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2 . SC I ENTI FIC UNDERSTANDI NG OF ATMOSPHERE-BI OSPHERE INTERACTIONS: A HI STORICAL OVERVIEW Scientific appreciation of the linkage between the atmosphere and the biosphere has developed along several lines over the past four centuries. The first clue must have come from the act of breathing, and the work of Boyle, Hooke, Lower, and Mayow in the 17th century demonstrated that air contains an active component that is required both for breathing and burning (Dampier 1948, Wilson 1960, Taylor 1963). A century later, in 1780, Lavoisier and Laplace showed that as oxygen is consumed in breathing, carbon and hydrogen are oxidized into carbon dioxide and water that are given off along with heat (Gabriel and Fogel 1955). That plants draw nourishment from the air around them, as well as from the water in the soil, was suggested by Hooke, on the basis of experiments by Thomas Br other ton in the 17th century tHooke 1687, see also Gorham 1965). Other experiments by Hales (1738) supported this conclusion; the significance of Hooke's and Hales's observations could not be fully appreciated at the time, however, because the nature of atmospheric gases was not understood until the work of Scheele, Priestley, and Lavoisier in the latter part of the 18th century. It was Priestley (1772) who showed that plants can restore the capacity of air to support burning and breathing. Moreover, he recognized that this mechanism must be important in maintaining the capacity of the atmosphere to support animal life and combustion, thus intimating the interactions of the carbon and oxygen cycles in the atmosphere that maintain the balance of nature. Soon after, in 1779, Ingenhousz proved it was the green parts of plants that were necessary for This chapter was prepared by Eville Gorham. It focuses strongly on acid rain, partly because of the current significance of the problem in relation to fossil fuel combustion, partly because the history of the problem has not been treated adequately elsewhere, and partly because of the author's own involvement with the subject. The author wishes to thank Leonard G. Wilson, Rudolph B. Husar, and Thomas C. Hutchinson for suggesting certain source materials. 9

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10 restoration of the air, which took place only in sunlight (Gabriel and Fogel 1955~. Between 1783 and 1788 Senebier showed that the chemical change involved conversion of "fixed air" {carbon dioxide) into "dephlogisticated air" (oxygen) and carbon, and in 1804 de Saussure made much more quantitative studies of the assimilation of carbon dioxide and water accompanied by the release of oxygen during photosynthesis (Nash 1957~. Both de Saussure and Senebier believed that the oxygen so released came from the carbon dioxide assimilated. It was not until the second quarter of this century that studies of photosynthetic bacteria by van Niel, of isolated chloroplasts by Hill, and the use of oxygen isotopes by Ruben and his associates (Gabriel and Fogel 1955) proved conclusively that oxygen came instead from water molecules, as suggested long before by Berthollet (Baker and Allen 1971~. The importance of the carbon dioxide cycled through the atmosphere and the biosphere to the process of rock weathering became appreciated in the first half of the 19th century--the major cycles of the atmosphere, biosphere, and lithosphere being thus tied together (Davy 1821, Jamie son 1856~. The involvement of the biosphere in the nitrogen cycle was demonstrated by de Saussure, whose water-culture experiments showed the stimulation of plant growth by nitrate (Baker and Allen 1971~. Gay Lussac and Thenard recognized nitrogen as an important component of plants (Davy 1821), occurring in the form of gluten and also as albumen, more characteristic of animals. Liebig persuaded scientists by 1840 that plants could be produced from carbon dioxide, water, ammonia (NH3), and certain minerals--the ultimate products of the decay of plants (Singer 1959, Holmes 1973~. He thus controverted the older agricultural theories that plants utilize complex, soluble organic compounds released during the breakdown of manures (e.g., Woodward 1699, Hales 1738, Davy 1821~. Liebig later found ammonia in plant sap, and came to believe that as it was also present in the atmosphere it must be absorbed by plants aerially like carbon dioxide in amounts sufficient to meet their full needs for nitrogen (Eriksson 1952). Boussingault proved during the 1850s that most plants obtain their nitrogen from nitrate in the soil (Singer 1959~. His earlier experiments, in the 1830s, had shown that legumes were an exception to this rule. He had suggested atmospheric fixation (Aulie 1973), but he could not explain the process, and a fuller understanding awaited the discovery in 1886, by Hellriegal and Wilfarth, that legumes reduce atmospheric nitrogen by means of nodules on their roots and can grow independently of other fixed nitrogen (Russell and Russell 19501. Biejernick cultured the nitrogen-fixing bacteria from nodules in 1888 (Collard 1976~; Berthelot, already in 1885, had suggested that bacteria were responsible for the fixation he observed in soils (Crosland 1973~. The general involvement of soil microorganisms in the biological cycles of the elements was postulated in 1872 by Cohn to account for the breakdown of dead plant material and for the fact that organic manures restored the fertility of soils exhausted by continued

