Authors use the airborne CH4, CO2, CO observations over Alaska to test surface flux models and inventories and find a good correlation between model-simulated and observed differences between partial column-averaged representing lower troposphere below 3000m and above. The difference between the lower and mid-troposphere is used to avoid a need for accurately matching the seasonal cycle in the global and hemispheric scale and to focus on the impacts of the regional emissions and sinks. The application of the method can be considered successful overall, and progress in surface flux modeling was demonstrated, some future improvements are still desirable, as mentioned further in the review. The manuscript is well written and can be published after minor revision.
Line 75 The target is ‘to evaluate the ability of current land surface flux models’, but the conclusions indicate that the goal is not fully achieved – separating contributions of model simulated fluxes from inside and outside the study domain is difficult, as well as separating the impacts of surface fluxes from meteorology and tracer transport. It would be natural to extend evaluation target to a combination of the surface flux models and the transport model.
Line 224 References may be needed to point to past results, and GCP-CH4 regional estimates are available for comparison.
Line 245-250 Justification for the setting of 3000 m as a boundary between PBL and free troposphere was not discussed (any suitable reference?), while the PBL heights diagnosed from potential temperature, humidity, and tracer profiles are often lower than 3000 m. As there is a good volume of evidence on the connection between tracer and potential temperature profiles in the troposphere (Jin et al, 2021), an alternative approach would be to test lower altitude for separator or make it linked to isentropic vertical coordinate.
Line 295 Here, one would guess that using inversion optimized fluxes, even made with another transport model would give a better match with observations than the unoptimized models and inventories used in the study (as mentioned on Line 510).
Line 503 Said: “Modeled North Slope CH4 is underestimated throughout the measurement period pointing to deficiencies in the wetland flux specifications over this ecoregion”. What is the confidence level for this conclusion, given that the impact of the fluxes from outside of the study domain is considered significant, as discussed in Section 3.1.11?
Line 508 Authors cite the improvements since the survey by Fisher et al (2014). This looks like a good point, should it be supported by a table or figure in the analysis?
Line 141 fix square to round brackets
Line 173 what does sw mean in pco2sw? – need description
Line 190 Table 1. In second LPJ-wsl reference – year is missing
Line 264 words ‘CH4 enhancements’ can be removed - appear twice in a sentence
Jin, Y., Keeling, R. F., Morgan, E. J., Ray, E., Parazoo, N. C., and Stephens, B. B.: A mass-weighted isentropic coordinate for mapping chemical tracers and computing atmospheric inventories, Atmos. Chem. Phys., 21, 217–238, https://doi.org/10.5194/acp-21-217-2021, 2021