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Physical characteristics of the aerosol

Many of the techniques developed to investigate cigarette smoke aerosols can be applied to e-cigarette aerosols. Both aerosols are sub-micron (200 – 500 nm) in diameter and have high particle concentrations on generation of up to 109 particles per cm3[1].

Both aerosols are dynamic and change in size and composition within the lung through coagulation, hygroscopic growth (water uptake by the soluble fraction of the aerosol) and evaporation.

The processes for particle deposition in the body are reasonably well understood, and the rate of penetration into and absorption by the lung is comparable to tobacco smoke. Particles with diameters less than 2,500nm (2.5μm) can penetrate into the deep lung where there is a huge surface area available for systemic uptake. From 50-1,000nm, particle deposition efficiency is least efficient with slow sedimentation of particles. Below 50nm particle deposition efficiency increases in the deep lung through increased Brownian Motion although mass deliveries can be small[2].

The exhaled e-cigarette aerosol will contain residual excipient with a very high percentage of water absorbed from the 100% humidity of the airways. The high water content would be expected to disperse rapidly in the air, as can be observed when e-cigarette users exhale the aerosol.


  1. Ingebrethsen, B.J., Cole, S.K., Alderman, S.L. 2012. Electronic cigarette aerosol particle size distribution measurements Opens new window. Inhalation Toxicology, 24(14): 976-984.
  2. ICRP, 1994. Human Respiratory Tract Model for Radiological Protection Opens new window. ICRP Publication 66. Ann. ICRP 24 (1-3)
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