In addition to dry puff, solvent front and catalytic effects, there is another potential cause of ketene and other toxicant emissions at relatively low vaping power settings. We first reported the effect of aerobic conditions on vaping chemistry in 2017. Upon examining the aerosol chemical profiles obtained from vaping propylene glycol and glycerol it became clear to us that oxidation reactions, particularly hydrogen atom abstractions, were prevalent during vaping. Diaz had demonstrated in 2010 that O 2 initiates the thermal degradation of propylene glycol and glycerol at significantly lower temperatures compared to anaerobic (i.e., pyrolysis) conditions. For example, O 2 -promoted hydrogen abstraction from propylene glycol was shown to occur at temperatures as low as 127 °C, leading to products derived from carboncentered radicals.