Annual anthropogenic pollutant emissions in the United States and Southern Canada east of the Rocky Mountains

Atmospheric Environment, Vol. 14, pp. 961-970. 0 Pergamon Press Ltd. 1980. Printed in Great

‘X04-6981/80,0801-0961

sO2.00,Q

Britain.

ANNUAL ANTHROPOGENIC POLLUTANT EMISSIONS IN THE UNITED STATES AND SOUTHERN CANADA EAST OF THE ROCKY MOUNTAINS TERRY L. CLARK* Environmental Sciences Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, U.S.A. (First received 27 April 1979 and

infinalform

5

November 1979)

Annual anthropogenic pollutant emissions of sulfur dioxide, nitrogen oxides, and hydrocarbons from point and area sources were apportioned to 80-km grid squares on a 35 x 30 grid network. The grid network was superimposed on a polar stereographic projection map true at 60”N. The domain of the network included southern Canada and the United States east of the Rocky Mountains, excluding southern Texas and northern New England. The emissions data were obtained from the 1977 United States Environmental Protection Agency’s National Emissions Data System (NEDS) file as well as from data compiled by the Ontario Ministry of the Environment and Environment Canada. These emission inventories, the design of the gridding procedures, and the major source classifications responsible for much of the emissions are discussed. Abstract -

1. INTRODUCTION

2.

POLLUTANT EMISSION INVENTORIES

2.1 United States National

Long-range or regional-scale air quality simulation models aid in studying the effects of transport, transformation, and surface deposition of pollutants on local air quality and lake acidity. In addition, these models can identify pollutant source regions contri-

Emissions

Data System

(NEDS)

buting to the deterioration of local air quality. Such models require pollutant emissions to be apportioned on a grid network. To provide emissions data for air quality studies, the United States Environmental Protection Agency (EPA) maintains a comprehensive inventory of annual estimated anthropogenic emissions (hereafter referred to as annual emissions) of five pollutants-particulates, sulfur dioxide, nitrogen oxides, hydrocarbons, and carbon monoxide. In addition, the Ontario Ministry of the Environment and the Canadian counterpart of EPA, Environment Canada, maintain similar emission inventories. The inventory designers realised that surveying every point and area source in the United States and Canada would be both a costly and time-consuming task. Therefore many assumptions and approximations were made to minimise the cost and time. Thus, in most cases, annual emissions were estimated using fuel consumption emission rates and EPA emission factors. Since many factors were involved in determining the rates, assessing the accuracy of the annual emission estimates would be very difficult, if not impossible. Consequently, the annual emission rates should be treated only as estimates of reality.

*On assignment from National Oceanic and Atmospheric Administration, U.S. Department of Commerce. 961

In 1970 the United States Congress passed an amendment to the Clean Air Act which required the individual state governments to compile, maintain, update, and submit to the federal government an annual pollutant emission inventory of point sources within their jurisdictions. Point sources were defined as stationary sources with the potential of emitting at least 100 tons (90.7 metric tonnes) per day of any of five primary criteria pollutants. The five criteria pollutants were particulates, sulfur dioxide, nitrogen oxides, hydrocarbons, and carbon monoxide. Potential emissions were defined as those emitted from a source after the air pollution control equipment was removed or deactivated. Since 1971 the National Air Data Branch (NADB) of the EPA Office of Air Quality Planning and Standards (OAQPS), via the ten EPA regional offices, has maintained and analysed point source emissions data compiled by state air pollution agencies. As of December 1977, NEDS contained approximately 200,000 point source records. Data in these records included, but were not limited to, the following : (a) Location of source (state, county, Air Quality Control Region, Universal Transverse Mercator (UTM) coordinates); (b) Stack parameters (stack height, stack diameter, flow rate, temperature of the exhaust); (c) Normal operating schedule (seasonal, days per week, hours per day); (d) Classification of source;

962

TERRY L. CLARK

(e) Annual emissions of the five primary pollutants ; and (f) Pollutant control information. Details of the contents of the NEDS point source inventory are furnished in EPA’s Guidefor Compiling a Comprehensive Emissions inventory (1973b). The annual emissions from point sources were determined from a method employing one of the following :

