Search

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. [ABSTRACT FROM AUTHOR]

Abstract: Measurements were conducted at three sampling sites located at different altitudes in the centre of France during two years, both in the rain and aerosol phases. The rain was sampled at a boundary layer site while the aerosol particles were collected at two different altitudes, which allow a better characterization of the vertical atmospheric column being washed out. Various chemical analyses were performed to characterize reactive (NO3 −, SO4 2−, NH4 + and K+) and inert (7Be, 210Pb and 137Cs) species transfer from the aerosol to the rain phase. This set-up was ideal to calculate the washout ratio (WR) using different concentrations of the aerosol phase. Using the classical WR calculated with the aerosol concentration sampled at the same altitude than the rain collectors, we observed a seasonality of WR, with higher value in winter and lower value in summer for radionuclides. At the higher altitude site, local contaminations do not influence the aerosol concentration, which then should be representative of the whole atmospheric column. The annual variability is high at this site maybe because aerosol concentrations can be less concentrated than the whole atmospheric column when this later one is not well mixed. In order to increase the reliability of the WR, we propose a new method for calculating washout ratio from measurements at the rain collector level. This new calculation takes into account the height of the boundary layer, we observed that it decreased the variability of the washout ratio (for 7Be, 210Pb and NO3 −), with less dependence to the season. [Copyright &y& Elsevier]

Abstract: The presence of cesium-137 (137Cs) in the environment is mainly due to past nuclear tests and accidental reactor releases. Due to the half-life of 137Cs (30.2 y), amounts of this radionuclide releases are in fact still detectable in soils, and at trace levels in the vegetation and the atmosphere. Since the middle of the 1990’s, the presence of 137Cs in the atmosphere has long been attributed to the resuspension of terrestrial dust. Recently, modelling studies have demonstrated that an additional and possibly dominant source of this anthropogenic radionuclide is biomass burning. Here, we report the variations of atmospheric 137Cs activity levels over a 2-year period at the puy de Dôme (1465 m a.s.l.), France in combination with measurements of the aerosol chemical composition, in particular with indicators for biomass burning (levoglucosan and potassium) and soil dust (calcium). Temporal co-variations of these chemical compounds in addition to back-trajectories are used to identify common source emissions. Significant correlation is found between these compounds. Hence, we experimentally confirm the modelling study highlighting the fact that the atmospheric 137Cs is partly released by biomass burning. In addition, we observed that the correlations between the 137Cs concentrations and levoglucosan and biomass burning K+ differ according to the season. This is in agreement with the temporal evolution of levoglucosan concentration, which has maxima in winter and minima in summer. [Copyright &y& Elsevier]

Abstract: Aerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component arising from natural and/or anthropogenic sources. This paper presents physicochemical characterization of aerosols observed during meteorological conditions characteristics of coastal areas. In particular, we study the influence of sea-breezes and land-breezes as well as the fetch variation, which superpose on larger synoptic conditions, on aerosol properties. This was achieved using a physical, chemical and optical analysis of the aerosol data acquired in May 2007 on the French Mediterranean coast. The aerosol distributions were measured using a TSI SMPS 3081 model and the chemical characterization was made using an Ion Chromatography analysis (IC) and a thermo-optical technique. In addition, aerosol optical characteristics were provided by aethalometer (absorption) and nephelometer (scattering) measurements. For low wind speeds, we detect high aerosol number concentrations as well as high and carbonaceous compounds contributions, which are observed even when the aerosol is sampled in pure maritime air masses. These results indicate that air masses are strongly impacted by pollution transported over the Mediterranean. In addition, the combination of low wind speeds and land/sea-breezes lead to the production of new ultrafine particle formation events that seem to take place over the sea before being transported back to the coast. Under higher wind speed conditions, aerosol number and mass concentrations of smaller sizes are significantly lowered due to the dispersion of anthropogenic pollutants. Optical measurements reveal that mean scattering and absorbing coefficients are about 15.2 Mm−1 and 3.6 Mm−1, respectively. Associated mean aerosol single scattering albedo is found to be about 0.87 and 0.94 (at 520 nm) for continental and maritime influences. [Copyright &y& Elsevier]