Global Sensitivity of Tropospheric Ozone to Precursor Emissions in Clean and Present-Day Atmospheres: Insights from AerChemMIP Simulations

Wang, Wei; Gao, Chloe Yuchao

doi:https://doi.org/10.5194/egusphere-2024-4091

Preprints

https://doi.org/10.5194/egusphere-2024-4091

Preprints

05 Mar 2025

| 05 Mar 2025

Global Sensitivity of Tropospheric Ozone to Precursor Emissions in Clean and Present-Day Atmospheres: Insights from AerChemMIP Simulations

Wei Wang and Chloe Yuchao Gao

Abstract. Ozone (O₃) is a Short-lived Climate Forcer (SLCF) that contributes to radiative forcing, influences secondary aerosol formation, and indirectly affects the atmospheric lifetime of methane, a major greenhouse gas. This study investigates the sensitivity of global O₃ to precursor gases in a clean atmosphere, where hydroxyl (OH) radical characteristics are approximately uniform globally, using data from the PiClim experiments of the Aerosols and Chemistry Model Intercomparison Project (AerChemMIP) within the CMIP6 framework. We also evaluate the O₃ simulation capabilities of four Earth system models (CESM2-WACCM, GFDL-ESM4, GISS-E2-1-G, and UKESM1-0-LL). Our analysis reveals that the CESM and GFDL models effectively capture seasonal O₃ cycles and consistently simulate vertical O₃ distribution. In contrast, the GISS and UKESM models effectively replicate the positive correlation between tropospheric O₃ and temperature but exhibit lower sensitivity to natural precursor sources than anthropogenic ones. While all models successfully simulate O₃ responses to anthropogenic precursor emissions, CESM and GFDL do not capture tropospheric O₃ forcing from natural NO_x emissions (e.g., from lightning). The sensitivities of O₃ to its natural precursors (NO_x and VOCs) in GISS and UKESM models are also very low. These findings refine our understanding of O₃ sensitivity to natural precursors in clean atmospheres and provide insights for improving O₃ predictions in Earth system models.

Received: 21 Dec 2024 – Discussion started: 05 Mar 2025

Competing interests: The contact author has declared that neither of the authors has any competing interests.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

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Journal article(s) based on this preprint

04 Nov 2025

Global sensitivity of tropospheric ozone to precursor emissions in clean and present-day atmospheres: insights from AerChemMIP simulations

Wei Wang and Chloe Yuchao Gao

Atmos. Chem. Phys., 25, 14535–14550, https://doi.org/10.5194/acp-25-14535-2025,https://doi.org/10.5194/acp-25-14535-2025, 2025

Short summary

Wei Wang and Chloe Yuchao Gao

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-4091. A lot of improvements needed', Anonymous Referee #2, 25 Mar 2025

General comments

The paper presents the sensitivity of ozone on precursor gases, anthropogenic ozone depleting gases and aerosol in the framework of a comparison of chemistry climate models. The main focus is on tropospheric ozone but results are presented only in crude integral quantities where effects often cancel out. One figure shows that the noise due to meteorology appears to be dominating in the 'time-slice' simulations (?) where correlations between ozone and temperatures even change sign arbitrarily. There is some lack of significance, especially if only the arbitrary values of the last simulation year are picked because of model dependent interannual variability like e.g. the QBO (Quasi-Biennial Oscillation) which is even not mentioned in the text.

A problem in this paper is that the figures are in a poor quality concerning definition of the shown quantity, unclear units, ignoring conventions for axes and too many lines in a frame which cannot be distinguished (Figs. 5 - 8). The worst of this is Fig. 2 with arbitrary z-axes (model levels?). Please use here a logarithmic pressure axis or altitude and more ticks.

The conclusions cannot be drawn from the presented figures and should be expanded.
Specific comments

Line 18: In preindustrial atmospheres OH is not globally uniform due to seasonal variation, a latitude dependence, land sea differences, convection and land cover. This sentence is misleading and has to be improved.

