The manuscript by Petropavlovskikh et al. provides an overview of the current status, recent achievements and future outlook of the Network for the Detection of Atmospheric Composition Change (NDACC). About six years after the last comprehensive review of NDACC by De Maziere et al., the manuscript is a useful reference for the more recent developments, current challenges and future directions. I recommend publication in Atmos. Chem. Phys. after consideration of the following specific – mostly minor – comments.

I was surprised that the manuscript does not include a figure or table of the NDACC stations. I would encourage the authors to consider a world map with NDACC and Cooperative Networks stations included.

I didn’t see in the manuscript any reference to the special issue. Maybe it would make sense to point to the special issue, if this paper is meant as an introduction?

Specific comments:

p2, l49: “11” -> “eleven”

p2, l56: “most of” -> “large parts of”?

p5, l155: reference to Appendix A either here or in line 144, but not needed twice

p10, l254-263: I am not convinced about the information content of the introductory paragraph. The most useful information in this paragraph is that in total nearly 500 papers since 2018 have been published – clearly an important achievement. I suggest shortening the introductory paragraph to Sec. 4.

p12, l304/305: “trends…compared well”: can this statement be made stronger? E.g. “NDACC data provided support for the trend detection”, or “NDACC data confirmed the in-situ trends”?

p12, l313: 10°S-60°N: typo? the figure says 60°S-60°N!

p14, l345: “20S”-> “20°S”

 p16, l394: “affiliated networks” -> “Cooperative Networks”?

Fig.10: Text in the figure too small to read!

p16, l411: “The HEGIFTOM-derived trends mark a turning point for the tropospheric ozone community.” How? What exactly does this mean?

p17, l420: You may add, that OCS is also a tracer for CO2 uptake by the biosphere?

Fig. 11: Please provide the station names (and maybe latitudes?) in the caption. What does the explained variance quantify? What exactly is correlated here? Please give a few more details.

p17, l434: “dynamics” is jargon here. While aerosols, clouds and ozone directly affect UV radiation, it is not immediately clear how “dynamics” affect UV. Please explain or remove “dynamics”.

p21, l517: “See Table A1 (Appendix B)”: do you mean Table C1 in Appendix C?

p22, l549: “The Global Lidar Analysis Software Suite (GLASS).” should be part of the previous sentence(?)

p22, l561: “Like the FTIR CDPS (see below)…”: Text would flow better if this statement is moved after the CDPS discussion.

p23, l604-611: in this section on the Data Handling Facility (DHF), it is not clear if CLaMS model data (and which) are available through the DHF

Section 4.4.3: Suggestion: say something about mirroring of NDACC data at other data centers

Table C1: Please use subscripts in chemical formulas

General remarks:

This paper serves as the introductory article for the ACP/AMT special issue on the achievements and perspectives of NDACC after 35 years of operation. In this context, the paper outlines NDACC's organizational structure, recent accomplishments, and its strategic response to challenges regarding resource sustainability, aging infrastructure, and data gaps. The network proposes a three-pronged strategy to modernize stations, promote data usage, and expand coverage in under-sampled regions. Furthermore, the paper reviews and updates the accomplishments of NDACC since De Mazière et al. (2018).

Both as a reference paper for NDACC and as an introduction to the ACP/AMT special issue, it is well-structured and well-written. Its content is of good to excellent quality in most technical and scientific aspects. Therefore, I recommend it for publication, albeit with some revisions.

I have a few critical remarks for revision concerning:

(i) Chapters 2 and 3 on the organizational structure of NDACC. These chapters, particularly Chapter 3, are too long and too detailed, while their scientific content is rather low. Much of this content, along with Figures 3 and 4, should be moved to an appendix.

(ii) Section 4.4, where the level of detail could be reduced, particularly in Section 4.4.3.

(iii) A table and figure displaying the NDACC stations and their respective measurements is missing; as a NDACC reference paper, these should be included.

Minor comments:

L172: In Figure 2, the IAGOS aircraft programme is missing; it is essential for the troposphere and UTLS.

L292: The reference Millan et al., 2025 is missing.

L708: Section 5.1.2.2 on "Enhancing network efficiency and expanding NDACC."

In this context, a more general discussion on NDACC-role in “Tiered Networks” or “Integrated Networks” is missing. Hereby FTIR or Brewer/Dobson could be used as examples.

L796: Section 5.2.3.4

Is NDACC anticipating on “Potential Atmospheric Accumulation and Radiative Impact of the Coming Increase in Satellite Reentry Frequency”, from Maloney et al, JGR, 2025 ?

What is missing in the paper is a section on the recent and future role of AI within NDACC and its applications…..