the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 May 2025
Shifts in global atmospheric oxidant chemistry from land cover change
Abstract. Human activities have profoundly altered natural vegetation, primarily by converting pristine land for agriculture and grazing. Land cover change (LCC) influences the Earth system through modifications of surface albedo, roughness length, evapotranspiration, and atmospheric composition. This work investigates how LCC-driven changes in BVOC fluxes, anthropogenic surface emissions, natural soil NO emissions, and O3 deposition fluxes affect atmospheric chemistry. The chemistry–climate model EMAC was used to compare: (1) present-day land cover, which includes areas deforested for crops and grazing, with the potential natural vegetation (PNV) cover simulated by the model, and (2) an extreme reforestation scenario where grazing land is restored to natural vegetation. Our results show that the expansion of agricultural land reduces global BVOC emissions, leading to lower annual average surface OH concentrations (−5.7 %) and CO mixing ratios (−6.2 %), despite increased CO from agricultural burning. Meanwhile, NOx mixing ratios increase (+7.8 %) due to enhanced anthropogenic and natural soil sources. While regional ozone responses vary, global ozone production sensitivity shifts from a NOx- to a VOC-sensitive regime. These changes influence radiative forcing: reductions in tropospheric O3 and CH4 lifetimes exert a combined net cooling of −60 mW m−2, partially offset by warming from reduced BVOC-driven SOA formation. Reforestation of grazing areas reverses these trends to some extent, though with a weaker response.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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.-
Notice on discussion status
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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Preprint
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Supplement
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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.
- Preprint
(13620 KB) - Metadata XML
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Supplement
(12424 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-1800', Anonymous Referee #1, 01 Jun 2025
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AC1: 'Reply on RC1', Ryan Vella, 18 Jun 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1800/egusphere-2025-1800-AC1-supplement.pdf
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AC1: 'Reply on RC1', Ryan Vella, 18 Jun 2025
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RC2: 'Comment on egusphere-2025-1800', Anonymous Referee #2, 06 Jun 2025
Summary
This study investigates how deforestation- and afforestation-induced changes in BVOC and NOx emissions influence OH reactivity, trace gas lifetimes, ozone production sensitivity, and radiative effects from ozone and methane changes. The authors employ a coupled climate-chemistry model (EMAC) with a dynamical vegetation model (LPJ-GUESS). Simulations were conducted for 2000-2011 under three scenarios: 1) a hypothetical no-deforestation case (PNV), 2) a present-day case with deforestation on both cropland and grazing land (DCGL), and 3) a case with deforestation exclusively on cropland, representing an extreme afforestation scenario with food production maintained (DCL). The study is well-designed, well-executed, and well-written in general. The methodology is solid with meticulous model setup and decision-making. The results exhibit a wealth of information, and the authors manage to present them clearly with in-depth and comprehensive discussions. The research question and findings are of novelty and great scientific implications. I recommend publication with only minor revisions needed.
Major Comments:
- The afforestation part (section 3.2) is surprisingly short compared to the deforestation part (section 3.1). I assume the intent is to avoid repetition since these two effects share great similarities though opposite in sign; however, I’d recommend either moving this DCL scenario entirely to supporting info, or the authors should elaborate more on how much of the deforestation impacts are “reversible” and what impacts are “irreversible”.
- There is an excess use of acronyms throughout the manuscript. I don’t think it is worth introducing acronyms if they are only used once or twice, such as DGVM (line 63), PPFD (line 144), TOA (line 311), etc. Scenario naming is also a bit opaque, as DCL and DCGL are visually similar and not intuitively distinguishable. Renaming may improve clarity.
Minor Comments:
Line 270: Previously you mentioned “changes in canopy densities changes dry deposition O3 fluxes”, but this O3 deposition flux decrease (1.5%) seems proportional to overall O3 decrease (1.6%)? Did you mean that spatial redistribution, rather than total flux, is the key point?
Figure 7: I’d recommend adding “VOC-sensitive”, “transitional”, and “NOx-sensitive” in panel (a) color bar, and adding “<-- more VOC-sensitive” and “more NOx-sensitive -->” in panel (b) color bar. It will help the audience to understand the figure even by it alone.
Line 290: Please justify the choice of 0.7 and 0.9 as thresholds for ozone regime classification. Are these based on prior literature or model-specific sensitivity tests?
Line 441: typo: “DCGl” to “DCGL”
Citation: https://doi.org/10.5194/egusphere-2025-1800-RC2 -
AC2: 'Reply on RC2', Ryan Vella, 18 Jun 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1800/egusphere-2025-1800-AC2-supplement.pdf
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-1800', Anonymous Referee #1, 01 Jun 2025
This study investigates how human-driven land cover changes impact atmospheric chemistry and radiative forcing. The research found that compared to natural vegetation, present-day land use reduces global biogenic volatile organic compound (BVOC) emissions, leading to a decrease in global surface OH concentrations and CO mixing ratios, while increasing NOx. These shifts seem to cause regionally significant changes in ozone production with regionally varying VOC-sensitive ozone formation regimes. Ultimately simulations show a surprisingly large net cooling effect due to reduced tropospheric ozone and methane lifetimes, partially offset by warming from decreased biogenic SOA. The study highlights the critical need to understand land-use change impacts on the Earth system.
