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4. ANTHROPOGENIC SOURCES OF ATMOSPHERIC SUBSTANCES An enormous number and variety of anthropogenic sources emit substances into the atmosphere. Manufactured products are atomized and vaporized; particulate matter and dust are released from construction, mining, and industrial activities; gases and vapors form at high temperatures during the combustion of fossil fuels, ore smelting, and cement manufacturing. In this report we concentrate on the combustion of fossil fuels because this is the source of a major part of the anthropogenic substances in the atmosphere (see, e.g., Bertine and Goldberg 1971, Keeling and Bacastow 1977, Robinson 1977, Galloway and Whelpdale 1980, Shinn and Lynn 1979~. Fossil fuels represent the largest mass of raw materials subject to high-temperature combustion processes. Certain types of coal and petroleum are enriched with potentially toxic metals {e.g., Hg, Se, As, Cd, and Zn) as well as radioactive elements and organic compounds, many of which are released to the atmosphere during combustion. Significant changes in the qualitative and quantitative patterns of fossil fuel consumption are expected during the next few decades with consequent changes in emissions to the atmosphere. Some emissions from the combustion of fossil fuels enter the atmosphere as gases, such as sulfur dioxide, nitrogen oxides, elemental mercury, and volatile organic compounds (U.S. EPA 1978a, Morris et al. 1979, Lindberg 1980~. Others enter as solid or liquid particles, the so-called primary aerosols (Robinson 1977, Block and Dams 1976~. In addition, so-called secondary aerosols form from the gases--e.g., sulfur dioxide is transformed into ammonium sulfate (Husar et al. 1978, NRC 1978a). Volatile inorganic trace elements can also undergo transformations to particulate form during dispersion and cooling of combustion gases (Kaakinen et al. 1975~. Atmospheric transformations, transport, and deposition of fossil fuel pollutants will be discussed in the next chapter. 35 ,

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36 PATTERNS OF FOS S I L FUEL USE Global patterns of fossil fuel consumption and associated emissions have evolved over the past century in response to demographic, economic, and technological factors. Recent papers by Brown (1976), Hafele and Sassin (1977), and others have documented historical patterns of fossil fuel use. We review selected data on spatial and temporal patterns of fossil fuel use here to illustrate the potential for changing patterns of anthropogenic emissions to the atmosphere. A central task for an assessment of atmosphere-biosphere interactions is the development of emissions inventories and projections. But because quantitative data on fuel consumption are generally available for most countries, while emissions data are often of poor quality or are not available at all, we must focus on consumption. With fuel consumption data, projections of emissions can be made using knowledge or assumptions concerning variables such as combustion technology, emissions-control technology, and patterns of operation (e.g., seasonal variations in electrical energy demand). Total consumption of fossil fuel energy has grown at an average rate of 5 percent per year since 1900. Primary fossil fuel consumption over the past few decades is summarized in Figure 4.1. In the early stages of growth in fossil fuel use, coal was the most widely used fuel, whereas since 1950 oil and gas have become predominant, accounting for approximately 73 percent of present primary energy consumption (Hafele and Sassin 1977). The pattern of increasing global energy demand and fossil fuel use reflects the transition from a totally agricultural society to a partially industrialized one. Industrial development has been accelerated by the transition from a wood-fueled economy to a coal-fueled and then to an oil- and gas-fueled one; each successive energy source has provided increased energy efficiency with consequent positive feedback increasing total consumption. There has also been a tendency to centralize the location of fossil fuel burning usually near large urban areas. Figure 4.2 shows proportional shares of the global energy market that each of these 4 fuel sources has supplied over time. Marchetti (1975) has demonstrated that primary fuel transitions to date have all exhibited similar dynamics. Each new energy source has taken roughly 100 years to grow from 1 percent to 50 percent of the global energy market. These data have important implications for the development of inventories and projections of global pollutant emission. An emissions forecast must include proper time dependence on the introduction of new pollution sources and the phasing out of replaced sources. Most pollutants do not have sufficiently long residence times in the atmosphere to become globally distributed (see Chapter 5). With the exception of CO2, lead, mercury, and perhaps a few other compounds, energy-related emissions are primarily of concern at present because of potential effects on atmospheric and ecological processes within a local, interregional, or continental area. Thus,

