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Quantification des vitesses de dépôt par temps sec et documentation des processus d’émission des aérosols sur couvert naturel : du nanomètre au micron

Abstract : The particles emitted into the atmosphere during chronic or accidental release by the nuclear plants can be subjected, after dispersion, to vertical flows by dry weather: dry deposition and resuspension. Vertical flows in dry weather are characterized by the vertical transfer rate, which is the ratio between the particle flux and the atmospheric concentration of the aerosol in the vicinity of the surface. When this speed is positive, it is a dry deposition rate (Vd in m.s-1) and conversely, when it is negative, it is a transmission rate. It is important to study their dry deposition in a prairial environment. Indeed, the products resulting from this environment are a component of the human food chain via livestock. For particles less than 1 μm, there is a lack of experimental data, which results in uncertainty about the results of the models, which can reach up to two orders of magnitude. In addition, there are no in situ deposition rate measurement data available for particles less than 10 nm. These particles are derived from the gas / particle conversion (nucleation) and may relate to certain radionuclides such as iodine (129, 131I).After their deposition, these radionuclides can be resuspended under the effect of the stress submitted by the wind on the canopy. Such a phenomenon is suspected around the Fukushima nuclear power plant. The aerosol resuspension processes are characterized by the vertical transfer rate (m.s-1) but also by the re-suspension coefficient (Ks in m-1) which is the ratio of atmospheric concentration to surface concentration of particles. Relative uncertainties of 2 to 3 orders of magnitude on the resuspension coefficients exist. The resuspension concerns all the particles present on the canopy, whether they are inert or living (fungi, bacteria, yeasts, etc.). Unlike inert particles, these living particles can assimilate and concentrate radionuclides. However, there is very little data on the resuspension of microorganisms and bacteria in particular. In this context, the objectives of the thesis are to quantify the dry deposition rate as a function of the particle size and the main micrometeorological parameters in the range 1.5 nm - 1.2 μm. The second objective is to document the processes of emission of the bacteria
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Geoffrey Pellerin. Quantification des vitesses de dépôt par temps sec et documentation des processus d’émission des aérosols sur couvert naturel : du nanomètre au micron. Physique [physics]. Université Paris-Est, 2017. Français. ⟨NNT : 2017PESC1086⟩. ⟨tel-01794047⟩

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