Air Quality and Stationary Source Emission Control (1975) / Chapter Skim
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7 Sulfates and Acidity in Precipitation: Their Relationship to Emissions and Regional Transport of Sulfur Oxides
7 Sulfates and Acidity in Precipitation: Their Relationship to Emissions and Regional Transport of Sulfur Oxides
Pages 276-312
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From page 276... ...
Such inf ormation is needed to complement the somewhat limited data provided by direct measurements of ambient concentrations of suspended sulfates. This chapter of the report summarizes observations of sulfates in precipitation, and uses them to amplify the evidence given in Chapter 6 for regional transport of sulfur oxides and a secular increase in sulfate concentrations.
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From page 278... ...
Two principal processes lead to the occurrence of sulfates, including sulfuric acid, in precipitation: (a) the absorption of sulfur dioxide into cloud droplets, with subsequent oxidation (Miller and de Pena 1972, Dana et al.
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From page 279... ...
, whose map of "excess" 3 sulfur deposition is reproduced here as Figure 7-1. It will be seen that the rates of sulfur deposition were relatively high throughout the northeastern United States ; the highest rates [up to 13 kilograms of sulfur per hectare per year (kg~halyr)
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From page 281... ...
This estimate is a minimal figure for the fraction of sulfur dioxide converted to sulfates, because some airborne sulfates must be carried eastwards over the North Atlantic ocean. During -the 1 7-year period under review, total deposition of sulf ates in eastern North America has roughly dolled (Table 7- 2)
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From page 283... ...
, assuming that 80 of power plant emissions and 50 of other emissions were in the area considered (cf. 13-10 and Figure 6-2)
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From page 284... ...
Very f ew data are a~raila}'le on sulf ates in precipitation prio to the 1955 survey. 6 ACIDITY OF PRECIPITATION IN EASTERN NORTH AMERICA Acid rain and snow have been reported in a number of localities in the eastern and northeastern United States (Likens et al.
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From page 286... ...
ACID FORM I NO . 1 NEUTRALIZED t SEA SALT _ C | t AN I ONS 286 CATI ONS l I it' ~ 1 1 SO4 CL SO4 N O3 H+ NH4+, Ca++ Mg++, K+ Ca++, Mg++, K+ Na+ FIGURE 7-3: Chemical Composition of Rainfall at Hubbard Brook, New Hampshire (from Cogbill and Likens, in press, 1975)
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From page 287... ...
at 13 stations in eastern North Americans: the principal difference from Figure 7-4 is that the former survey showed lower pH values at Nantucket, Massachusetts, and in northern Maine, suggesting greater northeastward extension of the area atf ected by acid precipitation than indicated by COgtill and Likens' maps. An earlier report had indicated significantly acid precipitation in Nova Scotia (Herman and Gorham 19571.
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From page 288... ...
Ace: 288 1965-1966 ~>—V Em. f: J ~ ~v ~ I 5.00 ' (1 4.70 J ^62~ 4-89 ' 5-0 :75 Ml LES ~ city of precipitation in FIGURE 7-4: Act s in 1965-66 (after Cog rn nited State 4 )
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From page 289... ...
5. ~ 4 Likens and Bormann have suggested that the acids if ication of rain began about 1 9 50 ~ as a consequence of the decrease in emissions of alkaline f ly ash from coal-burning plants, in combination with increasing emissions of sulfur oxides and nitrogen oxides {Likens and Bormann 1 974)
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From page 290... ...
The principal acids involved are sulfuric and nitric acids, with small quantities of hydrochloric acid at some stations (see Figure 7-3 ~ . Data from all the surveys indicate that the ratio of sulfuric to nitric acids in precipitation has decreased substantially since 1955, because the concentrations of dissolved nitrates have increased more rapidly than those of sulfates.
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From page 291... ...
In f act, if attention is confined to high level emissions (power plants, smelters, and industrial processes) , the geographical and temporal patterns of emissions of sulfates and nitrates appear to match well the patterns of emission of sulf ur and nitrogen oxides.
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From page 292... ...
All deposition rates are expressed as Id multiples of the chemical equivalent weight, so that rates for different chemical species can be compared directly. 1 ton H+ is equivalent to 49 tons sulfuric acid or to 63 tons nitric acid.
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From page 293... ...
