Concentration variation and relationship between concentrations of major ionic constituents in fog water and precipitation near the summit of Mt. Yahiko in Japan

Abstract

In order to learn about the concentration variations and relationship between concentrations of major ionic constituents in fog water and precipitation, fog water and precipitation were collected near the summit of Mt. Yahiko (634 a.s.l.), which is located in the western part of the Niigata Plain in Japan, from the end of May through the end of December, 2001, and the major ion constituents were measured. The concentrations of all measured constituents in fog water were higher than those in precipitation, and a significant difference was observed in the concentrations of NH₄⁺, nss-SO₄^2-, NO₃^- and sea salt components, contrasting with relatively small differences in those of nss-Ca²⁺ and others. The concentrations of sea salt components, such as Na⁺, Cl^-and Mg²⁺ in fog water increased when a cold air mass was above the Sea of Japan; however, the concentrations in precipitation did not always increase at the same time. The concentrations of nss-SO₄^2-, NO₃^-, NH₄⁺ and nss-Ca²⁺ in fog water and precipitation varied depending on the amount of collected fog water, precipitation depth, meteorological conditions and the influence from emission sources in Japan and overseas. A high correlation was not observed between the concentrations in fog water and those in precipitation, especially in the NH₄⁺ concentration. The median of equivalent ratio of NO₃^- to nss-SO₄^2- in fog water is 1.75 and 0.49 in precipitation. This suggests nitric acid contributes more to the acidification of fog water than sulfuric acid.