Line 26: Surface temperature? Or some tropospheric average?

Line 29: Do you mean here "radiative forcing"? Or just photochemical smog reactions?

Line 30ff: What is the main result? Just noise? Please be more specific.

Line 44 or later: OH is also sensitive to absolute humidity (i.e. temperature dependent for fixed relative humidity) and CO.

Line 56ff: I miss some key references and mentioning 'NOx-limited' and 'VOC-limited'.

Table 1: Contains 1 useless column (content can be in caption or text) but also definitions are missing (number of gridpoints, Eulerian or spectral model?). Here other important properties, e.g. chemistry module or boundary conditions (BVOC) might be included.

Line 110 or later (line 240?): Important information concerning emissions and boundary conditions for gases like CO and CH₄ is missing, as well as a table

containing emission inventories (references) for the used gases and aerosol particles. Some information on a subset of species is scattered over the text.

Line 186: Right wording? Do you use CO and HCHO as intermediate products of NMVOC oxidation?

Line 189: WMO, dynamical or O₃? Mention what is used, if models are different here it should be included in Table 1.

Line 194: This should also go into Table 1.

Line 215: Are these free running 'time-slice'-simulations with fixed boundary conditions for about the year 1850 without and with perturbations?

Line 221ff: It would be good to have some list or table in an Appendix with what is included in VOC, BVOC, aer, HC and NTCF. The assumptions in the scenarios are rather restricted, do you e.g. assume that soil and forest fire sources for NOx stay unchanged?

Line 227: Inconsistent with line 400. Halocarbons include CFCs and HCFCs but also compounds containing bromine. CH₃Cl, CH₃Br and CCl₄ are the most important with natural emissions. What is used? I hope that for increased CFCs consistent initial conditions with upscaling are used for ClY and BrY concentrations to prevent a drift lasting decades.

Table 2: Include a row in the header with main features of the scenarios.

Line 240: Emission data here? Or in line 243? Please more details.

Line 266f: The numbers would be different for the 29^th year. Use at least a 2 year average because of QBO. This holds for all results shown later. For the greenhouse forcing the upper and mid tropospheric ozone matters more than the surface one.

Line 276: Does this refer to troposphere or stratosphere? Austral summer? Known is the Antarctic vortex in the lower stratosphere in Austral winter as transport barrier and its relation to the present day ozone hole. Please be more precise here. This is confusing as well as the caption of Fig. 1 where the season names appear to refer to the Northern hemisphere.

Line 312ff: This cannot be seen from Fig. 2 which is distorted for each model in a different way (see also general remarks). Here it might be useful to show DJF and JJA seasons instead of the annual average.

Fig.3: I suppose you mean density weighted vertical average with variable tropopause and stratopause? Please specify in caption. Better use fixed levels like 100 and 1hPa because of the radiative heating characteristics. Surfacetro? This is not a common meteorological word. Do you mean temperature of the surface layer? For scientific interpretation this figure is of rather limited value, due to compensating effects in different altitude levels from chemistry and radiation.

Fig. 4: Looks like noise due to meteorological variation in different altitudes. It is known from textbooks and the IPCC reports that the correlation of O₃ in different altitudes with surface temperature can change sign. Please redesign or skip this figure.

Table 3: Please provide this for the stratosphere or better the lower stratosphere (below 10hPa). The total average numbers are almost useless because of compensating effects. For surface climate only the lower stratosphere matters. Here also some sentences on the Antarctic and Arctic ozone hole formation and model differences in the HC-scenario would useful. Provide proper definition of what is shown in the caption (or refer at least to figure captions or an expanded Table 2).

Table 4: Expand caption as above.

Line 401: Isn't it PiClim-N₂O?

Line 422: Why? Wrong initialization?

Figure 5: Split into more panels, 20 curves in one panel cannot be distinguished.

