エーロゾル粒子の洋上拡散にともなう粒径分布の変形

Abstract

When the aerosols originated on land are dispersed over the ocean, they are not only decreased in the concentration, but deformed in the pattern of size distribution. This deforma-tion was ascertained by the experiments aboard an observation ship in 1972 and 1974.Based on the mobility spectrometry of atmospheric ions using the apparata we have developed, and the concurrent size spectrometry of large particles using a Royco Optical Counter, the whole size distribution of aerosol particles covering the radius range from 3 nm to 4μm was determined over the cruising course of 1000 km from Tokyo.With the aid of the result of 222Rn concentration measurements, the effect of dilution associated with the spatial dispersion was estimated. Subtracting the dilution factor from the apparent decay rate of the aerosol concentration, the residence time of aerosols was determined in relation to the particle size.In both the expeditions in 1972 and 1974, the deformation of the size distribution was found to take place in such a way that the center of gravity of the distribution was shifted towards smaller size with the increasing age of aerosols.