Highly oxygenated organic molecule (HOM) formation in the isoprene oxidation by NO<sub>3</sub> radical

Abstract. Highly oxygenated organic molecules (HOM) are found to play an important role in the formation and growth of secondary aerosol (SOA). SOA is type with significant impact on air quality climate. Compared oxidation volatile compounds by ozone (O3) hydroxyl radical (OH), HOM nitrate (NO3), oxidant at nighttime dawn, has received less attention. In this study, reaction isoprene NO3 was investigated SAPHIR chamber (Simulation Atmospheric PHotochemistry a large Reaction chamber). A number HOM, including monomers (C5), dimers (C10), trimers (C15), both closed-shell open-shell peroxy radicals (RO2), were identified classified into various series according their formula. Their pathways proposed based observed known mechanisms literature, which further constrained time profiles after sequential addition differentiate first- second-generation products. containing one three N atoms (1–3N-monomers) formed, starting carbon double bond, forming radicals, followed autoxidation. 1N-monomers formed direct first-generation 2N-monomers (e.g., C5H8N2On(n=7–13), C5H10N2On(n=8–14)) likely termination products C5H9N2On?, C5-hydroxynitrate (C5H9NO4), product bond. 2N-monomers, products, dominated accounted for ?34 % all indicating + under our experimental conditions. H shift alkoxy form subsequent autoxidation (“alkoxy–peroxy” pathway) be pathway formation. mostly accretion monomer RO2 via reactions dimer possibly C5–RO2 isoprene. RO2. The concentrations different showed distinct during reaction, linked pathway. either typical profile or combination both, multiple and/or isomers. Total molar yield estimated 1.2 %-0.7%+1.3%, corresponded ?3.6 assuming molecular weight C5H9NO6 as lower limit. This suggests that may contribute fraction NO3.