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 delta S-34. 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 mu S/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 delta S-34 value of SO4 (2-) in precipitation ranged from +2.1 to +12.8aEuro degrees with an average value of +4.7aEuro degrees. The delta S-34 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 delta S-34 values in winter. Moreover, the delta S-34 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.