Chemical Transformation of Vaping Emissions under Indoor Atmospheric Aging Processes

E-cigarette emissions, which contain a variety of hazardous compounds, contribute significantly to indoor air pollution and raise concerns about secondhand exposure to vaping byproducts. Compared to fresh vape emissions, our understanding of chemically aged products in indoor environments remains incomplete. Terpenes are commonly used as flavoring agents in e-liquids, which have the ability to react with the dominant indoor oxidant ozone (O₃) to produce reactive oxygenated byproducts and result in new particle formation. In this study, mixtures of propylene glycol (PG), vegetable glycerin (VG), and terpenes as e-liquids were injected into a 2 m³ FEP chamber to simulate the indoor aging process. 100 ppbv O₃ was introduced into the chamber and allowed to react with the fresh vape emissions for 1 h. Complementary online and offline analytical techniques were used to characterize the changes in the aerosol size distribution and chemical composition during the aging processes. We observed more ultrafine particles and a greater abundance of highly oxygenated species, such as carbonyls, in aged e-cigarette aerosols. Compared with their fresh counterparts, the aged emissions exhibited greater cytotoxic potential, which can be attributed to the formation of these highly oxygenated compounds that are not present in the fresh emissions. This work highlights the dynamic chemistry and toxicity of e-cigarette aerosols in the indoor environment as well as the indirect risks of secondhand exposure.