Identification of chemical states of acidic atmospheric aerosols and sensitivity analysis of rainwater acidification by microscopic model

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Mixing thin film was prepared on a Nuclepore filter by dual vacuum deposition of barium chloride and nitron in order to detect the mixing states of sulfate and nitrate in individual aerosol particles. Applicability was examined using sulfate and/or nitrate particles generated by a nebulizer. The mixing thin film method was applied to detect the mixing states of atmospheric aerosols collected by Andersen samplers at Uji in summer and winter seasons. In winter, internally mixed sulfate-nitrate particles were not detected, while internally mixed particles were found to be a few percent in number concentration to the total particles collected on each stages of the sampler in summer.We have applied the depth selective XAFS spectrometry using SR to determine the chemical states of sulfur and silicon in atmospheric aerosols sampled at Uji and Sakurajima. X-ray fluorescence yield (XFY) and total electron yield (TEY) was measured simultaneously. Most of aerosol samples showed only S^<6+> peak a … More nd no other peaks were detected except one sample collected at Sakurajima, which indicated that the particles consist of S^<6+> sulfur atoms (sulfate) and their surfaces contain both S^<6+> and S^<2-> chemical species. X-ray absorption spectra of atmospheric aerosols sampled at Sakurajima showed two peaks. One is for Si^<4+> and the other lies between Si^<4+> and SiO.The former peak comes from SiO_2 and the latter one is considered to be attributable to chemical shift in the Si K-edge of silicate minerals.One-dimensional and time-variant model was presented for simulating below-cloud scavenging of gaseous and particulate matters. The model includes size distribution of raindrops, gas absorption, particle capture and aqueous chemical reactions in rainwater. We analyzed quantitatively the effects of below-cloud acidification on precipitation chemistry at ground level. Contribution of aerosols to sulfate and nitrate concentrations in rainwater was extremely small in our calculation conditions. Simulation results of S(VI) and Ca_2^+ concentrations (C) in rain at ground level indicated that C/r-dependence (relation between C and raindrop radius) was different after long precipitation times. The difference can be explained by the fact that Ca_2^+ in rain attributes from the scavenging of coarse calcium particles, while aqueous-phase oxidation of SO_2 is the major contribution to S(VI) in rainwater. Less