The manuscript by Fernandez et al. describes the implementation of short-lived halogen chemistry already available in CESM1 into CESM2, thereby making it accessible to the broader CESM community. It provides a detailed description of the implemented SLH chemistry (incl. offline/online emissions, chemical reactions and deposition), an analysis of the SLH budgets, spatial/vertical distributions and impacts on oxidants. The analysis is very detailed and can act as benchmark evaluation for future studies using CESM2-SLH. It fits well into the scope of GMD and I see no reason why it should not be published after addressing the following minor comments.

General comments

1.

Parts of the manuscript (especially the beginning of Section 2 and Section 2.5) read a bit like a CESM user manual. The information is without doubt very useful for CESM users. However, some adaptions might help to make it easier to follow for readers outside the CESM community. The manuscript is also relatively long, so the authors might want to consider moving some more technical parts to the supplement.

Suggestions:

Abstract: Avoid using the (I think) CESM-specific term “compset” in the abstract.

l. 138 – l. 164: The authors might want to consider merging this section and Section 2.5 as some of the information is redundant (e.g. CESM branches, compsets), and it would be beneficial to have the information at the same place. Additionally, a definition/introduction of “compset” would be helpful. I understand that it is the CESM name for “simulation setup” and specifies the used BC and emissions, and settings like resolution etc.. It would be helpful if Table 6 would be referenced here (if not merged) to summarise the mentioned compsets. Additional columns could be introduced in Table 6 to explain the difference between compsets. For example, I assume that FCnudged means nudged meteorology and FCHIST historical free-running, bit it is not explained explicitly. Also the difference between FCnudged and FWnudged is not explained explicitly. What is FCASE?

l. 606: It is not clear to me what the difference between cesm2.2-asad-branch_slh and cam_cesm2_2_rel09_slh is. Could you clarify why you need two branches?

l. 610-619: Could be moved to the supplement? The information could be presented in a table listing the additional species, and if they emit, dry/wet deposit etc.

l. 662-686: Could be moved to the supplement?

Also Section 4 “Final Remarks is quite technical (e.g. l. 1602 – 1606). I think it would be valuable here to discuss if the performance of CESM2-SLH (regarding SLH budgets and impact on atmospheric composition) is similar/better/worse compared to CESM1-SLH/ CAM4-Chem, and other models including SLH chemistry.

2.

The comparison with observations is somewhat limited. In Section 3.2.2. “Evaluation of SLH Abundance with Observations” Source Gas Injection and Product Gas Injection to the stratosphere is compared to observations. It would be beneficial to extend the evaluation to SLH abundance to the (lower) troposphere, MBL or surface (for example comparison to station data). In Section 2, a comparison of VSL halocarbons to observation is mentioned (e.g. in l. 273), but no details are given.

Specific comments

1. l. 214: Another model with SLH chemistry would be TOMCAT (Hossaini et al., 2016; https://doi.org/10.1002/2016JD025756).
2. l. 241: Could you explain which VSL halocarbons are compared to observations, and add references for the surface and aircraft observations you compare to?
3. l. 292: Did you compare VSL chlorocarbons to observations as well (if yes, please provide more details), or is the rationale being consistent with the scaling of natural emissions?
4. l. 340: What is the reasoning for assuming free-regime approximation, i.e. why is diffusion not considered (Schwartz 1986)? Could it play a role for larger SSA particles?
5. l. 396: Could you provide the formula to calculate the yield (e.g. add it in Table 1). I could not find the formula in the referenced publication Li et al., 2022 either.
6. l. 520: Could you clarify what is meant by "following the HNO3 acid displacement developments from Hossaini et al., 2016"? The HNO3 acid displacement is het_ss_9, isn't it? Do you mean that a similar approach as for this reaction is used? Hossaini et al., 2016 also implemented heterogeneous recycling on non-SSA particles (e.g. their reaction 6).
7. l. 708: What about the study by Mirrezaei et al. (https://essopenarchive.org/doi/full/10.22541/essoar.175288325.58779694/v1). They seem to use CESM2.2.-SLH in a CH4-emission driven setup.
8. Figure 2 and Figure 3: Would it be possible to show the interannual variability (e.g. standard deviation) for CESM1 Cyclical_slh? Or is it negligible?

