It is mainly SO{sub}2 that bring about acid rain in China. Changchun City, which is located in Northeast China, is a typical city that is polluted by SO{sub}2 from coal combustion in winter. In winter, the daily mean concentration of atmospheric SO{sub}2 is about 0.10mg/m{sup}3 and about 5 times as high as in summer, and the daily highest concentration usually appears in daybreak and nightfall. The monitored lowest pH value of rainwater was 4.8 in spring and the range of pH value of rain /snow was 5.2-6.0 in winter, 4.8-5.8 in spring, 5.4-6.4 in summer, 5.6-6.4 in autumn, and the annual mean pH value of rainfalls was 5.8 (1999-2000). Because the alkaline aerosol from soil, meteorological conditions etc., is unfavorable to acid rain formation, even though high SO{sub}2 emission intensity existed in winter, the acid rain did not appear obviously. The aerosol character, climate conditions in Northeast China are important factors for the acid rain formation, although SO{sub}2 emission is the original cause.
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