The authors have responded carefully to each of the 2 reviewers' comments, and have added to the Appendix extra analysis of the SOCOL simulated Antarctic PSCs in 2 other austral winters (in addition to the 2007 winter that comprises the analysis for the main results section of the paper).

There is now additional model information given in section 2.1, which helps explain to the reader the specifics of the NAT and STS treatment in the model.

I am able then to recommend the paper be published, with only a few additional very minor corrections to the revised section 2.1 in my editor review.

Within these very minor corrections from my editor review, there is only one
of these that are significant -- and that is that I am recommending the
authors avoid using the acronym "SBS" for aqueous sulphuric acid
binary solution.

The term STS is firmly established within the polar stratospheric composition science community, to denote "Super-cooled Ternary Solution", but I have
never seen the term SBS be used before -- and in my mind this acronym
does not help explain the background aqueous sulphuric acid aerosol particles.

Rather the authors should refer either to "binary solution" to "aqueous sulphuric acid aerosol" -- the term "super-cooled" is not useful here.

The binary solution particles are simply aerosol particles, and in my opinion introducing an acronym here only further entrenches the tendency for PSCs to be seen as somehow separate from the stratospheric aerosol, when in fact the STS particles are liquid aerosol particles after all.

That said, the referees have identified the paper as a valuable contribution, and the authors have addressed all the comments made by the reviewers, improving the manuscript to be almost ready for publication.

And once the very minor revisions I am listing below are attended to (which includes to avoid use of the SBS term), I am happy to recommend publication.

List of very minor revisions required:
-----------------------------------------

1) Page 4, line 124 -- please do not use the term "SBS" -- as per my comments above, adding a new acronym for the sulphuric acid aerosol does not help the paper, and to me will serve only to further separate PSC research from other related science, in particular I am thinking about the stratospheric aerosol community here. Much better simply to state "also known as binary solution". Also the word "solutions" is odd, the word should be singular.
So my recommended revision here is to replace "(supercooled binary solution, SBS)" with "(also known as binary solution)".

2) Line 136 -- replace "for the SBS particles" with "for the sulphuric acid aerosol particles".

3) Line 144 -- when you state "mean radius" be precise about the type of mean radius -- I think you mean geometric mean radius here right (with a log-normal distribution and assumed geometric standard deviation)? If so please add "geometric" before "mean radius", and if a poly-disperse aerosol is assumed then add "(poly-disperse NAT particle size with log-normal distribution at geometric standard deviation of 1.x/2.x)" . Or if the calculation is for mono-disperse particle size, then just replace the word "mean" with "mono-disperse NAT particles of".

4) Line 150 -- insert comma before "the PSC routine".

5) Line 153 -- insert "the" after "equilibrium between" and replace "phase" with "phases", deleting the hyphen between "gas" and "phase".

6) Line 153 -- add "(i.e. the process is fast)" after "timescale is very short"

7) Lines 154-155 -- replace "the equilibrium between particulate and gas-phase is hardly reached, as shown by observations" with "the progression towards equilibrium of the particulate NAT phase and the gas phase is much slower, as inferred from observations". Replace also "and additional particles can nucleate" with "for example additional particles potentially nucleating"

8) Line 178 -- This new sentence "All years are without volcanic influence" needs to be clarified. I think what you mean here is that the prescribed dataset providing the SAD of the binary solution is based on SAGE-II measurements that are outside periods of strong volcanism (e.g. during the unusual 1998-2002 period when the stratospheric aerosol layer was at background conditions). Assuming that is the case, then please add "(i.e. the prescribed SAD dataset representative of a background stratosphere, such as was the case in the 1998-2002 period)". However, if the CMIP6 dataset is used, then the dataset for the pre-industrial control is not a zero-volcanic background case, but more an average-volcanism case. Please consult with co-authors and re-word accordingly.

The authors have addressed each of the minor revisions (mostly in the Model Description part of the text) that I identified in my "decision-stage editor review", and have changed the text in the manuscript accordingly.

Reading the results section, I noticed there were a few sentences where the wording still required some improvement, and I've listed below the 7 places where I had noticed this -- in each case I'm recommending specific revisions for improved wording in this decision stage technical-review.

These changes are however only at the "technical correction" level, and I am recommending publication once these final minor wording changes are made.

