Trace Metals chemistry in mediterranean rainwaters
The aim of this study is to show how some selected elements are dissolved by the rain water. We chose a set of elements for their importance in the biogeochemical cycles and the rain water chemistry (Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn, Fe, Cu, Zn, Pb). To carry this work off, we have developed working methods in ultra clean conditions, being insistant about the washing of our material. The sampling and analytical methods are then described. Next, we discuss about the origin of the elements incorporated in the rainwater droplets, and we conclude that Al, Si, Fe and Mn are coming from the Saharan eolian erosion, Cu, Zn, Pb from the human activities, and P from both the sources with equivalent contributions. All the scavenged material is coming, either from local marine aerosol, or for long range transport, without any significant local emissions, for crustal and anthropogenic elements. The studies of the associated air-masses trajectories confirm this conclusion and show the frontal type of most rain events. This facilitates mixings between the European pollutants and the African crustal dusts. The pH variations show that its value is determined by the neutralization of nitric and sulfuric acids, which are coming from polluted regions, with calcium carbonat e which is coming from the Saharan eolian erosion. Na, S and Cl are completly in the solu b le phase in ours samples. Fe and Al are in an equilibrium state with a coating of their hydr o xyde . Zn, Pb and Cu make an adsorption-desorption equilibrium on hydrated oxydes of iron, manganese or al u minium . At last, the other studied elements show a solubility strongly dependent on their origin: the marine and polluted fractions of each element is soluble and, by opposite, their crustal contribution is less soluble, or even i nsoluble . It is now a strong evidence that if an element is in an equilibrium state, its behaviour is dependent on the receiving environment, on the contrary of the elements which solubility is controled by their origin.