The Ea values obtained in the bulk carbon experiments were generally lower than our ramp 2 Ea, but this is not surprising. The Ea measured in any experiment is a rate-weighted average over reactions at all available surface sites, and because our experiments were at much higher temperatures, our rates would have had contributions from sites with high Ea values, which would been unreactive in the lower temperature bulk experiments. The tendency for the average Ea to increase at high temperature can also be seen in the bulk graphite etching experiment of Wongtanakitcharoen et al., who reported an increase in the extracted Ea for experiments above ~950 K.