General Comments:

In this study, Mottungan et al. demonstrate the use of correlative measurements of CO, CO2, and CH4 data from eleven TCCON sites to identify local and regional airmass characteristics and estimate the relative contributions of local and regional sources at each TCCON site. They use different regression techniques and enhancement ratio algorithms in the analysis. The paper addresses important science questions, is well-structured, and contains informative figures. It fits into the scope of AMT. The current TCCON GGG2020 data are available for several more years than shown in the analysis, and it might be nice to have the new data included in the analysis. The paper is suitable for publication in AMT after minor revisions, data updation/extension, and technical changes.

Specific Comments:

L91: This is just a personal preference – maybe equations could be used instead of text to explain the two methods. Some of the text could also be moved to the ‘Data and Methods’ section.

L115: "While previous studies have used enhancement ratios to examine the source attribution of CH4, CO, and CO2 at regional and/or local scale, we note that few have investigated bulk characteristics on a source type basis using all these 3 species and using these combinations of regression algorithms for globally distributed column-integrated measurements." – Please cite a few examples of studies that have used all 3 species and combinations of regression algorithms.

L123 and Table 1: The TCCON data are used from 2012 to 2019, as also mentioned in Table 1.  The Public TCCON data (GGG2020) are currently available until 2023 for Pasadena/Caltech, Garmisch, Sodankyla, Burgos, and Wollongong. The data are available until 2022 for Hefei and Darwin and until 2020 for Reunion. In Table 1, the data for these sites are listed for shorter time periods (and in Figure S1). I am curious if the analysis can be expanded and updated to include the additional years of available data.

The data link provided in the ‘Data Availability Statement' points to the TCCON website, which currently does not list the TCCON data for Ascension Island and Anmyeondo (for GGG2020).

Please indicate the data version used. Is it GGG2014 (data for Ascension Island and Anmyeondo are available) or GGG2020? In Table 1, the References are used for both data versions (e.g., Sodankyla – Kivi et al. (2014) for GGG2014 and Kivi et al. (2022) for GGG2020).

Oh et al. (2018) are cited in Table 1. Please add it to the References section.

Liu et al. (2018) are listed in the References section but not cited in the manuscript.

L124: If the data version is GGG2020, please consider citing Laughner et al. (2023) (https://doi.org/10.5194/amt-16-1121-2023) and https://doi.org/10.5194/essd-2023-331.

Figure 1:  Please consider listing location names on all sub-plots/panels. The background colors make it difficult to focus on the makers. Please consider changing the maker type and color.

L137: “Qualitatively, MOPITT and GOSAT retrievals show reasonable agreement between the retrieval of CO, CO2, and CH4 column abundance relative to TCCON at these locations.” – Please elaborate.

L219: Wu and Yu, 2018 has been cited but not listed in the References section.

Figure 2: This is just a personal preference - maybe the position of the legends that indicate the name of the species could be fixed.

The CO between ~ 2015 and 2017 is very high for Darwin. Do we know why this is the case?

L250: “The figure shows a clear seasonal cycle in the abundance of CO over all the locations and the seasonal amplitude is higher over Hefei (38.3±0.0 ppb), Sodankyla (37.2±3.9 ppb) and Pasadena (36.0±4.5 ppb) compared to other locations.” – Hefei isn’t plotted in Figure 2.

L253: “Furthermore, a large variability in CO is observed in the seasonal amplitude over Burgos (15.5 ppb), Darwin (10.2 ppb), Reunion (9.2 ppb) and Wollongong (8.5 ppb) during this period.” – Burgos isn’t plotted in Figure 2. Please consider stating “(not shown)” next to “Burgos”.

L271: “We also see a decreasing trend in CO in most of the selected TCCON sites (-0.20 to -0.98 % ppb/year), except at Ascension (3.51±0.43 % ppb/year), Pasadena (0.01±0.22 % ppb/year), and Wollongong (0.27±0.35 % ppb/year).” – Why is the trend different over these three TCCON sites?

L277: Does Anmyeondo show the highest CO2 trend and Ascension the lowest? If so, please consider stating this explicitly.

Technical Comments:

L116: “all three species” instead of “all these 3 species”

L123: “during 2012 to 2019” instead of “during the period 2012 to 2019”

L146: “than its western counterpart” instead of “than its the western counterpart”

L246: “Firstly, it is informative to understand…” – Please consider changing “informative” to “pertinent”.

L264: “as” instead of “like that is”

L276: Please consider rephrasing “CO2 and CH4 are showing an increasing trend in all locations” to “Increased CO2 and CH4 trends are observed at all locations”.

L278: For Sodankyla, “high” instead of “higher” and “low” instead of “lower”.

L279: “This is possibly due to”, not “This is may due to”.

L281: over “the” Atlantic Ocean

L287: “necessary” instead of “needed”.

L296: “… we show in Figure 3” instead of “… we also show in Figure 3”

L297: “We provide estimates” instead of “We also provide estimates”.

