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

Abstract

Abstract. 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 SO2 and NH3 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 SO2 and/or NH3. Here, we show that SO2 emission could considerably enhance aerosol particle formation due to SO2-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 SO2-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 NH3-involved experiments, results demonstrated a positive correlation between NH3 levels and particle volume as well as number concentrations. The effects of NH3 on SOA composition were slight under SO2-free conditions but stronger in the presence of SO2. A series of multifunctional products with carbonyl, alcohols, and nitrate functional groups were tentatively characterized in NH3-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 SO2 and NH3 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 SO2, NH3, and aromatics emissions.

Secondary organic aerosol formation from monocyclic aromatic hydrocarbons: insights from laboratory studies

“…Third, the enhancement in aromatic SOA was observed in the presence of SO 2 or acidic seed particles. 15,31,35,86 The identi-cation of aromatic SOA composition revealed the generation of heterogeneous reaction-derived organosulfates. In addition, some chamber studies measured the chemical functional groups of aromatic SOA.…”

“…The acidity effects have also been observed for organosulfate production in trimethylbenzene SOA through the highresolution mass spectrometry measurement of SOA composition. 15,31 SO 2 -induced acidic sulfates can react with hydroperoxides or epoxides to generate organosulfates in the trimethylbenzene/NO x /SO 2 system. 15,31 These laboratory results highlight the importance of aromatic hydrocarbons for organosulfate formation in the presence of acidic particles.…”

“…15,31 SO 2 -induced acidic sulfates can react with hydroperoxides or epoxides to generate organosulfates in the trimethylbenzene/NO x /SO 2 system. 15,31 These laboratory results highlight the importance of aromatic hydrocarbons for organosulfate formation in the presence of acidic particles. Aerosolphase sulfur in the form of S(VI) has been generally suggested to mainly exist as inorganic sulfate.…”

“…12 de Gouw et al reported that SOA produced in urban plumes could represent 35% and 8.5% of the total organic matter in the United States and of the global organic matter, respectively. 13 Many studies highlighted that the amount of ASOA was considerably underestimated, particularly in urban and industrial regions, 2,11,14,15 motivating numerous studies to be carried out to investigate ASOA formation from anthropogenic emissions.…”

SO2 enhances aerosol formation from anthropogenic volatile organic compound ozonolysis by producing sulfur-containing compounds

“…A summary of experimental conditions and results is listed in Table 1. Detailed experimental equipment and methods have been described in our previous studies (Yang et al, 2022;Yang et al, 2021). Briefly, cyclooctene was introduced into the chamber by passing zero air through a tube containing a known volume of cyclooctene 90 (95%, Alfa).…”