(a) Stack

test results or other emission measurements; tb) Material balance using engineering knowledge and expertise of process ; (cl Emission factors from EPA’s Compilation of Air Pollution Emission Factors (1973a) ; and (d) Guess. Further details concerning emission estimation procedures and reporting requirements can be found in EPA’s AEROS panel Series, Vol. 1 (1976a). State agencies are required to update some of these point source emission rates semi-annually. The update requirement applies to the following point sources: (a) Those achieving final compliance with a state implementation plan, emission limitation regulation, or strategy; (b) New or modified sources receiving approval to begin construction or operation; and (c) Those terminating operations during a reporting period. However, much of the point source emissions data in NEDS for some states has not been updated since 1973. Table 1 indicates the percentage of point source records entered or updated in NEDS for each year for each state east of the Rocky Mountains. In the table parentheses enclose numbers in two adjacent columns indicating the two-year period when the greatest number of records was added to NEDS. In February 1979 the author requested and received from the state government agencies and the regional ofices updated annual emission rates from those point sources emitting, according to NEDS, in excess of 90,000 tons of any of the pollutants. Emissions data from those sources not classified as point sources were contained in the NEDS area source inventory. This inventory included mobile and stationary sources individually emitting less than 100 tons per year, but collectively, emitting a significant amount. Miscellaneous sources such as forest fires and agricultural burning were also included in the area source file. Since the 1970 Clean Air Act Amendments did not require the states to compile and submit an area source inventory, EPA and EPA contractors compiled area source inventories for each state. Due to the large number of area sources, the compilation and storage of data pertaining to individ~ area sources were not practical. Therefore, as an alternative, annual emis-

sions from these sources in each of the approx 3100 counties in the United States were summed and stored in NEDS county-wide records. Each area source record included, but was not limited to, the following: (a) Location (state. county, and Air Quality Control Region only) ; (b) Estimated annual emissions from county sources ; (c) Quantity of fuels burned for residential, commercial, and industrial heating and transportation ; (d) Number of vehicle-miles traveled within the county ; and (e) Population data. No coordinates were included in the area source records. Emissions from area sources were estimated from emission factors and data compiled by county, state, and federal agencies. The compiled data included vehicle-miles traveled, fuel retail sales records, fuel evaporative losses, population statistics, acreage of forests burned, etc. For details, see EPA’s Guide for Compiling

a

Comprehensive

Emissions

Inventory

(1973b). Every year, EPA-NADB updated the NEDS area source emissions inventory either by estimating area source emissions from updated information gathered from various governmental agencies or by accepting emissions estimates voluntarily submitted to EPA by the state agencies. These state-submitted data were reviewed by EPA for accuracy and completeness. Duplication of emissions data reported in the point source inventory was avoided. Upon final acceptance, the data were included in the NEDS area source emissions file. 2.2 Ontario Pollutant inventory System As early as 1969, the Ontario Ministry of the Environment conducted detailed emission surveys in urban areas of the southeastern portion of the province. As a result, comprehensive annual point and area source inventories for particulates, sulfur dioxide, nitrogen oxides, hydrocarbons, and carbon monoxide were compiled for Toronto, Hamilton, and the Niagara Peninsula. Later, only industrial emissions from sources in the Windsor-Ottawa corridor and along the northwestern shore of Lake Superior were added to the inventories. When the emission inventories were delivered to EPA, they did not include sources from other parts of the province (e.g. north of Lakes Huron and Superior). The omitted region included the cities of Sault Ste. Marie, North Bay, and Sudbury, where an enormous smelter was located. To supplement these inventories, estimates of total 1973 emissions of particulates, sulfur dioxide, and nitrogen oxides from sources in the cities of Wawa, Sudbury, Thunder Bay, and Sault Ste. Marie were

Annual anthropogenic pollutant emissions in the U.S. and southern Canada

963

Table 1. The percentage of NEDS point source records created each year during 1969-1977 for the states east of the Rocky Mountains State Alabama Arkansas Colorado Connecticut Delaware Washington, D.C. Florida Georgia Illinois Indiana Iowa Kansas Kentucky Louisiana Maine Maryland Massachusetts Michigan Minnesota Mississippi Missouri Montana Nebraska New Hamnshire New Jersey New Mexico New York North Carolina North Dakota Ohio Oklahoma Pennsylvania Rhode Island South Carolina Tennessee Texas Vermont Virginia West Virginia Wisconsin Wyoming

