Contribution of Saharan dust on radionuclides aerosol activity levels in Europe ? The 21-22 february 2004 case study
Résumé
In February 2004, a spectacular dust event was observed in the south of France. Associated with huge particulate matter deposition, unusual 137Cs concentrations were found in samples. Using the transport model CHIMERE-DUST, we first show that these dust aerosols came from North Africa. More precisely, the question is whether this sudden increase of measured 137Cs concentrations was due to a huge amount of dust over a large region (with an usual radionuclide content) or due to an import of more concentrated air masses over a limited area. This question is connected to the open debate about the contribution of 137Cs concentrations in Europe from "Gerboise" sites, where former French nuclear tests in the 1960s were performed. With the model in scenario mode, this study attempts to track down 137Cs concentrations recorded in the south of France. To quantify the origin and percentage of dust originating from North Africa to the south of France, three simulations are performed: (1) with the complete dust emissions inventory of Africa, (2) with only emissions in the eastern Maghreb, and (3) only considering the Gerboise sites. It is showed that the majority (80%) of the dust was coming from eastern Maghreb, but only 0.7% of the African emissions were from Gerboise, leading to 1-5% of the concentrations recorded in the south of France for the day of the peak.
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