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11 cropping (Geison 1971, Collard 1976). Liebig had held that decay, putrefaction, and fermentation were purely chemical, but the role of microbes in these processes was becoming known through the work of Pasteur and others from 1857 on (Collard 1976, see also Smith 1872~. (Pasteur's work on this subject was anticipated in 1837 by Schwann and in 1838 by Cagniard-Latour, but their results unfortunately were not accepted by Liebig and others; see Brock 1961.) The person who did most to confirm Cohn's hypothesis was Winogradski, who isolated several microbes involved in the cycles of nitrogen, sulfur, and carbon and investigated their metabolism (Collard 1976~. By the 1890s the existence of heterotrophs, chemoautotrophs, and photoautotrophs was established, together with their ability to use and transform diverse organic or inorganic molecules or both in their energy metabolism. But only recently has much attention been devoted to the circulation through the atmosphere and the biosphere of a variety of gaseous compounds--such as carbon monoxide, methane, dimethyl sulfide, hydrogen sulfide, sulfur dioxide, ammonia, nitrous oxide, nitric oxide, and nitrogen dioxide--which contain biologically significant elements (cf. Hutchinson 1954, Goldberg 1974~. Among the more interesting recent discoveries is the role of microbial methylation in the cycle of mercury and other elements. Although the vapor-phase transfer of elemental mercury from the soil to the atmosphere is of major importance, the formation of monomethyl mercury, a potent neurotoxin, probably enhances such transfer, locally. Dimethyl mercury is even more volatile (U.S. Geological Survey 1970, Wood 1974.) An aspect of atmosphere/biosphere interactions that was discovered long ago is the involvement of plants in returning water to the atmosphere. In the mid-17th century van Helmont observed that a 169-pound willow tree had grown in 5 years from a 5-pound stem planted in a tub of soil and watered only with rain or distilled water (Baker and Allen 1971~. He believed the tree's substance to be transmuted water. Woodward (1699) refined van Helmont's experiment and concluded that most of the water a plant used was evaporated via pores to the atmosphere, especially during warm weather, and that the plant grew from the terrestrial vegetable and mineral material contained in all waters, even rain. Early in the following century Hales (1738) made many careful measurements of the absorption of water and its transpiration to the atmosphere, in one case comparing the amount of water transpired from the plants in a hop field with the amount evaporated from the soil. At the same time that the above-mentioned studies were going on, Halley was examining the nature of the hydrological cycle described by Aristotle and quoted by William Harvey (1628), and he was demonstrating quantitatively that evaporation from the ocean and from watercourses is adequate to replenish river flow (Biswas 1970a, b). The hydrologic role of plant transpiration was recognized by de la Methiere in 1797, according to Biswas (1970b). The mineral nutrition of plants was first suggested, as noted above, by Woodward. In 1733 Tull, a celebrated agriculturist, reiterated the view that minute earthy particles of soil were the true nourishment of plants (Davy 1821~. It was left to de Saussure to

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12 demonstrate by analysis in the early 19th century the uptake of diverse mineral elements from the soil (Taylor 1963~. A table of his data was given by Davy (1821), who indicated that alkalis and alkaline earths were essential ingredients of plants and that silica might serve as a structural material. The possibility that certain plants might depend upon atmospheric sources for some of their mineral nutrients was suggested by several authors as long ago as the 17th century (Guerlac 1954), and again in the 18th century by Hales (1738~. Early in the following century a few agriculturists (Naismith 1807, Aiton 1811, Dau 1823) realized that the plants of certain kinds of peatlands were not influenced at all by water that has percolated through mineral soil but depended solely upon rain and snow (see DuRietz 1949; Gorham 1953, 1978a). Smith (1852) placed the earlier conjectures upon a more scientific basis when he pointed out that rainwater contains enough nutrients (such as ammonia) to allow plants to grow, though scantily. The chemical composition of surface waters from rain-fed peat bogs was first analyzed by Ramann in 1895 (Kivinen 1935~. Witting (1947, 1948) contrasted the ionic composition of rain-fed bog waters with that of fen waters receiving water