L298: “… for the period listed in Table 2” instead of “… for the whole analysis period as presented in Table 2”.

L300: “suggest” instead of “suggests”.

L321: “sites in SH” instead of “sites in SH locations”.

L352: “The local enhancement ratio appears to dominate over the regional ratios for Pasadena in all seasons and relative to the regional ratio, the magnitude of local enhancement ratios in CO/CO2 and CO/CH4 are more significant during Fall.” – Please consider splitting the sentence into two.

L410: “comes from” instead of “is coming from”

Mottungan et al., analyses the variations between CO, CO2, and CH4 data from the ground-based  TCCON network. They use different regression techniques and enhancement ratio algorithms to understand and separate the regional and local sources at the studied TCCON sites. In general, the paper is scientifically sound; however, it is still a subject to few modifications that need to be addressed before publishing, as outlined below.

General comments:

• Can the authors clarify if method 2 refers to the calculation of enhancement ratios in previous studies (i.e., Line 115)? If yes please say that directly in the Methods section, if not then an additional analysis to these methods would be very useful. We need to understand better how these methods compare to other generally used methods in the science community, as well as uncertainties between methods.
• Please, use XCO2, XCO and XCH4 in the whole paper when referring to column measurements, instead of CO2, CO and CH4.
• Table 3, Figure 6, Table 4 and 5 do we have any uncertainty estimates or error bars?

Specific comments:

• Line 81: could you please change ‘emission/enhancement’ to ‘emission or enhancement’ and comment on the difference between the two
• Line 91: although this is a known method, a reference or two might be useful
• Line 110: this sentence is slightly confusing. ‘because of emissions’: emission are not transported or transformed in the atmosphere, the atmospheric amounts that are a result of emissions are transported. Perhaps re-phrase.
• Line 126: Please see https://amt.copernicus.org/articles/10/2209/2017/ for the original convention of writing XCO2, CO2 should be a subscript.
• Line 127 ‘in the global carbon’ -> ‘in global carbon’. Note, I won't be editing all the text for grammar errors or better readability, unless there is a larger error. There are a few grammar errors in the text, nothing major but please re-read the text carefully.
• Section 2.1 Please explain why are these sites selected and not others (i.e., Lauder)?
• Section 2.1 Why May 2018? Is there another, better date when we also have TCCON measurements at others sites?
• Line 137: ‘Qualitatively’ Could the authors point to the numbers that suggest this?
• Figure 1: These are all column measurement so should use XCO2 etc.
• Table 1: This could go into an Applendix/Supplement
• Line 175: ‘The data period and a summary of the characteristic’ - The table shows the data period and reference; however, the characteristics are not shown. I suggested moving Table 1 to an Appendix; however, if the authors keep the Table I would suggest to summarize the region/source influence and meteorology characteristic described in this section in Table 1. For this publication, it is more important than the Data Period information. Data Period can go to Appendix or Supplement.
• Line 227: what is the explanation for taking the difference of average morning values from the average afternoon values?
• I am not sure if section 3.1 (including Figure 2 and Table 2) is needed in the main text. These sites were all already analysed in other publications and the conclusions of this section agree with those publications. Instead, I would move this to the Supplement and only copy the important analysis when discussing the enhancement ratios in later Sections (e.g. line 322). Or perhaps mention the most importance points/publications when discussing each site in Section 2.1. I would however keep Figure 3 and the analysis and focus this section on that.
• Figure 4: Explain the error bars, how was it calculated?
• Lines 364-367: can the authors explain why we see this behaviour? Same question goes for the whole paragraph. Please provide more explanation.
• Lines 398-405: This should be in the Method section
• Line 477: This is an interesting comparison, add as a separate subsection
• References: Appreciate all the reference; however, the publication does have a higher then usual number of references. I careful review of the references might be useful.

Technical comments:

• Define CO, CO2 and CH4 in the abstract
• Same goes for the main text, including other species (e.g., OH)
• Line 64: fossil fuel –> fossil-fuel, be consistent throughout the text
• Line 77: ICOS, define since everything else was defined
• Line 108: ground based -> ground-based
• Line 122: ‘As mentioned’ - Terms like this are not necessary, just start with 'We make'
• Line 123: period from 2012 to 2019
• Line 134: FTS - You don't use this abbreviation, so it is no needed
• Line 128: data sets -> datasets
• Line 133: be consistent 11 and six, use either numbers of words, or re-check the journal guideline.
• Line 148: Sodankyla -> Sodankylä, please, also re-check that original spelling is used for all sites.
• Line 156: ‘at measurement locations in’ -> ‘at’ is enough
• Line 262-264: Sentences like this are not really needed. Just start with the next sentence and reference Figure 2.
• Section 3.2: Add these as subsection 3.2 and 3.3 (i.e., Enhancement Ratio as 3.2)
• Line 575: The link doesn't work anymore, new link https://eccad.sedoo.fr
• Line 575: ‘for’ shows up blue (i.e., as a link)