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

Hydrofluoroolefins (HFOs) are important synthetic compounds replacing other halocarbons in phase-down from usage (e.g., as refrigerants, propellants, foam blowing). Little is known about their atmospheric abundance, distribution and trends, nor about their emissons. Here, we report atmospheric observations of the widely used HFO-1234yf (2,3,3,3-tetrafluoroprop-1-ene), and HFO-1234ze(E) (E-1,3,3,3-tetrafluoroprop-1-ene), and the hydrochlorofluoroolefin (HCFO) HCFO-1233zd(E) (E-1-chloro-3,3,3-trifluoroprop-1-ene) observed as part of the Advanced Global Atmospheric Gases Experiment (AGAGE) network. Over the observational period 2011-2025, pollution events have grown in magnitude and frequency at sites which are influenced by regional emissions, while remote stations show first appearances of these substances. By 2024/2025 winter peak mole fractions in background northern hemisphere air have reached similar to 0.25 ppt (picomol mol(-1), parts-per-trillion in dry air) for HFO-1234yf and HFO-1234ze(E) and similar to 0.45 ppt for HCFO-1233zd(E). Using European observations and the inverse modeling frameworks InTEM, ELRIS, and RHIME we determine emission trends and regional distributions. For Northwest Europe, emissions of HFO-1234yf increased steadily and rapidly from < 0.1 Gg yr(-1) in 2014 to 1.50 [1.23-1.74, range of 16-84 percentile] Gg yr(-1) by 2023, presumably due to its introduction in mobile air conditioning and stationary refrigeration. HFO-1234ze(E) emissions were low during 2014-2017, followed by a rapid increase in 2018/2019, potentially due its introduction as an aerosol propellant, after which they increased more slowly to 0.96 [0.82-1.13] Gg yr(-1) by 2023. HCFO-1233zd(E) emissions are derived from 2017 onward, showing a steady increase from 0.15 [0.07-0.23] to 1.04 [0.93-1.15] Gg yr(-1) in 2023.

Abstract. The perfluorocarbons CF4 and C2F6 are among the most potent greenhouse gases with lifetimes of fifty and ten thousand years, respectively. They are both primarily emitted during aluminum smelting and electronics manufacturing. We perform the first regionally resolved global inversion of CF4 and C2F6, providing atmospheric measurement-based top-down emission estimates for 2006–2023 using the FLEXPART transport model and the FLEXINVERT+ framework. Introducing a global-total constraint to align the inversion results with the relatively accurate global total emissions from the AGAGE 12-box model stabilizes the emissions in poorly monitored regions. Compared to the global bottom-up inventory EDGAR, the inversion increases global CF4 and C2F6 emissions by factors of 2.6 ± 0.3 and 3.1 ± 0.7, respectively, for 2018–2023. China dominates global emissions, contributing 56 % (CF4) and 58 % (C2F6) in 2018–2023. The contribution of South and Southeast Asia to global emissions rose from about 6 % and 10 % in 2006–2011 to 22 % and 18 % by 2018–2023, respectively, though large uncertainties remain due to a lack of measurements in the region itself. European emissions declined until 2010, then stabilized and contribute 2 %–3 % to global emissions by 2018–2023. U.S. CF4 emissions remain constant and C2F6 emissions decreased steadily (reaching 3 %–4 % by 2018–2023), with a temporary drop in 2009 likely linked to the financial crisis. On the global scale, our results suggest a contribution of 81 % by the aluminum industry to total CF4 emissions and 48 % by the electronics industry to global C2F6 emissions.

