- Isotopologues of carbon dioxide (CO2), water (H2O), methane (CH4), carbon monoxide (CO), oxygen (O2), carbonyl sulfide (COS), and nitrous oxide (N2O)
- Novel tracers and biological analogues
- Polyisotopocules including "clumped isotopes"
- Non-mass-dependent isotopic fractionation and related isotope anomalies
- Intramolecular stable isotope distributions ("isotopomer abundances")
- Quantification of isotope effects
- Analytical, methodological, and modelling developments
- Flux measurements
Progress in the development of pure CO2 gas standards for δ13C, δ18O and Δ47 measurements as well as CO2 in air gas standards (with mole fractions in the range 350 µmol/mol to 800 µmol/mol) for δ13C, δ18O measurements are described. Initial results indicate the potential to produce standards with internal consistencies at the 0.005 ‰ level for δ13C and standard uncertainties of 0.015 ‰ in relation to the VPDB scale, with the magnitude of the latter principally limited by the homogeneity of primary carbonate reference materials.
An initial driver for standards development was the requirement for appropriate calibration strategies and standards [1] to support commercially developed laser-based instruments that have grown in number over the last decade. These analysers can measure real-time isotopic ratio variations of greenhouse gases, and notably CO2, allowing their application across a wide range of scientific and technical disciplines. The development of appropriate standards and calibration methods has required the links and traceability to primary carbonate materials via the IRMS dual inlet reference method to be re-examined.
Outputs of the project so far include:
Establishment of a facility to produce stable pure CO2 gas standards in 6L cylinders at 2 bar with δ13C values from -1 ‰ to +45 ‰ vs VPDB, with internal consistency approaching the 0.005 ‰ level, and an effective calibration option for dual inlet IRMS systems as demonstrated in the international comparison CCQM-P204 completed in 2021 [2];
Studies of Δ47 values of mixtures of different pure CO2 gas, and the reproducibility and stability of these and their potential to act as reference standards for clumped isotope ratio measurements with IRMS systems;
The development and validation of a cryogenic Air Trapping system to extract CO2 from air for determination of δ13C and δ18O-CO2 with IRMS, including a correction for the N2O present in samples. The facility is currently being used for another international comparison (CCQM-P239) of CO2 in in air standards from 15 institutes containing CO2 over the range of 380 μmol mol−1 to 800 μmol mol−1 and δ13C and δ18O-CO2 values from 1 ‰ to -43 ‰ and -7 ‰ to -35 ‰, respectively. The method demonstrates excellent reproducibility, with standard deviations of 0.005% and 0.05% for δ13C and δ18O-CO2, respectively, and will demonstrate the level of equivalence of new CO2 in air isotope ratio standards currently being produced.
[1] Flores, E., Viallon, J., Moussay, P., Griffith, D. W. T. & Wielgosz, R. I. Calibration strategies for FT-IR and other isotope ratio infrared spectrometer instruments for accurate δ13C and δ18O measurements of CO2 in air. Anal. Chem. 89, 3648–3655 (2017).
[2] J Viallon et a, Final report of CCQM-P204, comparison on CO2 isotope ratios in pure CO2, 2023 Metrologia 60 08026 DOI 10.1088/0026-1394/60/1A/08026
How to cite: Viallon, J., Wielgosz, R., Flores, E., Choteau, T., and Moussay, P.: New standards for isotope measurements of CO2 for atmospheric and biogeoscience applications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-443, https://doi.org/10.5194/egusphere-egu25-443, 2025.
During the AMT31 research cruise (Southampton–Montevideo, December 2024), we measured CO2 polyisotopologues using a tuneable infrared laser direct absorption spectrometer (Aerodyne TILDAS-FD-L2). Dried marine air from an inlet at the bow of the ship was alternated with a working reference every 2 min to correct for instrument drift.
Compared with land-based measurements, ship motion (roll, pitch, heave) was found to deteriorate isotope ratio precision by a factor of 3 to 10 (depending on the sea state). However, after averaging over hourly intervals, precisions better than 0.05 µmol mol–1 for y(CO2) and better than 0.03 ‰ for δ(13C), δ(18O) and δ(17O) were achieved. For the 17O isotope excess, Δ(17O), hourly precision was often better than 10 ppm (0.01 ‰), but unfortunately, target tank results showed unexplained day-to-day variability of the order of ±35 ppm.
Preliminary corrections for this day-to-day variability indicate that southern hemisphere δ(18O) is 1.2–1.8 ‰ higher and Δ(17O) is about 60 ppm higher than northern hemisphere marine background air. This interhemispheric Δ(17O) gradient is twice as high as predicted by atmosphere-biosphere exchange models (Koren et al., 2019) and could indicate a stronger than expected influence of the 17O-enriched stratospheric return flux in austral spring or a stronger biospheric exchange signal in boreal autumn.
How to cite: Kaiser, J., Pickers, P. A., Forster, G. L., Marca, A., Paxton, R. B., and McManus, B.: Atlantic Meridional Transect of polyisotopic carbon dioxide: Challenges of ship-based laser spectroscopy and implications for atmosphere-biosphere exchange, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13314, https://doi.org/10.5194/egusphere-egu25-13314, 2025.
Measuring stable carbon isotope ratios is a powerful method to study both the environment and ecosystems. The isotope ratios can be used as evidence of geological development or in climate sciences to study system interactions where it provides crucial insights about the ecosystem gas exchange. Mass spectrometry has remained the golden standard for stable carbon isotope analysis in solids and Isotope Ratio Mass Spectrometry (IRMS) has been applied in numerous use cases due to its precision and selectivity. However, the demand for on-site and in-situ capable carbon isotope monitoring methods is increasing.
In this work, we present an in-situ-capable, all-optical method for stable carbon isotope ratio measurements in solid samples that combines laser ablation and on-chip tunable diode laser absorption spectroscopy (TDLAS). Laser ablation is used to transform the samples from solid to gas phase. The gas is then transported with a carrier flow through a microfluidic system, passing a particle filter and into the µl detector volume. The small sample volume is enabled by a suspended nanophotonic waveguide-based TLDAS sensor which was recently demonstrated for isotope-specific CO2 detection with a 20 ppb detection limit and isotope ratio accuracy of 0.2 ‰. Thus, the combination of an on-chip CO2 detector and laser ablation enables the construction of a compact and portable, all-optical sensor for stable carbon isotope ratio measurements.
The presented measurement technology generates a paradigm shift in studies integrating the ecological, biological, and geochemical processes. This approach has high sample throughput with ~1 min measurement time due to the minimal requirement of sample treatment, enabling measurement of large sample sets. In addition, the measurement system can be applied to both solid and liquid samples enabling rapid, on-site screening of ecosystem carbon cycle.
How to cite: Seton, R., Jágerská, J., and Viljanen, J.: In-situ stable carbon isotope measurements with laser ablation and on-chip laser absorption spectroscopy , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20440, https://doi.org/10.5194/egusphere-egu25-20440, 2025.
To study the geochemical cycles of important greenhouse gases, it is helpful to go beyond measuring their concentrations. Measurements of isotopic ratios can help identify emission sources and study biological and chemical processes. This can include laboratory incubation experiments in soil, agricultural and grass lands, wastewater, and other microbial active aqueous solutions.
The abundances of the 15N and 18O isotopes can be compared to the main isotope 14N14N16O, revealing the distinct isotopic signatures. As a linear molecule with two nitrogen atoms, N2O has two structural isomers of identical mass, which cannot be distinguished by mass spectroscopy. Therefore, a geometry sensitive laser spectroscopy-based approach is required.
The new MGAi-N2O from MIRO Analytical simplifies the monitoring of N2O isotopic composition by enabling simultaneous online measurements of up to 5 major isotopologues of N2O at high measurement rates, while providing excellent stability and precision at a fraction of the cost of isotope mass spectrometers.
In our presentation we will demonstrate the simultaneous measurement of 5 isotopologues of N2O including 17O using our recently launched MGAi-N2O analyzer. Measurements of different samples, showing high stability and precision, illustrate the potential but also the limitations of this novel analyzer. In addition to continuous flow, a batch sampling mode option will be introduced and characterized. Recent improvements in the measurement of novel tracers such as OCS and HONO, combined with up to 9 other gases in a single instrument, will also be presented.
