Long-term trends in nitrate to non-seasalt sulfate ratio in precipitation collected in western Japan

Abstract

Precipitation monitoring was conducted at the six sites in western Japan during the period 1987–1996. The results indicated that the annual mean concentration of NO₃⁻ in precipitation generally increased at all sites during that period. As a result, the NO₃⁻/nssSO₄²⁻ ratio in precipitation significantly increased by 27–51% over the past 9 years. Since the 1980s, NO_x and SO₂ emissions in East Asia have rapidly increased. The increase rate for NO_x emissions in the region was larger than that for SO₂ emissions. Therefore, the results suggested that the contribution of HNO₃ to the acidity of precipitation in a large area in western Japan increased due to the changes in the emissions in East Asia.