Seasonal variation of methanesulfonic acid in the atmosphere over the oki islands in the sea of ] Japan

Seasonal variation of methanesulfonic acid (MSA) in the atmosphere over the Oki Islands in the Sea of Japan was measured over a 9-year period. The results show that the variation was strongly influenced by the primary production activity (e.g., phytoplankton) in the sea around the islands. The MSA concentration ranged from 3 to 95 ng m−3, which is 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 values differed from year to year, affected by the algal growth activity and the weather conditions (e.g. amount of rainfall) during the year. Higher densities of phytoplankton and higher MSA concentrations seemed to be related to the coldness of the air and to the deeper mixing of the 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 dimethylsulfate (DMS) decomposition in the atmosphere. This means that the anthropogenic sulfur compounds considerably contributed to the NSS-sulfate concentration on this island. The seasonal variation of MSA clearly differed from that of the atmospheric methylarsenic compounds (which may be produced biologically in the sea and then released into the atmosphere), suggesting differences in their sources and production mechanisms.