Enhancement of secondary organic aerosol formation and its oxidation state by SO<sub>2</sub> during photooxidation of 2-methoxyphenol

Abstract

Abstract. 2-Methoxyphenol (guaiacol) is derived from the lignin pyrolysis and taken as a potential tracer for wood smoke emissions. In this work, the effect of SO2 at atmospheric levels (0–56 ppbv) on secondary organic aerosol (SOA) formation and its oxidation state during guaiacol photooxidation was investigated in the presence of various inorganic seed particles (i.e., NaCl and (NH4)2SO4). Without SO2 and seed particles, SOA yields ranged from (9.46±1.71) % to (26.37±2.83) % and could be well expressed by a one-product model. According to the ratio of the average gas-particle partitioning timescale (τ‾g-p) over the course of the experiment to the vapor wall deposition timescale (τg−w), the determined SOA yields were underestimated by a factor of ∼2. The presence of SO2 resulted in enhancing SOA yield by 14.04 %–23.65 %. With (NH4)2SO4 and NaCl seed particles, SOA yield was enhanced by 23.07 % and 29.57 %, respectively, which further increased significantly to 29.78 %–53.43 % in the presence of SO2, suggesting that SO2 and seed particles have a synergetic contribution to SOA formation. The decreasing trend of the τ‾g-p/τg-w ratio in the presence of seed particles and SO2 suggested that more SOA-forming vapors partitioned into the particle phase, consequently increasing SOA yields. It should be noted that SO2 was found to be in favor of increasing the carbon oxidation state (OSC) of SOA, indicating that the functionalization or the partitioning of highly oxidized products into particles should be more dominant than the oligomerization. In addition, the average N∕C ratio of SOA was 0.037, which revealed that NOx participated in the photooxidation process, consequently leading to the formation of organic N-containing compounds. The experimental results demonstrate the importance of SO2 on the formation processes of SOA and organic S-containing compounds and are also helpful to further understand SOA formation from the atmospheric photooxidation of guaiacol and its subsequent impacts on air quality and climate.

Increased Primary and Secondary H<sub>2</sub>SO<sub>4</sub> Showing the Opposing Roles in SOA Formation from Ethyl Methacrylate Ozonolysis

“…Higher OSc of Factor 2 (-0.81) relative to that Factor 1 (-0.85) also supported above conclusion. This also implied that the chemical conversion from Factor 2 to Factor 1 could occur only when the H2SO4 proportion (acidity) in the particle-phase reached a certain concentration (Offenberg et al, 2009;Liu et al, 2019a). As shown in Figure 3C, the maximum production of both Factor 1 and Factor 2 increased with increasing SO2.…”

“…CC BY 4.0 License. / of organosulfate (Zhang et al, 2019;Liu et al, 2019a;Shu et al, 2018). However, the similar S/C ratio and sulfate fragments distribution between neutral and acidic seed 363 experiments excluded the contribution of organosulfate formation to increased OSc 364 ( Figure S14).…”

“…Recent studies have suggested that a higher proportion of H2SO4 in aerosol can result in greater formation of oligomers and high-oxygenated organic aerosol via acceleration of the acid-catalysis process (Zhang et al, 2019;Liu et al, 2019a;Shu et al, 2018). In order to make clear whether the homogeneous or heterogeneous formation of H2SO4 could also affect SOA composition.…”

“…alone seed particles, however, increased particle acidity will not always enhance SOA formation and may have a negligible effect on the SOA formation (Zhang et al, 2019;Kristensen et al, 2014;Wong et al, 2015;Han et al, 2016;Surratt et al, 2010;Eddingsaas et al, 2012;Riva et al, 2016). Furthermore, it is worth noting that several studies have indicated that an increase in SO2 can promote the average oxidation state (OSc) of SOA due to organosulfate formation (Zhang et al, 2019;Shu et al, 2018;Liu et al, 2019a). whereas other studies have suggested that an increase SO2 can have a suppression effect on SOA OSc (Friedman et al, 2016).…”

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

“…The length of sampling pipes of various monitoring instruments ranged from 0.5-1.0 m. A scanning mobility particle sizer (SMPS, TSI, Inc.), consisting of differential mobility analyzer (DMA; model 3082), condensation particle counter (CPC; model 1720), and Po210 bipolar neutralizer, was applied to measure number size distribution. Total particle number and mass concentrations were calculated assuming a uniform density for aerosol particles of 1.4 g cm −3 (Liu et al, 2019b;. The sheath flow and aerosol flow in the SMPS were set to 3.0 and 0.3 L min −1 , respectively.…”