On the characteristics of the wet deposition process using radon as a tracer gas

A quantitatively characterised atmospheric process can provide important information on a variety of atmospheric models and help one to understand the deposition process in the atmosphere. In this study, the total activity concentrations of 214Pb and 214Bi and the activity ratios of 214Bi/214Pb in collected rain samples were measured by two-inch well-type NaI(Tl) detectors. Observed precipitations were classified by the origins of their air mass (continental/maritime) and their meteorological conditions (cold/warm front, high/low pressure). The result shows that (1) when the air mass passed over the continent of Asia 5 d prior to the precipitation, the activity concentration of radon decay products in the rainwater tended to be higher than when the air mass passed over from the Pacific Ocean; (2) higher activity concentrations were more frequently observed in precipitations accompanied with a cold front than warm/stationary front; (3) in general, the activity ratios of 214Bi/214Pb decrease with increase in rain intensity.