Chemical Composition of Fog Water near the Summit of Mt. Norikura in Japan

Abstract

Chemical measurements of fog water have been made near the summit of Mt. Norikura (altitude 2770m) in central Japan, during the summer and autumn from 1994 to 1996. Highly acidic fogs (pH<4) were observed both in the summer and autumn. The SO^2-₄ was the most dominant anion in fog water. The [SO^2-₄]/[NO^-₃] equivalent ratio was much less than that measured in the 1960s. The results may reflect the difference between the characteristics of air pollution in Japan during the 1960s, and that of the 1990s.
The ratio of [SO^2-₄]/[NO^-₃] in the fog water was significantly higher during the summer than in autumn. In addition, the [Cl^-]/[Na⁺] ratio was much higher than that of seawater in the summer. The non-sea-salt Cl^- also seems to contribute to the fog water acidification. The ratio of the summertime [NH⁺₄]/[SO^2-₄] was also higher than that in the autumn. A relatively high pH (pH>6) of fog water was observed, despite the high concentration of SO^2-₄ during July 1994. The hydrogen peroxide (H₂O₂) concentration during the summer varied over a range of 3-180μM, with an average concentration of 60μM. Relatively high concentrations of H₂O₂ (60-70μM) were observed, even in the autumn.