Figure 6: Please use the same vertical axis for every model (log p). The unit appears to be wrong or is a time integral meant? A tendency is always per time unit (s, day, year).

Figure 7: Please use the same vertical axis for every model.

Figure 8: Please use the same vertical axis for every model. Rearrange the factor with power of 10 in the label of the y-axis of panel c.

Figure 6-8: Better split into more panels.

Conclusions: You should clearly distinguish between troposphere and (lower) stratosphere. O₃ precursor gases like NOx and VOCs almost don't affect the stratosphere, except via aerosol formation which is not discussed. The uncertainty due to the lightning NOx parameterizations is a well known phenomena since decades. You might also mention that the models reproduce stratospheric ozone depletion by CFCs and N₂O.
Technical corrections

Line 226: ' ' missing.

Line 227: Case typo?

Line 239: 'ta' listed 2 times.

Line 268: Isn't it WMO?

Citation: https://doi.org/10.5194/egusphere-2024-4091-RC1
- AC1: 'Reply on RC2', Wei Wang, 14 Jul 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4091/egusphere-2024-4091-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-4091-AC1
- AC2: 'Reply on RC1', Wei Wang, 14 Jul 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4091/egusphere-2024-4091-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-4091-AC2
RC2:
'Comment on egusphere-2024-4091', Anonymous Referee #1, 30 Mar 2025

General comment:
The article “Global Sensitivity of Tropospheric Ozone to Precursor Emissions in Clean and Present-Day Atmospheres: Insights from AerChemMIP Simulations” by Wang and Gao presents the sensitivity of ozone using four different simulation global models with specific parameters and specifications. The paper's main concern is the difficulties that appear from the figures' understanding. The conclusions derived from these figures should be expanded and figures should not just be explained in the text with minimal discussions. The comparisons between the models are somehow affected by the figure’s clarity.
Specific comments:
Line 15: “secondary organic aerosol”, please use “organic” in the text since the ozone is affecting mostly organic species.
Line 28: What is tropospheric O3 forcing? Please explain.
Line 77: “hydroxyl radicals (HOₓ)”, please avoid confusion
Table 1. Please build up the table in Word and not import it as a picture as it appears. Difficult to read in the tables ….. all tables. What do you mean by “sophistication of gas-phase chemistry”? please use “lat x long”. Please use units of pressure for vertical levels for the UKESM model too.
Line 275: please be more precise and consistent with spring, summer, fall vs autumn, and winter when referring to the Arctic and Antarctic for one specific year.
Figure 4 needs improvements for a better understanding. The explanations in the article body decipher figure 4, but actually, the figure itself should be explanatory for the data.
Line 400: HCFCS probably is HCFCs.
Table 3 and 4 are hard to read.
Figures 6, 7, and 8 are difficult to read and to interpret.
Please introduce in the text Figure 6a representing ozone production.
The GISS model observed a notably high concentration of NOx at around 500 hPa altitude. Could the authors link this variation with other compounds whose concentration is induced by NOx (i.e. HONO)? Has been observed these insides of elevated NOx correlated with other chemicals?
Technical:
Line 226: concentrations.HC
Line: 256: (Shindell et al. (2006)

Citation: https://doi.org/10.5194/egusphere-2024-4091-RC2
- AC1: 'Reply on RC2', Wei Wang, 14 Jul 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4091/egusphere-2024-4091-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-4091-AC1

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-4091. A lot of improvements needed', Anonymous Referee #2, 25 Mar 2025

General comments

The paper presents the sensitivity of ozone on precursor gases, anthropogenic ozone depleting gases and aerosol in the framework of a comparison of chemistry climate models. The main focus is on tropospheric ozone but results are presented only in crude integral quantities where effects often cancel out. One figure shows that the noise due to meteorology appears to be dominating in the 'time-slice' simulations (?) where correlations between ozone and temperatures even change sign arbitrarily. There is some lack of significance, especially if only the arbitrary values of the last simulation year are picked because of model dependent interannual variability like e.g. the QBO (Quasi-Biennial Oscillation) which is even not mentioned in the text.

