Acid Particle Formation and Their Effects on Acidification of Rain

本研究调查了以下三个研究对象。1) SO_2气体中硫酸颗粒的形成及其转化率：利用流动型雾霾室研究了SO_2气粒转化为硫酸颗粒的过程。测定了颗粒总数浓度和粒径分布。收集到核孔过滤器上的硫颗粒的数量通过PIXE分析来估计转化率。还研究了二甲硫醚形成气溶胶粒子的过程。SO_2和DMS对颗粒的转化率分别为10^<-2>和10^<-4>h^<-1>数量级。2)雨水对大气气溶胶的清除作用：降雨开始后每0.1mm收集一次雨滴。雨水通过0.2 μ m孔径的过滤器，分为可溶组分和不溶组分。用离子色谱法测定溶质组分中的离子浓度。用pixie法测定了两组分的元素浓度。降雨前和降雨期间采样的大气气溶胶元素浓度也通过PIXE分析进行了测量。几乎所有的S和Cl都溶解在雨水中。主要来源于土壤的铁、钛、硅以不溶态被清除。3)气溶胶颗粒湿扫的数值模拟：建立了模拟气溶胶颗粒湿扫的数值模型。研究了粒径分布和降雨强度对气溶胶颗粒冲刷的影响。铁、钛、硅元素主要存在于大于1.0 μ m的粗颗粒中，被有效清除。另一方面，主要由细颗粒组成的S和Pb不容易被冲走。建立了考虑SO_2-to-SO_4^<2->转化及SO_2和SO_4^<2->干湿沉积的五层拉格朗日模型。

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.