Sulfur hexafluoride (SF6) is a greenhouse gas with an estimated atmospheric lifetime of about 850-1280 years and a global warming potential of 24,700 over 100 years. As this strong greenhouse gas continues to be used in switchgear, circuit breakers, transformers and in other applications; monitoring emissions worldwide is essential. Some global and regional measurement networks, including the AGAGE, NOAA and ICOS programmes, have been measuring surface-based SF6 for several years. Through these measurements and inverse modelling, it has been shown that there are still significant SF6 emissions in western Europe, the largest source estimated to be in southern Germany.Here we present the first time series of all available SF6 observations in Germany to localise the most important source regions of SF6. Data from the following stations were used: Taunus Observatory (AGAGE), Zugspitze / Schneefernerhaus (UBA Germany, GAW, ICOS), Karlsruhe (DWD, ICOS), Hohenpeissenberg (DWD, GAW, ICOS), Lindenberg (DWD, ICOS), Ochsenkopf (MPI-BGC, ICOS), Steinkimmen (ICOS), Gartow (ICOS) and Schauinsland (UBA Germany, GAW, ICOS). This distribution of observation sites provides good resolution of SF6 emissions in Germany. Despite the annual National Inventory Reports to the UNFCCC suggesting a decline in SF6 emissions in Germany, observations show continued episodes of elevated mixing ratios. This is indicative of continuing local emissions in Germany. Depending on wind direction, the highest levels of SF6 were measured at Zugspitze, Schauinsland, Karlsruhe and the Taunus Observatory, consistent with a source in southern to south-western Germany. The Karlsruhe station stands out in particular, with maximum mixing ratios of more than 70 ppt. In addition to an analysis of such pollution events, the observations are also used in the top-down inverse model InTEM (Inversion Technique for Emission Modelling) coupled to the atmospheric transport model NAME (Numerical Atmospheric Dispersion Modelling Environment).

Abstract. Atmospheric observations of the widely used hydrofluoroolefins (HFOs) HFO-1234yf (2,3,3,3-tetrafluoroprop-1-ene), and HFO-1234ze(E) (E-1,3,3,3-tetrafluoroprop-1-ene), and the hydrochlorofluoroolefin (HCFO) HCFO-1233zd(E) (E-1-chloro-3,3,3-trifluoroprop-1-ene) are reported from the Advanced Global Atmospheric Gases Experiment (AGAGE) network. Since 2011, pollution events have grown in magnitude and frequency at sites which are influenced by regional emissions, while remote stations show first appearances of these substances. For HFO-1234yf and HFO-1234ze(E) winter peak mole fractions in background northern hemisphere air have grown from 0.03 ppt (picomol mol-1, parts-per-trillion in dry air) in the mid-2010s to 0.25 ppt in 2024, while the atmospherically more stable HCFO-1233zd(E) showed an increase from 0.06 ppt to 0.45 ppt. This suggests increasing usage of these haloolefins to replace hydrofluorocarbons (HFCs), which are regulated for phase-down over the next decades. Using European observations and the inverse modeling frameworks InTEM, ELRIS, and RHIME we determine emission trends and regional distribution. For Northwest Europe, emissions of HFO-1234yf increased steadily and rapidly from <0.1 Gg yr-1 in 2014 to 1.50 Gg yr-1 by 2023, presumably due to its introduction in the mobile air conditioning and refrigeration sectors. HFO-1234ze(E) emissions were low during 2014–2017, followed by a rapid increase in 2018/2019, potentially due its introduction as aerosol propellant, after which they increased more slowly to 0.96 Gg yr-1 by 2023. HCFO-1233zd(E) emissions are derived from 2017 onwards, showing a steady increase from 0.2 Gg yr-1 to 1.0 Gg yr-1 in 2023.

Abstract. Many halogenated trace gases are important greenhouse gases and/or contribute to stratospheric ozone depletion, yet their spatial distribution and temporal evolution in the stratosphere remain poorly constrained. We here present a new high-altitude dataset of a large range of these gases. The results are based on a large balloon flight in the Arctic in summer 2021. Air samples were collected using a passive (AirCore) as well as an active (cryogenic) technique; the former being the largest AirCore flown to date, thus enabling the quantification of an expanded variety of halogenated gases. The evaluation of the results demonstrates good comparability in most cases, but also revealed strengths and weaknesses for both sampler types. In addition, we show examples of the scientific value of this data, including the identification of air masses likely originating from the Asian Monsoon region, and the derivation of the average stratospheric transit times (i.e., the mean ages of air) from multiple tracers.

