Particle size analysis of emissions has emerged as an important physical property for the health and safety evaluation of electronic nicotine delivery systems (ENDS) within this product category and for comparison with other product categories, including traditional combustibles. Although particle size measurement has been conducted with gravimetric cascade impactor instruments for decades, more recently developed electrical low-pressure impactors (ELPIs) electrostatically charge incoming aerosol particles to enable live electrical readouts of particle flux between filter stages, providing more sensitive and timely data collection. In fact, the high sensitivity of these modern measurement techniques requires volumetric dilution of ENDS aerosols for optimal performance. This contrasts with the capabilities of gravimetric cascade impactors which can capture and measure undiluted aerosols.

To investigate the equivalency of experimental aerosol properties between different puff generation and measurement techniques, a comparative study was conducted using electronic cigarettes as the test products. Puff profiles were generated using either a dual syringe pump engine or a 2-stage flow dilution apparatus and analyzed by either a traditional gravimetric cascade impactor or ELPI+ instrument, respectively, with differing numbers of impactor stages and stage cut sizes. Results were compared principally based on mass median aerodynamic diameter (MMAD), count median aerodynamic diameter (CMAD) and geometric standard deviation (GSD), with multiple calculation methods explored. We find no statistically significant difference between these reported aerosol metrics based on puff generation and measurement combinations explored in this study. However, the obtained MMAD, CMAD and GSD values from a given data set are shown to be relatively sensitive to the calculation method used and emphasize the need to clearly define and justify particle size reporting methods.