Use of stable lead isotopes and trace metals to characterize air mass sources into the eastern North Atlantic

Stable lead isotopes (Pb-204, Pb-206, Pb-207, Pb-208) and trace metals (Mn, Ai, Fe, Ni, Cu, Cd, Zn, Pb) have been analyzed in aerosol collected during the Atlantic Stratocumulus Transition Experiment-Marine Aerosol and Gas Exchange (ASTEX-MAGE) cruise that transited between Miami and the Azores from May to July 1992. Our goal was to define the continental signatures of the air masses encountered between the Azores and the subtropical regions. The combination of air mass trajectories, trace metal concentrations and stable lead isotopes allowed us to characterize the anthropogenic character of encountered air masses. The average Pb-206/Pb-207 ratio was 1.148+/-0.021 and corresponded to a mixing between well defined European (such as Great Britain with 1.115<Pb-206/Pb-207<1.125 and France with Pb-206/Pb-207 = 1.141+/-0.000) and North American sources (with Pb-206/Pb-207 = 1.184+/-0.000). On the basis of air mass trajectories and trace metal concentrations, the background isotopic signature associated with the trade winds (Pb-206/Pb-207 = 1.161+/-0.004) is consistent with previous reports by Church et al. [1990] such as Pb-206/Pb-207 = 1.154+/-0.004 in 1988, (Veron et al., 1993), Pb-206/Pb-207, 1.155+/-0.004 in 1989, and Hamalin et al. [1996] (Pb-206/Pb-207 = 1.158+/-0.006) in 1991. Short-term variations of continental air mass sources was particularly investigated by considering the anthropogenic character of aerosols collected during two Lagrangian experiments conducted as part of the ASTEX-MAGE cruise. We demonstrated the utility of stable lead isotopes to assign a "continental source signature" (or mixture thereof) to air masses beyond that normally possible by conventional air mass trajectory analysis in remote oceanic regions.