The chemistry of the severe acidic precipitation in Shanghai, China

Abstract

Seventy-six rain samples from forty-seven rain events and TSP aerosol samples throughout the entire year of 2005 were collected in Shanghai, China. The annual mean pH in rain was 4.49 with the lowest pH of 2.95, and the frequency of acid rain was 71% in 2005. The acidity of rain increased more than 15 times in the past 8 years compared to 1997. The volume-weighted mean ionic concentrations of the acidic ions, SO 4 2− and NO 3 − in rainwater were 199.59 and 49.80 μeq/L with maximum of 832.67 and 236.59 μeq/L, respectively. The concentration of SO 4 2− was higher than the most polluted cities abroad, indicating Shanghai has been a severe polluted city over the world. The high coal/fuel consumption from urbanization and the rapid increase of vehicles resulted in the high emission of SO 2 and NO x , the precursor of the high concentration of acidic ions, SO 4 2− and NO 3 −, which were the main reason of the severe acid rain in Shanghai. The major ions showed clear temporal variations with higher concentrations of SO 4 2−, NO 3 −, NH 4 +, and Ca 2+ in spring/winter, of Na +, Cl −, K +, and Mg 2+ in autumn, and the lowest of all the ions in summer. SO 4 2− and NO 3 − were mainly in the form of CaSO 4 and Ca(NO 3) 2, which showed the dominant neutralization effect of Ca 2+ over NH 4 +. Source identification indicated that SO 4 2−, NO 3 −, NH 4 + and most Ca 2+ derived from anthropogenic sources, K +, Mg 2+ and partial Ca 2+ originated from mineral, and almost all the Cl − and Na + from the sea. The chemistry of precipitation in Shanghai was under the influence of local pollution sources and the long- and moderate-range transport through back trajectory analysis.