A case study of the size-resolved individual particles collected at a ground-based site on the west coast of Japan during an Asian dust storm event

To investigate the nature of individual Asian dust storm particles, an intensive field measurement was carried out on the west coast of Japan during a dense Asian dust storm event in March 2002. The giant particles (>5 μm) marked 124 times higher number concentration in the Asian dust storm event than in a non-Asian dust storm period. For the quantification analysis of the ultratrace elements in the size-resolved individual particles, an X-ray microprobe system equipped with super photon ring-8 GeV (SPring-8) BL-39XU was employed. By using this SPring-8 system we could successfully carry out the reconstruction of elemental maps and the quantification analysis of multiple elements in individual particles. The mass of Si showing the maximum value in individual particles was varied in the range from 1.2×10−2 pg to 1.1×100 pg with median 1.4×10−1 pg. In the case of S, mass ranged from 1.6×10−2 pg to 6.7×10−2 pg with median 3.9×10−2 pg, while several minor trace elements like V, Cr, Cu, and Zn show relatively low masses. A strong particle-size dependency of elemental masses was found for all elements, in particular the elemental masses of soil-derived components showed the monomodal maximum values around 2.05–5.07 μm particle size. From the X-ray, fluorescence images replayed corresponding to individual particles, we could simply categorize the visualized particles into two groups, namely internally mixed particles and externally mixed particles. From the factor analysis with variables of each elemental mass in individual particles, 79% of total particle population was found to be modified by sea-salt and sulfur.