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 a high 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 organic nitrate (RONO2) OOMs with high yields. The effective saturation concentration (C∗) of RONO2 OOMs is mostly lower than the OOMs formed by OH oxidation, more easily distributed into the particle phase. The estimated C∗ of the generated OOMs is 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 RONO2 OOMs, would be conducive to molecular structure identification of OOMs in atmospheric monitoring and atmospheric chemical model refinement.