The Multi-Compartment Hg Modeling and Analysis Project (MCHgMAP): Mercury modeling to support international environmental policy

Dastoor, Ashu; Angot, Hélène; Bieser, Johannes; Brocza, Flora; Edwards, Brock; Feinberg, Aryeh; Feng, Xinbin; Geyman, Benjamin; Gournia, Charikleia; He, Yipeng; Hedgecock, Ian M.; Ilyin, Ilia; Keating, Terry; Kirk, Jane; Lin, Che-Jen; Lehnherr, Igor; Mason, Robert; McLagan, David; Muntean, Marilena; Rafaj, Peter; Roy, Eric M.; Ryjkov, Andrei; Selin, Noelle E.; De Simone, Francesco; Soerensen, Anne L.; Steenhuisen, Frits; Travnikov, Oleg; Wang, Shuxiao; Wang, Xun; Wilson, Simon; Wu, Rosa; Wu, Qingru; Zhang, Yanxu; Zhou, Jun; Zhu, Wei; Zolkos, Scott

doi:https://doi.org/10.5194/gmd-2024-65

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https://doi.org/10.5194/gmd-2024-65

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Submitted as: model experiment description paper

24 May 2024

Submitted as: model experiment description paper |

| 24 May 2024

Status: a revised version of this preprint is currently under review for the journal GMD.

The Multi-Compartment Hg Modeling and Analysis Project (MCHgMAP): Mercury modeling to support international environmental policy

Ashu Dastoor, Hélène Angot, Johannes Bieser, Flora Brocza, Brock Edwards, Aryeh Feinberg, Xinbin Feng, Benjamin Geyman, Charikleia Gournia, Yipeng He, Ian M. Hedgecock, Ilia Ilyin, Terry Keating, Jane Kirk, Che-Jen Lin, Igor Lehnherr, Robert Mason, David McLagan, Marilena Muntean, Peter Rafaj, Eric M. Roy, Andrei Ryjkov, Noelle E. Selin, Francesco De Simone, Anne L. Soerensen, Frits Steenhuisen, Oleg Travnikov, Shuxiao Wang, Xun Wang, Simon Wilson, Rosa Wu, Qingru Wu, Yanxu Zhang, Jun Zhou, Wei Zhu, and Scott Zolkos

Abstract. The Multi-Compartment Hg (mercury) Modeling and Analysis Project (MCHgMAP) is an international multi-model research initiative intended to simulate and analyze the geospatial distributions and temporal trends of environmental Hg to inform the effectiveness evaluations of two multilateral environmental agreements (MEAs): the Minamata Convention on Mercury (MC) and Convention on Long-Range Transboundary Air Pollution (LRTAP). This MCHgMAP overview paper presents its science objectives, background and rationale, experimental design (multi-model ensemble (MME) architecture, inputs and evaluation data, simulations and reporting framework), and methodologies for the evaluation and analysis of simulated environmental Hg levels. The primary goals of the project are to facilitate detection and attribution of recent (observed) and future (projected) spatial patterns and temporal trends of global environmental Hg levels, and identification of key knowledge gaps in Hg science and modeling to improve future effectiveness evaluation cycles of the MEAs. The current advances and challenges of Hg models, emission inventories, and observational data are examined, and an optimized multi-model experimental design is introduced for addressing the key policy questions of the MEAs. A common set of emissions, environmental conditions, and observation datasets are proposed (where possible) to enhance the MME comparability. A novel harmonized simulation approach between atmospheric, land, oceanic and multi-media models is developed to account for the short- and long-term changes in secondary Hg exchanges and to achieve mechanistic consistency of Hg levels across environmental matrices. A comprehensive set of model experiments is developed and prioritized to ensure a systematic analysis and participation of a variety of models from the scientific community.

How to cite. Dastoor, A., Angot, H., Bieser, J., Brocza, F., Edwards, B., Feinberg, A., Feng, X., Geyman, B., Gournia, C., He, Y., Hedgecock, I. M., Ilyin, I., Keating, T., Kirk, J., Lin, C.-J., Lehnherr, I., Mason, R., McLagan, D., Muntean, M., Rafaj, P., Roy, E. M., Ryjkov, A., Selin, N. E., De Simone, F., Soerensen, A. L., Steenhuisen, F., Travnikov, O., Wang, S., Wang, X., Wilson, S., Wu, R., Wu, Q., Zhang, Y., Zhou, J., Zhu, W., and Zolkos, S.: The Multi-Compartment Hg Modeling and Analysis Project (MCHgMAP): Mercury modeling to support international environmental policy, Geosci. Model Dev. Discuss. [preprint], https://doi.org/10.5194/gmd-2024-65, in review, 2024.