How to cite: Bruckhuisen, J., Hundt, M., Hlubucek, J., Smith, E., and Aseev, O.: High precision QCL based direct detection of stable isotopes and tracers in bio-geoscience, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17839, https://doi.org/10.5194/egusphere-egu25-17839, 2025.
Carbonyl sulfide (OCS) is the major long-lived sulfur-bearing gas in the atmosphere. The main sink for COS occurs when it diffuses through the plant leaves stomata and enters the mesophyll cell, where it reacts with the enzyme carbonic anhydrase. Since CO2 enters the leaves by a similar pathway, COS has been used to estimate the rates of regional and global photosynthesis. For example, recently 1, it was suggested that the global GPP is ~30% higher than estimated so far, based on COS observations and new modeling of COS internal conductance, which relates to the diffusion into the active site in the mesophyll. Sulfur isotope analysis (34S/32S ratio, δ34S) of COS was shown 2 to be useful for improving the determination of atmospheric COS sources and sinks. The sulfur isotopic fractionation during COS uptake in plants is needed for using this tool, but so far, has only been established in the lab. In that study, the fractionation was found to be −1.6 ± 0.1‰ for C3 plants, −5.4 ± 0.5‰ for C4 plants, and the carbonic anhydrase fractionation was estimated indirectly as −15 ± 2‰. Field studies of leaves' COS uptake enable the study of the effects of varying light conditions in the tree canopy. Here, we measured the COS fractionation during uptake in an Austrian alpine forest, using branch chambers at three height levels in a Pinus sylvestris canopy. In addition, we directly measured the fractionation of carbonic anhydrase in vitro in the lab. The isotopic analysis was conducted by pre-concentrating the air samples and subsequent δ34S analysis by gas chromatography (GC) connected to a multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS). The results of this research are important for improving both leaves scale COS transport models and global budgets of COS and CO2.
1. Lai, J., Kooijmans, L. M., Sun, W., Lombardozzi, D., Campbell, J. E., Gu, L., ... & Sun, Y. (2024). Terrestrial photosynthesis is inferred from plant carbonyl sulfide uptake. Nature, 634, 855-861.
2. Davidson, C., Amrani, A., & Angert, A. (2021). Tropospheric carbonyl sulfide mass balance based on direct measurements of sulfur isotopes. Proceedings of the National Academy of Sciences, 118(6), e2020060118.
3. Davidson, C., Amrani, A., & Angert, A. (2022). Carbonyl sulfide sulfur isotope fractionation during uptake by C3 and C4 plants. Journal of Geophysical Research: Biogeosciences, 127(10), e2022JG007035.
How to cite: Angert, A., Spielmann, F. M., Bazanov, B., Wohlfahrt, G., and Amrani, A.: Carbonyl sulfide sulfur isotopes fractionation and leaves' internal conductance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3476, https://doi.org/10.5194/egusphere-egu25-3476, 2025.
Carbonyl sulfide (OCS), the most abundant sulfur-containing trace gas in Earth's atmosphere, plays a central role in stratospheric aerosol formation and can serve as a proxy for terrestrial carbon dioxide uptake. In this context, quantifying its atmospheric sources and sinks is of great interest, but especially the role of marine emissions is poorly constrained. Analysis of sulfur isotopic ratios (34S/32S; d34S) is a valuable tool to quantify the relative contributions of different sources to the atmospheric budget of OCS. However, the d34S values for marine OCS emissions are based on a data set that has so far been limited to a few measurements in coastal and shelf areas. Here, we present a first global ocean mixed-layer model of OCS sulfur isotopes, building on experimentally derived fractionation factors for the most important biogeochemical processes of marine OCS cycling, i.e. photochemical production, dark production and degradation by hydrolysis. The model is tested against incubation experiments and novel measurements along an Atlantic transect. We calculate the d34S values of marine OCS emissions, with the ultimate aim to decipher their relative contributions to the atmospheric budget. Our simulations show regional and temporal variations in the d34S values of OCS, suggesting a distinct latitudinal gradient with lower d34S in the tropics and higher d34S in high latitudes. The spatially weighted average of d34S values of OCS is used to update a global mass balance approach to infer the role of direct marine emissions of OCS in the atmospheric budget.
How to cite: Lennartz, S., Amrani, A., Avidani, Y., Davidson, C., Simon, H., and Angert, A.: Modeling the sulfur isotopic signature of marine carbonyl sulfide emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13223, https://doi.org/10.5194/egusphere-egu25-13223, 2025.
The application of isotope effects from photodissociation processes in nature date back to Viking and the observation of a massive 15N in the Martian atmosphere, derived from combined photolysis and gravitational escape. Large observed effects in meteorites, interstellar molecular clouds, and pre solar nebulae utilize photodissociation as a source of the wide range in isotopic composition. CO, which is isoelectronic with nitrogen, has also been widely used, but models do not agree with experiments suggesting models do not include all parameters.
We report precise novel measurements of the isotopic branching ratio in the photodissociation of N2 in the VUV at the advanced light source, Berkeley with quantitative scavenging of the nascent N atoms. We here report an integration of these measurements with state-of-the-art dynamics modeling and light shielding. The measured photodissociation enrichment in 15N with wavelength with a down trend above 90 nm is shown to arise from dynamical effects. There are two effects identified by the computations, the branching between exit channels and the more subtle role of the non-monotonic variation in the individual line widths that in the higher energies begin to significantly overlap. The widths have a significant effect on both the shielding computations at the higher energies and on the cross sections themselves. The modeling requires accurate quantum dynamical simulations using state of the art multireference potential energies and their state-dependent couplings. As the excitation energy increases, competition between different coupled exit channels, some leading to reactive N (2D) and some leading to significantly less reactive N (2P) in an isotope dependent way, modulates the selectivity for the 15N atoms. As a result, the dissociation lifetimes of initial states close in energy vary in a nonmonotonic isotopic dependent manner as a function of energy. Our work shows that modelling can interpret the novel experimental observations and account for the exceptionally high selectivity. Additional progress requires accurate high resolution UV spectra for entire UV bands, both measured and computed to complement fractionation measurements. The complexity of the non-statistical dynamics and the role of the light shielding make such high-resolution work necessary for the detailed understanding of isotope enrichment fractions in the higher energy regime for nitrogen and also for other molecules of interest in cosmochemistry such as CO. Given the massive range in isotopic composition, the interpretation of e.g the Mars atmosphere and photolysis intersection, meteoritic nitrogen may be modeled better. Samples from the earth’s interface with space where N2 photolysis occurs would be an interesting application and testing of the model.
How to cite: Thiemens, M., Komorova, K., Gelfand, N., Remacle, F., Levine, R., Chakraborty, S., Jackson, T., and Kostco, O.: Measurement and Full Model of Isotope Fractionation During Photodissociation and Applications in Cosmo and Geochemistry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3828, https://doi.org/10.5194/egusphere-egu25-3828, 2025.
Formaldehyde is a short-lived intermediate formed by the oxidation of virtually every VOC in the atmosphere. It is the source of half of atmospheric hydrogen, and a large source of CO and CO2, and plays a role in particle growth. Efforts to better understand the remarkable transformations of formaldehyde are hindered due to lack of knowledge of some of the basic processes in formaldehyde photolysis. Here, we present a combined quantum and molecular mechanics, Rice–Ramsperger–Kassel–Marcus (RRKM) and experiment-based model that significantly advances our ability to describe photolytic kinetic isotope effects and their pressure dependencies. RRKM theory was used to calculate the decomposition rates of the S0, S1 and T1 states using CCSD(T)/aug-cc-pVTZ, ωB97X-D/aug-cc-pVTZ and CASPT2/aug-cc-pVTZ levels of theory. Experimental internal conversion and intersystem crossing rates were used and modified with the density of states of the isotopologues based on Fermi’s ‘Golden Rule’. The following isotopologues of formaldehyde were investigated: HCHO, DCHO, DCDO, D13CHO, H13CHO, HCH17O, HCH18O, HC13H17O and HC13H18O. The method and mechanism were validated by comparison to all existing and newly obtained experimental data. The model was able to accurately replicate the experimental pressure trends of the kinetic isotope effects (KIEs) and was in excellent agreement. The model was used to predict the KIEs and the molecular hydrogen yields of the deuterated species at varying altitudes.
