All ETDs from UAB

Advisory Committee Chair

Ilias G Kavouras

Advisory Committee Members

Claudiu T Lungu

Philip Demokritou

Vamsee Raju

Marie-Cecile G Chalbot

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) School of Public Health


The widespread use of electronic cigarettes (e-cig) among youths and adolescents is a growing public health problem due to exposures to harmful byproducts formed during heating. These byproducts include particulate matter, benzene, and toluene. However, the mechanisms and variables governing their formation including the chemical content of e-cig liquid (e-liquid) are not fully understood. This study aimed to assess exposures to particulate matter, benzene, and toluene in e-cig vapors (e-vapors) and their coupling to e-liquid chemical content. A novel nuclear magnetic resonance spectroscopy method was developed to characterize e-liquids (propylene glycol, glycerol, and nicotine) and the functional content of flavorings. E-liquids were classified into five clusters based on the relative distribution of flavorings’ non-exchangeable functional proton concentrations. The mean relative abundance of flavorings ranged from 2.4 to 4.7% for the five clusters. The saturated aliphatic fraction was the predominant group in clusters II-V, representing from 35-55 % of non-exchangeable protons, followed by saturated oxygenated (32-33%). In Cluster I, the saturated oxygenated fraction had the highest abundance. The highest abundance of aryl proton was estimated for cluster I and IV, while carbonyls accounted for up to 1.5%. Tobacco-flavored e-liquids had an average flavorings molar ratio of 1.8% with saturated oxygenated being the predominant non-exchangeable proton and considerable quantities of aryl (6.8%) and carbonyl (1.5%) protons. Overall, this analysis allowed for the qualitative and quantitative determination of flavorings in e-liquids. Particles were generated at a high number concentration (106–107 part/cm3) following a multimodal distribution over time. The first peak appeared 2-3 seconds following the puff and was attributed to homogenous and/or heterogeneous nucleation of propylene glycol and glycerol vapors due to the cooling of e-vapors. The second maximum was attributed to the formation of secondary particles through the condensation of low-vapor species formed from the oxidation of propylene glycol, glycerol, and flavorings. The oxidation reactions are fast and capable of producing compounds with carbonyl and carboxyl functional groups. The heterogeneous nucleation mechanism may be favored by preexisting particles, although supersaturating conditions may also occur. The particle size distribution was bimodal with maxima at 200 nm and 1 µm. Propylene glycol, glycerol, and nicotine and trace metals (potassium and sodium) were detected in e-vapors. Benzene and toluene in the range of 100–38,000 ppbv/puff were detected in e-vapors, too. The chemical content of e-vapors varied by e-cig brand, type, flavor additives, user puffing pattern (duration and frequency), and voltage. Overall, in this study, the formation of ultrafine particles and benzene in e-vapors and their relationship to e-liquid chemical composition determined by NMR spectroscopy was determined.

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