Homogeneous and air-water interface properties of nicotine relative to aqueous aerosol: Adsorption, oxidation, and the influence for the HNCO formation

Nicotine is the most abundant alkaloid compound in cigarette smoke and a known “emerging contaminant” in gas and aqueous environments. The main environmental behavior of nicotine is to be deposited on various surfaces. Aerosol droplets have a rich specific surface area, which has a great influence on air quality and human health. However, the microscopic interaction between aqueous nanoparticles and nicotine has not been revealed. In this work, the theoretical simulation of the adsorption and reaction properties of nicotine onto aerosol droplets is performed. The strong preference for nicotine on aqueous particle surfaces is firstly proven, and its interface retention rate is about 73 %, 4–7 times larger than that in the air/water phase. The k value of the interface reaction (heterogeneous reaction) is 4.34 × 10−9 cm3 molecule−1 s−1, which is about 80 and 571 times higher than that of the gaseous and aqueous reactions (homogeneous reaction). Interface environment can promote the oxidation of nicotine by •OH, and indirectly promote the rapid generation of toxic HNCO. The reaction rate constant of nicotine with •OH decreases with the increase of aerosol acidity, subsequently impeding the formation of HNCO. Considering the larger rate constant at the interface environment, the total effect of aqueous aerosol should be to improve the formation of HNCO. This work provides insight into the adsorption and oxidation of nicotine on the surface of the aerosol and is helpful in accurately evaluating its environmental fate and risk.