GMD Topical Editor review of "Simulating volcanic emissions in MESSy -- New submodel for Explosive
Volcanic ERuptions (EVER v1.1)" by Matthias Kohl, Christoph Bruehl, Jennifer Shallock et al.

This manuscript presents a methodological study, describing the operation of a sub-model to process
a set of specified volcanic emissions, to then enact gridded tracer-increments within an atmospheric model,
commensurate with the host modelling system's horizontal and vertical discretization specifications.

I should first of all apologise for the delay in providing this TE review, the authors having uploaded
the revised manuscript on 10th February, around 6 weeks ago. Last week was the last week of semester 2
teaching at the University I teach in, and with my leadership role in the APARC Hunga activity,
it was only possible to secure the time for this review this week.

I have seen that reviewer 1 has given a "reject" decision, based on identifying 1 of the 4 criteria
(scientific significance) to be at the "Poor" level, with reviewer 2 finding major revisions required,
and all 4 criteria consistent with publication, the scientific significance assessed to be "Good".

Reviewer 1's comments do not give a specific reason for the rejection, and the review raises relatively
minor issues, with some omissions. The two most critical comments related to requesting to assess also
stratospheric aerosol properties (aligned to the fact that climate impacts arise from volcanic aerosol)
and a request to assess a very large eruption case (specifically the Pinatubo case).

One of Reviewer 1's other concerns relates to acknowledging the loss pathway for emitted SO2, and
the revised manuscript now better describes the two alternate chemistry schemes, recognising
a key difference between the stratospheric Nabro case and the tropospheric Kilauea case, with
resolving the intermediate species sulfur trioxide resolved in the former case.

Reviewer 2 has confirmed the manuscript's suitability for GMD, in describing the new automated emissions
processing module, and its focus to evaluating SO2 in the case studies presented, but also found some
restructuring of the manuscript was required.

From my initial TE review in September, whilst this was not a review of the manuscript, did assess
the manuscript topic's suitability for GMD, that being to describe the operation of the emissions
sub-model, and the observational case studies to validate the global model simulated SO2, for both
stratospheric case (Nabro) and tropospheric case (Kilauea).

I feel I should state here also that my own area of academic expertise aligns closely with this study's
topic, and that GMD specifically recognises volcanic emissions as one of my main areas of expertise,
within the GMD editorial team.

I have carefully read through the reviewer comments, and with 10 years experience as a GMD Editor,
and my research expertise aligning with the study, I feel qualified to adjudicate towards a decision
to publish the study with minor revisions.

I state with full transparency here, that my decision for accepting with minor revisions, is with
Reviewer 1's reject decision not being justified within the comments, founded from a request for
additional stratospheric aerosol evaluation, and the Pinatubo case study (the poor significance
aligned to volcanic impacts on climate originating from aerosol effects).

The relevance to climate of moderate SO2 emission stratospheric-injecting eruptions was established
clearly in the literature since AR5, with key studies on the hiatus, and quantifying the radiative
forcing from the observed increased optical depth of stratospheric aerosol layer since the early 2000s
(e.g. Solomon et al., 2011; Vernier et al., 2011; Ridley et al., 2014).

The significance of the topic to better represent such moderate-SO2 stratospheric injecting eruptions
seems clear, and I would concur with reviewer 2's finding that the scientific significance is good.

Were this to be a model evaluation paper, e.g. for the EMAC interactive stratospheric aerosol capability,
a requirement for greater stratospheric aerosol evaluation would then potentially be justified, but the
study here is documenting the volcanic emissions module, and evaluating SO2 within global interactive
model simulations using this new automated pre-processing system. I feel I should also add that still
a paper evaluating the model on moderate eruptions can still potentially be valid, without necessarily
requiring a Pinatubo case.

With the topic being this new automated system for enacting tracer increments, from the new specified
inventory of volcanic emissions, for the manuscript's evaluation focuses on evaluated stratospheric SO2
is actually more appropriatem this being the main initial response of the stratosphere to the eruption.

