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

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.