Long range transport of sulfur compounds over the western North Pacific: Deposition samples obtained on Islands

Continuous sampling of deposition and determination of chemical species in it were performed at two small, less populated and less industrialized islands in the Pacific Ocean, southern part of the Japanese islands, in order to evaluate the deposition amount over the Pacific. The chemical characteristics of the deposition on both islands were mostly maritime in nature, with some non-seasalt sulfate (nss-sulfate), non-seasalt calcium (nss-calcium), ammonium and a small amount of nitrate. At Amami O-shima (Naze), the ratio of nss-calcium to total calcium was found to be higher than that of Hachijo-jima, indicating some influence of crustal materials. The seasonal trend of the deposition amount of nss-sulfate was found to be similar at both islands, i.e., high during winter to spring and lower during summer to autumn. The net deposition amount of nss-sulfate was a little lower at Naze than at Hachijo-jima, depending upon the net precipitation amounts of both sites. Considering meteorological conditions, it was suggested that significant parts of the deposition amounts of nss-sulfate and nss-calcium at both islands were under the influence of the Asian Continent, though in the case of Hachijo-jima, some of the pollution might be due to the western part of Japan.