Thèse de doctorat de l'Université Paris-Est

Organic aerosol formation in the atmosphere is investigated via the developpement of a new model named H2O (Hydrohilic/Hydrophobic Organics). First, a parameterization is developped to take into account secondary organic aerosol formation from isoprene oxidation. It takes into account the e ect of nitrogen oxides on organic aerosol formation and the hydrophilic properties of the aerosols. This parameterization is then implemented in H2O along with some other developments and the results of the model are compaired to organic carbon measurements over Europe. Model performance is greatly improved by taking into account emissions of primary semi-volatile compounds, which can form secondary organic aerosols after oxidation or can condense when temperature decreases. If those emissions are not taken into account, a signi cant underestimation of organic aerosol concentrations occurs in winter. The formation of organic aerosols over an urban area was also studied by simulating organic aerosols concentration over the Paris area during the summer campaign of Megapoli (July 2009). H2O gives satisfactory results over the Paris area, although a peak of organic aerosol concentrations from tra c, which does not appear in the measurements, appears in the model simulation during rush hours. It could be due to an underestimation of the volatility of organic aerosols. It is also possible that primary and secondary organic compounds do not mix well together and that primary semi volatile compounds do not condense on an organic aerosol that is mostly secondary and highly oxidized. Finally, the impact of aqueous-phase chemistry was studied. The mechanism for the formation of secondary organic aerosol includes in-cloud oxydation of glyoxal, methylglyoxal, methacrolein and methylvinylketone, formation of methyltetrols in the aqueous phase of particles and cloud droplets, and the in-cloud aging of organic aerosols. The impact of wet deposition is also studied to better estimate the impact of clouds on organic aerosol concentrations. 7 pa st el -0 07 78 08 6, v er si on 1 18 J an 2 01 3