Characterizing the Physical, Chemical, and Toxicological Properties of Secondhand Aerosols Generated from Electronic Nicotine Delivery Systems in Indoor Environments

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In 2019, 10.9 million American adults used Electronic Nicotine Delivery Systems (ENDS) such as e-cigarettes, e-hookahs, and vape pens. According to the National Youth Tobacco Survey in 2020, 33.8% of U.S. middle and high school students report that they have been exposed to secondhand ENDS aerosols in indoor spaces. Despite extensive studies on aerosols directly generated from the ENDS mouthpieces, the properties of secondhand ENDS aerosols are insufficiently understood because these aerosols need to be generated by human subjects using ENDS devices. The use of human subjects is very limited, introduces uncertainty due to uncontrolled other variables (e.g., existing diseases, lung functions, and smoking habits), and raises ethical concerns. The knowledge gaps caused by this lack of data lead to confusion and potential delays in regulating ENDS usage in indoor environments. This research aims to examine the physical, chemical, and toxicological properties of secondhand ENDS aerosols generated from a simulated respiratory system recently developed by the research team. The successful completion of this project will benefit society through the development of new knowledge in understanding the environmental and health impact of secondhand ENDS aerosols. Further benefits to society will be achieved through student education, training, and public outreach. STEM training will be enhanced through integration of research findings into course modules, participation of researchers in K-12 summer science camps, and a partnership with local public library to disseminate the project findings to the public. Due to the limited data on the properties of secondhand ENDS aerosols, several fundamental questions are still not answered: 1) What are the typical size distributions of secondhand ENDS aerosols, and how do they evolve under controlled environmental factors? 2) Will secondhand ENDS aerosols in actual indoor environments induce oxidative stress and cytotoxicity? 3) What are the roles of metals and flavorings in determining the size distribution and toxic effect of secondhand ENDS aerosols? This project proposes to answer these questions by conducting experiments in a walk-in environmental chamber and an experimental house to relate measurements to real-world indoor environments. An array of online and offline measurement and modeling techniques will be deployed in this study to examine the physical, chemical, and toxicological properties of secondhand ENDS aerosols in realistic indoor environments. The collected data will be used to establish an aerosol dynamics model to predict the evolution of secondhand ENDS aerosols under the influence of evaporation, coagulation, wall deposition, and ventilation. This work has the potential to produce a transformative understanding of the behavior and control of indoor secondhand ENDS aerosols. Furthermore, it eliminates the need for human subject studies and creates an environment that effectively controls other potential variables in order to isolate underlying causes of secondhand ENDS aerosol dynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.