Atmospheric deposition of 7Be, 210Pb and 210Po during typhoons and thunderstorm in Shanghai, China and global data synthesis

Atmospherically-delivered Be-7, Po-210 and Pb-210 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 Be-7, Pb-210 and Po-210 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 Be-7, 5.7 for Pb-210, 7.4 for Po-210, and 7.0 for Be-7/Pb-210 activity ratios (AR). Such large observed variations in the depositional fluxes of Be-7, Pb-210, Po-210 and Be-7/Pb-210 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 Be-7/Pb-210 activity ratios, we estimated the variations in the fraction of maritime and continental air masses into the typhoon. Observed constancy in the Po-210/Pb-210 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 Be-7 and Pb-210 during pulse events (precipitation >= 50 mm from single rainout event), we quantify the importance of pulse events in the atmospheric fallout of these radionuclides.