An Observation of Washout Ratios of Some Major Ion Species in Precipitation in the Yahiko-Kakuda Mountains Area in Niigata, Japan

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The major ion species (Na+, nss-S042-, NO3-, NH4+, nss-Ca2+) in precipitation, which was collected at the top (620m a.s.l.) and foot (47m a.s.l.) of the Yahiko-Kakuda mountains area in Niigata, Japan, were measured. The washout rates of the ion species between the top and foot of the mountain were calculated for non-snowy and snowy seasons from the differences in deposition fluxes between the two sites. The atmospheric concentrations of gas and aerosols were also measured at the top of the mountain, and the washout ratios (W, W=Cprecipitation/Cair in which Cprecipitation and Cair are the ion concentrations (mg/kg) in precipitation and in the air (mg/kg) at ground level, respectively) were calculated for the two seasons separately, in order to discover the precipitation scavenging above the top of the mountain. It was estimated that about 30% of Na+ in precipitation collected at the foot of the mountain is incorporated to precipitation between the top and foot of the mountain. Little amount of nss-SO42- is incorporated between the two sites both in non-snowy and snowy seasons, in contrast a large amount of nss-Ca2+ is incorporated in both the seasons. The washout ratios for Na+, nss-SO42-, and NH4+ in precipitation collected at the top of the mountain showed higher vales in the snowy season than the non-snowy season, while there was little difference in those for nss-Ca2+ and NO3- between the two seasons.
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