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Functional group (FG) analysis provides a means by which functionalization inorganic aerosol can be attributed to the abundances of its underlyingmolecular structures. However, performing this attribution requiresadditional, unobserved details about the molecular mixture to provideconstraints in the estimation process. We present an approach forconceptualizing FG measurements of organic aerosol interms of its functionalized carbon atoms. This reformulation facilitatesestimation of mass recovery and biases in popular carbon-centric metrics thatdescribe the extent of functionalization (such as oxygen to carbon ratio,organic mass to organic carbon mass ratio, and mean carbon oxidation state)for any given set of molecules and FGs analyzed. Furthermore, this approachallows development of parameterizations to more precisely estimate theorganic carbon content from measured FG abundance. We use simulatedphotooxidation products of <i>α</i>-pinene secondary organic aerosolpreviously reported by Ruggeri et al. (2016) and FG measurements by Fouriertransform infrared (FT-IR) spectroscopy in chamber experiments by Sax etal. (2005) to infer the relationships among molecular composition, FGcomposition, and metrics of organic aerosol functionalization. We find thatfor this simulated system, ∼ 80 % of the carbon atoms should bedetected by FGs for which calibration models are commonly developed, and∼ 7 % of the carbon atoms are undetectable by FT-IR analysisbecause they are not associated with vibrational modes in the infrared.Estimated biases due to undetected carbon fraction for these simulations areused to make adjustments in these carbon-centric metrics such thatmodel–measurement differences are framed in terms of unmeasured heteroatoms(e.g., in hydroperoxide and nitrate groups for the case studied in thisdemonstration). The formality of this method provides framework for extendingFG analysis to not only model–measurement but also instrumentintercomparisons in other chemical systems

Technical note: Relating functional group measurements to carbon types for improved model–measurement comparisons of organic aerosol composition