Sulfur isotopic composition and source identification of atmospheric environment in central Zhejiang, China

Sulfur dioxide and sulfate aerosols in the atmosphere are significant factors leading to acidification of the atmospheric environment and worsening the pollution of acid deposition. Because of the fingerprint characteristics of the stable sulfur isotopic composition, sulfur isotope has been widely adopted in environmental researches concerning sulfur cycle and source identification. In this study, the atmospheric environment of Jinhua City, central Zhejiang Province, was continuously monitored, and the sulfur isotopic composition of SO(2) and sulfate aerosols in the atmosphere was analyzed. The results indicate that the variation of delta(34)S values for SO(2) ranges from 1.0 parts per thousand to 7.5 parts per thousand, and annual average is 4.7 parts per thousand +/- 2.3 parts per thousand, whereas that of sulfate aerosols ranges from 6.4 parts per thousand to 9.8 parts per thousand, and annual average is 8.1 parts per thousand +/- 1.0 parts per thousand. The delta(34)S values for SO(2) have significant seasonal variations, which are 7.0 parts per thousand in winter and 3.3 parts per thousand in summer. These variations cannot be attributed to a single factor, and we suggest a temperature-dependent isotope equilibrium fractionation and elevated biogenic sulfur emissions of isotopically light S in summer may be the main controlling mechanisms. Furthermore, we also discuss the delta(34)S model of atmospheric SO(2) oxidation to form sulfate, and suggest that heterogeneous oxidation dominates in the oxidation reactions of atmospheric SO(2) in the central Zhejiang Province. We further suggest that the relative humidity in the atmosphere plays an important role in the oxidation mechanism of atmospheric SO(2).