UV/Vis stratospheric air mass factors considering photochemistry at two Antarctic stations

Gómez-Martín, Laura; Prados-Roman, Cristina; Chipperfield, Martyn P.; Van Roozendael, Michel; Puentedura, Olga; Navarro-Comas, Monica; Ochoa, Hector; Yela, Margarita

doi:10.5194/amt-19-4393-2026

Articles | Volume 19, issue 13

https://doi.org/10.5194/amt-19-4393-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-19-4393-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 13

Research article

|

03 Jul 2026

Research article |

| 03 Jul 2026

UV/Vis stratospheric air mass factors considering photochemistry at two Antarctic stations

Laura Gómez-Martín, Cristina Prados-Roman, Martyn P. Chipperfield, Michel Van Roozendael, Olga Puentedura, Monica Navarro-Comas, Hector Ochoa, and Margarita Yela

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Final revised paper (published on 03 Jul 2026)
Supplement to the final revised paper
Preprint (discussion started on 03 Feb 2026)
Supplement to the preprint

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2026-17', Anonymous Referee #1, 17 Mar 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-17/egusphere-2026-17-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2026-17-RC1
- AC1: 'Reply on RC1', Laura Gómez Martín, 20 Apr 2026
  
  The authors would like to thank the Referee for his/her insightful comments, the constructive evaluation of our manuscript and the time dedicated to reviewing our manuscript. We appreciate the positive feedback regarding the clarity of the writing and the systematic investigation of the Air Mass Factors (AMFs), which the Referee found recommendable for publication.
  The Referee’s comments have been very helpful in identifying areas where our description of the methodology—specifically regarding the treatment of horizontal inhomogeneity and the integration of the chemical model with the Radiative Transfer Models (RTMs)—needed further clarification or refinement. We have addressed each of the general and detailed comments (in blue, following the Referee’s comments in black) in the attached file.
  
  Citation: https://doi.org/10.5194/egusphere-2026-17-AC1
RC2:
'Comment on egusphere-2026-17', Anonymous Referee #2, 20 Mar 2026

The paper of Gomez-Martin et al. adresses the calculation of Air Mass Factors (AMFs) for ground-based zenith DOAS observations at twilight for two Antarctic stations. The subject is complicated in particular due to the need to account for the earth sphericity and photochemical variations of several of the measured species. The authors use the models SLIMCAT (CTM) to derive effective concentration profiles along the light path, and MYSTIC (RTM) to calculate corresponding AMFs. They then compare these calculations with DOAS measurements of NO2, O3, BrO, and OClO, finding a good agreement except for BrO, which is explained by tropospheric contributions not considered in the model.
This study is important for the community, the method is new and robust and the results consistent so I have only minor comments on the content. However some work could be useful to improve the presentation before publication.
In several sections (2.2 and especially 4.1) the text should be split in paragraphs to make it digestible. For instance, when they introduce a new figure, it is normal to start a new paragraph. Same for a new line of reasoning.
Carefully using a LLM could improve the text readability as several sentences are hard to read, with for instance the subject too far away from the verb. Exemples of complicated sentence which could be improved in my opinion

L. 248 'To check the validity of these approximations, SCDs of the four target species obtained using AURA in 2-D mode and

considering the photochemical model concentration profiles (different for each SZA), have been compared with the SCDs

obtained with AURA in 1-D mode, using a single averaged concentration profile (eq. 12)'
L. 165 Thus, the concentration of a given gas in a given atmospheric layer encountered

by the sunlight reaching an instrument at the surface, for SZA =  ( 𝑐􀯟,􀰏 ), is actually an average of the concentrations

corresponding to all values of the SZAs encountered by all the beams passing through this layer along their optical paths (see