Final minor wording changes (technical corrections)
--------------------------------

1) Page 9 line 235 -- the text "we compare SOCOL with CALIPSO along a single flight track" is not adequate. Firstly because CALIPSO is the name of the satellite, the name of lidar instrument being CALIOP. I appreciate the authors may prefer a writing style in brief sentences, but the wording needs to be precise when they do so. Also "flight track" could confuse some readers, the term "orbit" or "orbital transect" more appropriate for the satellite comparisons. Suggest to re-word to "we evaluate the vertical profile of SOCOL simulated PSCs, comparing to lidar measurements from the CALIPSO satellite, along specific orbital transects" or similar.

2) Page 12, lines 314-316

These 3 sentences beginning "These values...", "However, the..." and "For example, the..." each need to be more specific

2.1) Suggest to change "These values had once been chosen based on what was known about PSCs back then." to "The values used for such PSC microphysics parameters tend to inherit early choices based on initial comparisons with limited observational datasets". Or if a particular study or choice was meant with the "back then" wording, then could instead explain that specifically, citing the paper the authors have in mind.

2.2) Suggest to improve "However, the current parameter setting might not be optimal" to "Also, the initial parameter values chosen may reflect specific conditions in a particular polar winter, and may require adjustment to be more representative over the broader range of conditions experienced across several winters."

2.3) With the text "For example, the rather low value of n_ice of 0.01 cm-3...", suggest to cite the study that provided the basis for this value, or the modelling study where this value was first chosen, if possible. Basically that sentence needs to be more specific as to why that value is now thought to be "rather low", whereas originally it was (presumably) a best-estimate.

3) Page 16, lines 371-372 -- The sentence beginning "Both indicates a more efficient denitrification than in S$_{REF}$" needs to be improved. Suggest to add "features" after "Both", change "indicates" to "indicate" (grammar) and replace "a more efficient denitrification" with "greater denitrification". Suggest also adding "in the increased n$_{NAT,max}$ run (sensitivity run S$_{n(NAT,max)}$) )" before "than in S$_{REF}$".

4) Page 18, lines 404-406 -- The term "mimicking" is non-scientific, and does not really communicate adequately what is being done. The method is explained in the paper, and in my opinion it would be sufficient to just state "comparing to the space borne lidar measurement" rather than "mimicking a lidar measurement" (also changing "compared modelled" earlier in the sentence instead to "evaluated simulated" to avoid duplication of "compared"). If the authors want to communicate some specifics about their method for doing that, they should choose a better word than "mimicking". Maybe reword "mimicking a lidar measurement on the model output" to "deriving an equivalent backscatter metric from the model, along CALIPSO orbital transects, and aligning with optical thresholds used in the CALIOP type algorithm" or similar.

5) Page 18, lines 410-412. The wording in these 2 sentences need to be improved

5.1) suggest adding "In the model, " at the start of the sentence and replacing "without taking" with ", whereas NAT particles are known to require several days to grow to larger sizes, their size then being dependent on..". I'm not sure why the authors have added "the pre-existing PSC distribution", although I guess maybe they mean the sequestering of HNO3 into liquid STS particles. If that was what was meant then I think that effect would already be resolved in the current PSC scheme (even with the simplified NAT approach). In which case I suggest to delete "and pre-existing PSC distributions into account" and cite a paper that has shown the effect explained re: the impact of resolving the time required for growth compared to a PSC scheme with instantaneous NAT formation, for example Feng et al. (2011, ACP).

5.2) The 2nd sentence, which begins "The approach" again needs to be more specific -- suggest to reword to "The instantaneous NAT formation approach". Also, the word "states" is not appropriate -- suggest to replace to "therefore represents". The latter part of the sentence can also be improved, inserting "several" before "other models" and deleting "as well".

6) Page 18, lines 413-419 -- these sentences were poorly worded in places.

6.1) Lines 413-414 -- Please insert "simplified" before "PSCs scheme" improve the wording of "includes several fixed microphysical parameters" -- suggest to re-word to "then requires to assign representative constant values for several PSC microphysics parameters." or similar wording.

