Role of desert aerosol in metal fluxes in the Mediterranean area

The chemical composition of aerosols and precipitation collected over Sardi nia primarily reflect Saharan and European inputs. European background aero sols 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. P artitioning of total atmospheric deposition between soluble and insoluble p hases shows that Al, Si, Fe and Pb originating from the atmosphere are most ly in an insoluble form. For Ca, Cd and Cr metals, the dissolved fraction r epresents 50-90% of the total input. Aerosol dissolution experiments perfor med at particle concentrations ranging from 3 to 300 mg l(-1) show that Cd and Pb have low solubilities at high mass particle concentrations. The solu bility of Pb increases with EFcrust values and the finest grain-size of the aerosols (<1 mu m), and is also affected by pH. Dissolution of Al and Fe d ecreases 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 gr eater than 100 mg l(-1). The fluxes (dry + wet) of metals in Sardinia show that similar to 30% of the Cd and Pb to more than 80% of the Fe and Al come from the Sahara. (C) 1999 Elsevier Science Ltd. All rights reserved.