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 (NO₃^-) and sulfate(SO₄^2-) found in coarse particles were related with the particle size. In consequence of quantitative analysis, it became clear that both NO₃^- and SO₄^2- distributed mostly in a surface layer of Kosa particles. It is satisfactory to consider NO₃^- as being due to Ca(NO₃)₂ formed by the reaction of HNO₃ of the atmosphere and Ca contained in Kosa particles. On the other hand, we can conclude that SO₄^2- is due to fine (NH₄)₂SO₄ particles absorbed on the surface of the Kosa particles.

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A new batch type electrical mobility analyzer, or electrical sedimentation particle sizer, has been developed and the basic performance has been evaluated. Two types of electrical sedimentation cells, with concentric cylinder electrodes and parallel disk electrodes, are constructed and evaluated. It was found that the size distribution of sodium chloride particles measured by these cells agreed well with that measured by the conventional DMA (Differential Mobility Analyzer). Since this method measures particles in a closed sedimentation cell, it is advantageous for measuring aerosol particles which fluctuate in size and number concentration with time.

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