LAUSR

Atmospherically-delivered 7Be, 210Po and 210Pb in bulk precipitation and air samples collected around the globe have provided valuable quantification on the rates of removal, as well as proportional mixing of attendant air masses; however, such studies during thunderstorm and typhoon events are limited. We report the first continuous time-series rainwater sampling and analysis of 7Be, 210Pb and 210Po from two typhoons and one thunderstorm during 2015 summer in Shanghai. The depositional fluxes within individual rain events of typhoons and thunderstorms varied by a factor of 10 for 7Be, 5.7 for 210Pb, 7.4 for 210Po, and 7.0 for 7Be/210Pb activity ratios (AR). Such large observed variations in the depositional fluxes of 7Be, 210Pb, 210Po and 7Be/210Pb activity ratios were attributed to air masses injected from surrounding high pressure system adjoining the typhoon to low pressure system within the typhoon. Based on 7Be/210Pb activity ratios, we estimated the variations in the fraction of maritime and continental air masses into the typhoon. Observed constancy in the 210Po/210Pb AR indicates that the residence times of air masses contributing to the typhoon during heavy rain are similar. From a synthesis of global fallout of 7Be and 210Pb during pulse events (precipitation≥50 mm from single rainout event), we quantify the importance of pulse events in the atmospheric fallout of these radionuclides.