In Fig. , only 19% of the total mass loss occurred with no N2O added, and of the 81% that occurred during periods with added N2O, most was due to etching during the higher PN2O periods. Thus, during the ~4.5 hours of heating and N2O exposure (Figs. ) that occurred between the two 1900 K experiments, the NP evolved to become more reactive toward N2O, while at the same time subliming more slowly. The higher reactivity toward N2O can also been seen in the EEN2O values (insets to each figure), which were ~60% larger, on average, in Fig. , compared to 2A. substantially over time, particularly at 1900 K. This behavior is similar to that observed in our study of sublimation for a large number of graphite and graphene NPs, which found that the NPs initially sublimed faster than bulk graphite, but with rates that slowed substantially over time. Graphitic NPs have distributions of surface sites (basal planes, basal plane edges, defects) The mass was first monitored as the NP was exposed to an N 2 O pressure ramp from 0.022 to 1.4 mTorr ("a" -"d"). Then at "e", the mass was monitored for 11.5 hours as the NP was exposed to 2.2 mTorr of N 2 O .