from the mineral soil, and Gorham later (1961) demonstrated the chemical similarity of bog waters and rain waters. The geochemical contrast between bog and fen peats was shown by Mattson, Sandberg, and Terning (1944) and Mattson and Koutler-Andersson (1954~. Recently, study of the atmospheric inputs to the nutrient budgets of ecosystems has greatly increased (e.g., Galloway and Cowling 1978~. The early history of research on the elements and ions in atmospheric precipitation dealt largely with the study of nitrogenous compounds, as pointed out in a thorough review by Eriksson (1952~. Nitrate was observed in rainwater by Marggraf in the winter of 1749-50, along with calcium and chloride (see Miller 1913, who reviewed the earliest literature of rain chemistry). Ammonia was found in the atmosphere by Scheele in 1788-89 and by de Saussure in the early 1800s. In the latter half of the 19th century, numerous investigations of atmospheric nitrogen supply were made, chiefly in Europe, but also in Asia, Africa, and New Zealand. Among them, those of Boussingault in the 1850s, cited by Smith (1872), are of particular interest. Boussingault showed a clear decline of ammonia concentration during the course of a given rainfall and also observed especially high concentrations in fog and dew. Systematic studies of chloride were also made in the mid-19th century, when the role of sea spray was clearly demonstrated by Smith (1872), who set up a network of stations in the British Isles to make a short-term study of rain chemistry. He also pointed out the abundance and importance of sulfate in urban areas (Smith 1852, 1872~. The general nature of the cycles of chloride and sulfur was given a major review by Eriksson (1959, 1960~. Only in the last few decades have thorough analyses been made of the full suite of major cations and anions in atmospheric precipitation. Networks for long-term regional studies are equally recent; the first was the Scandinavian {later European) network

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13 (E)nanuelsson, Eriksson, and Egner 1954~. Data on trace elements and specific organic constituents (both major and minor) in air and precipitation are mostly recent and are still scattered and sporadic {see, e.g., Katz 1961; Stocks, Commins, and Aubrey 1961; Lazrus, Lorange, and Lodge 1970; Lunde et al. 1976; Galloway and Cowling 1978~. In the 19th century, however, some trace elements were observed in rain, such as iodine (Pierre, quoted by Smith 1872) and arsenic (Russell, quoted by Cohen and Ruston 1912~. Two general topics in the subject of atmosphere/biosphere interactions deserve mentioning. The first is the major evolutionary change about two billion years ago from a reducing to an oxidizing atmosphere, owing to the development of photosynthesis. This was apparently still a somewhat controversial matter even after World War II (Hutchinson 1954), although it had been proposed by Goldschmidt in 1933 (Rankama and Sahama 1950~. The evidence from paleobiology and geochemistry has been thoroughly reviewed by Cloud (1968, 1976~. The second topic is the reciprocal fitness of the evolving atmosphere and biosphere, in agreement with the classic argument of Henderson (1913) that "fitness of environment is quite as essential as the fitness which arises in the process of organic evolution." HUMAN ALTERATIONS OF THE ATMOSPHERE Radioactivity in rainfall was observed as long ago as 1906 (Eriksson 1952), but it has received serious attention only in the era since World War II, as a result of concern over the threat to human health posed by radioactive fallout from atomic weapons. Early work in the 1950s was thoroughly reviewed by Caldecott and Snyder (1960~. The many radioisotopes that were released proved to have an unanticipated utility in tracing both physical and biological aspects of atmosphere/biosphere interactions (Nelson and Evans 1969, Broecker 19741. Among the most interesting phenomena was the striking concentration of several isotopes along the food chain from mosses and lichens to reindeer and caribou and thence to Laplanders and Eskimos (Gorham 1958a, 1959; Liden 1961; Miettinen 19691. The buildup of carbon dioxide in the global atmosphere due to the combustion of fossil fuels has also become a major concern, because of the possibility that it may increase the temperature of the atmosphere and alter the world's climatic patterns quite substantially through the so-called greenhouse effect. The development of our knowledge of this problem has been reviewed by Plass (1956~. He reports that Fourier in 1827 compared the atmosphere to a pane of glass beneath which the earth is warmed. The role of carbon dioxide in the greenhouse effect was mentioned by Tyndall in 1861 and worked out by Arrhenius in 1896. Over the next three years Chamberlin presented in detail the geological implications of the carbon dioxide theory of climatic change. Callendar (1938) suggested that combustion of fossil fuel by man was enriching the atmosphere in carbon dioxide sufficiently to induce perceptible climatic warming. He later (Callendar 1949, cf.

