Katharina Meixner

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-western Europe our results show an overall steady decline in total HFC emissions from 40 ± 3 Tg CO ₂ -eq yr ⁻¹ in 2016 (prior to enhanced regulation) to 29 ± 2 Tg CO ₂ -eq yr ⁻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 multi-model inversions to provide robust emission estimates with realistic, hence actionable, uncertainty characterisation.

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.

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.

Sulfur hexafluoride (SF6) is a highly potent greenhouse gas (GHG). Despite its high global warming potential (GWP), it continues to be produced and used in Germany. The reported emission estimates can be used to calculate expected concentrations at measurements sites. Within the PARIS (Process Attribution of Regional Emissions) project we used the operational numerical weather prediction model ICON (ICOsahedral Nonhydrostatic) and its extension module for aerosol and trace gases (ART) as an Eulerian forward model to calculate the expected mixing concentrations response of Germany's largest point source of SF6. We compared the modelled concentration peaks that occur when the modelled plume crosses the measurement site of the Taunus observatory (TOB) with the respective observed signals (requiring background subtraction). The 4-year period of 2020-2023 was covered, and the uncertainty of the meteorological transport was estimated using a 20-member ensemble in our limited area model for Europe, which was run with a horizontal grid resolution of 6.5 km and 74 vertical levels.The model predicts well when peaks are measured but weWe found that most observed peaks at TOB are considerably higher than in the model, suggesting that prior emissions estimates were too low. This indicates that the independent, observation-based emission estimate of our ICON-ART based system is in the range of double-digit tons, which is considerably higher than the self-reported SF6 emission estimate for this point source, also if the model uncertainties are taken into account.

Measurement-based emission estimates derived from atmospheric observations provide an independent and important approach for identifying emission sources, quantifying emissions and verifying reported inventories. This is particularly relevant for halogenated gases, which due to their role as ozone depleting substances and potent greenhouse gases are regulated under various international and national frameworks. Here, we present two studies highlighting the urgency and the challenges of the measurement-based emission estimates of sulfur hexafluoride (SF6) and fluoroform (HFC-23) with a particular focus on the influence of point sources.SF6 and HFC-23 are two of the most potent greenhouse gases with a GWP100 of approximately 24,000 and 14,700, respectively. Previous studies consistently showed a dominant emission source in southern Germany contributing to a large share of European SF6 emissions. Meixner et al., 2025 analysed emission estimates based on 22 European measurement sites revealing an underestimated SF6 emission point source in southern Germany in contrast to the national inventory reports.Recent studies highlighted major challenges in quantifying HFC-23 emissions (Adam et al., 2024; Rust et al., 2024). We investigate the effects of intermittency in emissions and explore different possibilities based on a priori assumptions about specific emission sources. Forward calculations from these potential emission sources are used to derive expected time series at observational sites. These are compared to observations from different European stations situated in the regions influenced by the potential point sources. We present different approaches based on European atmospheric measurements combined with multiple model approaches, including ICON-ART, FLEXPART and NAME.Adam, B., Western, L.M., Mühle, J., Choi, H., Krummel, P.B., O’Doherty, S., Young, D., Stanley, K.M., Fraser, P.J., Harth, C.M., Salameh, P.K., Weiss, R.F., Prinn, R.G., Kim, J., Park, H., Park, S., Rigby, M., 2024. Emissions of HFC-23 do not reflect commitments made under the Kigali Amendment. Commun. Earth Environ. 5, 783. https://doi.org/10.1038/s43247-024-01946-yMeixner, K., Wagenhäuser, T., Schuck, T.J., Alber, S., Manning, A.J., Redington, A.L., Stanley, K.M., O’Doherty, S., Young, D., Pitt, J., Wenger, A., Frumau, A., Stavert, A.R., Rennick, C., Vollmer, M.K., Maione, M., Arduini, J., Lunder, C.R., Couret, C., Jordan, A., Gutiérrez, X.G., Kubistin, D., Müller-Williams, J., Lindauer, M., Vojta, M., Stohl, A., Engel, A., 2025. Characterization of German SF6 Emissions. ACS EST Air 2, 2889–2899. https://doi.org/10.1021/acsestair.5c00234Rust, D., Vollmer, M.K., Henne, S., Frumau, A., van den Bulk, P., Hensen, A., Stanley, K.M., Zenobi, R., Emmenegger, L., Reimann, S., 2024. Effective realization of abatement measures can reduce HFC-23 emissions. Nature 633, 96–100. https://doi.org/10.1038/s41586-024-07833-y

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.