Overall, I find the study to be sound, robust, interesting and relevant, increasing our understanding of how ES-processes can work together on a fundamental level. The text is very well written and shows a high degree of consistency with minor slips here and there that are easy to remedy. I have no major concerns and only some minor comments which can be found in the attached file. I think this manuscript fits well within the scope of ACP and should be published after the comments have been addressed.
I found Code Availability to potentially contravene EGU/Copernicus requirements because reviewers have not been given access to the entire model (EMAC, etc.) and would have to reveal their identity if they would like to do so (by joining the consortium). This policy has previously lead to papers being rejected. I want the editor to be aware of this issue.
-
AC1: 'Reply on RC1', Ryan Vella, 18 Jun 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1800/egusphere-2025-1800-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Ryan Vella, 18 Jun 2025
-
RC2: 'Comment on egusphere-2025-1800', Anonymous Referee #2, 06 Jun 2025
Summary
This study investigates how deforestation- and afforestation-induced changes in BVOC and NOx emissions influence OH reactivity, trace gas lifetimes, ozone production sensitivity, and radiative effects from ozone and methane changes. The authors employ a coupled climate-chemistry model (EMAC) with a dynamical vegetation model (LPJ-GUESS). Simulations were conducted for 2000-2011 under three scenarios: 1) a hypothetical no-deforestation case (PNV), 2) a present-day case with deforestation on both cropland and grazing land (DCGL), and 3) a case with deforestation exclusively on cropland, representing an extreme afforestation scenario with food production maintained (DCL). The study is well-designed, well-executed, and well-written in general. The methodology is solid with meticulous model setup and decision-making. The results exhibit a wealth of information, and the authors manage to present them clearly with in-depth and comprehensive discussions. The research question and findings are of novelty and great scientific implications. I recommend publication with only minor revisions needed.
Major Comments:
- The afforestation part (section 3.2) is surprisingly short compared to the deforestation part (section 3.1). I assume the intent is to avoid repetition since these two effects share great similarities though opposite in sign; however, I’d recommend either moving this DCL scenario entirely to supporting info, or the authors should elaborate more on how much of the deforestation impacts are “reversible” and what impacts are “irreversible”.
- There is an excess use of acronyms throughout the manuscript. I don’t think it is worth introducing acronyms if they are only used once or twice, such as DGVM (line 63), PPFD (line 144), TOA (line 311), etc. Scenario naming is also a bit opaque, as DCL and DCGL are visually similar and not intuitively distinguishable. Renaming may improve clarity.
Minor Comments:
Line 270: Previously you mentioned “changes in canopy densities changes dry deposition O3 fluxes”, but this O3 deposition flux decrease (1.5%) seems proportional to overall O3 decrease (1.6%)? Did you mean that spatial redistribution, rather than total flux, is the key point?
Figure 7: I’d recommend adding “VOC-sensitive”, “transitional”, and “NOx-sensitive” in panel (a) color bar, and adding “<-- more VOC-sensitive” and “more NOx-sensitive -->” in panel (b) color bar. It will help the audience to understand the figure even by it alone.
Line 290: Please justify the choice of 0.7 and 0.9 as thresholds for ozone regime classification. Are these based on prior literature or model-specific sensitivity tests?
Line 441: typo: “DCGl” to “DCGL”
Citation: https://doi.org/10.5194/egusphere-2025-1800-RC2 -
AC2: 'Reply on RC2', Ryan Vella, 18 Jun 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-1800/egusphere-2025-1800-AC2-supplement.pdf
Peer review completion
Journal article(s) based on this preprint
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Cited
1 citations as recorded by crossref.
Sergey Gromov
Clara M. Nussbaumer
Laura Stecher
Matthias Kohl
Samuel Ruhl
Holger Tost
Jos Lelieveld
Andrea Pozzer
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(13620 KB) - Metadata XML
-
Supplement
(12424 KB) - BibTeX
- EndNote
- Final revised paper
This study investigates how human-driven land cover changes impact atmospheric chemistry and radiative forcing. The research found that compared to natural vegetation, present-day land use reduces global biogenic volatile organic compound (BVOC) emissions, leading to a decrease in global surface OH concentrations and CO mixing ratios, while increasing NOx. These shifts seem to cause regionally significant changes in ozone production with regionally varying VOC-sensitive ozone formation regimes. Ultimately simulations show a surprisingly large net cooling effect due to reduced tropospheric ozone and methane lifetimes, partially offset by warming from decreased biogenic SOA. The study highlights the critical need to understand land-use change impacts on the Earth system.
Overall, I find the study to be sound, robust, interesting and relevant, increasing our understanding of how ES-processes can work together on a fundamental level. The text is very well written and shows a high degree of consistency with minor slips here and there that are easy to remedy. I have no major concerns and only some minor comments which can be found in the attached file. I think this manuscript fits well within the scope of ACP and should be published after the comments have been addressed.
I found Code Availability to potentially contravene EGU/Copernicus requirements because reviewers have not been given access to the entire model (EMAC, etc.) and would have to reveal their identity if they would like to do so (by joining the consortium). This policy has previously lead to papers being rejected. I want the editor to be aware of this issue.