The final interesting point concerns the slow mass losses observed after carbon NPs of all types had become inert to O2 etching at long times. For example, after the graphene oxide NP in Fig. finally became inert at ~16 hours, it lost an additional ~90 kDa of mass over the next 6 hours, and the graphite NP in Fig. lost ~80 kDa in the 11 hours after it finally became inert. These slow mass losses were under oxidizing conditions, but it is not clear they result from O2 etching, sublimation, or both.