In this paper, an atmospheric chemistry general circulation model was used to simulate the volcanic plume from the 1991 Pinatubo eruption. The authors conducted several sensitivity tests and compared the simulations with satellite-based SO₂ and aerosol retrievals. They showed that the injection height, water vapor injection, and volcanic ash all played an important role in the loading and the transport of volcanic aerosols in the stratosphere. They also showed that heterogenous reactions on volcanic ash aerosols had an impact on the formation of sulfate aerosols. Overall, this is a quite comprehensive modeling study with some very interesting results. The paper is generally well written although a bit too long. I would recommend that the paper be accepted for publication in Atmos. Chem. Phys., after the specific comments have been addressed.

Specific comments:

1. The authors may consider shortening the paper. There are sentences that do not provide much additional information and can be removed. For example, lines 457-458 basically repeats the previous sentence.
2. In most sensitivity tests, volcanic material was injected in a relatively thin layer in the atmosphere. There is recent evidence that the plume height can be quite different for different parts of the plume (and not necessarily 20 km). Can the authors comment on how this may or may not affect the simulations and conclusions?
3. Similarly, as the recent Tonga eruption showed, ash and SO2 could be separated during the initial stage of the eruption. Can the authors also comment on any potential impact on the simulations, if ash was indeed injected at a different height than SO2 for Pinatubo?
4. Introduction: Lines 57 and 87 seem to be redundant. Overall, the introduction is quite long and can be shorter.
5. Figure 1 is only mentioned in the passing in the text. Perhaps it is not completely necessary.
6. Section 3.1: I'm not entirely sure if R1-R5 need to be included in a research paper.
7. Line 223: Fig. 8 doesn’t show refractive index.
8. Line 232: specify what RRTM is.
9. Line 233-234: It appears that IR absorption by SO2 was ignored? Would that have any significant effects on the plume transport?
10. Lines 405-415: elaborate a bit more on how NOx and NOy are affected?
11. Figure 8, 9, 11, 13, 15: missing letters from labels.
12. Figure 9: are the data points in the plot temporally averaged? The initial mass does not match with the injected amount.
13. Figure 12 and lines 520-524: what is the mechanism for OH change between the cases with and without ash aging?
14. Conclusions - given the results here, can the authors make some comments on the Tonga eruption? For example, with the strong perturbation of water vapor in the stratosphere, do the authors expect any significant differences in terms of sulfate formation for Tonga?

Review of “The effect of ash, water vapor, and heterogeneous chemistry on the evolution of a Pinatubo-size volcanic cloud” by Abdelkader et al.

In this study, the effects of varying injection parameters and heterogeneous chemistry are modelled for the Pinatubo 1991 eruption. For this, the coupled chemistry climate model EMAC is run with prescribed Sea Surface Temperature and nudged Quasi-Biennial Oscillation. Model experiments are compared with available limited observations and reanalysis data. The study is of scientific interest and includes novel aspects. It may be publishable after considering the following general and minor comments carefully.

General comments:

This study follows previous model work from some of the co-authors. In Osipov et al 2020 & 2021 and Stenchikov et al 2021, the effects of interactive SO2 and photolysis rates (next to volcanic ash) were simulated for the Toba super eruption and the Pinatubo eruption using the EMAC and WRF models, respectively. Why were these effects not taken into account in this study as well? The ratio and consequences of the missing effects need to be explained and discussed. Also why choosing a different EMAC model set-up as in Osipov et al 2020/2021 or is it the same one?

The authors run 5 ensemble members for each of their experiments. Which atmospheric initial conditions were chosen and how large is the spread among the different ensemble members? Please give some background and discuss the variability of the SAOD response and its effects at northern high latitudes as observed and modeled for the Pinatubo eruption (Toohey et al, 2014).

Why was the latitudinal band 3s10-25km experiment chosen? The motivation for this is rather vague. There is a bunch of other model studies, f.e., Dhomse et al (2014) and Mills et al (2016) next to Brühl et al (2015).

Stratospheric temperature response: Here it would be rather helpful to show the results from the other experiments. Suddenly the 20 km 12 Mt injection SO2 scenario comes up as a best analogy, but what do the others experiments show? As the MERRA2 reanalysis is based on a model as well, what do observations show for Pinatubo (cf. Labitzke and McCormick, 1992)?

Overall, it would be interesting to see some of the results (SO2, SO4, SAOD, R_eff, and stratospheric temperature) for all experiments, which would certainly lengthen the manuscript. Thus, I leave it up to the authors to decide but I think it would be very helpful for a better understanding and model intercomparison.

The abstract and conclusions need some overall take home messages i) on the overall study conclusion, and ii) from the set of model experiments: Which model experiment fits best with observations?

