate emissions from industrial processes have been reduced substantially due to
installation of improved control equipment mandated by air pollution control programs. Since
1970, actual emissions from industrial processes declined by 75 percent. Table 23 shows
estimated emissions for specific processes. These annual emissions estimates reflect changes
in production levels along with an increase in average control levels from 1970 to 1988.
52
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Source Category
TABLE 29
1988 NATIONAL EMISSION ESTIMATES
WITH 1970 LEVEL OF CONTROL
(TERAGRAMS/YEAR)
PM
SO2
NOX
VOC
CO
Percentage of 1970 Actual Emissions
*Pb emissions are expressed in gigagrams/year.
Pb'
Transportation
Highway Vehicles
Non-Highway
Transportation Total
Stationary Source Fuel Combustion
Electric Utilities
Industrial
Residential/Commercial
Fuel Combustion Total
Industrial Processes (SIC)
Mining Operations (10,12,13,14)
Food and Agriculture (02,07 ,20)
Wood Products (24,26)
Chemicals (28)
Petroleum Refining (29)
Mineral Products (32)
Metals (33)
Miscellaneous
Industrial Processes Total
Solid Waste
Miscellaneous
Total
1988 Actual Emissions (Table 1)
Theoretical 1988 Emissions As a
Percentage of 1988 Actual Emissions
1970 Actual Emissions (Table 1)
Theoretical 1988 Emissions As A
1.7
0.2
1.9
5.3
1.4
1.1
7.8
4.3
1.3
1.1
0.3
0.7
2.4
1.2
0.0
11.3
1.2
0.9
23.1
6.9
336.4
18.5
124.5
0.6
0.3
0.9
25.4
2.4
0.7
28.5
0.4
0.0
0.3
0.8
1.2
0.6
2.8
0.0
6.1
0.1
0.0
35.6
20.7
172.1
28.3
125.7
12.4
1.9
14.3
8.3
3.1
0.6
12.0
0.0
0.0
0.0
0.3
0.2
0.2
0.0
0.0
0.7
0.3
0.2
27.5
19.8
138.9
18.5
148.6
15.5
1.3
16.8
0.0
0.1
0.7
0.8
0.0
0.2
0.0
2.1
0.9
0.0
0.2
6.8
10.2
2.0
2.4
32.2
18.6
173.5
25.0
129.1
105.2
7.2
112.4
0.3
0.6
6.6
7.5
0.0
0.0
0.9
2.9
2.3
0.0
2.7
0.0
8.8
7.3
6.0
142.0
61.2
232.2
101.4
140.0
200.1
4.7
204.8
0.6
9.2
0.0
9.8
0.2
0.0
0.0
0.1
0.0
0.4
14.9
0.1
15.7
2.8
0.0
233.1
7.6
3,063.1
203.8
114.4
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Comments on Paniculate Emission Estimates
Several caveats should be noted with respect to the paniculate emission estimates pres-
ented here. First, the estimates represent total paniculate emissions, without any distinction of
particle sizes. Thus, both large particles and small particles are included. Emissions of very
large particles are more likely to settle out of the atmosphere and not be measured as total
suspended paniculate by air quality monitoring equipment. Small and intermediate size particles
are more likely to remain airborne and are more efficiently captured by total suspended par-
ticulate air monitoring equipment. Small particles are also capable of being inhaled into the
human respiratory system, possibly causing adverse health effects. The particulate emission
controls that have been employed to date have been most effective in reducing emissions of
large and intermediate size particles. The trend in the emissions of small particles is not clearly
known. However, it is very doubtful whether small particle emissions have been reduced to the
extent that total particulate emissions have been reduced. It should be noted that some small
particles may be formed in the atmosphere as the result of various chemical and physical pro-
cesses. Such particles are not included in the estimated total particulate emissions.
A second caveat is that fugitive particulate emissions (emissions from unconfined sources
such as storage piles, material loading, etc.) are incompletely accounted for in the emission
totals. Rough estimates of industrial process fugitive emissions are included for some industries.
Area source fugitive dust emissions (unpaved roads, construction activities, etc.) are not included
at all. Similarly, natural sources of particulate, such as wind erosion or dust, are not included.
