Intra-Annual Deposition of Atmospheric 210Pb,210Po and the Residence Times of Aerosol in Xiamen, China

Abstract

Atmospheric deposition of 210Pb，210Po from Nov. 2010 to Jan. 2012 were analyzed to reveal their temporal variations, as well as applications in constraining the residence times of aerosol. The monthly depositional fluxes varied from 2.42 to 29.31 Bq/m2/mon and from 0.160 to 3.388 Bq/m2/mon for 210Pb，210Po, respectively. High fluxes of 210Pb，210Po were observed in the southwest monsoon prevailing months, while low fluxes corresponded to the northeast monsoon seasons, revealing the monsoon control over 210Pb，210Po deposition on seasonal timescales. There were significant positive linear correlations between the daily depositional fluxes and precipitation, supporting the predominant removal passage of 210Pb，210Po through rainfall. The inverse relations between specific activities and precipitation indicated that the removal efficiencies were much higher at the beginning of rainfall. In contrast, the dry deposition only accounted for 22% and 29% of the bulk depositional fluxes of 210Pb，210Po, respectively. The depositional flux ratios of 210Po to 210Pb varied between 0.015 and 0.223 with a mean of 0.091 ± 0.012, corresponding to the residence times of 3.1–57.5 d with an average of 20.8 ± 3.0 d. Investigations on size-fractionated 210Po and 210Pb could provide better understanding of the resident timescales of aerosol.