A 40-year retrospective European radon flux inventory including climatological variability

In this work, a 40-year retrospective European radon flux inventory has been calculated. Average values of the radon exhalation rate, probability distributions and seasonal fluctuations have been obtained. To achieve this, a numerical model of radon transport through finite, heterogeneous and porous media has been implemented, enabling us to calculate the radon exhalation rate of European soils with a horizontal resolution of 0.5' (~1km). Geological, geochemical and climatological parameters derived from European and international databases (FOREGS, HWSD, ERA-40) have been coupled to the model.The theoretical model is based on the fundamental equation of radon transport in porous media, taking into account the dependency of the transport coefficient on temperature and humidity. It also includes a simple model that evaluates the effect of snow cover. In general, the results show wide variations depending on location and season of the year, with a spatial standard deviation close to the annual average value (30Bqm^-2h^-1) In turn, the seasonal deviation is about 25% of the annual average value.The inventory can be easily integrated into atmospheric transport models acting as baseline that could be used for policy decisions regarding the identification of areas with a high risk of exposure to radon. The gridded data are available for the scientific community upon request. The limitations and sources of errors and uncertainties of the model are also discussed in detail.