(An exception is forest fires, some of which result from natural causes). In total, these fugitive
emissions may amount to a considerable portion of total particulate emissions. The controls
applied to these sources have so far been minimal. Due to the lack of adequate emission factors
and emission inventory techniques for these sources, fugitive particulate emissions have not
been included in most emission inventories. As additional data become available, it is expected
that estimates of fugitive particulate emissions will be included in future emission inventories.
It should be noted, however, that a major portion of the fugitive particulate emissions are
relatively large particles that are not readily captured by particulate air quality monitors. A
mitigating factor which applies to this situation may be that these large particles do not effectively
enter into the human respiratory system.
4.2 Sulfur Oxides (SOx)
1940-1970
From 1940 to 1970, major increases in sulfur oxide emissions occurred as the result of
increased combustion of fossil fuels such as coal and oil. Industrial process emissions also
increased, but to a lesser extent. Sulfur oxide emissions from other source categories decreased,
primarily as the result of the obsolescence of coal-fired railroad locomotives and a decrease in
coal refuse burning.
1970-1988
Since 1970, total sulfur oxide emissions have declined about 27 percent. This result is
due to the use of fuels with lower average sulfur contents, some scrubbing of sulfur oxides from
flue gases, and controls on industrial process sources (Table 29, Figure 13). Significant emission
reductions from industrial processes have occurred, mostly from non-ferrous smelters and
sulfuric acid plants. By-product recovery of sulfuric acid at smelters has increased since 1970
meaning that sulfur oxide emissions that previously would have been released to the atmosphere
are recovered as sulfuric acid. Since 1972, new sulfuric acid manufacturing plants have been
subject to New Source Performance Standards requirements. These rules have contributed to
decreased emissions, as new plants built to meet new product demands or replace old facilities,
must achieve more stringent emission control than old facilities. As shown in the tables, since
55
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1970 emissions from electric utilities account for more than half of the total sulfur oxide
emissions. Combustion of sulfur-bearing fuels, chiefly coal and residual fuel oil, is primarily
responsible for this increase. Figure 14 shows how SO2 and NO, emissions from electric utility
coal combustion have changed from 1940-1988. Between 1970 and 1988, utility use of coal
more than doubled. Emissions from utilities have decreased, however, because fuels with low
sulfur content have been used to the extent that they were available. Also, flue gas desulfurization
systems have been installed by the late 1970's helped to prevent increases in electric utility
emissions. 1988 electric utility emissions would have been approximately 60 percent higher
without the operation of flue gas desulfurization controls. The theoretical 1988 national emission
estimates given in Table 29 for stationary fuel combustion sources are based on (1) 1988 fuel
amounts, (2) fuel sulfur contents that represent 1970 average levels for fuel oil and (3) an
estimated average sulfur content of coal that would have been consumed if there were no changes
in air pollution regulations since 1970. It is estimated that the average sulfur content of coal
burned nationwide would have declined anyway even without new air pollution regulations due
to the greater use of coal from the Western U.S., which generally has a lower sulfur content
than coal from the Eastern States. On this basis, electric utility emissions would have increased
60 percent. In fact, emissions decreased by 14 percent. Sulfur oxide emissions from other fuel
combustion sectors decreased, primarily due to less coal burning by industrial, commercial and
residential consumers.
Comments on Sulfur Oxide Emission Estimates
Emissions of sulfur and nitrogen oxides have been identified as precursors of acidic
precipitation and deposition. To support Federal research activities on the subject, more detailed
historical emissions estimates of sulfur and nitrogen oxides have been developed. Interested
readers may wish to review Reference 30, which contains State level estimates of sulfur and
nitrogen oxide emissions from 1900 through 1980.
4.3 Nitrogen Oxides (NOx)
1940-1970
Nitrogen oxide emissions result almost entirely from fuel combustion by stationary
sources and motor vehicles. From 1940 through 1970, NO, emissions increased steadily as the
result of increased fuel combustion.
