AS3.40 | Attribution of greenhouse gas (GHG) emissions using isotope ratios and other tracers: analytics, source data, modelling, and metrology
Attribution of greenhouse gas (GHG) emissions using isotope ratios and other tracers: analytics, source data, modelling, and metrology
Convener: Tim Arnold | Co-conveners: Joachim Mohn, Rona Thompson, Penelope Pickers, Javis Nwaboh
| Fri, 19 Apr, 08:30–10:15 (CEST)
Room 1.85/86
Posters on site
| Attendance Fri, 19 Apr, 16:15–18:00 (CEST) | Display Fri, 19 Apr, 14:00–18:00
Hall X5
Orals |
Fri, 08:30
Fri, 16:15
Atmospheric measurements of greenhouse gases (GHGs) are routinely incorporated into atmospheric chemistry transport modelling systems to estimate sources and sinks at various temporal and spatial scales (the so called ‘top-down’ approach). Top-down approaches are important as they provide independent emission estimates that are consistent with the observed changes in the atmosphere. However, temporal variations in GHG mixing ratios alone only provide a weak constraint (if at all) on the sources. Information on the contribution from specific sources and processes is vital to aid effective and timely policy for mitigating emissions. The attribution of atmospheric GHG mixing ratio changes to anthropogenic or natural sources, and to source sectors, can be aided by the measurement and interpretation of isotope ratios of the GHG (e.g. stable isotopes of CH4, N2O or radio-carbon for CO2) or of gaseous tracers that are correlated with sources or sinks of the target pollutant (e.g. atmospheric potential oxygen - APO for CO2 or ethane for CH4).

This session invites contributions from the community working on the use of isotope ratios and other tracers in understanding the sources / sinks of GHGs to the atmosphere. This includes but is not limited to:
- Advances in analytics for GHG isotope ratios or tracers including developments in metrology, e.g. reference materials or methods, to improve sustainability of monitoring,
- Incorporation of isotope or trace gas measurements into models for improved understanding of the sources and/or sinks,
- Studies contributing data on GHG isotope ratio source signatures or tracer/target species emission factors.

Orals: Fri, 19 Apr | Room 1.85/86

Chairpersons: Penelope Pickers, Rona Thompson, Tim Arnold
On-site presentation
Giulia Zazzeri, Lukas Wacker, Negar Haghipour, and Heather Graven

Radiocarbon (14C) is an optimal tracer of methane emissions, as 14C measurements enable distinguishing fossil from biogenic methane. However, we are not yet applying these measurements in monitoring programs for quantification of sources contribution, because of the technical challenges associated with the 14C analysis and the bias introduced by 14C emissions from nuclear power plants.

Studies in London and in Switzerland demonstrate how the nuclear influence should be accurately modelled for a quantitative interpretation of 14C measurements and that a robust uncertainty estimate of the fossil and biogenic proportion of CH4 emissions is highly needed.

Here we present the technological advances in the 14CH4 analysis, including the achievement of high precision 14CH4 measurements (5 ‰) using a new portable sampler developed at the laboratory of Ion Beam Physics, and the potential of expanding these measurements for an improved understanding of sources. We will present the first quantification of fossil methane emissions in London using 14C, demonstrating that, by increasing the measurement capability, we can use 14C to constrain the methane budget at regional scale.

How to cite: Zazzeri, G., Wacker, L., Haghipour, N., and Graven, H.: Analysis of radiocarbon in atmospheric methane: technological advances and interpretation of measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7848,, 2024.

On-site presentation
Lori Bruhwiler and Youmi Oh

Observations indicate accelerating growth of atmospheric CH4, creating a challenge for meeting the Global Methane Pledge that aims to achieve 30% cuts in global emissions by 2030. A recent UNEP report proposes that feasible CH4 emission cuts could result in a 45% reduction in anthropogenic emissions, avoiding 0.3 ºC of warming by mid-century while having a positive impact on human health through air quality improvements. However, given that the most feasible methane emissions reductions are in the oil and gas sector, it will be difficult to achieve the goals of the Global Methane Pledge with current signatories without also considering emissions from agriculture and waste. It is therefore important to be able to quantify and monitor anthropogenic and natural microbial emissions.

Measurements of the 13C stable isotope of CH4 could be useful for partitioning emissions between fossil fuel and microbial sources, and global analyses imply that recent increases in atmospheric growth are dominated by microbial sources. Atmospheric observations of methane and 13CH4 were used to constrain the NOAA CarbonTracker-CH4 inversion modeling system. Results show that the largest share of recent growth in CH4 is due to increasing microbial and fossil fuel emissions in the developing economies of Asia. A smaller contribution to the recent growth in atmospheric CH4 is also from increasing microbial emissions in tropical South America and Africa, possibly a combination of emissions from natural wetlands and agriculture. At global scale there is little change in fossil fuel emissions, however this result is highly dependent in how stable isotope measurements are used in the inversion. In this presentation we highlight uncertainties associated with using isotope measurements and how they affect our understanding of the atmospheric methane budget.

How to cite: Bruhwiler, L. and Oh, Y.: What do we learn about regional and global methane budgets using stable methane isotope measurements in a global inverse model?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13985,, 2024.

On-site presentation
David Lowry, Rebecca Fisher, James France, Mathias Lanoisellé, Semra Bakkaloglu, Julianne Fernandez, Giulia Zazzeri, Aliah al-Shalan, Ceres Woolley Maisch, and Euan Nisbet

The carbon isotopic signature (ð13C) of CH4 fugitive emissions to atmosphere has been measured in downwind plumes from nearly 400 sources in the United Kingdom by the RHUL group since first measurements of the natural gas supply in 1998. The isotopic measurements have the ability to distinguish the main source categories, separating combustion, fossil fuels, waste and agriculture. Further isotopic subdivisions are possible between solid and gaseous fuels, and between different types and methods of waste processing, such that signatures can be assigned to the categories used for the UK reporting to UNFCCC and in production of mapped inventory products.

For many source categories the current spread of ð13C signatures is small, such as onshore natural gas distribution at -39.3 ±2.6‰ (171), or landfill sites at -57.1 ±2.5‰ (54). This has allowed production of isotopic prediction maps and an assessment of the changing source mix isotopic signature emitted by the UK, which contributes to long-range transport and eventually the changing signatures recorded at background measurement sites. The predicted ð13C for averaged UK emission of CH4 changed from -50.5‰ in 1990 to -59.3‰ in 2021 based on the most recent NAEI inventory. Approximately 75% of this 13C depletion is explained by changing proportions of the different sources, particularly emissions reduction from coal mining, landfill sites and gas leaks, but 25% is the result of changing signatures within source categories, particularly in gas distribution with the switch from southern North Sea fields to sources further north, and from changes in landfill practice. This signature is depleted by 3‰ compared to the lowest signature calculated by Miller-Tans analysis of multi-year UK background records, suggesting discrepancies between actual emissions and the inventory source mix. Isotopic mass balance of sources to match observations would require additional fossil fuel emissions, unless there are enrichments rather than depletions occurring in other source sectors.

Changes to sources in the last decade, particularly within the agricultural sector and agricultural waste, has created added complexities to the sector isotopic separations and potential isotopic enrichments. These include C4 plant supplements to diets of animals such as maize that enriches the eructation in 13C, whereas the grass-fed and sustainable cattle have a tightly constrained eructation ð13C signature of -70.5 ±1.7‰ (14). Even more extreme is the range of signatures generated by the burgeoning ‘green’ biogas industry fed by energy crops such as maize at one end of the spectrum with ð13C up to -35‰ to NH3-mediated CH4 production from chicken waste feedstock with signatures around -80‰. Surveys in 2023 highlighted emissions underestimation and the preponderance of maize use in this expanding sector. New isotopic data changed the assigned sector source signature by +1.5‰.

How to cite: Lowry, D., Fisher, R., France, J., Lanoisellé, M., Bakkaloglu, S., Fernandez, J., Zazzeri, G., al-Shalan, A., Woolley Maisch, C., and Nisbet, E.: Carbon isotope measurements of methane for UK sources: spatial and temporal changes and implications for inventories and model inputs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18380,, 2024.

