Measured values of the dry deposition velocities of atmospheric aerosols carrying natural and fallout radionuclides using artificial collectors

The dry deposition velocitiesVg of aerosols carrying (a) fallout beta activity from nuclear tests, (b) natural radioactivity due to thoron daughter²¹²Ph (Th-B) and (c) cosmic-ray produced⁷Be have been measured in Bombay, India, using artificial collectors consisting of trays with a thin layer of water to retain the deposited material. The location of Bombay is eminently suitable for such measurements in view of the existence of a long dry period of several months without any rainfall. The measuredVg values (cm s^?1)) are 0.063 ± 0.06 (1 S.D.) for fallout beta activity from 900 daily readings, 0.033 ± 0.03 (1 S.D.) for²¹²Pb from 80 daily measurements and 0.023 ± 0.014 (1 S.D.) for⁷Be from 23 bi-monthly measurements. A study of the associated meteorological parameters showed some correlation with wind velocity only in the case of radioactive fallout.