New insights into the gas-phase oxidation of isoprene by the nitrate radical from experiments in the atmospheric simulation chamber SAPHIR

Experiments at a set of atmospherically relevant conditions were performed in the simulation chamber SAPHIR, investigating the oxidation of isoprene by the nitrate radical (NO3). An extremely comprehensive set of instruments detected trace gases, radicals, aerosol properties and hydroxyl (OH) and NO3 radical reactivity. The chemical conditions in the chamber were varied to change the fate of the peroxy radicals (RO2) formed after the reaction between NO3 and isoprene from either mainly recombining with other RO2 or mainly reacting with hydroperoxyl radicals (HO2). These major atmospheric pathways for RO2 radicals lead to the formation of organic nitrate compounds which then have different atmospheric fates. The experimental concentration profiles are compared to box model calculations using both the current Master Chemical Mechanism (MCM) as well as recently available literature data alongside new quantum chemical calculations. The discussion here focusses on the resulting RO2 distribution and deviations in the predictions of early products and total alkyl nitrate yields for the different chemical conditions. Preliminary results for instance show too high night time losses of alkyl nitrates due to ozonolysis in the current MCM.