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Etude de la composante organique de l'aérosol atmosphérique : cas de deux vallées alpines (Chamonix et Maurienne) et développement analytique

Abstract : Atmospheric particles are known to contain organic carbon material in variable amounts, depending on their location. This class of particulate matter is important in a wide range of geophysical and environmental problems, ranging from local issues (pollution) to the global scale (climate change). Unfortunately, the knowledge of the physicochemical properties and formation mechanisms of this organic fraction, called POM (Particulate Organic Matter), is still very insufficient. This work thus fits in the category of obtaining a better knowledge of the organic fraction of the aerosol.
As part of the PO.V.A. program (POllution des Vallées Alpines), whose principal objectives are to understand air pollution phenomena and the dispersive mechanisms specific to the mountainous systems, two 15 days intensive sampling campaigns were performed in two sensitive valleys : the valley of Chamonix and the valley of Maurienne. The first sampling campaign was performed in summer 2000 and the second in winter 2001 to investigate seasonal variations and to obtain good air pollution fingerprints at these two valleys before reopening the tunnel of Mont Blanc.

After the presentation of the problems (chapter I) and the methods used (chapter II), the results of two types of analyses are presented (chapter III). The first type is focused on a class of compounds: Polycyclic Aromatic Hydrocarbons (PAH). Next to the public health concern, the study of atmospheric PAHs is of geochemical interest as they are emitted by combustion processes (oil derivatives and biomass) and are therefore good indicators of these emissions. The second type of analyses, more exploratory, consists in carrying out the quantitative speciation of the organic fraction and to establish relationships between chemical composition, and sources, seasons and physical parameters. Compounds like guaiacol, vanillin, syringol (...) emitted by wood combustions or nopinone known as secondary compound could be quantified. The results obtained made it possible to highlight:

- an important anthropic contribution in the aerosols collected in the two valleys, for the two seasons and more particularly in winter when very important PAHs concentrations were observed (maximum 150 ng.m-3);
- primary anthropic compounds with concentrations systematically more important in the valley of Chamonix, in spite of the absence of heavy traffic;
- an overwhelming importance of the geomorphology of the valleys and of the meteorological conditions for the dispersion of pollutants;
- a very marked contribution of wood combustion in the valley of Chamonix during winter.

The quantitative speciation of POM (chapter III) made it possible to determine overall between 10 and 74% of organic carbon mass. The identified fraction depends on the season and is higher during winter (34-74%) when the anthropic primary sources contribution is dominating. This seasonal variability highlighted the gaps of the analytical protocol used, which does not allow us to quantify the polyfunctional oxygenated compounds and thus secondary organic compounds. Alternative sampling and analysis methods of these compounds were developed and presented in Chapter IV.
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Submitted on : Friday, October 10, 2003 - 5:57:05 PM
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Nicolas Marchand. Etude de la composante organique de l'aérosol atmosphérique : cas de deux vallées alpines (Chamonix et Maurienne) et développement analytique. Autre. Université de Savoie, 2003. Français. ⟨tel-00003533⟩

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