Abstract
Information of the chemical properties of rain fallen during the Asian dust (AD) event will help us to better understand the wet scavenging processes of dust particles. In this study, the chemical characteristics of rainwater and individual raindrops fallen during the AD storm have been investigated. The yellowish rainwater and individual raindrops were collected simultaneously in Kyoto, Japan on 7 April 2001. Particle induced X-ray emission (PIXE) was employed in the determination of chemical properties of soluble and insoluble fractions of rainwater. In addition, micro-PIXE was applied to the chemical analysis of residual materials retained in the initial individual raindrops. The pH level of yellowish rainwater was measured around 6.7. In compliance with the general expectation, major components in rainwater were of soil-origin such as Si, K, Ca, Ti and Fe. These soil-related components contributed to as much as 92% of total elemental composition in both soluble and insoluble fractions. By scanning a micro-beam, the residual particle cluster in individual raindrops was reconstructed in terms of an elemental map. This visualized elemental map in fact enabled us not only to estimate the chemical mixing state of raindrop residual particles but also to presume the wet scavenging of dust particles by rainfall.
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