Figs. 1, 2, and S1-S3 summarize the results of a sequence of experiments on a single graphite NP with initial mass (Minitial) near 25 MDa, illustrating the ability of the method to probe individual NPs over long and complex reaction sequences. Fig. starts by showing the typical process used to clean freshly trapped NPs, which may have surface contaminants from handling the feedstock in air or from the ESI solution, all of which are expected to desorb below ~1500 K. Therefore, TNP was initially ramped to ∼1900 K to desorb contaminants along with sublimed carbon, then dropped to 1400 K for Q stepping (purple background) to determine the initial Q and M values, and finally reheated to ∼1900 K to desorb any contaminants that might have adsorbed during Q stepping. It was not possibly to track M during the first 1900 K period due to rapid thermionic electron emission, but during the 2 nd 1900 K period, M decreased by ~750 kDa due to sublimation, corresponding to ~0.8 MLs-worth of carbon. M for the cleaned NP was Rbaseline and the baselinesubtracted RN2O to be extracted. These conditions were chosen because they would have resulted in fast etching for O2 at the same partial pressure. Below 1700 K, the mass was essentially constant in both Ar and N2O/Ar, implying that sublimation was slow, as expected , and that no significant etching occurred when N2O was added. At 1700 K, there was small, but noticeable mass loss in Ar, and the mass loss rate accelerated slightly when N2O was added, i.e., both sublimation and etching occurred, albeit quite slowly. At 1800 K, the mass loss rate in argon (i.e., Rsublimation) increased substantially, as expected, but there was little change in the mass loss rate when N2O was added, showing that for the low PN2O used here, RN2O << Rsublimation.