Measurement of the 210Po/210Pb activity ratio in size fractionated aerosols from the coast of the Japan sea

The seasonal variation of the 210Po/210Pb activity ratio in aerosols, as a function of particle size, have been studied at Kamo, on the west coast of Japan from July 1995 to June 1996. It was shown that 70% of 210Po and 77% of 210Pb activities were measured in aerosols with a diameter smaller than 0.7 μm. On the other hand, the abundances of 210Po and 210Pb in aerosols with a diameter larger than 10.9 μm were 3 and 1%, respectively. In general, the maxima of the 210Po/210Pb ratio were observed in aerosols of 5.4–10.9 μm, but the maxima in January and April 1996 appeared in the largest and the smallest size fractions, respectively. The results suggest that the size distribution of the 210Po/210Pb activity ratio may be modified by changes in the nature and intensity of aerosol sources.