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38 an assessment of potential effects of fossil fuel use on environmental quality must consider the geographical distribution of fossil fuel emissions. Regional energy flux density is shown in Figure 4.3. About 90 percent of fossil fuels are consumed in the Northern Hemisphere. Three centers of industrial activity are especially important: eastern North America, Europe, and China-Japan region. As we shall discuss in Chapter 5, this has important implications for pollutants that are transported interregionally in the hemisphere but not globally. A detailed tabulation of annual energy consumption for each nation can be obtained in reports published by the United Nations (1976, 1978). The past increase in total energy consumption and shifts from one fuel to another in the United States have largely paralleled the patterns of global use. Coal represents over 90 percent of U.S. fossil fuel reserves but currently supplies only 20 percent of U.S. energy needs. Its use will probably grow as a result of the recent oil crisis and public opposition to nuclear power. While total coal consumption has remained more or less constant through most of this century (Figure 4.4), there has been a dramatic shift in the economic sectors that consume coal. Before 1940, coal consumption was divided among railroad power, residential and commercial heating, oven coke production, and other industrial processes. The railroad demand was particularly high during the war years of the mid-1940s. Then, within one decade, the l950s, coal consumption by railroads and by the residential-commercial sector all but vanished. Currently, electric utilities are the main coal consumers, and the trend of total coal use in the United States since 1960 has been determined by the demands of the electric utilities. The result has been that, in recent years, a higher proportion of coal emissions has come from large point sources with very tall smoke stacks. This means that the emissions can spread over a larger area before they fall or are washed to the ground. At the same time, increased use of air-conditioning has meant increased demand for electricity during the summer, a season that may favor more rapid chemical transformation in the atmosphere of the power plant emissions because of the higher ambient temperatures. ATMOSPHERIC EMISSIONS FROM FOSSIL FUEL BURNING In the absence of direct measurements of emissions, an assessment of atmospheric emissions of specific substances is dependent on quantitative inventories of the total mass (e.g., of coal used) or surface exposure (e.g., for volatile emissions from natural soils or vegetation) of the various sources and their chemical composition. An emission flux is obtained by multiplying the mass of the source by the appropriate emission rate. Some data on rates of fossil fuel use and raw-material refining for production of industrial materials are available in publications by the United Nations, World Bank, U.S. Department of Energy, and U. S. Bureau of Mines. Omission rates,

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40 800 0 700 ~ ,~ 6CO Z O ~ 500 ~ O O ~ 400 ~ O >_ 300 200 100 /' l '>rorAr RES.& COMM ~HTlKI7lRE~ 1900 10 20 30 40 50 60 70 YEAR 80 90 2000 FIGURE 4.4 Coal consumption in the United States. Initially, coal was used primarily for railroads and for residential and commercial heating. Since 1960, however, the trend in total coal use has been determined by electric utility use. SOURCE: NRC (1978a).

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41 particularly for high priority, health-related pollutants, are compiled by the U.S. Environmental Protection Agency (U.S. EPA 1977~. A comparison of natural and anthropogenic emissions at the global, national, and regional levels is a first key step in a careful assessment of potential ecological consequences. An example of this approach for sulfur sources in eastern North America is summarized in Table 4.1. Oxides~of Sulfur and Nitrogen Sulfur dioxide was emitted from man-made sources in the United States at an estimated rate of 30 x 1012 g per year in 1973 (Figure 4.5~. Fuel combustion exclusive of transportation accounted for 78 percent, industrial processes (metal smelting, chemical industries and manufacturing, etc.) for 20 percent, and transportation for 2 percent. With the exception of fuels used in transportation, about 65 percent of the national anthropogenic sulfur oxide emissions came from coal combustion and about 13 percent from oil combustion. Some 85 percent of the sulfur dioxide emitted in the United States is released east of the Rocky Mountains, with the highest emission density in the vicinity of the Ohio River Valley (Ohio, Pennsylvania, and Indiana). The emission density for the states in the Ohio River Valley region ranges between 10 and 30 g/m2 per year of sulfur dioxide. East of the Rocky Mountains coal contributes 71 percent and oil, 20 percent of the total sulfur dioxide emissions. Hence, coal combustion and, to a lesser degrees oil consumption are a proper index of the emissions of sulfur oxides (SOx) over the eastern United States, and state-by-state trends of coal consumption are useful indicators of regional SOX emission trends. Emissions from electric utilities constitute a growing share of the total SOx emissions (Figure 4.5). In 1973, utilities contributed about 60 percent of the SOX emissions east of the Mississippi. According to EPA estimates, SOX emissions will increase by about 30 percent in Texas by 1985. Even with more stringent standards applied to new power plants SOX emissions are predicted to continue at about their present level while the nitrogen oxide (NOx) emissions are projected to increase (Figure 4.67. The national NOX emissions of about 22 x 1012 g per year arise in roughly equal proportions from automobiles, industry, and electric utilities. The emission density of NOX, as seen in Figure 4.7, is highest in the Boston-Washington corridor, and second highest in the Ohio River Valley states of Indiana, Ohio, and Pennsylvania. The oxides of nitrogen play important roles in a wide range of atmospheric processes which include the formation of aerosols, photochemical reactions in both the troposphere and stratosphere, the formation of acid precipitation, and the degradation of air quality in urban areas (NRC 1977c and 1978d, Crutzen 1979, Kelly et al. 1980~. Figure 4.8 illustrates the major sources, pathways, and removal mechanisms for atmospheric nitrogen species--exclusive of molecular nitrogen--that are of particular significance to atmosphere-biosphere interactions.

