Abstract:In recent years, heated tobacco products (HTPs), due to the release of fewer harmful substances than conventional smoking, have gained increasing popularity worldwide. To evaluate their environmental and health impacts, it is necessary to study their physical and chemical properties. This work employs a scanning mobility particle sizer to measure in real time the puff-resolved concentration of heated tobacco smoke aerosols, generated by two types of heating devices: an electromagnetic heating device and an infrared heating device. The puff-resolved concentrations of monodisperse particles at multiple selected sizes are measured and used to derive the overall size distributions. Subsequently, the puff-by-puff total particle number concentrations and mode diameters of the tobacco aerosols are determined in real time. Key findings are obtained from the experiments: (1) Due to their different heating mechanisms, the aerosols produced by the two devices exhibit distinct puff-resolved distribution characteristics. The electromagnetic heating device has relatively high heating efficiency but provides uneven heating. As a result, the concentration of heated tobacco aerosol fluctuates within the range of (6.3 – 8.9) × 106 particles·cm-3, and the mode particle size varies between 220 and 283 nm. The infrared heating device provides more uniform heating but has low heating efficiency, leading to a gradually increasing operating temperature during puffing, especially with insufficient preheating. The aerosol concentration increases puff-by-puff from 2.3 × 106 to 8.7 × 106 particles·cm-3, with mode diameters increasing from 151 to 319 nm. (2) Heated tobacco aerosol particles in different size ranges exhibit inverse dependence on the heating temperatures. Smaller particles (≤ 80 nm) tend to be produced in large quantities at lower temperatures, while larger particles (≥ 300 nm) are more likely to be produced at higher temperatures. (3) The total particle concentrations and mode diameters of heated tobacco smoke aerosols exhibit synchronous variation during the experiments. The temperature of the heating device significantly affects both the total particle concentration and the mode diameter. As the heating temperature increases, both the aerosol concentration and the mode particle size increase significantly. These results demonstrate that the total particle number concentrations and mode diameters of heated tobacco aerosols are highly sensitive to the operating temperature and heating mechanism. Thus, the substantial release of small particles under insufficient heating conditions poses challenges for the design of heating control modules in these devices, such as ensuring adequate preheating and maintaining stable operating temperatures. Close-