Size-Resolved Characterization of Secondhand Vaping Aerosols: Implications for Indoor Exposure and Toxicity

LINHUI TIAN, Wonsik Woo, Ying-Hsuan Lin, University of California, Riverside

     Abstract Number: 229
     Working Group: Health-Related Aerosols

Abstract
The growing use of electronic cigarettes (e-cigs) and increasing reports of vaping-related lung illnesses have raised significant concerns about their broader public health impacts, particularly regarding indoor air quality and passive exposure. According to survey data from 2025, 6.5% of adults aged 18 and over were current e-cigarette users; the percentage of adults who used e-cigarettes increased from 4.5% in 2019 to 6.5% in 2023. Vaping transforms e-liquids, typically composed of propylene glycol (PG), vegetable glycerin (VG), nicotine, and various flavorings, into inhalable aerosols with various particle sizes. These particles exhibit different respiratory deposition behaviors; smaller particles can penetrate deeper into the lungs and are associated with greater health risks.

In this study, we compared fresh and aged e-cig emissions relevant to primary and secondhand vaping aerosols and found that the latter contained significantly higher levels of highly oxygenated compounds. Volatility Basis Set (VBS) estimations indicated that these oxidized products possess lower volatility and a stronger tendency to contribute to new particle formation, thereby exacerbating indoor air pollution. Additionally, we investigated how e-liquid formulation influences aerosol size distribution using online measurement techniques and a MOUDI sampler in controlled chamber experiments with commercial flavored liquids. MOUDI results revealed that highly oxygenated compounds were more enriched in the lower stages (i.e., smaller particle sizes), suggesting a greater potential for deep lung deposition. Cell viability determined by the XTT cell proliferation assay further confirmed that fine particles exhibit higher cytotoxicity toward exposed cells.

These findings underscore the need to consider both vaping aerosols' physical and chemical properties in exposure assessments and regulatory frameworks. The elevated reactivity and toxicity of secondhand emissions reinforce the urgency of protecting both users and non-users in indoor environments.