Droplet Sizes of Electronic Cigarette Aerosols

Philip Chi Lip Kwok, Philippe Rogueda, Lu Hou

Electronic cigarettes (ECs) produce aerosols by heating e-liquids that subsequently condense into droplets upon cooling. The e-liquid vehicle commonly consists of a mixture of common solvents including water, ethanol, glycerol, and propylene glycol. However, the effects of the solvents on EC aerosol characteristics are unknown. This study measured the droplet size distribution of five e-liquids (four self-made solvent-only mixtures and one commercial e-liquid) by laser diffraction. The reason for using this sizing technique was to gather data that can be compared with those obtained from pharmaceutical inhalers in the future. Interestingly, the droplet size distribution was monomodal and comparable between all five e-liquids, despite their different compositions. The volumetric droplet diameters ranged from 1-10 μm, with high variability around the peak sizes. The variability could be due to the poor control of the heating of the e-liquid at the coil. Glycerol and propylene glycol were essential for aerosol generation. On the other hand, pure water and pure ethanol could not produce aerosols. Their presence in the mixtures did not affect the droplet size either. The micron-sized droplets measured in this study were much larger than the nano-sized droplets reported in other studies. This could be due to a difference in the testing setup, experimental procedure, and/or the EC model. Further investigation using aerodynamic impaction is needed to confirm the laser diffraction data.

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