Outdoor exposure due to long-range atmospheric transport of radon can it be assessed by modelling?

International audience; Radon-222 is a progeny of U-238, naturally present in the Earth’s crust. After diffusing out of the soil, it reaches the atmosphere. As a noble gas, it does not interact with other gas or aerosol particles. Transported by the atmosphere, it can be breathed. Its disintegration inside the lung can damage the cells, increasing the risk of cancer. Radon-222 is therefore a major public health issue in some regions. Significant Radon-222 air concentration at one location is the combination of a potentially high local source – within few kilometers – and a long-distance origin – dozens or hundreds of kilometers. A local source can be estimated by modelling or measuring the ground exhalation rate. A distant origin is far more problematic to determine since it involves all the atmospheric processes and many potential exhalation sites. Therefore, the simulation of Radon-222 air concentrations must be made at regional or continental scale. We built a Radon-222 atmospheric transport modelling calculation chain, from input data to model-to-measurement comparisons. The main issues about the input data were to get reliable the radon exhalation rate and meteorological data. The quality of the modelling was then evaluated by a model-to-measurements comparison. Hundreds of gamma dose rate monitoring stations are available in France, recording data each five minutes all year round. They record dose rate peaks due to the Radon-222 progenies concentrated in rainfall events. Preliminary results are presented.