Chemical and sulfur isotopic composition of precipitation in Beijing, China

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; SO4 2− and NO3 − were the dominant anion in precipitation. Our study showed that SO4 2− and NO3 − originated from coal and fossil fuel combustion; Ca2+, Mg2+, and K+ were from the continental sources. The δ34S value of SO4 2− 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 SO4 2− in winter precipitation.