Analysis of Japanese nationwide wet deposition dataset and comparison with recent observation

Abstract

Association of local governmental environment research institutes are conducting national wide acid rain monitoring survey since 1991. Precipitation samples were collected at more than 50 locations nationwide for net 19 year in the period of 1991-2015. Cations and anions concentrations are analyzed and monthly values are available from the database maintained by Center for Global Environmental Research, National Institute for Environmental Studies. Outliers such as pollution, probably by sample handling, and the influence of strong local emission sources are removed from this data set. A piper plot following the data representation of groundwater observation was suitable for characterization of the precipitation samples. The plots for cations and anions aligned along lines having sea salts end member and nationwide uniform slopes for magnesium to calcium and for nitrate to sulfate. The regionality, seasonality and secular trends are analyzed, mainly by the ratios of components. Since December 2018, we have collected daily precipitation and snowfall samples in Hirosaki and Goshogawara, Aomori. Cations and anions have been analyzed by ion chromatography. The observational data are compared with the national database and are analyzed focusing the information given by the daily sampling.