The NPs undoubtedly have contaminants from being handled in air, and methanol and ammonium acetate from the ESI process, chosen because they decompose to volatile species at temperatures well below the temperature range of interest here. Because the silica NPs were preheated to ~2000 K, subliming material from the NP surface, we expect that most contaminants should have decomposed/desorbed prior to the kinetics measurements. Any residual carbon left on the surface by pyrolysis of organics should also quickly oxidize away under our reaction conditions. The identity of the species carrying the NP charge at high TNP is unknown, but possibilities include protons (from decomposition of NH4 + used in ESI) or residual alkali metal cation from the feedstock or handling. The important point here is that experimental conditions were designed to trap NPs with Q/M < 10 -5 e/Da, implying the coverage of these charged species are small enough to have negligible effects on the kinetics. No changes in emission spectra or on reaction kinetics are seen when Q is changed during experiments.