A problem in this paper is that the figures are in a poor quality concerning definition of the shown quantity, unclear units, ignoring conventions for axes and too many lines in a frame which cannot be distinguished (Figs. 5 - 8). The worst of this is Fig. 2 with arbitrary z-axes (model levels?). Please use here a logarithmic pressure axis or altitude and more ticks.

The conclusions cannot be drawn from the presented figures and should be expanded.
Specific comments

Line 18: In preindustrial atmospheres OH is not globally uniform due to seasonal variation, a latitude dependence, land sea differences, convection and land cover. This sentence is misleading and has to be improved.

Line 26: Surface temperature? Or some tropospheric average?

Line 29: Do you mean here "radiative forcing"? Or just photochemical smog reactions?

Line 30ff: What is the main result? Just noise? Please be more specific.

Line 44 or later: OH is also sensitive to absolute humidity (i.e. temperature dependent for fixed relative humidity) and CO.

Line 56ff: I miss some key references and mentioning 'NOx-limited' and 'VOC-limited'.

Table 1: Contains 1 useless column (content can be in caption or text) but also definitions are missing (number of gridpoints, Eulerian or spectral model?). Here other important properties, e.g. chemistry module or boundary conditions (BVOC) might be included.

Line 110 or later (line 240?): Important information concerning emissions and boundary conditions for gases like CO and CH₄ is missing, as well as a table

containing emission inventories (references) for the used gases and aerosol particles. Some information on a subset of species is scattered over the text.

Line 186: Right wording? Do you use CO and HCHO as intermediate products of NMVOC oxidation?

Line 189: WMO, dynamical or O₃? Mention what is used, if models are different here it should be included in Table 1.

Line 194: This should also go into Table 1.

Line 215: Are these free running 'time-slice'-simulations with fixed boundary conditions for about the year 1850 without and with perturbations?

Line 221ff: It would be good to have some list or table in an Appendix with what is included in VOC, BVOC, aer, HC and NTCF. The assumptions in the scenarios are rather restricted, do you e.g. assume that soil and forest fire sources for NOx stay unchanged?

Line 227: Inconsistent with line 400. Halocarbons include CFCs and HCFCs but also compounds containing bromine. CH₃Cl, CH₃Br and CCl₄ are the most important with natural emissions. What is used? I hope that for increased CFCs consistent initial conditions with upscaling are used for ClY and BrY concentrations to prevent a drift lasting decades.

Table 2: Include a row in the header with main features of the scenarios.

Line 240: Emission data here? Or in line 243? Please more details.

Line 266f: The numbers would be different for the 29^th year. Use at least a 2 year average because of QBO. This holds for all results shown later. For the greenhouse forcing the upper and mid tropospheric ozone matters more than the surface one.

Line 276: Does this refer to troposphere or stratosphere? Austral summer? Known is the Antarctic vortex in the lower stratosphere in Austral winter as transport barrier and its relation to the present day ozone hole. Please be more precise here. This is confusing as well as the caption of Fig. 1 where the season names appear to refer to the Northern hemisphere.

Line 312ff: This cannot be seen from Fig. 2 which is distorted for each model in a different way (see also general remarks). Here it might be useful to show DJF and JJA seasons instead of the annual average.

Fig.3: I suppose you mean density weighted vertical average with variable tropopause and stratopause? Please specify in caption. Better use fixed levels like 100 and 1hPa because of the radiative heating characteristics. Surfacetro? This is not a common meteorological word. Do you mean temperature of the surface layer? For scientific interpretation this figure is of rather limited value, due to compensating effects in different altitude levels from chemistry and radiation.

Fig. 4: Looks like noise due to meteorological variation in different altitudes. It is known from textbooks and the IPCC reports that the correlation of O₃ in different altitudes with surface temperature can change sign. Please redesign or skip this figure.

