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

TY - JOUR

T1 - Atmospheric oxidation mechanism and kinetics of indole initiated by •OH and •Cl

T2 - a computational study

AU - Xue, Jingwen

AU - Ma, Fangfang

AU - Elm, Jonas

AU - Chen, Jingwen

AU - Xie, Hong-Bin

PY - 2022/9/7

Y1 - 2022/9/7

N2 - 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.

AB - 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.

KW - SECONDARY ORGANIC AEROSOL

KW - INTRAMOLECULAR HYDROGEN SHIFT

KW - UNIMOLECULAR REACTION SYSTEMS

KW - GAS-PHASE OXIDATION

KW - CHEMICAL-REACTIONS

KW - RADICALS KINETICS

KW - MULTIPLE-WELL

KW - CHLORINE

KW - CHEMISTRY

KW - PHOTOOXIDATION

UR - http://www.scopus.com/inward/record.url?scp=85140296460&partnerID=8YFLogxK

U2 - 10.5194/acp-22-11543-2022

DO - 10.5194/acp-22-11543-2022

M3 - Journal article

SN - 1680-7316

VL - 22

SP - 11543

EP - 11555

JO - Atmospheric Chemistry and Physics

JF - Atmospheric Chemistry and Physics

IS - 17

ER -