SO 2 and NH 3 emissions enhance organosulfur compounds and fine particle formation from the photooxidation of a typical aromatic hydrocarbon

Yang, Zhaomin; Xu, Li; Tsona, Narcisse T.; Li, Jianlong; Luo, Xin; Du, Lin

Aromatic hydrocarbons can dominate the volatile organic compound budget in the urban atmosphere. Among them, 1,2,4-trimethylbenzene (TMB), mainly emitted from solvent use, is one of the most important secondary organic aerosol (SOA) precursors. Although atmospheric SOinline-formula2 and NHinline-formula3 levels can affect secondary aerosol formation, the influenced extent of their impact and their detailed driving mechanisms are not well understood. The focus of the present study is to examine the chemical compositions and formation mechanisms of SOA from TMB photooxidation influenced by SOinline-formula2 and/or NHinline-formula3. Here, we show that SOinline-formula2 emission could considerably enhance aerosol particle formation due to SOinline-formula2-induced sulfate generation and acid-catalyzed heterogeneous reactions. Orbitrap mass spectrometry measurements revealed the generation of not only typical TMB products but also hitherto unidentified organosulfates (OSs) in SOinline-formula2-added experiments. The OSs designated as being of unknown origin in earlier field measurements were also detected in TMB SOA, indicating that atmospheric OSs might also be originated from TMB photooxidation. For NHinline-formula3-involved experiments, results demonstrated a positive correlation between NHinline-formula3 levels and particle volume as well as number concentrations. The effects of NHinline-formula3 on SOA composition were slight under SOinline-formula2-free conditions but stronger in the presence of SOinline-formula2. A series of multifunctional products with carbonyl, alcohols, and nitrate functional groups were tentatively characterized in NHinline-formula3-involved experiments based on infrared spectra and mass spectrometry analysis. Plausible formation pathways were proposed for detected products in the particle phase. The volatility distributions of products, estimated using parameterization methods, suggested that the detected products gradually condense onto the nucleation particles to contribute to aerosol formation and growth. Our results suggest that strict control of SOinline-formula2 and NHinline-formula3 emissions might remarkably reduce organosulfates and secondary aerosol burden in the atmosphere. Updating the aromatic oxidation mechanism in models could result in more accurate treatment of particle formation for urban regions with considerable SOinline-formula2, NHinline-formula3, and aromatics emissions.

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Yang, Zhaomin / Xu, Li / Tsona, Narcisse T. / et al: SO2 and NH3 emissions enhance organosulfur compounds and fine particle formation from the photooxidation of a typical aromatic hydrocarbon. 2021. Copernicus Publications.

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