Abstract
The influence of soil dust transported from Asian continent by Kosa phenomenon on the atmosphere in Japan was investigated using analytical results of NASN (National Air Surveillance Network) for 10 years periods from 1977 to 1987. The NASN has 15 sampling stations, Sapporo, Nohoro, Sendai, Niigata, Tokyo, Kawasaki, Nagoya, Kyoto-hachiman, Osaka, Amagasaki, Kurashiki, Matsue, Ube, Chikugoogori, and Omuta in Japan, at which aerosols have been regularly collected every month and the collected samples have been analyzed by NAA (Nutron Activation Analysis) and XRF (X-ray Fluorescence).
High concentrations of Al and Ca in the atmosphere were observed in all sampling stations in NASN every spring from March to May when Kosa phenomenon was observed in Japan. The concentrations of Al and Ca in the atmosphere during Kosa period were 2 to 6 times higher than those during non Kosa period. The concentration ratios between Ca and Al (Ca/Al) in metropolitan and industrial areas slightly decreased during Kosa period, while the concentration ratios (Ca/Al) in local areas increased during Kosa period, so that the concentration ratios (Ca/Al) at 15 sampling stations in NASN were centered at a narrow range during Kosa period in comparison with these ratios during non Kosa period. This fact indicates that aerosols in each city in Japan were widely influenced by soil dust transported by Kosa phenomenon and the concentration ratio (Ca/A1) in the atmosphere during Kosa period was closed to the concentration ratio (0.82-0.85) of the transported soil dust.
The contribution of soil dust transported by Kosa phenomenon to the total soil dust in each city in Japan was 56-80%, and its average value was 68%. The calculated deposition amount of transported soil dust to each city was 0.4-2.3 ton/km2·month. It was found that the western part of Japan, especially Kyushu area, was strongly affected by Kosa phenomenon judging from the deposition amount of the transported soil dust.
