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 NOx 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 NOx are 2–3 times higher than those in the absence of NOx 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 NOx. Based on gas-phase products and possible reaction pathways, functionalization of benzoic acid via the phenolic pathway is favored in the presence of NOx. Thus, our study highlights the significant SOA formation from aromatic ketone IVOCs, especially in the presence of NOx during long-time photooxidation.
In this study, we propose a passive air sampler (PAS) that mainly consists of activated charcoal sorbent, a radial diffusive body, and a protective shield for the outdoor monitoring of volatile organic compounds (VOCs). Due to its reusable accessories and small size, this PAS is cost-effective and highly convenient for outdoor deployment. The estimated sampling rates (SRs) for 28 VOCs were very close to the theoretical values over a 6-month field test. We evaluated the performance of the PAS with benzene, toluene, ethylbenzene, and xylenes (BTEX) and determined the method detection limits (MDLs) (0.02–0.04 µg m –3 ), recovery values (95.3 ± 9.8–99.8 ± 7.5%), repeatability (3.2 ± 2.2–4.6 ± 2.9%), and uncertainties (10.1 ± 3.8–12.9 ± 4.5%), which are comparable to those of previously reported samplers and meet the requirements of European Standards (EN) 13528. The deployment times for obtaining reliable time-weighted average (TWA) atmospheric concentrations of BTEX ranged from 2 days to a minimum of 3 months according to corresponding background concentrations in the ambient air. Moreover, the atmospheric concentrations of BTEX measured by the sampler in this study compared favorably with values from both active and passive sampling methods, with R 2 ≥ 0.97 ( p < 0.0001). Finally, a 12-month field test was performed after evaluating the sampler, and the results showed apparent seasonal variations of atmospheric VOC concentrations, which were dominated by the sampling location and wind direction.
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