The trace metal chemistry of atmospheric dry deposition samples collected at Cap Ferrat: a coastal site in the Western Mediterranean

A series of 10 dry deposition samples were collected on a surrogate plate o ver a period of 8 months at Cap Ferret, a site on the Western Mediterranean coast, and analysed for Al, Fe, Mn, Ni, Co, Cr, Cu, Zn and ph. Relatively few data sets for trace metal dry deposition are available in the literatur e, and considerable difficulties are inherent in the use of surrogate plate s for the collection of dry deposition. However, the trace metal chemistry of the plate-collected dry deposition at the Cap Ferrat site generally mimi cs the trends predicted from theoretical metal deposition velocities. The d ry deposition is dominated by the fall-out of larger-size particles and dur ing the parent aerosol --> dry deposition sequence there is a strong, parti cle size-mediated, fractionation of the crust-dominated, non-enriched eleme nts (NEEs) from the anthropogenic-dominated, anomalously enriched elements (AEEs), with the latter being depleted in the dry deposition. As a result, although the AEEs in the dry deposition are still enriched relative to aver age crustal material, the dry deposition and the parent aerosols have diffe rent 'chemical characters'. Further, the dry deposition has a more homogeno us trace metal composition than the parent aerosol. The depletion of the AE Es in the dry deposition, relative to the parent aerosol, has important imp lications for sea water solubilisation. To assess this, a technique is outl ined which allows the solubilities of Cu, Zn and Pb to be estimated on the basis of their EF,,, values in atmospheric particulates. The technique reve als that the solubilities of Cu, Zn and Pb from the dry deposition are less than those which would be predicted from data on the parent aerosol. A com parison between the dry and wet trace metal deposition fluxes at the Cap Fe rret site shows that the particulate fraction dominates the dry deposition of all the metals. However, in wet deposition Cu and Pb switch character an d the soluble fraction becomes dominant. (C) 1999 Elsevier Science B.V. All rights reserved.