The initial 1200 K EEO2 was ~1.2 x 10 -3 Da/O2 collision, i.e., lower, but in the same range as the initial 1200 K EEO2 for the diamond NP in Fig. , presumably reflecting the NP-to-NP variations in shape and surface structure. Note that the mass loss rate slowed significantly during the 10 minute initial oxidation period (curvature in M vs. time), such that the average EEO2 was only ~6.1 x 10 -4 Da/O2 collision. After two TNP ramps, EEO2 during the 2 nd oxidation period was zero within our sensitivity -at least 250 times less reactive.