On-site presentation
Jacoline van Es, Carina van der Veen, Malika Menoud, Calin Baciu, Mustafa Hmoudah, Stephan Henne, and Thomas Rockmann

Methane (CH4) plays a crucial role in the Earths’ radiative balance, since it
is a potent greenhouse gas with a shorter lifetime compared to CO2. Mitigating
methane emissions could help mitigate climate change in a short time frame.
This requires a solid understanding of the emissions on the location, strength and
the type of the source. Isotopic analysis can help with the source partitioning
since different sources emit CH4 with slight but significant differences in the
isotopic composition.
Utrecht University developed an isotope ratio mass spectrometer (IRMS)
system capable of measuring δ13C and δD of CH4 at high precision with ap-
proximately hourly time resolution for both isotope signatures. Under the Hori-
zon Europe project PARIS (Process Attribution of Regional Emissions) we ex-
panded the coverage of high time resolution isotope measurements in Europe by
deployment of this system in Cluj-Napoca. The goal is to investigate the typical
source mix of methane in this region and investigate whether the observations
agree with emission inventories. This data is combined with a mobile surveys
to investigate suspected sources.
The work performed on the continuous data-series indicate that the night
time accumulation has an important role in the mixing ratio and the signatures
of both the δD and δ13C. Furthermore it suggest that the enhancements can be
explained by a combination of leakages from the gas network, combined with
microbial sources. Wind directions indicates that the city centre has significant
contributions to these emissions.

How to cite: van Es, J., van der Veen, C., Menoud, M., Baciu, C., Hmoudah, M., Henne, S., and Rockmann, T.: Continuous monitoring of the isotopic composition of methane in Cluj-Napoca., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9424,, 2024.

On-site presentation
Bibhasvata Dasgupta, Malika Menoud, Carina van der Veen, Ceres Maisch, James France, Stephen Platt, Cathrine Myhre, Ingeborg Levin, Heiko Moossen, Sylvia Michel, Sudhanshu Pandey, Sander Houwelling, Nicola Warwick, Euan Nisbet, Ryo Fujita, and Thomas Roeckmann

Atmospheric models, ranging from simple box models to advanced 3-D transport models, play a crucial role in interpreting observations related to atmospheric pollution and global warming. Their ubiquitous use has provided valuable insights, yet understanding the trade-offs and benefits of model complexity requires careful consideration, as the specific limitations and advantages depend on the application at hand. In an attempt to monitor atmospheric levels of methane with a 2-box inversion model, powered by global CAMS inventories for 5 major emission categories namely Agriculture, Wetlands, Pyrogenic, Fossils and Waste, sink specific lifetimes for troposphere, stratosphere and soil, hemispheric gradients and 40 years of polar observations of methane mole fraction and isotope composition from 10 stations, we identified several caveats of the methane budget. This work investigates the production and consumption of methane at source and sinks respectively, by the optimization of either CH4 emissions exclusively or both emissions and the isotopic signatures from the five emission categories. In addition, the significance of model parameters such as source isotopic composition, sink kinetic isotopic effects, errors associated with emissions and isotopic measurements, as well as model spin-up/spin-down criteria and the mutual controls of the tracers are evaluated to understand the dynamics of the atmospheric methane cycle. Incorporation of δ2H alongside methane mole fraction (χ(CH4)) and δ13C into inversion models has improved our understanding of the methane sources and sinks significantly, however the simplifications and assumptions need to be tested for model sensitivity to yield more accurate results as well as build more robust models. 

How to cite: Dasgupta, B., Menoud, M., van der Veen, C., Maisch, C., France, J., Platt, S., Myhre, C., Levin, I., Moossen, H., Michel, S., Pandey, S., Houwelling, S., Warwick, N., Nisbet, E., Fujita, R., and Roeckmann, T.: Towards a better understanding of the constraints and biases of atmospheric methane inversions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19794,, 2024.

On-site presentation
Malavika Sivan, Jiayang Sun, Thomas Röckmann, Patricia Martinerie, James Farquhar, Maarten C. Krol, Sudhanshu Paandey, Malika Menoud, Bibhasvata Dasgupta, Mojhgan A. Hagnegedar, Carina van der Veen, and Maria Elena Popa

The global atmospheric methane mole fractions have risen since the pre-industrial times, primarily attributed to anthropogenic emissions, overlayed by significant multi-annual variability. Atmospheric methane is influenced by different methane sources, variations in the atmospheric OH concentration and other sink reactions. Understanding the contribution of each of these factors is crucial for a comprehensive understanding of the methane cycle.

Recent modelling studies have suggested that measurements of clumped isotopologues (13CH3D and 12CH2D2) can help constrain the global methane budget [1,2]. The first measurements of present ambient air (2022-23) show that the clumping anomalies of atmospheric methane have distinct signatures of about 1 ± 0.3 ‰ for Δ13CH3D and 44 ± 3 ‰ for Δ12CH2D2, strongly enriched in Δ12CH2D2 compared to all known sources [3,4].

We have measured the bulk and clumped isotope composition of methane from firn air samples (~ 500 L volume) collected at the East Greenland Ice core Project (EGRIP) site in high-pressure cylinders. At this location, open porosity allows the collection of air samples from firn down to a depth of 70 m, dating back to the 1990s.

These are the first-ever measurements of the clumped isotopic composition of atmospheric methane from the past. Results of bulk isotope measurements are in line with the known temporal evolution, supporting the integrity of the sampling and analysis procedure. The clumped isotope results reveal a clear increase of 10 ± 2 ‰ for Δ12CH2D2 over the last 30 years (~1993 to 2018), while Δ13CH3D remains constant within the experimental uncertainty. We use a 2-box atmospheric model to investigate source and sink scenarios that are consistent with this trend in the clumped isotope anomalies as well as the bulk isotopic composition of methane.






How to cite: Sivan, M., Sun, J., Röckmann, T., Martinerie, P., Farquhar, J., Krol, M. C., Paandey, S., Menoud, M., Dasgupta, B., Hagnegedar, M. A., Veen, C. V. D., and Popa, M. E.: Evolution of atmospheric methane clumped isotope anomalies since the 1990s reconstructed from firn air measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7562,, 2024.

On-site presentation
Irène Xueref-Remy, Ludovic Lelandais, Aurélie Riandet, Pierre-Eric Blanc, Alexandre Armengaud, Sonia Oppo, Gregory Gille, Sanne Palstra, Bert Scheeren, Huilin Chen, Bert Kers, Pauline Bosio, Marvin Dufresne, Stéphane Sauvage, and Thérèse Salameh

The Aix-Marseille metropolis is the second most populated urbanized area of France. It aims at reaching carbon neutrality in 2050. Located in the south-east of France under a Mediterranean climate, this area is known as a hot-spot regarding climate change. Its west part is strongly industrialized. The local air quality monitoring agency  ATMOSUD delivers a high resolved greenhouse gas emissions inventory that represents the reference for local stakeholders in matter of emissions trajectory. However, this inventory is still quite uncertain and requires independent assessments. In this aim, in the framework of the ANR COoL-AMmetropolis projet (2019-2025) we set-up a local greenhouse gas monitoring network based on Cavity Ring Down Spectrometry analyzers. This local network comprises the OHP ICOS-France station, located 80 km north of Marseille city. Local meteorological features such as sea and land breezes impact local greenhouse gas concentrations through advection and boundary layer dynamical processes. Isotopic analysis of 14C and 13C in CO2, as well as CO2 correlations with NOx, CO, black carbon and SO2, show a strong impact of fossil fuel emissions on the CO2 local urban greenhouse gas atmospheric plumes. The identified fossil sources are mostly traffic, building, industrial and maritime activities. Modern sources such as wood burning may account for a larger part than assessed by the local inventory.

How to cite: Xueref-Remy, I., Lelandais, L., Riandet, A., Blanc, P.-E., Armengaud, A., Oppo, S., Gille, G., Palstra, S., Scheeren, B., Chen, H., Kers, B., Bosio, P., Dufresne, M., Sauvage, S., and Salameh, T.: A top-down assessment of CO2 and CH4 atmospheric variability and emission sources in the Aix-Marseille metropolis area, France., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6754,, 2024.

