Influence of E-Liquid humectants, Nicotine, and Flavorings on aerosol Particle Size Distribution and Implications for Modeling Respiratory Deposition.

Introduction:
This article reports on a study examining the influence of e-liquid composition on aerosol particle size distribution and its implications for modeling respiratory deposition. The study uses laboratory-prepared e-liquids and a reference second-generation e-cigarette to generate aerosols, which are then analyzed using a low-flow cascade impactor (LFCI) and real-time mobility sizers. The resulting data are used to model regional and total particle deposition in the respiratory tract of e-cigarette users and estimate the exhaled fraction, which could serve as a source of secondhand exposure to bystanders.

Key Points:

* The study used laboratory-prepared e-liquids with varying ratios of humectants, water, ethanol, and/or flavorings and nicotine in accordance with the association Française de Normalization (aFNOR) standard D90-300-2.
* aerosol generation was achieved using an automated E-cigarette aerosol Generator (ECaG) to control power delivered to the e-cigarette heating coil and maintain a consistent coil temperature.
* aerosol characterization was performed using a LFCI to measure mass-based size distribution, real-time instruments to monitor number-based PSD during puffing, and a mass loss experiment to verify the LFCI impactor flow rate and gravimetric weighing procedure.
* The study found that humectant ratio, flavorings, and nicotine significantly influenced MMaD values, but these differences did not translate into meaningful differences in estimates of regional particle deposition throughout the respiratory tract.
* The use of a LFCI permitted determination of mass-based MMaDs with minimal bias from evaporation during sampling, while monitoring using a FMPS demonstrated significant evaporation of volatile aerosol particle constituents.
* The improved method to characterize physical properties of volatile aerosol particles yielded MMaD values more representative of e-cigarette aerosol in situ, which can help to improve validity of size distribution values input to dosimetry models to estimate exposures to users and bystanders.
* Particle deposition modeling conceptually supported the premise that e-cigarettes can be a source of secondhand exposure to persons in proximity to users, whether at home, in a vehicle, or in a workplace.

Main Message:
The study highlights the importance of using an improved method to characterize the physical properties of volatile aerosol particles in e-cigarette aerosols. The use of a LFCI to measure mass-based particle size distribution without dilution and a reference e-cigarette to standardize aerosol generation allowed for the determination of MMaD values more representative of e-cigarette aerosol in situ. These improved methods can help to improve the validity of size distribution values input to dosimetry models to estimate exposures to users and bystanders. The study also emphasizes the potential for e-cigarettes to be a source of secondhand exposure to bystanders, and the need for accurate dosimetry modeling to estimate the magnitude of aerosol deposition in the respiratory tract of users and the exhaled fraction that could serve as a source of secondhand exposure.

Stefaniak aB, Ranpara aC, Virji Ma, LeBouf RF. Influence of E-Liquid humectants, Nicotine, and Flavorings on aerosol Particle Size Distribution and Implications for Modeling Respiratory Deposition. Frontiers in public health. 2022;10:782068. doi:10.3389/fpubh.2022.782068