Next, TNP was dropped to 1300 K (purple background) to allow Q to be measured (+71e) using the Q-stepping process illustrated in Fig. , and then TNP was set to 1500 K. Rbase was near zero (~constant mass) because 1500 K is well below the range where graphite sublimation is significant. At the ~1.39 hour point, 4.3 x 10 -5 Torr of O2 was added (cyan background), resulting in a significant mass loss rate, attributed to etching reactions in which CO (and possibly CO2) desorb. The raw etching rate accelerated during the ~10 minute oxidation period, from -680 Da/sec to -1239 Da/sec after a few minutes, corresponding to an EEO2 of ~1.44 x 10 -3 Da/O2 collision, averaged over the oxidation period. A total of ~0.6 MDa was oxidized away, corresponding to ~0.5 ML for a spherical NP.