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

Liu, Changgeng; Chen, Tianzeng; Liu, Yongchun; Liu, Jun; He, Hong; Zhang, Peng

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 inline-formulaSO2 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 inline-formula(NH4)2SO4). Without inline-formulaSO2 and seed particles, SOA yields ranged from (inline-formula9.46±1.71) % to (inline-formula26.37±2.83) % and could be well expressed by a one-product model. According to the ratio of the average gas-particle partitioning timescale (inline-formula M9inlinescrollmathml true italic τ normal ‾ normal g - normal p ) 27pt15ptsvg-formulamathimgc1f0715597d045e637f429235d9eea86 acp-19-2687-2019-ie00001.svg27pt15ptacp-19-2687-2019-ie00001.png over the course of the experiment to the vapor wall deposition timescale (inline-formulaτg−w), the determined SOA yields were underestimated by a factor of inline-formula∼2. The presence of inline-formulaSO2 resulted in enhancing SOA yield by 14.04 %–23.65 %. With inline-formula(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 inline-formulaSO2, suggesting that inline-formulaSO2 and seed particles have a synergetic contribution to SOA formation. The decreasing trend of the inline-formula M16inlinescrollmathml true italic τ normal ‾ normal g - normal p / italic τ normal g - normal w 50pt16ptsvg-formulamathimg55a0081107ab58d88238bd5131f13a29 acp-19-2687-2019-ie00002.svg50pt16ptacp-19-2687-2019-ie00002.png ratio in the presence of seed particles and inline-formulaSO2 suggested that more SOA-forming vapors partitioned into the particle phase, consequently increasing SOA yields. It should be noted that inline-formulaSO2 was found to be in favor of increasing the carbon oxidation state (OSinline-formulaC) 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 inline-formulaN∕C ratio of SOA was 0.037, which revealed that inline-formulaNOx participated in the photooxidation process, consequently leading to the formation of organic N-containing compounds. The experimental results demonstrate the importance of inline-formulaSO2 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.

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Liu, Changgeng / Chen, Tianzeng / Liu, Yongchun / et al: Enhancement of secondary organic aerosol formation and its oxidation state by SO2 during photooxidation of 2-methoxyphenol. 2019. Copernicus Publications.

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