Received: 01 Apr 2024 – Discussion started: 24 May 2024

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 preprint. The responsibility to include appropriate place names lies with the authors.

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CC1:
'Comment on gmd-2024-65', Panos Panagos, 29 May 2024

This is a very interesting manuscript which address the whole Hg cycle in all media.
As expert in soils, i would recommend that the Hg content in soils is better addressed. Reading the manuscript, you tend to explain the Hg content in soils due to natural factors while there is an important contribution by anthropogenic sources. In EU, we have done a very detailed assessment of Hg content in topsoils trying to explain both the natural and the anthropogenic drivers.
This can be done taking into account 22,000 measured samples taken with LUCAS topsoil survey in Europe. More insights can be given by the recent work Ballabio et al 2019. A spatial assessment of mercury content in the European Union topsoil .
In this assessment, authors can consider the findings of the large EU study as this is the largest harmonised and recent measured Hg campaign:
- large proportion of atmospheric Hg that is bound to soil organic matter.
- In addition, the findings indicate that soil Hg is not only bound to organic matter but associated with iron oxide and clay minerals.

- Hg accumulation increases with pH, starting from a pH of 4 and reaching a maximum at a pH of 6.5..

- Parent material also increase Hg. Highest Hg content are found in mineralized regions characterized by subduction zones and volcanic deposits.

- High correlation with NDVI - dense vegetation (higher concentration in forests and grasslands compared to croplands).

- Elevated temperatures reduce activation energy required to release Hg from soil or vegetation and subsequently increase Hg volatilisation rates to the atmosphere
- However, the outliers are explained by anthropogenic activities. 1% of the samples show very high Hg values due to proximity to mining sites. Particular high Hg values have been found close to Almaden (spain), Monte Amiata (Italy) and Idrija mine in Slovenia.

- Another source of Hg is represented by coal combustion in power plants in the European Union.

- Also, sampling points close to active or past Chrol-alkali plants have shown very high Hg values .
Important to notice the impact of erosion and sediment removal to transfer Hg in aquatic systems (oceans, river-basins, lakes).
Future Projections for Hg in topsoils are mainly positive as the decrease of coal combustion and the better treatment in Chrol alkali plants have positive effects. In addition, specific control technologies and legal biding regulations (in the European Union, Soil Monitoring Law, Mercury Regulation) will have positive impact in reducing Hg concentrations.

Many thanks for taking those remarks into account.

Citation: https://doi.org/10.5194/gmd-2024-65-CC1
- AC3: 'Reply on RC1', Ashu Dastoor, 18 Nov 2024
  
  The comment was uploaded in the form of a supplement: https://gmd.copernicus.org/preprints/gmd-2024-65/gmd-2024-65-AC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/gmd-2024-65-AC3
CEC1:
'Comment on gmd-2024-65', Juan Antonio Añel, 14 Jun 2024

Dear authors,
Unfortunately, after checking your manuscript, it has come to our attention that it does not comply with our "Code and Data Policy".

https://www.geoscientific-model-development.net/policies/code_and_data_policy.html
You have archived your data in three repositories that does not comply with our trustable permanent archival policy. These include https://edgar.jrc.ec.europa.eu/, https://www.amap.no/mercury-emissions, and https://ftp.as.harvard.edu/. You must archive the data that you use for your manuscript in one of the repositories that we can accept according to our policy. Therefore, please publish your data in one of the appropriate repositories, and reply to this comment with the relevant information (link and DOI) as soon as possible, as we can not accept manuscripts in Discussions that do not comply with our policy. Therefore, the current situation with your manuscript is irregular.
Also, you must include in a potentially reviewed version of your manuscript the modified 'Data Availability' section, with the DOI of the data.
Juan A. Añel

Geosci. Model Dev. Executive Editor

Citation: https://doi.org/10.5194/gmd-2024-65-CEC1
- AC1: 'Reply on CEC1', Ashu Dastoor, 15 Nov 2024
  
  Dear Executive Editor,
  Thank you for pointing out the need for archiving the datasets according to the journal’s policy.
  We have now archived the three mentioned datasets at GMD trustable permanent archival repositories. The new data links/DOI are as follows: https://doi.org/10.5281/zenodo.12155169 ; https://doi.org/10.34894/F3J91I ; and https://doi.org/10.5281/zenodo.11717314 .
  We have modified the 'Data Availability' section in the reviewed version of our manuscript as follows:
  Data availability. The anthropogenic emissions datasets analyzed in this study are available publicly [EDGAR: https://doi.org/10.5281/zenodo.12155169 (Muntean et al., 2018); AMAP: https://doi.org/10.34894/F3J91I and https://doi.org/10.34894/SZ2KOI (Steenhuisen and Wilson, 2019); Streets: https://doi.org/10.5281/zenodo.11717314 (Streets et al., 2019b)].
  Best regards, Ashu Dastoor
  