Stratospheric mean age of air is an important metric and much-used proxy for the speed of the residual overturning circulation in the stratosphere. Much effort has been put into better constraining observation-based estimates of age of air over the past two decades. Yet substantial uncertainties remain for some aspects such as the long-term evolution, especially at higher altitudes that are hard to reach for most in situ-measurement platforms.We here present a newly derived age of air data set, which is based on high precision measurements of inert trace gases that were derived from a) AirCore samples from multiple weather balloon-based deployments since 2017 (updated from Laube et al., 2020), and also b) recently collected as well as archived reanalysed air samples from high altitude aircraft and large balloon campaigns between 1976 and 2017. Utilised trace gases include SF6, C2F6, C3F8, CHF3 (HFC-23), and C2HF5 (HFC-125), all of which have been proven to be suitable as age tracers (Leedham Elvidge et al., 2018). We evaluate the uncertainties connected to the trace gas measurements as well as the derivation of the mean age of air, and compare our estimates to published data sets such as the one from Engel et al. (2017). ReferencesEngel, et al., Atmos. Chem. Phys., 2017, https://doi.org/10.5194/acp-17-6825-2017.Laube et al., Atmos. Chem. Phys., 2020, https://doi.org/10.5194/acp-20-9771-2020.Leedham Elvidge et al., Atmos. Chem. Phys., 2018, https://doi.org/10.5194/acp-18-3369-2018.

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.

Halogens from long-lived anthropogenic substances contribute to the depletion of stratospheric ozone. Besides these long-lived substances, chlorinated and brominated substances with lifetimes of less than 6 months are additional sources of stratospheric halogens. These substances, also known as very short-lived substances (VSLSs), have both natural and anthropogenic origins. The contribution of chlorinated VSLSs (Cl-VSLSs) to stratospheric chlorine is a few percent. In comparison, brominated VSLSs (Br-VSLS) contribute to about a quarter of the stratospheric bromine. The relative contribution of VSLSs to stratospheric halogen loading is expected to increase as the Montreal Protocol controlled substances progressively decrease. Due to their short lifetimes, VSLSs rapidly release their halogen content into the lowermost stratosphere, a region where changes in ozone have a relatively large impact on surface climate. Here we present the global seasonal distribution of the two major Br-VSLSs CH2Br2 and CHBr3, which account for about 80 % of total organic Br-VSLS. Measurements from four High Altitude and Long Range Research Aircraft (HALO) missions, the HIAPER Pole-to-Pole Observations (HIPPO) mission, and the Atmospheric Tomography (ATom) mission were used for this purpose. Observational results show a similar seasonality of CH2Br2 in the free and upper troposphere of both hemispheres and less clear seasonality with larger variations for CHBr3. The distribution of CH2Br2 in the lowermost stratosphere suggests differences in hemispheric autumn, where the influx of tropospheric air seen in northern hemispheric summer to autumn is not evident in the Southern Hemisphere. However, the southern hemispheric database is insufficient to quantify this difference. The observed distributions were additionally compared to distributions based on model results of TOMCAT and CAM-Chem, both using the emission inventory of Ordóñez et al. (2012). Neither model was able to reproduce the seasonal distribution of CH2Br2 in the Southern Hemisphere. In contrast, both models show a pronounced seasonality of CHBr3 in both hemispheres, which is not confirmed by observations. The distributions of both substances in the lowermost stratosphere are overall well captured by the models, except for southern hemispheric autumn with considerably lower mixing ratios in the observations.

We report on measurements of organic, inorganic and total bromine (Brtot) in the upper troposphere and lower stratosphere (UTLS) over southern Argentina and surroundings extending down to the Antarctic Peninsula in September and November of 2019. These measurements were recorded from the German High Altitude and LOng range research aircraft (HALO) as part of the Transport and Composition of the Southern Hemisphere UTLS (SouthTRAC) research campaign. Brtot is inferred from measured total organic bromine (Brorg), i.e., the sum of bromine contained in CH3Br, the halons and the major very short-lived brominated species, added to inorganic bromine (Bryinorg), evaluated from measured BrO and photochemical modelling. Lagrangian transport modelling as well as in situ measured transport (CO and N­­2O) and air mass lag-time (SF6) tracers are used to identify air mass transport pathways into the UTLS and indicate the likely origins of bromine-rich air masses reaching the Southern Hemisphere (SH) lower stratosphere. Additionally, the SH bromine volume mixing ratios are compared with previous measurements from fall 2017 observed in the Northern Hemisphere as part of the Wave-driven ISentropic Exchange (WISE) research campaign, and the long term trend in stratospheric bromine.