On-site presentation
Marya el Malki, Antoon Visschedijk, and Hugo Denier van der Gon

Accurately attributing CO2 emissions is key to mitigating greenhouse gas (GHG) emissions under the European Green Deal. However, this poses significant challenges. To this end, the CO2MVS Research on Supplementary Observations (CORSO) project will support establishing the new European anthropogenic CO2 emissions Monitoring and Verification Support capacity (CO2MVS), which is being implemented within the Copernicus Atmosphere Monitoring Service (CAMS). To better separate the contribution of fossil fuels and natural sources to atmospheric CO2 emissions, CORSO will be using supplementary observations focused on co-emitted species, as well as other auxiliary observations, such as gaseous tracers. One such tracer is Atmospheric Potential Oxygen (APO), that integrates both emitted CO2 and the corresponding O2 uptake through the derivation of an oxidative ratio (OR). Here we present  the development and further refinement of a regional APO inventory that spans the European domain from 2005 to 2020 at a resolution of 6 x 6 km. The inventory builds upon earlier work conducted under the CO2 Human Emissions (CHE) project for the year 2015, leveraging CO2 and co-emitted species emissions from the CAMS-REG-v4 dataset produced by TNO. It expands on the methodology used to develop the COFFEE global dataset (Steinbach et al., 2011) by introducing several improvements. Oxygen consumption from fossil fuel combustion is dominated by CO2 but we also incorporated the O2 uptake from the production of the co-emitted species NOx, CO and SOx. Furthermore, the oxidative ratios associated with sea shipping are refined using detailed fuel classification data from the Finnish Meteorological Institute (FMI). We will compare the results against global APO datasets, including COFFEE and GridFED, and drawing conclusions on consistency across the different inventories. Finally, we aim to collaborate closely with end-users of the inventory under the CORSO project, to assess the interpretability of results and ascertain the dataset’s relevance in supporting robust modelling practices. Through these refinements, we aim to contribute to the growing body of knowledge dedicated to more accurately quantify anthropogenic CO2 emissions, to help inform effective policies that support nations in achieving their objectives under the European Green Deal.

How to cite: el Malki, M., Visschedijk, A., and Denier van der Gon, H.: A high resolution gridded European Atmospheric Potential Oxygen (APO) inventory 2005 - 2020, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16750,, 2024.

On-site presentation
Carlos Gómez-Ortiz, Guillaume Monteil, Ute Karstens, Sourish Basu, and Marko Scholze

CO2 is one of the most important greenhouse gases responsible for global climate change. Today’s atmospheric CO2 concentration has risen by nearly 49% compared to pre-industrial times, mainly caused by fossil fuel combustion and cement production. CO2 emission reports under the Paris Agreement are crucial in understanding the main sources responsible for these emissions, and spatial and temporal distributed emission inventories such as EDGAR and ODIAC have been important tools to gain additional insights about when and where these emissions happen. However, increasing the resolution comes with an increment in the uncertainty at sub-annual and sub-national scales. One way to improve the knowledge on these emission inventories is by inverting in situ observations of CO2 and Δ14CO2 at regional scales. Radiocarbon (14C) is the radioactive isotope of carbon, and due to its half-life time of ~5730 years, it is not present in fossil fuels, making it a good tracer for the natural carbon cycle.

In this study, we evaluate the impact of incorporating Δ14CO2 observations from the Integrated Carbon Observation System (ICOS) network and its sampling strategy over Europe into the Lund University Modular Inverse Algorithm (LUMIA) for optimizing fossil CO2 and the biosphere fluxes in a horizontal grid of 0.5° x 0.5° and on a weekly temporal resolution. Δ14CO2 is currently mostly measured in 2-weekly integrated samples. As part of the EU-funded CORSO (CO2MVS Research on Supplementary Observations) Project, an intensive campaign collecting 1-hour flask samples every third day at 10 Western/Central European sampling stations will be performed during 2024. W perform a series of Observing System Simulation Experiments (OSSEs) using various model products (EDGAR/ODIAC, LPJ-GUESS/VPRM) as prior fluxes and as assumed true fluxes for fossil and biosphere fluxes to generate a time series of synthetic observations. We first demonstrate the impact of adding Δ14CO2 observations in addition to the CO2 observations to recover the true fossil and biosphere flux time series and the assumed true total CO2 annual budget over Europe. Further, we assess the impact of the sampling strategy by comparing a simulation using only Δ14CO2 integrated samples against a simulation including the CORSO sampling strategy. In the latter case, we find a notable improvement in recovering the fossil CO2 emissions in Western/Central Europe and countries such as Germany and France. We also evaluate other sampling strategies, such as selecting observations with the largest apportionment of fossil CO2 and the lowest impact of nuclear emissions. Such approaches seem to be a promising way to improve the quantification of fossil CO2 emissions in regions with a dense sampling network and neighbouring regions such as Eastern Europe.

How to cite: Gómez-Ortiz, C., Monteil, G., Karstens, U., Basu, S., and Scholze, M.: Evaluating the impact of using Δ14CO2 observations in quantifying fossil CO2 emissions over Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10553,, 2024.


Posters on site: Fri, 19 Apr, 16:15–18:00 | Hall X5

Display time: Fri, 19 Apr 14:00–Fri, 19 Apr 18:00
Chairpersons: Joachim Mohn, Javis Nwaboh, Tim Arnold
Measurement interpretation, use of models and inversion systems
Rebecca Fisher, Ceres Woolley Maisch, Dave Lowry, James France, Julianne Fernandez, Nicola Warwick, and Euan Nisbet

Use of both δ13C and δ2H measurements can be used to constrain methane sources. δ13C isotopes have been used to help identify the reasons for the continued growth in atmospheric methane, which since 2007 has coincided with a decline in δ13C. δ2H could offer a third dimension to help constrain the global methane budget, but its use has been limited because less data are available. There is a need for better identification of δ2H isotopic source signatures, and more long-term atmospheric data records.

We present results of field campaigns carried out in a variety of source regions to characterise isotopic signatures and consider complexities in constraining source signatures for some categories. We also consider use of methane isotopic measurements at different scales for source partitioning.

The isotopic signatures of urban emissions of methane have been characterised in London, Bucharest and Ho Chi Minh City. Methane sources in these cities are very different, with emissions being mostly from gas leaks in London, from wastewater and gas leaks in Bucharest, and from waste and traffic in Ho Chi Minh City.

Measurements of cattle methane emissions in Jersey and Kenya show different isotopic signatures in methane from manure and eructation. Cattle diet, the age of manure and waste management practices cause variability in the isotopic signature of emitted methane.

Wetland methane emissions from sites across Finland and Canada were collected in summer 2022. The Finnish boreal wetland methane isotopic signatures were δ2H -326 ± 19 ‰ and δ13C -68 ± 4 ‰, comparable with the results from Canada. Both δ2H and δ13C  in methane from boreal wetlands tends to be more depleted in the heavier isotope than in tropical wetland methane emissions.

Both δ13C and δ2H can be used in the UM-UKCA chemistry climate model which includes multiple methane tracers tagged by isotopic composition and source type. It is hoped that better characterisation of the regional variability in isotopic signatures of some sources will help improve the ability to model the global methane budget.

How to cite: Fisher, R., Woolley Maisch, C., Lowry, D., France, J., Fernandez, J., Warwick, N., and Nisbet, E.: Source apportionment of methane using δ13C and δ2H , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19065,, 2024.

Adrien Martinez, Marielle Saunois, Antoine Berchet, Isabelle Pison, and Philippe Bousquet

Estimating methane emissions using atmospheric inversion methods that assimilate only methane observations presents challenges in accurately attributing methane sources and sinks to specific emission sectors.

We explore the potential of co-assimilating observations of co-emitted species alongside methane observations to address this challenge and provide improved sectoral distribution of methane emissions.

Ethane is a promising candidate for this purpose. It is primarily co-emitted with methane in the fossil fuel emission sector, particularly through fugitive emissions from natural gas extraction, and is also co-emitted in the biomass and biofuel burning emission sectors, with negligible emissions in other sectors.

To assess the potential of co-assimilating ethane observations with methane observations, we use a global chemistry-transport model, LMDZ-SACS, with the Community Inversion Framework (CIF) to perform response functions analysis on methane and ethane emissions over a multi-year period.

