In the following, we examine changes to the optical properties and surface composition of silica NPs driven by heating above the temperature range where silica becomes unstable with respect to SiO, O2, and O desorption. We then use the O2 etching kinetics as a probe of the surface reactivity, and compare the TNP and reaction time dependence of silica NPs etching, with similar measurements for Si, SiC, and carbon NPs.