Wet deposition monitoring was conducted at six rural stations in western Japan, during the period from 1987 through 1996. Long-term trends in the concentration of non-sea salt ions were analyzed on the basis of the data obtained. The monitoring results indicated that annual average concentrations of NO3- and NH4+ in precipitation significantly increased on the order of 45%, and that of nss-Ca2+ and nss-SO42-, concentrations did not change over the past 10 years. The ratio of NO3-/nss-SO42- in precipitation significantly increased, the ratio of NO3-/NH4+ showed no marked fluctuations, and the ratio of [nss- Ca2++NH4+]/[nss-SO42-+ NO3-] slightly increased during the period. These findings suggested that the wet deposition of NO3- and NH4+ in western Japan, particularly that in the winter season, was influenced by the long-range transport of nitrogen oxides and ammonia from the Asian continent.
ASJC Scopus subject areas