I 69

70

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4 6 0

11

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0 0

18

6) 3 22 0 1) 3 10 2 3

15

16

77

(6:

24 13) 24) 0 1 175 ‘15 (57

13 ;

8) 0 0 0 4 0

0 0 0 0

9 1 0

(37 0 0

26) (79 0

19 1)

6

2

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0’

0 23 3 4 0 0

0 17 4 0 0 0

0 (22 I4

(82 21) 14

17) 13 (20

2 (92

0 4 30) 0 79)

0 1 16 0 0

0 0 0 1 0

0)

1 46)

0

0

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73

1 6 0 (64 0 18) 1 17 2 15 12 14 19 24) 17) (30 2 0 42) 0’ (32 0 (42 0

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3 2 (100) . 1’ 0 (29

72

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0 27 5) 2:)I

0 0

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(2 7 5 7 19 15) 2 1 0 (20 33) 7 1) 0

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48) 1 76) 17j 3 0 0 78) 61) 11 1 6;)

1 2 0 0 8 0 1 0 9 0 3 0

0 2 0 0 0 0 0 0 0 3 0 0 0

22 (3

6

2 0

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Total number of records 3861 1760 744 516 771 101 4376 1890 3552 6488 6237 7238 7192 2787 1982 1974 2523 3384 1944 5482 2438 535 4351 692 5081 1531 32,182 6012 2571 5897 1908 5273 913 2077 8716 10,398 782 2948 1146 1373 465

Parentheses enclose numbers in two adjacent columns for each state indicating the two-year period when the most point source records were created. NEDS percentages are rounded to the nearest unit.

incorporated (McMahon et al., 1976). Since they were not categorised as point or area source emissions, these total emissions were assumed to be point source emissions. The Ontario point source inventory contained 800 records pertaining to individual stationary sources

emitting at least 100 pounds (45.4 kg) per day of any of the five pollutants previously mentioned. The inventory contained basically the same type of information as the point source inventory of the United States National Emissions Data System. However, the Ontario point source inventory included more detailed information concerning plant operations (i.e. weekly and diurnal variations of normal plant operations). Essential plant operations data were first gathered by inspectors and engineers from the Ontario regional

offices through personal contacts with plant managers. The basic data collected in the surveys were then reviewed for accuracy and validity. Upon acceptance of the data, reahstic emission estimates were derived by applying engineering knowledge and judgment to the type of technology, fuel, and operating and maintenance conditions of the source. Emission factors detailed in EPA’s Compilation of Air Pollutant Emission Factors (1973a) were used when needed. Fieldmeasured emissions and not emission estimates were recorded when available. Emissions data for new point sources or for modifications of existing point sources were supplied to emissions inventory personnel by compieted construction or modification approval applications. Other changes, such as fuel switches and mo~fi~tion of manufacturing processes were updated by periodic

964

TERRY t. CLARK

solr~ce surveys conducted by regional officers. The periodic surveys were conducted every one or two years for each source depending on the amount of emissions released from the source. In contrast to the similarities of the Ontario and United States point source inventories, the contents of the Ontario area source inventory were much different from the contents of the United States area source inventory. The records in the Ontario area source inventory contained emission estimates from all area sources within l-km grid squares, whereas emissions from the United States area sources were summed for each county. Geographical coordinates, accurate to 1.0 km, were included in the 16,000 Ontario area source records; while none were given in the United States area source records. The 0n:ario area source inventory only included emission estimates, normal diurnal emission patterns, source locations, and source descriptions, while the United States area source inventory contained much more information. The Ontario inventory only included area sources in the Windsor to Ottawa corridor, whereas the United States area source inventory was complete for all states. Estimated pollutant emissions from the Ontario area sources were determined by methods similar to those used for the United States inventory. Automobile emissions were estimated by applying emission factors to fuel sales records and traffic flow records compiled by the Ministry of Transportation and Communication. Emissions from small industrial and commercial complexes were estimated from fuel consumption rates obtained by individual telephone contacts and emissions resulting from residential heating were estimated from fuei-sales records. Land-use and population distribution information were used to apportion the emissions to l-km grid squares.