The paper is sometimes a bit lengthy and could be cut at certain points; see suggestions below.

Minor comments:

Abstract:

“The volcanic cloud interacts with tropopause and stratopause,… coupled with the ozone cycle.” This sentence needs to be revised (science and grammar).  

Pls add an overall conclusion wrt to the SO2, ash and water vapour injection impacts.

Pls add an overall model vs observation conclusion. Which model experiment is the closest to the Pinatubo observations within the EMAC model world?

Introduction:

“Volcanic activity is a major natural cause of climate variation…” Pls correct as not all volcanic activity is climate relevant. You are referring to major explosive volcanic eruptions reaching stratospheric levels only.

Graft et al 1995 > Graf et al 1995

>>Volcanic<< Explosivity Index

dacitic magma: Explain dacitic and relate it to your research work here.

A positive phase of the Arctic Oscillation is not simulated by recent CMIP models. See the more recent studies by Driscoll et al (2012); Charlton-Perez et al (2013); Toohey et al (2014); Bittner et al (2016a/b), and following work. This statement has to be updated with more recent research work and model results.

Line 36: Over which time period erupted Pinatubo?

“…and has been neglected in many previous studies (Niemeier et al 2009; Oman et al 2006).” Pls cite also more recent papers here.

From line 49 onwards:

Pls clarify and disentangle observational versus model studies here. Right now, the paragraph mixes both although having quite different reasons for the spread and uncertainties.

Timmreck et al (2018) gives an uncertainty of 10-20 Mt SO2 injection into the stratosphere for the Pinatubo eruption based on available observations and model work, which should be referred to here. Then the details before can be shortened.

Line 76-77: Fig. 1 is nice to have but you can also just refer to McCormick et al (1995); Robock (2000); Timmreck (2012); and Zhu et al 2020. There is nothing new you add here, or? Next, there are also processes displayed you do not address or mention (c.f. ocean circulation and biogeochemistry).

Line 95 >: The difference to Stenchikov et al 2021 is mentioned partly, but it still lacks that SO2 heating is not included next to online photolysis rates of volcanic aerosols in your study. Pls try to explain what you do in contrast to Stenchikov et al 2021 and Osipov et al 2020 and 2021 and why. This list is not complete yet.

2 Data:

How good is the MERRA2 assimilation product for the Pinatubo? Pls check the new S-RIP 2022 report. Pls compare with observations f.e Labitzke and McCormick, 1992.

Line 196: “ sulphate represents by the soluble mode” grammar correct?

3 Model:

Line 164-167: I assume you also take into account natural and anthropogenic surface halogen emissions as background (such as CHBr3, CH2Br2, CH3Br, CFCs, halons)?

3.4 Section: Pls clarify

-AEROPT: EMAC module?

-RAD: EMAC module?

-Fouquart and Bonnel (1980) part of EMAC?

-RRTM part of EMAC?

-SO2 is not radiative active in this (EMAC) model study but it is included in EMAC used by Osipov et al 2020 and 2021, why not here? Pls explain the ratio and the effects of neglecting it.

4 Experimental Setup:

Line 251: Why choosing different injecting heights? This is not really motivated and explained in the introduction.

Line 256: 3s10-25km: So the injection layer is 22.5-27.5 km or …?

Line 265: “Based on different atmospheric initial conditions” Which are?

Results:

Line 296: “The cloud height is essential…” Do you mean injection height? This whole sentence needs an overall rewording to make scientifically sense.

Line 301: “lofting driven by radiative heating of volcanic debris” So what is the effect of the missing SO2 radiative heating in your results? (see also Osipov et al 2020/2021; Stenchikov et al 2021)

Line 305-306 and ff manuscript:

Why not continuing with model experiment 3s10-25km if it shows such a good comparison with observations? The ratio for this is missing.

Line 385: Stenchikov et al 2021 and Osipov et al 2020&2021 included online photolysis rates (of volcanic aerosols) in addition in contrast to your study here, nor?

Section 5.1.5 and Figure 6:

Can you show O3 as well which would be interesting to see and to understand and interpret the stratospheric temperature response in Fig. 15?

Section 5.6:

Pls compare also with observations cf. Labitzke and McCormick (1992).

Conclusions:

Line 594-596: “Because of the coarse resolution…similar to other global models…too fast aerosol poleward transport… “ This statement comes as a surprise. Can you pls elaborate a bit more on this and give references to it: Toohey et al (2014) simulates the effects of different Pinatubo aerosol forcing fields in MPI-ESM based on observations and MAECHAM5HAM model simulations (for 17 Mt SO2 injections representing different states of the NH polar vortex and thus aerosol transport and SAOD at high latitudes).

