Electrically tobacco heating system: Mapping of thermal conditions controlling soot particles formation

The tobacco industry transitions to Heated Tobacco Products (HTPs) from combustible cigarettes. This study focused on the systematic mapping of thermal conditions leading to (or avoiding) soot particle formation when heating tobacco in experimental tobacco heating systems (THSs). The emissions produced under different thermal conditions were analysed to understand under which thermal conditions the formation of the soot particles, characteristic of smoke, starts to occur. Experiments were conducted to examine particulate matter emissions at incremental temperatures ranging from 200 to 550 °C using particle number and mass concentration measurement techniques. A catalytic stripper (CS) was employed and the measurements were performed upstream and downstream of it to distinguish between volatile and potentially solid aerosol fractions. The findings revealed that soot particle formation is significantly influenced by the operating temperature and the presence of oxygen, with distinct patterns emerging only at temperatures exceeding 400 °C in air, which are well above the normal operating range of commercial THSs. Below 400 °C, most of the aerosol emissions were effectively removed by the CS, revealing that the particulate matter was composed of condensed volatiles. Solid soot particles started to be formed, evidenced by sudden peaks in downstream of the CS particle number and soot mass concentrations, only when combustion of the tobacco was triggered. These results contribute to the expanding research on emissions from HTPs, emphasising the need for comprehensive assessments and the importance of regulatory frameworks to differentiate product emissions based on the proper characterisation of tobacco product emissions. • In Tobacco Heating Systems, soot forms above 400 °C in air, marking combustion's onset. • Below 400 °C, particulate matter consists only of volatiles, without any solid soot particles. • Soot formation depends on oxygen presence, as inert atmospheres did not produce soot across the tested temperatures. • A catalytic stripper distinguishes volatile from solid aerosol fractions for accurate emission analysis in THSs.