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

• Published in: Marine chemistry Vol. 68; no. 1; pp. 15 - 30
• Main Authors: Chester, R, Nimmo, M, Preston, M.R
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.1999
• Subjects: Cap Ferrat; Marine; trace metal; Western Mediterranean; MED, Ligurian Sea; MED, France, Provence-Cote d'Azur, Cap Ferrat; Cap Ferrat; Western Mediterranean; trace metal
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/S0304-4203(99)00062-6

A series of 10 dry deposition samples were collected on a surrogate plate over a period of 8 months at Cap Ferrat, a site on the Western Mediterranean coast, and analysed for Al, Fe, Mn, Ni, Co, Cr, Cu, Zn and Pb. Relatively few data sets for trace metal dry deposition are available in the literature, and considerable difficulties are inherent in the use of surrogate plates for the collection of dry deposition. However, the trace metal chemistry of the plate-collected dry deposition at the Cap Ferrat site generally mimics the trends predicted from theoretical metal deposition velocities. The dry deposition is dominated by the fall-out of larger-size particles and during the parent aerosol→dry deposition sequence there is a strong, particle size-mediated, fractionation of the crust-dominated, non-enriched elements (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 average crustal material, the dry deposition and the parent aerosols have different `chemical characters'. Further, the dry deposition has a more homogenous trace metal composition than the parent aerosol. The depletion of the AEEs in the dry deposition, relative to the parent aerosol, has important implications for sea water solubilisation. To assess this, a technique is outlined which allows the solubilities of Cu, Zn and Pb to be estimated on the basis of their EF crust values in atmospheric particulates. The technique reveals 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 comparison between the dry and wet trace metal deposition fluxes at the Cap Ferrat site shows that the particulate fraction dominates the dry deposition of all the metals. However, in wet deposition Cu and Pb switch character and the soluble fraction becomes dominant.