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 Pb-214 and Bi-214 and the activity ratios of Bi-214/Pb-214 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 Bi-214/Pb-214 decrease with increase in rain intensity.