Sulfur hexafluoride (SF₆) is a highly potent greenhouse gas with a Global Warming Potential (GWP) of 24,700 over 100 years and is globally mainly used as an electrical insulator in switchgear. Several measurement networks have tracked SF₆ for many years and their European data reveal significant emissions in southern Germany. This study focuses on German SF₆ emissions (2020–2023), using atmospheric measurements from 22 European sites, offering high spatial and temporal resolution for robust emission assessments. While German UNFCCC inventory bottom-up emission estimates report a major source of SF₆ through the disposal of soundproof windows, the spatial distribution of German SF₆ emissions derived on top-down inversion techniques (InTEM and Flexinvert+) reveals a different picture: The continuous pattern of high emissions from a particular region is responsible for one-third of total SF₆ emissions in Germany. Despite this, total German SF₆ emissions have decreased from 112 ± 26 t in 2020 to 89 ± 15 t in 2023 (InTEM), with estimates from all methods (both bottom-up and top-down) showing similar trends. Our findings suggest that the emissions from soundproof windows are overestimated, while industrial sources - particularly from SF₆ production and recycling in the focus region - are likely underestimated.

Within the HEMERA balloon infrastructure project, a stratospheric balloon carrying a multi-instrument payload to a maximum altitude of 31.2 km was launched on 12 August 2021. On board the openly constructed gondola, several types of instruments were used for simultaneous air sampling and in-flight measurements to characterize climate-relevant trace gases in the stratosphere and troposphere, as well as to compare and evaluate different instrumental approaches and sampling techniques. For observations of the main greenhouse gases carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and sulfur hexafluoride (SF₆), flask with AirCore sampling and in-flight spectrometry were deployed. Overall, results from different methods agree well. While better precision was achieved for the post-flight measurements of AirCore devices and flask sampling, in situ spectrometry provided a higher degree of detail on the vertical structure of the CH₄ profile. Age of air was derived from mixing ratios of CO₂ and SF₆. As seen in previous studies, higher values were obtained from SF₆ than from CO₂. Correcting for chemical losses, maximum values of 4.4–5.1 years were derived from SF₆ mixing ratios at altitudes above 20 km compared to 4.2–5.0 years from CO₂ mixing ratios. The resulting dataset should be well suited for multi-tracer approaches to derive age of air, particularly in combination with a large suite of halocarbons measured from flask and AirCore sampling and one more AirCore sample which was reported in a companion publication (Laube et al., 2025).

Within the HEMERA balloon infrastructure project, a stratospheric balloon carrying a multi-instrument payload to a maximum altitude of 31.2 km was launched on 12th August 2021. Aboard the openly constructed TWIN gondola, several types of instruments were used for simultaneous air sampling and in-flight measurements to characterize climate relevant trace gases in the stratosphere and in the troposphere, and to compare and evaluate different instrumental approaches and sampling techniques. For observations of the main greenhouse gases carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O) and sulfur hexafluoride (SF₆), sampling with AirCores, flask sampling and in-flight spectrometry were deployed. Overall, results from different methods agree well. While better precision is achieved for the post-flight measurements of AirCores and flask sampling, in-situ spectrometry provides a higher degree of detail on the vertical structure of the CH₄ profile. Age of air was derived from mixing ratios of CO₂ and SF₆. As seen in previous studies, higher values were obtained from SF₆ than from CO₂. Correcting for chemical losses, maximum values of 4.4–5.1 years were derived from SF₆ mixing ratios at altitudes above 20 km compared to 4.2–5.0 years from CO₂ mixing ratios. The resulting dataset should be well suited for multi-tracer approaches to derive age of air, in particular in combination with a large suite of halocarbons measured from flask samples and one more AirCore which are reported by a companion publication.