Sources of sulfate in winter aerosols over the Sea of Japan, as inferred from selenium composition

Aerosol samples were collected in winter at the Mikuni and Mihonoseki sites facing the Sea of Japan and analyzed for non-sea-salt sulfate (nss-SO42−), Se(IV) and Se(VI). Episodes of a high nss-SO42− concentration were observed 5 times during the observation period of 14 days. Based on the weather conditions as well as the Se/Snss-SO42− and Se(VI)/Se(IV) ratios, these episodes could be classified into three types, i.e., continental-coal, local-coal and local-petroleum types. The continental-coal type was characterized by the high Se/Snss-SO42− (5.0–7.6×10−4) and high Se(VI)/Se(IV) ratios (6.9–8.9). It was produced by a long-range transport of aerosols originating from coal-combustion sources in the Asian Continent. The local-coal type was due to aerosols from local coal-combustion sources around the observation sites together with high Se/Snss-SO42− (3.9×10−4) and low Se(VI)/Se(IV) ratios (0.2). The local-petroleum type was accompanied by low Se/Snss-SO42− (2.4×10−4) and low Se(VI)/Se(IV) ratios (3.3) and it was caused by aerosols from local petroleum-combustion sources. The boundary of the Se(VI)/Se(IV) ratio between continental and local types would be around 2.