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Objectives The aim of this study is to review the literature on the composition of aerosols from electronic cigarettes (ecigarettes) 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. Methods 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. Results The review identified eight previous investigations on the composition of aerosols from e-cigarettes originated by human vaping and indicated that emissions from ecigarettes 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/m 3 in the e-cigarette user home and 9.53 and 9.36 μg/m 3 in the smoke-free homes, with PM 2.5 peaks concurrent with the e-cigarette puffs. Conclusion 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 ecigarettes and to assess secondhand exposure to e-cigarette aerosol using biological markers.

Background: Some countries have recently extended smoke-free policies to particular outdoor settings; however, there is controversy regarding whether this is scientifically and ethically justifiable.Objectives: The objective of the present study was to review research on secondhand smoke (SHS) exposure in outdoor settings.Data sources: We conducted different searches in PubMed for the period prior to September 2012. We checked the references of the identified papers, and conducted a similar search in Google Scholar.Study selection: Our search terms included combinations of “secondhand smoke,” “environmental tobacco smoke,” “passive smoking” OR “tobacco smoke pollution” AND “outdoors” AND “PM” (particulate matter), “PM2.5” (PM with diameter ≤ 2.5 µm), “respirable suspended particles,” “particulate matter,” “nicotine,” “CO” (carbon monoxide), “cotinine,” “marker,” “biomarker” OR “airborne marker.” In total, 18 articles and reports met the inclusion criteria.Results: Almost all studies used PM2.5 concentration as an SHS marker. Mean PM2.5 concentrations reported for outdoor smoking areas when smokers were present ranged from 8.32 to 124 µg/m3 at hospitality venues, and 4.60 to 17.80 µg/m3 at other locations. Mean PM2.5 concentrations in smoke-free indoor settings near outdoor smoking areas ranged from 4 to 120.51 µg/m3. SHS levels increased when smokers were present, and outdoor and indoor SHS levels were related. Most studies reported a positive association between SHS measures and smoker density, enclosure of outdoor locations, wind conditions, and proximity to smokers.Conclusions: The available evidence indicates high SHS levels at some outdoor smoking areas and at adjacent smoke-free indoor areas. Further research and standardization of methodology is needed to determine whether smoke-free legislation should be extended to outdoor settings.