Chemical and sulfur isotopic composition of precipitation in Beijing, China

Zhu, Guangxu; Guo, Qingjun; Chen, Tongbin; Lang, Yunchao; Peters, Marc; Tian, Liyan; Zhang, Hanzhi; Wang, Chunyu

Chemical and sulfur isotopic composition of precipitation in Beijing, China

2016

China is experiencing serious acid rain contamination, with Beijing among the worst-hit areas. To understand the chemical feature and the origin of inorganic ions in precipitation of Beijing, 128 precipitation samples were collected and analyzed for major water-soluble ions and δ³⁴S. The pH values ranged from 3.68 to 7.81 and showed a volume weighted average value (VWA) of 5.02, with a frequency of acid rain of 26.8 %. The VWA value of electrical conductivity (EC) was 68.6 μS/cm, which was nearly 4 times higher than the background value of northern China. Ca²⁺ represented the main cation; SO₄²⁻ and NO₃⁻ were the dominant anion in precipitation. Our study showed that SO₄²⁻ and NO₃⁻ originated from coal and fossil fuel combustion; Ca²⁺, Mg²⁺, and K⁺ were from the continental sources. The δ³⁴S value of SO₄²⁻ in precipitation ranged from +2.1 to +12.8‰ with an average value of +4.7‰. The δ³⁴S value showed a winter maximum and a summer minimum tendency, which was mainly associated with temperature-dependent isotope equilibrium fractionation as well as combustion of coal with relatively positive δ³⁴S values in winter. Moreover, the δ³⁴S values revealed that atmospheric sulfur in Beijing are mainly correlated to coal burning and traffic emission; coal combustion constituted a significant fraction of the SO₄²⁻ in winter precipitation.

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