Particle size is an important aerosol property related to dosimetry and aerosol dynamics. For e-cigarettes which produce condensation aerosols from propylene glycol and/or glycerin, measuring aerosol particle size can be particularly challenging due to the volatile and dynamic nature of these aerosols. In particular e-cigarette aerosol particle size measurements may be convoluted by evaporation due to high dilution ratios required for measurements made with conventional aerosol instrumentation and coagulation due to long residence times between sampling and measurement. To address these measurement issues, we have developed a particle size measurement system for e-cigarette aerosols using a low flow cascade impactor. This measurement system is not limited by the concentration of the particles and minimal dilution air is required for impactor operation, thereby minimizing the effects of evaporation. The impactor is interfaced with a sampling system that is capable of generating a puff on an e-cigarette and directly introducing the aerosol into the inlet flow of the impactor, thereby minimizing the time for coagulation.

With this system we have compared the median particle size of both cigarette smoke (0.4 microns) and electronic cigarette aerosols (0.6 - 0.8 microns). Measurements of the aerosol particle size produced by several commercially available e-cigarettes indicate that a majority of the products generate aerosols with median particle sizes within the sub-micron range. This measurement system has also been used to study the parameters that may affect the aerosol particle size. Particle size is found to be highly dependent on the puff flow rate, with higher puff flow rates reducing the aerosol particle size. Conversely particle size was found to be independent of the puff duration. An additional factor found to affect the particle size was the concentration of glycerin in the flavor formulation. The addition of 5% glycerin to a propylene glycol based flavor formulation reduces the median particle diameter from ~0.8 microns to ~0.6 microns.