Test of chemical mechanisms for the NO3 oxidation of isoprene in the atmospheric simulation chamber SAPHIR

A month long series of experiments were performed in the atmospheric simulation chamber SAPHIR investigating the night-time oxidation of isoprene by the nitrate radical (NO₃) in absence and presence of seed aerosol. A comprehensive set of instruments detecting trace gases, radicals, aerosol properties and hydroxyl (OH) and NO₃ radical reactivity were used during the experiments which were performed most of the time at atmospheric-like concentrations. Chemical conditions in the chamber were varied, so that peroxy radicals (RO₂) formed after the reaction between NO₃ and isoprene would either mainly recombine (approximately 80%) or mainly react with hydroperoxy radicals (HO₂, approximately 60%). Theses major atmospheric pathways for RO₂ radicals lead to the formation of organic nitrate compounds that will have different atmospheric fates. Here, the comparison between measured and calculated trace gases concentrations are discussed with a focus on the first reaction steps in the oxidation of isoprene by NO₃ and the further oxidation of the first-generation oxidation products. Calculated concentrations are obtained from a chemical box model using the Master Chemical Mechanism which is compared and implemented with recent available literature data.