How to cite: Johnson, M., Pennacchio, L., Liasi, Z., Erbs Hillers-Bendtsen, A., Röckmann, T., and Mikkelsen, K. V.: New experiments and quantum-molecular mechanics model of isotopic fractionation in formaldehyde photolysis explains atmospheric dD-H2 anomaly and shows extreme isotopic fractionation in CO, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15335, https://doi.org/10.5194/egusphere-egu25-15335, 2025.
In the global nitrous oxide (N2O) budget, various processes can influence the natural isotope abundances, often enriched with 15N with a site-specific preference δ15NSP that serves as a unique natural isotope tracer. Unlike δ18O and δ15Nbulk, δ15NSP is independent of the substrate’s isotopic signature and remains unchanged during N2O diffusion. However, while δ 15NSP can reveal mechanisms of N2O formation and reduction [1], distinguishing between production and consumption processes remains challenging due to overlapping isotopic signatures and variable fractionation factors. Current approaches, such as dual isotope plots (e.g., δ15NSP/δ15Nbulk), help constrain dominant pathways but rely on experimental fractionation data. Which can be difficult considering that for the determination of 15NSP values with isotope ratio mass spectrometry (IRMS) methods it was shown that they are highly reliant on the choice of calibration with differences of up to 30 ‰ [2]. At the same time, laser absorption spectroscopy (LAS) of rotational-vibrational transition is prone to interferences by other trace gases, requires rigorous calibration and needs preconcentration units [3-4]. We propose using matrix-isolation Fourier-transform infrared (MI-FTIR) spectroscopy, which provides a calibration-free measurement of site-specific N2O isotopic composition by determining the absorption cross-section of the pure vibrational features of the respective isotopocules
[1] Toyoda, S., Yoshida, N. and Koba, K. (2017), Isotopocule analysis of biologically produced nitrous oxide in various environments. Mass. Spec. Rev., 36: 135-160
[2] Westley, M.B., Popp, B.N. and Rust, T.M. (2007), The calibration of the intramolecular nitrogen isotope distribution in nitrous oxide measured by isotope ratio mass spectrometry†. Rapid Commun. Mass Spectrom., 21: 391-405.
[3] Harris, E., Zeyer K., Kegel R., et al. (2015), Nitrous oxide and methane emissions and nitrous oxide isotopic composition from waste incineration in Switzerland. Waste Management, 35: 135-140
[4] Ostrom, N.E., Ostrom, P.H. (2017), Mining the isotopic complexity of nitrous oxide: a review of challenges and opportunities. Biogeochemistry, 132: 359–372.
How to cite: Schlagin, J., Dinu, D., Liedl, K. R., Stolzenburg, D., Grothe, H., and Mohn, J.: Towards a calibration-free analysis of 15N site preference in N2O reference materials using matrix-isolation infrared spectroscopy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11143, https://doi.org/10.5194/egusphere-egu25-11143, 2025.
Anthropogenic activities have led to a rapid increase of reactive nitrogen (Nr) in the Earth system, contributing to climate change, biodiversity loss, acid deposition, and air pollution. Among Nr species, particulate ammonium (pNH4+) and nitrate (pNO3−) derived from ammonia (NH3) and nitrogen oxides (NOx) are key pollutants affecting air quality. However, their sources and formation pathways vary by location and remain poorly understood. This study investigates the sources and atmospheric processing of Nr in an East Asian mountain forest, using nitrogen (δ15N) and oxygen (δ18O) isotope compositions of pNH4+ and pNO3−. A field campaign was conducted in Xitou, Taiwan (23.40°N, 120.47°E, 1179 m above sea level) from April 17 to 24, 2021. Size-segregated aerosol particles ranging from 0.056 to 18 µm were collected using a micro-orifice uniform deposit impactor (MOUDI) and analyzed for mass concentrations and isotopic compositions using Fourier-transform infrared spectroscopy with attenuated total reflection (FTIR-ATR) and gas chromatography-isotope ratio mass spectrometer (GC-IRMS), respectively. Additionally, a stable isotope mixing model (MixSIAR) was applied to quantify source contributions of Nr based on δ15N signatures. Xitou, located downstream of metropolitan coastal areas during the daytime, receives air pollutants transported inland by sea breezes and valley winds, combined with local emissions. During the campaign, the average mass concentrations of pNH4+ and pNO3− were 3.7 and 2.4 µg m−3, respectively. The mean δ15N values of pNH4+ (10.8 ± 2.7‰) and pNO3− (−3.0 ± 2.0‰) reflect their emission sources and isotopic fractionation during gas-particle partitioning. δ18O values of pNO3− ranged from 32.0‰ to 73.3‰, indicating distinct chemical formation pathways: pNO3− formed via O3 reactions exhibited higher δ18O values, while those formed via peroxy radicals (RO2) had lower values. Two distinct groups of pNO3− were identified based on δ15N-pNO3−and δ18O-pNO3− signatures. The first group, characterized by higher δ15N (−5.6 to 0.8‰) and δ18O (55 to 83‰), likely formed in metropolitan areas via O3 oxidation before being transported to the mountain observation site. The second group, consisting of smaller particles with lower δ15N (−10.1 to −2.1‰) and δ18O (8.6 to 38‰), was likely produced locally with RO2 as the dominant oxidant. Source apportionment analysis of δ15N revealed that combustion-related sources, including fossil fuel combustion and NH3 slip, accounted for 63% of NH3 emissions, while anthropogenic NOx sources such as biomass burning, coal combustion, and mobile sources contributed approximately 68% of total NOx emissions. These findings highlight the importance of targeted emission control policies to reduce Nr pollution and mitigate its adverse environmental impacts, including air quality degradation and ecosystem harm.
How to cite: Lee, W.-C., Huang, M.-H., Huang, W.-C., Chen, J.-P., Ren, H., and Hung, H.-M.: Source apportionment and evolution of reactive nitrogen in an East Asian mountain forest: A dual-isotope and modeling approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14144, https://doi.org/10.5194/egusphere-egu25-14144, 2025.
Earth atmospheric dioxygen is mainly produced by biosphere photosynthesis, and biosphere respiration is also one of the main consumers of this gas. The evolution of atmospheric O2 is thus linked to global biosphere productivity.
In ice cores we extract air from bubbles to study the composition of the past atmosphere. However, as O2 concentration in air bubbles is affected by close off processes, it is difficult to reconstruct its variations in the past atmosphere from ice core analyses. In turn, the isotopic composition of O2 (δ18O and δ 17O), is also influenced by biological processes and is less influenced by close-off processes so that this tracer should provide useful information on the past biosphere activity.
Quantitative interpretation of the isotopic composition of O2 in the past relies on robust estimate of oxygen fractionation coefficients associated with the relevant biological processes: photosynthesis and respiration. In the past decades, some determinations of these biological fractionation coefficients were performed in uncontrolled large-scale environments or at the scale of the micro-organisms in conditions very different from the natural environment. There are thus inconsistencies in previous determinations of the O2 fractionation coefficients limiting the interpretation of δ18O and δ 17O of O2.
In order to come up with coherent estimates of oxygen fractionation coefficients during biological processes, we developed closed biological chambers as a biosphere replica, with controlled environment parameters (light, temperature, CO2 concentration), which were used in combination with a newly designed optical spectrometer for continuous measurements of O2 concentration and of its isotopic composition.
In this presentation, we show the design and realisation of our aquatic biological chambers as well as the associated development of the multiplexing system to be able to run parallel experiments with the same environmental conditions. Then, we show the results obtained for light and dark periods, and the corresponding fractionation coefficients calculated for photosynthesis and respiration. Finally, we use the newly determined fractionation coefficients to improve interpretation of the δ18O of O2 record in air bubbles from ice cores.
How to cite: Bienville, N., Landais, A., Fiorini, S., Piel, C., Sauze, J., Prie, F., Joussoud, O., Chollet, S., and Abiven, S.: A multiplexing set-up of aquatic biological chambers to study the isotopic fractionation of oxygen: application to the interpretation of the δ18O of O2 records found in deep ice cores., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12431, https://doi.org/10.5194/egusphere-egu25-12431, 2025.
Marine photosynthesis (or gross primary productivity, GPP) is one of the main mechanisms for carbon fixation and global oxygen formation, contributing around half of the oxygen produced on Earth and sustaining aquatic ecosystem. Understanding the mechanisms that regulate GPP is essential for gaining insights into biological oxygen and carbon cycles. The combined study of GPP with net primary productivity (NPP) and net community productivity (NCP) will greatly improve our understanding of the interactions between biological processes, linking photosynthesis, respiration and the carbon cycle.
