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Abstract Aerosols emitted into the atmosphere are dispersed by atmospheric air masses and then removed by dry or wet deposition processes. In some cases, if there are no episodes of precipitation, dry deposition may be the main processes in particular on a local scale. Dry deposition is characterized by the dry deposition velocity Vd (m.s−1), which is generally standardized at the friction velocity u* (m.s−1). From 2005–2016, we conducted experimental campaigns on-site with fluorescein tracer to determine dry deposition velocity of aerosols on grass. The particle sizes tested were 0.24, 0.27, 0.5, 0.6, 1.2, 3, and 7.8 µm. We described here the experimental method, the results obtained in terms of Vd/u* by particle size and we compared our results to the values usually simulated from the main models used by the scientific community. The results show that the Vd/u* parameter varies in a range from 2 to 6 10−3 for particle diameters from 0.2 to 1.2 µm. Beyond 1.2 µm the Vd/u* ratio increases rapidly with a value of 5.4 10−2 to 7.8 µm. Based on our experimental results, Vd/u* relationships were proposed for potential applications in operational models for a grass-type rural cover, which has a constant mean value of 3.7 ± 1.9 10−3 for particles in the size range of 0.2 and 1.2 µm, and as a linear function of particle size (Dp, diameter) expressed as 0.0082 × [Dp]− 0.0106 for larger particles between 1.2 and 8 µm. Highlights • Dry deposition velocities of fluorescein aerosol particles between 0.24 and 7.8 µm. • On-site measurements of dry deposition velocities on grass. • Correlation between the dry deposition velocities and the diameter of the particles. • Vd/u* varies in a range 2 10−3 to 6 10−3, for particles diameters from 0.2 to 1.2 µm. • Beyond 1 µm, Vd/u* increase rapidly, with value of 5.1 10−2 to 7.8 µm. [ABSTRACT FROM AUTHOR]

Abstract: Deposition velocities of aerosol on building and monument vertical surfaces have scarcely been documented and modeled so far. A methodology is proposed based on simultaneous measurements of artificial aerosol tracer fluorescein emissions, concentrations and depositions, and of high frequency turbulent variables. The results are compared to year-long deposition of 7Be, a naturally produced airborne radioactive particle tracer. A three-dimensional simulation of the turbulent flow and concentration fields in the vicinity of the wall specifies the flow structure responsible for deposition on the facade. It also allows comparison of the measured fluorescein deposition velocities with two semi-empirical models. [Copyright &y& Elsevier]

Abstract: Atmospheric transport plays an important role in the transfer of pollutants to ecosystems. During such transport, the atmospheric aerosol is one of the key factors in terms of deposition. Over 18 months, we studied the concentrations of Zn, Pb, Ni, Cd, Hg in air and precipitations in a wetland site in the north west of France. The objective of this study was to characterise the quantities transferred by dry and wet deposition. An eddy correlation technique was used to measure dry deposition velocities and determine the dry deposition fluxes from atmospheric concentration. In this site, wet deposition is almost always preponderant, except for Pb and Cd over several months. Measurements in the air and in rainwater are low and show that the site is protected from important anthropogenic influences, with levels that can be considered as background levels. In terms of deposition fluxes, the configuration of the site and the meteorological conditions (low wind speeds, low thermal fluxes) lead to low dry depositions. Wet depositions, although more important are also relatively low compared to the literature, directly linked to the pluviometry during the study period. [Copyright &y& Elsevier]

To assess the impact of an accidental or chronic radionuclide release in form of aerosol particles in the atmosphere, it is important to study their dry deposition in a rural environment. For particles of less than 1 µm, there is a lack of experimental data in this regard, leading to uncertainty in terms of the results of models, which can reach up to two orders of magnitude (Petroff Mailliat, Amielh, & Anselmet, 2008). Moreover, there is no in situ deposition velocity measurement data available for particles that are smaller than 10 nm. The objective of this study is to measure and analyse the dry deposition velocity for aerosol particles with a particle size of between 2.5 nm and 1.2 µm, with particular focus on the particle size range of 2.5–14 nm. To this end, an in situ experimental method based on eddy correlation was used. This method uses an Electrical Low Pressure Impactor (ELPI, DEKATI) for particles of between 7 nm and 1.2 µm and an original method that entails coupling two condensation particle counters (CPC 3788 and 3786, TSI). Seven experimental campaigns were conducted between 2007 and 2015, during which the dry deposition velocities ( Vd in m.s −1 ) were obtained for atmospheric aerosol particles of size between 2.5 nm and 1.2 µm in size, above different natural surfaces (maize, grassland, bare soil and forest). The findings highlight the influence of the following parameters: friction velocity of the wind, surface sensible heat flux and atmospheric stability (quantified by the length of Monin-Obukhov). Comparing the findings for each natural surface revealed it can reasonably be assumed that the influence of each natural surface on deposition is mainly explained in the data provided by friction velocity ( u* m.s −1 ). The other parameters related to the natural surface, such as the Leaf Area Index (LAI) or vegetation cover properties (adherence, micro roughness), have a second order impact on all the findings. [ABSTRACT FROM AUTHOR]

Abstract: Dry deposition of a submicron aerosol is studied in a wind tunnel to measure dry deposition velocities onto horizontal and vertical urban surfaces of glass, cement facing and grass for several wind speeds and to measure the turbulence parameters associated with these deposition velocities. These deposition velocities are then compared to data of the literature and to the results of two models for dry deposition. The dry deposition velocity of the fluorescein aerosol increases with the intensity of the turbulence. This highlights the importance of the turbulent processes of impaction and interception in deposition. However, the ratio of dry deposition velocity to friction velocity depends on the surface type. It depends on the turbulence conditions in the boundary layer. These turbulent dry deposition processes thus vary in importance depending on the studied surface. Finally, settling represents a significant part of the deposition for low wind speeds and for smooth surfaces. This wind tunnel study permits the study of the deposition as a function of turbulent processes. It should be supplemented by in situ experiments to take into account all the physical processes involved under real conditions. [Copyright &y& Elsevier]