EPA
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 1989
EPA-450/4-88-022
AIR
NATIONAL AIR POLLUTANT
EMISSION ESTIMATES
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EPA-450/4-88-022
NATIONAL AIR POLLUTANT
EMISSION ESTIMATES
1940 - 1987
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 1989
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This report is published by the U.S. Environmental Protection Agency (EPA) to report
information 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-450/4-88-022
11
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ABSTRACT
This report presents estimates of trends in nationwide air pollutant emissions for six
major pollutants: paniculate matter (with TSP as the indicator pollutant), sulfur oxides,
nitrogen oxides, reactive volatile organic compounds, carbon monoxide, and lead.
Estimates are presented for each year from 1940 through 1987. Emission estimates are
discussed according to major classifications of air pollution sources. A short analysis of
trends is given, along with a discussion of methods used to develop the data.
111
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CONTENTS
Section Page
LIST OF FIGURES vi
LIST OF TABLES vii
1. SUMMARY 1
2. NATIONWIDE EMISSION TRENDS, 1940-1987 3
2.1 Paniculate Matter (with TSP as the indicator pollutant) 3
2.2 Sulfur Oxides 4
2.3 Nitrogen Oxides 4
2.4 Reactive Volatile Organic Compounds (VOCs) 5
2.5 Carbon Monoxide 5
2.6 Lead 6
3. METHODS 46
3.1 Transportation 47
.3.1.1 Motor Vehicles 47
3.1.2 Aircraft 48
3.1.3 Railroads 48
3.1.4 Vessels 48
3.1.5 Non-highway Use of Motor Fuels 49
3.2 Fuel Combustion in Stationary Sources 49
3.2.1 Coal 49
3.2.2 Fuel Oil 49
3.2.3 Natural Gas 49
3.2.4 Other Fuels 50
3.3 Industrial Processes 50
3.3.1 Miscellaneous Industrial Processes for Lead 51
3.4 Solid Waste Disposal 51
IV
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CONTENTS (continued)
Page
3.5 Miscellaneous Sources 51
3.5.1 Forest 51
3.5.2 Agricultural 51
3.5.3 Coal Refuse 51
3.5.4 Structural Fires 52
3.5.5 Nonindustrial Organic Solvent Use 52
4. ANALYSIS OF TRENDS 53
4.1 Particulate Matter (with TSP as the indicator pollutant) 54
4.2 Sulfur Oxides 58
4.3 Nitrogen Oxides 60
4.4 Reactive Volatile Organic Compounds 64
4.5 Carbon Monoxide 65
4.6 Lead 66
5. REFERENCES 69
TECHNICAL REPORT DATA AND ABSTRACT 73
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LIST OF FIGURES
Figure Page
1. Trends in Emissions of Paniculate Matter, 1940-1987 7
2. Trends in Emissions of Sulfur Oxides, 1940-1987 8
3. Trends in Emissions of Nitrogen Oxides, 1940-1987 9
4. Trends in Emissions of Reactive VOCs, 1940-1987 10
5. Trends in Emissions of Carbon Monoxide, 1940-1987 11
6. Trends in Emissions of Lead, 1970-1987 12
7. Emissions of Paniculate Matter by Source Category, 1940, 1970
and 1987 40
8. Emissions of Sulfur Oxides by Source Category, 1940, 1970
and 1987 41
9. Emissions of Nitrogen Oxides by Source Category, 1940, 1970
and 1987 42
10. Emissions of Reactive VOCs by Source Category, 1940, 1970
and 1987 43
11. Emissions of Carbon Monoxide by Source Category, 1940, 1970
and 1987 44
12. Emissions of Lead by Source Category, 1970 and 1987 45
13. Theoretical Estimate of 1987 Nationwide Emissions of TSP, SOX,
NOX, VOC and CO with 1970 Level of Control 56
14. Emissions of Sulfur and Nitrogen Oxides from Electric
Utility Coal Combustion 59
15. Emissions of Nitrogen Oxides from Highway Vehicles 61
16. Emissions of Reactive VOCs from Highway Vehicles 62
17. Emissions of Carbon Monoxide from Highway Vehicles 63
18. Theoretical Estimate of 1987 Nationwide Emissions of Lead
with 1970 Level of Control 68
VI
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LIST OF TABLES
Table Page
1. Summary of Estimates of Nationwide Emissions 2
2. Summary of Estimated Emissions of Paniculate Matter, 1940-70 13
3. Summary of Estimated Emissions of Sulfur Oxides, 1940-1970 14
4. Summary of Estimated Emissions of Nitrogen Oxides, 1940-1970 15
5. Summary of Estimated Emissions of Reactive VOCs, 1940-1970 16
6. Summary of Estimated Emissions of Carbon Monoxide, 1940-1970 17
7. Estimates of National Emissions of Paniculate Matter, 1970-1987 18
8. Estimates of National Emissions of Sulfur Oxide, 1970-1987 19
9. Estimates of National Emissions of Nitrogen Oxide, 1970-1987 20
10. Estimates of National Emissions of Reactive VOCs, 1970-1987 21
