Single-particle characterization of four aerosol samples collected in ChunCheon, Korea, during Asian dust storm events in 2002

Abstract

A single-particle analytical technique, named low-Z particle electron probe X-ray microanalysis (low-Z particle EPMA), employing an ultrathin window X-ray detector and enabling the quantitative determination of even low-Z elements such as C, N, and O, was applied to characterize "Asian dust" samples, collected in ChunCheon, Korea, during four Asian dust storm events on 21 March, 9 April, 17 April, and 11 November in 2002. In this study, it is demonstrated that single-particle analysis using the low-Z particle EPMA provides detailed information on various types of chemical species in the samples. The most abundantly encountered particles, both in coarse and fine fractions, are soil-derived particles such as aluminosilicates and silicon dioxide, except for the sample collected on 11 November 2002, where reacted CaCO 3 particles are the most abundantly encountered. All four samples are found to have experienced chemical modifications during long-range transport because the samples contain a significant number of particles composed of chemical species, such as nitrate and sulfate, which resulted from atmospheric reactions of CaCO 3 and sea-salt particles. This finding implies that CaCO 3 and sea-salt particles reacted with sulfur and nitrogen oxide species during long-range transport. The sample collected on 11 November 2002 experienced the most extensive chemical modification during its transport. For this sample, the overall relative abundances of reacted CaCO 3 and reacted sea-salt particles are 29.9% and 23.2%, respectively. In addition to the observation of the reacted CaCO 3 and sea-salt particles, reacted K-containing particles are also encountered in this sample. In this work, it is observed that chemical modification of sea-salt particles was more extensive than that of CaCO 3 particles. By considering the relative abundances of nitrate- and sulfate-containing particles, nitrate formation from CaCO 3 and sea-salt particles in the air is found to be more favorable than sulfate formation. Copyright 2005 by the American Geophysical Union.