<p>Environmental conditions exert strong influence on the formation and evolution of thermally generated aerosols, particularly those derived from semi-volatile organic compounds (SVOCs). In this study, a temperature–humidity-controlled platform was developed to investigate how ambient temperature and relative humidity individually influence aerosol dynamics across puff sequences in a heated tobacco product (HTP) system under controlled baseline conditions, used here as a representative thermally generated SVOCs aerosol source. Puff-by-puff aerosol size distributions and number median diameters (D50) were measured using a Scanning Mobility Particle Sizer (SMPS), while particulate- and gas-phase constituents were analyzed using GC–MS. The results show that low ambient temperature enhances gas–particle partitioning and condensation processes, leading to significantly higher particle number concentrations and larger contributions from condensation-driven growth. In contrast, elevated humidity was associated with shifts in aerosol number distribution and median diameter, reflecting humidity-dependent modulation of aerosol formation processes rather than hygroscopic growth during measurement. Temperature and humidity were found to independently influence aerosol formation pathways, affecting particle size evolution, number concentration, and the distribution of major aerosol constituents. These findings provide mechanistic insight into how environmental gradients modulate the physicochemical evolution of thermally generated SVOCs aerosols and offer a framework for future studies in aerosol engineering and environmental aerosol modeling.</p>