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Formation de l’aérosol organique secondaire dans les modèles de qualité de l’air : développement d’une paramétrisation sur la base de simulations explicites

Abstract : The gaseous oxidation of organic compounds emitted into the atmosphere leads to the formation of thousands of secondary organic compounds (SOC). A fraction of these SOC is low volatile, and can partition between the gaseous phase and the particulate phase, forming secondary organic aerosols (SOA). The SOA are a main component of the particles, representing between 20% and 80% of the total mass of fine aerosols. Therefore, SOA contribute to the impact of aerosols on the environment, in particular air quality and climate. The quantification of the SOA impacts is estimated using chemical-transport models (CTM). Comparisons with in situ measurements show that the spatial and temporal variations of SOA mass are not correctly simulated by CTM. In these models, the SOA formation is represented in a simplified way, using empirical parameterizations developed on the basis of observations performed in atmospheric simulation chambers. Improving the representation of organic aerosols in CTM is therefore required to diagnose the origin of air pollution by fine particles, improve the reliability of pollution episode prediction and assess the impact of aerosols on the environment. The objectives of this thesis are :• to explore the influence of environmental conditions on SOA formation and properties,• to develop a new parameterization of SOA formation based on a deterministic representation of atmospheric chemistry,• to evaluate this parameterization in CTM by comparison with in-situ measurements. Deterministic models represent the non-linearity of SOA formation processes. The model GECKO-A (Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere) is a numerical modelling tool that integrates the elementary data (kinetics and thermodynamics) from laboratory studies. In this thesis, oxidation scenarios representative of various environmental conditions were developed and GECKO-A was used to study the impact of environmental factors (temperature, NOx concentrations, solar radiations, etc.) on the formation and the properties of the SOA. On the basis of these simulations, a new parameterization for SOA formation was developed: VBS-GECKO. The evaluation of the VBS-GECKO in box model has shown a good reproduction of the organic aerosol (OA) concentrations with RMSE lesser than 20%.The VBS-GECKO was integrated into the CHIMERE CTM to simulate summer concentrations of OA over Europe. Simulated OA are significantly improved compared to the reference parameterization used in CHIMERE. The VBS-GECKO was also used to study (i) the sources and properties of SOA and (ii) different representations of emissions of semi-volatile and intermediate volatility organic compounds by road traffic
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Victor Lannuque. Formation de l’aérosol organique secondaire dans les modèles de qualité de l’air : développement d’une paramétrisation sur la base de simulations explicites. Sciences de la Terre. Université Paris-Est, 2017. Français. ⟨NNT : 2017PESC1129⟩. ⟨tel-02863053v2⟩

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