  Citation: https://doi.org/10.5194/gmd-2024-65-AC1
- AC2: 'Reply on CEC1', Ashu Dastoor, 15 Nov 2024
  
  Dear Executive Editor,
  Thank you for pointing out the need for archiving the datasets according to the journal’s policy.
  We have now archived the three mentioned datasets at GMD trustable permanent archival repositories. The new data links/DOI are as follows: https://doi.org/10.5281/zenodo.12155169 ; https://doi.org/10.34894/F3J91I ; and https://doi.org/10.5281/zenodo.11717314 .
  We have modified the 'Data Availability' section in the reviewed version of our manuscript as follows:
  Data availability. The anthropogenic emissions datasets analyzed in this study are available publicly [EDGAR: https://doi.org/10.5281/zenodo.12155169 (Muntean et al., 2018); AMAP: https://doi.org/10.34894/F3J91I and https://doi.org/10.34894/SZ2KOI (Steenhuisen and Wilson, 2019); Streets: https://doi.org/10.5281/zenodo.11717314 (Streets et al., 2019b)].
  Best regards, Ashu Dastoor
  
  Citation: https://doi.org/10.5194/gmd-2024-65-AC2
RC1:
'Comment on gmd-2024-65', Anonymous Referee #1, 14 Jul 2024

This paper presents the ambitious plan of the Multi-Compartment Hg Modeling and Analysis Project (MCHgMAP) for a multi-model ensemble approach to supporting the Minamata Convention as it seeks to assess the degree to which international efforts are achieving the convention’s goals of reducing Hg in the environment. Since anthropogenic emissions to the atmosphere that lead to transboundary air pollution are the subject of another international treaty, the Convention on Long-Range Transboundary Air Pollution consideration is given to those policy goals as well.
The scope of the task envisioned by the MCHgMAP is huge. The length and the depth of the paper is commensurate to that task. Despite the paper’s great length, and the complexity of the issues that it brings up, the paper has a clear structure that keeps the many parts of the paper from getting in the way of each other. The text is also commendably well-written, with just a few places where some clarification is needed. The survey of the literature is similarly well-done, building confidence that the knowledge base going into the modeling exercise draws on much of the relevant literature – even though that literature is developing rapidly – which is a reflection of how the understanding of Hg cycling continues to develop.
I have two major concerns, as well as some smaller points for the authors to consider.
The first of the major concerns regards the value of providing examples of similar efforts to use multi-model ensembles to support policy efforts. As a reader feeling overwhelmed by the scope of what is to be attempted, and trying to get a clearer vision of where the overall process presented in this paper is heading, it would be helpful to be given other examples where MME’s have been applied. (I presume the work of the IPCC has such examples.) So please try to present what is envisaged for supporting the Minamata Convention in relation to what has been achieved in modeling other global scale pollution issues to support the policy process.
My other suggestion concerns Section 8 where I am missing treatment of the Terrestrial-Hydrological modeling. Earlier in the paper, three classes of models are presented (Atmosphere, Ocean and Terrestrial-Hydrological models (Sections 2.1-2.3, and the “Contemporary Cycle” in Figure 1.). These all seem to have a place in the lower part of Fig 1, the “Long-Term Cycle” of “Multi-Media Mass Balance models”. But when one gets to “Section 8 Modeling analysis: process-understanding”, there are two sections, 8.1 on atmospheric models and 8.2 on ocean models. The issues addressed for these two classes of models would have been appropriate for Terrestrial-Hydrological Models as well. More generally, I find the presentation of the Terrestrial-Hydrological modeling as hard to understand fitting into the global scope of the MCHgMAP, since there are so many more potential compartments in the terrestrial-hydrological modeling domain compared to the ocean or atmosphere..

