Particulate Matter from Electronic Cigarettes and Conventional Cigarettes: a Systematic Review and Observational Study

The aim of this study is to review the literature on the composition of aerosols from electronic cigarettes (e-cigarettes) originated by human vaping and to describe the emission of particulate matter ≤2.5 μm in diameter (PM_2.5) from conventional and e-cigarettes at home in real-use conditions. We conducted a systematic literature search in PubMed and Web of Science. We measured PM_2.5 in four different homes: one from a conventional cigarette smoker, one from an e-cigarette user, and two from non-smokers. The review identified eight previous investigations on the composition of aerosols from e-cigarettes originated by human vaping and indicated that emissions from e-cigarettes can contain potential toxic compounds such as nicotine, carbonyls, metals, and organic volatile compounds, besides particulate matter. In the observational study, the PM_2.5 median concentration was 9.88 μg/m³ in the e-cigarette user home and 9.53 and 9.36 μg/m³ in the smoke-free homes, with PM_2.5 peaks concurrent with the e-cigarette puffs. Both the literature review and the observational study indicate that e-cigarettes used under real-conditions emit toxicants, including PM_2.5. Further research is needed to characterize the chemicals emitted by different types of e-cigarettes and to assess secondhand exposure to e-cigarette aerosol using biological markers.