European HFC emissions evaluated with multiple atmospheric inverse models and UNFCCC national inventories

De Longueville, Hélène; Melo, Daniela B.; Redington, Alison; Ramsden, Alice; Danjou, Alexandre; Andrews, Peter; Pitt, Joseph; Murphy, Brendan; Constantin, Lionel; Stanley, Kieran M.; O'Doherty, Simon; Wenger, Angelina; Young, Dickon; Engel, Andreas; Schuck, Tanja; Meixner, Katharina; Wagenhaeuser, Thomas; Gad, Fides; Vollmer, Martin K.; Reimann, Stefan; Maoine, Michela; Arduini, Jgor; Lunder, Chris; Schmidtbauer, Norbert; Haszpra, László; Molnár, Mihály; Frumau, Arnoud; Couret, Cedric; Rigby, Matthew; Henne, Stephan; Manning, Alistair; Ganesan, Anita

doi:10.5194/egusphere-2026-194

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https://doi.org/10.5194/egusphere-2026-194

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05 Feb 2026

| 05 Feb 2026

European HFC emissions evaluated with multiple atmospheric inverse models and UNFCCC national inventories

Hélène De Longueville, Daniela B. Melo, Alison Redington, Alice Ramsden, Alexandre Danjou, Peter Andrews, Joseph Pitt, Brendan Murphy, Lionel Constantin, Kieran M. Stanley, Simon O'Doherty, Angelina Wenger, Dickon Young, Andreas Engel, Tanja Schuck, Katharina Meixner, Thomas Wagenhaeuser, Fides Gad, Martin K. Vollmer, Stefan Reimann, Michela Maoine, Jgor Arduini, Chris Lunder, Norbert Schmidtbauer, László Haszpra, Mihály Molnár, Arnoud Frumau, Cedric Couret, Matthew Rigby, Stephan Henne, Alistair Manning, and Anita Ganesan

Abstract. Hydrofluorocarbons (HFCs) are potent greenhouse gases widely used in refrigeration, air-conditioning, and heat pump systems. Accurate monitoring of HFC emissions is essential to evaluate compliance with climate regulations and inform mitigation strategies. This study presents trends of HFC emissions across north-western Europe between 2013 and 2024, derived from atmospheric inverse modelling combining atmospheric measurements at eleven monitoring stations with two transport models (NAME and FLEXPART) and three Bayesian inversion systems (InTEM, ELRIS, RHIME). Although global emissions continue to rise for most HFCs, in north-west Europe our results show an overall steady decline in total HFC emissions from 40±3 TgCO₂-eqyr^-1 in 2016 (prior to enhanced regulation) to 29±2 TgCO₂-eqyr^-1 in 2023, following EU F-gas Regulations. This reduction is driven primarily by decreasing emissions of HFC-134a, HFC-143a and HFC-125 despite increasing HFC-32 emissions due to its adoption as a lower-global-warming-potential alternative refrigerant. Comparisons with national inventories reported to the United Nations Framework Convention on Climate Change (UNFCCC) show generally good agreement over north-western Europe but reveal discrepancies for specific compounds and countries, particularly for HFC-134a and HFC-125 in France and Germany during the earlier years of the study period. The recent expansion of the European measurement network demonstrates potential to improve spatial coverage and resolution of inverse emission estimates, especially in southern and central Europe. This study highlights the value of combining atmospheric observations with multiple inversion systems to provide independent HFC emission estimates to support climate policy evaluation.

How to cite. De Longueville, H., Melo, D. B., Redington, A., Ramsden, A., Danjou, A., Andrews, P., Pitt, J., Murphy, B., Constantin, L., Stanley, K. M., O'Doherty, S., Wenger, A., Young, D., Engel, A., Schuck, T., Meixner, K., Wagenhaeuser, T., Gad, F., Vollmer, M. K., Reimann, S., Maoine, M., Arduini, J., Lunder, C., Schmidtbauer, N., Haszpra, L., Molnár, M., Frumau, A., Couret, C., Rigby, M., Henne, S., Manning, A., and Ganesan, A.: European HFC emissions evaluated with multiple atmospheric inverse models and UNFCCC national inventories, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2026-194, 2026.

Received: 13 Jan 2026 – Discussion started: 05 Feb 2026

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.

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RC1:
'Comment on egusphere-2026-194', Anonymous Referee #1, 17 Mar 2026
De Longueville et al. presents top-down emission estimates of regulated HFCs, including in the European regions. These top-down estimates were derived using surface measurements from 11 European stations, including 6 AGAGE stations and 4 European F-gas network stations, and combined with various inverse modeling frameworks, including NAME and FLEXPART. Total NW European and country-level emission estimates were reported for 11 controlled HFCs, including the most abundant HFC-134a, HFC-143a, and HFC-125, HFC-32, HFC-23, and the less abundant HFC-227ea, 365mfc, 245fa, 152a, 236fa, 4310mee.
This is an impressive effort; a timely publication of these results will offer valuable insights for the 2026 WMO Ozone Assessment. While the analysis is comprehensive and the discussion is sound, I have included several suggestions below to help enhance the clarity and impact of the presentation.
Major comments:
The Introduction provides a great foundation, but at 2.5 pages, it feels a bit dense. To help the reader get to the core of your argument faster, I’d suggest condensing this section. For instance, the EU regulation details are excellent, but they might carry more weight if moved to the later sections where you discuss derived emissions, trends, and their relationships with the enforcement. Similarly, moving the specific species reporting details to Section 2 would keep the Intro focused on the 'big picture' while still preserving that valuable data for later.

