The wet deposition of acid and some major ions over the Japanese Archipelago

Abstract

The wet deposition of acid and some major ions over the Japanese Archipelago was presented. The country was divided into 15 climatic regions with 114 grid squares, and the annual and seasonal fluxes of non-sea salt sulfate, nitrate, ammonium and non-sea salt calcium were estimated. Wet deposition fluxes were determined from CRIEPI’s regional monitoring data at 21 sites between October 1987 and September 1990. The concentration of these ions in precipitation increased during the cold season, and this tendency was noted on the northwestern region facing the continent across the Japan Sea. Estimated wet deposition of [nss-SO₄²⁻]+[NO₃⁻], here defined as the acidic component (AC), was approximately 75 meq m⁻² yr⁻¹, and that for [NH₄⁺]+[nss-Ca²⁺], here defined as the basic component (BC), was approximately 52 meq m⁻² yr⁻¹. If the concentration difference of AC − BC was converted to the wet deposition of H⁺, it was approximately 23 meq m⁻² yr⁻¹, or the total deposition over the Japanese Archipelago was approximately 17 Geq yr⁻¹. For Japan as a whole, wet deposition of inferred H+ in the warm season and the cold season accounted for 45% and 55%, respectively. In the warm season, the major receptor of acid was the climate regions facing the Pacific Ocean, while in the cold season it was the climate regions facing the Japan Sea. The wet deposition over the Japanese Archipelago was influenced by two factors: meteorological conditions such as the wind system and rainfall pattern due to Asian monsoons, and the geographical distribution of emission sources of chemical substances through natural and anthropogenic activities in East Asia. It was suggested that in-flow of chemical substances from outside the region plays an important role in the wet deposition field over the Japanese Archipelago.