Nicotine is the most abundant alkaloid chemical in smoke emission. In this work, we investigated the gas-phase oxidation mechanism of nicotine initiated by its reactions with the OH radical and ozone. Both initiation reactions start dominantly by hydrogen atom abstractions from the C1, C3, and −CH 3 groups of the methylpyrrolidinyl group and form radicals nicotinyl-1, nicotinyl-3, and nicotinyl-6, respectively. The nicotinyl radicals would recombine rapidly with O 2 , forming RO 2 with rapid intramolecular hydrogenatom transfers (HATs) with rate coefficients from 4 s −1 to greater than 10 4 s −1 . The rapid HATs in peroxy radicals suggest rapid autoxidation of nicotine in the gas phase. Formation of HCNO and HC(O)NH 2 , being observed in previous studies, arises likely from secondary reactions or photolysis of intermediate products.

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