Regional characteristics of dry deposition of sulfur and nitrogen compounds at EANET sites in Japan from 2003 to 2008

The regional characteristics of estimated dry deposition and total atmospheric deposition, including dry and wet deposition, at 10 EANET sites in Japan from April 2003 to March 2008 are discussed. The components examined for dry deposition were sulfur compounds (SO2 and particulate SO42−) and nitrogen compounds (HNO3, NH3, particulate NO3−, and NH4+). Dry deposition was calculated by the product of the deposition velocity estimated by the inferential method for forest and grass surfaces and the air concentration of each compound. The 5-year mean annual dry deposition amounts for sulfur and nitrogen compounds were in the range of 5–37 and 7–50 mmol m−2 year−1, respectively. The regional characteristics of dry deposition amounts were similar between sulfur and nitrogen compounds, which showed higher deposition in the Sea of Japan side and in the Western Japan. The 5-year mean annual total deposition amounts for sulfur and nitrogen compounds were in the range of 28–77 and 22–130 mmol m−2 year−1, respectively. The contribution of dry deposition to the total deposition amounts was 10–55% and 13–56% for sulfur and nitrogen compounds, respectively. The regional characteristic of total deposition was different between sulfur and nitrogen compounds. Total deposition amounts in Japan were larger than those in CASTNET and EMEP because of high wet deposition, which implied that the increasing emissions of air pollutants in East Asia caused high atmospheric depositions.

Research highlights
► The regional characteristic of dry and wet depositions for S and N was discussed.
► Dry deposition in Japan was evaluated by the modified inferential method.
► The dry deposition was higher in the Sea of Japan side and the western Japan.
► Higher total deposition for S was possibly caused by transboundary air pollution.
► Dry and wet depositions in Japan were larger than those in CASTNET and EMEP.