The authors response to reviewers has also been very thorough, and it is clear substantial effort has
gone into addressing each comment raised in the reviews. The requested refactoring of the study's
results has improved the manuscript, and a notable other main change is greater context for this
now citing studies that have established other volcanic SO2 inventories for global models
(e.g. Mills et al., 2016; Carn et al., 2017; Diehl et al., 2012).

Both reviewers constructive criticism has helped improve the manuscript substantially, and the
revisions have addressed the comments re: the SO2 oxidation sink, and the re-factoring to
better organise how the main results are presented.

The scientific writing remains generally at a high standard, but in some cases, the added text
requires some further minor revision.

In summary, my decision as handling Topical Editor, is first that the scientific significance
of this study is good, in documenting the operation of a system to automatically include, from an
inventory of individual eruptions, the series of emissions of volcanic SO2 as tracer increments
in a global model, with.the observational evaluation of the global model simulated SO2.

Secondly, I have assessed carefully the revisions of the manuscript, and the re-structuring of
the results, and can see several of the key requested additions from reviewer 1 have been addressed.
And in my opinion, the requirements of reviewer 2 for major revisions are also now addressed.

And then with both reviewers finding the other 3 categories at the "Fair" or "Good" level,
I find that the revised manuscript, pending a final set of minor revisions, can then
achieve the requirements for publication in Geoscientific Model Development.

List of minor revisions (n.b. line numbers refer to the Track-Changes manuscript)
-----------------------

1) Introduction, line 93: This is one of the new segments of text added, from reviewer 1's comments,
and although this now refers to several of the papers documenting other volcanic SO2 emission inventories,
the wording needs to be amended slightly, to first introduce the concept. A suggested change is to replace:

"Volcanic SO2 emission databases are the basis for the correct implementation of volcanic eruptions
in atmospheric models..."

instead with

"Several volcanic SO2 emission databases have been developed, each providing a basis for implementing
best-estimate source parameters for individual eruptions into global atmospheric models...."

or similar text to better introduce the concept. It's quite common to colloquially refer to the
individual volcanic emissions as "simulating the eruption" or similar, which in a sense it is, but
better to be clear it's the emission not the eruption that's being simulated.

2) Introduction, line 94: Please re-word this short sentence "Timmreck et al. (2018) recommend four
different emission inventories" to be clear you mean within this intercomparison of interactive
stratospheric aerosol models. Remember it's a relatively small proportion of the global atmospheric
models that simulate stratospheric aerosol interactively, so this needs to be clear you mean for this
co-ordinated intercomparison of global interactive stratospheric aerosol models.

3) Introduction, line 96: Related to this point, please change "Carn et al. (2017) a very detailed list
of tropospheric and stratospheric volcanoes" to be "The emission database of Carn et al. (2017) provides
a comprehensive list of individual explosive volcanic SO2 injections, covering both tropospheric
and stratospheric eruptions....", or something similar to this.

4) Introduction, line 113: Please change "...studied small- and medium-sized eruptions from 2008 to 2012"
instead to "...analysed how small- and medium-sized eruptions (from 2008 to 2012) are represented within
interactive models.." or similar. I realise it was only explored within 1 model framework, but the analysis
was within that broader context of assessing impacts when different emission inventories are used etc.
A further suggestion here is to be clearer re: "small- and medium-sized", either add the word "explosive"
before "eruptions" or change to "moderate-SO2 stratosphere-injecting eruptions" or similar.

5) Introduction, line 115: Again, remember there are volcanic plume model, and models to predict the
volcanological progression of eruptions etc., so please change "Most volcanic model studies" instead
to "Most of these interactive aerosol volcanic model studies..." or similar.

6) Introduction, line 128: Although GMD papers can include a good depth of technical information,
please change "a newly developed historic default namelist setup" to be clear you mean "historic eruptions"
and to explain this re: automation of the previous manual approach that established the magnitude of
each individual tracer adjustment. Suggested minor re-wording is to delete the word "default", which I think
is meant re: this automated approach, to instead mention that automated functionality later in the sentence.
I mean "...this newly developed historic eruption namelist setup then automates this functionality"
or similar.

6) Introduction, line 149: "evalaute" --> "evaluate" (please use ispell or other spell-checker).