2.3 ~us~utc~ewa~ and ~unitQ6a emission i~ventovies In late 1976, annual emission estimates of the five pollutants from sources in Saskatchewan and Manitoba were obtained from Environment Canada. At that time, Environment Canada was in the process of accumulating, processing, and organising emissions data in the newly-created computerised National Emissions Inventory System (Choquette, 1976). As a result, detailed information, such as stack data and normal plant operation schedules for point sources, were not available. Since estimated emissions were not availabIe for individual point and area sources, emission estimates for point sources in each major urban area, as well as the general coordinates of the urban areas, were furnished. Emissions from area sources in the portions of the two provinces included in the emissions grid domain were estimated by Environment Canada to be 20% of the total area source emissions for each province. When site locations were unavailable, emissions from sources traditionally defined as point

sources were included in the area source emtsslort inventory. 3. EMISSIQN GRIDDING PROCEDURE

Annual emission rates of sulfur dioxide, nitrogen oxides, and hydrocarbons were allocated to a 35 x 30 grid network encompassing southern Ontario, southern Manitoba, southeastern Saskatchewan, and the United States east of 105” West longitude (Fig. 1). Southern Texas and northern New England were omitted from the network. Each grid square was approx 80 km in length. The grid network was superimposed on a poIar stereographic projection map true at 60” North latitude and parallel to 105’ West longitude. This grid map was first used in the prognostic Planetary Boundary Layer Model developed at the United States National Weather Service by Schaffer and Long (1977). For the most part, the procedure to allocate the annual emission rates to the grid network was straightforward. Since the Ontario point source emissions inventory included source coordinates accurate to 0.5 km for each data record, the emission rates were allocated to the grid squares containing the exact location of the point source. The Ontario area source emission rates, reported as the total emissions from area sources in l-km grid squares, were allocated to the grid network based on the location of the center of the l-km inventory grid square. The gridding procedure was identical for most of the annual emissions from the United States point sources. However, a modified procedure was required for approx 207; of all data records. For example, almost all the records for Kansas in the point source emissions inventory had incomplete sets of UTM coordinates. An additional 2.37; of the data records had source location errors exceeding 40 km. The modified procedure involved replacing the inadequate coordinates of each point source with the coordinates of the geographical center of the county containing the point source. The emission rates of the point source were allocated to the grid square containing the geographical center of the county. The dimensions of a typical county in the United States east of 105” West longitude were smaller than the X0-km grid square. Similarly, United States area source emission rates were allocated to the grid network based on the coordinates of the geographical center of the county. The annual area source emission rates from any county were allocated to only one grid square. Unfortunately, if an urban area, where most of the county emissions were actually emitted, was located in one grid square and the geographical center of the county was located in an adjacent grid square, all the area source emissions for the county would be systematically allocated to the latter grid square. This inaccuracy occurred for several U.S. cities, including

Annual anthropogenic ~llutant

965

emissions in the U.S. and southern Canada l1.44”N i7.21”W 10 18

105.38”W

‘3.33 N 80.15 W

x

Fig. 1. The 35 x 30, SO-kmemission grid networK superimposed on a polar stereographtc map or sournern

Canada and the United States east of 105”West longitude. Chicago, Detroit, and New Orleans. In the three specified cases, however, the area source emissions were transferred to the grid square containing the city. The procedure for gridding annual emissions from point sources in Saskatchewan and Manitoba involved allocating the emissions to grid squares containing the urban centers in which the sources were located. Emissions from area sources in the two provinces, on the other hand, were apportioned to grid squares based on the assumption that emissions from area sources were proportional to population density. The population in each grid square in Saskatchewan and Manitoba was estimated using an international atlas. The emissions apportioned to each grid square depended upon the percentage of population in the grid square. 4. DIS~U~ION

OF THE ELISION

GRID MAPS

Each of the six figures appearing in this section depicts annual emissions of one of three criteria pollutants from either point or area sources. The numbers printed in the grid squares signify the annual emissions in rounded units of 10,000 tons per year. For example, the sources within a grid square where the number “20” appears emit 195,OOO-204,999 tons of the pollutant annually. The sources within the grid squares where no number appears emit less than So00 tons annually.