The triple isotopic composition of dissolved oxygen has been proposed as a tracer of gross oxygen productivity in aquatic ecosystem (Luz & Barkan, 2000). The reasoning behind this is that the ∆17O of dissolved O2 is determined by two main end-members: the marine photosynthesis (∆17O ~ 249 ppm) and the atmospheric O2 (∆17O ~ 8 ppm), as ∆17O is not much affected by other processes that fractionate oxygen in a mass-dependent manner. However, subsequent studies have highlighted potential sources of uncertainty or bias in this proxy. Uncertainties about fractionation factors and transport parameters call the tracer into question (Levine et al., 2009; Nicholson et al., 2014; Li et al., 2022).
To address this issue, we have recently implemented the triple isotopic composition (δ17O and δ18O) of dissolved O2 into the 3D Earth System Model of intermediate complexity, iLOVECLIM. We will present our preliminary results of model comparing them with observation and discussing sensitivity experiments; we further compare our results to previous findings that used 1D or 2D modeling approaches.
How to cite: Clermont, E., Yang, J.-W., and Roche, D. M.: Modelling the triple-isotopic composition of dissolved oxygen using a 3D Earth System Model of intermediate complexity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17262, https://doi.org/10.5194/egusphere-egu25-17262, 2025.
Isotopic fractionation of O2 is an important tracer for estimating primary production in aquatic environments because it helps to disentangle the respective contributions from O2 production, consumption, and gas-exchange. Isotope-based methods for estimating primary productivity typically involve measurements of either only 18O/16O ratios or, in the case of triple oxygen isotope approaches, also 17O/16O ratios. Aerobic respiration is generally assumed to be the only process consuming O2, with a constant value for O-isotopic fractionation, expressed as ε or λ values, respectively. However, emerging evidence suggests that in the photic zone of lakes and oceans, photochemical O2 consumption can be of similar magnitude as microbial respiration and photosynthetic O2 production. To determine whether photochemical O2 consumption should be included in isotope-based assessments of primary productivity, we measured the O-isotopic fractionation (as 18O-ε and λ values) of two important photochemical O2 consumption reactions. First, we investigated the energy transfer from photochemically excited dissolved organic matter (DOM) to O2, leading to the reversible formation of singlet oxygen, which can irreversibly react with several functional groups within DOM. Under realistic conditions for sunlit surface waters, this photochemical O2 consumption reaction is associated with 18O-ε values of -25 ‰ to -30 ‰, which are larger than typical values for respiration (approx. -20 ‰). The second photochemical process investigated was the reaction between O2 and photochemically produced organic radicals, which yielded substantially smaller values for 18O-ε (0 ‰ to -15 ‰). 18O-ε values for photochemical O2 consumption may thus be distinguishable from those for respiration. Yet, the overall isotopic fractionation in sunlit surface water will depend on the relative contributions of the different photochemical O2 consumption reactions. Although some studies have measured the isotopic fractionation of photochemical O2 consumption in natural water samples, additional research is needed for properly implementing these processes into isotope-based estimations of primary production. Finally, results from triple oxygen isotopic fractionation measurements suggest an overlap of λ values in the range of 0.51-0.53 for photochemical O2 consumption (as determined in this study) and for respiration experiments from literature.
How to cite: Pati, S. G., Brunner, L. M., Hofstetter, T. B., and Lehmann, M. F.: Isotopic fractionation of O2 during photochemical O2 consumption: A relevant process for estimating primary production in sunlit surface waters?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6805, https://doi.org/10.5194/egusphere-egu25-6805, 2025.
Methane emission budgets based on isotopic analysis (e.g. 13C-CH4, D-CH4, 13CH3D CH2D2, CHD3, and/or CD4) correct composition for the isotopic fractionation of atmospheric oxidation reactions. They rely on a handful of laboratory measurements obtained at only a couple of temperatures. The goal of this study is to better characterize KIEs of the reactions and especially the temperature dependence of the KIEs.
As a first step we have calculated the temperature dependent reaction rates using tunneling corrected Transition State Theory. We examine the reaction of methane with Cl and OH including all possible transition states with the isotopologues: CH4,13CH4, 14CH4, 13CDH3, CDH3, CD2H2, CD3H, and CD4. Transition State Theory has been used with M06-2X, ωB97X-D, and CAM-B3LYP level of theory, with the two basis sets 6-31++G(d,p) and 6-311++G(d,p). The KIE is calculated for all reactions and compared with literature. Results for the 13CH4 + Cl reaction show that the KIE changes with -12.0 ‰ per 100 K. Whereas for 13CH4 + OH the KIE changes by -1.14 ‰ from 300 to 200 K. For all isotopologues we predict that the KIE’s change significantly with temperature. Including this correction in isotopic mass balance top down emissions estimates will significantly change the results.
In future work we will examine the reaction path and molecular dynamics in detail. To do these calculations, we will perform ab initio multiple spawning (AIMS) trajectories interfaced with the TeraChem electronic structure program. This study will increase our understanding of the oxidation of methane and compare the quantum chemical understanding of isotope budgeting to observations.
How to cite: Mikkelsen, M. K., Elholm, J. L., Mikkelsen, K. V., and Johnson, M. S.: Large temperature dependencies for the D, 13C and clumped kinetic isotope effects in methane oxidation by OH and Cl predicted by quantum chemical and transition state theory., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10604, https://doi.org/10.5194/egusphere-egu25-10604, 2025.
Methane (CH4) has a global warming potential 28-36 times that of carbon dioxide over a 100-year period [1]. Different sources of CH4 have distinct isotopic signatures, with CH4 from biological sources having a lighter signature than those from fossil sources [2]. Greenhouse gas (GHG) emissions are typically reported using bottom-up methods (based on data such as emission factors) that are verified using top-down methods (based on atmospheric transport models (ATMs) and observations) which infer fluxes, often through Bayesian methods [3]. Isotope ratio data are generally used in atmospheric models to understand individual contributions of various CH4 sources, globally and regionally. However, there is uncertainty regarding isotopic signatures due to large temporal variabilities and regional specificities [4].
Methane isotope ratio source signature information is typically gained through discrete mobile measurement campaigns, with the aim of capturing the emissions directly from the sources, through downwind transection of plumes as closely as possible to the source [5]. These measurements fill databases that are used for atmospheric modelling [2,6,7].
Continuous measurements of CH4 isotope ratios are also carried out at from varying sampling heights [7,8,9] (ranging from tens to hundreds of meters) with the lower heights, closer to emissions sources, capturing more local influences and higher heights capturing more regional emissions. While they offer the advantage of being continuous, they are further away from the emission sources, therefore have larger uncertainties.
Understanding the information that can be gained from continuous CH4 isotope ratio measurements at different sampling heights and locations will be an important factor to consider when using observational data in inversion frameworks, in terms of accurately quantifying source signatures. We present results of mean isotopic signatures from continuous measurements, resolved using the Keeling approach and compare to modelled data to understand the inferred source contributions.
Continuous measurements of CH4 isotope ratios have been carried out at 10 European atmospheric GHG monitoring stations. This study focuses on two sites: Heathfield (an inland, 100 m a.g.l tall tower) and Krakow (an urban, 35 m a.g.l site). We present CH4 isotope ratio datasets from these sites and aim to use them to interpret isotopic signatures in the surrounding areas.
[1] IPCC 2021. Cambridge University Press.
[2] Sherwood et al. 2017. Earth Syst. Sci. Data. 9, 639-656.
[3] Manning et al. 2021. Atmos. Chem. Phys. 21, 12739-12755.
[4] Ramsden et al. 2022. Atmos. Chem. Phys. 22, 3911-3929.
[5] Bakkaloglu et al. 2022. Atmos. Environ. 276, 119021.
[6] Menoud et al. 2020. Tellus B. 72, 1823733.
[7] Menoud et al. 2022. Earth Syst. Sci. Data. 14, 4365-4386.
[8] Röckmann et al. 2016, Atmos. Chem. Phys. 16, 10469-10487.
[9] Rennick et al. 2021. Anal. Chem. 93, 10141-10141.