We utilize the response functions results to meaningfully construct full source-receptor relationship matrices at available observation site, as well as, error covariance matrices for a control vector that includes both species emissions and initial conditions, and perform a large set of analytical inversions that assimilate in-situ and flask observations of both methane and ethane, as well as methane-only observations.

This methodology can not only provide improved estimates of the sectoral distribution of methane sources and sinks, but also extends the scope of the analysis to include ethane emissions.

How to cite: Martinez, A., Saunois, M., Berchet, A., Pison, I., and Bousquet, P.: Enhancing Methane Source Attribution through Co-Assimilation of Ethane Observations in Atmospheric Inversion Methods, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6317,, 2024.

Eunchong Chung, Tim Arnold, Chris Rennick, Emmal Safi, Dafina Kikaj, Brett Thornton, Alistair Manning, Stephan Henne, Anita Ganesan, and Ute Karstens

Greenhouse gas (GHG) emissions require accurate quantification for the development of effective mitigation strategies. Top-down methods to estimate GHG emissions combine ambient GHG measurements, atmospheric chemical transport models (ACTMs), and prior independent information on what is understood of fluxes (including isotopic source signatures where applicable). High frequency stable isotope ratio measurements of δ13C-CH4 and δH-CH4 have potential to help differentiate changes in the sources of CH4 emissions at regional scales. While independent efforts to make in situ, high frequency observations are being made at multiple locations, currently there is no network of harmonised measurements across Europe (with each site using different calibration and traceability strategies tailored to their specific analytical setup).


In this work we study CH4 isotope ratio measurements made at independently managed sites (Heathfield, UK; Heidelberg, Germany; and Zeppelin, Norway) using three different combinations of ACTMs and associated meteorology: NAME with the UK Met Office Unified Model; FLEXPART with ECMWF IFS analysis and short-term forecasts; and STILT with ECMWF IFS analysis and short-term forecasts. The use of multiple models aims to investigate the magnitude of simulated differences to evaluate model uncertainty in this system. We will demonstrate the extent to which model simulations can be used to investigate analytical problems (e.g. measurement offsets between sites) as well as provide initial results on the potential for a network of high-frequency in situ isotope ratio measurements to understand changes in European CH4 emissions over the coming decades.

How to cite: Chung, E., Arnold, T., Rennick, C., Safi, E., Kikaj, D., Thornton, B., Manning, A., Henne, S., Ganesan, A., and Karstens, U.: Use of multiple atmospheric chemistry transport models to interpret high frequency methane isotope ratio measurements at independently managed sites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19775,, 2024.

Pauline Bosio, Irène Xueref-Remy, Pierre-Éric Blanc, Aurélie Riandet, Grégory Gille, Alexandre Armengaud, and Sonia Oppo

Methane (CH4) is the second most important direct anthropogenic greenhouse gas after carbon dioxide (CO2). Its lifetime is 10 times shorter than that of CO2, and its warming potential 80 times greater over a 20-year period. Reducing methane emissions therefore represents a lever for rapid action on global warming. The Sud-PACA region (south-eastern France), classified by IPCC as a climate "hotspot", is part of these efforts to reduce CH4 emissions, with the aim of achieving carbon neutrality by 2050. To achieve this, it is essential to reduce the uncertainties of regional CH4 emissions. Although over 50% of regional methane is estimated to be emitted in the south-western part of the region, there are few CH4 measurements in this highly urbanized and industrialized area. With a view to filling this gap and better characterizing anthropogenic sources of CH4, a PICARRO G2401 CRDS analyser and meteorological station were set up in May 2021 as part of the ANR COol-AMmetropolis project at Port-de-Bouc (43°24'7.056''N; 4°58'55.459''E), surrounded by numerous petrochemical industries. This station continuously measures CH4, CO2 and CO concentrations to study the variability of these species for the different wind sectors.  The spatio-temporal variability of CH4 concentration and the identification of its sources using co-emitted species will be presented. All these data represent the first measurements of CH4 in this industrial area and will also be used to independently verify regional inventories. 

How to cite: Bosio, P., Xueref-Remy, I., Blanc, P.-É., Riandet, A., Gille, G., Armengaud, A., and Oppo, S.: Continuous in-situ measurements of atmospheric CH4 at the Port-de-Bouc urban-industrial station (south-east of France): a two-year analysis of CH4 spatio-temporal variability and source identification using co-emitted species., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10170,, 2024.

Balázs Áron Baráth, Tamás Varga, István Major, László Haszpra, Danny Vargas, and Mihály Molnár

The global impact of COVID-19 on communities and economies has led to questions about decreasing environmental risks and pollution due to the decreased industrial and transport activity. One of the key concerns revolves about the atmospheric rise in CO2 levels and the associated arising fossil carbon load, constituting the global climate change. The quantification of fossil-origin atmospheric carbon load is addressed through the use of natural radiocarbon (14C), a unique scientific tool. Fossil sources lack 14C activity, while recent biogenic carbon contains radiocarbon. This study centers on revealing long-term trends in atmospheric 14C levels, particularly during the year of the pandemic, in comparison to the preceding five years in Hungary. Atmospheric CO2 and tree rings from the studied six years were subjected to 14C analysis from three distinct locations.

One of the examined cities, Budapest - Hungary's capital - is a highly urbanized land with a reported 1.7 million population. Despite the city's extensive vehicular and human activity, a "state of danger" was in effect in Hungary from March to June 2020 due to the first wave of COVID-19. The sampling sites had been characterized by a busy urban environment, with a mix of vehicular activities contributing to the local atmosphere.

The second urban sampling site is Debrecen, a smaller but evolving city that can be found in the eastern part of Hungary. It’s the second largest Hungarian city - around 200 thousand citizens – and it is currently experiencing an industrial revolution by the construction of major factories. Significant contribution to pollution in this area come from urban vehicular traffic and the surrounding agricultural regions.

The background 14C signal used in the study is from the easternmost Integrated Carbon Observation System(ICOS) atmospheric regional background station (HUN) and NOAA background site, at Hegyhátsál. Mole fraction has been continuously monitored at four elevations at HUN station since September 1994. For this research integrated atmospheric 14CO2 samples, supplemented with CO2 mole fraction measurements, were used from October 2014 to December 2020. The data was studied from the aspect of temporal variation and altitudinal differences. CO2 mole fraction data of the free tropospheric background ICOS station at Jungfraujoch (Switzerland) were used. The outcomes of the trend analysis reveal the fluctuations in atmospheric fossil carbon load throughout the pandemic, which offers valuable insights into the environmental effects of reduced human activities in Hungary.

Prepared with the professional support of the Doctoral Student Scholarship Program of the Co-operative Doctoral Program of the Ministry of Innovation and Technology financed from the National Research, Development and Innovation Fund and supported by the PARIS project (Grant Agreement No. 820846), which is funded by the European Commission through the Horizon 2020 research programme.

How to cite: Baráth, B. Á., Varga, T., Major, I., Haszpra, L., Vargas, D., and Molnár, M.: Investigating the impact of COVID-19 on the atmospheric 14C trend and fossil carbon load at urban and background sites in Hungary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13083,, 2024.

Tamás Varga, István Major, Sándor Bán, Balázs Áron Baráth, Thomas Röckmann, Jacoline van Es, Carina van der Veen, and Mihály Molnár

The increasing level of atmospheric greenhouse gases and the effect of this trend, climate change, is one of the greatest environmental issues of the anthropogenic era. The increasing trend of greenhouse gas levels after industrialization is related to urban environments, where industrial and traffic-related activity and emissions are concentrated. In response to this, the European system, the ICOS (Integrated Carbon Observation System) was established and started the ICOS cities program, where coordinated greenhouse gas observations are carried out besides the regional background measurements and samplings. Similarly to this program, atmospheric air samples were collected at the Institute for Nuclear Research, Debrecen. During the sampling campaigns in three different seasons (winter, spring and summer), a minimum of 23 samples were collected in the morning and afternoon during weekdays and weekends as well. The samples are processed within a collaboration between Utrecht University, where the stable isotope composition of CO2 and CH4 were measured, and the Institute for Nuclear Research, Hungary, where the mole fraction of CO2 and CH4 and radiocarbon ratio of CO2 were measured. Based on the isotope composition results and stable isotope fingerprint of carbon dioxide and methane sources, the differentiation of the possible emission sources of these gases can be made. Using the radiocarbon, we can estimate the fossil CO2 contribution in urban areas. The preliminary results show that there is a great fossil contribution to the CO2 fraction, on the other hand, a great local biological contribution was observed in the CH4 fraction in every season. Based on measurements and literature, the source of the massive biological discharge could be the sewage pipeline system, even in winter. Our dataset shows that this kind of CH4 emitter can exceed fossil sources in Debrecen, Hungary.

