Key Role of Nitrogen-containing Oxygenated Organic Molecules (OOMs) in SOA Formation Evidenced by OH/NO₃-induced Terpinolene Oxidation

Abstract. Oxygenated organic molecules (OOMs), generated from the oxidation of various biogenic volatile organics with diverse yields, are a great contributor to SOA formation. Terpinolene is an isomeride of limonene, with an even higher SOA yield. Herein we investigated the elaborate oxidation mechanism of terpinolene by OH and NO₃, elucidating the new formation mechanism of OOMs and their yield profiles based on the newly-built zero-dimensional chemical model under three typical atmospheric conditions. For terpinolene oxidation by OH, H shift imposes restrictions on continuous autoxidation, instead by the reactions with HO₂/NO/NO₂ resulting in chain termination. For the reaction of terpinolene with NO₃, the transfer of the radical center via bond breaking, triggering a new round of autoxidation, is newly found to be pivotal in the formation of nitrogen-containing OOMs with high yields. The effective saturation concentration (C^*) of nitrogen-containing OOMs is mostly lower than the OOMs formed by OH oxidation, more easily distributed into particle phase. The estimated C^* of the generated OOMs are distinctly varied among OOM isomers, which emphasizes the necessity of determining their molecular structures, peculiarly the number of rings. The comparative analysis of OH-initiated (daytime) and NO₃-driven (nocturnal) terpinolene oxidation mechanism, highlighted the formation of nitrogen-containing OOMs, would be conducive to molecular structures identification of OOMs in atmospheric monitoring and atmospheric chemical model refinement.