The NP was held at 1900 K for ~10 minutes, during which time it sublimed at a rate of ~0.5 Da/sec/nm 2 , losing ~7% of its initial mass. The 1900 K rate was similar to those seen in Figs. , and S6B for graphitic and carbon black NPs (0.29 to 0.44 Da/sec/nm 2 ). When the TNP was set to 1500 K, Rbase was 4.7 x 10 - 3 Da/sec/nm 2 , also similar to those for other black carbon NPs, and when 4.3 x 10 -5 Torr of O2 was added, the initial EEO2 (~1.3 x 10 -3 Da/O2) was also comparable to the values typical of black carbon NPs. Note, however, that EEO2 dropped monotonically, much more quickly, and with much less mass lost, compared to the other black carbon NPs. EEO2 for the nano-onion NP slowed by an order of magnitude for less than 3% mass loss, while the equivalent mass losses were 35 to 37% for graphite (Figs. and), 15% for graphene oxide (Fig. ), and 5 to 6% for carbon black (Figs. and). The total oxidative mass lost as EEO2 dropped to just above our sensitivity limit was only ~4%, again much less than for any of the other black carbon materials.