Atmospheric oxidation mechanism and kinetics of indole initiated by •OH and •Cl: a computational study

Jingwen Xue, Fangfang Ma*, Jonas Elm, Jingwen Chen, Hong-Bin Xie*

*Corresponding author for this work

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review

Abstract

The atmospheric chemistry of organic nitrogen compounds (ONCs) is of great importance for understanding the formation of carcinogenic nitrosamines, and ONC oxidation products might influence atmospheric aerosol particle formation and growth. Indole is a polyfunctional heterocyclic secondary amine with a global emission quantity almost equivalent to that of trimethylamine, the amine with the highest atmospheric emission. However, the atmospheric chemistry of indole remains unclear. Herein, the reactions of indole with ·OH and ·Cl, and subsequent reactions of resulting indole radicals with O2 under 200 ppt NO and 50 ppt HO2· conditions, were investigated by a combination of quantum chemical calculations and kinetics modeling. The results indicate that OH addition is the dominant pathway for the reaction of ·OH with indole. However, both ·Cl addition and H abstraction are feasible for the corresponding reaction with ·Cl. All favorably formed indole radicals further react with O2 to produce peroxy radicals, which mainly react with NO and HO2 to form organonitrates, alkoxy radicals and hydroperoxide products. Therefore, the oxidation mechanism of indole is distinct from that of previously reported amines, which primarily form highly oxidized multifunctional compounds, imines or carcinogenic nitrosamines. In addition, the peroxy radicals from the OH reaction can form N-(2-formylphenyl)formamide (C8H7NO2), for the first time providing evidence for the chemical identity of the C8H7NO2 mass peak observed in the ·OH + indole experiments. More importantly, this study is the first to demonstrate that despite forming radicals by abstracting an H atom at the N site, carcinogenic nitrosamines were not produced in the indole oxidation reaction.

Original languageEnglish
JournalAtmospheric Chemistry and Physics
Volume22
Issue17
Pages (from-to)11543-11555
Number of pages13
ISSN1680-7316
DOIs
Publication statusPublished - Sept 2022

Keywords

  • SECONDARY ORGANIC AEROSOL
  • INTRAMOLECULAR HYDROGEN SHIFT
  • UNIMOLECULAR REACTION SYSTEMS
  • GAS-PHASE OXIDATION
  • CHEMICAL-REACTIONS
  • RADICALS KINETICS
  • MULTIPLE-WELL
  • CHLORINE
  • CHEMISTRY
  • PHOTOOXIDATION

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