Table 3: Please provide this for the stratosphere or better the lower stratosphere (below 10hPa). The total average numbers are almost useless because of compensating effects. For surface climate only the lower stratosphere matters. Here also some sentences on the Antarctic and Arctic ozone hole formation and model differences in the HC-scenario would useful. Provide proper definition of what is shown in the caption (or refer at least to figure captions or an expanded Table 2).

Table 4: Expand caption as above.

Line 401: Isn't it PiClim-N₂O?

Line 422: Why? Wrong initialization?

Figure 5: Split into more panels, 20 curves in one panel cannot be distinguished.

Figure 6: Please use the same vertical axis for every model (log p). The unit appears to be wrong or is a time integral meant? A tendency is always per time unit (s, day, year).

Figure 7: Please use the same vertical axis for every model.

Figure 8: Please use the same vertical axis for every model. Rearrange the factor with power of 10 in the label of the y-axis of panel c.

Figure 6-8: Better split into more panels.

Conclusions: You should clearly distinguish between troposphere and (lower) stratosphere. O₃ precursor gases like NOx and VOCs almost don't affect the stratosphere, except via aerosol formation which is not discussed. The uncertainty due to the lightning NOx parameterizations is a well known phenomena since decades. You might also mention that the models reproduce stratospheric ozone depletion by CFCs and N₂O.
Technical corrections

Line 226: ' ' missing.

Line 227: Case typo?

Line 239: 'ta' listed 2 times.

Line 268: Isn't it WMO?

Citation: https://doi.org/10.5194/egusphere-2024-4091-RC1
- AC1: 'Reply on RC2', Wei Wang, 14 Jul 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4091/egusphere-2024-4091-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-4091-AC1
- AC2: 'Reply on RC1', Wei Wang, 14 Jul 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4091/egusphere-2024-4091-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-4091-AC2
RC2:
'Comment on egusphere-2024-4091', Anonymous Referee #1, 30 Mar 2025

General comment:
The article “Global Sensitivity of Tropospheric Ozone to Precursor Emissions in Clean and Present-Day Atmospheres: Insights from AerChemMIP Simulations” by Wang and Gao presents the sensitivity of ozone using four different simulation global models with specific parameters and specifications. The paper's main concern is the difficulties that appear from the figures' understanding. The conclusions derived from these figures should be expanded and figures should not just be explained in the text with minimal discussions. The comparisons between the models are somehow affected by the figure’s clarity.
Specific comments:
Line 15: “secondary organic aerosol”, please use “organic” in the text since the ozone is affecting mostly organic species.
Line 28: What is tropospheric O3 forcing? Please explain.
Line 77: “hydroxyl radicals (HOₓ)”, please avoid confusion
Table 1. Please build up the table in Word and not import it as a picture as it appears. Difficult to read in the tables ….. all tables. What do you mean by “sophistication of gas-phase chemistry”? please use “lat x long”. Please use units of pressure for vertical levels for the UKESM model too.
Line 275: please be more precise and consistent with spring, summer, fall vs autumn, and winter when referring to the Arctic and Antarctic for one specific year.
Figure 4 needs improvements for a better understanding. The explanations in the article body decipher figure 4, but actually, the figure itself should be explanatory for the data.
Line 400: HCFCS probably is HCFCs.
Table 3 and 4 are hard to read.
Figures 6, 7, and 8 are difficult to read and to interpret.
Please introduce in the text Figure 6a representing ozone production.
The GISS model observed a notably high concentration of NOx at around 500 hPa altitude. Could the authors link this variation with other compounds whose concentration is induced by NOx (i.e. HONO)? Has been observed these insides of elevated NOx correlated with other chemicals?
Technical:
Line 226: concentrations.HC
Line: 256: (Shindell et al. (2006)

Citation: https://doi.org/10.5194/egusphere-2024-4091-RC2
- AC1: 'Reply on RC2', Wei Wang, 14 Jul 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4091/egusphere-2024-4091-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-4091-AC1

