E-cigarettes are increasing in popularity, yet few studies have investigated how they impact indoor concentrations of fine particulate matter (PM_2.5; aerodynamic diameter ≤ 2.5μm), and ultrafine particles (UFPs, aerodynamic diameter ≤ 0.1μm). Short-term elevations of PM_2.5 and UFP concentrations have been shown to adversely impact cardio-respiratory health. To investigate how e-cigarettes’ influence indoor air, our study estimated PM_2.5 and UFP concentrations at two close-proximity distances from an e-cigarette user, and evaluated whether these concentrations varied across different types of e-cigarettes.

One e-cigarette user tested three types of e-cigarettes with the identical fruit-flavoured nicotine solution on three separate occasions. PM_2.5 and UFP concentrations were measured at distances of 0.5 and 1 meter in a 14 m² office. An adjustable voltage, 1st generation, and pen-style tank e-cigarette were tested. One-second concentrations were measured for 22-minutes divided into: baseline (5.5minutes), exposure (7 puffs in 6.5minutes), and post-exposure (10minutes) periods. The mean concentrations across replicates for each period were calculated. Concentrations between e-cigarettes were compared using analysis of variance.

At 0.5 meters from an e-cigarette user, the mean PM_2.5 concentrations across replicates during the exposure periods were 364 (adjustable voltage), 709 (1st generation), and 1117 (pen-style tank) μg/m³. At 1 meter, the corresponding means were 235, 168, and 1193μg/m³. The baseline PM_2.5 concentrations ranged from 2–3μg/m³ and the post-exposure concentrations ranged from 2–31μg/m³. The differences between PM_2.5 concentrations among e-cigarettes were statistically significant (P<0.03). At 0.5 meters, the UFP mean counts were 8060 (adjustable voltage), 11,106 (1st generation), and 14,541 (pen-style tank) count/cm³, and at 1 meter the means were 9699, 10,366, and 26,424 count/cm³, respectively. The baseline UFPs ranged from 922–4522 count/cm³ and post-exposure from 4353–9990 count/cm³. Counts of UFPs were different between e-cigarette types (P<0.001). UFP counts did not return to baseline 10-minutes after the last e-cigarette puff.

At close distances, one e-cigarette notably increased PM_2.5 concentrations and UFP counts in the indoor air, but there was high variability between replicates.