USE OF STABLE LEAD ISOTOPES AND TRACE-METALS TO CHARACTERIZE AIR-MASSSOURCES 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 collec ted during the Atlantic Stratocumulus Transition Experiment-Marine Aer osol and Gas Exchange (ASTEX-MAGE) cruise that transited between Miami and the Azores from May to July 1992. Our goal was to define the cont inental signatures of the air masses encountered between the Azores an d the subtropical regions. The combination of air mass trajectories, t race metal concentrations and stable lead isotopes allowed us to chara cterize the anthropogenic character of encountered air masses. The ave rage Pb-206/Pb-207 ratio was 1.148+/-0.021 and corresponded to a mixin g between well defined European (such as Great Britain with 1.115<Pb-2 06/Pb-207<1.125 and France with Pb-206/Pb-207 = 1.141+/-0.000) and Nor th American sources (with Pb-206/Pb-207 = 1.184+/-0.000). On the basis of air mass trajectories and trace metal concentrations, the backgrou nd 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., 19 93), 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 conti nental air mass sources was particularly investigated by considering t he anthropogenic character of aerosols collected during two Lagrangian experiments conducted as part of the ASTEX-MAGE cruise. We demonstrat ed the utility of stable lead isotopes to assign a ''continental sourc e signature'' (or mixture thereof) to air masses beyond that normally possible by conventional air mass trajectory analysis in remote oceani c regions.