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

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