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14 Hutchin son 1954) suggested that land clearance and cultivation might also be important. The magnitude of the carbon dioxide release was shown clearly by Keeling (1970~. If continued, the carbon dioxide enrichment and consequent climatic warming could have diverse and serious consequences for the biosphere, including major displacements of agriculture (Kellogg 1978; Committee on Government Affairs 1979; see, however, Idso 1980~. Such displacement would come about because of the predominant role of climate in determining the distribution of the biota. The influence of climate has of course been known since antiquity, but early in the 19th century it was studied scientifically by the great geographer van Humboldt (e-~.~ van Humboldt 1805~. The modern view of an interactive control of plant distribution by temperature, moisture, topography, and geology was clearly expressed shortly thereafter by Watson (1833, cf. Gorham I954~. Depletion of the stratospheric ozone layer could result from - microbial transformation of nitrogenous fertilizers (Crutzen 1970)' emissions of water vapor and nitrogen oxides from supersonic transports (Harrison 1970, Crutzen 1970, Johnston 1971), and the use of chlorofluorocarbons (freons) in refrigerators and especially as propellants in aerosol sprays (Molina and Rowland 1974, Wilkniss et al. 1975~. Serious damage to the ozone layer would greatly increase the penetration of ultraviolet radiation through the atmosphere, with a variety of damaging effects upon plants and animals--including an increase in human skin cancers (NRC 1976a). Chlorinated hydrocarbons, such as the pesticide DOT and the industrial PCBs, everywhere undergo a distillation to the atmosphere that allows them to spread throughout the world ecosystem {Goldberg 1975~. DDT is likewise spread throughout the atmosphere on particles of talc used as a carrier and diluent in aerial pesticide sprays and is observed ubiquitously in atmospheric dust samples (Windom, Griffin, and Goldberg 1967~. These toxicants are of especial concern because they can accumulate significantly along food chains. Such biological magnification was discovered in the 1950s, and the early work is cited by Rachel Carson (1962) in "Silent Spring." The injection of fine particulate pollutants, including a variety of sulfates and condensed hydrocarbons, is interfering with atmospheric visibility on a regional scale (NRC 1979a). The possibility of atmospheric particulates forming from chemical reactions of gases was pointed out long ago by Rafinesque (1819, 1820~. The role of air pollution in reducing local visibility has probably been known ever since coal came into use as a major energy source and was noted by Evelyn in 1661 (Brimblecombe 1977~. Crowther and Ruston (1911) and Cohen and Ruston (1912) remarked on the substantial reduction in hours of sunshine and light intensity by air pollution in the city of Leeds. More recently, Flowers, McCormick, and Kurfis (1969) showed that atmospheric turbidity is unusually high in the heavily polluted eastern United States, and there has been a distinct trend over the past half century toward increasing turbidity (McCormick and Ludwig 1967) both in and near cities. Increasing regional haze in the eastern United States and its possible

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15 climatologica~ consequences were discussed by Husar and his colleagues (1979~. The nature of photochemical smog of the Los Angeles type was first elucidated by Haagen-Smit (1952, 1953~. Its effects were first investigated by Middleton and his associates (1950, 1958, 1961), and have been reviewed recently by the National Research Council (1977b). Atmospheric haze may also be a consequence of natural biospheric activity such as the large-scale production of terpenes by coniferous and other kinds of vegetation. This effect has received rather little investigation since its identification by Went (1960; see also NRC 1976b; Curtin, King, and Mosier 1974; Simoneit and Mazurek 1980~. Natural eolian transport of partially biogenic dust also contributes to haze. Its transport over long distances from Africa to the Atlantic Ocean was described in the mid-19th century by Darwin (1846) and Ehrenberg (1849, cf. Simoneit 1979~. Acid rain is one of the most serious and far-reaching results of air pollution. The phenomenon was noted by Hales in 1738; he remarked that dew and rain "contain salt, sulphur, etc. For the air is full of acid and sulphureous particles . . .," and he said that these constituents "make land fruitful" after plowing. (Nash, 1957, pointed out that these particles were not to be taken as the materials themselves, but as their alchemical principles). The true local significance of acid rain appears to have been recognized first by Smith (1852), who from his analyses of rain in and around the heavily polluted city of Manchester, in England, remarked, "We may therefore find easily three kinds of air, -- that with carbonate