11. Estimates of National Emissions of Carbon Monoxide, 1970-1987 22
12. Estimates of National Emissions of Lead, 1970-1987 23
13. Emissions of Paniculate Matter from Transportation 24
14. Emissions of Sulfur Oxides from Transportation 25
15. Emissions of Nitrogen Oxides from Transportation 26
16. Emissions of Reactive VOCs from Transportation 27
17. Emissions of Carbon Monoxide from Transportation 28
18. Emissions of Paniculate Matter from Fuel Combustion 29
19. Emissions of Sulfur Oxides from Fuel Combustion 30
20. Emissions of Nitrogen Oxides from Fuel Combustion 31
VII
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LIST OF TABLES (continued)
Table Page
21. Emissions of Reactive VOCs from Fuel Combustion 32
22. Emissions of Carbon Monoxide from Fuel Combustion 33
23. Emissions of Paniculate Matter from Industrial Processes 34
24. Emissions of Sulfur Oxides from Industrial Processes 35
25. Emissions of Nitrogen Oxides from Industrial Processes 36
26. Emissions of Reactive VOCs from Industrial Processes 37
27. Emissions of Carbon Monoxide from Industrial Processes 38
28. Emissions of Lead from Industrial Processes 39
29. Estimates of Theoretical 1987 National Emission with 1970
Level of Control 55
Vlll
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NATIONAL AIR POLLUTANT EMISSION ESTIMATES
1940-1987
1. SUMMARY
The primary objective of this publication is to provide current estimates of
nationwide emissions for six major air pollutants: paniculate matter with TSP as the
indicator pollutant (PM/TSP), sulfur oxides (SO,), nitrogen oxides (NOX), 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 1987 as an indication of recent trends.
These data entirely replace those published earlier for 1940-1970 and 1975-1986 in the
Environmental Protection Agency report National Air Pollutant Emission Estimates,
1940-1986 (EPA-450/4-87-024). 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 procedure. 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, 1940-1987
Table 1 presents a summary of total national emission estimates for 1940-1987.
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 1986 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
processes.
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 categoriesonly 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 10* metric tons and ap-
proximately 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 Particulate Matter (PM/TSP)
Emissions of paniculate matter (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 matter emissions from these sources were estimated 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 matter 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 paniculate matter 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 matter emissions
have not been included in most emission inventories. As additional data become
available, it is expected that estimates of fugitive paniculate matter emissions will be
included in future emission inventories. It should be noted, however, that a major
portion of the fugitive paniculate matter emissions are relatively large particles that are
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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. Paniculate matter emissions from
transportation decreased substantially from 1940 to 1960 as the result of the
obsolescence of coal-burning railroad locomotives. From 1960 to 1987, paniculate
matter 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 1987 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 1986, 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.
2.3 Nitrogen Oxides (NOX)
Emissions of nitrogen oxides are produced largely by stationary source fuel com-
bustion 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 1987, 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 1978 peak. Emissions of nitrogen oxides by industrial
processes increased from 1940 to 1970, but have remained about constant since then.
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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.
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. NOTE: The relevant emission factors for residential wood combustion,
i.e., pounds of reactive VOC emitted per ton of wood burned, were recently changed,
but the changes were received too late to be used in developing the data for this report.