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42 TABLE 4.1 Atmospheric Sulfur Budget for Eastern North America (X 10} 2 g/year) Magnitude for Eastern Canada U.S.A. North America Inputs Man-made emissions 2.1 14 16 Natural emissions, sea spray, internal 0.06 0.06 terrestrial biogenic 0.06 0.04 0.1 marine biogenic 0.2 0.4 0.6 Inflowfrom oceans 0.04 0.02 0.06 Inflow from west 0.1 0.4 0.5 Inflow to U.S. from Canada 0.7 Inflow to Canada from U.S. 2.0 Total 4.6 15.6 17.4 Outputs Wet deposition 3.0 Dry deposition 1.2 Outflow to oceans 0.4 Outflow from Canada to U.S. 0.7 Outflow from U.S. to Canada 2.0 2.5 3.3 3.9 5.5 4.5 4.3 Total 5.3 11.7 14.3 SOURCE: Galloway and Whelpdale. Reprinted with permission from Atmospheric Environment, vol. 14, J.N. Galloway and D.M. Whelpdale, "An Atmospheric Sulfur Budget for Eastern North America". Copyright (~)1980 by Pergamon Press, Ltd.

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43 dOI,,,,l,.,.~..,,i,,,,I,l,,l,,i,l,,,ll.,,,l,,.,l,,,,l,,lil,I,, 30 20 lo 10 A Sx TOTAL / . IND. fUEI ~ C OMB k [IECTRIC / Ul~ , . / \; "'' WIFIO Pg~C . " \ - _. __ RESIDENTIAL - ...,I,.,,I,.,,lit,,l,,,,l,lllllllllllillli 80 90 2 1940 50 60 70 YEAR FIGURE 4.5 Sulfur oxide emissions in the United States by source, 194~1975. From 1940 to 1960 the reduction of SOX emissions from industrial fuel con- sumption was balanced by increase of SOX emissions from electric utilities. Since 1960 the sharp increase in SOX emissions was essentially due to electric utilities. SOURCE: NRC (1978a).

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44 Nitrogen Oxides 20 vat o - to . _ KEY STATIONARY SOURCES Other Industrial Combustion Electric Utilities TRANSPORTATION SOURCES EM Trucks ~ Automobiles 1 ///////' / /, / /.' ////// ////// ////~// O _ ~ _ ///// / ///// ////// ////// ///// ////// ////// /////// /////// 1975 1990 Sulfur Oxides 35 30 . _ ._ _ ~ 20 _ o ~15 _ _ _ _ _ ~5 10 s o _., i_ 1 975 KEY Non-Energy Transportation Industrial Combustion Electric Utilities Other Energy Post 7 Coa ~ Utl~ltlrS . ~ 1 985 1 990 Post 75 Co. 1 Ut~llt~es FIGURE 4.6 Net emissions of nitrogen oxides and sulfur oxides for the United States by source for 1975 and projections for 1990. Projections are based on 1979 emissions regulations and national energy use projections. SOURCE: Mitre Corporation (1979).

