EEO2 was initially 1.4 x 10 -3 Da/O2 collision -comparable to the values for the black carbon NPs in Figs. and. Etching gradually slowed over the first ~4 hours (II -VI) as the NP lost ~4 MDa, dropping below 10 -6 Da/O2 collision just before the 5 hour mark. EEO2 remained <10 -6 for ~45 minutes, followed by two additional waves of etching, during which EEO2 abruptly increased by nearly three orders of magnitude then gradually dropped back below 10 -6 with 1 to 1.5 MDa of mass lost in each wave. The experiment was terminated at 10 hours after a 1.25 hour period with insignificant mass loss. In total, the NP lost ~12% of its initial mass. For reference, a spherical carbon black NP with mass in this range would have ~3% of its mass (~1.7 MDa) in the surface monolayer, thus the mass losses during the 1 st , 2 nd , and 3 rd etching waves correspond to ~2.4, ~0.6, and ~0.9 ML's worth of material. Fig. shows a similar experiment for a larger carbon black NP (104.5 MDa) at 1500 K, with PO2 = 2.1 x 10 -5 Torr. The results for all NPs are aggregated and discussed below, but in brief, the initial EEO2 (1.8 x 10 -3 Da/O2 collision) and evolution behavior were similar to those for the carbon black NP in Fig. , except that oscillations in EEO2 were weaker (~1 order of magnitude).