Using the PIXE method to evaluate the characteristics of aerosols in Kumamoto City, Southwestern Japan, from March 2004 to March 2007

Abstract

Recently, atmospheric particles, including Asian dust, have attracted considerable attention because of their potential effects on the environment and human health. From March to May, a huge volume of Asian dust is whipped up over China and carried to Japan by the westerly winds. In this study, we analyzed the elemental compositions of 72 aerosol samples collected biweekly in Kumamoto City from March 2004 to March 2007, to investigate the characteristics of Asian dust. The mass concentrations of the aerosol in Asian dust events were 1.5 times higher than non-Asian dust events. The concentrations of elements were determined by the Proton Induced X-ray Emission (PIXE) method. Concentrations of Si, Al, Fe, Ca, Ti, Mg and K in Asian dust events were 2.3, 2.0, 2.0, 1.6, 1.6, 1.5 and 1.4 times higher than those in non-Asian dust events, respectively. These elements are considered indicators of a soil-derived fraction. The concentrations of the soil-derived fraction were calculated, assuming that the Al concentration in the soils is 7%. The predicted mean concentration of the soil-derived fraction in Asian dust events (16.92 μg·m−3) was twice that in non-Asian dust events (8.39 μg·m−3). Moreover, in Asian dust events, the soil-derived fraction was the main component in aerosols and accounted for 43% of the total aerosol mass.