Below are more minor points for the authors to consider:
Line 1615. There will be perturbation modeling and sensitivity modeling. It seemed hard for me to understand the need to differentiate these, since the two seem so closely related.
I have a sense that a major challenge for global Hg modeling is the apparent discrepancy between increasing anthropogenic emission inventories during recent decades, and the regional decline in atmospheric Hg over Europe. If this is indeed the case in the eyes of the authors, it would be nice to see this lifted up as an example of the type of issue that the MCHgMAP will address.
In section 2.3, a number of terrestrial hydrological models are mentioned. I missed one published in Environmental Science and Technology that seems appropriate to include: Eklof, Karin, et al. "Parsimonious model for simulating total mercury and methylmercury in boreal streams based on riparian flow paths and seasonality." Environ. Sci. Technol. 49.13 (2015): 7851-7859.
Lines 1212-1218. Here the authors state that

“It is currently not possible to determine the origin (anthropogenic/geogenic) or period of origin of the primary emission of Hg that are currently being reemitted from the ocean based on traditional measurements of Hg concentrations (for an explanation on how the Hg(0) evasion flux is determined see Sect. 4.4 and Appendix B). However, both box and 3D models can be used to gain insights into the extent of the Hg(0) evasion flux from the ocean, the fraction that different sources or historic periods contribute, and how concentrations will change in response to changes in Hg ocean inputs as a result of measures under the Hg MEAs.”.

This would seem like great place to mention the use of Hg isotopes to resolve these issues as Jiskra et al. did in their 2021 Nature publication. That article is cited in the first paragraph of the papers introduction (line 75), and one other place, but not in relation to where it is most relevant, specifically in this section at line 1212-1218. I am also concerned that the power of isotopes is not going to be brought to bear in the MCHgMAP as fully as they could be. But I expect that is something that will have to be wrestled with when looking at the results of the MCHgMAP.
In the reference list there are three references where the first author is Li, C. But there are actually two different people involved. So good that their names are distinguished…
Line 1506 begins a new paragraph. It was difficult to understand that this new paragraph had started taking about lake sediments. (The previous paragraph was about tree-rings).

Citation: https://doi.org/10.5194/gmd-2024-65-RC1
- AC3: 'Reply on RC1', Ashu Dastoor, 18 Nov 2024
  
  The comment was uploaded in the form of a supplement: https://gmd.copernicus.org/preprints/gmd-2024-65/gmd-2024-65-AC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/gmd-2024-65-AC3
RC2:
'Comment on gmd-2024-65', Anonymous Referee #2, 10 Aug 2024
This reviewer commends the authors’ endeavor to have produced such an ambitious proposal on multi-medium modeling and analysis to support the Minamata Convention and CLRTAP. The document is well structured for the most part, and the literature is fairly up to date. Below are a couple of main comments.
This document is essentially a proposal, which should be clearly reflected in the title, and in the same vein, the approach or the set of modeling experiments proposed were not exactly “developed”, which implied evaluation or demonstration of validity and effectiveness.

The goal, objectives and the time periods for the present day and the future scenario should be presented upfront, rather than being buried two-thirds of the way through the document.

Did I miss whether the physical input data for all models were to be harmonized? For example, interannual variability in meteorology can significantly impact transport, deposition, chemistry, and emissions/releases. To quantify the impact of changing emissions, the influence of physical parameters needs to be assessed.

The difference between “perturbation” and “sensitivity” runs appeared to be rather subtle (L1615-1621). The latter seemed to encompass the former. They might need to be better defined.

Sections 5 and 7 included not only atmospheric and ocean models but also other environmental mass balance models. Sections 6 and 8 appeared to include atmospheric and ocean models only.

Provide a glossary of terminology used in the document.

Next are specific comments:
Abstract: L66, L67: Instead of "is developed", it might be more appropriate to say "is proposed".
L156: What is the difference between “emission” and “release”?
L201-202: For regional models, BCs can be the most dominant factors in determining GEM concentrations.
L202: There is a "constant" ring to "prescribe", but that’s not exactly how emission fluxes are handled in some models.
L224-226: A most recent version of CMAQ-newHg-Br v2 included a newly developed gas-particle partitioning scheme with most up-to-date gas-phase redox reactions (Wu et al., 2024, JAMES, https://doi.org/10.1029/2023MS003823), which is probably one of the latest breakthroughs in atmospheric Hg modeling.
L394: What does the term “secondary Hg emission” refer to? Legacy emission? Release? Or chemically formed?
L472-477: These definitions should be presented upfront, instead of being buried here after having already used such terms in the preceding text. Or provide a glossary as suggested in one of my main comments.
L779-L784: This part is confusing. It was said that 2010 should be used as the baseline year. Then later, in scenario design, the period of 2010-2020 was said to be the present-day period.
L846: What is the “mass-flow” approach? Add a reference.
L944: Under “Scenario design”, there’s no scenario design. It’s unclear what was meant to be shown there.
L1124-1127: On what was this statement based? This statement is valid only if those parameterizations were correct, but are they? It seems unclear which causes larger uncertainty: the air-surface exchange models or scaling up measured fluxes, unless work is done to compare the two.
L1298-1299: It's such a popular result. The dry deposition flux of Hg° may exceed that of HgII, but it doesn't make the former more "important" than the latter. The question is how much of the deposited Hg° gets oxidized.
L1584: Present: 2010-2020; Future: Spell out the simulation period. It was said to be “up to 2050” - unclear.
L1605-1613: Simulation objectives: Came too late and buried.
L1625: What is “an analogous strategy”?
L1807: Why interpolate twice?
L1948-1949: “for different years of the period 2010-2020 to reveal their temporal changes and causes” - It should probably just be said as “interannual variability and its driving factors”.
L1950: “On the annual basis and for different seasons” – Awkward wording.
L2271: “Coupled offline”: If it’s coupled, then it’s online. If it’s offline, then it’s decoupled.
Citation: https://doi.org/10.5194/gmd-2024-65-RC2
- AC3: 'Reply on RC1', Ashu Dastoor, 18 Nov 2024
  
