Studies on Equivalent Ratio of Nitrate to Sulfate in Acid Precipitation

Abstract

Precipitation of atmosphric pollutants was collected by bulk type filtered acid precipitation sampler (Filtered sampler, Japan Environmental Agency type) in Japan from April, 1984 to Match, 1988.
Assum ing that precipitation acidity originates primarily from sulfuric and nitric acids, the equivalent ratio of NO₃^- to SO₄^2- (N/S ratio) was discussed in oder to assess the relative importance of their contributions to precipitation acidity. The ratio was higher in urban areas on Pacific Ocean coast ranging from Hiroshima to Sendai. Particularly, Musashino, Tokyo receives the heaviest deposition of NO₃^- (3.3 g°m^-2°y^-1) in the 29 stations, reflecting large amount of NOx emitted in Tokyo Metoropolitan, which resulted in the highest N/S ratio as well as lowest pH. In contrast, this ratio was lower on Japan Sea coast, from Kyoto to Hokkaido. This region was characterized by considerably large SO₄^2- deposition during winter months. In Toyama, for instance, SO₄^2- deposition amounted to as large as 8.4 g°m^-2°y^-1 as an annual mean. The N/S ratio-pH relations demonstrated that the potential contribution of SO₄^2- to acidity exceeded that of NO₃^2-, especially in Toyama and Ishikawa areas.