In the ensuing discussion, the areas of southern Canada and the United States emitting the largest quantities of the three pollutants are identified. In addition, the classification of point sources (e.g. electric generating plant, steel mill, petroleum refinery) and area sources (e.g. residential heaters, vehicles) emitting much of the pollutants both in the United States as a whole and in the high-emission grid squares are discussed. The point source classification codes were obtained from the point source emission inventories, and deciphered using appendix A of EPA’s Guide for Compiling

a

Comprehensive

Emission

Inventory

(1973b). Information concerning dominant area source classifications was obtained from the EPA’s 1973 National Emissions Report (1976a). Whenever reference is made to a high emission grid square, the grid map coordinates (x, y) were furnished. 4.1 Sulfir dioxide emission The annual point source emission rates of SO2 are depicted in Fig. 2. In the United States, nearly 57 % of the total point source emissions of SO2 was emitted by bituminous coal-fired electric generating plants. The primary metals industry emitted nearly 12% of the emissions. Almost 7 y0 of the emissions resulted from the burning of bituminous coal for industrial fuel, while another 4 % resulted from petroleum industrial sources. Over 90 % of the SO, emissions in the United States was emitted from point sources.

966

TtRRl

L.

Cl.ARk

26

I8

Fig. 2. Gridded annual point source emissions (10,000 tony- ‘) of sulfur dioxide for the U.S. and Canada.

Fig. 3. Gridded annual area source emissions (10,000 ton y-l) of sulfur dioxide for the U.S. and Canada

Annual anthropogenic pollutant emissions in the U.S. and southern Canada The largest single point source of SO, appearing in the grid domain was the ore smelter in Sudbury, Ontario, Canada (21, 30), which emitted over one million tons (McMahon et al., 1976). The large quantities of SO2 emitted in the greater Pittsburgh area (25, 23 ; 26, 23) and in the area south-west of Pittsburgh along the Ohio River (24, 20; 24, 21; 25, 22) were attributed largely to bituminous coalfired electric generating plants. Similarly, the burning of bituminous coal at electric generating plants was responsible for much of the SO2 emissions along the Mississippi River between St Louis (16, 17) and Cairo, Illinois (18, 15) ; along the Tennessee River southwest, west, and northwest of Nashville (21, 15); in the area north of Detroit (22, 25); near Gary, Indiana (18, 22); in the Louisville (21, 18) to Cincinnati (22, 19) corridor; the area to the southwest of Chicago (16, 20); and in the area to the southwest of Philadelphia (29, 24). The SO2 emissions in the New York City area (30, 26) and the Philadelphia area (30, 24) resulted from the burning of both bituminous coal and residual oil at electric generating plants. Figure 3 illustrates the annual area source emission rates of SOz. As can be readily observed, the SOz emission rates from area sources were much lower than the emission rates from point sources. About 80 % of the area source emissions was attributed to external combustion sources and 20% was attributed to land vehicle exhaust. Five classes of area sources contributed equally to the annual national area source emission rate. The classes were residential combustion (distillate oil, bituminous coal, anthracite coal, and residual oil), industrial combustion (bituminous coal), industrial combustion (residual oil), commercialinstitutional combustion (residual oil), and land vehicular combustion (diesel fuel and gasoline). In the New York City area (30,26; 31,26), 43 % of the SO2 area source emissions was attributed to the oil for of residual and distillate burning commercial-institutional fuel; 25 y0 of the burning of distillate and residual oils for residential fuel ; 18 % to the burning of residual and distillate oils for industrial fuel ; 7 % to the burning of gasoline and diesel fuel by land vehicles ; and 5 % to the burning of residual oil for vessel fuel. In the Cleveland area (23,23 ; 24,23), 76 and 13 % of the area source emissions were attributed to the burning of bituminous coal for industrial and for commercial-institutional fuel, respectively. An additional 4 % of the area source emissions resulted from the burning of gasoline and diesel fuel by land vehicles. Similar to Cleveland, the largest contributor to area source emissions of SOz in the Chicago area (18, 22) was industrial bituminous coal burning (36% of the total). Residential bituminous coal and residual oil burning accounted for 30%. Commercialinstitutional burning of residual and distillate oils accounted for 16 ‘A, while diesel fuel and gasoline consumed by land vehicles accounted for 12% of the area source emissions. *E14.8

