Chemical speciation of individual atmospheric particles using low-Z electron probe X-ray microanalysis: characterizing "Asian Dust" deposited with rainwater in Seoul, Korea

Chemical speciation of individual microparticles is of much interest in env ironmental atmospheric chemistry; e.g. the determination of the elemental c oncentrations in individual atmospheric aerosol particles is important to s tudy the chemical behavior of atmospheric pollution. Recently, an EPMA tech nique using an X-ray detector equipped with an ultra-thin window, allowing EPMA to determine concentrations of low-Z elements, such as C, N, and O, in individual particles of micrometer size, has been developed. This techniqu e, called low-Z electron probe X-ray microanalysis (low-Z EPMA), is applied to characterize the water-insoluble part of "Asian Dust", deposited by was hout in the form of rainwater during an Asian Dust storm event and collecte d in Seoul, Korea. In this study, it was demonstrated that the single parti cle analysis using low-Z EPMA provided detailed information on various type s of chemical species in the sample. In addition to alumino silicates, sili con oxide, iron oxide, and calcium carbonate particles, which are expected to be present, carbonaceous particles are also observed in a significant fr action. This unexpected finding that particle sample originated from an and area contains significant amount of carbonaceous particles is supported by the investigation of a "China Loess" sample. In addition, we also performe d single particle analysis for a local soil sample, in order to check the p ossible influence from local sources on "Asian Dust". The characteristics o f the local soil particle sample, e.g. the types of aluminosilicate particl es and the abdundance of particles with deviating chemical species, are cle arly different from "Asian Dust" and "China Loess" samples, whereas those t wo are similar, implying that the "Asian Dust" sample was not much influenc ed by local sources. (C) 2001 Elsevier Science Ltd. All rights reserved.