The age of stratospheric air is a concept commonly used to evaluate transport timescales in atmospheric models. The mean age can be derived from observations of a single long-lived trace gas species with a known tropospheric trend. Commonly, deriving mean age is based on the assumption that all air enters the stratosphere through the tropical (TR) tropopause. However, in the lowermost stratosphere (LMS) close to the extra-tropical (exTR) tropopause, cross-tropopause transport needs to be taken into account. We introduce the new exTR–TR method, which considers exTR input into the stratosphere in addition to TR input. We apply the exTR–TR method to in situ SF6 measurements from three aircraft campaigns (PGS, WISE and SouthTRAC) and compare results to those from the conventional TR-only method. Using the TR-only method, negative mean age values are derived in the LMS close to the tropopause during the WISE campaign in Northern Hemispheric (NH) fall 2017. Using the new exTR–TR method instead, the number and extent of negative mean age values is reduced. With our new exTR–TR method, we are thus able to derive more realistic values of typical transport times in the LMS from in situ SF6 measurements. Absolute differences between both methods range from 0.3 to 0.4 years among the three campaigns. Interhemispheric differences in mean age are found when comparing seasonally overlapping campaign phases from the PGS and the SouthTRAC campaigns. On average, within the lowest 65 K potential temperature above the tropopause, the NH LMS is 0.5±0.3 years older around March 2016 than the Southern Hemispheric (SH) LMS around September 2019. The derived differences between results from the exTR–TR method and the TR-only method, as well as interhemispheric differences, are higher than the sensitivities of the exTR–TR method to parameter uncertainties, which are estimated to be below 0.22 years for all three campaigns.

The TWIN - Hemera stratospheric balloon flight took place on 12 - 13-Aug-2021 from the Esrange Space Center near Kiruna, Sweden (67°N).The project was supported by Hemera (www.hemera-h2020.eu) via the first call of proposals, and the flight was managed by the CNES (Centre national d'Etudes Spatiales) and SSC (Swedish Space Corporation). The scientific payload was developed in collaboration by several institutions from the Netherlands, Germany and France. The main objectives were: (1) to characterize the vertical structure of COS mole fraction and isotopic composition; (2) to characterize the CFCs, other ozone depleting substances and climate relevant trace gases in the present atmosphere, linked to their change over the past decade; and (3) to compare and evaluate several instruments and sampling techniques. The payload included several AirCores (U. Frankfurt, CIO and FZJ), two Pico-SDLA mid-infrared in-situ diode laser spectrometers (GSMA/DT-INSU), and devices for taking large whole air samples of stratospheric air for subsequent laboratory measurements: the BONBON whole-air cryosampler (U. Frankfurt) and LISA (CIO). IMAU is involved for the analysis of isotopic composition and mole fractions of samplers from the cryo-sampler. This approach allows obtaining a comprehensive dataset covering a range of spatial resolutions: from the multitude of gas species to be measured in the high-volume samples, to the subset of gases at higher vertical resolution from AirCores, and finally to the continuous in-situ CO2 and CH4 data from tunable diode laser spectroscopy. We expect this dataset to lead to novel and important knowledge on the trace gases in the stratosphere. In this presentation we will describe the overall setup of the scientific payload, the flight characteristics, and we will give an overview of the already performed and planned measurements.

