Development and optimization of methodologies for the measurement of aerosol physical properties from mainstream heated tobacco aerosol

This study addresses critical gaps in the standardization of methods for measuring aerosol design parameters—particle size distribution (PSD), PM2.5, and particle number concentration (PNC)—in aerosols emitted from heated tobacco products (HTPs). These parameters are important for regulatory submissions under the Premarket Tobacco Product Applications (PMTAs) and Recordkeeping Requirements Final Rule set forth by the FDA. To overcome challenges posed by the intermittent puffing profiles of HTPs, a novel interface was developed to bridge the variable flow rates of HTP aerosols with the constant flow rates required by cascade impactors. This interface enables accurate measurement of PSD while accommodating bell-shaped puff profiles recommended by ISO and CORESTA standards. The study systematically investigates the impact of experimental conditions, such as dilution air humidity, dilution ratio, and puff profile shape, on PSD. Results demonstrate that dry dilution air accelerates aerosol evaporation, leading to smaller particle sizes, while humidified air minimizes this effect, ensuring more accurate PSD measurements. Additionally, the study introduces an optimized methodology for measuring primary PM2.5 concentrations, highlighting the importance of humidified air in mitigating aerosol evaporation during sampling. PM2.5 concentrations across various products, including the 1R6F reference cigarette and three HTPs, were found to be within the same order of magnitude. Furthermore, a novel setup capable of real-time, puff-by-puff PNC measurements was developed. PNC values for HTPs were comparable to those of 1R6F cigarettes, with concentrations in the order of 109 particles per cm³. This research establishes a robust foundation for future studies and regulatory assessments by providing standardized methodologies on aerosol design parameters for HTPs. The findings underscore the importance of controlling environmental conditions during aerosol sampling and offer insights into the physical properties of HTP aerosols compared to traditional cigarette smoke.