-G

967

4.2 Nitrogen oxide emissions The annual point source emission rates of NO, are depicted in Fig. 4. In the United States, about 47 % of the NO, emissions was emitted from point sources. Two-thirds of these emissions resulted from the buming of fuels at electric generating plants (44% from bituminous coal, 12 % from natural gas, and 10 % from residual oil). The remaining one-third was attributed to point source classes individually contributing less than 10 y0 of the point source emissions. These classes, listed in order of significance, include industrial external combustion (natural gas); industrial external combustion (bituminous coal); petroleum industrial processes ; industrial external combustion (residual oil) ; mineral production processes, and chemical manufacturing processes. Bituminous coal burning at electric generating plants resulted in much of the point source emissions of NO, in the Pittsburgh area (25, 23; 26, 23); the Detroit area (22, 25); the St Louis area (16, 17); the area to the southwest of Chicago (16, 20); the area to the east of Cairo, Illinois (20, 16); and the area to the west of Philadelphia (29, 24). Residual oil burning at electric generating plants resulted in much of the point source emissions of NO, in the Chicago-Gary area (18, 22) ; the Philadelphia area (30, 24); and the New York City area (30, 26; 31, 26). Approximately half of the NO, point source emissions in southern Louisiana (16-20, 5) and along portions of the Texas coast (12, 2; 15, 4) resulted from the burning of natural gas and residual oil at electric generating plants. The remaining NO, point source emissions were produced by industrial burning of natural gas and petroleum industrial processes. The area source emission rates of NO, are depicted in Fig. 5. Of the 11.5 million tons of NO, emitted from area sources, 9.3 million tons were emitted in land vehicular exhaust (over 80 %). The industrial burning of natural gas, distillate oil, residual oil, and bituminous coal accounted for 7% while the commerical-institutional burning of distillate oil, residual oil, and natural gas accounted for 5% of the NO, area source emissions. Since land vehicles were by far the greatest source of NO, area source emissions and land vehicular usage can be assumed to be proportional to the population density, much of the NO, area source emissions was produced in the largest cities. The largest population centers in the grid domain, listed in decreasing order, were New York City (30, 26; 31, 26); Chicago (18, 22); Detroit-Windsor (22, 24); Philadelphia (30, 24); Baltimore-Washington (29, 23; 29, 22) and Boston (32, 29).

4.3 Hydrocarbon emissions Figure 6 depicts the annual point source emissions of hydrocarbons. Only 30% of the hydrocarbon emissions in the United States was emitted from point sources. Half of the national point source emissions resulted from the evaporation of stored petroleum

968

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2E

24

2i

E

20

16

16 Y 14

1 1 1 1

12

10

8

_

6

Q.

4

2

2

4

6

I?

8

l?

14

16

18

20

22

24

26

28

30

32

34

Fig. 4. Gridded annual point source emissions (10,000 tony - ‘) of nitrogen oxides for the U.S. and Canada.

26

26

24

22

20

18

i6 Y 14

12

10

6

6

4

2 ,

6

6

8’”

10

12

,4

,6

18

20

Fig. 5. Gridded annual area source emissions (10,000 tony-‘)

22

24

26

28

30

32

34

of nitrogen oxides for the U.S. and Canada.

969

Annual anthropogenic pollutant emissions in the U.S. and southern Canada

2

4

6

10

-6

12

14

16

16

20

22

24

26

28

30

32

34

30

26

16

16

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\I

2

4

6

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6

10

12

14

16

16

20

22

24

26

28

30

32

34

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Fig. 6. Gridded annual point source emissions (10,000 tony-‘)

products. Nearly 25 % of the emissions was attributed to chemical man~actu~ng processes, while 12% was attributed to petroteum industrial processes. The highest emission areas were the oil-refining regions of southeastern Texas (13, 2; 13,4; 15, 4) and southeastern Louisiana (19, 5; 18, 6). In southeastern Texas, nearly 40 % of the point source emissions was a result of the evaporation of petroleum products in storage. The remaining emissions resulted equally from chemical manufacturing and petroleum industrial processes. Half of the point source emissions in southeastern Louisiana were attributed to petroleum industrial processes. Almost 40% was attributed to chemical manufact~ing processes, while the remainder was attributed to evaporation of stored petroleum products. The evaporation of petroleum products in storage was responsible for much of the point source emissions in the Philadelphia area (30,24); the New York City area (30, 26); Baltimore (29,23); the Chicago-Gary area (18, 22); and the Detroit area (21, 24). The area source emission rates are shown in Fig. 7. Like NO, area source emissions, area source emissions of hydrocarbons were emitted primarily from land vehicular exhaust. Of the 17.4 million tons estimated to be emitted annually from area sources in the United States, 12.2 million tons, or 70% of the total, was emitted by land vehicles. An estimated 1.6 million tons

of hydrocarbons for the U.S. and Canada.

