Aerosol PG/VG mass ratio-based regulatory indicators for electronic cigarette device oversight: Linking heating temperature to harmful carbonyl formation in aerosols.

Electronic cigarettes (ECs) operate at various power settings, which can lead to significant differences in the concentrations of toxic compounds in EC aerosols. Carbonyl compounds are strongly influenced by the vaporization temperature of the e-liquid. However, owing to the structural differences in EC devices and varying user conditions, accurately measuring this temperature is difficult. To address this issue, in this study, we propose using the propylene glycol (PG)/vegetable glycerin (VG) mass ratio in EC aerosols as a surrogate indicator to estimate the formation of harmful compounds. E-liquids with varying PG/VG mass ratios were thermally treated at 200-400°C, and the resulting aerosols were analyzed for PG, VG, nicotine, and thermally decomposed carbonyl compounds. The mass of carbonyl compounds sharply increased at temperatures above 350°C. Simultaneously, the PG/VG mass ratio in aerosols decreased exponentially with increasing temperature, with a strong correlation (R2 = 0.89 ± 0.06). Based on these results, three exposure zones were defined according to the PG/VG mass ratio: low, conditionally high, and high risk, with average carbonyl compound masses of 9.63, 52.1, and 76.1 μg per 20 μL of e-liquid vaporized, respectively, showing clear distinctions between zones. These findings demonstrate that the PG/VG mass ratio in EC aerosols can be used as a reliable and practical indicator to assess the toxic potential of EC devices. This approach provides a scientific basis for the development of effective safety guidelines and regulatory measures.