1970-1988
Controls applied to sources of NOX emissions have had a limited effect in reducing
emissions through 1988. Table 29 (Figure 13) shows that with the 1970 control level, national
NOX emissions would have been about 39 percent higher than actual 1988 emissions. The
emissions from stationary fuel combustion sources largely reflect the actual growth in fuel
consumption. For electric utilities, NSPS control requirements have, somewhat, held down the
growth in NOX emissions. Nevertheless, NOX emissions from electric utilities increased 61
percent from 1970 to 1988. For mobile sources, NOX emissions were controlled as a result of
the Federal Motor Vehicle Control Program (FMVCP). Nitrogen oxide emissions from highway
vehicles would have increased 97 percent, had there been no change in control level since 1970.
The estimates of actual NOX emissions show a 3 percent increase. Figure 15 shows how NOX
emissions from major highway vehicle categories have changed from 1970 to 1988.
56
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4.4 Reactive Volatile Organic Compounds (VOC)*
1940-1970
From 1940 through 1970, reactive VOC emissions increased about 65 percent. Major
increases in highway vehicle travel and industrial production were chiefly responsible. Emis-
sions from these source categories were about two and a half times higher in 1970 than in 1940.
However, emissions from other contributing categoreis—residential fuel combustion and forest
fires-declined substantially. In 1940, residential fuel combustion and forest fires accounted
for 32 percent of total national reactive VOC emissions. By 1970, their contribution to total
reactive VOC emissions had been reduced to 4 percent.
1970-1988
Since 1970, emissions of reactive VOC decreased primarily due to motor vehicle controls
and less burning of solid waste. Without controls, a substantial increase in emissions from
highway vehicles would have occurred. From 1970 to 1988, vehicle-miles of travel in the U.S.
increased by about 81 percent.4 A 70 percent increase in emissions would have occurred had
1970 control levels remained unchanged. As a result of the controls put in place, reactive VOC
emissions from highway vehicles actually decreased 46 percent (Table 29, Figure 13). Figure
16 shows how reactive VOC emission from major highway vehicle categories have changed
from 1970-1988. Reactive VOC emissions also decreased due to the substitution of water-based
emulsified asphalts (used for road paving) for asphalts liquefied with petroleum distillates
(cutback asphalts). This is reflected in the decreased emissions reported for miscellaneous
organic solvent use.
Through 1978 these decreases were offset by increases in industrial process emissions.
Since then, industrial process emissions have also declined, so that overall total reactive VOC
emissions were reduced about 5 percent from 1970 to 1988. Industrial process emissions
increased due to higher production levels, particularly in industrial sectors such as petroleum
refining, organic chemical production, and industrial uses of organic solvents. However, control
procedures employed were effective in limiting the growth in emissions. In addition, source
production levels in 1981 through 1983 were relatively low due to poor economic conditions.
However, industrial process emissions increased slightly (3 percent) from 1987 to 1988 due to
increased industrial activity. Through the mid-1970's, emissions from petroleum product
storage and marketing operations also increased as the result of increased demand for petroleum
products, particularly motor gasoline. Since 1978, emissions from this source sector are esti-
mated to have decreased as the result of more effective control measures.
*The volatile organic compounds discussed in this document are those defined as having
reactive properties. Non-reactive VOCs are not included in this discussion.
In 1970, reactive VOC emissions from residential fuel combustion were insignificant.
However, in the late 1970's emissions began to increase due to the popularity of wood stoves
and fireplaces for residential space heating. In 1988, residential fuel combustion accounted for
about 4 percent of total reactive VOC emissions.
Comments on Reactive VOC Emission Estimates
Volatile organic compounds along with nitrogen oxides are participants in atmospheric
chemical and physical processes that result in the formation of ozone and other photochemical
oxidants. Emissions of reactive VOC that are most likely to have a role in such atmospheric
processes are included in the reported emissions estimates. Photochemically non-reactive
compounds such as methane are not included in the estimated emissions of reactive VOC.
Biogenic sources of organic compounds, such as trees and other vegetation, are not included
either. Initial estimates are that emissions of reactive VOC from naturally-occurring sources
exceed the amount of anthropogenic emissions. However, the extent to which biogenic sources
of reactive VOC contribute to oxidant formation, if at all, has not been clearly established.
59
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Ambient concentrations of ozone are typically higher during the summer months. As a result,
analysis of seasonal rather than annual, reactive VOC emissions may be more appropriate to
understand the relationship between reactive VOC emissions and high ozone concentrations in
the atmosphere. Sources such as residential space heating, which occurs primarily during the
winter, would have little impact on summer ozone levels.
