Probing oxidation of hydroxy-polycyclic aromatic hydrocarbons at air-water interface in water microdroplets

Hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) are toxic and environmentally persistent pollutants. However, their transformation at the air-water interface remains poorly understood. Using 2-naphthol as a model compound, the oxidation of OH-PAHs in water microdroplets was investigated. The structure of products was determined by high-resolution, tandem mass spectrometry technologies and Fourier transform infrared spectroscopy. The quenching and capturing experiments suggested the 2-naphthol oxidation was driven by radicals, in which the O₂·- played a significant role. Furthermore, the molecular electrostatic potential was calculated to predict the reaction sites. Collectively, the mechanism was proposed concerning a series of radicals, including O₂·-, ·CH₃, ·OC₁₀H₆OH. Similar reactions could be observed in various OH-PAHs, illustrating the universality of this oxidation reaction. Notably, the toxicity prediction indicated that the OH-PAH oxidation products pose a greater risk for human health than the corresponding OH-PAHs. This study uncovers a new oxidation pathway for OH‑PAHs and provides novel insight into microdroplet‑driven chemistry in the atmosphere.