7) Introduction, line 151: I am not sure re: this sentence "and refined using observations from",
is referring to something that was done within this study's activity, or if the present study only evaluates
this. If the former please change "and refined using ..." to "and we further refine it here using...".

8) Title of section 2 -- "New MESSy submodel for Explosive Volcanic ERuptions (EVER)"

Although I get that the MESSy framework provides the basis for implementing the EVER sub-model,
the wording of this section, putting the "MESSy" at the start of the title ("New MESSy submodel...")
gives too much emphasis to this coupling, when the primarily functionality being documented
is the EVER model for processing the individual eruptions to tracer increments.

Suggest to change the section 2 title to "New emissions submodel for Explosive Volcanic ERuptions (EVER)"

9) Section 2, lines 242 to 245 -- The 2nd of these two sentences here seems the main information to
begin this paragraph, or I am suggesting to integrate the point about the tracer tendencies into
a re-worded version of the 2nd sentence here (then deleting the first). A suggested wording for this
could be "The EVER module code converts the individual volcanic emissions into tracer increments..."
(the text says "tendencies per second", but multiplying "tendency" by a unit of time gives an increment".

10) Section 2.1.1, line 260 -- The wording "offers" is quite business-oriented or transactional, and
a better scientific wording would be "provides" or "includes". THe fact is these are included in
the the source-code, and then suggest the latter, i.e. "The MESSY framework includes several alternative
submodels" and rather than "numerically simulating atmospheric aerosols" I think the authors mean
"interactively simulating atmospheric aerosols" (i.e. the models hare for online-simulated aerosol).

11) Section 2.2, line 312 -- "...about 800 significant explosive volcanic eruptions", the wording
"about 800" here seems too colloquial, for peer-reviewed journal paper. From the context of this para
I wonder if could re-word also with combining with the preceding sentence, changing the start of the
"Therefore, we established a default namelist configuration...." to (rather than "default", say something
like "The inventory we have established, we advocate to become a standard namelist configuration...",
and then give the actual number of explosive injections included there.

12) Section 2.2, lines 348-350 -- ".. For eruptions occurring before 2007, or those not observed..."
Please re-word "not observed", you mean within the "not observed by IASI", right?
I think you mean in these cases it's done fully interactively, (i.e. via an explicit emission flux of SO2),
rather than making a tracer mixing ratio adjustment. Then suggest to change "we utilize the" instead
to "an explicit emission of SO2 is carried out at the geographical location, with the source parameters
for the corresponding eruption...." or similar.

13) Section 3.2.1, line 496 -- "IASI faces limitations capturing the mid-term evolution of volcanic plumes
with SO2 columns falling below the detection limit." I'm not sure I'm understanding the point being made
here, but I guess you mean a limitation with the satellite-nudged tracer adjustment approach, right?
I mean any satellite instrument would have that limitation (not only IASI), and its more a limitation
of the approach to adjust the tracers, rather than the instrument itself.

Please re-word accordingly, but in fact since the requirement of the method is to realistically capture
the enhancement to SO2 very-soon after the eruption, I don't see what the issue is here. I mean the
model predicts the progression of the tracer concentrations, after the initial adjustment, and then
doesn't require to continually adjust the tracers as the plume disperses.

I'm not sure if maybe the authors mean in the case of two eruptions occurring within a few days of
each other (e.g. from two neighbouring volcanoes) or from an explosive eruption occuring near to
a continuing significant high-altitude volcanic emission source?

But even in that case I'm not sure this "mid-term evolution" would be an issue, because there presumably
are relatively few cases where that is the case, within this particular inventory's time-period anyway.

I'd suggest to potentially delete the lines 496 and 497 (including the ". Conversely "),
and just have the paragraph begin "Observations from the ..." I'm not 100% sure of the distinction
being pointed out here between IASI and MIPAS, the current wording is not so clear about that.
Suggest to re-word into a combined sentence that then makes clearer the difference seeking to be
communicated here.

