Chemical characterization of acid snowfall in the coast and inland areas of Akita Prefecture in Japan.

Abstract

To investigate the characteristics of chemical composition of precipitation, especially, of snowfall, samples were collected on a daily basis in Akita City(39°43'N, 140°08'E, 10m a.s.l)from April 1993 to March 1994 and in Yuzawa City(39°09'N, 140°30'E, 96 m a.s.l.)from January to March 1994. Ions such as H+(as pH), Na+, NH4+, K+, Ca2+, Mg2+, Cl-, NO3- and SO42- were analyzed for 185 samples collected at Akita and for 59 samples at Yuzawa. The pH values at Akita in the winter were lower than those of other seasons, this tendency was the same at other coastal cities of the Japan Sea. It was concluded that the source of acid in the snowfall was non-sea-salt (nss)-SO42-.It is well-known that the sea-salt concentration in the precipitation decreases exponentially with the distance from the coast; however, the sea-salt concentration in the winter precipitation at Yuzawa, which is located about 50 km to the east of the coast, occasionally did not show marked decrease in comparison with the case at Akita which is 6.5 km from the coast. It was likely that when the surface wind direction was nearly NW, Na+ and nss-SO42- were transported from Akita to Yuzawa; high Na+ concentrations at Yuzawa were mainly affected by the surface pressure pattern and the surface wind direction during snowfalls.