Measurements of halogenated trace gases such as CFCs, halons, HCFCs, HFCs, and PFCs are highly relevant due to their impact on the stratospheric ozone layer as well as their high Global Warming Potentials. Yet in situ profiles of the abundances of many of these species in the stratosphere have been increasingly rare in the last two decades, especially above the altitude range accessible by aircraft (i.e. up to 20 km). More recently, the AirCore technique, which was initially utilized for measurements of more abundant trace gases such as carbon dioxide and methane (Karion et al., 2010), has been demonstrated to also enable stratospheric mixing ratio determination for six halogenated species (Laube et al., 2020). However, a direct measurement comparison of AirCore-based air samples with those collected via a more established technique has been missing so far for such low-abundant species. We here present results from a large balloon flight in Esrange, Sweden (67.8877°N, 21.0838°E) in August 2021. An established cryogenic whole-air sampler (Engel et al., 2009) was flown on the same gondola as a so-called “MegaAirCore”, which has, at ~15 liters, a much larger internal volume than common AirCores (~1-1.5 liters). The air collected between ~32 km and ~5 km by this “MegaAirCore” was transferred into 51 sub-samples immediately after the flight, and these were subsequently analysed for their content of >30 halogenated trace gases. The 13 larger air samples collected by the cryosampler were also measured on the same mass spectrometry-based instrument.Results compare well for many species, which represents an independent verification of AirCore-based measurements of halogenated trace gases at mixing ratios of parts per trillion levels or below – while at the same time demonstrating the viability of stratospheric air sampling at a much higher vertical resolution than previously possible. This opens up new possibilities for studying stratospheric chemistry and dynamics as well as for improvements of the independent validation of remote sensing-based observations. References Engel et al., Nat. Geosci., 2, 28–31, 2009 Karion et al., J. Atmos. Ocean. Technol., 27(11), 1839–1853, 2010 Laube, et al., Atmos. Chem. Phys., 20, 9771–9782, 2020, https://doi.org/10.5194/acp-20-9771-2020

The mean age of air is a powerful diagnostic tool to investigate stratospheric transport processes. It can be derived from suitable trace gas measurements and from model calculations. In contrast to the Northern Hemisphere (NH), data coverage of in situ measurements of such trace gases in the Southern Hemisphere (SH) is sparse. Due to its tropospheric trend and its very long atmospheric lifetime, SF6 is such a suitable trace gas. SF6 mixing ratios were measured with an airborne in situ GC-ECD system during several HALO aircraft campaigns, including locations in the SH polar vortex. Here we present the mean age derived from in situ SF6 measurements during the POLSTRACC campaign (Polar Stratosphere in a Changing Climate) in NH winter/spring 2015/2016 and during the SouthTRAC campaign (Transport and Composition of the Southern Hemisphere UTLS) in SH winter/spring 2019. Mean age values over 4 years were observed in both polar vortices. On average, higher mean age values were observed at lower levels of potential temperature during SouthTRAC 2019 than during POLSTRACC 2015/2016. The findings will be discussed in context of the Brewer-Dobson circulation.

Abstract. Inorganic chlorine (Cly) is the sum of the degradation products of long-lived chlorinated source gases. These include the reservoir species (HCl and ClONO2) and active chlorine species (i.e. ClOx). The active chlorine species drive catalytic cycles that deplete ozone in the polar winter stratosphere. This work presents calculations of inorganic chlorine (Cly) derived from chlorinated source gas measurements on board the High Altitude and Long Range Research Aircraft (HALO) during the Southern hemisphere Transport, Dynamic and Chemistry (SouthTRAC) campaign in late winter and early spring 2019. Results are compared to Cly of the Northern Hemisphere derived from measurements of the POLSTRACC-GW-LCYCLE-SALSA (PGS) campaign in the Arctic winter of 2015/2016. A scaled correlation was used for PGS data, since not all source gases were measured. Cly from a scaled correlation was compared to directly determined Cly and agreed well. An air mass classification based on in situ N2O measurements allocates the measurements to the vortex, the vortex boundary region, and mid-latitudes. Although the Antarctic vortex was weakened in 2019 compared to previous years, Cly reached 1687 ± 20 ppt at 385 K, therefore up to around 50 % of total chlorine could be found in inorganic form inside the Antarctic vortex, whereas only 15 % of total chlorine could be found in inorganic form in the southern mid-latitudes. In contrast, only 40 % of total chlorine could be found in inorganic form in the Arctic vortex during PGS and roughly 20 % in the northern mid-latitudes. Differences inside the respective vortex reaches up to 565 ppt more Cly in the Antarctic vortex 2019 than in the Arctic vortex 2016 (at comparable distance to the local tropopause). As far as is known, this is the first comparison of inorganic chlorine within the respective polar vortex. Based on the results of these two campaigns, the difference of Cly inside the respective vortex is significant and larger than reported inter annual variations.