the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Aug 2024
Evaluating present-day and future impacts of agricultural ammonia emissions on atmospheric chemistry and climate
Abstract. Agricultural practices are responsible for a major source of ammonia (NH3) to the atmosphere which has implications for air quality, climate and ecosystems. Due to the intensification of food and feed production, ammonia emissions are expected to increase significantly by 2100 and would therefore affect atmospheric composition such as nitrate (NO−3 ) or sulfate (SO2−4 ) particle formation and surface deposition feedback. Chemistry-climate models which integrate the key atmospheric physicochemical processes along with the ammonia cycle represent a useful tool to investigate present-day and also future ammonia pathways and their impact on the global scale. Ammonia sources are, however, challenging to quantify because of their dependencies on environmental variables and agricultural practices and represent a crucial input for chemistry-climate models. In this study, we use the chemistry-climate model LMDZ-INCA with agricultural and natural soil ammonia emissions from a global land surface model (ORCHIDEE with the integrated CAMEO module) for the present-day and 2090–2100 period under different socio-economic pathways. We show that this new set of emissions improves the spatial and temporal atmospheric ammonia representations in Africa, Latin America, and the US compared to the static reference inventory (CEDS). Higher ammonia emissions in Africa, as simulated by CAMEO compared to other studies, reflect enhanced present-day reduced nitrogen (NHx) deposition flux. This partially contributes to the 20 % higher NHx deposition in our results compared to other modeling studies at the global scale. Future CAMEO emissions lead to an overall increase of the global NH3 burden ranging from 37 % to 70 % while NO−3 burden increases by 38 %–50 % depending on the scenario even when global NOx emissions decrease. When considering the most divergent scenarios (SSP5-8.5 and SSP4-3.4) for agricultural ammonia emissions the direct radiative forcing resulting from secondary inorganic aerosol changes ranges from -114 to -160 mW.m−2. By combining a high level of NH3 emissions with decreased or contrasted future sulfate and nitrate emissions, the nitrate radiative effect can either overshoot (net total sulfate and nitrate effect of -200 mW.m−2) or be offset by the sulfate effect (net total sulfate and nitrate effect of +180 mW.m−2). We also show that future oxidation of NH3 could lead to an increase in N2O emissions of 0.43 to 2.10 Tg(N2O)yr−1 compared to the present-day levels. Our results suggest that accounting for nitrate aerosol precursor emission levels but also for the ammonia oxidation pathway in future studies is particularly important to understand how ammonia will affect climate, air quality, and nitrogen deposition.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2024-2022', Anonymous Referee #1, 24 Sep 2024
- RC2: 'Comment on egusphere-2024-2022', Anonymous Referee #2, 28 Sep 2024
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RC3: 'Comment on egusphere-2024-2022', Anonymous Referee #3, 10 Oct 2024
This is an interesting paper on present-day and future impacts of NH3 emissions. After careful reading I find the study also somewhat limited. The big sales-argument of the study is the new CAMEO agricultural emission module- and the authors spend a lot space to demonstrate that the overall model performance using CAMEO derived emissions compared to CEDS emissions is better. The model is consequently used to explore some future SSP-like scenarios- unfortunately without contrasting to the impacts of the NH3 emissions from the more well-known existing SSP marker scenarios that have e.g. been assessed in Chapter 6 of the AR6 WG1 report. On a first glance- at least for global totals- the IPCC WG future SSP emission ranges (e.g. Figure 6.18) look quite similar to the CAMEO emission changes reported in Table 1- and a valid but unanswered question is to what extent the exploration of the future impacts (aerosol burden, deposition, N2O production) would have looked very different if the scenarios used by the CMIP community would have been used. Is this study new, or confirming existing results?
The second limitation, acknowledged by the authors, is the use of present-day climate conditions to explore future NH3 emissions (and impacts). To my opinion, this aspect is of particular importance (along with the inclusion of compensation point approaches), where the use of CAMEO could represent a step forward. The authors promise to develop a separate study on this aspect- I understand the material could be too much for a single publication- but it does undermine undermine the relevance of the ‘future’ evaluation in this paper.
Ass the paper stands it relies qstrongly on the evaluation of the model system with satellite and in-situ data. Obviously the authors have done a substantial and commendable effort, and I am not always convinced how relevant and constraining the comparisons are. In addition the addition the manuscript is very lengthy, and the length of the model evaluation section is contributing to this. My suggestion is to move a lot of detailed evaluation material to supplementary material and instead making an effort to better summarize and discuss the signficance of these evaluation findings in the main manuscript. An example of where better discussion is warranted is the discussion of the match of seasonal cycles (vs annual average) - where it is not made very clear why the effort is done, and what we can learn from this.
