Aerosol deposition doses in the human respiratory tree of electronic cigarette smokers

Aerosols from eight e-cigarettes at different nicotine levels and flavoring were characterized as particle number size distributions in the range 5.6-560 nm by FMPS and CPC. Results were used to provide dosimetry estimates applying the MMPD model. Particle number concentrations varied between 3.26 × 10⁹ and 4.09 × 10⁹ part cm^-3 for e-liquids without nicotine and between 5.08 × 10⁹ and 5.29 × 10⁹ part cm^-3 for e-liquids with nicotine. No flavor effects were detected on particle concentration data. Particle size distributions were unimodal with modes between 107-165 nm and 165-255 nm, for number and volume metrics, respectively. Averagely, 6.25 × 10¹⁰ particles were deposited in respiratory tree after a single puff. Highest deposition densities and mean layer thickness of e-cigarette liquid on the lung epithelium were estimated at lobar bronchi. Our study shows that e-cigarette aerosol is source of high particle dose in respiratory system, from 23% to 35% of the daily dose of a no-smoking individual.