Exposure assessment to e-cigarettes part 2: A pilot laboratory study on formation of volatile carbonyls from propylene glycol – a major e-cigarette carrier solvent

Electronic cigarettes are combustion-less battery-powered devices that are able to vaporize a liquid solution. An e-cigarette usually has a heating element, and uses propylene glycol, glycerin or a mixture of the two as a carrier solvent. In this paper, we report a pilot laboratory study investigating the effect of heating temperature on the formation of carbonyls from propylene glycol. We vaporized pure propylene glycol on petri-dish in stainless steel micro-chambers at controlled temperatures of 150, 200 and 250 ºC, respectively, and collected volatile carbonyls at the chamber outlet. We observed the formation of formaldehyde, acetaldehyde and propionaldehyde at these elevated temperatures. There was a general trend for an exponential increase of these carbonyls with increasing temperature. At 250 ºC, there were clear concentration elevations in all three carbonyls. Additional tests on more carrier solvents using a tubular reactor are ongoing to cover broader temperatures and to better mimic e-cigarette flow pattern.