General Comments

As TCCON is one of the highest spectral resolution datasets and the most widely used as validation data for greenhouse gases observing satellites, vertical profiles for a priori described in this paper are important topics. The number of vertical measurements especially of stratosphere is limited and uncertainties in profile measurements are larger compared with total column measurements, the new algorithm is useful for the TCCON data users. The paper is well written. It will become more comprehensive if authors add a brief description of “how much does the new algorithm improve the TCCON retrieval quantitatively” in the abstract and/or conclusion even though required accuracy is described in the introduction and the supplement. I recommend publication after minor revisions.

Specific Comments

(1) Line 83, “Negatively impact”,

Definition of “negative” or more detailed explanation will improve reader’s understanding.

(2) Section3, ACE-FTS data

Even though number of data is limited and measurement of the lower troposphere is difficult, vertical profile from solar occultation data are accurate. What is the lower -altitude limit for the application of the paper?

(3) Section 5.1 Validation with Air CORE

Description of ideal numbers of AirCore measurement at each site and discussion on ideal global distributions of AirCore sites will be helpful for readers.

Technical Corrections

(1) Lines 53 and 202 “Potential Vorticity”

Potential Vorticity (PV) appears twice.

(2) Line 524 the Armstrong Air Force Base TCCON site, Lines 531, 535 Armstrong

Figure 15 Armstrong AFB

Line 524 “the Armstrong Air Force Base (AFB) TCCON site”?

Lines 531, 534 Armstrong AFB.

Review of Laughner et al. “A new algorithm to generate a priori trace gas profiles for the GGG2020 retrieval algorithm”

General comments:

This manuscript introduces a set of updated a priori trace gas profiles in the GGG2020 package. The profiles are the critical inputs for TCCON retrievals and have also been adopted by OCO2/3, and will have a broader usage for many existing/incoming GHG-targeted missions. Deliberate processing methods have been developed for long-lived trace gases (CO2, N2O, CH4) based on flask measurements at MLO and SMO, and more variable trace gases (CO, H2O, HDO, O3) based on model simulations from GEOS5. The generated profiles are compared with independent measurements and show encouraging improvements. Overall, this paper is very well structured and written, and the motivation/rationale for this work is very well explained. This paper is suitable for AMT and can be published after several minor changes, please see my comments below.

Specific comments:

The comparison result from CO in Section 5.1 is a little bit disappointing, but not surprising given that CO is very variable. The explanation of model simulations using static emissions makes sense to some extent but is not enough and may make users less confident in the CO a priori profiles. Re-running the whole model using different model simulations of CO may take a long time, but I would like to see two extra comparisons that can be done quickly. One is the improvements of GGG2020 compared to GGG2014 after removing Armstrong and Lamont sites; The other is the comparison between GEOS-5 CO with other observation-assimilated CO simulations (for example, the CAMS global atmospheric composition forecast model, link below) over these two sites to see if the CO overestimate/underestimate is heavily model-dependent.

https://ads.atmosphere.copernicus.eu/cdsapp#!/dataset/cams-global-atmospheric-composition-forecasts?tab=overview

Line 44: The description of the “1%” error in the shape of CO2 is a little bit ambiguous to me, and can be more specific, although you already have supplementary materials to explain that. One or two more sentences to explain that in the main text may help. Also, a change in the lower troposphere by 4ppm is not the same as changing the XCO2 by 1%. Similarly, the different scenarios in Figure S1 may represent different changes in XCO2, which may be confusing when compared to the retrieval error of <0.025% which is for XCO2.

Minor comments

• Line 6: “improving the description of CO2, CH4, N2O, HF, and CO in the stratosphere”, please rephrase.
• Figure 12: Please add a unit (or is it just fraction/ratio?) for the x-axis of the lower panel.
• Figure 12: In the caption: The fit is a robust fit using a Tukey biweight function with no intecept. Please explain “Tukey biweight function”. Also "intecept" is a typo.