Depositional fluxes and concentrations of 7Be and 210Pb in bulk precipitation and aerosols at the interface of Atlantic and Mediterranean coasts in Spain

Abstract

Bulk depositional fluxes of 7Be and 210Pb in precipitation measured over a period of 16 months (April 2009-July 2010) in Huelva, Spain varied between 5.6 and 186 Bq m-2 month-1 (annual mean: 834 Bq m-2 year-1) and 0.8 and 8.1 Bq m -2 month-1 (annual mean: 59 Bq m-2 year -1), respectively, with the lowest depositional fluxes occurring during dry summer months. Quantitative evaluation of the precipitation- normalized seasonal depositional fluxes of 7Be and 210Pb indicates that the enrichment factor in winter is < 1.0 while in 2010 spring, it is significantly higher than 1, possibly indicating input of air from the stratosphere-troposphere exchange (for 7Be). The specific activities of 7Be and 210Pb varied from 0.03 to 7.42 Bq L -1 (mean = 2.5 Bq L-1) and 0.005 to 1.07 BqL-1 (mean = 0.23 Bq L-1), respectively, with the highest values corresponding to the spring season. The spatial and temporal variations of 7Be and 210Pb in aerosols from three stations are evaluated and compared to their monthly depositional fluxes. The mean depositional velocity of aerosols using 7Be and 210Pb are similar, ∼0.5 cm s-1 and are compared to other published values. This is the first time the fractional amounts of 7Be and 210Pb in monthly bulk precipitation are compared to the fractional amount of precipitation and provides insight on how the amount of precipitation plays a key role on the scavenging of these nuclides. The importance of dry fallout is evaluated for the study site which has direct implications for other areas in the Mediterranean Climate Zone. © 2011 by the American Geophysical Union.