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                            3.   METHODS

  The generation  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.
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.
Since NEDS uses  a  more detailed  procedure involving calculation  of
emissions for individual sources  and summation of these individual
emission  totals  to produce national totals,  there  is a much  greater
chance for errors  or omissions to occur in the NEDS  data.  Because  of
the basic similar  ty 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.  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
necessarily  represent a consistent trend in estimated  emissions.

  Because it  is  impossible to test  every pollutant source  indivi-
dually, 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  must  be
understood.   In  general, emission factors are not precise indicators
of emissions  from a single source; rather, they are quantitative
estimates of  the average rate of  pollutant  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 determining 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 determining estimates of emissions  from
various source categories.
                                27
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  A 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.

  For the  years  prior to  1970, published  references containing
industrial  production or fuel  use data  consistent with  the  data
reported  for 1970  to 1980  are  not available  for some  source
categories.   Likewise, rel'able estimates  of  the  extent  of  air
pollution  controls employed in  1940, 1950  and  1960 are very limited.
As a result many more assumptions were required to estimate emissions
for these  years.  The reliability of the emissions estimates for  these
early years is therefore not as good as for  the  years from 1970  to
1980.  Estimates  of  the accuracy of the data for  any year are  not
possible,  since the true values of emissions  and  the source activity
levels  used  to  calculate the emissions  are usually unknown.   In
addition,  it  is impossible  to measure the extent  of probable errors
introduced  through the use of various assumptions inherent in  the
methodology.

  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.   Seven
vehicle categories  are considered;  light  duty gasoline  (mostly
passenger  cars), light duty diesel passenger  cars, light duty trucks
(trucks  less  than 6000 pounds  in  weight), light  duty trucks 6000  to
8500 pounds in weight, 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 2 model,  developed by the EPA Office of Mobile Source  Air
Pollution  Control was  used to calculate emission  factors for each
year.  The  factors are based on national average  conditions and do  not
include  corrections for specific geographical areas to account  for
local model year distributions, altitude, temperature, or hot/cold
vehicle  operation differences.  For each of these variables, only
national averages were considered in the emission factors.  Average
speed is taken into account on a nationwide  basis  according to  the
published  distribution of veh'cle-miles travelled  (VMT) for urban and

                              28
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rural fractions.  These data are published in Reference 4.   For rural
VMT, the average speed is considered to be 45 miles  per hour,  and for
urban VMT, 19.6 miles per hour.

3.1.2 Aircraft

  Aircraft emissions are based on emission factors and aircraft acti-
vity statistics reported by the  Federal  Aviation  Administration.5
Emissions are based on the number  of landing-takeoff (LTD)  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.    Average emission factors
applicable to diesel  fuel consumption were  used to calculate -emis-
sions.  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.°>^  Gasoline  use is based on national boat
and motor registrations, coupled with a  use  factor (gallons/motor/
year) from Reference 8.  Emission factors from AP-42^ 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  combus-
tion in boilers was used.

3.1.5 Nonhighway Use of Motor Fuels

  Gasoline and diesel  fuel are 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 lawnmowers  and snowthrowers,  snowmobiles,  and
motorcycles.  Fuel  use is estimated for each category from estimated
equipment population and an annual  use factor of  gallons per  unit  per
year.°

3.2 Fuel Combustion in Stationary Sources

3.2.1  Coal

  Bituminous coal,  lignite, and  anthracite coal use are reported by
the Department of Energy.7,11  Most coal  is  consumed  by electric
                                29
-------
utilities.   Average  emission factors and the sulfur content of  each
type of coal  were  used to estimate emissions.  Degree of particulate
control was based  on a report by Midwest  Research Institute9 to-
gether 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  re-
ported in Reference  7 and average sulfur  contents of coal shipped  from
each production  district as  reported in Reference 13 or 24.   For
electric utilities,  S0£ emissions are adjusted to account for flue
gas desulfurization  controls, based on data  reported  in reference  11.
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.^  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 also  reported by the Department  of
Energy ^    Average  emission factors from  AP-42^ were used to
calculate  the  emission estimates.

3.2.4 Other Fuels

  Consumption of wood and  bagasse is based  on data reported  in
NEDS.10  Sales of  liquefied petroleum gas  (LPG) are reported in
Reference  25.   Estimated consumption of coke  and  coke-oven  gas  are
based on References  13 and 26, together  with data from NEDS.   Average
emission  factors were  used  to calculate  emissions, which  are
relatively minor  on  a national basis.