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47 But many of the details of the sources, transport, sinks, and reaction kinetics of most tropospheric trace nitrogen species are incompletely understood. The major anthropogenic source of NOX (NO and NO2) in the United States is fossil fuel combustion, and a decline in NOX emissions projected for automobiles will more than be offset by increased emissions from stationary sources (Figure 4.6~. By 1985 stationary sources are expected to account for 70 percent of anthropogenic NOX emissions (US EPA 1980~. Trends in total NOX emissions have been strongly upward, with almost a three-fold increase over the past 25 years (Table 4.2~. Significant increases in NOX emissions are forecast for the remainder of the century, primarily due to emissions associated with increased coal use in the electric utility and industrial sectors of the U.S. economy. Nitrogen oxides produced by fossil fuel combustion can create local pollutant levels that are 10 to 100 times greater than natural. However, the regional and global significance of anthropogenic NOX emissions remains a major problem area for research. Recent estimates of global NOX production by lightning range from 1.8 x 1012 g to 18 x 1012 g of nitrogen per year (Chameides et al. 1977, Levine et al. 1981~. If the lower value is correct, NOX emissions from anthropogenic sources, estimated to be at least 20 x 1012 g of nitrogen per year, may be a major source of NOX to the global troposphere (Levine et al. 1981~. Biomass burning is also postulated to be an important source of NOX, with a calculated potential source strength of 20 to 100 x 1012 g of nitrogen per year (Crutzen et al. 1979~. Clearly, reducing the uncertainty in estimates of natural sources of NOX is fundamental to an assessment of the significance of anthropogenic NOX emissions on regional and global air quality. NOx emissions are hypothesized to affect the biosphere through human health effects (NRC 1977c) and through conversion to nitric acid, which may contribute substantially to the acid rain problem (NRC 1978d). These, and other problems related to the nitrogen cycle, can only be resolved by increased research on the biogeochemical cycling of nitrogen oxides. Trace Metals Data on emissions of trace metals are very limited, and there is an urgent need for quantitative data on specific rates of emission for both industrial processes and natural volatilization from soils and vegetation. Goldberg (1976) and Harriss and Hohenemser (1978) have discussed emission factors for mercury, for example, but critical difficulties are encountered in obtaining data on the mercury content of certain fossil fuels and raw materials used for metals production and, more importantly, in rates of volatilization from natural surfaces. A summary of various attempts at quantification of anthropogenic mercury emissions is illustrated in Table 4.3. The range in these estimates demonstrates that uncertainties over anthropogenic mercury emissions are at least one order of magnitude.

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48 TABLE 4.2 Total U.S. NOX Emissions for the Years 1950 and 1975 (X 10~2 g/year) 1950 1975 Utility combustion Other combustion Non-ferrous smelters Other industrial processes Transportation Total 1.1 6.1 3.7 neg. 0.3 3.0 8.1 5.5 neg. 0.7 9.9 22.2 NOTE: Values are prorated on the basis of five categories of emission sources. For 1975 the U.S. point sources are at their 1977-1978 emission rate, whereas area sources are at their 1973-1977 emission rate. SOURCE: U.S.-Canada Research Consultation Group on LRTAP (1979).

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49 TABLE 4.3 Range in Emanates of Anthropogenic Mercury Emissions to the Global Atmosphere (X 10 g/year) Emission Source Mercury Flux Estimatesa Coal combustion Oil and gas combustion Metals refining Chlor-aLkali production Cement manufacturing Total emissions 11.5-137.4 0.017-63.8 0.6-22.9 7.3-20.0 2.6-30.0 1.0-1.3 aThe range in global mercury emission fluxes were obtained from a review of Bertine and Goldberg (1971), Garrets et al. (1975), Joensau (1971), Harriss and Hohenemser (1978), NRC (1978c), and Lantzy and Mackenzie (1979).

