Characteristics of Fog and Fog Collection with Passive Collector at Mt. Oyama in Japan

Fog is formed frequently in mountain areas and is apt to cause forest decline, because fog has highly concentrated air pollutants and is readily acidified. The elucidation of the fog characteristics in the areas has been limited because successive observation is difficult in mountains. We have observed wet depositions and meteorological conditions at Mt. Oyama, located about 56 km west–southwest of Tokyo. The mountain meteorology was observed with various devices and the fog frequencies dependent on the altitude were roughly estimated from the meteorology of the base of the mountain. The precipitation amount of the throughfall at the mountain is much larger than that of rainfall, and the large deposition on the canopy is caused by not only fog but also drizzle. Fog and drizzle sample was collected by string-type passive fog collector, PFC, and the meteorological data relating to the collecting rate of PFC sample were observed. PFC samples were affected by rainwater under windy condition and the contribution of the rain to the PFC sample volume was evaluated to be about 30% in average. The sampling rate of PFC was related to the precipitation intensity of throughfall, and it became possible to estimate the air pollutants deposition on the canopy via wet deposition by the analysis of the samples of PFC as well as rain. The fog and drizzle may cause several times larger deposition of air pollutants on the canopies than the deposition via rain at high mountain forest.