Contribution of saharan dust on radionuclide aerosol activity levels in Europe? The 21-22 february 2004 case study

[1] 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 of¹³⁷Cs 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 down¹³⁷Cs 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.