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Measurements of zloPb concentrations in ground level air at two stations in India, viz., Bombay and Srinagar, are presented. Sampling of the atmospheric particulates was done using Hollingsworth and Vose H-70 filter papers and powerful blowers. Radiochemical separation of210Pb from the air-filter collection was carried out after ashing of the filters at 250°C. The samples were counted in low-level end-window G.M. counters using the 1.17 MeV betas of daughter product 210E$ both for activity estimation and for checking the radiochemical purity of the samples. . It can be seen from the results that the activity concentrations varied from 6 ppCi/lOOO m3 to 60 ppCi/IOOO m3. The presence of a seasonal variation in concentrations with maximum in winter and minimum in summer of each year is also observed. The likely causes for these variations and their differences with the seasonal variation of 13' Cs and other fission products are discussed.

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Lead-210 activity in ground level air and rainwater at a number of stations in India covering the latitude band 11" to 34" N has been studied and the data is presented. Seasonal variations in activity levels with maximum values in winter have been observed in the surface air at several stations. The time of occurrence of peak values of lead-210 differs from that of stratospheric cesium-137 but generally agrees with radon levels. It is therefore concluded that lead-210 is mainly controlled by radon activity in the ground level air. The possible reasons for the winter peak in radon and lead-210 are discussed.The latitudinal variation of lead-210 and the likely reasons for these are examined. The lead-210 activity levels in India are compared with the values reported by other laboratories for temperate latitudes.

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