4.5 Carbon Monoxide (CO)
1940-1970
From 1940 through 1970, the relative contribution by the various source categories to
total CO emissions changed considerably. In 1940, highway vehicles contributed only about
27 percent of carbon monoxide emissions. Residential fuel combustion (primarily of wood and
coal), forest fires and other burning (agricultural crop residues and coal refuse) contributed about
50 percent of total CO emissions. From 1940 to 1970, highway vehicle emissions nearly tripled,
while emissions from residential fuel combustion and miscellaneous burning sources decreased
substantially. As a result, in 1970 highway vehicles accounted for 64 percent of total CO
emissions. Industrial process CO emissions increased from 1940 to 1970 by about 35 percent.
The largest increase occurred in the petroleum refining sector, primarily as the result of expansion
of catalytic cracking capacity to meet increased demand for gasoline and other middle distillates.
1970-1988
Since 1970, highway motor vehicles have been the largest contributing source of CO
emissions. Figure 17 shows how CO emissions from major highway vehicle categories have
changed from 1970-1988. The implementation of the Federal Motor Vehicle Control Program
(FMVCP) has been successful in reducing CO emissions since the early 1970's. From 1970
through 1978, motor vehicle miles of travel increased 38 percent, but because of controls on
new vehicles, total CO emissions from highway vehicles decreased 15 percent. From 1978 to
1980, VMT declined by 1.7 percent. This lack of growth in vehicle travel, together with an
increased degree of control because of stricter emission standards for new vehicles and the
gradual disappearance of older uncontrolled vehicles from the vehicle fleet, produced an esti-
mated 12 percent drop in highway vehicle emissions in the two year period from 1978 to 1980.
Since 1980, VMT have grown each year. From 1980 to 1988, VMT increased by 33 percent.
However, due to the FMVCP controls, CO emissions from highway vehicles actually decreased
30 percent during this period. Overall from 1970 to 1988, without the implementation of
FMVCP, highway vehicle emissions would have increased 61 percent (Table 29, Figure 13).
By comparison, actual emissions are estimated to have decreased 48 percent.
CO emissions from other sources have also generally decreased. In 1970, emissions from
burning of agricultural crop residues were greater than in more recent years. Solid waste disposal
emissions have also decreased as the result of implementation of regulations limiting or pro-
hibiting burning of solid waste in many areas. Emissions of CO from stationary source fuel
combustion occur mainly from the residential sector. These emissions were reduced somewhat
through the mid-1970's as residential consumers converted to natural gas, oil, or electric heating
equipment. Recent growth in the use of residential wood stoves has reversed this trend, but
increased CO emissions from residential sources continue to be small compared to highway
vehicle emissions. Nevertheless, in 1988 residential wood combustion accounted for about 10
percent of national CO emissions, more than any source category except highway vehicles. CO
emissions from industrial processes have generally been declining since 1970 as the result of
the obsolescence of a few high-polluting processes such as manufacture of carbon black by the
channel process and installation of controls on other processes. However, industrial process
emissions increased slightly (4 percent) from 1987 to 1988 due to increased industrial activity.
60
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4.6 Lead
1970-1988
The emissions of lead have decreased due to the implementation of the Federal Motor
Vehicle Control Program (FMVCP). The implementation of FMVCP has resulted in the use
of catalytic converters to reduce NOX, VOC, and CO emissions and has required the use of
unleaded gasoline for vehicles with converters. From 1970 through 1975, the highway use of
gasoline increased 16 percent, but because of the decrease in lead content in leaded gasoline,
lead emissions from highway vehicles decreased 24 percent. From 1975 to 1988, the percent
of unleaded gasoline sales increased from 13 to 82 percent, and the lead emissions decreased
98 percent (Table 12 and 29, Figure 18). A major reduction in lead emissions occurred between
1984 and 1986 when EPA issued rules which required petroleum refiners to lower the lead
content of leaded gasoline to 0.5 grams per gallon in 1985 and .1 grams per gallon in 1986.
Previously, the lead content of leaded gasoline had been 1.1 grams per gallon or more. From
1970 through 1988, off highway consumption of gasoline decreased 31 percent and associated
lead emissions decreased 98 percent.