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 derived from literature data.   Generally, the Minerals
Yearbook,13 published by the Bureau of Mines,  and Current Indus-
trial Reports,1^  published by the Bureau of the Census, provide
adequate data  for  most industries.  Average emission  factors were
                               30
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applied to production  data to obtain emissions.   Control efficiencies
applicable to various  processes were estimated  on the basis  of pub-
lished 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.
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 infor-
mation on the number of forest fires and the acreage  burned.1?
Estimates of the amount of material burned per  acre are  made  to  esti-
mate the total  amount of material burned.  Similiar 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 study1^ 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.
                               31
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3.5.3 Coal  Refuse

  Estimates of  the number of burning  coal-refuse piles  existing in
the United  States are made in reports  by the Bureau of Mines.^
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, in  their
statistical  abstracts,  information on  the  number  and types of
structures  damaged by fire^O.   Emissions were estimated by  apply-
ing average emission factors for wood  combustion to these totals.

3.5.5 Nonindustrial Organic Solvent Use

  This category  includes ncnindustrial  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 Reference  21, together
with estimates  of the portion of total production for  use  as  solvent
for each chemical.'^  it  is assumed that all solvent  production  is
equal to the amount  necessary  to make  up for solvent  lost  through
evaporation.  Estimated emissions  from organic solvent  use by  indus-
trial processes and selected nonindustrial  solvent use  categories  were
obtained from Reference 15.  Solvent  use not accounted  for by  indus-
trial processes is reported as nonindustrial organic  solvent use,  with
annual estimates adjusted according to solvent, production levels.
                              32
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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, 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  particulate  emission
inventories include both suspended and  settled  particulates generated
by man's  activities.  Likewise sulfur dioxide (SOo)  and nitrogen
dioxide (N02) ambient air  monitors measure only  those two com-
pounds 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.
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-orpducing  reactions, were developed  from current emission
factors.2,3 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 nonmethane 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.

4.1 Particulates

  Particulate emissions  result primarily  from fuel  combustion  in
stationary sources and from industrial  processes.   Substantial
reductions in particulate  emissions  have  occurred because of the
installation of control equipment on these sources.  The extent  of


                             33
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                                        TABLE 23

                      THEORETICAL 1980 NATIONAL EMISSION ESTIMATES
                             BASED ON 1970 LEVEL OF CONTROL

                                    (TERAGRAMS/YEAR)
Source Category
PM
SOX
NOX
As A Percentage of 1970 Actual
Emissions
voc
CO
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 Agricultural (02,07,20)
Wood Products (24,26)
Chemicals (28)
Petroleum Refining (29)
Metals (33)
Mineral Products (32
Miscellaneous
Industrial Processes Total
Sol id Waste
Miscel laneous
Total
1980 Actual Emissions (Table 1)
Theoretical 1980 Emissions
As A Percentage of 1980
Actual Emissions
1970 Actual Emissions (Table 1)
Theoretical 1980 Emissions

1.3
0.3
1.6

4.1
1.0
0.3
5.4

2.8
1.1
0.6
0.3
0.1
1.5
3.7
0.0
10.1
1.2
1.2
19.5
7.8
250%


17.6
111%

0.4
0.5
0.9

27.0
2.6
0.8
30.4

0.3
0.0
0.1
0.8
0.8
3.3
0.7
0.0
6.0
0.1
0.1
37.5
23.7
158%


27.9
134%

7.8
2.5
10.3

7.6
3.3
0.6
11.5

0.0
0.0
0.0
0.3
0.3
0.0
0.2
0.0
0.8
0.4
0.3
23.3
20.7
112%


18.5
126%

14.6
1.4
16.0

0.0
0.1
0.1
0.2

0.0
0.1
0.0
2.0
1.1
0.1
0.1
8.3
11.7
2.0
3.3
33.2
21.8
152%


27.1
122%

104.8
7.3
112.1

0.3
0.6
1.2
2.1

0.0
0.0
0.6
2.5
2.2
2.9
0.0
0.0
8.2
7.1
7.4
136.9
85.4
160%


110.9
123%
                                            34
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the reduction  is  most evident from the data in Table 23 which shows
theoretical  1980  national emission estimates,  assuming that pollutant
control  levels did not  change since 1970.   Overall, particulate
emissions would have increased by about  11  percent  from 1970 to 1980
with no change in  the degree of control  from 1970.  In comparison,  as
shown in Table 1,  particulate  emissions decreased  about  56 percent
from 1970 to 1980.  Thus, 1980 actual  particulate emissions were less
than half of what they might  have been without additional control
efforts since  1970.

