Sulfate concentrations and sulfur isotopic compositions were measured in rainwater in Guiyang city in Southwest China between October 2008 and September 2009 to identify sulfur sources and their impacts on sulfur isotopic composition. The delta S-34 values of 1235 samples collected during this period ranged from - 12.0 to + 9.4 parts per thousand, with a volume-weighted mean of - 2.8 +/- 9.8 parts per thousand, suggesting that rainwater sulfate in Guiyang was mainly derived from SO2 produced during coal combustion. The delta S-34 values of rainwater sulfate increased from 1987 to 2009, with an increment of about + 0.16 parts per thousand per year, reflecting a gradual reduction in S-34-depleted SO2 emitted during coal combustion. Seasonal variations in delta S-34 values were pronounced, with higher values in winter than in summer. Long-distance transport of SO2 from coal burned in northern cities (which was higher than the component from southern cities), and more importantly, the aqueous oxidation of SO2 during transport affected the seasonal variation of rainwater delta S-34 values in Guiyang. Temperature-dependent aqueous oxidation of SO2 suggested that lower rainwater delta S-34 coincides with higher temperature. (C) 2014 Elsevier B.V. All rights reserved.