When 4.3 x 10 -5 Torr of O2 was added, the mass loss rate increased, but only by ~25%, to ~3.4 x 10 -2 Da/sec/nm 2 , corresponding to an initial EEO2 of just ~5.5 x 10 -5 Da/O2 collision. The mass loss rate gradually decreased to ~1.3 x 10 -5 Da/O2 collision during the ~4.7 hour oxidation period, and when the O2 flow was stopped, Rbase also had decreased substantially, as expected because Rbase in this TNP range is due to reactions with background gases. The initial EEO2 was also much lower than the 1500 K initial EEO2 values (~10 -3 Da/O2 collision) observed for graphite, graphene oxide and carbon black NPs, and the total mass loss (~2%) was much smaller than those seen for the more reactive NPs.