The prevalence of the use of e-cigarettes is increasing. They are marketed as an alternative to
smoking tobacco that only produces harmless water vapor, with no adverse impact on indoor air
quality. E-cigarettes use a small electrical heater to vaporize a liquid, typically propylene glycol
and/or glycerol, that contain varying amounts of nicotine (e.g., 0-36 mg/ml), as well as
flavorants. When the user draws on the e-cigarette, the vaporized fluid is delivered to the user as
a visible aerosol, as depicted below in Figure 1.