Role of desert aerosol in metal fluxes in the Mediterranean area.

Aerosols and precipitations collected over Sardinia are mainly controlled by two end-members: Saharan and European. European background aerosols in Sardinia show a 3 to 25-fold decrease in EFcrust values for Cd, Zn, Pb, and Cr compared with coastal stations in the Western Mediterranean. Partitioning of total atmospheric deposition between the soluble and the insoluble phases shows that Al, Si, Fe and Pb originating from the atmosphere are mostly in the insoluble form. For Ca, Cd, Cr metals the dissolved fraction represents 50-90 % of the total input. Aerosol dissolution experiments performed at particle concentrations ranging from 3 to 300 mg l-1 show Cd and Pb exhibiting low solubility at the high mass particle concentration. Solubility of Pb increases with the EFcrust values and the finest grain-size of the aerosols (<1µm), and is less affected by pH. Al and Fe solubilities appear to be mainly controlled by the particulate load. Dissolution of both metals decreases significantly from 30% (13 % for Fe) at aerosol loads lower than 5 mg l-1, to less than 1% for both metals, at total aerosol concentrations greater than 50 mg l-1, which are encountered during Saharan transport. Fluxes (dry +wet) of metals at Sardinia show that ~ 30% for Cd and Pb, to more than 80 % for Fe and Al are due to Saharan contribution

On the dynamic of the atmospheric input of copper and manganese into the Western Mediterranean Sea

International audienceDaily 24-h aerosol samples have been collected at a coastal location in northwestern Corsica, between February 1985 and March 1988. Total deposition has been sampled between February 1985 and October 1987 with a time span of about 15 days.Three-dimensional air-mass trajectory analysis indicates that atmospheric Cu and Mn over the western Mediterranean are long-range transported from continental source regions.We show that the scavenging of atmospheric Cu and Mn by rain generates a seasonal cycle with high aerosol concentrations during the dry season and lower aerosol concentrations during the wet season. Sporadic but intense Saharan dust transport events are responsible for the highest atmospheric concentrations of Mn.The ratios between the atmospheric deposition of Cu and Mn and the corresponding mean daily precipitation rate reach a maximum during the Mediterranean summer. We attribute this behaviour to the wet scavenging of a more loaded atmosphere during the dry season than during the wet season. The precipitation frequency (Fp) is a major factor influencing the seasonal variability of the atmospheric Cu deposition and, this is in agreement with what we observe for the atmospheric Pb deposition.Our results also suggest that the relationship between the seasonal variability of Mn deposition and the Fp is less direct. This is due to the occurrence of Saharan dust transport events which strongly influence the variability of the Mn total deposition