From our exposure analyses in Table 2, e-cigarette users inhale extremely high concentrations of
condensed submicron droplets of propylene glycol, up to 78,930 mg/m3 with each 70 ml puff,
resulting in a 24-hour time-weighted inhaled concentration of 48 mg/m3. For non-users,
passively exposed at work for 8-hours, the 24-hour exposure time-weighted inhaled
concentration is 1.15 mg/m3, assuming zero exposure when away from work. Thus, we believe
that the propylene glycol aerosols produced by e-cigarettes can cause eye and respiratory
irritation to both users and non-users. Similar irritant effects may be caused by e-cigarettes that use glycerol based liquids.