Figures:

-The figures in the pdf file seem to have some problems. At same pages, letters are missing cf. Page 38 y-axes labels on the right side, and Fig. 9 titles, etc.

-Numbers at the legends are often unreadable cf. Fig. 6. This has to be checked and revised for all figures.

-Figure captions need to explain the shown figures, which is often not the case, f.e. SPARC in Fig. 3 is missing etc.

Fig. 4 and elsewhere: Pls show meridional sections from 90N to 90S.

Fig. 5: SAGEII vs SAGE/ASAP ?

Fig. 6: Ozone should be shown here as well.

Fig. 8 and elsewhere: AOD, AO, vs SAOD is written, pls homogenize.

References:

Bittner, M., Timmreck, C., Schmidt, H., Toohey, M., & Krüger, K. (2016a). The impact of wave-mean flow interaction on the northern hemisphere polar vortex after tropical volcanic eruptions.  Journal of Geophysical Research: Atmospheres, 121, 5281–5297. https://doi.org/10.1002/2015JD024603

Bittner, M., Schmidt, H., Timmreck, C., & Sienz, F. (2016b). Using a large ensemble of simulations to assess the northern hemisphere stratospheric dynamical response to tropical volcanic eruptions and its uncertainty. Geophysical Research Letters, 43, 9324–9332. https://doi.org/10.1002/2016GL070587

Charlton-Perez, et al, On the lack of stratospheric dynamical variability in low-top versions of the CMIP5 models, J. Geophys. Res.-Atmos., 118, 2494–2505, doi:10.1002/jgrd.50125, 2013.

Driscoll, S., Bozzo, A., Gray, L. J., Robock, A., and Stenchikov, G.: Coupled Model Intercomparison Project 5 (CMIP5) simulations of climate following volcanic eruptions, J. Geophys. Res., 117, D17105, doi:10.1029/2012JD017607, 2012.

Labitzke, K. and McCormick, M. P.: Stratospheric temperature increases due to Pinatubo aerosols, Geophys. Res. Lett., 19, 207– 210, doi:10.1029/91GL02940, 1992.

McCormick, M., Thomason, L. & Trepte, C. Atmospheric effects of the Mt Pinatubo eruption. Nature 373, 399–404 (1995). https://doi.org/10.1038/373399a0

Mills, M. J., Schmidt, A., Easter, R., Solomon, S., Kinnison, D. E., Ghan, S. J., Neely III, R. R., Marsh, D. R., Conley, A., Bardeen, C. G., and Gettelman, A.: 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, 2016. 

Osipov, S., Stenchikov, G., Tsigaridis, K., LeGrande, A. N., & Bauer, S. E. (2020). The role of the SO2 radiative effect in sustaining the volcanic winter and soothing the Toba impact on climate. Journal of Geophysical Research: Atmospheres, 125, e2019JD031726. https://doi.org/10.1029/2019JD031726

Osipov, S., G. Stenchikov, K. Tsigaridis, A.N. LeGrande, S.E. Bauer, M. Fnais, and J. Lelieveld, 2021: The Toba supervolcano eruption caused severe tropical stratospheric ozone depletion. Commun. Earth Environ., 2, no. 1, 71, doi:10.1038/s43247-021-00141-7.

SPARC Reanalysis Intercomparison Project (S-RIP) Final Report. Masatomo Fujiwara, Gloria L. Manney, Lesley J. Gray, and Jonathon S. Wright (Eds.), SPARC Report No. 10, WCRP-6/2021, doi: 10.17874/800dee57d13, 2022. (available at www.sparc-climate.org/publications/sparc-reports)

Timmreck, C. (2012), Modeling the climatic effects of large explosive volcanic eruptions. WIREs Clim Change, 3: 545-564. https://doi.org/10.1002/wcc.192

Timmreck, C., Mann, G. W., Aquila, V., Hommel, R., Lee, L. A., Schmidt, A., Brühl, C., Carn, S., Chin, M., Dhomse, S. S., Diehl, T., English, J. M., Mills, M. J., Neely, R., Sheng, J., Toohey, M., and Weisenstein, D.: The Interactive Stratospheric Aerosol Model Intercomparison Project (ISA-MIP): motivation and experimental design, Geosci. Model Dev., 11, 2581–2608, https://doi.org/10.5194/gmd-11-2581-2018, 2018.

Toohey, M., Krüger, K., Bittner, M., Timmreck, C., and Schmidt, H.: The impact of volcanic aerosol on the Northern Hemisphere stratospheric polar vortex: mechanisms and sensitivity to forcing structure, Atmos. Chem. Phys., 14, 13063–13079, https://doi.org/10.5194/acp-14-13063-2014, 2014.