14) Section 3.2.1, line 501-502 -- "Indeed, MIPAS observations become more reliable approximately
three weeks after the initial eruption". There is no citation given here, and although the scientific
writing style is generally good, this is an isolated instance of poor writing. Suggest to delete this
or cite the specific case being referred to here (with citing a study that found this to be the case),
as this is presumably relating to a study or report that analysed the observations through a specific
post-eruption period? If the sentence is deleted, note the follow-on sentence "Its ability to provide..."
then needs to be adapted accordingly, to state the instrument name again.

15) Section 3.2.1, line 504 -- I'm not sure if a grammar-tool such as "grammarly" or similar has
recommended to split the text into 2 sentences, but the 2nd of the two sentences here seems to be
the 2nd half of a logical sentence that's then been split into a separate short sentence, that
no longer makes sense. Although shorter sentences sometimes make for easier reading, within an
academic peer-reviewed journal paper, that rule may not always apply, and the information
being explained may require a longer sentence than might be seen to be better practice in a
more informal communication, such as a webpage or similar primarily online-accessed info-resource.

16) Section 3.2.2, lines 511-521 --- "Second, we performed a numerical simulation spanning from...."
For a journal paper, paragraphs needs to be stand-alone (grammatically) and suggest to simply replace
"Second, we performed a numerical simulation spanning January 2008 to December 2011 to evaluate..."
with "To evaluate the implementation (within EMAC) of the new EVER historic eruption module ...."
or similar.

17) Section 3.2.2, line 517 --- "To additionally validate the simulation, we evaluate the extinction.."
Further to the general comments re: Referee 1's rejection being primarily from requiring more aerosol
evaluation, suggest here to explain the strategy of the study being to assessing the operation of the
EVER module, via evaluating simulated SO2, but to show also this Figure for context within the
climate impacts originating from simulated aerosol.

Suggest to replace the sentence with something like "Whilst this study focuses primarily to analyse
simulated SO2, that being the emitted species handled by EVER, we present here also the EMAC simulated
extinction and sAOD at 750nm.... ".

18) Section 3.2.2, lines 527-529 -- further to comment 17) this one-sentence para I'm not sure
if maybe is then explained in the suggested edit above. And then this comment could potentially
be deleted.

19) Section 3.2.3 title (line 530) and lines 531-544 -- further to the differences in the chemistry
regime with the Kilauea case, re: the short-lived duration of the volcanic SO2 oxidation product,
suggest to hint at this with adding the word "tropospheric" before degassing, and maybe replace
"volcanoes" with "case" -- i.e. "SO2 from tropospheric degassing case -- Kilauea (2018)"

I leave it to the authors whether to make that change, but the test here needs to give some
recognition of the issue raised by reviewer 1, re: chemical sinks for SO2 also being important.
The text added now mentions a difference between the SO2 oxidation products in the stratospheric
chemistry and tropospheric chemistry schemes available within EMAC.

However, I'm not sure if the model actually switches between these 2 schemes, within the operation
of the model integration here, i.e. do only gridboxes above the tropopause "see" this extra
intermediate oxidation product in the stratospheric SO2 oxidation approach (sulphur trioxide).
Are there two different chemistries being integrated within the same model run, or is the scheme
applying the same chemical integration across the troposphere and stratosphere.

Obviously air is exchanged between the stratosphere and troposphere, and for eruptions emitting
near the tropopause, and then if two chemistries are integrated, is the cut-off for the
change at the tropopause, or some distance below the tropopause (e.g. considering the upper
tropospheric air likely has more commonalities with the stratosphere, albeit considering the
dehydration etc. re; the water vapour affecting the sulphur trioxide chemical-sink timescale.

Whichever approach is used, this needs to be set clearly within this section, and with the
re-factoring of the text there is some space to set out a good depth of information to
clarify the operation of the two SO2 oxidation schemes now mentioned in the approach
(and where the intermediate product is resolved).

I must admit it wasn't 100% clear to me whether the Kilauea case used the tropospheric chemistry
scheme because this operates only over the lower-atmosphere domain or so, as presumably this is
one integration through the entire period with the same chemistry scheme, albeit presumably
operating a hybrid approach of both schemes being integrated.