  The estimated particulate emissions  for  1940, 1950  and 1960 are  15
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 particulate emissions.   Also, for
the years 1940 and 1950, particulate emissions from coal combustion  by
railroads and  from forest wildfires were significant.

  A large portion  of the particulate emissions from stationary source
fuel combustion,  result from the combustion of coal.   In  1940, coal
was consumed largely in the industrial  and  residential sectors. Resi-
dential  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 have decreased  by 1980 to only
about 10 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 to 570
million  tons  in 1980.  This  increased  consumption  resulted in
increased  emissions from  1940 to 1960.  Since then, particulate
emissions from electric utilities have decreased, despite continued
increases in  coal  consumption.   Installation of  improved control
equipment is responsible for  this  reduction.  New  facilities con-
structed 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 23, it can be seen that  if the 1970 level  of control
had remained in effect in 1980, electric utility emissions  would have
increased about  70  percent,  from  2.4  teragrams to  4.1  teragrams.
Estimated actual  1980  emissions  from  electric utilities were 0.8
teragrams,  a decrease of 67 percent  from 1970.

  Particulate  emissions from industrial  processes increased from 1940
to 1950, declined  slightly to 1970,  and  subsequently have been reduced
substantially  due to installation of improved control  equipment man-
dated by air pollution control  programs.  Since 1970, actual  emissions
from industrial  processes declined by  over 60 percent.   If the 1970
control  level  had remained unchanged  to  1980, emissions  would have
stayed about the  same.  It should be noted that industrial  production
levels for many sectors in 1980 were significantly lower than  in the


                              35
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previous  few years, reflecting  poor  economic  conditions.  This
downturn in  industrial  production also  contributes to a  decreased
level of  emissions relative to  1970.   Table 18  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 1980.

  Caveats that  should  be noted with respect to these particulate
emission  estimates are first that the  estimates  represent total
particulate  emissions,  without any distinction  of particle sizes.
Thus, both large particles and  small particles are included.   Emis-
sions of very large particles are more likely to settle out of  the
atmosphere and not  be measured  as  total  suspended  particulate by  air
quality  monitoring  equipment.  Small and intermediate size  particles
are more likely  to  remain airborne and are more efficiently captured
by total  suspended particulate  air monitoring equipment.   Small
particles  are also  capable of being inhaled into  the  human respiratory
system,  posibly causing adverse health  effects.   The particulate
emission  controls  that have been employed  to  date have  been most
effective in reducing emisssions of  large and intermediate size
particles.   The trend  in the emissions  of  small  particles is  not
clearly  known.   It  is very doubtful whether small  particle  emissions
have been  reduced to the extent that total particulate emissions have
been reduced, however.  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 emissions.  A second caveat  is that  fugitive
particulate  (emissions from unconfined sources such  as storage piles,
material loading, etc.)  emissions  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 particulates,  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 thes.e  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  ernissi-ons are relatively large  particles that  are  not
readily  captured by particu'ate air quality monitors.   Similarly,
these large  particles do  not effectively enter  into  the human
respiratory system.
                              36
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4.2 Sulfur oxides

  Fuel  combustion  by  stationary  sources produces  most sulfur  oxide
emissions.   In addition,  certain industrial  processes,  such  as
smelting of copper, lead, and zinc ores,  sulfuric acid manufacturing,
and other industries  also produce sulfur oxide emissions.  From  1940
through 1970,  major increases in sulfur oxide emissions occurred  as
the result of  increased combustion of fossil fuels such as coal  and
oil. Since 1970, total sulfur oxide emissions have  declined slightly
as the result  of use  of fuels with lower average sulfur contents, some
scrubbing of sulfur oxides from fluegases,  and controls on industrial
process sources.   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.  As  a result 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 meet
more stringent  emission limitations than  old facilities.

  As shown  in  the tables,  since 1970 sulfur oxide emissions  from
electric utilities account  for  more than half of total emissions.
Combustion of  sulfur-bearing  fuels, chiefly coal  and  residual  fuel
oil, is  responsible.  Between  1970 and 1980, utility use of  coal
increased by over  75  percent.  Emissions  from utilities have increased
only slightly,  because fuels with lower sulfur content have been  used
to the extent  that they were  available.  Flue gas  desulfurization
systems have seen  only limited  use to date, but by  the late 1970's
enough  units  were in service to prevent additional  increases  in
electric utlity emissions.   1980 electric  utility emissions would have
been approximately 8  percent higher without the operation of flue  gas
desulfurization controls.    The  theoretical  1980  national emission
estimates given in Table 23 for stationary  fuel combustion sources are
based on 1980  fuel amounts but 1970 average sulfur  contents.  On  this
basis,  electric utility emissions would  have increased 73 percent.   In
fact, emissions increased only 2 percent.  Sulfur oxide emissions from
other fuel combustion sectors decreased, primarily due to less  coal
burning by these industrial, commercial  and residential  consumers.
                              37
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4.3 Nitrogen  oxides

