High sulfate and nitrate concentrations in precipitation at Nagasaki impacted by long-distant and local sources

Wet-only event-basis precipitation data at Nagasaki, the border area between the Asian Continent and Japan, with high non-sea-salt (nss-) SO2-4 and NO-3 concentrations from November 1983 through March 1988 were analyzed in terms of wind conditions at upper and surface levels to assess both long-distant and local sources. In order to investigate the high nss-SO2-4concentration events occurring with similar transport patterns, the wind conditions were grouped into the following three types: type 1, the upper air flow from the Asian Continent and the surface wind from the sea; type 2, the stagnant upper air and the surface wind from the land at and around Nagasaki; and type 3, the upper air flow from the Continent and the surface wind from the land. In the case of high NO-3 concentration events, their wind-condition types were similar to those for high nss-SO2-4 concentration events. These three types for both ions were discussed to estimate their sources as follows: type 1, long-distant sources in the Asian Continent; type 2, local sources at and around Nagasaki; and type 3, both long-distant and local sources. From the viewpoint of precipitation chemistry, the ratios of H+/(nss-SO2-4+NO-3) were evaluated for the high concentration events so as to examine the degree of neutralization of acidic input, H2SO4 and HNO3. High ratios events corresponded to wind-condition type 2 whereas low ratios were associated with types 1. This suggested that the acidic input from local sources were little neutralized to cause much higher acidity in precipitation than those from long-distant sources.