And whilst the explanation of the chemistry schemes added does partly address reviewer 1's concerns,
it should also be clarified here, within this re-structured section 3, the methodological specifics
of how the two chemistry schemes mentioned are combined and operate for this hindcast EMAC integration.

20) Section 3.2.3, lines 550-551 -- Please re-word these 2 sentences, and again I think it might be
easier to explain what's being communicated here within 1 longer sentence here. The 2nd sentence
seems to be the 2nd half of the same point being explained, but has been cut-off part-way through
making the point. Please also mention the specific satellite instrument here (S5P-TROPOMI),
and clarify the specifics of the approach to fit to these observations. OK this is explained in
Appendix B, but some summary-specifics should be given here so the reader can get the general gist
of the issue being summarised..

21) Section 4.1.2, lines 788-790 -- The approach to begin the para "So far, we focused on..."
is to colloquial, suggest to re-word again to be clear the SO2 is the main focus of the
manuscript's observational evaluation (that being the emitted species handled by the EVER module).
That's what the 1st sentence says, but please expand the sentence slightly to communicate that
more formally (less colloquially).

22) Section 4.1.2, line 837 -- "Interestingly, in the sensitivity simulations..."
Similar to comment 21, please re-word for more formalised and objective language
(delete "Interestingly" -- it's a subjective point, different readers will find
different aspects more or less interesting).

23) Section 4.2, lines 871-872 -- delete the 2nd instance of "would need to" here
(can simply say "and simulations performed at higher horizontal resolution").

References
----------
Carn, S. A., V. E. Fioletov, C. A. McLinden, C. Li and N. A. Krotkov (2017)
"A decade of global volcanic SO2 emissions measured from space"
Science Reports, vol. 7, 44095, https://doi.org/10.1038/srep44095

Diehl, T., Heil, A., Chin, M., Pan, X., Streets, D., Schultz, M. and Kinne, S. (2012)
"Anthropogenic, biomass burning, and volcanic emissions of black carbon,
organic carbon, and SO2 from 1980 to 2010 for hindcast model experiments",
Atmos. Chem. Phys. Discuss., 12, 24895–24954, 2012
https://doi.org/10.5194/acpd-12-24895-2012

Mills et al., M. J. , A. Schmidt, R. Easter, S. Solomon, D. E. Kinnison et al. (2016)
"Global volcanic aerosol properties derived from emissions, 1990–2014, using CESM1(WACCM)"
J. Geophys. Res. Atmos., 121, 2332–2348, https://doi.org/10.1002/2015JD024290 .

Ridley, D. A., S. Solomon, J. E. Barnes, V. D. Burlakov, T. Deshler, et al., (2014)
"Total volcanic stratospheric aerosol optical depths and implications for global climate change"
Geophys. Res. Lett., 41, 7763–7769, https://doi.org/10.1002/2014GL061541.

Solomon, S, J. S. Daniel, R. R. Neely III, J.-P. Vernier, E. G. Dutton and L. W. Thomason, (2011)
"The Persistently Variable 'Background' Stratospheric Aerosol Layer and Global Climate Change"
Science 333, 866, https://doi.org/10.1126/science.1206027

Vernier, J.-P., L. W. Thomason, J.‚ÄêP. Pommereau, A. Bourassa, J. Pelon et al., (2011)
"Major influence of tropical volcanic eruptions on the stratospheric aerosol layer during the last decade"
Geophys. Res. Lett., vol. 38, L12807, https://doi.org/10.1029/2011GL047563

GMD 2nd post-review TE review of "Simulating volcanic emissions in MESSy -- New submodel for Explosive
Volcanic ERuptions (EVER v1.1)" by Matthias Kohl, Christoph Bruehl, Jennifer Shallock et al.

This manuscript presents a methodological study, describing the operation of a sub-model to process
a set of specified volcanic emissions, to then enact gridded tracer-increments within an atmospheric model,
commensurate with the host modelling system's horizontal and vertical discretization specifications.

I reviewed last week the post-review version of this manuscript, and noted reviewer 1 had given a "reject" decision, based on identifying 1 of the 4 criteria (scientific significance) to be at the "Poor" level, with reviewer 2 finding major revisions required, and all 4 criteria consistent with publication, the scientific significance assessed to be "Good".

