Antoine Roose's thesis defense

Summary of the thesis Many uncertainties are still associated with the reaction mechanisms used in atmospheric chemistry models, in particular on the chemistry of the ROx (OH, HO2, RO2) radicals. In particular, the absence or an approximate description of heterogeneous processes (capture of radicals) on the surface of aerosols represents a point for improvement. The objective of this thesis is to combine an experimental (macroscopic) and theoretical (molecular point of view) approach to the capture of peroxyl radicals on the surface of organic aerosols. In the first part of this work, a laminar flow reactor coupled to a HO2 and RO2 measurement system by chemical amplification was developed and characterized. This experimental device makes it possible to measure the capture of the HO2 radicals on organic aerosols and also that of the RO2 radicals over time. In the context of this study, the capture of HO2 radicals was measured on glutaric acid aerosols and compared with data from the literature which showed disagreements. The second part of this work consisted in using molecular modeling tools (molecular dynamics and / or quantum chemistry) in order to describe the different processes of the capture of the HO2 radical on a model particle of glutaric acid. The accommodation coefficient was determined and a first characterization of the heterogeneous reactivity was carried out using the hybrid QM / MM (quantum / classical) ONIOM method.
Keywords: organic aerosols; catch coefficient; molecular dynamics; peroxy radicals; modelization; flow tube