How to cite: Varga, T., Major, I., Bán, S., Baráth, B. Á., Röckmann, T., van Es, J., van der Veen, C., and Molnár, M.: Methane and carbon dioxide observations at Debrecen, Hungary: mole fraction and isotope ratio measurements in three different seasons, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7845,, 2024.

Roberto Di Martino, Sergio Gurrieri, Antonio Paonita, Stefano Caliro, and Alessandro Santi

The atmospheric concentration of CO2 is crucial in urban areas due to its connection with air quality, pollution, and climate change. Monitoring airborne CO2 concentrations is vital for environmental management and public safety.  In the lower 50 meters of the atmosphere, CO2 emissions impact human health and ecosystems, making data at this level essential for addressing carbon-cycle and public-health questions. In volcanic zones, CO2 variations may correlate with volcanic activity, impacting local ecosystems and human health. In certain regions with high natural CO2 emissions, geogenic CO2 profoundly affects the environment. Despite volcanoes' local impact may be important, hydrocarbon combustion is the primary driver of increased atmospheric CO2 and global warming climate.

This study presents survey results on stable isotope composition of carbon and oxygen of CO2 and airborne CO2 concentration in the Campi Flegrei caldera, a high volcanic risk area threatening the Naples metropolitan area. In the last 50 years, two major volcanic unrests (1969–72 and 1982–84) were monitored using seismic, deformation, and geochemical data. The current unrest started in 2005, involving pressurization of the underlying hydrothermal system as a causal factor of the current uplift in the Pozzuoli area.

This research illustrates the use of a mobile laboratory to better understand emissions dynamics and quantify volcanic-origin emissions. Results shows that CO2 levels in Napoli's urban area exceed background atmosphere levels, indicating an anthropogenic origin from fossil fuel combustion. Conversely, in Pozzuoli's urban area, the stable isotope composition reveals a volcanic origin of the airborne CO2. This study demonstrates how a spatial survey of stable isotope composition of airborne CO2 is crucial for understanding emission dynamics. Distinguishing geogenic from anthropogenic emissions is challenging, especially through air CO2 concentration measurements alone. The findings emphasize the importance of monitoring atmospheric CO2, especially in areas with volcanic risks, contributing valuable insights for environmental and public health management.

How to cite: Di Martino, R., Gurrieri, S., Paonita, A., Caliro, S., and Santi, A.: Unveiling urban atmospheres: a comprehensive study on CO2 dynamics, air quality, and volcanic impacts in Napoli and Pozzuoli, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3765,, 2024.

Isotopic characterization of methane emissions in Malaga, Spain
(withdrawn after no-show)
Lucía Ojeda, Hossein Maazallahi, Iñaki Vadillo, Carina van der Veen, Antonio F. Castro-Gámez, and Thomas Röckmann
Sylvia Englund Michel, Pieter Tans, John Miller, John Ortega, Kerstin Braun, Taline Leon, Bruce Vaughn, Reid Clark, Jianghanyang Li, and James White

Monitoring the long-term changes in the stable carbon isotope ratio of carbon dioxide (expressed as δ13C-CO2) is a useful tool to track the fate of atmospheric CO2 and variations in the global carbon cycle. Due to the small but significant change in global mean atmospheric δ13C-CO2 of approximately -0.75‰ over the last three decades, a robust and traceable method is required to track the long-term change in δ13C-CO2 globally. The Stable Isotope Lab at the INSTAAR of the University of Colorado Boulder has been partnering with NOAA’s Global Monitoring Laboratory since 1990 to measure CO2 stable isotopes within the Global Greenhouse Gas Reference Network. Here, we present our latest data product, globally distributed observations of δ13C-CO2 in the past 32 years. We have improved our traceability by moving our data onto the CO2 -in-air JRAS-06 isotopic scale (a representation of V-PDB). We also have established robust quality management systems and have improved our methods of quantifying uncertainty.  Our data demonstrate how the interactions among the atmosphere, the biosphere and anthropogenic activities had been recorded in δ13C-CO2 from more than 70 sites worldwide. The data reveal distinct seasonal variations of δ13C-CO2 that change with latitude, highlighting spatial differences in the influence of anthropogenic activities, net photosynthesis, and ocean-atmosphere CO2 exchange. Long-term observations also show that the spatiotemporal patterns of δ13C-CO2 vary interannually, which is mainly related to the impact of climate variability on the terrestrial biosphere. We are actively engaged in using these data in complex modeling frameworks to better understand the inter-relationships between climate and the global carbon cycle.

How to cite: Michel, S. E., Tans, P., Miller, J., Ortega, J., Braun, K., Leon, T., Vaughn, B., Clark, R., Li, J., and White, J.: Thirty-two years of high precision data on the stable isotopes of carbon dioxide from a successful collaboration between NOAA and INSTAAR , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14041,, 2024.

Measurement advances and experimentation
Andrew Houston, Orestis Gazetas, Sara Defratyka, Tim Arnold, and Matthieu Clog

The multiply-substituted isotopologues of methane are of significant interest due to their increased ability to distinguish between methane formation and destruction processes, in comparison to singly-substituted isotopologues, as shown previously by Thiagarajan et al.(2022) and Sivan et al.(2022). Methane isotopologues, unlike the isotopologues of carbon dioxide, do not easily transition towards thermodynamic equilibrium in the atmosphere and therefore, ambient air methane isotopologues, offer constraints on the atmospheric methane sources and sinks (Chung and Arnold, 2021). These processes potentially offer new insight into the causes of variation in methane concentrations in the last two decades.

We present developments in the separation of the components of air, using a helium-cooled cryostat. Working on both pre-concentrated air mixtures and laboratory created gas mixtures, we extract methane from the contaminants and other atmospheric gases using the cryostat, applicable to a minimum methane concentration of ~1% (Stolper et al., 2015), then we analyse using a TFS Ultra HR-IRMS. We demonstrate that our cryostat separations successfully extract methane and krypton from laboratory gas mixtures containing the components of atmospheric air, without causing methane fractionation.

We also present further developments in measuring and calibrating the isotopologues of methane by high-resolution mass spectrometry. We successfully created thermodynamically equilibrated samples of methane in the 250-500oC range using a nickel catalyst and are working on the 1-250oC range using a γ-Al2O3 catalyst (Eldridge et al., 2019). It is essential to have an extensive calibration curve to best constrain the effects of scale compression on the calculated deltas and therefore reduce sources of further error, hence the extension of this calibration range.

Further work will add additional reference and sample points to the absolute reference frame created by the equilibrated samples, optimise the cryogenic/gas chromatographic purification methods for more complex gas mixtures, and optimise the IRMS workflow to reduce the necessary air sample sizes.



  • Chung, E. and Arnold, T., 2021. Potential of clumped isotopes in constraining the global atmospheric methane budget. Global Biogeochemical Cycles, 35(10), p.e2020GB006883.
  • Eldridge, D.L., Korol, R., Lloyd, M.K., Turner, A.C., Webb, M.A., Miller III, T.F. and Stolper, D.A., 2019. Comparison of Experimental vs Theoretical Abundances of 13CH3D and 12CH2D2 for Isotopically Equilibrated Systems from 1 to 500 C. ACS Earth and Space Chemistry, 3(12), pp.2747-2764.
  • Liu, Q., Li, J., Jiang, W., Li, Y., Lin, M., Liu, W., Shuai, Y., Zhang, H., Peng, P. and Xiong, Y., 2024. Application of an absolute reference frame for methane clumped-isotope analyses. Chemical Geology, p.121922.
  • Sivan, M., Röckmann, T., Slomp, C.P., van der Veen, C. and Popa, M.E., 2022, May. Isotopic characterization of methane: insights from clumped isotope (13CDH3 and CD2H2) measurements. In EGU General Assembly Conference Abstracts (pp. EGU22-4029).
  • Stolper, D.A., Martini, A.M., Clog, M., Douglas, P.M., Shusta, S.S., Valentine, D.L., Sessions, A.L. and Eiler, J.M., 2015. Distinguishing and understanding thermogenic and biogenic sources of methane using multiply substituted isotopologues. Geochimica et Cosmochimica Acta, 161, pp.219-247.
  • Thiagarajan, N., Pedersen, J.H., Brunstad, H., Rinna, J., Lepland, A. and Eiler, J., 2022. Clumped isotope constraints on the origins of reservoir methane from the Barents Sea. Petroleum Geoscience, 28(2), pp.petgeo2021-037.

