In summary, NPs of all the carbon materials, except diamond, had initial EEO2 values of ~10 -3 Da/O2 collision, and diamond NPs also had similar initial EEO2 values provided that they were never heated above 1200 to 1300 K. O2 etching requires that O2 adsorb on the NP surface, which almost certainly implies dissociative adsorption at the high temperatures of our experiments. This creates oxidized surface sites of various structures, which then decay by desorption of CO, CO2, or O. Minton and co-workers have reported experiments that show primarily CO desorption in the 1200 to 1500 K range, with significant O atom desorption above 1500 K, which would not result in mass loss in our experiments. O2 is known to have near-zero dissociative sticking probability on perfect graphite basal planes, but the edges of graphite basal planes, and basal plane defects are reactive due to the presence of under-coordinated carbon sites. Thus, the similarity in initial EEO2 values suggests that all the carbon NP feedstocks have similar initial densities of reactive sites.