Comment on egusphere-2025-4864

Abstract. We present a HYbrid REtrieval Framework (HYREF) that predicts subcolumn carbon monoxide (CO) concentrations from Cross-track Infrared Sounder (CrIS) observations, trained to replicate the TRopospheric Ozone and its Precursors from Earth System Sounding (TROPESS) retrievals based on optimal estimation (OE). Unlike the OE algorithm, which produces retrievals for only a small fraction of available CrIS observations due to expensive but physically accurate radiative transfer, the addition of machine learning (ML) techniques enables full coverage by providing high-resolution predictions for every valid CrIS sample. Importantly, in addition to CO concentrations, TROPESS-HYREF also predicts key retrieval diagnostics, namely column averaging kernels, degrees of freedom, and retrieval errors, that are essential for meaningful comparison with other observations, models, and ingestion into data assimilation. The new framework achieves excellent performance with correlation coefficients r>0.99 and a bias