As I explained with full transparency there, I gave my Topical Editor decision to accept with minor revisions, finding Reviewer 1's reject decision was not justified within the comments, and was founded on a request that the manuscript should have included additional stratospheric aerosol evaluation and a Pinatubo case study (the poor significance being from volcanic impacts on climate originating from aerosol effects).

I noted in my TE decision-point review there, that were this to be a model evaluation paper, e.g. for the EMAC interactive stratospheric aerosol capability, then there could well be a requirement for greater stratospheric aerosol evaluation.

But the study here is documenting a volcanic emissions module, and evaluating SO2 within global interactive
model simulations using this new automated pre-processing system. I added also that still a paper evaluating an interactive stratospheric aerosol model on moderate eruptions can still potentially be valid, without necessarily requiring a Pinatubo case.

I also transparently set out in the review the assessment of each of the relatively minor main issues reviewer 2 raised, and specifically set out the two most critical comments, these relating to the request to assess stratospheric aerosol properties, and a request to assess a very large eruption case.

My own research expertise is recognised by the GMD editorial board explicitly to align closely with the topic of the manuscript, and I contend then to be very well-qualified to assess this situation, where I am identifying an unfortunate misunderstanding from 1 of the 2 reviewers re: the requirements for a manuscript to achieve publication in GMD.

The topic of the manuscript is to document a new automated volcanic emissions module, to enacting tracer increments, from any specified inventory of volcanic emissions, and that the manuscript's evaluation focuses on evaluated stratospheric SO2 is appropriate, this being the main initial response of the stratosphere to the eruption. The reviewer is of course correct that volcanic impacts on climate arise primarily from the volcanic aerosol, but that does not mean that assessing the main precursor gas is necessarily insufficient for a manuscript of this type.

The authors response to reviewers has also been very thorough, and it is clear substantial effort had
gone into addressing each comment raised in the reviews. The authors had refactored the study's
results section, which improved the manuscript, and several other substantial change, including greater context for explaining the multiple volcanic SO2 inventories now available to global models of this type (e.g. Mills et al., 2016; Carn et al., 2017; Diehl et al., 2012).

In summary, in my decision-point review last week, I recommended publish pending minor revisions, and gave there an initial list of minor revisions that required addressing before the manuscript could then be suitable for publication.

I have read the authors replies to the comments, and can see they have made each of these minor edits, the manuscript now much improved. There were still just a few minor issues, with also a larger number of grammar/typo re-wordings, and I give these below.

There were a few of these that require replies to clarify, the others being typo-level/grammar issues.

Further minor revisions (line numbers from Track Changes MS)

1) Lines 582-583, and follow-on paragraphs of discussion on lines 584-600.

I don’t get the point being made on lines 582-583, the manuscript arguing there that emissions constrained to a single gridbox tend to “potentially result in localized and exaggerated mixing ratios of SO2”.

I can see there is a follow-on point referring to “when volcanic plumes span areas exceeding one gridbox”, but the logic here was unclear to me.

I’d argue that point sources tend more to more likely be under-representing the local (to the volcano) SO2 mixing ratio, within grid-box average values.

For coarse-spatial-scale global models, there is the issue of whether the model can represent regimes where a depletion of oxidants can affect predicted sulphate production (for example), and more generally variations between the concentrated emitted species (at the plume-scale) viz-a-viz the larger-scale volcanic enhancement in the model, that determining the magnitude predicted impacts.

There is quite a good depth of Discussion already within section 5, and suggest to re-word the main points here into just 1 paragraph, rather than the 3 paragraphs here on lines 584 to 600.

2) Lines 322-325 – Please revise this new sentence added here “shall not evaluate the microphysics”. Further to the main comments above, since the topic of this manuscript is re: the emissions sub-model, there should be no expectation of requiring to validate the simulated aerosol.
What I suggest here, is to refer to a “self-consistency check” for the model, in the sense that global models may tend to focus mainly on evaluating predicted aerosol, and may be less concerned with accurately predicting volcanic SO2. I realise that’s perhaps what you mean by “additional evaluation”, but since this study is not a model evaluation paper (in that sense) better to be clear this is more a case of analysing the aerosol predicted from the validated SO2, than it is validating the predicted aerosol.