Lead emissions also decreased from other sources. The 95 percent decrease in stationary
source fuel combustion is a result of the decrease in lead concentration in waste oil utilized in
industrial boilers. Lead emissions decreased 92 percent for industrial processes from 1970
through 1988. Part of this decrease reflects the changes that result from installation of air
pollution control equipment. As shown in Tables 12 and 29, the change in emissions as a result
of changes in operating rates would be a 34 percent reduction. However, industrial process
emissions increased slightly (5 percent) from 1987 to 1988 due to increased industrial activity.
Lead emissions from solid waste disposal have decreased 63 percent from 1970 through 1988
as a result of the decreased amount of solid waste disposed of by incineration.
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5. REFERENCES
* 1. National Emissions Report, National Emissions Data System (NEDS). NADB, OAQPS, US
Environmental Protection Agency, Research Triangle Park, NC. 1987 NEDS Data Base
July 1989.
2. Compilation of Air Pollutant Emission Factors, Fourth Edition, Volumes I and II. US Envi-
ronmental Protection Agency, Research Triangle Park, NC and Ann Arbor, MI. Publication
No. AP-42.
3. User's Guide to MOBILES (Mobile Source Emissions Model), US Environmental Protection
Agency, Office of Mobile Source Air Pollution Control, Ann Arbor, Michigan. Publication
No. EPA-460/3-89-002. June 1984.
*4. Highway Statistics. Federal Highway Administration, US Department of Transportation,
Washington, DC. 1988.
*5. FA A Air Traffic Activity. Federal Aviation Administration, US Department of Transportation,
Washington, DC. 1988.
*6. Petroleum Supply Annual 1988, Energy Information Administration, US Department of Energy,
Washington, DC. Publication No. DOE/EIA-0340(88)/1. May 1989.
*7. Coal Distribution January-December, Energy Information Administration, US Department of
Energy, Washington, DC. Publication No. DOE/EIA-25(88/4Q). March 1988.
8. Exhaust Emissions from Uncontrolled Vehicles and Related Equipment Using Internal
Combustion Engines. Southwest Research Institute, San Antonio, TX. Prepared for US
Environmental Protection Agency, Research Triangle Park, NC. EPA Contract No. EHS
70-108. Oct 1973.
9. Paniculate Pollutant Systems Study. Midwest Research Institute, Kansas City, MO. Prepared
for US Environmental Protection Agency, Research Triangle Park, NC. National Air Pollution
Control Administration Contract No. CPA 22-69-104. May 1971.
10. Standard Computer Retrievals from the National Emissions Data System (NEDS). Unpub-
lished computer report available from NADB, OAQPS, US Environmental Protection
Agency, Research Triangle Park, NC.
* 11 .Cost and Quality of Fuels for Electric Utility Plants-1988, Energy Information Administration,
US Department of Energy, Washington, D.C. Publication No. DOE/EIA-0191(88). August
1989.
*12.Natural Gas Annual, Energy Information Administration, US Department of Energy,
Washington, DC. Publication No. DOE/EIA-0131 (88)/l. October 1989.
* 13.Minerals Yearbook. Bureau of Mines, US Department of the Interior, Washington, DC. 1987.
* 14.Current Industrial Reports. Bureau of the Census, US Department of Commerce, Washington,
DC.
15.End Uses of Solvents Containing Volatile Organic Compounds, The Research Corporation of
New England, Wethersfield, CT, EPA Publication EPA-450/3-79-032, May 1979.
These publications are issued periodically. The most recent publication available when
this document was prepared is cited.
65
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16.1968 National Survey of Community Solid Waste Practices. Public Health Service, US
Department of Health, Education, and Welfare, Cincinnati, OH. PHS Publication No. 1867.
1968.
*17.Wildfire Statistics. Forest Service, US Department of Agriculture, Washington, DC. 1987.
IS.Emissions Inventory from Forest Wildfires, Forest Managed Burns, and Agricultural Burns.
US Environmental Protection Agency, Research Triangle Park, NC. Publication No.
EPA-450/3-74- 062. November 1974.