Peer review completion

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

AR by Wei Wang on behalf of the Authors (14 Jul 2025) Author's response

EF by Katja Gänger (16 Jul 2025) Manuscript Author's tracked changes

ED: Referee Nomination & Report Request started (05 Aug 2025) by Pedro Jimenez-Guerrero

RR by Anonymous Referee #2 (19 Aug 2025)

Suggestions for revision or reasons for rejection

General remarks
There are some improvements in the text and the figures but some key issues concerning figure quality addressed by both reviews are ignored. Also the presentation of the results in Table 3 has to be improved to be useful. Climate forcing or radiative forcing is mentioned in the first sentence of the abstract but not addressed later except for the introduction.
The paper still needs major revision to be acceptable but there is the risk of rejection.

Specific remarks
Line 76: Typo, OH and HO2 were spelled out earlier.
Line 84: 'uniform'?
Line 104: 'computational'?
Line 111ff: 'via OH changes'.
Table 1: Remove the column with 'interactive' (valid for all models and written in text, line 92) or include instead module names there (only if available for all models) or number of species and reactions (sum). Use superscript for exponent. Add after 'resolution' '(number of gridpoints)'.
Line 216ff: Does this include the natural fractions of the halocarbons CH3Cl and CH3Br?
Line 221ff: Improve grammar: 'doubles' at end 'to doubling of' after 'represents' (2 times!).
Line 226ff: Full scenario names please. Put the anthropogenic substances representing halocarbons in parentheses.
Line 229: Please define all scenarios listed in Table 2.
Table 2, 3, 4: Better move 'control' to the left or right most column. Breaks of names please only at the hyphen.
Line 277ff: This JGR paper (please correct your reference!) was for a specific region in northern midlatitudes where enough NOx and PAN is available. Except for downward transport from the unperturbed lower stratosphere (no ozone hole in 1850) the southern hemisphere should be different.
Figure 1: If done include '(density weighted)' at the end of the first sentence of the caption. If not done please recalculate the values in a proper way.
Figure 2: Please obey scientific standards and use for all 4 models the same log pressure axis with regular spacing. Truncate it around the stratopause (or the pressure level of the model with the lowest top, 1 hPa) since the mesosphere and higher layers do not contribute to climate effects, and to allow for a comparison.
Table 3: Include only the layers below the cut-off in Figure 2. Using different model tops in the weighted averages introduces additional errors even if the contribution might be small due to the low density near the top. It might be better to average here only over the stratosphere and write this in the caption. This is more logical with respect to Table 4. Don't use 'concentration' for a 'volume mixing ratio' in the caption (also Table 4).
Line 356: Most important is not temperature but ozone production during CH4 oxidation in case of enough NOx in the troposphere.
Line 360: More nitrous oxide leads to stratospheric ozone depletion, not more methane (you corrected the wrong word!).
Figure 3: Please provide labels at the axes, including units (left and bottom). Also the panel-row letters are missing. Add also 'the 4 models are represented by different line colors'. Why are the values near Antarctica so large? Is there a problem with artifacts from orography?
Line 373: Something missing. 'with simulation time at low latitudes'?
Line 383: Why?
Line 395: 'In the shown subset of PiClim'.
Line 398: 'in the 4 simulations performed by the 4 models'.
Line 419: This scenario is not shown in Fig. 4.
Line 451, 462: 'these 4' (not 'all' since subset).
Line 470: Where are the other 7 experiments? In a supplement not cited? Just to list it with integral numbers in a table is not sufficient.
Figure 4, 5, 6: Use for all 4 models the same log pressure axis with regular spacing (and not the irregular spacing of model levels!). Include the model name at the 4 columns. Are the results for the 29th and 30th year as in the other figures? Please be consistent. Include panel-row letters. 'experiments' missing in caption of Figure 4. Units wrong in panel-row c of Figure 6.
Line 483: 'response' instead of 'dynamics'? This sentence is not on winds!
Line 510: A quantitative remark on climate or radiative forcing by ozone derived from the simulations is missing.
References: Several times journal names are missing or a too short abbreviation is used. There are also incomplete or messed up author lists.

