A comprehensive investigation of aqueous-phase photochemical oxidation of 4-ethylphenol

Zhaolian Ye; Zhenxiu Qu; Shuaishuai Ma; Shipeng Luo; Yantong Chen; Hui Chen; Yanfang Chen; Zhuzi Zhao; Mindong Chen; Xinlei Ge

doi:10.1016/j.scitotenv.2019.06.276

A comprehensive investigation of aqueous-phase photochemical oxidation of 4-ethylphenol

Sci Total Environ. 2019 Oct 1:685:976-985. doi: 10.1016/j.scitotenv.2019.06.276. Epub 2019 Jun 19.

Authors

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 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: 31390715
DOI: 10.1016/j.scitotenv.2019.06.276

Abstract

Secondary organic aerosol (SOA) species formed in atmospheric aqueous phases is recently recognized as an important contributor to fine aerosols, which is known to be a prominent human health risk factor internationally. This work, for the first time, systematically investigated aqueous-phase photochemical oxidation of 4-ethylphenol (4-EP) - a model compound from biomass burning and a surrogate of intermediate volatility organic compounds, under both ultraviolet (UV) (Hg lamp) and simulated sunlight (Xe lamp). We found that 4-EP could degrade upon hydroxal radical (OH) oxidation under UV light nearly 15 times faster than that under simulated sunlight, but large aqueous SOA (aqSOA) yields (108%-122%) were observed under both situations. AqSOA masses and oxidation states continuously increased under simulated sunlight, yet they increased first then decreased quickly under UV light. We proposed a reaction scheme based on identified products, showing that oligomerization, functionalization and fragmentation all can occur during 4-EP oxidation. Our results demonstrate that OH radical may suppress oligomerization and functionalization, but is favorable for fragmentation. Under UV light with H₂O₂ (high OH), fragmentation was dominant, producing more volatile and smaller molecules, and less aqSOA in later oxidation; Under simulated sunlight with H₂O₂ (moderate OH), functionalization that can form hydroxylated monomer was more important. Moreover, 4-EP oxidation by the organic triplet excited state (³C*) could form species with stronger visible light absorptivity than those from OH-mediated oxidation, and the absorptivity showed positive link with contents of humic-like substances.

Keywords: Aqueous oxidation; Biomass burning; Brown carbon; Secondary organic aerosol; Triplet excited state.