Measurements of number-, mass-, and volume-size distributions of' free tropospheric aerosols were made over Japan in the spring of 1991-1994. Number-size distribution frequently shows a peak in the area of a diam eter of D� 1 11.m in the free troposphere during observational periods. A few peaks are identified in the volume-size distribution as estimated on the basis of number-size distribution having single mode in a coarse range. Mass-size distribution frequently indicate enhancement in the

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... arse size range. This feature of the distribution is more frequent in those measurements made at 4.4 (±0.3) km than those at 2.3 (±0.3) km. On the basis of a backward trajectory anal)rsis of an air mass containing those particles, soil particles originati11g in the Asian continent affect the features found in the size distributions as well as vertical change in those size distributions. (