Size-separated particulate matter samples were collected during the largest Kosa phenomenon in scale observed at Sakai, Osaka in 1990. Obtained samples were investigated by instrumental neutron activation analysis and ion chromatography. Concentrations of nitrate (NO
3-) and sulfate(SO
42-) found in coarse particles were related with the particle size. In consequence of quantitative analysis, it became clear that both NO
3- and SO
42- distributed mostly in a surface layer of Kosa particles. It is satisfactory to consider NO
3- as being due to Ca(NO
3)
2 formed by the reaction of HNO
3 of the atmosphere and Ca contained in Kosa particles. On the other hand, we can conclude that SO
42- is due to fine (NH
4)
2SO
4 particles absorbed on the surface of the Kosa particles.
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