Fig. shows a similar experiment for a nano-onion NP, using the same protocol as Fig. . In this case, there was so much thermionic emission during the initial 1900 K pre-heating period that it was impossible to measure the sublimation rate. After Qstepping and setting TNP to 1500 K, EEO2 was measured to be ~1.2 x 10 -4 Da/O2 collision, i.e. already an order of magnitude lower than the initial EEO2 for the nano-onion NP in Fig. , or typical initial EEO2 values for black carbon NPs. Furthermore, after just ~5 minutes of oxidative etching, having lost ~0.15 MDa (~0.3% of the initial mass), the NP became unreactive toward O2. We interpret both the low initial EEO2 and the rapid transition to inertness during oxidation as indicating that this particular nano-onion NP had very little defective or non-onion carbon on its surface after the 1900 K sublimation period, resulting in low initial EEO2 and rapid evolution to inertness as that reactive carbon etched away. The NP was held at 1500 K in argon for a ~26.6 hour annealing period, during which the NP lost ~0.42 MDa (~0.8% of the initial mass), corresponding to Rbase ≈ 7.8 x 10 -4 Da/sec/nm 2 . Given that the NP was already inert before annealing, it is not surprising that it was still inert after annealing (no mass change during the 2 nd oxidation period). , where EEO2 was measured at 1500 K, but omitting the 1900 K sublimation period (which, however, had no obvious effect).