A compendium of current research on acid rain produced by the assessment program fills a book the size of the District of Columbia telephone directory.
Despite the uncertainty that still exists in many elements of the problem, these general conclusions emerge:
– Acid rain is man-made, not natural, with 90 percent of this pollution in the Northeast coming from industrial burning of fossil fuels and cars. In the East, the main component of acid rain is sulfur dioxide, with nitrogen oxides also playing a key role.
– These pollutants are transported through the atmosphere long distances from their sources and acid rain increases in proportion to the emission of these pollutants.
– Several thousand lakes and streams, mostly in the Northeast so far, have been acidified, with life in them being killed or reduced or at risk of acidification.
– The impact of acid rain depends on several factors other than the acidity of the precipitation, including the buffering capacity of the soil and water, the nature of the watershed, and the rate at which acidification occurs.
– The rate of sulfur emissions and acid precipitation has stabilized in the east, but the impact of acid rain may intensify if the effects are cumulative.
– Forests throughout the East are affected by anthropogenic air pollution, perhaps in combination with natural pressures. Acid rain may contribute to deforestation, although other pollutants, particularly ozone and nitrogen produced by industrial processes and motor vehicles, may play a more important role.
– Crops are probably not significantly affected by acid rain, and if they are, the effects can be mitigated. Ozone is the most likely culprit among air pollutants that reduce crop yields.
– Buildings, monuments and other man-made structures are corroded by air pollution and could be the most “sleeping” issue of the acid rain problem, said Dr. J. Christopher Bernabo, executive director of the national assessment program.
Understanding What's Happening
In general, great strides have been made in understanding the processes by which sulfur and nitrogen oxides are converted in the atmosphere to acid deposition, how pollution is transported over long distances, the processes by which they enter watersheds, and how acidification affects fish and other aquatic organisms.
“We've gone from complete speculation to relatively defensible positions in a relatively short period of time,” said Robert T. Lackey, an ecologist who directs the lab's acid deposition effects research program.
Among the aspects of the problem that continue to elude understanding are the effects of acid rain on trees and soil. Questions about terrestrial effects seem particularly “difficult” at this point, said Dr. Lackey.
