The Ruthenium-106 plume over Europe in 2017: a source-receptor model to estimate the source region

Between the end of September and the beginning of October 2017, low but detectable air concentrations of Ruthenium-106 (R106u)were measured throughout the European atmosphere. To date, the source has not been clearly identified. This study aims at constraining the location of the most likely emission source, by combining HYSPLIT back trajectories and a multi-site source-receptor model. The model follows a concentration weighted trajectory (CWT)approach, based on a R106u measurement dataset gathered by the International Atomic Energy Agency (IAEA)shortly after the event and shared by the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN). The back trajectories are computed using Global Data Assimilation System (GDAS)and ERA-Interim meteorological data, with horizontal resolution from 1.5° to 0.5°. The effect of the starting altitude was also investigated. The source-receptor model results show that the most likely emission source region extends from Ukraine to the West to the Russian Volga and Ural regions to the East, in accordance with two previous studies. The analyses also show that the identified source region is relatively insensitive to the type of meteorological data, their horizontal resolution and values of starting altitude. The model precision is found to increase with increasing number of receptors. The method is fully open-source, requires low computational resources and is therefore suited to estimate the source origin of radioactive pollutants on a real time basis, providing an additional tool to more sophisticated atmospheric models.