Perhaps that is what you meant by “evaluation”, but again, given reviewer 2’s comments, suggest to word this more towards a “self-consistency check” for predicted aerosol (or similar alternative label than evaluation or validation).

3) Lines 204 to 209 -- Need to explain re: the default emissions-altitude, where IASI heights are used

The revised manuscript now refers to “with the same vertical distribution”, but it’s actually not been explained what reference-altitude is given in these cases where IASI can’t observe the plume-top height.

From checking the file in the Supplement, I see the default emissions-altitude is 15km, but this is not stated currently within the manuscript (to my reading). Please add “at 15km” at the end of line 205, and also re-wording the earlier part of the revised sentence (re: IASI and “or those not observed”) as this is still slightly unclear, and should be worded more concisely.

Suggest “For eruptions before 2007, or other volcanic SO2 plumes not observable from IASI, we distribute the column SO2 at 15km, with the Gaussian x-km vertical dispersion.” (or similar).

Re: the latter, the text “all injections optimized using the IASI observations are marked accordingly” needs to give an indication of how many eruptions are where this further optimization from IASI. You can also delete “on the date provided by the emissions inventory from Schallock et al. (2023)”, as that’s implicit.

Also, again from checking the “ever_historic_stratVolcanoes” namelist, I saw the text-flag “IASI optimised” is given for eruptions 544 to 548 (2019 Raikoke), 550 (2019 Ulawun) and 568 (2020 Taal), and then please also add to note “for example 2019 Raikoke, 2019 Ulawun, 2020 Taal” where a revised observed plume-height has been found from the original inventory (Schallock et al., 2023).

Other typo/grammar re-wordings

4) Lines 84-85 –- two minor edits here

-- Re-word “down a third of the distance to the Earth’s surface” to “down to one third of that altitude”

-- Change “has to be aligned with the emission inventory derivation” to “this approach may not align with how the emissions inventory was derived”.

5) Lines 171-172 –- change “defined in the” to “specified in the” and change “namelist emission entry” to simply “emissions namelist”.

6) Lines 187-188 –- “which we extended” to “which we have now extended” --- I get that this is different author-set from that study, but given this is mainly the same Mainz group developing the system, this can be referred to as a progression from the original inventory.

7) Line 222: Change section 3.2 title “Model setup and numerical experiments” to “EMAC model and experiment set-up”

8) Lines 224-230: This para needs somewhere to specify the model horizontal and vertical resolution.

I guess this may have been omitted with different model resolutions being used for the tropospheric de-gassing than the stratospheric case, but then give both here “at T63 for the stratospheric Nabro case, and T255 for the tropospheric degassing case”.

Maybe simplest to put this at the end of the paragraph.

9) Lines 265-267 – The wording here needs reducing: “To comprehensively evaluate volcanic SO2 emissions with the EVER submodel and the impact of simplifications and adjustments to emissions data, and we conducted a reference simulations along with a series of sensitivity simulations of stratospheric SO2”.

Suggest to simplify to “For the Nabro eruption, we carried out a series of EMAC simulations to assess the sensitivity to difference emissions source parameters”.

Putting “Nabro” earlier in the sentence so the reader can realise these sensitivity runs are for this one particular eruption.

The subject of the manuscript is EVER, so that doesn’t need to be stated, but since the model is not mentioned at any point in section 3.2.1, do need to specify EMAC there.

The ”We applied a horizontal resolution...” needs to be impersonal tense, to “These simulations applied a horizontal resolution...” or similar.

10) Line 267 –- Change “We applied a horizontal resolution of T63...” to “For the stratospheric injecting case, the simulations were at T63 horizontal resolution

Depending on how change 8 specifies the model resolutions in section 3.2, this sentence could be reduced, but actually I think good here to re-iterate as many readers may go straight to read this subsection.

11) Line 270 –- The text here says “MIM1” but shoudn’t this be simply “MIM”?

