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<p>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 <span class="inline-formula"><span class="Radical">⚫</span></span>OH and <span class="inline-formula"><span class="Radical">⚫</span></span>Cl, and subsequent reactions of resulting indole radicals with O<span class="inline-formula">₂</span> under 200 ppt NO and 50 ppt HO<span class="inline-formula">₂<span class="Radical">⚫</span></span> conditions, were investigated by a combination of quantum chemical calculations and kinetics modeling. The results indicate that <span class="inline-formula"><span class="Radical">⚫</span>OH</span> addition is the dominant pathway for the reaction of <span class="inline-formula"><span class="Radical">⚫</span>OH</span> with indole. However, both <span class="inline-formula"><span class="Radical">⚫</span>Cl</span> addition and H abstraction are feasible for the corresponding reaction with <span class="inline-formula"><span class="Radical">⚫</span>Cl</span>. All favorably formed indole radicals further react with O<span class="inline-formula">₂</span> to produce peroxy radicals, which mainly react with NO and <span class="inline-formula">HO₂<span class="Radical">⚫</span></span> 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 <span class="inline-formula"><span class="Radical">⚫</span>OH</span> reaction can form N-(2-formylphenyl)formamide (C<span class="inline-formula">₈</span>H<span class="inline-formula">₇</span>NO<span class="inline-formula">₂</span>), for the first time providing evidence for the chemical identity of the C<span class="inline-formula">₈</span>H<span class="inline-formula">₇</span>NO<span class="inline-formula">₂</span> mass peak observed in the <span class="inline-formula"><span class="Radical">⚫</span>OH</span> <span class="inline-formula">+</span> 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.</p>