Temporal variations of atmospheric depositional fluxes of 7Be and 210Pb over 8years (2006-2013) at Shanghai, China, and synthesis of global fallout data

Abstract

7Be and 210Pb, two atmospherically delivered radionuclides, have been broadly applied to study the processes including air mass transport, soil erosion, and particle cycling in aqueous systems. These studies require temporal variations of their depositional fluxes. In the present work, monthly atmospheric bulk depositional fluxes of 7Be and 210Pb were measured over 8 years (December 2005 to December 2013) at Shanghai, China. The bulk depositional fluxes of 7Be and 210Pb varied from17.9 to 421 Bqm-2month-1 and 6.8 to 82.1 Bqm-2month-1, respectively. The volume-weighted activities ranged from 0.20 to 8.06 Bq L-1 for 7Be and 0.05 to 3.40 Bq L-1 for 210Pb. There were strong seasonal variations in the depositional fluxes of these nuclides. The seasonal fraction of depositional fluxes was >30% of the total annual depositional fluxes of 210Pb in winter and 7Be in spring. The lowest depositional fluxes were found in summer for both radionuclides, with precipitation-normalized enrichment factor (a) values of <1.0. The results from the synthesis of global fallout data indicate that there are latitudinal variations in the maximum depositional fluxes and volume-weighted activities of 7Be, both values increase with latitude fromthe equator to the midlatitudes. The 210Pb depositional fluxes increase with the distance fromthe coast in inland regions (distance fromthe coast>50 km) and increase with the amount of precipitation in onshore region (distance from the coast =50km). We also report that Shanghai, China, has the second highest bulk depositional fluxes of 210Pb in literature.