Effect of Heating on Physicochemical Property of Aerosols during Vaping

Abstract

Many electronic cigarette manufacturers have offered different types of "high-end mods" that allow for controlled heating of the e-liquid. However, the controlled heating condition can drastically alter the inhaled aerosols' physical properties and chemical substances, causing potential health risks. To investigate the contribution of heating on aerosol properties, we used four common power settings in the mods to conduct a physicochemical analysis. Our data showed that the aerosol mass and nicotine content in the aerosols increased at high power. Additionally, high power led to aerosolization of a viscous component in the e-liquid, increasing the viscosity of aerosol. However, the pH of the aerosol was constant regardless of the applied power. In addition, high-power operation made nicotine prone to oxidation, resulting in the color of the aerosol turning yellow. Lastly, we demonstrated that e-cigarette aerosol could contain various metals, including aluminum, arsenic, cadmium, chromium, copper, iron, magnesium, nickel, lead, and zinc. Even though these metal contents proportionally increased with the power setting, they remained far below the recommended exposure limits. Our finding demonstrates that the heating conditions of the e-cigarette change the physicochemical properties of the aerosols and their metal contents, thereby possibly affecting users' oral and respiratory systems.

Keywords: aerosol properties; e-cigarette; heavy metal; nicotine; toxicology.

Figure 1

Spatial and temporal temperature distribution of the vape tank. (a) Components of the vape tank. (b) Top-view IR images showing the temperature of heated e-liquids at 20 and 80 W power settings. (c) Maximum temperatures of e-liquid measured using an IR camera during device operation with respect to the operating power. (d) Side-view IR images showing heat distribution throughout the tank at a power range from 20 to 80 W. (e–i) Temperature profiles measured using thermocouples during 10 puffs at a power range from 20 to 80 W at (e) the center of the coil head, (f) inside and (g) outside of the mouthpiece, (h) the glass tube outside, and (i) the base outside. One puff consisted of a puff duration of 4 s (highlighted in red in Figure 1e–i) and an interval of 18 s.

Figure 2

Measurement of physical and chemical properties of collected aerosols at the power range from 20 to 80 W. (a) Generated aerosol mass per puff, (b) nicotine mass per puff, (c) viscosity of e-liquid and collected aerosols, and (d) pH values of e-liquid and collected aerosols. In (c,d), *: p-value <0.05, **: p-value <0.01.

Figure 3

(a) Photo of the e-liquid and collected aerosols at a power range from 20 to 80 W. (b) Color assessment results presenting CIELAB values (L*, a*, and b*) and calculated yellowness indices.

Figure 4

Metal release amount per puff derived from metal concentration in collected aerosols.

Figure 5

(a) A photo of a mesh-type heating coil. (b) SEM image and EDS elemental maps (Fe, Cr, and Al) of the heating coil. (c) The atomic concentrations of the heating coil obtained from the EDS analysis (b). (d) A photo of a coil head. (e) SEM image and EDS elemental maps (Ni, Cu, and Zn) of the surface of the coil head. (f) The atomic concentrations of the coil head obtained from the EDS analysis (e).