How to cite: Houston, A., Gazetas, O., Defratyka, S., Arnold, T., and Clog, M.: Further Cryogenic Separation and Mass Spectrometry Developments: Towards Ambient Air Methane Clumped Isotopes Measurements , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11447,, 2024.

Simon Leitner, Kathiravan Meeran, and Andrea Watzinger

The measurement of the stable carbon and oxygen isotope ratio of (atmospheric) carbon dioxide (CO2) is a useful technique for the investigation and identification of the sources and sinks of the most abundant greenhouse gas by far. For this reason, we are presenting a measuring system here that enables a wide range of users to carry out stable isotope analysis of atmospheric CO2 using off the bench hard- and software.

The fully automated system uses cryogenic and gas chromatographic separation to analyse CO2 from 12 mL whole air samples and consists of an autosampler, a Gasbench II, a downstream cryo trap and a continuous flow gas interface feeding into a sector field mass spectrometer (GC Pal/Gasbench II/Cold Trap/Conflo IV/DeltaV Plus). The evaluation of the system performance was based on the analysis of samples prepared from eight CO2 sources (four CO2 reference gases and four artificial air tanks).

The overall measurement uncertainty (averaged single standard deviation (1σ) of measurement replicates from each CO2 source) in the determination of the carbon and oxygen isotope ratio was 0.04 ‰ and 0.09 ‰ (n=24). Furthermore, we were able to show that the measurement data also allowed for the quantification of the CO2 mole fraction, with a precision of 1.2 µmol mol-1 in the analysis range of 400 to 500 µmol mol-1.

The method to be presented was summarized and published in the form of a protocol (DOI: 10.1002/rcm.9647) providing a detailed description of the measurement setup and the analysis procedure, how raw data should be evaluated and gives recommendations for sample preparation and sampling to enable a fully automated whole air sample analysis. We look forward to further discussion with interested users to elaborate on potential improvements/extensions/application options.

How to cite: Leitner, S., Meeran, K., and Watzinger, A.: Stable isotope analysis of atmospheric CO2 using a Gasbench II – Cold Trap – IRMS setting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8275,, 2024.

Noémy Chénier, Paul M. Magyar, Lukas Emmenegger, Moritz F. Lehmann, and Joachim Mohn

Nitrous oxide (N2O), a potent greenhouse gas, primarily stems from oxidative (e.g. nitrification) and reductive (e.g., denitrification) microbial processes in aquatic and terrestrial environments. To better understand spatial and temporal N2O production, the isotopic composition of N2O, specifically 15N/14N and 18O/16O ratios, and the intramolecular distribution of 15N (i.e., site preference, SP), are typically used[1]. Distinguishing multiple concurrent processes with three isotope parameters (δ15N, δ18O, SP) remains, however, a challenge, especially in light of uncertainties regarding the isotope effects for individual processes.

Here, we study the isotope effects of N2O production imparted by denitrification, focusing specifically on the intermediate step of nitrite (NO2-) reduction to nitric oxide (NO), which is catalyzed by various nitrite reductases. We study three bacterial denitrifiers: Pseudomonas chlororaphis subsp. aureofaciens, Pseudomonas chlororaphis, and Pseudomonas stutzeri. These bacteria utilize similar nitric oxide reductases (NorB) enzymes, but different nitrite reductase variants (NirS vs. NirK). We anticipate similarities in SP values, mostly controlled by NorB, but differences in δ15N-bulk and δ18O values for generated N2O, given the distinct nitrite reductase enzymes[2]. P. stutzeri strain JM300, expressing both NirS and NirK genes[3], offers a unique opportunity for studying each enzyme's distinct functions and isotopic signatures.

Selected strains are incubated in batch experiments of a 0.5 L bioreactor using nitrate as a substrate. The bioreactor's headspace is continuously purged with N2. We monitor bacterial growth, NO2- concentrations, dissolved O2, pH, and temperature throughout the experiment. Simultaneously, we daily collect one sample for nitrite and nitrate N and O isotope analysis. After removing CO2 and water, N2O concentrations are monitored with Fourier-transform infrared spectroscopy. The isotopic composition of N2O is measured online using quantum-cascade-laser spectroscopy, providing real-time analysis with high precision (< 0.1 ‰). This enables real-time tracking of changes in the N and O isotope systematics (i.e., fractionation), in response to changing reaction kinetics.

The preliminary data that we present will lay the basis for future investigations into the constraints on systematic heavy-isotope clumping (i.e., relative abundance of doubly substituted N2O isotopologues 15N15N16O, 14N15N18O, 15N14N18O) associated with microbial N2O production. Specifically, we will verify direct and indirect enzymatic controls (i.e., type of Nir; N-O bond equilibration with water) on the clumped-isotope abundance of 14N15N18O.


[1] Toyoda, S., et al. (2017). Isotopocule analysis of biologically produced nitrous oxide in various environments. Mass Spectrometry Reviews, 36(2), 135-160.

[2] Martin, T. S., et al. (2016). Nitrogen and oxygen isotopic fractionation during microbial nitrite reduction. Limnology and Oceanography, 61(3), 1134-1143.

[3] Wittorf, L., et al. (2018). Expression of nirK and nirS genes in two strains of Pseudomonas stutzeri harbouring both types of NO-forming nitrite reductases. Research in microbiology, 169(6), 343-347.

How to cite: Chénier, N., Magyar, P. M., Emmenegger, L., Lehmann, M. F., and Mohn, J.: Isotopic fractionation of N and O in N2O from denitrification: insights from the comparative analysis of Pseudomonas strains with distinct nitrite reductase enzymes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3351,, 2024.

Reinhard Well, Caroline Buchen-Tschiskale, Joachim Burbank, Michael Dannenmann, Dominika Lewicka-Szczebak, Joachim Mohn, Lena Rohe, Clemens Scheer, Salvatore Tuzzeo, and Benjamin Wolf

There is need to calibrate raw data of N2 and N2O isotopocules due to effects of non-linearity, instability, matrix effects and interference with trace gases. Our objective was thus to supply a variety of suitable standard gases for members of the DASIM research unit ( and their partners in sufficient amount for routine use to enable calibration for extended time. In total 23 different mixtures were produced to cover all isotopic approaches to study N2 and N2O production and cycling in soils with stable isotopes and suitable for IRMS and laser spectroscopy.

Standards for the 15N gas flux method should mimic mixtures of N2 and N2O emitted from highly 15N enriched nitrate in soil and atmospheric background. These must thus contain unlabelled, single-labelled  as well as double-labelled N2 and N2O.

N2O standards for natural abundance must cover a range of N2O concentrations and isotopocule values typically found in field flux and laboratory incubation studies to correct for non-linearity and bias.

Premixtures were prepared by mixing isotopically enriched or depleted gases which were either commercially available or produced in the lab. Moreover, pure N2O of natural abundance was supplied from a previous project (Mohn et al., 2022, Premixtures were diluted in artificial atmospheres and compressed in commercial tanks.

We will explain the production of mixtures, give an overview of the manufactured mixtures and show first results of analysis in comparison with ideal values.

How to cite: Well, R., Buchen-Tschiskale, C., Burbank, J., Dannenmann, M., Lewicka-Szczebak, D., Mohn, J., Rohe, L., Scheer, C., Tuzzeo, S., and Wolf, B.: Production of standard gases for routine calibration of stable isotope ratios of N2 and N2O , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11996,, 2024.