The changes are based on improved test data that indicate (1) the emissions of reactive
VOC from residential wood stoves have probably been generally overstated in the past
and (2) the emissions from newer stoves are substantially less than from older stoves.
Based on prelimary calculations, this report's estimate of the 1987 emissions of reactive
VOC from residential wood-burning appears to be about three times too large, i.e.,
about 700 gigagrams instead of the 2,120 gigagrams shown in Table 21.
2.5 Carbon Monoxide (CO)
Transportation sources are the largest emitters of carbon monoxide. Major in-
creases in emissions occurred from 1940 to 1970 as the result of increased motor
vehicle travel. From 1970 to 1987, 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 to 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.
Carbon monoxide emissions from solid waste disposal increased from 1940 to 1970, but
have subsequently declined as the result of air pollution control efforts. Substantial
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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 in-
dustrial 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 transportation 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 rulemaking 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.
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TABLE 2
1940-1970 SUMMARY OF ESTIMATED
EMISSIONS OF PARTICULATE MATTER (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
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
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
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
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
Misc. Total
3.7
2.5
1.8
1.1
Total of All Sources
23.1
24.9
21.6
18.5
13
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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
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
0.1
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
0.1
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
0.3
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
Misc. Total
0.5
0.5
0.5
0.1
Total of All Sources
17.6
19.8
19.7
28.3
14
-------
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
1.3
0.0
0.6
0.1
0.2
2.2
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
2.1
0.0
0.9
0.1
0.4
3.5
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
3.6
0.0
0.7
0.1
0.5
4.9
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
6.1
0.1
0.6
0.1
0.8
7.7
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
Misc. Total
0.9
0.6
0.4
0.3
Total of All Sources
6.8
9.3
12.8
18.3
15
-------
TABLE 5
1940-1970 SUMMARY OF ESTIMATED
EMISSIONS OF VOLATILE ORGANIC COMPOUNDS
(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
4.0
0.0
0.5
0.0
0.2
4.7
0.0
0.1
0.0
4.6
4.7
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
6.0
0.1
0.5
0.1
0.4
7.1
0.0
0.1
0.0
3.0
3.1
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
8.8
0.2
0.2
0.2
0.5
9.9
0.0
0.1
0.0
1.8
1.9
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
9.8
0.3
0.2
0.3
0.5
11.1
0.0
0.1
0.0
0.9
1.1
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
Misc. Total
4.5
3.6
3.1
3.3
Total of All Sources
18.1
20.2
22.6
26.2
16
-------
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
21.9
0.0
3.7
0.2
3.4
29.2
0.0
0.4
0.1
15.4
15.9
3.8
0.2
1.5
0.0
1.0
0.1
6.6
2.0
1.3
3.3
22.8
3.7
32.9
0.8
2.8
0.2
6.7
43.4
0.1
0.5
0.1
10.7
11.4
5.3
2.4
1.1
0.1
1.4
0.2
10.5
2.5
1.8
4.3
12.8
3.7
46.2
1.6
0.3
0.6
8.0
56.7
0.1
0.6
0.0
6.3
7.0
3.6
2.8
1.3
0.3
1.0
0.3
9.3
2.5
2.6
5.1
6.7
3.3
64.2
0.9
0.3
1.2
6.8
73.2
0.2
0.7
0.1
3.4
4.4
3.1
2.0
1.6
0.6
1.1
0.6
8.9
2.7
3.7
6.4
5.1
2.1
Misc. Total
26.5
16.5
10.0
7.2
Total of All Sources
81.5
86.1
i.l 100.2
17
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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 summation 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 matter 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 matters, 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 matter 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
matter emissions have not been included in most emission inventories. As additional
data become available, it is expected that estimates of fugitive particulate matter
emissions will be included in future emission inventories. It should be noted, however,
that a major portion of the fugitive particulate matter emissions are relatively large
particles that are not readily captured by particulate matter 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
46
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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 recognized, emission factors are extremely useful
in estimating emission levels. A detailed discussion 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 consid-
ered; 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 3.9 model,
47
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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 dis-
tribution 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 1975-87. 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 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.
48
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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 equip-
ment, 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/year 8,
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
paniculate matter 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
nationwide. 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.