How to cite: Safi, E., Kikaj, D., Röckmann, T., Chung, E., van Es, J., Rennick, C., van der Veen, C., Arnold, T., and Dasgupta, B.: The role of sampling height in interpreting methane isotope ratios for source attribution and inversion modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10857, https://doi.org/10.5194/egusphere-egu25-10857, 2025.
Methane (CH4), the second-largest contributor to global warming, necessitates a detailed examination of its sources and sinks to understand the recent rise in atmospheric CH4 mole fractions. Atmospheric isotopic signals, especially δ¹³C-CH4, offer critical insights for disentangling sectoral contributions and addressing these uncertainties.
This study focuses on enhancing our understanding of CH4 sources and sinks by incorporating updated δ¹³C-CH4 source signature datasets into atmospheric modeling. First, we updated these datasets to reflect the latest knowledge of methane emission processes. Next, we assessed the sensitivity of key modeling parameters such as atmospheric chemistry, the aggregation of δ¹³C-CH4 source signatures, and prior flux estimates on simulated CH4 signals and mole fractions. This analysis aims to validate the updated datasets and identify primary drivers of uncertainty in the simulations. We conducted forward modeling using the Global Circulation Model LMDZ coupled with the Community Inversion Framework (CIF), based on surface observations of methane and its isotopic signal from 1998 to 2022. These efforts lay the groundwork for improving the robustness of future isotopic inversions.
Building on these findings, our future work will focus on transitioning from forward simulations to atmospheric inversions to analyze global methane concentration trends. Initially, we will perform inversions using in-situ data from 1998 to 2022, leveraging the updated δ¹³C-CH4 source signature datasets and setups. Subsequently, we will analyze trends from 2018 to 2022 by integrating satellite observations of total methane columns with surface isotopic measurements. This approach utilizes the high-resolution, global coverage of TROPOMI (TROPOspheric Monitoring Instrument) onboard the Sentinel-5P platform, which measures column-averaged methane dry-air mole fractions X(CH4). By combining satellite and surface observations, we aim to enhance our ability to monitor methane dynamics and deepen our understanding of CH4 source and sink interactions. These advancements will provide critical insights for designing more effective climate mitigation strategies.
How to cite: Tapin, E., Berchet, A., Martinez, A., Menoud, M., Lan, X., Michel, S., and Saunois, M.: Assessing drivers of uncertainty in simulating δ¹³C-CH4 at global scale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12043, https://doi.org/10.5194/egusphere-egu25-12043, 2025.
The accumulation of organic matter in coal waste dumps can result in self-heating or spontaneous ignition, which lead to the release of various gaseous products into the atmosphere. GHGs and trace compounds emitted from self-heating coal waste dump located in the Nord-Pas-de-Calais region of Northern France were investigated under this study in September 2024. Tracking hotspot locations across coal waste dump confirmed various patterns of temperature and gaseous emissions from the investigated area. The temperature measured in boreholes drilled to the depth up to 0.6 meters on the top and slopes of the dump ranged between +51.0 and +83.1 °C. The non-uniform subsurface temperatures can be explained by the varied content of coal and carbon-containing rocks deposited at the dump, along with the diverse air inflow to the thermally active sites. The composition and source of the gaseous compounds emitted during self-heating were directly influenced by the various thermal activity stages and properties of the organic matter present in the dump.
Different generation patterns of released gases are related to the self-heating stage, including exothermic oxidation and pyrolysis. At thermally active sites (but below +68 °C) on the top of the dump (well-ventilated with free access of oxygen) the emission included CO2 12.8 vol%. Otherwise, at the sites on the wet dump slope (preventing oxygen entering), where prominent thermal activity was noted (temperature rise of about 80 ºC), the switch to pyrolysis was confirmed by showing a peak of CO2 (18.3 vol%), with a significant drop in O2 content (1.48 vol%). Apart from CO2, much higher was the concentration of CH4 reaching 4260 ppmv, and CO averaging 54 ppmv, above background H2, high levels of pyrolytic ethane 327 ppmv and propane 69 ppmv as well as C4 – C6 hydrocarbons.
The generation processes of the gases on both types of sites were confirmed by C and H isotopic analyses (CO2, CH4, C2H6, H2) and will be discussed in detail during the presentation of the paper. Recapitulating, the stable isotope tracing of the emitted gases was useful and can also be indicative for future monitoring of the thermal stage of self-heating coal waste dumps. Additionally, sulfur and nitrogen heterocyclic compounds such as furane, thiophene, and pyridine were detected in trace quantities. Although substantial amounts of gasses (mainly CO2 and CH4) escaped from the emission hotspot on the dump, their concentrations measured above the surface at sites without thermal activity were not significantly higher than local background levels. The surface flux mapping of entire dump, depth profiling of temperature and gas concentrations, their generative and degradation processes will be the main areas of future investigations.
This work was funded by the Polish Ministry of Science and Higher Education under Grant No. 2022/44/C/ST10/00112. The isotopic analysis has been supported by the ATMO-ACCESS (grant agreement No. ATMO-TNA-4—0000000041 and No. C1-ISOLAB/CESAR-9).
Acknowledgment for organization of and assistance during the onsite measurements and samples acquisition on the dump to Fabrice Quirin, Vincent Adam, Gaetan Bentivegna from Bureau de Recherches Géologiques et Minières, Unité Territoriale Après-Mine Nord, Billy-Montigny, France.
How to cite: Bezyk, Y., Strąpoć, D., Górka, M., Kruszewski, Ł., Nęcki, J., Więcław, D., van der Veen, C., and Röckmann, T.: Compositional analysis and isotope sourcing of gases generated from self-heating coal waste dump: the case study from France, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13790, https://doi.org/10.5194/egusphere-egu25-13790, 2025.
The presence of approximately 400,000 non-producing oil and gas wells (OGWs) in Canada and millions more globally poses significant environmental and safety issues. These wells leak methane (CH₄) and other pollutants, which exacerbate climate change, pose explosion hazards, contaminate drinking water, and damage plants and animals. Plugging all existing non-producing OGWs would cost several hundred billion dollars1, making this approach virtually impossible. However, since only 10% of these wells are responsible for >90% of the emissions2, a better strategy may be to identify and target high-emitting wells for more effective and economical mitigation efforts. It is therefore important to fully understand the processes governing methane leakage and their subsequent emissions through non-producing OGWs. Another important aspect of these efforts is the identification of well integrity failures, which may not necessarily cause high emissions to the atmosphere but can cause subsurface fluid migration, even for low-emitting wells. A modern OGW typically consists of a system of casings and cement, providing multiple barriers designed to prevent contamination. The surface casing vent (SCV), installed at the wellhead, is designed to vent gas from the annular space between the surface casing and the next casing string. Generally, methane emissions at the SCV are viewed as a sign of well integrity failure but could be unrelated if the casing intersects natural fluid migration pathways.
In this study, we compiled the geochemical data of 365 OGWs from Canada, with measurements made at the component level (wellhead, SCV and surrounding soil) wherever possible. By analyzing δ13C and δ2H isotopic signatures and gas compositions, we identified the origins of our samples as primary microbial, secondary microbial, thermogenic, or abiotic. These origins were only attributed to a third of the studied wells for at least one of the three components (wellhead, SCV and surrounding soil), due to the sensitivity of this approach. We found that the presence of thermogenic methane at the SCV is a good indicator of high-emitting wells, with magnitudes of emissions 100 times higher than microbial emissions. Furthermore, our analysis revealed that a considerable number of emitting wells (~23%) produce methane of microbial origin, which is higher than previously thought (8% in the only existing meta-analysis), and with emission magnitudes that exceed previous estimates by a factor of 1,000. These results suggest that non-producing OGWs could act as bridges facilitating the diffusion of subsurface microbial methane emissions into the atmosphere. Finally, we generally found similar geochemical signatures of methane in corresponding wellhead and SCVs, suggesting that the structural integrity of these wells has been compromised and they can act as one single entity.
- 1. Raimi, D., Krupnick, A. J., Shah, J.-S. & Thompson, A. Decommissioning Orphaned and Abandoned Oil and Gas Wells: New Estimates and Cost Drivers. Environ. Sci. Technol. 55, 10224–10230 (2021).
- 2. Williams, J. P., Regehr, A. & Kang, M. Methane Emissions from Abandoned Oil and Gas Wells in Canada and the United States. Environ. Sci. Technol. 55, 563–570 (2021).
