Rate constant and secondary organic aerosol formation from the gas-phase reaction of eugenol with hydroxyl radicals

Abstract

Abstract. Methoxyphenols are an important organic component of wood-burning emissions and considered to be potential precursors of secondary organic aerosol (SOA). In this work, the rate constant and SOA formation potential for the OH-initiated reaction of 4-allyl-2-methoxyphenol (eugenol) were investigated for the first time in an oxidation flow reactor (OFR). The rate constant was 8.01±0.40×10-11 cm3 molecule−1 s−1, determined by the relative rate method. The SOA yield first increased and then decreased as a function of OH exposure and was also dependent on eugenol concentration. The maximum SOA yields (0.11–0.31) obtained at different eugenol concentrations could be expressed well by a one-product model. The carbon oxidation state (OSC) increased linearly and significantly as OH exposure rose, indicating that a high oxidation degree was achieved for SOA. In addition, the presence of SO2 (0–198 ppbv) and NO2 (0–109 ppbv) was conducive to increasing SOA yield, for which the maximum enhancement values were 38.6 % and 19.2 %, respectively. The N∕C ratio (0.032–0.043) indicated that NO2 participated in the OH-initiated reaction, subsequently forming organic nitrates. The results could be helpful for further understanding the SOA formation potential from the atmospheric oxidation of methoxyphenols and the atmospheric aging process of smoke plumes from biomass burning emissions.

Aging of Atmospheric Brown Carbon Aerosol

“…The proposed mechanism for this reaction includes hydrogen abstraction of a phenolic hydrogen by either OH or NO 3 radicals, forming a β-hydroxyphenoxy radical, which subsequently reacts with NO 2 to form 4NC (Figure ). Similar reaction mechanisms have been observed for other biomass burning VOCs such as phenol, resorcinol, eugenol, guaiacol, and syringol. − This mechanism was also observed with the precursor trimethylbenzene (TMB), which did not produce as many NACs as toluene because the addition of NO 2 to the phenoxy radical formed is inhibited . This reaction pathway contributed to formation of nitrophenols …”

“…50 Similar reactions mechanisms have been observed for other biomass burning VOCs such as phenol, resorcinol, eugenol, guaiacol, and syringol. [108][109][110][111] This mechanism was also observed with the precursor trimethylbenzene (TMB), which did not produce as many NACs as toluene because the addition of NO2 to the phenoxy radical formed is inhibited. 100 This reaction pathway contributed to formation of nitrophenols.…”

Increased primary and secondary H<sub>2</sub>SO<sub>4</sub> showing the opposing roles in secondary organic aerosol formation from ethyl methacrylate ozonolysis

“…Recent studies suggested that the reaction between SO 2 and sCI dominated the formation of H 2 SO 4 particles and was enhanced with increased SO 2 concentration. An important reason for this is that the rapid homogeneous nucleation of H 2 SO 4 not only can provide greater surface area and volume for the condensation of low-volatile products but also reduce the fraction of these semi-volatile species lost to the wall (Chu et al, 2016;Liu et al, 2017;X. Zhang et al, 2014).…”

“…3c, the maximum pro- duction of both Factor 1 and Factor 2 increased with increasing SO 2 . One reasonable explanation is that the formation of more H 2 SO 4 particles with increasing SO 2 provided a greater surface area and volume for the simultaneous condensation of both less-oxygenated and more-oxygenated organic products (Chu et al, 2016;Liu et al, 2017;Zhang et al, 2019).…”

Current State of Atmospheric Aerosol Thermodynamics and Mass Transfer Modeling: A Review

“…Liu et al [382] find that ambient SO 2 enhances the formation of SOA in the OH ageing of eugenol via conversion into sulfate. Eugenol is used as a proxy for biomass burning products dominated by methoxyphenols.…”