of ammonia in the fields at a distance, -- that with sulphate of ammonia in the suburbs, -- and that with sulphuric acid, or acid sulphate, in the town" (Smith's italics). In the same article Smith pointed out that free sulfuric acid in city air was responsible for the fading of colors in prints and dyed goods and the rusting of metals. Twenty years later Smith (1872), then General Inspector of Alkali Works for the British government and a Fellow of the Royal Society, produced a classic account of the chemistry of air and rain, comparing country sites in England, Scotland, and Ireland with heavily populated urban sites in England, Scotland, and Germany. In this account he noted several important patterns (see Figure 2.1~: the decline of rain chlorides away from the seacoast, with the exception that city rains are secondarily enriched by chlorides from coal combustion. (Smith also remarked that even in coastal rains the ratio of sulfate to chloride was greater than in sea water). the presence of abundant sulfuric acid in urban rain, particularly in industrial areas because of the combustion of coal rich in sulfur. (Smith was the first to use the term "acid rain.") the liberation of hydrochloric acid into urban atmospheres by the interaction of sulfuric acid and sodium chloride during or after coal combustion (cf. Gorham 1958c,d; Eriksson 1958; Oden 1964; Hitchcock, Spiller, and Wilson 1980).

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16 14 12 _ _ Acidity a Oxidizable Organic Matter b /Ammonia 10 ._ 8 _ _ 6 _ _ 4 _ ~ _ 60 40 20: /\ - /\ - / ~ \ it' - fi . t ~ "A -: ~ 0 1 1 1 1 1 Rural Towns Urban/lndustrial ~ 0 ~ 0 _ ~ . ~ _ _ ~ O ~ ~ ~ ~ 0 ~ O a) cn c' ~ > ~ ~ ~ `,0 UJ Hi ~ tO aAcidity as concentration of H2SO4- bOxidizable organic matter was determined by a KMnO4 test and is given in parts of oxygen consumed per million parts of rain. FIGURE 2.1 Chemical composition of rain in the British Isles reported in 1872. SOURCE: Data from Smith (1872). Sulfate Chloride ____

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17 the liberation of sulfur and ammonia into the air, both by decomposition of dead organic matter in country areas and by coal combustion in cities, and their deposition together in rain. the likelihood of arsenic, copper, and other metals occurring in urban and industrial atmospheres. the general lack of vegetation in cities where the air contains enough acid to yield rains with 40 ppm of sulfuric acid. the interference of acid gases with development of the grain in wheat. the bleaching of chlorophyll in aquatic plants by very dilute acids. the possibility that acid gases from factories might weaken plants and expose them to attacks by fungi less susceptible to the same gases. the damage to stone, brick, mortar, iron, galvanized iron, and brass by acid rain. Smith quoted extensively from studies in 1854 and 1855 by a Belgian commission on damage to plants by acid emanations from chemical industries. The commission pointed out that such damage was related to numerous environmental factors such as distance from source, temperature, humidity, rainfall, wind direction and frequency, path of the smoke plume, topography, and shelter by obstacles to wind currents. Chimney height was noted as important. The commission described--and produced experimentally--a variety of types of damage to plants, including leaf spots and bleaching of chlorophyll, marginal leaf damage, early leaf-fall, and damage to buds and young twigs. It observed, moreover, considerable difference in sensitivity to acid gases, both between species and within varieties of the same species. In the course of its work it tested the acidity of raindrops upon plant surfaces with blue litmus paper and found the raindrops to be acid only near the chemical works whose effects they were examining. Further work upon acid rain in and near urban areas was done by Crowther and Ruston (i911; see also Cohen and Ruston 1912, Crowther and Steuart 1913) in and near the city of Leeds, England. They reported levels of total suspended matter, ash, tar, soot, nitrogen, sulfur, chloride, and acidity declining away from the center of the city. Cohen and Ruston (1912) also compared wet and dry fallout and the scavenging of suspended solids by rain and by snow. Crowther and Ruston (1911) showed that air pollution inhibited the growth of plants and their power to assimilate carbon dioxide. By watering soils with Leeds rain and with similarly dilute sulfuric acid, they arrested seed germination and growth and inhibited three aspects of the nitrogen cycle--ammonification, Vitrification, and nitrogen fixation. Timothy grass under such regimes became distinctly poorer in protein and richer in crude fiber. Cohen and Ruston (1912) demonstrated the clogging of leaf stomata by soot, the narrowing of tree rings owing to emissions from newly constructed shale works, and several changes in soil quality {including loss of carbonates) after leaching by acid rain and by similar concentrations of sulfuric acid.

