A particularly long and dense episode of airborne dust transport crossed Spain, France and part of Europe from 15 to 18 March 2022. This episode led to significant dust deposits on cars, roofs, etc., which may have caused surprise or concern among the general public. Based on association reports, several media published articles stating that this dust contained an artificial radionuclide, cesium-137 (137Cs), the source of which was attributed to the French nuclear tests conducted in the Sahara early in the 1960s. In order to provide a solid and representative scientific basis for a better characterisation of this dust and its radionuclide content, a participatory call for the collection of about ten grams of dust in different sites in France and Europe was launched on 17 March 2022 on the social network Twitter by Olivier Evrard. It was then relayed by Germán Orizaola, generating numerous reactions and the collection of several dozen samples in France, Spain and other neighbouring countries in Europe. The current dataset provides general information about the location/time of sample collection (n=110 samples) and data about the content of dust samples in cesium-137 (137Cs), an artificial radionuclide emitted by nuclear atmospheric tests and accidents (Evrard et al., 2020). Samples (2-80g) were analysed using the ultra-low background Germanium HyperPure gamma spectrometry detectors of LSCE installed in the underground facilities at both University Paris-Saclay (Gif-sur-Yvette) and Modane (Underground Lab of Modane, France). Filters were analysed for 80,000 to 200,000 s to obtain sufficient counting statistics (for the detection of the 137Cs peak at 662 keV). All results were expressed in Bq kg−1 with activities decay-corrected to the sampling date. Counting efficiencies and reliability were conducted using certified International Atomic Energy Agency (IAEA) standards (IAEA-444, 135, 375, RGU-1 and RGTh-1) prepared in the same containers as the samples. Additional data regarding additional physico-chemical properties analysed in these dust samples will be published by mid-2023.

{"references": ["Evrard O, Chaboche P-A, Ramon R, Foucher A, Laceby JP (2020): A global review of sediment source fingerprinting research incorporating fallout radiocesium (137Cs). Geomorphology 362, 107103.", "https://www.numerama.com/sciences/888695-ciel-orange-le-cesium-137-radioactif-dans-les-sables-du-sahara-est-il-dangereux.html", "https://www.leparisien.fr/meteo/la-pluie-de-sable-venue-du-sahara-qui-sabat-sur-la-france-est-legerement-radioactive-16-03-2022-7YFIVX3DOBFBPJG3SAVUQYDJRU.php", "https://france3-regions.francetvinfo.fr/normandie/calvados/caen/les-sables-du-sahara-tombes-sur-nos-voitures-sont-sans-doute-pollues-par-des-particules-radioactives-2503469.html"]}

This work benefited from the French state aid managed by the ANR under the "Investissements d'avenir" programme with the reference ANR-11-IDEX-0004 -17-EURE-0006. The support of the team from the Laboratoire Souterrain de Modane (Laboratoire de Physique Subatomique et de Cosmologie - LPSC Grenoble, CNRS, Université Grenoble-Alpes France) is also acknowledged.