Aerodynamic particle size distribution and dynamic properties in aerosols from electronic cigarettes

Abstract

Aerodynamic Particle Size Distribution (APSD) is an important factor governing if aerosols can be inhaled to different parts of a human's respiratory system. To understand the APSD of the aerosol produced from several brands of E-cigarettes, measurements using the Next Generation Pharmaceutical Impactor (NGI) were performed.The NGI impactor was operated at two different temperature conditions, ambient room temperature condition (20–25°C) and in a cold condition (4–8°C). The relative humidity (RH) in the latter case, cooled impactor, was close to 100%, similar to the human's respiratory system. Obtained Mass Median Aerodynamic Diameters (MMAD) for the investigated electronic cigarettes were in the range 0.5–0.9µm. The different NGI temperature conditions had a significant effect on the result and this is probably due to dynamic processes during the aerosol transport in the NGI pass ways.For each NGI measurements performed the nicotine present in both the droplets and in the gaseous phase were measured. This is different from the previously published data using physical aerosol sizing techniques (such as Scanning Mobility Particle Sizer, SMPS), where obtained droplet sizes is a result of all chemical components in the aerosol, not only nicotine. In principle, it could be only excipients in the droplets and all nicotine in gaseous phase. Thus, impactor and a gas trap with nicotine specific quantification is a good complement for more thorough understanding of droplet size distributions of E-cigarette.The APSD in vitro data was used in theoretical modeling using the Multiple-Path Particle Dosimetry Model (MPPD v 2.11), for estimation of the lung deposition. Using the model it was estimated that 75–90% of the nicotine droplets will be exhaled and 10–25% deposited in the respiratory system. However, when an aerosol is inhaled to a human's respiratory system it will be diluted and the evaporation of nicotine will increase. This will lead to overestimation of the fraction of exhaled nicotine using the MPPD model.