Flavoring Compound Chemical Class and Vaping Conditions Determine Toxic Carbonyl Emissions from E-Cigarettes

The increasing use of flavored electronic cigarettes (e-cigarettes) raises concerns about their potential impact on the emission of harmful chemicals, particularly carbonyl compounds. This study systematically examines the effects of eight representative flavoring chemicals from four major classes including esters (ethyl acetate, ethyl butyrate), alcohols (menthol, ethyl maltol), aromatic aldehydes (benzaldehyde, vanillin), and terpenes (limonene, linalool) under varying power outputs (50 and 90 W), base liquid composition [propylene glycol (PG)/vegetable glycerin (VG) ratios (80:20, 50:50, and 20:80)], and flavor concentrations (1 and 5 mg/mL). Across all conditions, flavored e-liquids tend to produce carbonyl emissions that are higher than those of unflavored controls. Terpene-based flavors showed the strongest effects, with formaldehyde emissions being up to 2-fold higher and acrolein emissions up to 8-fold higher, frequently exceeding short-term exposure limits. Aromatic aldehydes and alcohols also increased emissions, though to a lesser extent, while esters showed smaller or inconsistent effects. The influence of flavors was further modulated by their concentration, PG/VG ratio, and device power, with higher concentration, VG content, and power amplifying emissions. These results highlight the complex interactions among e-liquid composition, flavor class, and vaping conditions, demonstrating that certain flavorings substantially elevate toxicant emissions. These findings underscore the importance of considering flavor composition, device power, and base material in evaluating the potential health risks associated with e-cigarette use.