Secondary organic aerosol formation from 3C⁎-initiated oxidation of 4-ethylguaiacol in atmospheric aqueous-phase

Yantong Chen; Nanwang Li; Xudong Li; Ye Tao; Shipeng Luo; Zhuzi Zhao; Shuaishuai Ma; Hongying Huang; Yanfang Chen; Zhaolian Ye; Xinlei Ge

doi:10.1016/j.scitotenv.2020.137953

Secondary organic aerosol formation from ³C^⁎-initiated oxidation of 4-ethylguaiacol in atmospheric aqueous-phase

Sci Total Environ. 2020 Jun 25:723:137953. doi: 10.1016/j.scitotenv.2020.137953. Epub 2020 Mar 14.

Authors

Yantong Chen¹, Nanwang Li¹, Xudong Li¹, Ye Tao¹, Shipeng Luo¹, Zhuzi Zhao¹, Shuaishuai Ma¹, Hongying Huang¹, Yanfang Chen², Zhaolian Ye³, Xinlei Ge⁴

Affiliations

¹ College of Chemistry and Environmental Engineering, Jiangsu University of Technology, Changzhou 213001, China.
² Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Sciences and Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China.
³ College of Chemistry and Environmental Engineering, Jiangsu University of Technology, Changzhou 213001, China. Electronic address: bess_ye@jsut.edu.cn.
⁴ Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Sciences and Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China. Electronic address: caxinra@163.com.

PMID: 32213404
DOI: 10.1016/j.scitotenv.2020.137953

Abstract

In this study, we investigated aqueous-phase triplet excited states (³C^⁎)-induced photo-degradation of 4-ethylguaiacol (EG) under both simulated sunlight and ultraviolet (UV) light irradiations. Through quencher experiments, the relative contributions of reactive oxygen species (ROS, such as ¹O₂/O₂^-/·OH) and ³C^⁎ were calculated and results showed three reactive species, e.g., ³C^⁎, ¹O₂ and O₂^-, all seemed to play important roles in the photo-degradation of EG, but contribution from ·OH was relatively minor. High steady-state ¹O₂ concentration after 1 h irradiation further revealed the major contribution of ¹O₂ to photo-degradation under Xe light irradiation. The degradation experiment under three saturated gases (air, O₂ and N₂) showed that the degradation rate in air-saturated condition was the largest owing to synergistic effect of ¹O₂ and ³C^⁎. Oxidative capacity of aqueous secondary organic aerosol (aqSOA) increased with reaction time by monitoring oxygen-to‑carbon (O/C) ratio and carbon oxidation state (OS_c) via an aerodyne soot particle aerosol mass spectrometer (SP-AMS). Moreover, aqSOA mass yields were calculated via SP-AMS data. The UV-vis spectral change suggested formation of light-absorbing organics at first stage under simulated sunlight irradiation. Based on the identified products and the reactive intermediates, we postulated that ³C^⁎-induced oxidation might be attributed to direct reactions by ³C^⁎ and ¹O₂, chemical reaction by ROS, as well as oligomerization via H-abstraction. To the best of our knowledge, this is the first time to explore systematically reaction pathways of 4-ethylguaiacol under ³C^∗ radical on the basis of thorough analysis of products and reactive species. Our findings highlight the impacts of aqSOA from biomass burning emissions on air quality and climate change.

Keywords: Aqueous-phase secondary organic aerosol; Quenching experiment; Reactive oxygen species (ROS); oxidative characteristics; reaction mechanisms.