Secondary Organic\nAerosol Formation from the Photooxidation\nof Aromatic Ketone Intermediate Volatile Organic Compounds

Oxygenated aromatics are substantial secondary organic\naerosol\n(SOA) precursors, such as benzyl alcohol and phenolic compounds. Aromatic\nketone intermediate volatile organic compounds (IVOCs), as a subclass\nof oxygenated aromatics, were found in anthropogenic source emissions\nand may contribute to SOA formation. However, the SOA yields and formation\npathways of aromatic ketone IVOCs remain unknown. In this study, the\nphotooxidations of aromatic ketone IVOCs in the absence and presence\nof NO<sub><i>x</i></sub> were studied in an oxidation flow\nreactor, and the particle- and gas-phase oxidation products were measured.\nThe maximum SOA yields of benzophenone and 1,2-diphenylethanone are\n0.24 and 0.33–0.35, respectively, relatively high among oxygenated\naromatics. The SOA yields in the presence of NO<sub><i>x</i></sub> are 2–3 times higher than those in the absence of NO<sub><i>x</i></sub> in the late stage of oxidation. As the photooxidation\nproceeds, H/C of SOA slightly increases with O/C, and a greater amount\nof more-oxidized ring-retaining products exists in the particle phase\nin the presence of NO<sub><i>x</i></sub>. Based on gas-phase\nproducts and possible reaction pathways, functionalization of benzoic\nacid via the phenolic pathway is favored in the presence of NO<sub><i>x</i></sub>. Thus, our study highlights the significant\nSOA formation from aromatic ketone IVOCs, especially in the presence\nof NO<sub><i>x</i></sub> during long-time photooxidation.