Trend in total atmospheric deposition fluxes of aluminium, iron, and tracemetals in the northwestern Mediterranean over the past decade (1985-1997)

The total atmospheric deposition of aluminium (Al), cadmium (Cd), copper (C u), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) on the northwestern coast of Corsica (Pirio) was sampled for two years, and their respective concentrations were measured during that period. The sampling s tation was chosen for its isolation from any local and regional sources of contamination. The year-to-year variability of the total atmospheric deposi tion was found to be high (up to a factor of 2). Using Al as the crustal re ference indicates that Pb, Cd, and Zn are mainly associated with man-made a erosols (> 85%), and Fe is mainly associated with crustal aerosols (> 70 %) . However, our results indicate that Saharan dust is a potential source of "natural" lead, especially in the case of a major input of dust to the nort hwestern Mediterranean. To determine the spatiotemporal variability of the; trace metals over the northwestern Mediterranean Sea, the observed fluxes were compared to those found in the past decade using the same methodology. The comparison indicated a relative homogeneity of Cu and Ni fluxes over t he northwestern Mediterranean and over the past decade. The decrease found in Al and Fe since 1985 (by a factor of 4 to 6) can be related to the decre ase in Saharan dust fallout. The limitation in the use of lead additives in gasoline may have resulted in a decrease in the European atmospheric lead emissions by a factor of about 6 since 1985 and in a maximum decrease in th e total atmospheric flux by a factor of 12 at most if the natural interannu al variability of atmospheric deposition in this region is taken into accou nt. So the recorded decrease in the atmospheric lead flux since 1985 (by a factor of similar to 30) reveals a slight local contamination at the earlie r Corsican station. In the case of Cd and Zn, there was a decrease by a fac tor of 30 and 23, respectively, between the data obtained at La Tour du Val at (July 1988 to June 1989) and those at Pirio (March 1996 to March 1997); such a decrease cannot be the consequence of either a-reduction in emission s in Europe as a whole (the factor being at most 4), or the distance from t he emission sources. Hence, we can confirm that Zn and Cd fluxes at La Tour du Valat and Zn fluxes at Cap Ferrat were not representative of a long-ran ge transport to the Mediterranean but the result of a local/regional contam ination. The large decrease observed for metals (Cd, Zn, and Pb) mainly mob ilized by human activities, results from a combination of the actual diminu tion of the concentrations due to a reduction in the emissions and the occu rrence of local/regional contamination for some elements at some sampling s ites.