Magazine article Science News

Acid Precipitation Drops in United States

Magazine article Science News

Acid Precipitation Drops in United States

Article excerpt

Measurements of rainwater at selected locations across the United States reveal a significant decline in the pollution that causes acid rain, according to a report issued last week by the U.S. Geological Survey.

The study shows that between 1980 and 1991, the concentration of sulfate ions - a key component of acid precipitation - dropped at a statistically significant rate at 26 out of 33 rainwater i collection sites.

"The decreases are fairly substantial and they are widespread," says Timothy A. Cohn, who coauthored the report with William G. Baier, both at the USGS in Reston, Va. Although the national network of rain collection sites has some 200 stations, the two researchers focused on sites with the most extensive precipitation records.

The USGS study also found that the acidity of rainwater decreased over the same period at most of the sites. The pH of precipitation rose significantly at nine of the 33 stations, signaling decreasing acidity. An additional 16 stations showed an increase, but in these cases the changes were not large enough to be statistically significant.

Such trends represent the payoff from air pollution standards put in place in the 1970s during implementation of the Clean Air Act of 1970 and its 1977 amendments. Although not fashioned to address acid rain, the laws sought to improve air quality by reducing emissions of sulfur dioxide gas, which turns into sulfate in the atmosphere. These emissions come chiefly from power plants that burn fossil fuels, especially sulfur-rich coal. …

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