How to cite: Micucci, G. and Kang, M.: Investigating the role of Canadian non-producing oil and gas wells in subsurface-atmosphere methane fluxes through geochemical signatures and methane origins, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3259, https://doi.org/10.5194/egusphere-egu25-3259, 2025.
Methane (CH4) plays a crucial role in the Earth’s radiative balance because it is a potent greenhouse gas with a shorter lifetime compared to CO2. Mitigating CH4 emissions can potentially mitigate climate change over a short period [1]. Mitigating CH4 requires a solid understanding of the emissions, in particular, which source emits the CH4. Isotopic analysis can aid in source partitioning, as different production processes produce CH4 with subtle but significant differences in isotopic composition [3], enabling the differentiation of multiple sources.
CH4 isotopic source signatures are typically obtained through mobile where sources are sampled as close to the emission point as possible [2]. While these campaigns are valuable, they only capture for a short duration and miss many smaller and unknown emissions. In contrast, continuous CH4 measurements cover longer periods and can detect inaccessible or unknown sources. However, the downside is that identifying the exact source can be more challenging as the source origin is not always known.
Researchers at Utrecht University developed an isotope ratio mass spectrometer (IRMS) system that measures CH4 mole fraction, δD and δ13C at high
precision with a 40-minute resolution. This system was deployed from 15 April 2022 till 8 January 2023 at a tall tower in Lindenberg, Germany. Measurements were initialised at 40 m.a.g.l and later continued 98 m.a.g.l. The station is part of the Integrated Carbon Observation System (ICOS), providing mole fraction measurements of CO, CO2, and CH4. CH4 isotopic data were also compared with simulations from EMPA. These simulations include the CH4 emissions for each category, allowing us to assign an isotopic source signature to each emissions category, and thereby simulating a CH4 isotopic source signature. For the isotopic measurements, we observed 169 peaks shorter than 24 hours.
This corresponds to 67% of the deployment days. Most source signatures indicate a microbial fermentation source (δ13C : [-55‰, -62‰], δD : [-260 ‰, -360 ‰]). Additionally, we identified 19 multi-day elevations, lasting up to 20 days. Eight of these multi-day elevations displayed isotopic signatures similar to those of the diurnal peaks, while the remaining multi-day peaks showed distinctly different source signatures from one another and the diurnal elevations.
How to cite: van Es, J., van der Veen, C., Henne, S., and Rockmann, T.: Continuous methane (CH4) isotope measurements in Lindenberg, Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19970, https://doi.org/10.5194/egusphere-egu25-19970, 2025.
Mercury (Hg) stable isotopes have become a powerful tracer for understanding Hg sources and complex biogeochemical processes in the natural environment. Anomalies of even mass number mercury isotopes (even-MIF; Δ200Hg, Δ204Hg), in particular, have enabled the differentiation of Hg chemical forms (Hg0 vs. HgII) and their depositional pathways. This is because even-MIF occurs exclusively via upper atmospheric photo-oxidation, leaving HgII with a positive Δ200Hg value and Hg0 with a negative Δ200Hg value. Over the past several years, my research group has characterized even-MIF anomalies in atmospheric samples (gaseous Hg0, precipitation), seawater, zooplankton, and fish from high (Beaufort, Chukchi Sea) and mid-latitude oceans (West to Central Pacific Ocean). Our goal was to comprehensively trace sources, oxidation/removal pathways, and fate of Hg to open ocean food web. The results depict a clear Δ200Hg dichotomy, in which all samples from mid-latitude oceans have positive Δ200Hg (reflecting HgII) and the samples from high-latitude oceans have negative Δ200Hg (reflecting Hg0). The δ202Hg, which has been used to trace Hg sources (types of anthropogenic, natural sources) across a large spatial scale, show that, while high-latitude oceans exhibit values similar to that of background Hg, mid-latitude oceans have δ202Hg consistent with anthropogenic Hg. There is also a gradual dilution of zooplankton Hg concentration and anthropogenic δ202Hg signals from West to the Central Pacific Ocean. We summarize Hg sources and oxidation pathways as such, by using an isotope mixing model: In the West and Central Pacific, 52-60% of Hg0 emitted from anthropogenic sources is first circulated to the upper atmosphere for photo-oxidation prior to oxidation and removal to the open ocean. The remainder of Hg comes from riverine Hg export. In the Arctic, >70% of Hg is oxidized near the biosphere, not in the upper atmosphere, thereby conserving the even-MIF of Hg0 even upon oxidation. We speculate that the presence of abundant halogens and sea salt aerosols (SSA) is responsible for rapid Hg0 oxidation and removal to the open ocean. Our study showcases that Hg stable isotopes can be used to differentiate sources, pathways of removal, and fate of Hg across a large spatial scale. After compiling further dataset, we identify that near-surface Hg0 oxidation mediated by halogens and SSA in the Arctic explains elevated Hg levels reported in the Arctic fish, mammals, and polar bears. The pathway of anthropogenic Hg0 emission to bioaccumulation detected in the West and Central Pacific suggests that anthropogenic Hg0 abatement from continental Asia would lower Hg levels in the adjacent marine ecosystems.
How to cite: Kwon, S. Y., Motta, L., and Lim, S. H.: Mercury stable isotopes reveal atmospheric oxidation and removal processes to high and mid-latitude oceans , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2293, https://doi.org/10.5194/egusphere-egu25-2293, 2025.
Posters on site: Thu, 1 May, 14:00–15:45 | Hall X1
The central goal of this project is to establish long-term isotope-specific monitoring of H2O, CO2, CH4 and N2O exchange between terrestrial ecosystems and the atmosphere with high temporal resolution at grassland, arable land and forest sites. The exchange of H2O and CO2 between ecosystem and atmosphere will be determined online with rapid (10 Hz) isotope-specific laser analyzers using the eddy covariance (EC) method. The objective of this measurement is to determine the isotopologue fluxes of the respective gases and the source/sink partitioning, i.e., evaporation and transpiration in the case of water vapor or photosynthetic uptake and ecosystem respiration in the case of CO2. Measurements will be conducted using fully automated measurement systems for a minimum of two years. In addition, a mobile automated sampling system will be developed for isotope-specific recording of CH4 and N2O ecosystem exchange using the profile method with off-line isotope analysis by isotope ratio mass spectrometry to ensure the highest possible precision of isotope measurements. The aim of the isotope-specific flux measurements is to partition the CH4 flux into CH4 production (methanogenesis, if relevant) and CH4 uptake (methane oxidation), and the N2O flux into nitrification and denitrification as sources and N2O reduction as an N2O sink. Furthermore, the measurements will permit the determination of the isotopic composition across seasons and during peak emission periods, such as fertilization or freeze-thaw events. All approaches will be evaluated for their relevance in identifying greenhouse gas source/sink processes and their potential for long-term deployment. This presentation will introduce the measurement concepts and present first results.
How to cite: Claß, M., Rothfuss, Y., Schulz, D., and Brüggemann, N.: Long-term high-frequency isotope-specific monitoring of H2O, CO2, CH4 and N2O exchange between atmosphere and ecosystems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3453, https://doi.org/10.5194/egusphere-egu25-3453, 2025.
The net ecosystem exchange (NEE) of CO2 can be measured using the eddy covariance (EC) technique, but separating NEE into ecosystem respiration and gross primary productivity (GPP) relies on models and tracers, making it a persistent challenge. Beyond the established nighttime and daytime flux partitioning algorithms, the trace gas carbonyl sulfide (COS) shows promise as a robust proxy for constraining GPP. Unlike CO2, which is exchanged bidirectionally by leaves and its ecosystem level exchange being influenced by soil respiration, COS generally enters leaves unidirectionally and is fully catalyzed by carbonic anhydrase. Other sources and sinks of COS within ecosystems are typically minor and negligible.
Initial laboratory studies have determined the leaf relative uptake rate (LRU) – the ratio of COS to CO2 deposition velocities (LRU = (FCOS/χCOS)/(GPP/χCO2)) – to be relatively stable around 1.7 under optimal conditions. By knowing the LRU and measuring COS fluxes alongside CO2 and COS ambient mixing ratios, GPP can be calculated. However, most laboratory measurements have been conducted under optimal conditions and further research revealed the influence of environmental factors such as drought, vapor pressure deficit (VPD) and photosynthetically active radiation (PAR) on the LRU.