9. Figure 2: Could you provide a bit more context on the differences in the trends of O3, OH, and NO2 between CESM2-SLH and CESM1-SLH shown in Figure 2? You explain that these differences drive differences in the trends of halogen budgets. Are the differences of O3, OH, and NO2 mainly caused by differences in prescribed boundary conditions and emissions (e.g. NOx and VOCs) or by model updates? Are differences between CESM2 and CESM1 (without SLH) similar to the differences shown here? How do the trends compare to other models and observations (e.g. are differences between CESM1 and CESM2 small compared to inter-model differences or biases towards observations)?

10. l. 914: An even more recent estimate for GEOS-Chem might be given by Wang et al., 2021 (https://acp.copernicus.org/articles/21/13973/2021/)

11. l. 1227: Cly, Bry, and Iy are usually defined as total inorganic halogens including XOx as far as I know. Here it represents the reservoir only excluding XOx, which might be confusing. Maybe better to choose a slightly different abbreviation for the reservoir, and make clear that the striped and empty bars give total inorganic chlorine/bromine/iodine.

12. Table 9: This table provides really interesting information. Considering the following question might make it even more valuable:

    • How is stratospheric O3 defined, i.e. everything above the chemical tropopause? The footnote $ is missing.
    • Tropospheric mean OH could better be expressed as number concentration (in molecules cm-3) to facilitate comparison with other published estimates (e.g. multi-model comparison in Lee et al., 2021; https://doi.org/10.1073/pnas.2115204118).
    • How large is the interannual standard deviation compared to the difference?
    • How do the results compare to SLH effects in other models?

13. Figure 16: Panels c) and f) of Figure 16 suggests that the total ozone loss is the same in FCnudged_SLH and FCnudged_NOH, and that only the contribution of different families changes. Could you confirm that this is indeed the case? It might be worth mentioning.

14. l. 1618: By how much does SLH increase computing time?

Technical corrections

1. l. 52: "de" --> "the"
2. l. 53: “SLH have been shown”? SLH refers to short-lived halogens, or “SLH chemistry has been shown”?
3. l. 57: The acronym VSL refers to "very short-lived" only. Change to "VSL halocarbons"? Or define new acronym VSLS (for very short-lived species); same in l. 743
4. Table 1, Table 2 and Table 5: Rename “Molecular weight” to something more meaningful, e.g. “Molecular weight dependent factor ”. And provide units for it.
5. l. 606: "respectively" used twice
6. Caption of Figure 3 (l. 852): “compset_non” --> “compset_noh”
7. Table 8: How is present-day defined, i.e. average over which years is shown? Please provide the information in the caption. Units are missing for Long-lived halogens
8. Figure 5: “FCNudged_NON” --> “FCNudged_NOH”. Might need to check for a consistent naming of the setup without SLH in general.
9. Figure 7: “BRCL”  --> “BrCl” typo in legend of panel b
10. l. 1061: Figure 10 could be referenced here as it shows the geographical distribution.
11. l. 1097: Figure 8 shows profiles of the absolute VMR of the species I think. The “change in inorganic halogen product gases from the Earth’s surface to the stratosphere” could be misunderstood as “difference between the Earth’s surface and the stratosphere”.
12. l. 228: Do you mean “summer” instead of “winter” here?
13. Table 10: Units missing for PO3 – LO3, drydep, and O3 STE
14. l. 1422: The estimates in the text (505 and 522 Tg yr-1) refer to IOx loss according to Table 10.
15. Table 12: Please include in the table caption which years were analysed.
16. l. 1618: “chemitry” --> “chemistry”