Background:
E-cigarettes are becoming increasingly popular, yet, it is not clear what effect they may have on human health. In particular, there is not much research on the subject of secondhand exposure to vapor from e-cigarettes within indoor settings. Ultrafine particulates (UFPs) are associated with e-cigarette use as well as a myriad of adverse health outcomes. The objectives of this study are to characterize indoor air concentrations of UFPs in two commercial locations that allow the use of e-cigarettes (vaping) indoors, to determine to what extent vaping activities contribute to increased numbers of UFPs and to assess the time taken for UFP numbers to decline.

Methods:
We measured air quality (UFPs) in 2 shops for a portion of their regular business day (168-212 minutes). We also measured temperature, humidity and carbon dioxide. We conducted three separate sampling sessions, two in Shop A (1000ft²) and one in Shop B, (400ft²). In Shop A we could set up two monitors, one near the vaping activity and one set was kept ~50 meters away. For all sessions, we recorded the number of vapers and took air measurements on a minute-by-minute basis.

Results:
Results suggest that vaping activities result in increases in indoor concentrations of UFPs. Concentrations of UFPs ranged from10124 to 87940 particles/cm3. However, there were significant differences in concentrations between Shop A and Shop B. The number of persons vaping influenced the rate of decline of measured UFP numbers.

Conclusions:
Room size, distance from the vaping activity, air filtration systems and the number of persons vaping influence the number of UFPs measured during e-cigarette use. High UFP numbers suggest a possibility of increased health risk for exposed bystanders and employees in these shops. Similar studies conducted in real-world settings are required to make scientifically sound conclusions about effects of vaping on indoor air quality.