Bringing it back to my earlier comment- what is the difference of this study with earlier efforts: The relevance of the better performance for future climate impact could then focus on showing that the changes (e.g. in Africa and South America) make a sizeable difference for the overall global results.
Lastly, I recommend proofreading by a native speaker, in particular I noticed space for improvement in the abstract- the entry point for most readers. I made some suggestions for abstract and introduction, but the manuscript would benefit throughout from a proper proofreading.
Below I provide detailed comments- I have spent less effort to discuss details of the model evaluation section.
L1: are responsible for a major source=>English. Are a major source or responsible for a major fraction of emissions.
L2. Intensification is usually used I the context of agricultural production methods. The drivers are growing population and increasing food demand leading a.o. to intensification.
L4 Surface deposition feedback is not clear. Feedbacks of the carbon cycle to increased N-deposition?
L6 ammonia and ammonium pathways. Reduced nitrogen pathways?
L9 explain what is the CAMEO module about. Emissions,deposition, bidirectional? Note that the journal may require first-use explanation of acronyms.
L10 And what about the climate- was also for 2100 conditions, or remained present day?
L11 What is meant with ammonia representation? Comparison to observations (from satellite, in-situ?)
L12 Higherammonia emissions in Africa, as simulated by CAMEO compared to other studies, reflect enhanced present-day reduced nitrogen (NHx) deposition flux.This sentence is not clear: I suspect that the authors indicate that the emissions are also reflected in higher deposition fluxes, which is logical, and even more logical if these are confirmed by observational evidence.
L14 At this place a sentence introducing the scenario framework of this study would be needed; as there are probably more implementations. Also explain that apart from the magnitude of emissions changes, an important parameter is the ratio of NOx/NH3 emissions, and also SO2 emissions.
L 19 In climate sciences the word Overshoot is used in a very specific climate scenario context, related to emission pathways. Suggest: Overcompensate?
L20 could be useful to include here how much this is as a fraction of the current best estimate of the overall N2O budget.
L24 the issues wrg nitrogen deposition are mostly biodiversity loss (and climate)- maybe for abstract to mention these rather than nitrogen deposition.
l 29 surface deposition processes. Wet deposition is not a surface deposition process, but still important.
l32 account for 85 % of anthropogenic atmospheric NH3 emissions. I would doubt that this statement holds to NH3 abundance in general.
l39 very good agreement (can you add one sentence what you mean with this?
l45/48 clarfiy whether is this still referening to Hauglustaine 2014?
L49 not sure what is meant with ‘removal treatments’ ? Oxidation of NH3?
L55 Can you clarify shortly (and in later section somewhat more extenstively how the livestock distribution differ, and whether this study is using Beaudor, SSP or both?
L62 could improve the correspondence of modelled concentrations. …. with …
L70 importance for ..
L87 Two other reference databases that come to mind are EDGAR and IIASA/GAINS. One sentence quoting the numbers for these alternative would help understanding whether the quoted ‘improvements’ apply in comparison to all available databases.
l99 I guess not only indoor, but important also to understand the manure management aspects.I remember also a rather large contribution from fire emissions in CEDS- can you comment.
L109. Summarize what you found from this comparison, and why that is important.
L113 stringent emission regulations, but clarify that this is not necessarily the case for NH3 which is much less regulated.
L130 22 tracers representing aerosol.There is an extensive discussion of the microphysics, but relevant for this paper, it is not clear to me how the completion for nitrate between coarse and fine fraction aerosol is modelled.
L161 this an important limitation that should be mentioned upfront (i.e. not evaluating climate change influence on the emissions).
L164 The ocean emission estimate is probably an upper limit; e.g. Paulot et al. 2016 give twice lower estimates.
L171 I would recommend to include a set of simulations that also uses the SSP1. As eluded to previously, the lack of comparison of the community SSP scenarios to the ones from CAMEO, leaves an open question on the novelty of the results.
L200-214 It will be useful to also provide the relative changes in percent to the absolute numbers.
L212 Biomass burning inventory of NH3?
L217 Do I understand correctly that CEDS simulation was run without natural emissions? Isn’t that comparing apples and pears?
L225 the S and T markers in the Taylor plots are not terribly well explained- is it discussed somewhere what is evaluated with this?
L235 the monthly column comparison show indeed improvement of column levels over Africa and S. America, but not really or even contradicting elsewhere. What can we still learn about CAMEO vs GCM modelvs CEDS?
