Enhancement of Secondary Organic Aerosol Formation and its Oxidation State by SO<sub>2</sub> during Photooxidation of 2-Methoxyphenol

Abstract

<p><strong>Abstract.</strong> 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 SO<sub>2</sub> at atmospheric levels (0–56 ppb) on secondary organic aerosol (SOA) formation and its oxidation state during guaiacol photooxidation was investigated in the presence of various inorganic seed particles (NaCl and (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>). Without SO<sub>2</sub> and seed particles, SOA yields (9.46–26.37 %) obtained at different guaiacol concentration (138.83–2197.36 μg m<sup>−3</sup>) could be well expressed by a one-product model. The presence of SO<sub>2</sub> resulted in enhancing SOA yield by 14.05–23.66 %. With (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> and NaCl seed particles, SOA yield was enhanced by 23.06 % and 29.57 %, respectively, which further increased significantly to 29.78–53.47 % in the presence of SO<sub>2</sub>, suggesting that SO<sub>2</sub> and seed particles have a synergetic contribution to SOA formation. It should be noted that SO<sub>2</sub> was found to be in favor of increasing the carbon oxidation state (OSC) of SOA, indicating that the functionalization reaction should be more dominant than oligomerization reaction. In addition, the average N/C ratio of SOA was 0.037, which revealed that NO<sub>x</sub> participated in the photooxidation process, consequently leading to the formation of organic nitrates. The experimental results demonstrate the importance of SO<sub>2</sub> on the formation processes of SOA and organosulfates, and also are helpful to further understand SOA formation from the atmospheric photooxidation of guaiacol and its subsequent impacts on air quality and climate.</p>