Conversion of SO2 to particulate sulfate during transport from China to Japan - Assessment by selenium in aerosols -

Abstract

To examine transportation and oxidation states of sulfur compounds from China to Japan, the SO2 concentration in the atmosphere and the nss-SO42- concentration and selenium (Se) concentration in aerosols were observed at four sites in western Japan. High SO2 concentrations in the atmosphere and the nss-SO42- concentration and Se concentration in aerosols were found when the air mass passed through the planetary boundary layer (PBL) over large cities or industrial areas in China during winter with winds from the northwest. A bibliographic survey of Se and S concentrations in aerosols over eastern Asia during 1991-2004 revealed that the average Se and S concentrations in aerosols at seven sites of urban or industrial areas in China were, respectively, 15.7 ng/m3 and 7.4 μg/m3. The S concentration and Se concentration in aerosols in China were, respectively, about 3 times and 10-20 times higher than those of Korea and Japan. The Se/S ratios of aerosols in China were higher (avg. 2.5 × 10-3) than that of Korea (avg. 0.6 × 10-3) or Japan (avg. 0.7 × 10-3). The SO2 conversion rate was ascertained as 0.1% h-1 to 1.5% h-1 using the Se(sum)/S ratio technique, when the air mass passed over large combustion sources in China and later reached Japan. The Se/S (or its reverse) technique provides useful information to ascertain the SO2 to SO42- conversion rate. © Taiwan Association for Aerosol Research.