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50 Uncertainties regarding natural sources of mercury are much worse, thus we cannot begin to make reasonable comparisons of anthropogenic and natural mercury sources at present. And the data base on atmospheric emissions for other trace metals and even for most compounds is poorer than that for mercury, indicating the serious problems with uncertainty in making emissions inventories with such limited data. Estimates of the fluxes of metals to the atmosphere from fossil fuel burning have been made by Bertine and Goldberg (1971), using figures for the consumption of fossil fuels from 1967: 1.75 x 1015 g of coal; 1.04 x 1015 g of lignite; 1.63 x 1015 g of oil, and 0.66 x 1015 g of natural gas. The literature was surveyed for reasonable values of the elemental contents of these fuels, and the authors assumed that the fly ash released to the atmosphere from the burning of coals and oils is about 10 percent of the total ash and that 50 percent of the coal is used in the manufacture of coke. The results are given in Table 4.4. For such elements as barium and mercury, mobilization from fossil fuels to the atmosphere appears to be within an order of magnitude of the river fluxes of these metals to the oceans--which is to say that society has become an important geological agent. For certain elements these estimates may be low, because volatilization may be selective. Emission spectrographers have noted that there is a preferential volatility of some elements such as arsenic, mercury, cadmium, tin, antimony, lead, zinc, thallium, silver, and bismuth under the high temperature conditions they employ in the direct current electric arc. The fluxes of these metals given in Table 4.4 may be underestimated because they do not take this preferential volatility into account. There are few data on emissions to the atmosphere from human activities other than fossil fuel use. Nriagu (1979) has estimated the emissions of 5 metals--cadmium, copper, lead, nickel, and zinc--from a variety of anthropogenic activities and sources. These estimates are given in Table 4.5 along with the natural worldwide flux for these 5 trace metals. The data presented for trace metal fluxes from coal and oil combustion differ somewhat from those of Bertine and Goldberg given in Table 4.4, but in any case, anthropogenic emissions to the atmosphere exceed natural emissions for these 5 metals. Similar fluxes of some trace metals to the atmosphere appear to result from cement production, which equaled 5.7 x 1014 grams/year in 1972 (Goldberg 1976). About 95 percent of this output is Portland cement, whose chemical formulation can be considered as one-third shale and two-thirds limestone. Cement is produced by roasting such a mixture at temperatures between 1,450 and 1,600C, for 2 to 4 hours. Metals whose oxides have boiling points below 2,000C can be expected to be volatilized. Hypothesized mobilization of some trace metals to the atmosphere as a result of cement production is given in Table 4.6. Vaporization by this process appears greater than that by fossil fuel burning for such elements as arsenic, boron, lead, selenium, and zinc. This may be true for other metals for which data on boiling points are not at

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51 TABLE 4.4 Amounts of Elements Mobilized into the Atmosphere as a Result of Weathering Processes and the Combustion of Fossil Fuels Weathering Mobilization Fossil Fuel Concentration (ppm) Fossil Fuel Mobilization (X 109 g/year) (x 109 g/year) . Element Coal Oil Coal Oil Total River Flow Sediments Li 65 9 110 12 Be 3 0.0004 0.41 0.00006 0 41 5.6 B 75 0.002 10.5 0.0003 10.5 360 Na 2,000 2 280 0.33~ 280 230,000 57,000 Mg 2,000 0.1 280 0.02 280 148,000 42,000 Al 10,000 0.5 1,400 0.08 1,400 14,000 140,000 p 500 70 720 S 20,000 3,400 2,800 550 3,400 140,000 Cl 1,000 140 280,000 K 1,000 140 83,000 48,000 Ca 10,000 5 1,400 0.82 1,400 540,000 70,000 Sc 5 0.001 0.7 0.0002 0.7 0.14 10 Ti 500 0.1 70 0.02 70 108 9,000 V 25 50 3.5 8.2 12 32 280 Cr 10 0.3 1.4 0.05 1.5 36 200 Mn 50 0.1 7 0.02 7 250 2,000 Fe 10,000 2.5 1,400 0.41 1,400 24,000 100,000 Co 5 0.2 0.7 0.03 0.7 7.2 8 Ni 15 10 2.1 1.6 3.7 11 160 Cu 15 0.14 2.1 0.023 2.1 250 80 Zn 50 0.25 7 0.04 7 720 80 Ga 7 0.01 1 0.002 1 3 30 Ge 5 0.001 0.7 0.0002 0.7 12 As 5 0.01 0.7 0.002 0.7 72 Se 3 0.17 0.42 0.03 0.45 7.2 Rb 100 14 36 60(, Sr 500 0.1 70 0.02 70 1,800 600 Y 10 0.001 1.4 0.0002 1.4 25 60 Mo 5 10 0.7 1.6 2.3 36 28 Ag 0.5 0.0001 0.07 0.00002 0.07 11 0.03 Cd 0.01 0.002 0.5 Sn 2 0.01 0.28 0.002 0.28 11 Ba 500 0.1 70 0.02 70 360 500 La 10 0.005 1.4 0.0008 1.4 7.2 40 Ce 11.5 0.01 1.6 0.002 1.6 2.2 90 Pr 2.2 0.31 1.1 11 Nd 4.7 0.65 7.2 50 Sm 1.6 0.22 1.1 13 Eu 0.7 0.1 0.25 2.1 Gd 1.6 0.22 1.4 13 Tb 0.3 0.042 0.29 Ho 0.3 0.042 0.36 2.3 Er 0.6 0.001 0.085 0.0002 0.085 1.8 5.0 Tm 0.1 0.014 0.32 0.4 Yb 0.5 0.07 1.8 5.3 Lu 0.07 0.01 0.29 1.5 Re 0.05 0.007 0.001 Hg 0.012 10 0.0017 1.6 1.6 2.5 1.0 Pb 25 0.3 3.5 0.05 3.6 110 21 Bi 5.5 0.75 0.6 U 1.0 0.001 0.14 0.001 0.14 11 8 SOURCE: Bertine and Goldberg (1971). Bertine and Goldberg used values from a variety of sources discussed in their paper. Reprinted with permission from Science 172:233-235. Copyright C)1971 by the American Association for the Advancement of Science.

