Application of Vacuum Ultraviolet Photoionization Mass Spectrometry in the Aging Study of Smoke Aerosols

Smoke aerosols contain many harmful substances and have become one of the major sources of indoor pollutants. The smoke aerosols released into the environment are easy to react with various oxidants presented in the room, namely the aging process of the smoke aerosol, which can produce secondary organic aerosols. The chemical composition of smoke aerosol is an important factor affecting its indoor aging process, but so far, the change behavior of the composition and particle size distribution of smoke aerosol during the aging process remains to be studied, and the aging analysis of novel tobacco products has not been reported. Therefore, the present study applied a house-made vacuum ultraviolet photoionization time-of-flight mass spectrometer to detect the chemical composition of the smoke aerosols produced by combustion cigarette, and new tobacco products, e.g., heat-not-burn tobacco products and e-cigarette, achieving thein-situonline characterization of their gas-phase and particulate-phase components. The results showed that the chemical composition of the smoke aerosols generated by the three types of tobacco products is significantly different, among which the component content and species abundance of the combustion cigarette are much greater than those of the novel tobacco products, and the overall signal intensity of combustion cigarette in the gas-phase and the particulate-phase is about 100 times and 10 times that of novel tobacco products, respectively. In addition, it was found that the particulate-phase mass spectra of novel tobacco products contain a large amount of glycerol, which is almost absent in combustion cigarette, and its intensity is even more than nicotine. The detected aerosol components contain many unsaturated compounds, which are easily oxidized in the environment and generate new ultrafine particles (UFPs). The Teflon chamber was used to simulate the aging process of the above three smoke aerosols with different O₃ concentrations. The results of scanning mobility particle sizer showed that UFPs are generated in all of them. Corresponding to the results of photoionization mass spectrometry, the aging processes of the three smoke aerosols are completely different, in which the formation conditions of UFPs are related to the content and composition distribution of precursors. Specifically, the indoor concentration of O₃ (observed in this experiment was 40 μg/m³) can promote the formation of UFPs with a geometric mean diameter of about 26 nm in the combustion cigarette, while the UFPs formation of novel tobacco products requires a higher concentration of O₃ or a longer aging time. This is mainly facts that the whole composition concentration of the novel tobacco products is much lower than that of combustion cigarette, and the particulate-phase components contain a lot of glycerol. Due to the strong viscosity and encapsulation, glycerol may exist in the particulate-phase of the smoke aerosol in the form of coating other substances, such as nicotine, and further prevents the aging process of other substances, resulting in differences in particle size distribution. This study explains the reason of difference in UFPs formation of various smoke aerosols during the aging process and provides a basis for tobacco exposure risk assessment, which is expected to reveal the aging mechanism of smoke aerosols in the future.