Paul Magyar, Ivan Prokhorov, Simone Brunamonti, Noémy Chénier, Lukas Emmenegger, Béla Tuzson, and Joachim Mohn

Nitrous oxide (N2O), a greenhouse gas and ozone-depleting molecule with a 116-year atmospheric lifetime, is accumulating in the atmosphere at an accelerating pace. While it is known that the conversion of anthropogenic nitrogen pollutants to N2O by the environmental nitrogen cycle predominately drives this accumulation, essential questions remain regarding the spatial and temporal balance of N2O production and consumption. Stable isotope measurements of δ15N, δ18O, and 15N site preference (SP) in N2O provide valuable constraints on its sources and sinks. Given the complex array of nitrogen cycle processes and their overlapping isotopic signatures, they are often not sufficient to deconvolve them completely. The ‘clumped’, or multiply-substituted, isotopologues 14N15N18O, 15N14N18O, and 15N15N16O provide three additional independent constraints on N2O sources and processing, with potential to provide insight into source partitioning and reaction mechanisms.

Spectroscopic approaches have emerged as central tools for quantification of N2O isotopes in atmospheric and environmental samples due to their sensitivity, suitability for continuous or on-site measurement, and isotopologue-specificity. We present an updated approach to the measurement of the eight most abundant isotopic variants of nitrous oxide, including these rare clumped isotopologues, using a quantum cascade laser absorption spectrometer with a 36 m multipass cell. A dual-laser system offers the opportunity to choose a pair of spectral windows that contains strong ro-vibrational absorption lines of the rarest isotopologues, enabling precise clumped isotope ratio measurements on relatively small (<10 µmol) sample amounts. Samples are introduced to the spectrometer and compared to reference materials through a customized gas inlet system, which enables fast switching between samples and references, thereby maximizing reproducibility and sample throughput. Nitrous oxide heated in the presence of γ-alumina at 200 ºC has previously been found to approach equilibrium compositions of 15N14N18O, 14N15N18O, and SP. We constrain the controls on this catalytic reaction by varying temperature, pressure, substrate and catalyst concentrations, and catalyst activation conditions; and we confirm the equilibrium nature of this reaction under various conditions by heating reference gases prepared gravimetrically to have 15N14N18O, 14N15N18O, 15N15N16O, and 14N14N18O elevated above natural abundances. Finally, equilibrating N2O at several distinct temperatures gives multiple anchor points to an absolute reference scale for clumped and position-specific isotope measurements, enabling future measurement of samples from natural sources.

How to cite: Magyar, P., Prokhorov, I., Brunamonti, S., Chénier, N., Emmenegger, L., Tuzson, B., and Mohn, J.: Advances in clumped isotope measurements of nitrous oxide by laser spectroscopy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15126,, 2024.

Joachim Mohn, Kerstin Zeyer, Michelle J Müller, Paul Schlauri, Martin K. Vollmer, Daniela Brito Melo, and Stephan Henne

Methane (CH4) is the second most significant greenhouse gas after carbon dioxide. The concentration of methane in the atmosphere has been continuously increasing for several years and is currently at almost 2000 ppb. Methane emissions arise from a variable mix of thermogenic sources, such as oil, natural gas, and coal mining, or biogenic sources, such as wetlands and agriculture. Co-emitted gases such as ethane (C2H6) and other hydrocarbons can be utilised as a tracer to discern thermogenic (co-emission of ethane) and biogenic (no ethane is emitted) methane sources (Commane et al., 2023,

Ethane concentrations in the Northern hemisphere were decreasing between 1970 and 2010, which was attributed to better emission controls from oil and gas production, storage, and distribution, as well as exhaust emissions from cars and trucks. However, emissions are currently on the rise once again, linked to additional emissions from oil and gas production for example from the Eastern USA, (D Helmig et al., 2016,

In November 2023 we started CH4 / C2H6 measurements in ambient air from a rooftop air inlet (approx. 15 m above ground) at the Empa research campus in Dübendorf, Switzerland using a MIRA Ultra analyser (AERIS Technologies, USA). To correct for drift effects and to calibrate the analyser, two cylinders of compressed air were analysed in regular time intervals. To minimize interferences of water vapour, sample and calibration gases were dehumidified. Concentration measurements were compared to results of a CRDS analyser (model 2401, Picarro, USA) for CH4 and to a GC-MS system (model 5975C, Agilent Technologies, USA) for C2H6.

Compressed air measurements demonstrate that the MIRA Ultra gas analyser meets the manufacturer's specifications of sensitivity for CH4 and C2H6 of < 1 ppb/s and < 500 ppt/s, respectively. We will present a comparison of C2H6/CH4 data from the MIRA ULTRA analyser and GC-MS / CRDS. We foresee to complement CH4/C2H6 measurements with CH4 isotope analysis (δ13C, δD-CH4) by TREX-QCLAS and relate temporal variations to differences in CH4 source contributions by means of FLEXPART simulations.

How to cite: Mohn, J., Zeyer, K., Müller, M. J., Schlauri, P., Vollmer, M. K., Brito Melo, D., and Henne, S.: Measurement of atmospheric methane and ethane at a suburban site using mid-IR absorption spectroscopy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16736,, 2024.

Julius Havsteen, Mehr Fatima, Simone Brunamonti, Thomas Hausmaninger, Andrea Pogány, Reinhard Well, and Joachim Mohn

Nitrous oxide (N2O) has a significant global warming potential of about 300 times that of CO2 and a steadily rising atmospheric concentration. Therefore, understanding N2O production and consumption pathways in major source ecosystems, such as agricultural soils, coupled with accurate quantification of associated N2O emissions, is critically important in the context of climate change.

The relative abundance of 15N and 18O substituted N2O isotopocules (e.g.,14N15N16O, 15N14N16O, 14N14N18O) to the predominant isotopic form (14N14N16O) serves as valuable tracers for the distinction between important biogeochemical soil processes, such as nitrification and denitrification, which in turn enhances our understanding of N2O emissions. In this regard, advances in cavity-ring-down-spectroscopy (CRDS) have enabled precise measurement of isotopic species in ambient N2O, which holds key advantages over isotope ratio mass spectrometry in its ability to measure online, on-site and site-specific with respect to 15N substitution in the N2O-molecule.

Despite the CRDS technique's ease in measuring the isotopic composition of N2O-isotopocules, the apparent isotope data requires significant post-processing, since spectral fitting is controlled by a complex interplay between fundamental physical parameters, instrumental parameters, gas matrix composition, instrumental drift, and fitting algorithms, some of which also depend on the absolute N2O concentration. Therefore, to retrieve accurate and comparable results, it is necessary to apply appropriate reference gases with minimal differences in gas composition to the sample in the measurement sequence. Remaining deviations between sample and reference have to be post-corrected using predefined, analyser-specific correction functions.

This work provides a comprehensive and detailed correction and calibration protocol, exemplified by the reduction of N2O isotopic data obtained from a Picarro G5131-i isotopic and gas concentration analyser. This protocol outlines the theoretical and mathematical framework for the necessary corrections and suggests a logical order for applying these corrections. Moreover, the protocol provides a standalone MATLAB code for streamlined and automatic data reduction that can be employed once the required analyser-specific correction functions are established. The developed algorithms were validated on a suite of target gases, which accounts for concentration-based interferences from various species.

With this protocol, we aim to enable researchers to accurately and efficiently acquire high-quality N2O isotope data from CRDS instruments and similar devices and contribute to standardized community guidelines for post-processing N2O isotope data. In a prototype application, we analysed N2O from automated flux chambers to track biogeochemical processes in agricultural soils. Subsequently, these insights will be integrated into soil biogeochemical models, to enable upscaling of emission data.

How to cite: Havsteen, J., Fatima, M., Brunamonti, S., Hausmaninger, T., Pogány, A., Well, R., and Mohn, J.: Challenges in N2O isotope measurements using CRDS analysers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17480,, 2024.

