The initial diamond NP reactivity at 1200 K was high and constant over the first ~10 minute oxidation period, even though ~2.25 MDa was etched away, and the 1200 K EEO2 value was ~3 x 10 -3 Da/O2 collision, which is two to five times greater than the 1500 K EEO2 values for the black carbon NPs in Figs. and. We previously measured 1200 K Roxid values for a number of graphitic NPs, and the corresponding EEO2 values averaged ~1.7 x 10 -2 Da/O2 collision, i.e., the 1200 K reactivity for this diamond NP was lower than the average for graphite at 1200 K, but only by a factor of ~6. As TNP was stepped to 1600 K, however, the diamond NP EEO2 dropped to near zero by 1600 K, and remained near zero in the 2 nd ramp, indicating that a drastic, irreversible decrease in the number of under-coordinated reactive surface sites occurred as the NP was initially heated to 1600 K, losing 7.5 MDa of mass (nominally ~3 ML's worth). Heating/etching also caused irreversible changes in NP optical properties, as shown by the higher INP values seen during the 2 nd ramp, compared to the 1 st (note log scale). For example, at 1200 K, INP averaged ~4 x 10 7 during the 1 st ramp but doubled to ~8 x 10 7 during the 2 nd , with only a small change in the spectral shape (Fig. ). The evolution is also shown by the increase in INP during the higher TNP steps in the 1 st ramp. Irreversible emission brightening caused by NP heating was also observed for graphitic NPs, and those studies also noted the apparent correlation between emission brightening and decreasing rates of sublimation and oxidation, which was interpreted as suggesting a inverse correlation between brightness and numbers of under-coordinated surface sites.