Analysis and Scavenging Effect of Acid Fog

Abstract

In mountainous sites, acid fog is formed very frequently and lasts long. We collected fog samples at the midslope of Mt. Ohyama in the southwest of the Kanto area using a stringtype collector. The pH, conductivity, and the concentrations of major ions (Cl^-, NO₃^-, SO₄^2-, K⁺, Na⁺, Ca²⁺, Mg²⁺, and NH₄⁺) were measured. Rain water and aerosol were also sampled in Mt. Ohyama and Yokohama city, analyzed, and compared with the fog data. The fog samples in this work ranged in the pH value from 2.61 to 7.00 and the me an value was 3.95. The high salt concentration as well as the high acidity in fogwater will cause serious environmental problems. The pH of fogwater is lower than that of rainwater and the equivalent concentration ratio of nitrate to sulfate is about unity in both fogwater and rainwater samples, while the ratio was much less than unity in the aerosol samples. The concentration ratio of chloride ion to sodium ion in fogwater was almost equal to the ratio in sea salt but sometimes it was much higher than unity because of absorbing gaseous hydrogen chloride. The ion concentrations in fogwater were high at the beginning Of a fog event, decreased with time, and increased again at the end of the event. It was ascertained that the air pollutants (acid gas, ammonia, and aerosol) absorbed in fogwater were scavenged rapidly because the ionic loadings in air decreased rapidly at the beginning of a fog event. The pollutants scavenged from air were loaded on the leaf and the earth surface as the droplets with high solute concentrations although their loading amounts were small.