Christopher Rennick, Cameron Yeo, Freya Wilson, Emmal Safi, Emily Hopkinson, Aimee Hillier, Ruth Pearce, James France, Mathias Lanoiselle, David Lowry, and Tim Arnold

The stable isotopic signatures of atmospheric methane (CH4) – carbon δ 13C(CH4) and hydrogen δ 2H(CH4) – are tracers that can help distinguish the relative contributions from different emissions sources. Optical isotope ratio spectrometers (OIRS) deployed at atmospheric monitoring stations have the capability for continuous measurements, providing time series data that can complement sampling campaigns using isotope ratio mass spectrometry (IRMS). OIRS instruments, however, require larger volumes of calibration gases than IRMS and the measurement is of the isotopologues directly (12CH4, 13CH4 and 12CH3D) rather than conversion to CO2 and H2. Here, we demonstrate the calibration method for Boreas, a preconcentrator-OIRS system deployed at an atmospheric monitoring station in the South of England and show that these measurements are compatible with those made by IRMS. Measurements with Boreas are referenced to a whole air working standard that is sampled in sequence with air, following the principle of identical treatment. We show the results of a field comparison to IRMS measurements of bag samples taken from the same air inlet simultaneously with the preconcentrator.

The calibration method uses mixtures prepared gravimetrically at a range of amount fractions from a single high-purity CH4 parent that has been characterised for δ 13C and δ 2H by IRMS. This method is capable of calibration over a wide range of amount fraction and isotopic composition. A rigorously derived uncertainty budget shows that the major contributions are from the uncertainty in the assignment of δ 13C and δ 2H of the methane parent and the spectrometer, with minimal contribution from uncertainty in the amount fraction of the standards.

How to cite: Rennick, C., Yeo, C., Wilson, F., Safi, E., Hopkinson, E., Hillier, A., Pearce, R., France, J., Lanoiselle, M., Lowry, D., and Arnold, T.: Calibration uncertainty of optical isotope ratio spectroscopy measurements of methane and field comparison with mass spectrometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17623,, 2024.

Javis A. Nwaboh, Jelka Braden-Behrens, Anas Emad, Henning Bohlius, and Volker Ebert

Accurate measurements of amount fractions and isotopic compositions of greenhouse gas such as carbon dioxide (CO2) and methane (CH4) provide valuable insights on their atmospheric composition and origin. Commonly used field deployable commercial laser spectrometers that measure amount fractions and isotopic ratios are often calibrated with reference gases with certified amount fractions and/or isotopic composition. Reference gases, also known as calibration reference materials (CRMs), can be for example synthetic mixtures of e.g. CO2 in N2, where the gas matrix N2 does not match that of the sample (e.g. ambient air) to be measured. A mismatch in the composition of the gas matrix of a CRM and sample can lead to a considerable bias in the amount fraction or isotopic ratio results of the sample due to changes in the measured spectra which e.g. are not perfectly captured by the analysers’ fitting routine.

In this work, we demonstrate the quantification of matrix effects for two commercial CRDS analysers measuring CO2 and CH4 amount fractions and isotope ratios. In our experiments with synthetic air gas matrix where the O2 concentration was varied, we measured (for a 1 % change in the O2 concentration in the gas matrix) a relative change of 0.15 % for the amount fractions of two major CO2 isotopologues and 0.07 % for the amount fractions of two major CH4 isotopologues. Similarly, in terms of isotopic δ13C values, we found matrix effects larger than 0.2 for both CO2 and CH4. We present options for correcting the gas matrix effects and discuss the underlying assumptions made during the analysis. Amount fraction results for CO2 and CH4 are reported including δ13C isotope ratio results. Our work concludes that a matrix mismatch when using a commercial laser spectrometer can lead to considerable biases in amount fraction and isotope ratio results, and appropriate correction approaches have to be applied in order to achieve accurate and reliable results.

Acknowledgements: This work has received partial funding from the EMPIR programme (19ENV05 STELLAR project) co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme. Part of this work has also received funding from the European Partnership on Metrology (21GRD04 isoMET project), co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States. 


How to cite: Nwaboh, J. A., Braden-Behrens, J., Emad, A., Bohlius, H., and Ebert, V.: Quantifying and empirically correcting apparent gas matrix effects:Example measurements for two CRDS analyzers for CO2 and CH4 amount fractions and 13/12C isotope ratios , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18802,, 2024.

Olav Werhahn, Lukas Flierl, and Olaf Rienitz

The isotopic composition of carbon dioxide is a powerful tool in many scientific areas and normally reported as isotope δ’s, viz. δ13CVPDB in case of carbon and δ18OVPDB-CO2 in case of oxygen. These two isotopic quantities must be calculated from the measured molecular quantities. This includes an 17O correction, which is an important step in data evaluation. Due to the measurement conditions, typically available experimental information is insufficient on 17Oand the calculative correction must be done iteratively. The fact that there is no analytical solution complicates the calculation of δ13CVPDB and δ18OVPDB-CO2 as well as the calcuation of the associated uncertainties. Therefore, Brand et al. [1] suggested a linear approximation which performs quite well. Moreover, Brand et al. presented a simplified scheme for uncertainty estimation. Here, we present an alternative approximation [2] which outperforms the established one leading to much smaller deviations from the exact solutions and to uncertainty calculations according to the Guide to the Expression of Uncertainty in Measurement (GUM) [3]. These approximations are implemented in an EXCEL Add-in, which allows potential users to gain full control over their data evaluation and to check the data received from commercial IRMS software in a spreadsheet.

This work is embedded in PTB’s commitment to the metrology for environment and climate which is overseen by the Innovation Cluster Environment & Climate [4].



W. A. Brand, S. S. Assonov und T. B. Coplen, „Correction for the 17O interference in δ(¹³C) measurements when analyzing CO₂ with stable isotope mass spectrometry (IUPAC Technical Report),“ Pure Appl. Chem., Bd. 82, p. 1719–1733, January 2010.


L. Flierl und O. Rienitz, „OCEAN – an EXCEL Add-in for 17O Correction using a novel Approximation,“ MethodsX, p. 102529, 2023.


Joint Committee for Guides in Metrology, „JCGM 100: Evaluation of Measurement Data - Guide to the Expression of Uncertainty in Measurement,“ 2008.


Physikalisch-Technische Bundesanstalt, „Innovation Cluster Environment & Climate,“ [Online]. Available:


How to cite: Werhahn, O., Flierl, L., and Rienitz, O.: Isotope Analysis as a tool for climate metrology at PTB: a novel approach to oxygen-17 correction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20557,, 2024.

Mehr Fatima, Javis Nwaboh, Joachim Mohn, Tim Arnold, and Volker Ebert

Methane (CH4) is a greenhouse gas (GHG) with both anthropogenic and natural sources. It also contributes to air quality problems through its role in tropospheric ozone formation. Key source categories of anthropogenic CH4 emissions in Europe are the agricultural sector (~50 %), waste (~22 %), and energy (~15 %), which makes them the focus of intense research for developing mitigation actions. Stable isotope ratio measurement in CH4 provide the information needed to verify emissions by source type. To provide comparable and accurate atmospheric CH4 isotope ratios, there is an increasing need to develop metrological harmonized measurements protocols and procedures. In addition, there is a lack of a metrological infrastructure for source signature information needed to interpret atmospheric isotope ratio measurements, as well as an assessment of uncertainties in atmospheric transport models and inverse estimates of Europe's CH4 emissions.

Here, we present the isoMET project that aims to (a) develop a harmonised in situ CH4 isotope dataset of ambient air in Europe to resolve compatibility issues of measurements of δ13C or δ2H in CH4 across multiple laboratories, b) develop a sustainable metrological infrastructure for a dataset for δ13C(CH4) and δ2H(CH4)-emissions source measurements in Europe and to evaluate the potential for source apportionment through clumped isotopes, c) use atmospheric chemistry transport modelling to inform the work in (a) and (b), creating estimates of the minimum measurement requirements for deployed instruments.



[1] isoMET project available at:

[2] J. A. Nwaboh, J. Mohn, M. Fatima, T. Arnold, V. Ebert, Metrology for European emissions verification on methane isotopes (isoMET), CCQM GAWG-IRWG Workshop on Carbon Dioxide and Methane Stable Isotope Ratio Measurements, LATU (Uruguay), 2023

Acknowledgements: The project 21GRD04 isoMET project has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States.  Empa has received funding from the Swiss State Secretaritat for Education, Research and Innovation (SERI).


How to cite: Fatima, M., Nwaboh, J., Mohn, J., Arnold, T., and Ebert, V.: The isoMET project on ambient CH4 monitoring, source signature information and modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20560,, 2024.