49
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3.2.4 Other Fuels
Consumption of wood has been estimated by the Department of Energy.27-35
Consumption 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,1* 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 oper-
ations (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
50
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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 practices16 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.
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.19 Their publication presents a detailed
discussion of the nature, origin, and extent of this source of pollution. Rough estimates
51
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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
architectural 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.15>29 It is assumed that all solvent
production is equal to the amount necessary to make up for solvent lost through
evaporation.
52
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4. ANALYSIS OF TRENDS
National trends in air pollutant emissions are a function of many factors. Of all
contributing factors, air pollution control measures and general economic conditions have
the strongest impact on total emissions. Composite national emission trends do not provide
insight into the distribution or concentration of air pollution sources within individual States
or regions. Therefore, most 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 hourly, daily, monthly and yearly meteorological factors on air
quality data. Also, the estimates for PM, SOX, and NOX emissions include more substances
than are routinely measured by ambient air monitoring equipment. For example,
high-volume air samplers collect only suspended particulates approximately 0.3 to 100
micro-meters in diameter, but paniculate emission inventories include both suspended and
settled particulates generated by man's activities. Likewise, sulfur dioxide (SOj) and
nitrogen dioxide (NO2) ambient air monitors measure only those two compounds while
oxides of sulfur (SO,) and nitrogen (NOJ 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.23 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 nonmethane
VOC's.3
The following sections discuss the most important factors influencing the emission
trends for each pollutant.
53
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4.1 Paniculate Matter (PM/TSP)
1940-1970
The estimated paniculate matter 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 matter emissions.
Also, for the years 1940 and 1950, paniculate matter emissions from coal combustion
by railroads and from forest wildfires were significant.
A large portion of the paniculate matter 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 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
matter emissions from electric utilities have decreased, despite continued increases in
coal consumption. Installation of improved control equipment is responsible for this
reduction.
Paniculate matter 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.
1970-1987
Since 1970, paniculate matter 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 1987 national emission estimates, assuming
that pollutant control levels did not change since 1970. Figure 13 illustrates this
difference. Overall, paniculate matter emissions would have increased by about 20
percent from 1970 to 1987 with no change in the degree of control from 1970. In
reality, as shown in Table 1, particulate matter emissions decreased about 62 percent
from 1970 to 1987. Thus, 1987's actual particulate matter 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 particulate matter emissions from stationary source fuel
combustion result from the combustion of coal. In 1970, a larger portion of coal was
54
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TABLE 29
THEORETICAL ESTIMATES OF 1987 NATIONAL EMISSIONS
BASED ON 1970 LEVEL OF CONTROL
(Teragrams/Year)
Source Category
PM
S02
NOX
VOC
CO
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
1987 Actual Emissions (Table 1)
Theoretical 1987 Emissions As a
Percentage of 1987 Actual Emissions
1.6
0.2
1.8
5.0
1.4
1.1
7.5
3.9
1.2
1.1
0.2
0.7
2.3
1.1
0.0
10.5
1.3
1.0
22.1
7.0
315.1
0.5
0.4
0.9
23.8
2.5
0.7
27.0
0.4
0.0
0.2
0.7
1.2
0.6
2.5
0.0
5.6
0.1
0.0
33.6
20.4
164.9
11.1
1.8
12.9
8.0
2.8
0.6
11.4
0.0
0.0
0.0
0.2
0.2
0.2
0.0
0.0
0.6
0.4
0.2
25.5
19.5
131.1
16.0
1.2
17.2
0.0
0.1
2.2
2.3
0.0
0.2
0.0
2.2
0.9
0.0
0.1
6.6
10.0
2.1
3.3
34.9
19.6
177.7
98.6
7.4
106.0
0.3
0.6
6.3
7.2
0.0
0.0
0.9
2.8
2.3
0.0
2.4
0.0
8.4
7.7
7.1
136.4
61.4
222.1
198.1
5.0
203.1
0.6
9.2
0.0
9.8
0.2
0.0
0.0
0.1
0.0
0.5
13.8
0.1
14.7
2.8
0.0
230.4
8.1
2851.5
1970 Actual Emissions (Table 1)
Theoretical 1987 Emissions As A
Percentage of 1970 Actual Emissions
18.5 28.3 18.3 26.2 100.2 203.8
119.2 118.6 139.7 133.2 136.2 113.1
55
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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 1987 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 717 million tons in 1987.
