Spontaneous radical-mediated oxidation of nicotine at nanometer aerosol interfaces.

Spontaneous, radical-mediated oxidation of nicotine has been demonstrated to occur at nanometer aerosol interfaces under ambient conditions for the first time. The oxidation products were identified by vacuum ultraviolet photoionization aerosol mass spectrometry, whereas peroxy-radical adducts were detected by electron paramagnetic resonance spectroscopy, providing direct evidence for radical-mediated oxidation at the air-water interface of aerosols. The oxidation was markedly inhibited by sodium chloride and benzoic acid: the former attenuates interfacial electric fields that promote hydroxyl radical generation, whereas the latter forms a stable complex with nicotine, blocking reactive sites for hydrogen abstraction. These findings reveal a previously unrecognized transformation pathway for nicotine, clarifying its degradation under humid respiratory conditions while also uncovering a general interfacial mechanism for spontaneous oxidation of organic species confined in aqueous aerosols.