  The comment was uploaded in the form of a supplement: https://gmd.copernicus.org/preprints/gmd-2024-65/gmd-2024-65-AC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/gmd-2024-65-AC3
RC3:
'Comment on gmd-2024-65', Anonymous Referee #3, 13 Aug 2024

This manuscript provides a very ambitious and comprehensive description of the current status of global multi-compartment modelling of mercury and the key anthropogenic and environmental processes that are necessary to describe in the modelling. The initiative and the ambitious approach is driven by a strong policy need and thus represents an important step to provide a scientifically sound approach to answer policy-relevant questions and to provide support for developing common and realistic expectations of effects of emission reductions as well as for setting common and realistic policy targets. Descriptions of the relevant policy frameworks (Minamata Convention, LRTAP convention) are included as are the direct policy related questions posed by these frameworks.
The manuscript provides and excellent state-of-the-art review of mercury (occurrence, transformations, trends etc.) in the atmosphere and oceans, and to some extent for terrestrial systems, and provides a basis for designing the multi-compartment modelling which is described in the following sections. Uncertainties and lack of knowledge are also included.
A main part of the manuscript contains a description of the plans for modelling activities and how the results will be evaluated. This is quite lengthy but necessary to provide the scientific community to engage, comment/criticize and potentially contribute to the planned activities.
In summary, the opinion of this reviewer is that the publication of this manuscript will make an important contribution to the scientific understanding and development of models for global mercury cycling, and to supporting policy efforts to reduce mercury emissions and impacts globally.
Some specific comments/suggestions are:
- An important factor not described in detail is the importance of "permanent" sinks for mercury (oceanic sediments, deep soil layers etc), i.e. what is the current status of knowledge of these sinks, are they permanent and how can they be described in the models? From a policy perspective, a common understanding of the global permanent sinks and how important they are for setting the pace of reducing environmental mercury burdens in a scenario of emission reductions would be beneficial.
- In general, the current understanding of terrestrial mercury cycling/storage and factors that influence the mobility/releases of mercury to the aquatic compartments are very limited in comparison to the atmospheric and (to some extent) oceanic cycling and, consequently, the possibilities for modelling are limited. This is also reflected in the initial state-of-the-art sections. Nevertheless, a description of how mercury in the terrestrial compartment will be handled in the modelling activities would be beneficial. Soil-air, and vegetation-air exchange is covered but releases of soil-bound mercury to surface waters are not. For instance, land-use change (e.g. forestry) and climate (increased precipitation) are factors that can influence mercury (and methylmercury) burdens in freshwater and coastal systems and thus cause increased mercury concentrations in fish and seafood, the primary exposure route for most population groups.
- A large part of the manuscript concerns the ambitious plans for modelling activities and evaluation of results. As mentioned above, this is very positive but it would also be of interest for the reader (and for potential contributors) to understand if these plans are fixed and funded or if they are more of a long-term ambition, e.g. a brief description of the MCHgMAP initiative.

Citation: https://doi.org/10.5194/gmd-2024-65-RC3
- AC3: 'Reply on RC1', Ashu Dastoor, 18 Nov 2024
  
  The comment was uploaded in the form of a supplement: https://gmd.copernicus.org/preprints/gmd-2024-65/gmd-2024-65-AC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/gmd-2024-65-AC3

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Short summary

This paper introduces the Multi-Compartment Mercury (Hg) Modeling and Analysis Project (MCHgMAP) aimed to inform the effectiveness evaluations of two multilateral environmental agreements: the Minamata Convention on Mercury and Convention on Long-Range Transboundary Air Pollution. The experimental design exploits a variety of models (atmospheric, land, oceanic and multi-media mass balance models) to assess the short- and long-term influences of anthropogenic Hg releases in the environment.


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