Vertical structure of the troposhpere as revealed by radioactive tracer studies

The fallout of several radioisotopes of diverse origins (i.e., cosmogenic isotopes 7Be and 32P, radongenic 210Pb, 210Bi, and 214Bi, and bomb-produced 22Na) has been measured in precipitation at several stations on the Indian subcontinent. The average residence time of cosmogenic (and bomb-produced) isotopes in the troposphere is found to be longer than that of the radongenic isotopes. This behavior can be explained only if the rate of removal of aerosols, in general, decreases with altitude. Such a structure of the troposphere is probably seasonally variable. The concentrations of 210Pb, 7Be, and 32P have been measured in the air in the troposphere. The results, combined with similar data, suggest that the concentrations in the troposphere at 0-15° N latitude are unusually small. This effect seems to be a direct result of good vertical mixing and efficient washout in this belt