In the results section, the discussion focuses primarily on (1) observed trends in relation to current regulations and (2) the discrepancies between UNFCCC-reported data and top-down estimates from various inversion systems. While these technical comparisons are essential, there is an opportunity to situate these findings within a broader context. Specifically, the paper would benefit from discussing how European emissions factor into the global total and identifying which countries are the primary contributors to NW European emissions. While percentage contribution of each compound is presented in one sentence at the end of each compound section, adding a dedicated section for this broader analysis would significantly enhance the paper's impact, elevating it from a regional estimate to a study with wider relevance.

Minor comments:
L14-15. Isn’t this obvious – observations + modeling inversions is important? There is a community consensus on this. Is it really necessary to add this sentence at the end of the abstract?

Is the CBW station part of the AGAGE network or stand-alone observation sites? Please clarify. If it doesn’t belong to AGAGE, you may consider move it out of the AGAGE network paragraph.

Table 2. It would be helpful if you can add one column to show the fraction of NW Europe emissions out of the global emissions estimate for 2023. Providing the numbers will be useful to understand if there are variations of regional contribution among these compounds.

I see you use north-western most of the times, but north-west a few times. Please be consistent.

Why the less abundant species have larger relative uncertainties in their emissions estimates?

Section 4.6. I found this section very informative. Besides stating the absolute emission numbers, could you also add trends in %/yr, instead of just describing the general characteristics, e.g. plateau, slow decline, substantial decline, etc?
Citation: https://doi.org/10.5194/egusphere-2026-194-RC1
RC2: 'Comment on egusphere-2026-194', Anonymous Referee #2, 22 Mar 2026

In this inverse modelling study HFC emissions from Western European countries are evaluated against atmospheric observations from the AGAGE network. The results show posterior emissions that are in broad agreement with National Inventory Reports, despite some significant differences between the inventory reports and the EDGAR emission inventory that is used as first guess in the inversions. This provides a convincing demonstration of the consistency and added value of the European scale inverse models that are presented. Below are my minor comments and suggestions that will suffice in my opinion to prepare this important manuscript for its final publication.
General comments
The difference between EDGAR and the NIR estimates receives little discussion. Since EDGAR seems biased high, it makes me wonder if it wouldn’t have been better to use the NIR country totals as priors. Would in that case that inversion have ended up systematically lower than the NIRs? If the goal is to evaluate the NIRs, using those as priors seems a more logical choice. I understand that NIRs do not provide gridded emission maps, but that would easily be solved using EDGAR for the emission distribution.
The benchmarking of inversion performance against measurements that are withheld from the inversion would provide an essential confirmation that the posterior emissions have indeed improved compared with the prior. I understand that the authors would like to keep the paper focused and concise, but such a test is nevertheless important to include in my opinion.
The geometry of the network change over time with new sites joining. For the goal of assessing the impact of new regulations on HFC emissions since 2017 it should be excluded that the change in network around the same time could have interfered. The experiment that has been performed to test the enhanced observational constraint offered by the new sites confirms the sensitivity of the emission estimates to those sites. However, the question how the inferred trends could have been affected doesn’t receive the necessary attention.
If I understand correctly the a priori emissions are distributed uniformly within each year. While this seems a reasonable assumption, it would nevertheless have been useful to test if the posterior emissions show a significant seasonality. If so, this could provide important information about how well seasonal variations in atmospheric transport and vertical mixing are captured by the transport models.
Some discussion is missing of why the FLEXPART estimated emissions are systematically below those inferred using NAME.
Specific comments
Line 110: Please specific which supplement.
Table 1: The middle of the table seems to have an incomplete entry.
Line 126: ‘The estimated total … ‘ This refers to the a priori emissions I assume? In that case a reference is needed.
Line 134: Please specify which hourly intervals.
Line 138: Scaling factors to spatially and temporally constant boundary conditions?
Line 149: What is the a priori uncertainty on the station bias and what did the inferred biases look like?
Line 284: The posterior emissions for France seem to agree with EDGAR. Does the difference between EDGAR and the French NIR provide any clue why this is the case?

Citation: https://doi.org/10.5194/egusphere-2026-194-RC2

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Short summary

This study estimates emissions of hydrofluorocarbons, important greenhouse gases, in north-western Europe using atmospheric observations and atmospheric modelling. The estimates are compared with nationally reported emissions submitted to the United Nations. Overall, our results are consistent with reported values, although differences are found for some gases and countries. The findings indicate that emissions in north-western Europe are declining, reflecting the effects of climate regulations.


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