During the 1980s, the U.S. conducted a major ten-year scientific study of acidic precipitation. This study, the National Acidic Precipitation Assessment Program or NAPAP, found that the effects of acidic precipitation were not as great as once feared.
The study found that acidic precipitation had affected about 10 percent of eastern lakes and streams and that it had contributed to the decline of red spruce at high altitudes by reducing their tolerance of cold conditions. The study also found that acidic precipitation contributed to corrosion of buildings in affected are and that sulfuric particles had contributed to reduced visibility in the Northeast and parts of West.
The panel found that the lakes and streams that were most severely affected were those that lacked a natural buffering capacity. Lakes and streams surrounded by limestone subject to acidification because the limestone reacted with the acidic runoff to reduce its pH.
In the U.S., Canada, and Europe, pollutant controls and emissions trading programs have significantly reduced the amount of sulfur dioxide from industrial sources. European countries have reported a significant recovery of forests once considered to be particularly vulnerable to acidic precipitation.
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In the U.S., amendments made to the Clean Air Act in 1990 established sulfur emissions trading program that has been effective in reducing sulfur emissions. Nitrogen oxides from automobile exhaust remain a significant problem; older designs of catalytic converted not reduce nitrogen oxide emissions.
Asia is currently the region most affected by acidification; in China widespread burning of fuels high-sulfur coal in small stoves and an industrial burner has contributed to a serious air quality Problem.
Southwestern China is particularly affected, with damage to forests and crops from acidic conditions. China has taken steps to reduce emissions that contribute to acid rain, instituting I an emissions trading program similar to that used in the United States. China’s State Environmental Protection Agency has announced that it plans to reduce acidic precipitation levels by half by 2005. Other areas in Asia have experienced damage from acidic deposition; the Taj Mahal has I suffered significant damage from corrosion due to acidic precipitation.
In order to find out what have been the long-term effects of anthropogenic pollutants on the pH of rainwater in North India, Khemani compared the ionic composition and pH of rainwater samples collected during the summer monsoon seasons of 1963 and 1965 at Agra and Delhi respectively with those of samples collected during the 1984 summer monsoon season at the same places.
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He found that the pH values at Agra and Delhi have decreased from 9.1 to 6.3 and! From 7.0 to 6.1 respectively he explains that the decrease in pH at Agra is due to a combination of the increase of acidic components (S04 2 and NO 3) by 88 per cent and a simultaneous decrease’ of basic components (mainly Ca2+) by 50 per cent. However, the reduction of pH at Delhi is much less, because the cation concentration has decreased by only 21 per cent, while the anion concentration has increased by 32 per cent. Khemani concludes.
“In view of the above, it can be concluded that long-term effects of pollutants on the chemistry and pH of rain water have been observed for the first time in India. However, these effects are comparatively slow compared with those observed in Western countries.
The growth of industry in India is very slow and, therefore, the anthropogenic pollutants have still not overpowered the natural pollutants released from soil and sea.”