| Abstract | Combustion and air-pollution aerosol particles often contain a substantial mass fraction of carbon. In biomass or residual-fuel smoke, this carbon may span a continuum of molecular sizes and physical properties, from macromolecular black carbon (BC) and tarballs to smaller molecules of organic particulate matter (OM). The quantification of these materials presents a metrological challenge which rapid temperature programmed oxidation instruments (RTPOs) may address. RTPOs collect particles on filters, which are then rapidly heated (> 700 K/min) in ambient or synthetic air while CO₂ in the emitted gases is quantified either with (e.g. the “FATCAT” instrument) or without (e.g., “TCA08”) first passing gases over an oxidation catalyst. Both RTPOs monitor CO₂ concentrations in real time to provide thermograms; both report total carbon mass by reference to baseline-subtracted CO₂ thermograms. In this study, we investigated the response of these instruments to a variety of laboratory samples. Integrated carbon mass from the FATCAT and TCA08 agreed with one another, and with reference measurements, for both mature, fully graphitized soot (OC/TC < 0.1) and young, partially formed soot (OC/TC = 0.6 after denuding at 350 °C). However, due to its lack of an oxidation catalyst, the TCA08 CO₂ measurements were Equation10-fold lower than reference measurements for two model OM compounds (dioctyl sebacate and sucrose). Since a previous atmospheric study has observed consistency between a TCA08 and a reference instrument, our data imply a large difference in the evaporation kinetics of these surrogates and atmospheric OM, as expected for highly-viscous (glassy) atmospheric OM. Finally, we discuss the thermograms of nebulized BC surrogates (C₆₀, graphene, graphite), which showed two peaks at lower and higher temperatures, even after denuding at 350 °C. |
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