Variation of chemical composition of the atmospheric aerosol in Japan by Kosa phenomenon

Abstract

Dust originating in China continent is transported to Japan every spring. It is the wellknown Kosa (“yellow sand”) phenomenon. We collected samples of Kosa suspended in the atmosphere at five sites in Japan, Nagasaki, Okayama, Nagoya, Niigata, and Yokohama, in 1980 and 1981. The chemical composition and size distribution of these samples were measured in order to investigate the origins and physical and chemical properties of Kosa.
In 1980, remarkably big Kosa phenomena were observed twice, in April 20-23 and May 5-7, in Japan. During these Kosa periods, coarse particle (>2 μm) concentration in the atmosphere was more than 200 μg/m³, 4 to 7 times higher than that during non-Kosa periods. Therefore the size distribution of Kosa transported was predominantly coarse mode.
As the result of elemental analysis of Kosa samples by X-ray fluorescence methods, it was found that the concentrations of soil-origin elements such as Al, Si, K, Ca, and Fe in coarse particles were greatly increased during Kosa periods, but those of anthropogenic elements such as Cu, Ni, Zn, and Pb were remained unchanged. Judging from the high concentration of Ca in Kosa samples, the origin of Kosa seems to be deserts of Taklamakan and Gobi, whose soils are enriched with Ca.
An interesting fact was also found during Kosa periods, that is, the concentration of particulate sulfur in coarse particle increased, but that in fine particles decreased. However, the size distribution of sulfur in the atmosphere was usually fine mode during non-Kosa periods. The decrease of sulfur dioxide in the atmosphere was also observed during Kosa periods at each sampling sites. It can be explained by the meteological factor that a strong air flow from the moved air mass is generally occurred during Kosa periods. The increase of sulfur in coarse particles observed during Kosa periods is considered to be due to the finding that the transported Kosa itself contains much sulfur because the desert soil is abundant in CaSO₄ by calcification.