Hide

RR by Anonymous Referee #1 (21 Aug 2025)

ED: Reconsider after major revisions (02 Sep 2025) by Pedro Jimenez-Guerrero

AR by Wei Wang on behalf of the Authors (17 Sep 2025) Author's response

EF by Mario Ebel (17 Sep 2025) Manuscript Author's tracked changes

ED: Referee Nomination & Report Request started (18 Sep 2025) by Pedro Jimenez-Guerrero

RR by Anonymous Referee #2 (23 Sep 2025)

Suggestions for revision or reasons for rejection

There are important improvements in the manuscript, especially that stratospheric ozone is now shown separately in Table 3 with a common domain and that the figures showing vertical profiles have now a common top level. However, I still do not understand, why every model has a different vertical axis in Figures 2, 4, 5, 6 and S1 to S7. This is annoying for the reader, a common log pressure axis would be much more convenient. Usually every model has a different vertical resolution in the boundary layer near the surface but this should be not the focus of the figures and is also not mentioned in the text or captions. If the authors have software problems for graphics this should be mentioned in the reply. The paper might be published with the bad style of the figures in that case but it would be better to improve it to the standards first.

There are still further minor issues (line numbers refer to the revised manuscript):
Table 1: '(number of gridpoints)' should be under 'resolution' in the header of the second column. To provide the product in a separate column was not requested.
Line 216: Natural background for CH3Cl should be about 0.5 ppbv from wildfires etc and CH3Br about 5 pptv from oceanic sources, check and be more quantitative here.
Table 2: Is CESM2-WACCM really without PiClim-control? If yes this should be mentioned in the captions of Fig. 4-6.
Line 292 (caption of Fig.1): 'tropospheric' is missing.
Line 271, 287, 308: What is PiClim here? PiClim-control or some average? Refer to Table 2?
Line 332: Better write now here 'stratospheric and tropospheric'.
Line 333: Replace 'global' by 'stratospheric'.
Line 386: Typo.
Line 455: 'Five experiments' meant?
Figure 6c, label of vertical axis: Wrong symbol. Better write '*10 ^-12' instead of '?e-12' (^ means superscript).
What is 'SI file' in the reply to my remark to line 470? The data file mentioned in 'Data availability'? If yes, please refer to it at the end of section 3.3.

Hide

ED: Publish subject to technical corrections (30 Sep 2025) by Pedro Jimenez-Guerrero

AR by Wei Wang on behalf of the Authors (07 Oct 2025) Author's response Manuscript

Journal article(s) based on this preprint

04 Nov 2025

Global sensitivity of tropospheric ozone to precursor emissions in clean and present-day atmospheres: insights from AerChemMIP simulations

Wei Wang and Chloe Yuchao Gao

Atmos. Chem. Phys., 25, 14535–14550, https://doi.org/10.5194/acp-25-14535-2025,https://doi.org/10.5194/acp-25-14535-2025, 2025

Short summary

Wei Wang and Chloe Yuchao Gao

Data sets

Data from the PiClim experiments of the Aerosols and Chemistry Model Intercomparison Project (AerChemMIP) within the CMIP6 framework Vaishali Naik et al. https://esgf-ui.ceda.ac.uk/cog/search/cmip6-ceda/

Wei Wang and Chloe Yuchao Gao

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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We note that the CESM and GFDL models would not simulate the tropospheric O₃ forcing due to precursor gases from natural sources. Furthermore, the ozone simulated by them are also obviously less sensitive to natural precursors than to anthropogenic sources. This research suggests that existing theories about the sensitivity of O₃ to natural precursors might not be accurate in clean atmosphere.


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