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The high acidity of Leeds rain was ascribed to sulfuric acid, although Crowther and Rus ton noted that coal combustion greatly increased both sulfate and chloride levels in the center of the urban area. In fact, if one does a partial correlation of acidity at Crowther and Ruston's 11 stations with both anions, to eliminate the influence of correlation between the two anions, it appears that only the correlation (r) with chloride is significant: r values zero first (n = 11) order* significance order** significance H+ on C1- 0.795 p C 0.01 0.703 p ~ 0.05 H+ on SO4 0~543 P C 0.05 0.176 not significant * Influence of anion intercorrelation included. ** Influence of anion intercorrelation eliminated. Gorham (1958c), examining data compiled by Parker (1955), found a similar situation in two other cities in northern England. It appears that hydrochloric acid from coals rich in chlorine predominates in urban precipitation there, whereas sulfuric acid from the oxidation of drifting sulfur dioxide (slowed in the urban area by the presence of hydrochloric acid) predominates in rural rain (Gorham 1955, 1958d). Another early student of acid rain, Bottini (1939), found hydrochloric acid abundant in precipitation near the volcano Vesuvius. Damage to vegetation by sulfur dioxide from metal smelters has a long history. According to Almer and his colleagues (1978), it was recorded in 1734 by Linnaeus, on a visit to the 500-year-old smelter at Falun in the Swedish province of Dalarna. Smelter problems--including also livestock poisoning by arsenic--were investigated extensively in the United States both by observation and by experimental fumigation early in the 20th century (Swain 1949~. A long report by Holmes, Franklin, and Gould (1915) includes an extensive annotated bibliography of early American and German studies of the effects of sulfur dioxide upon plants and animals, including humans. Effects of sulfuric acid--resulting from fumigations with sulfur dioxide--upon the calcium status of soils poor in lime were also reviewed. Katz and his associates (1939) reported local acidification of soils and a lowering of their base saturation by sulfur dioxide emissions from a lead-zinc smelter in British Columbia. Severe local damage to vegetation by sulfur dioxide fumigation was also described by Katz, who reviewed the work in this field back to Schroeder and Reuss in 1883. A number of other investigators between 1939 and 1954 observed strongly acid to alkaline pH values in precipitation. Landsberg (1954) cited five beside himself, to whom may be added Atkins (1947) and Tamm (1953~. Tamm also measured pH in rain passing through forest canopies and the concentrations of several other elements. A long

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19 series of unpublished pH measurements since about 1930, at three adjacent stations a little to the north of London, England, has also been discovered very recently (Brimblecombe and Pitman 1980~. It reveals annual average pH varying around 4.6 between 1930 and about 1965-70, declining to about 4.0 today. The year 1955 saw a new emphasis on the study of acidity in precipitation, and the recognition of its spread from urban and industrial sources to distant rural areas, with the analysis of extensive data sets from the international network in Scandinavia by Barrett and Brodin (1955), from a number of British cities by Parker (1955), and from the rural English Lake District by Gorham t1955~. Houghton (1955) examined numerous samples of fog and cloud water from New England. Gorham continued to study the chemistry of atmospheric precipitation, with a series of papers on its nature, origin, and influence upon the geochemistry of oligotrophic lake waters, bog waters, and soils, culminating in a general review of the subject in 1961. He also examined, in a series of four papers with Gordon, the effects of fumigation with sulfur dioxide--and resultant acid rain--upon terrestrial and aquatic ecosystems around metal smelters in Ontario (see Gordon and Gorham 1963~. The Scandinavian (later European) network has provided the basis for a series of papers by diverse authors. International transboundary air pollution was noted long ago by Evelyn (1661), who remarked that farmers in parts of France to the southwest of England complained of smoke driven from England's coasts, which injured their vines in flower. By the mid-18th century, London's urban smoke plume was sometimes observable at distances of 100 km (Brimblecombe 1978~. Major international concern about acid rain as a serious, widespread pollution problem with severe ecological consequences began with the publication (Bolin 1971) of Sweden's report to