per year (or 9 %) was attributed to solvent evaporative losses, while another 1.2 million tons per year (or 7 %) was attributed to gas handling evaporative losses. The area source emissions map is very similar to the NO, area source emissions map. The emission rates of hydrocarbons exceed the NO, emission rates in nearly every grid square. The grid square encompassing the city of Detroit (22, 24) was an exception. 9. SUMMARY

Grid maps of annual anthropogenic point and area source emissions of sulfur dioxide, nitrogen oxides, and hydr~arbons were presented. Emissions data from the National Emissions Data System (NEDS) of the United States Environmental Protection Agency (EPA), the Ontario Pollutant Inventory System (OPIS) of the Ontario Ministry of the Environment, and estimates from Environment Canada were utilised in the construction of the emission grid maps. The actual gridded annual emissions could be used in long-range transport and regional-scale air quality simulation studies. However, several drawbacks existed in the emissions data used to construct the annual emission grids. First, the annual point source emissions in NEDS did not pertain to the same year: the annual pomt source emissions were determined from data valid in any one year from 1969 to 1977. Since the

970

~%.RRY

L.

CLARK

Fig. 7. Gridded annual area source emissions (10,000 ton y- ‘) of hydrocarbons for the U.S. and Canada

resolution

of the emission

grid network

was coarse

(80 km), the gridded emission maps would not be expected to change significantly if the annual point source emissions pertained to the same year. Secondly, the annual area source emissions in NEDS were reported on a county-wide basis. With the exception of the counties containing the cities of Chicago, Detroit, and New Orleans, whenever a county overlapped several grid squares, the total county area source emissions were appropriated to the grid square containing the geographical center of the county. Thirdly, approx 20 and 2.3 % of the point source emission records in NEDS contained incomplete source location inFormation and erroneous source location information, respectively. Whenever adequate point source coordinates were unavailable, the annual point source emissions were appropriated to the grid square containing the geographical center of the county in which the source was located. It was possible, therefore, that the emissions were appropriated to the grid square adjacent to the grid square actually containing the source. Finally, in many instances, the annual emissions were estimated from emission factors and fuel usage or fuel sales records. Thus, the gridded annual emissions should be treated simply as estimates of reality, rather than as actual figures. Ack~ow~e~~e~~ts - The author would like to acknowledge the cooperation of Dr George Nagy of the Ontario Ministry

of the Environment and Dr P. J. Choquette of Environment Canada. Without their efforts the inclusion of Canadian pollutant emissions in this report would not have been possible.

REFERENCES Choquette P. J. (1976) Canadian emissions data (unpublished). Environment Canada, Ottawa, Ontario, Canada. EPA. (1973a) Compilation ofAir Pollutunt Emission Factors. APTD-42, U.S. Environmental Protection Agency, Research Triangle Park, NC, U.S.A. EPA. (1973b) Guidefir Compiling a Comprehcnsiue Emissiun ~~~~t~r~. AF’TD-1135, U.S. Environmental Protection Agency, Research Triangle Park, NC, U.S.A. EPA, (1976a) AEROS Manual Series, Vol. 1: AEROS Overview. EPA-450/2-76/~1, U.S. Environmental Protection Agency, Research Triangle Park, NC, U.S.A., 92 pp. EPA, (1976b} 1973 National Emissions Report. EPA-450/276-007, U.S. Environmental Protection Agency, Research Triangle Park, NC, U.S.A., 436 pp. McMahon T. A., Denison P. J. and Fleming R. (1976) A longdistance air pollution transportation model incorporating washout and dry deposition components. Atmospheric Enuironment 10,751-761. Shaffer W. and Long P. (1978) The state of the Techniques Development Laboratory’s boundary layer model. TMNWS-TDL66, National Oceanic and Atmospheric Administration, Silver Spring, MD, U.S.A., 58 pp. Wong T. S. (1975) Ontario poliutant inventory info~at~on (unpublish~). Air Resources Branch, Ontario Ministry of the Environment, Toronto, Ontario, Canada, 42. pp.