However, paniculate matter 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 1987, electric utility emissions would have more than doubled,
from 2.3 teragrams to 5.0 teragrams. Estimated actual 1987 emissions from electric
utilities were 0.5 teragrams, a decrease of 78 percent from 1970.
Paniculate matter 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 76
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 1987.
Comments on Paniculate Matter Emission Estimates
Several caveats that should be noted with respect to the paniculate matter emission
estimates presented here. First, the estimates represent total paniculate matter emissions,
without any distinction of particle sizes. Thus, both large particles and small particles
are included. Emissions of very large panicles are more likely to settle out of the
atmosphere and not be measured as total suspended paniculate matter by air quality
monitoring equipment. Small and intermediate size particles are more likely to remain
airborne and are more efficiently captured by total suspended paniculate matter air
monitoring equipment. Small particles are also capable of being inhaled into the human
respiratory system, possibly causing adverse health effects. The paniculate matter
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 paniculate matter 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 processes. Such particles are
not included in the estimated total particulate matter emissions.
A second caveat is that fugitive particulate matter emissions (emissions from
unconfined sources such as storage piles, material loading, etc.) are incompletely
57
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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 paniculate matters, 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 paniculate matter
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 matter emissions have not been included in most emission
inventories. As additional data become available, it is expected that estimates of
fugitive paniculate matter emissions will be included in future emission inventories. It
should be noted, however, that a major portion of the fugitive paniculate matter
emissions are relatively large particles that are not readily captured by paniculate matter
air quality monitors. A mitigating factor which appliess 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.
1970-1987
Since 1970, total sulfur oxide emissions have declined about 28 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 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 1940-1987.
Between 1970 and 1987, utility use of coal more than doubled. Emissions from utilities
have decreased, however, because fuels with low sulfur content have been used to the
58
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59
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extent that they were available. Also, flue gas desulfurization systems have been
installed by the late 1970's helpd to prevent increases in electric utility emissions. 1987
electric utility emissions would have been approximately 50 percent higher without the
operation of flue gas desulfurization controls. The theoretical 1987 national emission
estimates given in Table 29 for stationary fuel combustion sources are based on (1)
1987 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 50 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 (N(X)
1940-1970
Nitrogen oxide emissions result almost entirely from fuel combustion by stationary
sources and motor vehicles. From 1940 through 1970, NOX emissions increased steadily
as the result of increased fuel combustion.
1970-1987
Controls applied to sources of NOX emissions have had a limited effect in reducing
emissions through 1987. Table 29 (Figure 13) shows that with the 1970 control level,
national NOX emissions would have been about 30 percent higher than actual 1987
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, NO, emissions
from electric utilities increased 57 percent from 1970 to 1987. For mobile sources, NO%
emissions were controlled as a result of the Federal Motor Vehicle Control Program
(FMVCP). Nitrogen Oxide emissions from highway vehicles would have increased 82
60
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percent, had there been no change in control level since 1970. The estimates of actual
NOX emissions show a 8 percent increase. Figure 15 shows how NOX emissions from
major highway vehicle categories have changed from 1970 to 1987.
4.4 Reactive Volatile Organic Compounds (VOO*
1940-1970
From 1940 through 1970, reactive VOC emissions increased about 45 percent
Major increases in highway vehicle travel and industrial production were chiefly
responsible. Emissions 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 42 percent of total national reactive VOC
emissions. By 1970, their contribution to total reactive VOC emissions had been
reduced to 6 percent.
1970-1987
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 1987,
vehicle-miles of travel in the U.S. increased by about 72 percent.4 A 63 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 52 percent (Table 29, Figure 13). Figure 16 shows how reactive
VOC emission from major highway vehicle categories have changed from 1970-1987.
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 7 percent from 1970 to 1987.
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. 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 estimated to have decreased as the result of
more effective control measures.
64
*The volatile organic compounds discussed in this document are those defined as having reactive properties. Non-reactive
VQCs are not included in this discussion.
