Science
By JULIE DUTTON

Acid rain under study

THE COMBUSTION of fossil fuels releases sulfur dioxides and nitrogen oxides into the atmosphere and is considered the primary cause of acid rain. Although there are natural sources for sulfur dioxide and hydrogen sulfide, such as volcanic eruptions, it is industrial and vehicular emissions which contribute most acid rain precursors.

Rain is formed when the temperature drops and causes water vapor to condense around minute particles in the air. Pure water can never fall as rain; there always has to be a particle to serve as the nucleus of the raindrop. When the sulfur and nitrogen oxides emitted by industries and power plants react chemically with atmospheric moisture, sulfuric acid and nitric acid can result.

Although there is general agreement on the cause of acid precipitation, there is disagreement over its severity and effects. Acid precipitation has been cited as the culprit in lake acidification, forest reduction, soil poisoning, fish population decline, harvest decrease, and building deterioration. But some findings suggest the nitrates and sulfates of acid precipitation contribute to the nutritional needs of some crops, thus increasing productivity.

The acid quality of rain (or any other liquid) is measured by a pH scale ranging from 0 to 14 where 7.0 is neutral, below 7.0 is acidic, and above 7.0 is basic. The pH of normal precipitation is usually agreed to be 5.6, still on the acidic side because of the weak carbonic acid formed when water vapor comes to equilibrium with atmospheric carbon dioxide. Any snow or rain falling below the 5.6 standard is classified acidic.

Calculated pH's for rainfall in the 1950's averaged around 5.8; the pH's of the 1960's approximated 4.8; by the late 1970's, when pH was measured not extrapolated, the pH of rainfall registered 4.3. Strictly on face value, the plummeting pattern is alarming since lower pH's mean higher acidity. But Dick Semonin of the State Water Survey explained that rather than explore why acidity is now increasing, he took the opposite approach: why was the pH so high in the 1950's? An investigation revealed that a drought occurred during that time, introducing dust particles in the air. These particles probably served as the centers of the raindrops and were usually basic, thus causing a pH (5.8) that was nearer to neutral than that now measured. Semonin questions the reliability of the 1950's figure too, as it is an extrapolation rather than an actual reading as is now done.

Semonin stresses the need for caveats in the acid precipitation issue because, too often, speculation is treated as fact. The result: an increasingly polarized environmental issue. "We do not have all the answers ... we need to go down the middle of the road to firm up some findings,'' says Semonin, who has been involved in precipitation chemistry since 1954.

Furthermore, Semonin said that although he has no evidence to support it, his hunch is that the standard precipitation pH of 5.6 is too high, that perhaps 5.0 is closer to "normal." He noted that the lack of thorough data is a serious detriment to diagnosing the acid precipitation phenomenon.

For purposes of studying acid rain, researchers divide the country into the regions of northeast, southeast, midwest and west, according to geological and meteorological traits. Differences in these traits are significant enough to account for the differences in acid rain effects.

For instance, although many of the devastating occurrences — forest reduction, soil spoilage, and building corrosion — blamed on acid rain have not been sufficiently documented to convince many acid rain researchers, the potential aquatic impact is generally acknowledged. This is seen particularly in the northeastern U.S., where the acid rain damaged the Adirondack lakes and brought national attention to the potential threat of acid rain. Hundreds of lakes in that region suffered extensive damage to fish populations and other biota. Illinois has also registered pH readings within the acid rain range. But because of Illinois' particular substrata, the state tends to be immune to aquatic problems. That is, the nature of the Illinois bedrock is such that weathering dissolves and releases ions which in turn serve a buffering or neutralizing function in the watershed.

Because most acid rain research is just getting underway, environmental impact remains to be determined. Says Dan Goodwin of the Illinois Environmental Protection Agency, "About all we know about it right now is that we don't know a lot about it."

