| Resumo: |
Over a period of eight months, a total of 26 atmospheric particulate matter samples were collected at the location of Tahiti and in other areas of French Polynesia, using a specially equipped sailboat. A 6-stage cascade impact or was used to separate aerosols in the following size classes: > 4,2-4, 1-2,0.5-1,0.25-0.5 and < 0.25 µm equivalent aerodynamic diameter. The resulting set of 156 size segregated aerosol samples was analyzed by particle-induced X-ray emission for 16 elements. This study deals with the concentrations of Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, Br, Sr and Pb. Enrichment factor calculations reveal that Na, Mg, S, A, K, Ca and Sr were little fractionated with respect to bulk sea water, whereas Al, Si, Ti, Mn and Fe presented no enrichment relative to the earth's crust. The anomalously enriched elements were Cu, Zn, Br and Pb. The multivariate technique factor analysis was used to identify the various aerosol sources. Dry and wet deposition modeling enabled us to estimate the atmospheric dry and wet transfer to the sea. Dry deposition velocities ranged from 0.04 to 0.2 cm S<sup>-1</sup>, while the scavenging rates were of the order of 2-3 x10<sup>-6</sup> S<sup>-1</sup>. The resulting deposition rates are within the range given in the literature, with a good agreement for the deposition of Mn, Cu and Zn. It was found that dry deposition dominates over wet deposition for the sea derived elements, while for the crustal elements, the situation was the opposite. The estimated annual atmospheric deposition of Cu is equal to that of other geochemical cycles such as marine sedimentation and vertical mixing, whereas the deposition rates of mineral aerosol and Pb are much higher than those reported previously, indicating direct influence of local emissions from Tahiti.
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