Characterization of Wet Deposition of Acid Precipitates along the Shore of the Japan Sea in the Northern Part of Honshu Island

Abstract

The characteristics of wet deposition of acid precipitates along the shore of the Japan Sea in the northern part of Honshu Island were investigated. Precipitation was sampled from January 1990 to December 1992 at two sampling sites in thewestern area of Yamagata Prefecture. Event sampling was done with wet-only collectors. In this area, the acidity of precipitation in winter was higher than that in summer. The acidification of precipitation in winter was mainly due to non-sea-salt-SO₄^2- (nss-SO₄^2-). Concentrations of NO₃^-in the precipitation did not show any conspicuous seasonal changes. In winter, the ratio of [NO₃^-]/[nss-SO₄^2-+NO₃^-] and that of [nss-Ca²⁺]/[nss-SO₄^2-+NO₃^-] in this area were consistent with those in northern China, while in summer they were consistent with those in eastern Japan. The analysis of weather charts at the time of precipitation in dicated that nss-SO₄^2-concentration and nss-Ca²⁺concentration of precipita tion due to the meteorological condition of typical winter and cold fronts were relatively high. These results suggested that the anthropogenic ions in this area mainly came from the Eastern Asian Continent in winter and from domestic sources in summer.