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52 To .s , Ct Cal o Cal A: _, Ha Cal Ct z Ct .o o o 3 - to x Cal o U: 3 Ct Cal Ct Ed s ., z v C) o _ ~ ~ o o X, ~ Go . . . . . ~ ~ o o ~ ~ ~ ~ ~ o Go ~ A) . . . . o ~ ~ ~ to ~ ~ ~ ~ Cal ~ ~ ~ ~ ~ o ~ ~ . . . . . . . . . . . o ~ 0 0 '_ ~ 0 to ~ ~ 0 1 ~ Be' U~ ~ o C~ U~ . . . . . . . . . oo t _ ~ ~ o o ~ ~ ~ ~ oo o oo ~ ~ . . . o ~ o oo c~ aN ~ ~ C~ e~ ~ u~ . . . . . . . . . o 0 ~ ~ ~ 0 ~ ~ 0 1 ~ oo o ~ o o ~ u~ ~ o ~ ~ o ~ ~ ~ oo ~ o o o o ~ ~ ~ ~ oo . . . . . . . . . . . . . . . o 0 ~ 0 - 1 0 0 0 0 0 0 ~ 0 1 t~ O o o ~ o oo ~o o . . . . . . ~o o ~ ~ o u~ ~ o o o o o oo o 1 o 0 d" O '_ ~ ~ oo ~ ~ ~ 1 o - - o c~ ~ . - - ~ ~ , ~ o~ ~ ~ o -~o ~ ~ - , - - ~ C<~ 'e ~ ~o ~ ~ ~ ~ . - ~ ~ ~ ~ c o o o e ~ ~ c E e E ', ~ O e E s s E E e _ c E 0 ~ , ~ ~ ~ Z ~ ~ ~ ~ ~ 0 ~ cd Z ct u, ce u: c~ - o ._ os u, ~ ce u, c, co o cn 0 _ ~ .9 c~ ._ ~ ~0 ~a ce ._ CQ u, c, ct ._ z c, X . . o v,

