Identification of Thermal Boundaries for Soot Particle Formation in Tobacco-Based and Cellulosic Substrates Using an Experimental Tobacco Heating System

Studying the thermal behaviour of biomass substrates in electrically heated tobacco systems is essential for determining the conditions under which liquid-based aerosol generation transitions to combustion and solid particle formation. In this work, three distinct biomass stick designs were evaluated: two tobacco-based formulations (one with an added botanical) and one non-tobacco cellulosic substrate. These substrates were tested using a temperature-controlled experimental tobacco heating device operated at 200–450 °C under both oxidative and oxygen-depleted conditions. Aerosol emissions were assessed using a multi-indicator framework that included total particle number, size-resolved particle counts at 80 nm, soot mass, and CO/CO 2 ratios. Measurements were conducted with and without volatile removal to distinguish between condensable aerosols and carbonaceous solid particles. Distinct substrate-specific thermal transitions were observed. The conventional tobacco substrate exhibited combustion-related signatures near 400 °C, while the botanical-modified formulation showed delayed solid particle formation at approximately 425 °C. In contrast, the non-tobacco substrate exhibited an earlier transition to combustion-dominated aerosol formation, with exothermic behaviour and solid-particle indicators emerging at approximately 350 °C. Experiments conducted under nitrogen demonstrated that oxygen availability is necessary for the formation of carbonaceous solid particles within the investigated temperature range. Additional tests with commercially available consumables in an induction-based tobacco heating system indicated that, under standard operating conditions, only liquid aerosols were emitted. These results indicate that the thermal boundaries governing combustion and soot generation depend on substrate composition but occur at temperatures significantly above those used in commercial heated tobacco products.