6.2) Lines 415-416 -- Please also re-word "The actual value for the NAT number density" because there is no single value for that -- it varies depending on the situation (e.g. the recirculation of air within the cold region or variations in the concentration of preferential-nuclei, e.g. meteoric smoke particles). This potential reasons for the variation do not need to be specified explicitly here -- but this sentence here is clearly trying to communicate that the constant value is a simplification, the situation much more variable. In which case, suggest to re-word by deleting "the actual value for" and "being". The reference to the active sites is referring to active sites on the NAT-freezing behaviour of aerosol particles containing preferential nuclei (e.g. meteoric particle) and seems too detailed for that 2nd part of the sentence. Suggest to first add after "because" the text "of different cold-pool and vortex situation (e.g. Mann et al., 2003), the availability of NAT nuclei (Voigt et al., 2005)". With that re-wording, then the "active sites" can be a continuation of the NAT nuclei point, changing "NAT nucleation themselves shows" instead to "NAT nuclei themselves showing". In addition to the Hoyle et al. (2013), suggest to also cite the James et al. (2018) ACP paper, which progresses this discussion re: the nature of the preferential NAT nuclei.

6.3) Line 418 -- Suggest to replace "tuning of the microphysical parameters to reasonably" instead to "testing to reach representative microphysical parameter values which reasonably"

6.4) Line 419 -- The sentence beginning "This was done here by various" similarly needs to be improved. Please replace those 6 words with "In this study, we have explored the implications of some of the values chosen in the simplified PSC scheme, analysing several". Then adding the following text before the full stop ", progressing to new values which we show perform reasonably well across the broader conditions found across several Antarctic winters" or similar.

7) Lines 462-468 -- again, this part of the text still requires improved wording.

7.1) Lines 462-464 -- the assertion "we do not expect any substantial drawbacks from the applied set-up" needs to more clearly be communicated to be specific to the "specified-dynamics" (i.e. nudged) situation. This can be done simply by replacing "the applied set-up. First the model was used" to "the applied set-up, provided the model is used" and change the comma after "dynamics mode" instead to a full stop.

7.2) Lines 464-465 -- With that re-wording in 7.1) above, please change "and we do not see major differences" to "The nudged approache ensures no significant differences" and delete "in nudged mode" at the end of the sentence.

7.3) The wording "Second, to capture mountain wave events, for example, we would need to go to" seems too sudden to discuss this without citing a reference -- suggest to re-word that text instead to "Although mountain waves are known to be important in triggering NAT nucleation (e.g. Carslaw et al., 1999), resolving such localised PSC formation explicitly would require", deleting "which are" and replacing "beyond the capabilities of" with "inconsistent with the computational constraints of".

7.4) Lines 466-468 -- Again the wording of this sentence should be improved -- suggest to change "This is supported by Khosrawi et al. (2017), who found only little differences" with "Also, Khosrawi et al. (2017) found only small differences", deleting also the "a" before "T42" and "T106", and adding "simulations of the cold 2015/6 Arctic winter" at the end of the sentence (to be clear that is for that particular winter.

Minor additional typo-/grammatical-improvements.
--------------------------------------------------------

1) Page 18, line 403 -- insert "have" before "presented an evaluation".

Papers
-------

Carslaw, K. S., Peter, T., Bacmeister, J. T. and Eckermann, S. D.
"Widespread solid particle formation by mountain waves in the Arctic stratosphere", J. Geophys. Res., vol. 104, no. D1, pp. 1827-1836 (1999).

Feng, W., Chipperfield, M. P., Davies, S., Mann, G. W., Carslaw, K. S. et al.
"Modelling the effect of denitrification on polar ozone depletion for the Arctic winter 2004/5", Atmos. Chem. Phys., vol. 11, pp. 6,559-6,573 (2011).

James, A. D., Brooke, J. S. A., Mangan, T. P., Whale, T. F., Plane, J. M. C. and Murray, B. J.: "Nucleation of nitric acid hydrates in polar stratospheric clouds by meteoric material", Atmos. Chem. Phys., vol. 18, pp. 4519-4531. (2018)

Mann, G. W., Davies, S., Carslaw, K. S. and Chipperfield, M. P.
"Factors controlling Arctic denitrification in cold winters of the 1990s"
Atmos. Chem. Phys., vol. 3, pp. 403-416, (2003)