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The aerodynamic size distributions of Pb-214, Pb-212, Pb-210 f Be-7, P-32, S-35 (as SOj}~), and stable SO §~ were measured using cascade impactors. The activity distribution of Pb-212 and Pb-214, measured by alpha spectroscopy, was largely associated with aerosols smaller than 0.52 urn. Based on 46 measurements, the activity median aerodynamic diameter of Pb-212 averaged 0.13 im (

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A comparative study of the seasonal variations of cosmic-ray produced Be-7 and fission product Cs-137 has been carried out in the surface air at Bombay and other stations in India. The resulta show that both isotopes attain peak values during the spring months of March-April. However it is obaerved that the amplitude of increaae is much lees in the caae of Be-7 compared to stratospheric Cs-137. This difference is explained aa being due to only a part of Be-7 in surface air being of stratospheric origin. By comparison with Cs-137, it is estimatad that the stratospheric component of Be-7 is about 00 % in spring decreasing to 25 % in the autumn.