Abstract
90Sr and 239+240Pu concentrations in the surface air were observed at Tsukuba and Tokyo during the period from 1978 to 1983. They showed remarkable seasonal variation with a spring maximum and a fall minimum. The pronounced peak in these concentrations observed in the spring season of 1981, which was maximum in this period of study, is attributed to the stratospheric fallout derived from the 26th Chinese explosion. Marked increases of the 90Sr and 239+240Pu concentrations were observed in the smallest particles (less than 1.6 μm) at the spring maximum. The resupension of the radionuclide bearing soil particles, as one of the sources besides the stratospheric fallout, will be significant for the airborne 239+240Pu rather than 90Sr in near future.
