Modeling organic aerosol: impact on long-range pollution in Europe.

Summary Particulate pollution covers many health and climate issues in Europe and worldwide. Organic aerosols, which represent a significant fraction of particulate pollution, are a complex material, emitted directly in condensed form or resulting from the oxidation of a very large number of volatile organic compounds in the atmosphere. Because of the great variety of its emission sources, whether biogenic or anthropogenic, the composition and the processes of formation and chemical ageing of organic aerosols remain today associated with many questions. Since field observation of the formation of organic matter and its evolution within air masses is difficult to implement, modeling remains an indispensable complementary tool to simulate organic aerosol and follow its transport over long distances. This is why this work was first focused on identifying the major processes governing both the formation and photochemical aging of the organic fraction of particles. Based on an innovative methodology, an operational chemical scheme dedicated to the emission and oxidation of semi-volatile compounds has been developed for air quality models. Its implementation and its evaluation within the CHIMERE model was carried out by confrontation with the data of the summer and winter campaigns of the MEGAPOLI campaign. Finally, this work also aimed at implementing in CHIMERE and discussing the mechanisms of oligomerization of organic compounds in condensed phase, a phenomenon which is nowadays recognized as one of the major process of aging of organic aerosol.