  Nitrogen oxide  emissions result  almost entirely from  transportation
and stationary  fuel combustion sources.  Controls applied  to  sources
of NOx emissions have had a limited  effect in reducing  emissions
through  1980.   Table. 23 shows that  with the  1970 control  level,
national  NOx  emissions would  have been  only 12 percent higher  than
actual 1980 emissions.  The emissions from stationary fuel  combustion
sources largely reflect the actual growth  in fuel consumption.   For
electric  utilities,  NSPS control  requirements have held down the
growth in NOx emissions somewhat.  Nevertheless, NOx  emissions  from
electric  utilities increased 34  percent from 1970 to  1980.  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 39  percent, had there  been no
change in  control  level  since 1970.   The  estimates of  actual  NOx
emissions show  an 18 percent increase.

4.4 Volatile  organic compounds

  From 1940 through 1970,  emissions  of VOC nearly doubled,  primarily
as the result  of growth in  motor  vehicle travel  and industrial
production.  Since 1970, emissions of VOC have decreased slightly.

  Emissions of  VOC decreased primarily due to motor vehicle controls
and less  burning  of solid waste.  Had controls not been implemented, a
substantial increase in emissions from  highway vehicles  would  have
occurred.  From 1970  to 1980, vehicle-miles of travel in the  U.S.
increased by  about 36 percent.^  A comparable increase  in
emissions would  have occurred had 1970 control  levels remained
unchanged. As  a  result of the controls  put  in place, VOC  emissions
from highway  vehicles actually decreased  40  percent.  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.

  These  decreases  were offset by  increases, in industrial  process
emissions so  that overall, total VOC emissions were reduced only about
20 percent from 1970 to 1980.   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.  Control procedures employed were
effective in  limiting the growth in  emissions,, however.  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.  In  1979  and  1980,
emissions from  this source sector  are estimated to have decreased as
the result of declining product demand  and more effective  control
measures.

                              38
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  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  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 VOC.  Biogenic sources
of organic compounds such  as  trees  and  other vegetation  are not
included either.  Initial estimates are that emissions of VOC from
naturally-occurring sources exceed  the  amount  of  anthropogenic
emissions.  The extent to which  biogenic sources of VOC contribute to
oxidant  formation, if  at  all, has  not been clearly established,
however.

4.5 Carbon  Monoxide

  Highway motor vehicles are the largest  contributing source of CO
emissions.  From  1940 through the early 1970's,  major increases in
emissions occurred as the result of increased vehicle travel.  The
implementation of the Federal Motor Vehicle  Control  Program (FMVCP)
has been successful in reducing  CO emissions  since then.  From 1972
through 1978, motor vehicle miles  of travel  increased 22 percent, but
because of  controls on new vehicles, total  CO emissions from highway
vehicles decreased 10 percent.   From 1978  to  1980, vehicle miles of
travel are  estimated to have declined  about one 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 just two years. Overall  from 1970 to 1980,  without the
implementation  of FMVCP,  highway  vehicle  emissions would have
increased 36 percent.  By comparison,  actual  emissions  are  estimated
to have decreased 20 percent.

  CO emissions from  other sources have  also generally decreased.
Prior  to 1970,  emissions  from forest wildfires  and burning of
agricultural crop residues were  substantial,  approximately equal to
highway vehicle emissions in 1940.  Emissions  from  these sources have
declined considerably since then and occur  primarily in  remote or
rural  areas.  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.  In
1940 and 1950, significant CO emissions  did  result from residential
combustion  of coal and wood. These emissions were reduced  substan-
tially in the 1960's and 1970's  as residential consumers converted to
natural gas, oil, or electric heating  equipment.   Recent growth  in the
use of residential wood stoves has produced  a slight  increase in CO
emissions,  but this remains insignificant compared  to highway vehicle
emissions.  CO emissions from industrial  processes  have generally been
declining  since  1950 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.