249 I would say that the ‘gold’ standard for quality controlled deposition observations is by the WMO GAW program. Vet et al.However, I think that not all data needed for this study where available. It would be relevant to mention this ‘lack’ of evaluated data in discussion (if considered important).
Figure 4,5,6 It is hard to get a general picture from the surface concentrations comparison, but overall in particular the measured particulate concentrations of NH4/NO3 seem to be up to a factor of 10 higher than the modelled ones for all networks. What are the possible consequences for this work? Have you considered mismatch of SO4 as one of the root causes for discrepeancies?
L512 Do you mean ‘reducing agricultural’ emissions- which can be done by e.g. reducing livestock numbers, but also practices (e.g. feed or manure management).
L534 twice higher than the deposition budget of the three alternative estimates.
L535 higher NH3 emissions in equatorial Africa (clarify)
L536. It is not well explained how wet deposition of NH3 is considered- where NH3 perse has a low Henry’s coefficient.
L539 what is meant with ‘good correlation’; and how are EMEP and CCMI modelling results entering the story?
L542 is deficient? Do you mean absent (i.e. they provide annual numbers)? The CCMI deposition dataset is a crucial…
L543 I would agree with this statement, but it raises the question why it was not included (or maybe it is, but not clearly described).In general it should be considered that it is probably to be considered that in the end we are talking about ecosystem emissions, which would included interactions between soil, vegetation and atmosphere.
L550 clearly state that this is future perspective.
L555 for sure future livestock is at the basis of many future emission estimates. It is the combination with ‘interactive’ soils that is probably not explored.
L560 (and throughout paper when talking about nitrate do you mean HNO3, NO3- or the sum of the two?
L595 It is not so clear to me what the Bertagni study is calculating. Still the N2O from atmospheric processes, or e.g. the additional N2O emission resulting from enhance NH3 deposition? Clarify.Agree that this is an important issue in particular if emissions from NH3 as an energy carrier are not well controlled (which it should as it is a quite dangerous and toxic component).
L597-602 I encourage the authors to persue this work, as it is probably going to be quite important.––
Citation: https://doi.org/10.5194/egusphere-2024-2022-RC3
Data sets
Global ammonia emissions from CAMEO throughout the century for 3 scenarios (2000-2100) Beaudor Maureen, Vuichard Nicolas, Lathière Juliette, and Hauglustaine Didier https://zenodo.org/records/10100435
Model code and software
LMDZ INCA - IPSL model Olivier Boucher, Jérôme Servonnat, Anna Lea Albright, Olivier Aumont, Yves Balkanski, Vladislav Bastrikov, Slimane Bekki, Rémy Bonnet, Sandrine Bony, Laurent Bopp, Pascale Braconnot, Patrick Brockmann, Patricia Cadule, Arnaud Caubel, Frederique Cheruy, Francis Codron, Anne Cozic, David Cugnet, Fabio D'Andrea, Paolo Davini, Casimir de Lavergne, Sébastien Denvil, Julie Deshayes, Marion Devilliers, Agnes Ducharne, Jean-Louis Dufresne, Eliott Dupont, Christian Éthé, Laurent Fairhead, Lola Falletti, Simona Flavoni, Marie-Alice Foujols, Sébastien Gardoll, Guillaume Gastineau, Josefine Ghattas, Jean-Yves Grandpeix, Bertrand Guenet, Lionel, E. Guez, Eric Guilyardi, Matthieu Guimberteau, Didier Hauglustaine, Frédéric Hourdin, Abderrahmane Idelkadi, Sylvie Joussaume, Masa Kageyama, Myriam Khodri, Gerhard Krinner, Nicolas Lebas, Guillaume Levavasseur, Claire Lévy, Laurent Li, François Lott, Thibaut Lurton, Sebastiaan Luyssaert, Gurvan Madec, Jean-Baptiste Madeleine, Fabienne Maignan, Marion Marchand, Olivier Marti, Lidia Mellul, Yann Meurdesoif, Juliette Mignot, Ionela Musat, Catherine Ottlé, Philippe Peylin, Yann Planton, Jan Polcher, Catherine Rio, Nicolas Rochetin, Clément Rousset, Pierre Sepulchre, Adriana Sima, Didier Swingedouw, Rémi Thiéblemont, Abdoul Khadre Traore, Martin Vancoppenolle, Jessica Vial, Jérôme Vialard, Nicolas Viovy, and Nicolas Vuichard https://cmc.ipsl.fr/ipsl-climate-models/ipsl-cm6/
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