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Rocky Mountain (sulfur) high.

Sometimes, they lucky combination of georgraphy and human activity provides just the right conditions for an important though unintentional field experiment. This was the situation that allowed a group of researchers to show recently that on the average, emissions of sulfur dioxide lead to corresponding sulfate ion concentrations in rain falling hundreds of miles away -- at least in the Rocky Mountain states.

The setting for the experiment was a mountainous region between the crest of California's Sierra Nevada and the Continental Divide, which winds through Colorado and other western states. In this region, a small number of metal smetlers, located mainly in New Mexico and Arizona, are responsible for most of the area's sulfur dioxide emissions.

From 1980 through 1983, emissions from these smelters fluctuated widely as plants responded to rapidly changing copper prices and general economic conditions. At the same time, National Acid Deposition Program (NADP) stations in Colorado, Wyoming and Idaho were measuring the concentration of various ions found in precipitation.

When annual sulfate concentrations for all of the monitoring stations are plotted against time, the graphy, year by year, very closely follows the ups and downs of total sulfur dioxide emissions from the smelters. Reporting in the Aug. 30 SCIENCE, Michael Oppenheimer and his colleagues at the Environmental Defense Fund, Inc. (EDF) in New York City conclude, "Our study illustrates a response of precipitation chemistry to large changes in emissions at distant locations."

Moreover, the EDF analysis is one of the first studies to show explicitly a linear relationship between emissions and sulfate deposition. Two years ago, a National Academy of Sciences panel concluded that over a large enough region and averaged over a long enough time period, this was probably true for eastern North America (SN: 7/2/83, p. 7; 7/30/83, p. 72). The new study bolsters that conclusion.

"It was a nice field experiment," says James H. Gibson, NADP director and an ecologist at Colorado State University in Ft. Collins. "The only thing that may detract from it is that certain other species, particularly calcium and nitrate and possibly some other ions, also seem to follow a somewhat similar pattern."

Because smelters aren't likely to emit nitrates, for example, this means that other factors may also have influenced ion concentrations in rainwater. "But the fact that sulfate behaves so beautifully with respect to the change in smelter activity," says Gibson, "is a pretty good indication that it plays a major role in that pattern."

Oppenheimer's argument could be strengthened if sulfate deposition mirrors sulfur dioxide emissions on a month-by-month rather than just on an annual basis. He is now completing that analysis and says preliminary results support the original conclusion.

It would also be helpful to find out which particular smelters contribute to sulfate deposition in given areas. That idea may be tested when a large new Mexican smelter begins to operate at Nacozari later this year. This smelter and another nearby, slated to be expanded, have no sulfur dioxide controls. It isn't clear which way the smelter's plume of pollution will tend to travel.

"When that smelter comes on and if the plume travels in a northerly direction," say Gibson," we ought to see its effect in the measurements."
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Title Annotation:acid rain research
Author:Peterson, Ivars
Publication:Science News
Date:Aug 31, 1985
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