The chemistry of organic compounds in clouds : multiphase explicit modeling ; La chimie des composés organiques dans les nuages : modélisation explicite multiphasique

The atmospheric oxidation of organic compounds is progressive and leads to the formation of a myriad of secondary organic compounds. These secondary organic compounds (SOC) can be hydrosoluble and react in the atmospheric aqueous phase. The scientific community is currently interested in the environmental impact of the atmospheric organic matter aqueous phase reactivity. For example, recent studies show that these modifications could increase the secondary organic aerosol (SOA) production. In order to explore effects of the aqueous reactivity, this work consists of a detailed modeling study of the SOC dissolution and their aqueous oxidation. The modeling is based on the extension of the explicit chemical schemes generator GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere).There is little known about the soluble fraction of SOC. It is thus needed to quantify it as a function of the liquid water content. GECKO-A enables the generation of explicit oxidation schemes for the gas phase. To integrate the dissolution of produced organic compounds, their Henry's law constants have been documented. The low number of available data (600) compared to the large number of formed secondary species (>103) requires the empirical estimate of the majority of Henry's law constants. We relied on an estimate method based on a structure-activity relationship developed at LISA, GROMHE (GROup contribution Method for Henry's law Estimates). This allowed us to describe the mass transfer of every soluble species generated during the oxidation of three precursors of atmospheric interest: isoprene, octane and α-pinene. For a liquid water content typical of a deliquescent aerosol, only a very small fraction of SOC is dissolved. However, we showed that a significant proportion of SOC could dissolve in a cloud aqueous phase. Dissolution and reactivity of SOC produced from the oxidation of long chain compounds need to be represented in models. In order to describe the aqueous reactivity of dissolved organic ...