UCLA

E-cigarettes (E-cigs) experienced its unprecedented popularity over the past ten years, especially among adolescents. Tank devices and JUUL pods are the newest and most widely-used e-cigarette devices. However, there are substantial differences between their device structures and e-liquid compositions. The characteristics of aerosols generated from these two devices warrant better understanding and cross-comparisons for future human exposure studies and policymaking. This work compared the relative effect of device type (Vapor-fi Volt II tank device vs. JUUL pods) and type of nicotine used in e-liquids (freebase nicotine vs. nicotine benzoate salt) on the characteristics of mainstream e-cigarette aerosols under one and three 4-second puffs. The e-cigarette aerosol was introduced into a 460-L mixing chamber and then measured for particle number concentration (PNC), PM2.5 mass concentration, size distribution, and evaporative properties (i.e., particle lifetime and volatility). All measurements were taken in both puffing levels. The results suggested similar PNC levels between tank and JUUL devices. Nevertheless, JUUL generated more than twice of ultrafine particles (diameter < 0.1 μm) than tank devices. PM2.5 from tank device were more than two times higher than from the JUUL. Device type was a significant indicator for PM2.5 (p < 0.05) but not for PNC. Bimodal size distribution was observed in all samples, with the first mode at 0.06-0.09 μm and second mode at 0.27-0.31 μm. Nicotine type was only a significant indicator for PNC in 1-puff samples, and it had almost no effect on PM2.5. Aerosols generated from tank devices were significantly less volatile than JUUL (p < 0.05), while volatility for the two nicotine types has no significant difference. Overall, device type had more substantial effects on aerosol characteristics than nicotine types in e-liquids. Future studies on e-cigarette exposures should consider treating tank devices and JUUL pods as two distinct emission sources.