Fig. 3).
Regarding the figures: the texts are often too small, especially in the legend. It s partly due to the fact that they are loaded. Some of the figures could be split in two or more, e.g. figure 7 (we dont see the value for ozone AMF relative difference due to the scale defined by OCLO). In Figure 8, some material could go the supplement. Do we need all the months in the main text?
Figure 5: There is nothing to see for 80° because the average profile perfectly matches the model. So showing 80° is not that useful. It would be interesting on the other hand to plot the ratio of the maximum average concentration with respect to the model, to see at which SZA the averaging starts to matter.
AMF calculation: it would be useful for readability to have a table for the inputs and algorithms used in p. 15.
L 428 'Figure 10' seems to relate to figure 11. I missed where the true figure 10 was presented in the text.
Specific comments:
L.54 Since 2012, the ground-based DOAS community working on stratospheric research [e.g. Adams et al., 2012]. If it s the DOAS community, there should be one more than one paper to refer to?
L 77 reads contradictory with L 81. Can you please explain or reformulate?
L. 77 'To our knowledge, the only publication showing OClO AMFs for SZA up to 95º is Pinardi et al. [2023].'... ''
L. 81 'Finally, in Kühl et al. [2004], OClO AMFs are estimated with the AMFTRAN radiative transfer model [Marquard et al., 2000] for different Gaussian vertical profiles and for SZAs between 40 and 95.'
Figure 1: SLIMCAT should be in the figure?

L 130: I think a_l is the box-AMF? but it s not explained in the text, could you add that in the text?
Equation (2) to (6) Do I understand correctly that this calculation is for one SZA at the station? If so, it would be pedagogical to explicitly state that VCDtotal_ph depends on this SZA.
L.151-152: 'In addition to gas phase chemistry ...' -> I assume you do not use this PSC module? If not, please indicate or remove this sentence, if yes, please give more details
L.162: 'The concentration ... representative for ... 2.8° -> In Chipperfield (2006), I read that the model grid is variable. So it s the model runs that you have that were calculated at 2.8°, not the model itself. If this it true, can you please reformulate?
l.172 takes chemistry into account -> photochemistry would be clearer
L.177: 'single scattering is already a good approximation' -> can you be quantitative on that?
Figure 4 y label should be 'scattering altitude' for clarity
L.303 'daily or even more resolved sampling is recommended for OClO'-> what would it mean, more resolved than daily? Two AMFs for the two twilights a day?
L.460 'source of error for all modelled SCDs could be the estimation of the reference ' -> measured instead of modelled?

Citation: https://doi.org/10.5194/egusphere-2026-17-RC2
- AC2: 'Reply on RC2', Laura Gómez Martín, 20 Apr 2026
  
  We would like to thank the reviewer for his/her constructive comments and the time dedicated to reviewing our manuscript. We agree that the suggested changes, particularly regarding the readability of the text and the presentation of the figures, significantly improve the clarity of the study.
  In the attached file, we provide a point-by-point response to the specific comments. The reviewer’s original comments are shown in black, and our responses are provided in blue.
  
  Citation: https://doi.org/10.5194/egusphere-2026-17-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

AR by Laura Gómez Martín on behalf of the Authors (20 Apr 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (23 Apr 2026) by Kimberly Strong

RR by Anonymous Referee #1 (13 May 2026)

Suggestions for revision or reasons for rejection

Dear authors,

Many thanks for the very detailed answers to the referee comments that really make a difference in understanding the study. Nevertheless I find that these answers are at times not sufficiently incorporated in the manuscript.

