Acid Particle Formation and Their Effects on Acidification of Rain

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The following three research subjects were investigated in this study.1) Formation of sulfuric acid particles from SO_2 gas and its conversion rate :The gas-to-particle conversion of SO_2 to sulfuric acid particles was investigated using a flow-type smog chamber. The total number concentration and the particle size distribution were measured. The amount of sulfur particles collected onto the Nuclepore filter was determined by PIXE analysis to estimate the conversion rate. Aerosol particle formation from DMS (Dimethyl sulfide) was also investigated. The conversion rates of SO_2 and DMS to particles were estimated to be order of 10^<-2> and 10^<-4>h^<-1>, respectively.2) Scavenging of atmospheric aerosols by rain water :Rain drops were collected every0.1mm rainfall from the beginning of rain. Rain water was divided into the soluble and insoluble components by passing through a 0.2mum pore-size filter. Ion concentration in solbule components was measured by ion-chromatography. The elemental concentrations in both components were determined by PIXE analysis. Elemental concentrations of atmospheric aerosols sampled before and during the rain were also measured by PIXE analysis. Almost all of S and Cl were dissolved in rain water. Fe, Ti and Si which originate mainly in soil source were scavenged in insoluble state.3) Modeling of wet scavenging of aerosol particles :A numerical model simulating the wet scavenging of aerosol particles was developed. The effects of particle size distribution and the rain intensity on the washout of aerosol particle were investigated. Elements of Fe, Ti and Si are contained mainly in the coarse particles with the size larger than 1.0mum and are scavenged effectively. On the other hand, S and Pb consisting mainly of the fine particles are not easily washed out.A five-layr Lagrangian model taking into consideration of the SO_2-to-SO_4^<2-> conversion and dry and wet deposition of SO_2 and SO_4^<2-> was also developed.