the United Nations Conference on the Human Environment, which arose out of studies by Ode n (1967, 1968~. Attention was drawn to the problem in the United States by Likens and his associates, beginning early in the 1970s (Likens, Bormann, and Johnson 1972; see also Likens 1976~. These authors noted the likely significance in the United States of nitric acid produced by the further oxidation of nitrogen oxides emitted from gasoline engines. The predominance of nitric acid in rain at Pasadena, California, has been reported recently by Liljestrand and Morgan {1978~. An historical resume of progress in scientific and public understanding of acid precipitation and its biological consequences has been given by Cowling (1981~. ENERGY AND AIR POLLUTION Acid rain is generally the result of severe air pollution by man's combustion of fossil fuels (for exceptions see Bottini 1939 and Hutchinson et al. 1979a). The record of pollution by coal smoke and of government action about it goes back at least to the 13th century in England, and the problem appears to have become extremely serious by the end of the 17th century (Straw and Owens 1925, Brimblecombe

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20 1975, 1976' 1977' Brimblecombe and Ogden 1977' Halliday 1961, Heidorn 1978, Lodge 1980)0 That air pollution from coal combustion is a serious factor in human mortality, especially from lung disease, was postulated as long ago as the mid-17th century by the Londoner John Evelyn (1661) in his "Fumifugium." He also noted corrosion of structures and materials and losses of plants and animals, and remarked that in 1644--when Newcastle (the source of "Sea Coale") was blockaded--gardens and orchards produced far more than in the years before and after. Evelyn suggested that industries, rather than residences, were the chief cause and called for their banishment to f ive or six miles downriver (usually downwind) from the city. The editor of the 1772 edition of Evelyn's "Fumifugium" claimed a marked worsening in the situation over a century, and called for a variety of ameliorative measures: the use of tall smokestacks to spread the smoke into "distant parts," better chimney construction to drive the smoke higher, changed methods of combustion using charred (coked) coal to lessen smoke emission, inducements for industries to move outside the city, and legal prevention of more such building within the city. Tall smokestacks had been suggested as early as the late 14th century (Lodge 1980), and coal cleaning was apparently tried as long ago as the 15th century (Yeager 1979~. Other early suggestions, such as a shift to wood or to anthracite from bituminous coal, seem not to have been followed (Brimblecombe 19751. The deleterious effects of air pollution (smoke) upon health and mortality were noted by John Graunt (1662) the founder of the science of statistics and demography. He reported that London was becoming increasingly unhealthful and blamed this largely upon the great increase in the use of coal over the preceding sixty years, although he did believe that population growth and crowding were partly responsible. Among the first detailed studies of the influence of coal smoke upon human health (as measured by mortality from nontubercular lung disease) were those of Ascher, given in an appendix by Cohen and Ruston (1912~. Lichens appear to be the plants most sensitive to air pollution, and Grindon in 1859 attributed the decline of certain species in the city of Manchester, England to pollution (Hawksworth and Seaward 1977~. According to Skye (1968), the absence of these plants from urban areas was recorded in Paris by Nylander in 1866. Further details about the influence of air pollution upon lichens are given by Barkman (1958) and by Ferry, Baddeley, and Hawksworth (1973~. Twentieth-century studies of the effects of air pollution upon human health, vegetation, and corrosion have been reviewed by the World Health Organization (1961) and by Higgins and his associates (NRC 1979a). Health effects have been examined statistically in great detail by Lave and Seskin (1977) and Mendelsohn and Orcutt (1979~. Their work has been questioned by Lipfert {1980) and McCarroll (1980~. Modern legislation against air pollution, beginning in the 19th century, has been reviewed by HalLiday (1961) and Lodge (1980) , who also described the evolution of control technologies.

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21 The development from local, point-source pollution of the kind seen in London or Los Angeles to the broad dispersion of acid rain over large parts of the European and North American continents has come to be recognized as a major anthropogenic perturbation of atmosphere/biosphere interaction