Due to the high cost and sensitivity of required instruments, few studies have examined COS fluxes at the ecosystem scale, and even fewer have performed long-term monitoring. Seasonal dynamics, particularly during winter, remain largely unexplored.
To address this gap, we conducted EC measurements of COS and CO2 fluxes at a Pinus sylvestris-dominated coniferous forest in Austria to investigate environmental influences on COS fluxes and LRU dynamics. Sampling has been continuous since May 2021, except for a two-month gap during the winter of 2021/22. We present the influence of VPD, PAR, temperature and snowfall on COS fluxes and the LRU at the ecosystem level, based on 3.5 years of measurements.
How to cite: Spielmann, F. M., Hammerle, A., De-Vries, A., Platter, A., and Wohlfahrt, G.: From Sunshine to Snowfall: Understanding concurrent CO2 and COS exchange in a Coniferous Forest, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8718, https://doi.org/10.5194/egusphere-egu25-8718, 2025.
Methane (CH₄) plays a critical role in the global carbon cycle, with its mole fraction currently 2.5 times higher than preindustrial levels. The increasing growth rate observed globally highlights the importance of accurate partitioning the atmospheric CH4. Oxidation of CH₄ by hydroxyl radicals (OH) in the troposphere accounts for approximately 85% of the global CH₄ sink. The resulting isotopic fractionation of δ13C-CH₄ and δD-CH₄ provides a valuable tool for understanding the global CH₄ budget. However, discrepancies exist in the reported kinetic isotope effect (KIE) values for CH₄ destruction by OH with 13CKIE ranging from 1.0036 to 1.010 and DKIE ranging from 1.25 to 1.31. These uncertainties significantly limit the precision of global CH₄ budget estimation.
This study aims to address these discrepancies by accurately characterizing the KIE values under varying temperature and pressure conditions. During the laboratory experiments, CH₄ is subjected to chemical reactions with OH, which is generated through the photolysis of vapor-phase hydrogen peroxide using a deep-UV light source (200-380 nm). To minimize interference from O(1D) reactions, a coated glass filter is employed. The photochemical reactions take place in a 5-liter, triple-quartz-layered reactor, maintained at stable pressure and temperature, with by-products removed using a low-temperature trap. The reactor is coupled to two Isotope Ratio Mass Spectrometers (IRMS), enabling continuous measurements of δ13C, δD, and δ18O in remaining CH₄ and CO throughout the experiment. By enhancing our understanding of CH₄-OH reaction kinetics under controlled conditions, this study can improve the accuracy of global CH₄ budget assessments and refine the distribution between fossil and biogenic CH4 sources.
How to cite: Chen, C., Adnew, G., van der Veen, C., and Röckmann, T.: Addressing discrepancies in 13CKIE and DKIE values for the CH₄-OH oxidation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11217, https://doi.org/10.5194/egusphere-egu25-11217, 2025.
Orbitrap mass spectrometers have proven highly effective for isotope ratio analysis in liquid chromatography (LC)-coupled workflows, offering high precision and resolution. We introduce an innovative expansion of this capability to gas-phase isotope ratio analysis of intact molecules, eliminating the need for complex sample preparation and molecular conversion required in traditional isotope ratio mass spectrometry (IRMS).
The MION-Orbitrap system is optimized for direct gas-phase sample introduction, enabling precise and accurate isotope ratio measurements for carbon (13C/12C), hydrogen (2H/1H), nitrogen (15N/14N), and sulfur (34S/32S) on intact molecular species. Its capability for online analysis of ambient air further enhances its applicability. By bypassing conventional combustion or molecular conversion steps, this approach simplifies workflows, reduces handling time, and minimizes potential isotopic fractionation.
Preliminary experiments demonstrate the feasibility of this method and first results will be presented. By preserving molecular integrity during analysis, the system opens new avenues for investigating complex organic compounds in environmental chemistry, atmospheric processes, biogeochemical cycles, and plant metabolism.
We also address some of the remaining challenges in advancing this methodology, including the need for standardized reference materials for intact molecular isotope ratio measurements and the mitigation of potential matrix effects. These efforts are critical for ensuring accuracy, reproducibility, and broader adoption of gas-phase isotope ratio analysis.
How to cite: Jost, H.-J., Finkenzeller, H., Shcherbinin, A., Partovi, F., and Mikkilä, J.: Expanding Isotope Ratio Analysis of Intact Molecules to Gas Phase Using a MION-Orbitrap System, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11425, https://doi.org/10.5194/egusphere-egu25-11425, 2025.
The greenhouse gas research community faces a growing demand for automated solutions tailored to isotopic measurements of greenhouse gases (e.g., isotopic CO2/CH4). Traditional solutions often entail significant initial and maintenance costs, intricate deployment and maintenance processes, and limited fieldwork adaptability. Anticipating this challenge, the Picarro Gas Autosampler is poised to attract growing interest for its anticipated compatibility with Picarro isotopic Carbon analyzers featuring low flow rates (<50 scc/m), promising efficient isotopic measurements. This report delves into the compatibility, efficiency, and advantages of the Picarro Gas Autosampler when paired with the Picarro G2201-i analyzer. Our experiments showcase remarkable precision and accuracy in isotopic measurements of greenhouse gases. Additionally, we explore factors such as linearity in dilution factors and characterize memory effects and variability across different gas species (e.g., comparing CO2 vs CH4). Moreover, the report offers practical recommendations on methods and best practices for conducting isotopic measurements of greenhouse gases. In summary, the Picarro Gas Autosampler, when combined with the Picarro G2201-i analyzer, emerges as a compelling, cost-effective, and user-friendly solution for isotopic measurements of greenhouse gases, offering a distinct advantage over traditional alternatives.
How to cite: Drori, K., Bhattacharya, J., Hofmann, M., Woźniak, J., and Hemenway, T.: Advancing Greenhouse Gas Isotopic Measurements: Evaluating the Compatibility and Efficiency of Picarro Gas Autosampler with Picarro Isotopic Analyzers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13624, https://doi.org/10.5194/egusphere-egu25-13624, 2025.
Carbon Dioxide (CO2), the primary anthropogenic greenhouse gas (GHG), plays a significant role in global warming. Earth’s global surface air temperate was higher by 1.09 °C in 2011–2020 than in 1850–1900. This rise is overwhelmed by 47% in atmospheric CO2 during the period (IPCC AR6, 2021). Analysis of carbon isotopes (13C and 14C) of CO2 plays a pivotal role in separating the anthropogenic and natural carbon release and uptake across land, ocean and atmosphere carbon pools. Despite their utility to understand carbon cycle dynamics, simulating the seasonal variations and long-term trends of 13C and 14C remains challenging. Bridging of the budget gaps requires robust modeling approaches to simulate the isotopic exchange fluxes since the rapid increase in fossil fuel emissions began in the 1950s.
This study has quantified the monthly exchange fluxes of 13C and 14C between the atmosphere and terrestrial biosphere, and between the atmosphere and ocean, as well as 13C and 14C emissions from fossil fuel, nuclear bomb tests, and nuclear power plants, for the period from 1940 to 2020. We have used fossil fuel emissions from GridFED (Jones et al., 2023), land biosphere fluxes are taken from LENS, LPJ and VISIT (NCAR ref., Scholze et al., 2008, Ito et al., 2007), and ocean exchange fluxes are taken from CESM2, LENS (NCAR ref., Danabasoglu et al., 2020). The Model for Interdisciplinary Research on Climate version 4 (MIROC4) atmospheric general circulation model (AGCM)-based chemistry-transport model (referred to as MIROC4-ACTM) has been used for the simulation of the prepared fluxes of 13C and 14C.