~ This finding is fully consistent with the hypothesis that acid precipitation results from regional transport of sulf ur oxides (and perhaps nitrogen oxides} emitted 300-1500 km upwind (Cogbill and Likens 197 4} . It thus provides indirect support
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From page 294... ...
, rates of conversion of nitrogen oxides to nitric acid are typically 3-4 times faster than those for conversion of sulfur dioxide to sulfates. Accordingly it might be expected that nitric acid would be more concentrated near major sources than sulfuric acid (see Chapter 1 53.
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From page 295... ...
1971, Oden 1968, Brosset 19733. By plotting atmospheric trajectories it teas been possible to relate acid precipitation and sulf ate deposition in northern Europe to sources in the industrialized regions to the south and west (Rodhe 1972, Bolin et al.
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From page 296... ...
(a) the f raction of SOx emissions that takes place in the eastern United States will be unchanged (assumed to be 8 0 percent of power plant emissions and 50 percent of others}; (b} similarly, the f raction of NOx emissions that takes place in the eastern United States will remain constant at about 7 0 percent (Table 14- 8 in the nitrogen oxides report)
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From page 297... ...
These results suggest two major conclusions: ~ {i) Seven if sulfur oxide emissions are not permitted to increase, there i8 likely to be a small increase in the acidity of ~ precipitation, as a consequence of increased nitrogen oxide emissions; {ii} if sulfur oxide emissions from power plants increase to twice the 1980 levels, the acidity of precipitation will increase by a larger factor.
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From page 299... ...
29g 00 dP · us + · lo .
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From page 300... ...
1971, O`rerrein 1972, Malmer 19733. Direct absorption of sulfur dioxide contributes to these effects, because it is oxidized to sulfuric acid in the soil.
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From page 301... ...
The full extent of the acidification of soils and surface waters in eastern North America has not been studied. However, as a broad generalization, much of the area of the United States and Canada most affected by acid precipitation is also characterized by acidic rocks and relatively thin soils.
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From page 302... ...
SU~RY AND cOt~CLUS! OBS butiOn ~ tion.
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From page 303... ...
11. If sulfur oxide emissions are allowed to double between 1970 and 1980, the average acidity of precipitation in the northeastern United states and in southeastern Canada is likely to increase by a factor of 2-3.
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From page 304... ...
Studies around a sulf ur extraction gas plant in Alberta Canada, showed similarly rapid oxidation of sulfur dioxide during rain {32-46 percent deposited as sulfate within 40 km}, but much slower oxidation in snow {Summers and Hitchon 1973, Summers 19741. However, studies around a smelter at Sudbury, Ontario, showed very slow oxidation of sulfur dioxide (less than ~ percent deposited as sulfate within 50-100 km} even when emitted during rain (Muller and Framer 1974, Wiebe and Whelpdale 1974~.
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From page 305... ...
The total rainf all during this 11-day period at selected stations was as follows: Boston ~ . 08n · New York City 2.17"; Philadelphia 2 49a , Chicago 2.78"; Louisville 3.88"; Birmingham 6 ~ 84" (from Daily Weather Maps, NOAA Environmental Data service)
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From page 306... ...
. 15 A similar conclusion holds a fortiorz f or nitrates, because the stoichiometric analysis summarized in Figure 7-3 assigns hydrogen ions to sulfates and nitrates in proportion to their ratio in the precipitation sample.
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From page 307... ...
Although this estimate is indirect and sub ject to some error, it is clearly much smaller than the total NOx emissions in the area (about 17 million tons} or even those derived f rom stationary fuel combustion (9 million tons}. Evidently deposition in precipitation is a substantial, but not the ma jor sink for nitrogen oxides emitted into the atmosphere.
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From page 308... ...
Acid precipitation in the northeastern United States. Water Resources Research: in press.
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From page 309... ...
and D.~. Fisher (1966; Chemical composition of rainfall in eastern North Carolina and southeastern Virginia.
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From page 310... ...
and D.W. Fisher {1971 } Chemical composition of atmospheric precipitation in the northeastern United States.
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From page 311... ...
U.S. Environmental Protection Agency (1973} Nationwide Air Pollutant Trends, 1940-1970.
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From page 312... ...
312 Symposium, USAEC Symposium series, Champaign, Illinois.
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