                             39
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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.
    Publication No.EPA-450/4-80-005.March 1980.
  2.Compilation of Air Pollutant Emission Factors,Third Edition (Inclu-
    ding Supplements 1-10).US Environmental Protection Agency,Research
    Triangle Park,NC.Publication No.AP-42.
  3.Mobile 2 Users's Guide and Supporting Background Documentation (Draft)
    US Environmental Protection Agency, Office of Mobile Source Air
    Pollution Control, Ann Arbor, Michigan.1979
 *4.Highway Statistics.Federal Highway Administration,US Department of
    Transportation, Washington,DC.1979.
 *5.FAA Air Traffic Activity.Federal Aviation Administration,US
    Department of Transportation,Washington,DC.1979.
 *6.Energy Data Reports,Deliveries of Fuel Oil and Kerosene,Energy Infor-
    mation Administration,US Department of Energy,Washington,DC 1979.
 *7.Energy Data Reports,Bituminous Coal and Lignite Distribution,
    Energy Information Administration,US Department of Energy,
    Washington,DC 1979.
  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.Particulate Pollutant Systems Study.Midwest Research Institute,Kansas
    City,MO.Prepared for US Environmental Protection Agency,Research
    Triangle Park,NC.Natural  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.
*11.Energy Data Reports, Cost and Quality of Fuels for Electric Utility
    Plants-1979, Energy Information Administration, US Department of Energy,
    Washington, D.C. Publication No. DOE/EIA-0191(79).June 1980.
*12.Energy Data Reports.Natural  Gas Production and Consumption,Energy
    Information Administration,U.S. Department of Energy,Washington,D.C.
    1979.
*13.Minerals Yearbook.Bureau of Mines, US Department of the Interior,
    Washington,DC.
*14.Current Industrial  Reports.Bureau of the Census,US Department of Com-
    merce, Washington,DC.
 15.Ends Use 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 Wei fare,Cincinnati,
    OH.PHS Publication No.1867.1968.
*These publications are issued periodically.  The most recent publication
available when this document was prepared is cited.
                                        40
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*17.Wildfire Statistics.Forest Service,US Department of Agriculture,
    Washington,DC 1977.
 18.Emissions Inventory from Forest Wildfires,Forest Managed Burns,
    and Agricultural Burns.US Environmental  Protection Agency,
    Research Triangle Park,NC 27711.Pub!ication 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.1977  (98th ed.)
*21.Chemical and Engineering News,Annual  Facts and Figures Issue,American
    Chemical Society,Washington, DC.June 8,1981.
 22.Volatile Organic Compound (VOC) Species  Data  Manual Second Edition,US
    Environmental Protection Agency,Research Triangle Park,NC.Publication
    No.EPA-450/4-80-qi5.July 1980.
 23.Standard Industrial Classification  Manual  1972, Executive Office of
    the President, Office of Management and  Budget, Washington, D.C.
*24.Energy Data Report,Coal Production,Energy Information
    Administration,US Department of Energy,Washington,DC.1979.
*25.Energy Data Reports,Sales of Liquefied Petroleum Gases and Ethane,
    Energy Information Administration,US Department of Energy,Washington,
    DC.1979.
*26.Energy Data Reports,Coke and Coal  Chemicals,Energy Information Admin-
    istration,US Department of Energy,Washington,DC.1979.
*These publications are issued periodically.  The most recent publication
available when this document was prepared is cited.
                                          41
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA-450/4-82-001
4. TITLE AND SUBTITLE
National Air Pollutant Emission Estimates, 1940-1980
7. AUTHOR(S)
Monitoring and Data Analysis Division
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Air, Noise and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
12. SPONSORING AGENCY NAME AND ADDRESS
3. RECIPIENT'S ACCESSIOWNO.
5. REPORT DATE
January 1982
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NC
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
13. TYPE OF REPORT AND PERIOD COVERE[
Final - 1940-1980
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT

  This report presents estimates of trends in nationwide air pollutant
  emissions for the five major pollutants:  sulfur oxides, particulates,
  carbon monoxide, volatile organic compounds, and nitrogen oxides.
  Estimates are broken down according to major types of air pollutant 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
a. DESCRIPTORS
trends, emissions, inventory, air
pollutants, nationwide, sulfur
oxides, carbon monoxide, particulates,
volatile organic compounds, nitrogen
oxides, controllable emissions,
miscellaneous sources
13. DISTRIBUTION STATEMENT
Release unlimited
b. IDENTIFIERS/OPEN ENDED TERMS

19. SECURITY CLASS (This Report;
Unclassified
20. SECURITY CLASS (This page)
Unclassified
c. COS AT I Field/Group

21. NO. OF PAGES
48
22. PRICE
EPA Form 2220-1 (9-73)
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EPA Form 2220-1 (9-73) (Reverse)
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