7Be, 210Pb and 137Cs concentrations in cloud water

Cloud water was sampled during 8 months, in 2008 and 2009, at the puy de Dome high-altitude atmospheric research station (France). The concentrations of 7Be and 210Pb, both naturally occurring radionuclides, and 137Cs of anthropogenic origin, were determined. Those values are useful for a better knowledge of the aftermath cloud deposition and more generally for wet deposition assessment of radionuclides. This is of primary interest in case of a nuclear accident, especially considering 137Cs deposition, both for high-altitude locations that are regularly embedded by clouds and also for lowlands where fog can occur. The 7Be and 210Pb average activity concentrations in cloud water found were 1.9±0.11mBqm−3 air and 140±10μBqm−3 air, respectively. For 137Cs, the average concentration was 0.14±0.02μBqm−3 air. This very low-level is representative of the long term post-accidental background level. Indeed, for the studied period, the last accidental 137Cs release was that of Chernobyl accident, in April 1986. To our knowledge this is the first data about 137Cs reference level determination in cloud water. The comparison between cloud water and rain water concentrations showed a ratio cloud/rain ranging between 3.4 and 8.1, in agreement with previous studies performed on inorganic compounds. Scavenging efficiencies of aerosols by cloud droplets were also calculated with the additional aerosol concentrations routinely measured at the station and were quite low (0.13–0.40) compared to what has previously been observed for inorganic soluble ions. •First determination of 137Cs activity levels in cloud water.•Improvement of the knowledge for 7Be and 210Pb cloud water activity levels.•Estimate of 7Be, 210Pb and 137Cs scavenging efficiencies by rainout process.