07 Dec 2021

07 Dec 2021

Review status: this preprint is currently under review for the journal ACP.

Optical properties and oxidative potential of aqueous-phase products from OH and 3C*-initiated photolysis of eugenol

Xudong Li1, Ye Tao1, Longwei Zhu1, Shuaishuai Ma1, Shipeng Luo1, Zhuzi Zhao1, Ning Sun1, Zhaolian Ye1, and Xinlei Ge2 Xudong Li et al.
  • 1College of Chemistry and Environmental Engineering, Jiangsu University of Technology, Changzhou 213001, China
  • 2Jiangsu 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

Abstract. In ambient air, aqueous-phase oxidation may turn precursors into more light-absorbing and toxic products, leading to air quality deterioration and adverse health effects. In this study, we investigated eugenol degradation in aqueous phase under direct photolysis, and triplet excited organic (3C*) and hydroxyl radical (OH) as oxidants. Results showed degradation rates of eugenol followed the order of 3C* > OH > direct photolysis. Relative contributions of reactive oxygen species (ROS) and 3C* were evaluated via quenching and O2-free experiments. 3C* played a dominant role in eugenol degradation for 3C*-initiated oxidation, while both O2 and O2-generated were important for eugenol degradation for OH-initiated oxidation. Rate constants under O2, air and N2 followed the order of ko2>kAir>kN2 under both direct photolysis and OH oxidation, and it changed to kAir>kN2>ko2 in 3C*-initiated oxidation. Light absorption spectra showed absorbance at 300–400 nm increased as photolysis progressed, and there were new broad fluorescent spectra at excitation/emission (Ex/Em) = 250/(400–500) nm, suggesting the formation of new chromophores and fluorophores, such as humic-like substances (HULIS). Additionally, distinct fluorescence peaks appeared at Ex/Em=(300–350)/300 nm at different stages. Concentration of generated HULIS increased gradually over time, then leveled off. Dithiothreitol (DTT) assay was applied to assess the oxidation potential of products, which was greater than pure eugenol, suggesting more harmful species were produced during oxidation. Detailed reaction pathways were elucidated via analyses of chemical characteristics of the products.

Xudong Li et al.

Status: open (until 18 Jan 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-895', Anonymous Referee #1, 16 Dec 2021 reply
  • RC2: 'Comment on acp-2021-895', Anonymous Referee #2, 02 Jan 2022 reply
  • RC3: 'Comment on acp-2021-895', Anonymous Referee #3, 03 Jan 2022 reply

Xudong Li et al.


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Short summary
This work for the first time investigated the fluorescent properties and oxidative potential of aqueous phase photo-oxidation products of eugenol, and elucidated the relationship between fluorescent properties and generated HULIS. Furthermore, to elucidate the role of each ROS, we should investigate the time-dependent variation of all ROS via high-sensitivity EPR in future.