Particle-Bound Highly Oxidized Organic Molecules Derived from Aromatic Hydrocarbons in an Urban Atmosphere
Ming Zhu, Sainan Wang, Yanli Zhang, Zhiqiang Yu, Yunjiang Yu, Xinming Wang
Abstract
Previous laboratory and theoretical studies have demonstrated that gas-phase oxidation of aromatic hydrocarbons can produce highly oxidized organic molecules (HOMs) via autoxidation, yet our molecular-level understanding of aromatics-derived HOMs existing stably in the particulate phase in ambient air remains unclear. In this study, filter-based ambient fine particle samples were collected in the Pearl River Delta region in south China and particle-bound HOMs derived from gas-phase autoxidation of aromatic hydrocarbons were assessed by using a Fourier transform ion cyclotron resonance mass spectrometer. The results revealed that aromatics-derived HOMs that survived in fine particles were more diverse than those observed in the laboratory or predicted by theory. O6–7 class species were the most abundant species (75–90% signal intensity) among the aromatics-derived CHO-HOMs. The aromatics-derived CHON-HOM monomers accounted for 7–10% of all observed CHON species. The observed aromatics-derived CHO- and CHON-HOMs accounted for 1.7–5.1‰ and 0.2–0.6‰, respectively, of the total particulate organic aerosol mass. The semiquantified concentrations of aromatics-derived HOMs were comparable to those of aromatics-derived SOA estimated by the tracer method and increased significantly with relative humidity. The results suggest a substantial contribution of aromatics-derived HOMs in aromatics-derived SOA in an urban atmosphere, particularly during haze days with higher relative humidity.