The influence of aerobic conditions on the formation of toxic degradation products via hydrogen atom abstraction is consistent with the studies of Son and Zhao who showed that hydroxyl radicals are produced during vaping. Moreover, subsequent studies by other researchers confirmed that O 2 is a major factor in promoting aerosol toxicant formation in the presence or absence of metal catalysts, and at relatively mild vaping temperatures. The results shown in Figure embody strong evidence that ketene emissions are O 2dependent. Dabbing EtOAc as well as geranyl acetate showed clear reductions in ketene yields under anaerobic versus aerobic conditions. As noted above, theoretical studies had shown that ketene is not expected to form, from VEA or EtOAc, for example, at vaping temperatures < 700 -850 ⁰C, respectively. The simulated reaction pathways had activation energies of > 50 kcal/mol, which is associated with temperatures much higher than normal vaping conditions. However, the simulations were done under anaerobic (pyrolysis) conditions, which therefore can account for the discrepancies between the theoretical and experimentally observed temperatures.