Alkyl nitrate (AN) and secondary organic aerosol (SOA) from the reaction of nitrate radicals (NO 3 ) with isoprene were observed in the Simulation of Atmospheric PHotochemistry In a large Reaction (SAPHIR) chamber during the NO 3 Isop campaign in August 2018. Based on 15 day-long experiments under various reaction conditions, we conclude that the reaction has a nominally unity molar AN yield (observed range 90 ± 40%) and an SOA mass yield of OA + organic nitrate aerosol of 13–15% (with ∼50 μg m –3 inorganic seed aerosol and 2–5 μg m –3 total organic aerosol). Isoprene (5–25 ppb) and oxidant (typically ∼100 ppb O 3 and 5–25 ppb NO 2 ) concentrations and aerosol composition (inorganic and organic coating) were varied while remaining close to ambient conditions, producing similar AN and SOA yields under all regimes. We observe the formation of dinitrates upon oxidation of the second double bond only once the isoprene precursor is fully consumed. We determine the bulk partitioning coefficient for ANs ( K p ∼ 10 –3 m 3 μg –1 ), indicating an average volatility corresponding to a C 5 hydroxy hydroperoxy nitrate.

<p>Experiments at a set of atmospherically relevant conditions were performed in the atmospheric simulation chamber SAPHIR, investigating the oxidation of isoprene by the nitrate radical (NO3). A 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, and seed aerosol of varying composition was added to initiate gas/aerosol partitioning. This presentation discusses observed gas/aerosol partitioning of the major organic nitrate products and summarizes the observations of secondary organic aerosol yield.</p>