12) Line 294 -- Add “(first week after the eruption)” after “short-term plume evolution”.
13) Line 305 –- Change “fixed lower integration limits” to “fixed lower plume-altitude”

14) Line 310 –- Section 3.2.2 sub-title “Multi-year simulation with the historic eruption namelist setup” to “Multi-year simulation with historic eruption namelist”

15) Lines 311-313 -- Change “To evaluate the newly developed historic volcanic eruption setup”.

Change “newly developed” to “new” and “historic volcanic eruption setup” to “historic eruption namelist”.
Replace “for the EVER sub-model (see Sect. 2.2)” with “(EVER v1.1, see Sect. 2.2)”.
Reduce “spanning from” to “spanning” or “from” and “using the same model configuration as detailed in” to “configured as detailed in Sect. 3.2.1”

16) Lines 319 -– add “this” before “being the...”

17) Lines 320-321 -– Add citation to Bourassa et al. (2007, 2012) after “…from the OSIRIS instrument”.

18) Lines 337 – Change "In addition to the evaluation of explosive volcanic eruptions...” (remember it’s not the eruptions being evaluated here) to “As well as evaluating emissions from explosive eruptions...” .

And then delete “following” later in the sentence so it’s focused to “analysing a series of”

19) Line 343 -- Change “We use a simplified chemistry globally in this simulation” to “For the tropospheric degassing case, we use a simpler chemistry in the global model..”.

20) Line 345 – change “reducing the high computational cost due to the increased horizontal resolution and decreased timestep” to “with a decreased timestep to reduce the computational cost at this increased horizontal resolution”.

21) Line 359 -- Change “In addition, we perform a simulation with...” to “To explore the potential for optimising further the emissions, we perform simulations with...” or something more meaningful to hint at why this extra simulation was run. Also please add “(see Figure 9)” after “tuned emissions rates”.

22) Lines 362-363 – Add a full-stop after “simulated SO2 columns” and resume with a new sentence “For each day in...”, then being able to add “(the first month post-eruption)” to clarify why June 2018.
Also replace “and subsequently use this linear relationship to derive” with “a linear relationship is used to derive”.

23) Caption to Figure 9 – Not sure what’s happened here, but the panel labels a), b), c) and d) seem to have been be shown in bold font, with an asterisk. Not sure if the LaTeX has corrupted to bold rather than italics. But these should be simply “a)”, “b)”, “c)” and “d)”, without bold-font or the asterisk.

References

Bourassa et al. (2007): “Stratospheric aerosol retrieval with optical spectrograph and infrared
imaging system limb scatter measurements”
J. Geophys. Res., vol. 112, https://doi.org/10.1029/2006JD008079, 2007

Bourassa et al. (2012): “Odin-OSIRIS stratospheric aerosol data product and SAGE III intercomparison”
Atmos. Chem. Phys., 12, 605–614, https://doi.org/10.5194/acp-12-605-2012

Carn, S. A., V. E. Fioletov, C. A. McLinden, C. Li and N. A. Krotkov (2017)
"A decade of global volcanic SO2 emissions measured from space"
Science Reports, vol. 7, 44095, https://doi.org/10.1038/srep44095

Diehl, T., Heil, A., Chin, M., Pan, X., Streets, D., Schultz, M. and Kinne, S. (2012)
"Anthropogenic, biomass burning, and volcanic emissions of black carbon,
organic carbon, and SO2 from 1980 to 2010 for hindcast model experiments",
Atmos. Chem. Phys. Discuss., 12, 24895–24954, 2012
https://doi.org/10.5194/acpd-12-24895-2012

Mills et al., M. J. , A. Schmidt, R. Easter, S. Solomon, D. E. Kinnison et al. (2016)
"Global volcanic aerosol properties derived from emissions, 1990–2014, using CESM1(WACCM)"
J. Geophys. Res. Atmos., 121, 2332–2348, https://doi.org/10.1002/2015JD024290 .

The authors have replied to the 2nd decision-point Topical Editor review, and made the few further minor-revisions, and typo/grammar-level final corrections.

And I am happy now to approve this further-revised manuscript can now proceed to publication in GMD.