Gas Phase Oxidation of Nicotine by OH Radicals: Kinetics, Mechanisms, and Formation of HNCO

Abstract

Cigarette smoke is recognized as having harmful health effects for the smoker and for people breathing second-hand smoke. In an atmospheric chemistry context, however, little is known about the fate of organic nitrogen compounds present in cigarette smoke. Indeed, the atmospheric oxidation of nicotine, a major nitrogen-containing component of cigarette smoke, by OH radicals has yet to be investigated. We measured the first rate coefficient between OH and nicotine to be (8.38 ± 0.28) × 10–11 cm3 molecule–1 s–1 at 298 ± 3 K. We use an online proton-transfer-reaction mass spectrometer (PTR-MS) to quantify nicotine’s oxidation products, including formamide and isocyanic acid (HNCO). We present the first evidence that HNCO is formed from nicotine’s gas phase oxidation, and we highlight the potential for this toxic molecule to be an indoor air pollutant after smoking has ended. Mechanistic pathways for the oxidation of nicotine by OH radicals were investigated by theoretical calculations at the M06-2X level of theory, and we find that there are many competitive H-abstraction sites on nicotine. Our findings suggest that the atmospheric removal of nicotine by OH radicals may compete with surface deposition and air exchange and may be a source of HNCO in indoor air.