An analysis of chemical composition of different rain types in `Minnan Golden Triangleʹ region in the southeastern coast of China

The pollutants from anthropogenic activities can affect precipitation composition and subsequently affect aquatic and terrestrial ecosystems. Here, we reported the results from the simultaneous collection and chemical analysis (including F−, Cl−, NO3−, SO42−, HCOO−, CH3COO−, Na+, NH4+, K+, Ca2+, Mg2+, pH) of spring rain, mold rain and typhoon rain during 1990 and 1991 in the region of Xiamen, Quanzhou, Zhangzhou and Tongan, which is called `Minnan Golden Triangleʹ and is a rapidly growing urban area in the southeastern Coast of China. It was found that the average pHs of spring rain, mold rain and typhoon rain in 1990 in this region were 4.51, 4.93 and 5.14, respectively. Obviously, the spring rain was the most acidic in the three types of rains in this region. The average concentrations of formic and acetic acids in Xiamen mold rain were 5.67 and 2.91 μeq/l, respectively, and the average maximum contribution of organic acids to free acidity was in the range of 2.8% to 100% (average 66.3%). The regression equations between acidity and ions showed that SO42, NO3−, NH4+ and organic acids (formic and acetic) made the major contribution to the precipitation acidity in this region. The chemical characteristics of different precipitation types in this region indicated that spring rain had the character of continental origin, but the mold rain and typhoon rain had more effects from ocean. Since spring rain, mold rain, and typhoon rain were caused by precipitation cloud approaching to this region from different directions and had different acidity, and the average pH of cloud rainwater on the mountain site was 4.90, it is suggested that acid rain in this region might be mainly caused by long-range transport of pollutants from the southern Chinese mainland, and the local pollution sources were less as significant.