The Acid Threat

They were measures that all ecologically minded citizens could applaud. By the 1950s, more and more communities in the industrial U.S. Northeast were switching from burning dusty, high-sulfur coal in their furnaces to extremely clean natural gas. Along with the fuel changeover, factories raised the height of smokestacks to help disperse smoke over a wider area and added sophisticated devices called particle precipitators to collect soot before it escaped. Yet for all of the good intentions, those anti-pollution efforts may have created a new headache: a marked rise in the acidity of rainfall, posing a serious ecological threat of its own.

That is the conclusion of two prominent environmental scientists, Aquatic Ecologist Gene E. Likens of Cornell and Forest Ecologist F. Herbert Bormann of Yale. Although rain and snow usually have no more acidity than a potato, Likens and Bormann found that measurements made at scattered sites in upper New York State and New England showed acid levels at least 100 times greater than normal -- and well above other areas in the U.S. They also noted a paradox: the rise in acidity seemed to coincide with the introduction of the new low-pollution fuels and soot-collection devices. Why?

Writing in Science, the two environmentalists lay the blame on sulfur dioxide, a common ingredient of smoke that can form highly corrosive sulfuric acid upon contact with moisture. In the bad old days, before pollution-control measures, great quantities of soot were released into the atmosphere along with the sulfur dioxide. Basically alkaline -- that is, the chemical opposite of acid -- the soot particles tended to neutralize the sulfur dioxide. But all that changed with the installation of soot precipita-tors. Though the devices trap most soot particles, thereby creating the appearance of a relatively fumeless smoke stack, they do not scrub out the more elusive sulfur-dioxide vapors that are given off even by low-sulfur natural gas.

Furthermore, the taller chimneys spread the vapors higher and wider. All in all, say Likens and Bormann, the antipollution measures "have transformed local soot problems into a regional acid-rain problem."

Other regions could take a lesson from the Northeast. Though scientists do not yet fully understand the effects of increased acidity in rain or snow, they strongly suspect that it is at the root of the noticeable reduction of forest growth recently observed in New England and even in pristine Scandinavia. Laboratory tests have shown that acidic water can badly stunt pine needles, deform birch leaves and decrease the reproductive rate of tomatoes. Other studies have linked fish-kills with increased acidity in the fresh-water lakes of Canada.

Finally, the very nature of acids suggests that contaminated rain water could severely corrode stone buildings, monuments and bridges -- another way in which smoke-pollution controls may al ready be backfiring.

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