Possible agricultural impacts of acid rain are being investigated at Argonne Laboratory in Illinois and Brookhaven National Laboratory in New York, and also at the universities of Cornell in New York and North Carolina State. In Kendall County, 50 miles southwest of Chicago, findings from field studies of soybeans and acid rain simulant conducted by Pat Irving of Argonne suggest that the sulfur and nitrogen content of the precipitation serve as part of the nutrient demand of the crop. Further, no visible damage to the soybean plants occurred in the Illinois field plots, and seed size was increased. What implications do these findings hold for other agricultural crops? Irving explained that the research results are too tentative to draw general conclusions, but Irving ventured that the results could be extrapolated with greater confidence to other crops harvested for seed growth than to leafy or group crops such as fruit. Irving also pointed out that because cultivated soils are routinely limed to neutralize acidity induced by fertilizers, agricultural ecosystems are less vulnerable to acid rain effects.

Acid rain in unglaciated forested areas in Southern Illinois has been monitored for the past two years by George Weaver, associate professor of forestry at Southern Illinois University at Carbondale. Presently, Weaver is "taking inventory" of the situation and then will investigate acid rain effects in a forest system.

Like Semonin, Weaver hypothesizes that dust introduced into the atmosphere during dry seasons may counterbalance the acidity of precipitation. The primary focus of Weaver's studies has been on possible neutralizing effects on acid rain by the forest canopy and soil. But as with most other research in this area, findings are preliminary and not conclusive.

Weaver did note that efforts have been made to identify the soil in the country that is sensitive to acid rain, but he said, "Illinois is not in the so-called sensitive area."

Numerous conferences are being held on the acid rain issue, such as the U.S. Environmental Protection Agency's interstate acid rain conference held in April. Illinois EPA's Goodwin attended the meeting,

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which directed attention to short-term easing of the problem while long-term resolutions are sought. One suggestion called for the national requirement that all high-sulfur coal be washed. Such a mandate would apply even to large, stationary pollution sources built before August 1971 — facilities which are presently exempt from U.S. EPA emission standards (see Illinois Issues, June). Another proposal was that coal-fired power plants be retrofitted with scrubbers. Goodwin calls the latter a "tongue-in-cheek'' short-term measure because with this option, "You're talking about five or six years into the future," due to the financial, legal and regulatory factors of such a mandate.

Acid rain represents a challenge to all the states, for air masses are no respecter of boundaries. Taller industrial and utility smokestacks built in an effort to comply with federal Clean Air Act standards (whose ambient air quality readings are taken at ground level) emit sulfur dioxide and nitrogen oxide particulates high into the atmosphere. Once in the prevailing winds, these precursors can be carried for miles, so one state's combustion emissions can become another state's acid rain.

Recognizing the "we're-all-in-this-together" nature of the acid rain issue caused-President Carter, in his environmental message of August 1979, to establish a 10-year comprehensive Federal Acid Rain Assessment Program. That program is about to get underway under the auspices of the Acid Rain Coordinating Committee. Carter also directed that $10 million be allotted annually for acid rain research.

Nationally, the National Atmospheric Deposition Program provides a monitoring network for precipitation chemistry. Through this system, federal, state and private agencies collaborate on precipitation data to assess environmental impacts. Eventually the network will include more than 50 monitoring stations across the country.

Legislative efforts to relax sulfur dioxide emission standards have met resistance because of the expectation that an increased sulfur dioxide output would then bring about an increase in acid rain. Such has been the case in proposed Illinois legislation (S.B. 1967 Rupp; S.B. 673 Knuppel, Johns, Rupp; H.B. 536 Rea, Harris, Richmond, Winchester). More lax sulfur dioxide standards would favor the marketability of high sulfur Illinois coal.

Just what is the prognosis of the acid rain situation? Says Goodwin with what appears to be the only certainty in the acid rain issue: "It's going to be a difficult one here in Illinois."

Support for this column is provided in part by a National Science Foundation grant to the Illinois Legislative Council Science Unit, where Julie Dutton is a science intern.

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