Factors influencing the atmospheric depositional fluxes of stable Pb, super(2) super(1) super(0) Pb, and super(7) Be into Chesapeake Bay

• Published in: Journal of atmospheric chemistry 2000-01, Vol.36 (1), p.65-79
• Main Authors: Kim, Guebuem, Hussain, N, Scudlark, J R, Church, T M
• Format: Article
• Language: English
• ISSN: 0167-7764

Atmospheric depositional fluxes of super(7) Be and super(2) super(1) super(0) Pb (bulk) and stable Pb (wet) were measured simultaneously for one year (from September 1995-August 1996) at Stillpond, Maryland on the upper eastern shore of the Chesapeake Bay. The annual total (bulk) depositional fluxes of super(2) super(1) super(0) Pb and super(7) Be were 0.78 and 13 dpm cm super(-) super(2) , respectively, and agree well with other previously reported results at nearby locations such as Norfolk, VA and Lewes, DE. The wet depositional flux of stable Pb (58 ng cm super(-) super(2) yr super(-) super(1) ) was also similar to that measured at other Chesapeake sites during 1990-1991 (55 ng cm super(-) super(2) yr super(-) super(1) , for both Wye and Elms, Maryland). This suggests that a constant Pb flux has been reached since the mandatory use of unleaded gasoline was instituted. The concentrations of super(7) Be, super(2) super(1) super(0) Pb, and to a lesser extent stable Pb were diluted exponentially by precipitation, based on concentrations versus precipitation plots. Due to higher enrichment of super(2) super(1) super(0) Pb in the lower troposphere, the dilution effect was largest on super(2) super(1) super(0) Pb (i.e., controlled mainly by below-cloud scavenging processes), and thus its depositional flux increase is negligible as precipitation amount increases. A good correlation between the amount of precipitation and total depositional flux of super(7) Be and stable Pb, which are more enriched in the upper troposphere, suggests that precipitation amount is important in controlling their fluxes (i.e., controlled by both below-cloud scavenging and in-cloud condensation processes). Based on super(7) Be versus super(2) super(1) super(0) Pb plots, it appears that super(7) Be, relative to super(2) super(1) super(0) Pb, is less efficiently scavenged by snowfall. Our results suggest that in addition to precipitation amounts, marine air-mass transport or snowfall may be important factors in controlling the seasonal variability of the fallout fluxes of trace metals in coastal areas.