2010 Volume 45 Issue 2 Pages 66-72
The impact of anthropogenic aerosols transported from East Asia on the summertime PM2.5 mass concentration in Japan was investigated, based on the results of intensive observations of airborne particulate matter from August 4 - 9, 2007, in Osaka. The mass concentration of PM2.5 was monitored by a β-ray absorption-based continuous monitor without any moisture control. The level of the PM2.5 mass concentration changed by 20-30 μg/m3 between the first and the second half periods, though the primary and secondary contributions from the nearest sources did not significantly change throughout the observations. The effect of the anthropogenic aerosols from East Asia was considered to be the major factor affecting the difference in the PM2.5 levels between the periods. Due to the effect of the East Asian aerosols, the mass concentrations of PM2.5 increased along with the water vapor concentration, seemingly because of the high hygroscopic constituents (i.e., ammonium sulfate). This kind of moisture dependence was not observed when the air masses were from the Pacific Ocean. East Asian anthropogenic aerosols directly affected the PM2.5 mass concentration by increasing the background levels, and indirectly by its more hygroscopic nature, when monitored by instruments without moisture control.
