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Modélisation des processus bio-physico-chimiques du milieu nuageux : devenir de la matière organique

Abstract : The role of clouds on the atmospheric chemical composition is still poorly known. The chemical compounds under the form of particles and gases are efficiently transformed in the cloud by photochemical and microbiological processes. The thesis objectives were to analyze the efficiency of these processes in the transformations of the chemical compounds using the multiphase cloud chemistry model CLEPS (CLoud Explicit Physico-chemical schema). The first work consisted in studying the cloud oxidizing capacity based on comparisons between HO• radical production rates for irradiated cloud water sampled at the puy de Dôme station determined experimentally in the lab data and modeled with CLEPS. These comparisons showed that the model overestimates the contribution of the iron photolysis in the production of HO• radicals. This is due to the complexation of iron in cloud water samples that is not considered in the model due to the lack of data. The model also showed that the photolysis of hydrogen peroxide represents the major source of the HO• radicals in the aqueous phase. Secondly, the new protocol for cloud aqueous phase oxidation of organic compounds developed to build the CLEPS model was validated based on irradiation experiments of a target compound, the tartronic acid that were simulated by the model. The experimental work confirmed the formation of glyoxylic acid predicted by the aqueous phase mechanism in the model. It reproduces the temporal evolution of the concentrations of tartronic acid and of its first oxidation product, the glyoxylic acid but underestimates the formation of formic acid which is one of final products of the tartronic acid oxidation. Finally, the model was developed to take into account biodegradation rates measured in the laboratory. The model allows comparing the efficiency of the chemical and microbiological processes for the degradation of four chemical species and testing the effect of key environmental parameters (temperature, actinic flow). The biological activity was recognized as more effective in the summer case than in the winter case and the contribution of microorganisms the night is dominant for both scenarios. A sensitivity test demonstrated that the contribution of the microbial activity in the degradation of the chemical compounds is strongly increased in comparison with the photochemical reactivity when the iron is supposed to be totally complexed.
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https://tel.archives-ouvertes.fr/tel-01764134
Contributor : Abes Star :  Contact
Submitted on : Wednesday, April 11, 2018 - 4:40:07 PM
Last modification on : Thursday, April 9, 2020 - 8:28:02 AM

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  • HAL Id : tel-01764134, version 1

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Hélène Perroux. Modélisation des processus bio-physico-chimiques du milieu nuageux : devenir de la matière organique. Sciences de la Terre. Université Clermont Auvergne, 2017. Français. ⟨NNT : 2017CLFAC058⟩. ⟨tel-01764134⟩

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