Secondary Organic Aerosol Formation from the Photooxidation of Aromatic Ketone Intermediate Volatile Organic Compounds.

Abstract

Oxygenated aromatics are substantial secondary organic aerosol (SOA) precursors, such as benzyl alcohol and phenolic compounds. Aromatic ketone intermediate volatile organic compounds (IVOCs), as a subclass of oxygenated aromatics, were found in anthropogenic source emissions and may contribute to SOA formation. However, the SOA yields and formation pathways of aromatic ketone IVOCs remain unknown. In this study, the photooxidations of aromatic ketone IVOCs in the absence and presence of NO_x were studied in an oxidation flow reactor, and the particle- and gas-phase oxidation products were measured. The maximum SOA yields of benzophenone and 1,2-diphenylethanone are 0.24 and 0.33-0.35, respectively, relatively high among oxygenated aromatics. The SOA yields in the presence of NO_x are 2-3 times higher than those in the absence of NO_x in the late stage of oxidation. As the photooxidation proceeds, H/C of SOA slightly increases with O/C, and a greater amount of more-oxidized ring-retaining products exists in the particle phase in the presence of NO_x. Based on gas-phase products and possible reaction pathways, functionalization of benzoic acid via the phenolic pathway is favored in the presence of NO_x. Thus, our study highlights the significant SOA formation from aromatic ketone IVOCs, especially in the presence of NO_x during long-time photooxidation.