-------
In 1970, reactive VOC emissions from residential fuel combustion were insig-
nificant. However, in the late 1970's emissions began to increase due to the popularity
of wood stoves and fireplaces for residential space heating. In 1987, residential fuel
combustion accounted for about 11 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. 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.
65
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1970-1987
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 1970-1987. 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 16 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 estimated 14 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 1987, VMT increased by 27 percent.
However, due to the FMVCP controls, CO emissions from highway vehicles actually
decreased 28 percent during this period. Overall from 1970 to 1987, without the
implementation of FMVCP, highway vehicle emissions would have increased 54 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 prohibiting 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 1987 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.
4.6 Lead
1970-1987
The emissions of lead have decreased due to the implementation of the Federal
Motor Vehicle Control Program (FMVCP). The implementation of FMVCP has resulted
66
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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 1987, the percent of unleaded gasoline sales increased from 13
to 76 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 1987, off highway consumption of gasoline decreased 34 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 1987. 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 38
percent reduction. Lead emissions from solid waste disposal have decreased 61 percent
from 1970 through 1987 as a result of the decreased amount of solid waste disposed of
by incineration.
67
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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.
1985 NEDS Data Base September 1985.
2. Compilation of Air Pollutant Emission Factors, Fourth Edition, Volumes I
and II. US Environmental Protection Agency, Research Triangle Park, NC
and Ann Arbor, MI. Publication No. AP-42.
3. User's Guide to MOBILE3 (Mobile Source Emissions Model), US Envi-
ronmental Protection Agency, Office of Mobile Source Air Pollution
Control, Ann Arbor, Michigan. Publication No. EPA-460/3-89-002. June
184.
*4. Highway Statistics. Federal Highway Administration, US Department of
Transportation, Washington, DC. 1987.
*5. FAA Air Traffic Activity. Federal Aviation Administration, US Department
of Transportation, Washington, DC. 1987.
*6. Petroleum Supply Annual 1987, Energy Information Administration, US
Department of Energy, Washington, DC. Publication No. DOE/EIA-
0340(87)71. May 1988.
*7. Coal Distribution January-December, Energy Information Administration, US
Department of Energy, Washington, DC. Publication No.
DOE/EIA-25(86/4Q). March 1987.
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). Unpublished computer report available from NADB, OAQPS, US
Environmental Protection Agency, Research Triangle Park, NC.
These publications are issued periodically. The most recent publication
available when this document was prepared is cited.
69
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*11. Cost and Quality of Fuels for Electric Utility Plants-1987, Energy
Information Administration, US Department of Energy, Washington, D.C.
Publication No. DOE/EIA-0191(87). July 1988.
*12. Natural Gas Annual, Energy Information Administration, US Department of
Energy, Washington, DC. Publication No. DOE/EIA-0131(87)/1. October
1988.
*13. Minerals Yearbook. Bureau of Mines, US Department of the Interior,
Washington, DC. 1986.
*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.
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.
18. 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. 1987 (107th ed.)
*21. Chemical and Engineering News, Annual Facts and Figures Issue, American
Chemical Society, Washington, DC. June 20, 1988.
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.
*These publications are issued periodically. The most recent publication available when
this document was prepared is cited.
70
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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.
*33. Synthetic Organic Chemicals, United States Production Sales, 1986, United
States International Trade Commission, Washington, DC 20436.
These publications are issued periodically. The most recent publication
available when this document was prepared is cited.
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*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.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
ERA-450/4-88-022
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
January 1989
National Air Pollutant Emission Estimates, 1940-1987
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
National Air Data Branch of the
Technical Support Division
3 ORGX
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 - 1940-1987
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report presents estimates of trends in nationwide air pollutant emissions for
six major pollutants: sulfur oxides, particulate matter with PM/TSP as the indicator
pollutant, carbon monoxide, reactive volatile organic coumpounds, nitrogen oxides,
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.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATl Field/Group
Trends, emissions, inventory, air pollutant:
nationwide, sulfur oxides, carbon monoxide,
particulate matter, TSP, reactive volatile
organic compounds, nitrogen oxides, lead,
miscellaneous sources, controllable
emissions, point sources, pollution
estimates
18. DISTRIBUTION STATEMENT
Release UNLIMITED
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
72
20. SECURITY CLASS (TMspage)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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