In particular:

GC.1.: The description about the state of the art 2D capabilities of RT models vs. justification of your approach has not found its way in the manuscript apart of just stating a single benefit of 1D version ("high vertical resolution while keeping the computational cost manageable"). In other words, the manuscript still misses weighting in on potential advantages a straightforward approach of a 2D capable model would have as well as making a credit to such models (or existing photochemical correction schemes) vs. benefits of your approach. In the AC you provided a good and detailed discussion which should be part of the state of the art description and for the motivation of the study.
GC.2.” The newly provided description “The considered concentration of a given layer for a given solar beam, each time the beam crosses this layer, is the mean value between: the concentration at the top of the layer and the “local” SZA at this point (theta2 for op1 in Fig. 3c, for instance), and the concentration at the bottom of the layer for the “local” SZA at this point (theta1 for op1 in Fig. 3c). This is true except if one beam does not reach the bottom of the layer (as optical path between op1 and op2 in Fig. 3c). In that case, the mean is performed for the values at the top of the layer and the minimum altitude reached (SZA=90⁰).” is absent from the updated manuscript. You should definitely put this information about how c_{b,l,i} is obtained in the manuscript.
DT.1. You have ignored the suggestion to use the equation formatting. Please make this equation as Eq1., the mathematical definitions of AMF few lines later should also be separated as equations.
DT.50. In logical terms, wide use of something does not make it true. Extensive validation is the argument but this should be properly referred to in the manuscript. E.g. in Sect. 2.1. references to the validation work done with emphasis on the polar atmosphere and, most important, twilight scenes for all 4 species must be added and still existing uncertainties mentioned. Alternatively, one can soften the statement in the conclusions making it conditional, e.g.: “Assuming that the model is accurate; this confirms the validity of the method employed and the approximations considered.”

Additional comments:

DT.5. “…Vertical Columns Densities (VCDs), which only depend on the concentration vertical profile of the considered molecule.”
Better write, to be more exact: "which are the integral of the concentration vertical profile of the considered molecule along altitude"
DT.6.
“It should be noted that the equivalence between these two definitions is strictly valid for weak absorbers, where the change in intensity due to absorption does not significantly alter the radiation field. While this approximation is appropriate for the species and spectral ranges investigated here, it could be problematic for strong absorbers, such as ozone in the short-wave UV.”
Please add some reference(s) here.
DT.9 “To our knowledge, the only publication providing explicit OClO AMFs values for SZA up to 95˚ obtained from measurements is Pinardi et al. [2022]”
I think this statement needs to be clarified given that their VCD used in the SCD/VCD ratio is not a directly measured quantity but are an estimation by a geometrical approximation and even is taken just at a single SZA (i.e. it is not taken at the actual SZA which should be according to your definition introduced earlier): You could add the citation from Pinardi et al. after your current statement: “To be more precise the AMF in Pinardi etal. is “defined as the ratio of the measured slant column to the vertical column estimated at 70° of SZA, assuming that at this solar elevation a simple geometrical AMF can be used.””
DT36. Given your explanation before, it is much better understandable now. What is still missing, is mentioning of the box model output resolution in the SZA domain and how concentration values at theta1, theta2, etc are obtained from that output (e.g. by linear interpolation?).

Some technical points:

L293 “. An assessment of polar stratospheric clouds effect can be found in e.g.”: This sentence is incomplete, the citation as in the former manuscript is missing.
L399 “Thus, this seems” -> “Therefore, this seems”
L428-429: “…but also the vertical profile of the species ((1): different profiles for different SZAs…” -> “…but also the vertical profile of the species: (1) different profiles occur for different SZAs …”
L735: There are two doi links provided; the second link should be removed.

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ED: Publish subject to minor revisions (review by editor) (23 May 2026) by Kimberly Strong

AR by Laura Gómez Martín on behalf of the Authors (27 May 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (14 Jun 2026) by Kimberly Strong

AR by Laura Gómez Martín on behalf of the Authors (22 Jun 2026) Manuscript

Short summary

The Antarctic ozone hole remains a critical global challenge. Accurately measuring the gases that cause it during twilights is difficult due to rapid chemical changes. We used advanced computer simulations to reproduce observations at 2 Antarctic stations to account for these fluctuations and the Earth's curvature. Our results improve the accuracy of atmospheric monitoring, helping scientists better track the recovery of the ozone layer and understand the complex chemistry driving its depletion.