19.Coal Refuse Fires, An Environmental Hazard. Bureau of Mines, US Department of the Interior,
Washington, DC. Information Circular 8515. 1971.
*20.Statistical Abstract of the United States. Bureau of the Census, US Department of Commerce,
Washington, DC. 1988 (108th ed.)
*21 .Chemical and Engineering News, Annual Facts and Figures Issue, American Chemical Society,
Washington, DC. June 19, 1989.
22. Volatile Organic Compound (VOC) Species Data Manual Second Edition, US Environmental
Protection Agency, Research Triangle Park, NC. Publication No. EPA-450/4-80-015. July
1980.
23.Standard Industrial Classification Manual 1987, Executive Office of the President, Office of
Management and Budget, Washington, DC.
*24.Sulfur Content in Coal Shipments 1978, Energy Information Administration, U.S. Department
of Energy, Washington, DC. Publication No. DOE/EIA-0263(78). June 1981.
*25. Standard Computer Retrievals from the Flue Gas Desulfurization Information System (FGDIS).
Unpublished Computer Report Available from the Air & Energy Engineering Research
Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC.
*26.Quarterly Coal Report, Energy Information Administration, U.S. Department of Energy,
Washington, DC. Publication No. DOE/EIA-0121(88/2Q). November 1988.
27 .Estimates of U.S. Wood Energy Consumption from 1949 to 1981. U.S. Department of Energy,
Washington, DC. Publication No. DOE/EIA-0341. August 1982.
28.Organic Solvent Use in Web Coating Operations, Emission Standards and Engineering
Division, US Environmental Protection Agency, Research Triangle Park, NC. Publication
No. EPA-450/3-81-012. September 1981.
29.AEROS Manual Series Volume IV: NADB Internal Operations Manual. OAQPS Guidelines
No. 1.2-041. U.S. Environmental Protection Agency, Research Triangle Park, NC. January
1978.
30.Historic Emissions of Sulfur and Nitrogen Oxides in the United States from 1900 to 1980. U.S.
Environmental Protection Agency, Research Triangle Park, NC. April 1985. Publication
No. EPA-600/7-85-009.
31.Electric Power Annual, Energy Information Administration, U.S. Department of Energy,
Washington, DC. Publication No. DOE/EIA-0348(87). September 1988.
32.Telephone communication between Jacob Summers, OAQPS, and Michael Petruska, Office
of Solid Waste, US EPA, Washington, DC, November 9,1984.
These publications are issued periodically. The most recent publication available when this
document was prepared is cited.
66
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*33.Synthetic Organic Chemicals, United States Production Sales, 1988, United States International
Trade Commission, Washington, DC 20436.
*34.Petroleum Marketing Monthly, Energy Information Administration, U.S. Department of
Energy, Washington, DC., Publication No. DOE/EIA-0380(88/06). September 1988.
35. Estimates of U.S. Wood Energy Consumption 1980-1983. U.S. Department of Energy,
Washington, DC. Publication No. DOE/EIA-0341(83). November 1984.
*These publications are issued periodically. The most recent publication available when this
document was prepared is cited.
67
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
EPA-450/4-90-001
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
March 1990
National Air Pollutant Emission Estimates, 1940-1988
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
National Air Data Branch
Technical Support Division
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Air and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
Final - 1940-1988
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report presents estimates of trends in nationwide air pollutant emissions for
six major pollutants: particulate (PM/TSP), sulfur oxides, nitrogen oxides, reactive
volatile organic compounds, carbon monoxide, and lead. Estimates are provided for
major categories of air pollution sources. A short analysis of emission trends is
given, along with a discussion of methods used to develop the data.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Trends, emissions, inventory, air pollutan
nationwide, particulate (PM/TSP), sulfur
oxides, nitrogen oxides, reactive volatile
organic compounds, carbon monoxide, lead,
miscellaneous sources, controllable
emissions, point sources, pollution
estimates
b.IDENTIFIERS/OPEN ENDED TERMS
C. COSATI Held/Group
S,
18. DISTRIBUTION STATEMENT
Release UNLIMITED
19 SECURITY CLASS (Tins Report/
Unclassified
21 . NO OF PAGES
67
20 SECURITY CLASS (Till-,
Unclassified
22 PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
68
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