In all the experiments with black carbon NPs (Figs. , S10-S11), reactivity was initially high, even with a period of 1900 K annealing/sublimation, but the NPs all eventually evolved to inertness after long periods of 1500 K O2 exposure, with oxidative mass losses ranging between ~7 and ~66% of the initial NP masses. Fig. shows a constant TNP, PO2 experiment for a diamond NP, where, in an attempt to preserve the initial high EEO2 (Figs. ), TNP was held at ~1200 K prior to the start of the oxidation period, done at 1400 K to try to slow the evolution. Minitial was ~26.5 MDa, probably corresponding to a small aggregate of nano-diamonds. M was stable during the initial ~1200 K period, but as TNP was ramped to 1400 K, M rapidly decreased by ~47 kDa, with Rbase ≈ 0.13 Da/sec/nm 2 , stabilizing at ~0.026 Da/sec/nm 2 as soon as TNP reached 1400 K. This behavior is attributed to desorption of some species that were stable at 1200 K, but not at 1400 K. For other carbon NPs experiments, these species would have been lost during the initial 1900 K pre-heating. The nature of the adsorbate is unclear, but C-H and C-O functional groups desorb in this temperature range, and the 47 kDa mass loss would be consistent with desorption of a monolayer of H, or loss of a few thousand CO groups from decomposing surface oxygen complexes.