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53 ._ I. _' ~ o ~ = ~ .= ~ ~ C~ C) C) x ~o ,,, .= U5 Ct _ ~ o o o ._ C) o o C~ C) x o C) . _ o o ._ ~3 ._ _ C~ ~o C) C) ~ ._ 4_ ,~ .= o .~ C) OCR for page 35
54 present available. In some cases where the oxides decomposed upon heating below 2,000C, the volatility of the metal was used. The calculated emissions for Pb, Cd, and Zn from cement production given in Table 4.6 compare satisfactorily with the emissions for these metals given in Table 4.5 for industrial applications. Such a comparison assumes that the fluxes listed for industrial applications result primarily from cement production, and also takes into account the fact that there may be a systematic bias for high fluxes in the cement production model used to calculate the values given in Table 4.6. Organic Compounds Anthropogenic emissions of organic compounds have received substantial attention because of their effect on air quality in urban areas. The emphasis has been on gaseous reactive hydrocarbons, which lead to photochemical smog including high ozone concentrations, and on particulate polycyclic compounds that have mutagenic and carcinogenic properties. This section summarizes current data on anthropogenic organic emissions and briefly discusses the possible effect of new energy technologies on the nature of these emissions. Global anthropogenic emissions of non-methane hydrocarbons are estimated to be approximately 80 x 1012 g per year (Duce 1978~. Duce derived this emission rate from the earlier estimates of Robinson and Robbins (1968) and more recent data from the U.S. Environmental Protection Agency (1976) for the United States. These emissions originate primarily from fossil fuel burning. Although global anthropogenic emissions of gaseous organics are approximately one order of magnitude lower than natural emissions, emissions are mostly confined to the industrialized regions of the Northern Hemisphere and have significant effect on air quality in these regions. Anthropogenic emissions of particulate organic carbon were estimated by Duce (1978) to be approximately 30 x 1012 g per year in 1973-74 period. Duce broke down emissions data by type of industrial source and separated particulates into two size fractions, greater than and less than 1 micron diameter (Table 4.7~. Four major sources--coal, petroleum, noncommercial fuel, and agricultural burning--account for approximately 80 percent of the total anthropogenic emissions of organic carbon particles. The molecular composition of these anthropogenic emissions has been reviewed (e.g. Grosjean 1977, Graedel 1978~. Because of their adverse health effects, the polycyclic aromatic hydrocarbons (PAM) have received considerable attention (NRC 1972), and specific emission factors for anthropogenic sources of benzofa~pyrene and other PAH are now available (U.S. EPA 1978b). Both increased emissions of existing organic pollutants and emissions of new pollutants may result from emerging fossil fuel technologies (coal gasification and liquefaction, shale oil and tar sand exploitation) and from increasing use of diesel and gasoline-alcohol ("gasohol") fuels. Moderate to large increases in

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56 particulate PAH emissions are expected to result from increased use of coal, fuels from coal gasification and liquefaction, and shale-derived fuels; use of diesel-powered vehicles (NRC 1981b); and burning of wood for domestic heating (e.g., Butcher and Sorenson 1979~. Organic pollutants other than PAN that may require attention include phenols from coal process waters (Guerin 1977), aldehydes in diesel-powered vehicle exhaust (NRC 1981b), and unburned alcohol as well as aldehydes in exhaust from gasohol-powered vehicles (Allsup and Eccleston 1980~. In addition, new heteroatomic organic pollutants including sulfur-containing and nitrogen-containing compounds may be emitted to the atmosphere as a result of fuel conversion processes. These organic gases include mercaptans, sulfides, thiophenes, furans, pyrroles, and pyridines (Sickles et al. 1977~. The environmental persistence and fate of these compounds have received little or no attention to date. SUMMARY Fossil fuel burning, primarily of coal and oil, contribute most of the anthropogenic constituents of the atmosphere, and the bulk of the burning is done in the Northern Hemisphere, primarily in North America, Europe, and Japan. The emerging fuel technologies (coal gasification, shale oil, tar sands, etc.) as well as the increased use of diesel and alcohol fuels may alter the magnitude and character of pollutant fluxes to the atmosphere in the future. Gaseous pollutants include sulfur dioxide, nitrogen oxides, organic compounds, and trace metals. After entering the atmosphere they may be oxidized (sulfur dioxide going to sulfate, the nitrogen oxides going to nitrate), associate with aerosols, or be degraded. Almost without exception they return quantitatively to the earth's surface. Trace metals from fossil fuel combustion or cement production may initially enter the atmosphere as gases but, in general t quickly become associated with the aerosols or form aerosols. Both fossil fuel combustion and cement production are introducing some metals to the atmosphere at rates comparable to river fluxes to the oceans, showing that such activities have made society an important geological agent. The particulate organic carbon releases that come from coal, petroleum, noncommercial fuel, and agricultural burning account for 80 percent of the fluxes. Of particular concern are the polycyclic aromatic hydrocarbons, which pose a direct health hazard.