Acid deposition and its effects in China: an overview

Acid rain is an increasing environmental problem in China. At present SO₂ emission is about 20–22 million tons. However with a growing number of large power plants the long-range transport of air pollutants is expected to increase. The highest acid deposition is near the emission sources. Wind-blown, alkaline soil dust is important in neutralizing the acidity of the emissions, especially in large parts of northern China. In the south, where alkaline soil dust contributes less to acid neutralization, the annual pH in precipitation was below 4.5 at monitoring stations in several provinces and as low as 4.1 in some urban areas. Total sulfur deposition has been estimated to be about 10 g S m?² year^?1 in heavily exposed areas. Negative effects on forests, including die-back, have been reported for relatively small areas near large cities. Since large, regional surveys have not been carried out, there are large uncertainties about effects on a regional level. The high concentrations of gaseous pollutants, especially within and near the cities, are likely to have severe effects on human health as well as on materials and vegetation. Several field and laboratory studies, as well as computer simulations, indicate that acidification of soil and soil water has occurred in the past few decades. This has probably caused elevated concentrations of toxic aluminum in soil water. At present, the toxic effect of Al is likely to be counteracted by high concentrations of calcium at many places. The Chinese authorities have recognized air pollution and acid rain as serious environmental problems, however, there are difficulties in implementing effective measures to reduce the problems. With respect to ecological effects we lack a comprehensive regional overview of the extent of the acid deposition problem in China. Such information is necessary before effective countermeasures can be developed.