SEASONAL-VARIATION OF METHANESULFONIC-ACID IN THE ATMOSPHERE OVER THEOKI ISLANDS IN THE SEA OF JAPAN

Seasonal variation of methanesulfonic acid (MSA) in the atmosphere ove r the Oki Islands in the Sea of Japan was measured over a 9-year perio d. The results show that the Variation was strongly influenced by the primary production activity (e.g., phytoplankton) in the sea around th e islands. The MSA concentration ranged from 3 to 95 ng m(-3), which i s very similar to the previously reported data for islands at similar latitude, such as Norfolk Island and Cape Grim. The seasonal maximum. of the MSA concentration occurred in May or June, corresponding to the spring bloom of phytoplankton in the Sea of Japan. These maximum valu es differed from year to year, affected by the algal growth activity a nd the weather conditions (e.g. amount of rainfall) during the year. H igher densities of phytoplankton and higher MSA concentrations seemed to be related to the coldness of the air and to the deeper mixing of t he sea surface water that occurred during the winter just before that spring. The non-sea-salt (NSS)-sulfate concentration was significantly higher than the expected concentration originating from the dimethyls ulfate (DMS) decomposition in the atmosphere. This means that the anth ropogenic sulfur compounds considerably contributed to the NSS-sulfate concentration on this island. The seasonal variation of MSA clearly d iffered from that of the atmospheric methylarsenic compounds (which ma y be produced biologically in the sea and then released into the atmos phere), suggesting differences in their sources and production mechani sms.