Our model simulated the observed concentrations of Δ14C at Jungfraujoch (JFJ; ICOS ref., Levin et al., 2021) and Baring Head (BHD; NIWA ref., Turnbull et al., 2007); e.g., the rise from -24.3 ‰ to 272.4 ‰ during 1950−1960, followed by a slow (near exponential) decay during 1965 to 2020. The two model cases using LENS and LPJ land model fluxes showed noticeable differences during 1970s. The model simulations of δ13C were compared with nine sites of SIO (Keeling et al., 2001); they successfully reproduced the long-term declining trend driven by the Suess Effect, which is the isotopic depletion of atmospheric CO2 caused by the combustion of δ¹³C-depleted fossil fuels. Seasonal variations were well captured, with enriched δ¹³C during photosynthetic periods (summer) and depleted δ¹³C during respiration periods (winter). In our simulations, the interhemispheric gradient in δ¹³C was evident, with stronger seasonal cycles and steeper declines in the Northern Hemisphere (e.g., Barrow, Mauna Loa) due to proximity to major anthropogenic CO2 sources, while Southern Hemisphere sites (e.g., Baring Head, South Pole) showed weaker seasonal variations, reflecting the dominance of ocean uptake and isotopic mixing. Discrepancies in Δ¹⁴C during 1955–1965 and 1980–2000 due to uncertainties in bomb-test emissions and biospheric uptake fluxes remain a challenge in accurately reproducing the observations.
How to cite: Chakraborty, U., Saitoh, N., Patra, P., Chandra, N., Belikov, D., and Scholze, M.: Simulating Long-Term Trends and Seasonal Dynamics of Carbon Isotopes in Atmospheric CO2 Using a 3D Transport Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14132, https://doi.org/10.5194/egusphere-egu25-14132, 2025.
Methane is experiencing an accelerating increase in the atmosphere globally. Of the tools researchers have to diagnosis and determine the cause of rapidly changing sources and sinks of methane, its carbon isotope composition, δ13C-CH4, is a promising option to reduce uncertainty and provide constraints on methane atmospheric inversions. A building consensus in literature points towards wetland emissions as the driving force behind increase emissions, yet our ability to be prescriptive of the wetland δ13C-CH4 flux remains uncertain. Of wetlands, northern permafrost and its thaw features add additional complexities just as they add a large potential carbon stock for future methane release. Early models attempting to determine the δ13C-CH4 of permafrost thaw predict that these landscapes will be isotopic endmembers, more depleted than any source on the planet. How does this prediction hold up against observations when downscaled to the site level?
We present an intercomparison between observations and two isotope-enabled methane production models targeting the thaw feature Big Trail Lake outside Fairbanks, Alaska. We compare the isotope-enabled version of the terrestrial ecosystem model–methane dynamics module (isoTEM) to the Arctic Lake Biogeochemistry Model (ALBM) with an added isotope mass balance. We benchmark both model runs against methane eddy-flux data and flask-collected methane isotope measurements onsite. Through this multi-model-observation intercomparison, we evaluate model mismatch of δ13C-CH4 flux at Big Trail Lake and evaluate how model physics can be improved to better capture permafrost thaw δ13C-CH4 flux for use in constraining atmospheric inversions.
How to cite: Rozmiarek, K., Oh, Y., Liu, X., Overeem, I., Miller, E., Morris, V., Vaughn, B., Hasson, N., Chase, B., Walter Anthony, K., Zhuang, Q., Rieker, G., and Jones, T.: Multi-model Insights into δ13C-CH4 from Arctic Permafrost Thermokarsts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14260, https://doi.org/10.5194/egusphere-egu25-14260, 2025.
Volcanoes are primary geological sources of carbon dioxide (CO2), while the combustion of fossil fuels significantly contributes to raise the CO2 concentration in the atmosphere, particularly within densely populated urban areas. Previous investigations have identified distinct sources of CO2 at the district scale in urban environments and that the short term evolutions in atmospheric CO2 concentration are influenced by meteorological parameters.
This study presents continuous monitoring of stable isotope compositions and CO2 concentrations in the urban environment of Palermo over a yearly period from 2023 to 2024. A laser-based isotope mass spectrophotometer was employed for measurements, detecting various isotopologues of CO2 (e.g., COO, 13COO, and C18OO isotopologues) through mid-infrared range laser absorption. The instrument calculated the 13C/12C ratio, 18O/16O ratio, and overall CO2 concentration. Measurements were conducted outside the Istituto Nazionale di Geofisica e Vulcanologia (INGV) laboratory at an elevation of 16.30 meters above the ground floor, referenced hourly, and calibrated daily using a known stable isotope composition standard of pure CO2.
Environmental parameters, including air temperature, atmospheric pressure, relative humidity, solar radiation and wind speed and direction, were recorded at a 5-minute sampling frequency. These data were utilized for processing the atmospheric CO2 dataset. The correlation between stable isotopic ratios and CO2 concentration, analyzed through the "Keeling plot" approach, enabled the determination of the isotopic signature of the predominant source of atmospheric CO2 in the Palermo urban zone.
The results indicated that wind speed and atmospheric pressure exerted opposing effects on atmospheric CO2 concentration. Elevated CO2 levels coincided with periods of high atmospheric pressure and low wind speed, while reduced CO2 concentrations were associated with increased air turbulence during windy periods. However, meteorological variables partly explain the variability in atmospheric CO2, considering contributions from various CO2 sources. The δ13C-CO2 measurements aligned with CO2 derived from fossil fuel combustion, attributed to urban vehicular mobility and residential heating, particularly during winter periods.
Analysis indicates that CO₂ levels in medium-sized urban areas like Palermo exhibit distinct seasonal and daily variations. Seasonal shifts primarily reflects CO2 emissions from hydrocarbon combustion during winter which was unbalanced by CO₂ uptake during productivity season (spring and summer). On the weekly timescale, CO₂ variations reflect population behaviors. CO2 concentrations are lowest during weekends and holiday periods contrasting raises of CO2 concentration on weekdays and in periods of atmospheric stability, especially in winter. Urban-scale observations, where the majority of greenhouse gases are emitted, allow for tracking high-frequency variations driven by environmental conditions and changes in human activities. Monitoring CO₂ in urban areas offers crucial insights for assessing the effectiveness of climate change mitigation measures.
How to cite: Gurrieri, S. and Di Martino, R. M. R.: Temporal Variations and Influencing Factors on Atmospheric CO2 in Urban Environments: A Stable Isotope Perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15597, https://doi.org/10.5194/egusphere-egu25-15597, 2025.
Stable isotopes are a powerful tool for constraining the sources and sinks of nitrous oxide (N2O), essential for identifying and mitigating the climate and air quality impacts of N2O emissions. Site preference (SP), the position-specific N stable isotope incorporation in N2O (14N15N16O vs 15N14N16O), has proven especially useful. Measurements of the clumped isotopologues 14N15N18O, 15N14N18O, and 15N15N16O are emerging as new constraints on the processes of N2O formation and destruction. An advantage of clumped and position-specific isotopic systems over conventional stable isotopes is the existence of an absolute reference frame: under equilibrium conditions, isotopes are randomly distributed among molecules at high temperatures, and deviations from this random distribution at lower temperatures can be both predicted by thermodynamic modelling and measured.
We use quantum cascade laser adsorption spectroscopy to measure the seven-dimensional stable isotopic composition of N2O (δ15N, δ18O, ∆17O, SP, ∆14N15N18O, ∆15N14N18O, and ∆15N15N16O). This spectroscopic approach provides key benefits for standardization studies, including the ability to measure each isotopologue directly without the need for the fragmentation and rearrangement corrections required by mass spectrometric methods. In addition, the ability to measure a sample in replicate (n = 3) in <30 min with precision better than ±0.3‰ for all isotopologues increases the throughput of N2O clumped isotope measurements and improves greatly on previous analytical approaches.
We present results for N2O equilibrated over g-alumina, which has been identified as a catalyst for the N-O isotope exchange equilibria, at temperatures between 170 °C and 230 °C. This range of temperatures represents an optimum where the kinetics of isotope exchange reactions outpace N2O thermal decomposition but proceed fast enough for readily repeatable experiments. Additionally, this range of temperatures is associated with a predicted variation in SP of 4.6‰, suitable for evaluating the temperature dependency of reactions among N2O isotopologues. We find the catalytic activity of g-alumina to be sensitive to its conditions of activation and to the N2O/catalyst ratio. We report equilibration and analyses of gases of a wide variety of starting isotopic compositions to demonstrate the equilibrium nature of these reactions by the principle of bracketing, to document the kinetics of isotope exchange for each isotopologue, and to establish a set of reference gases suitable for robust two-point calibration in all isotopic dimensions.
How to cite: Magyar, P., Kueter, N., Zhang, N., Chénier, N., Emmenegger, L., Tuzson, B., and Mohn, J.: An absolute reference frame for nitrous oxide position-specific and clumped isotopic measurements, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16221, https://doi.org/10.5194/egusphere-egu25-16221, 2025.
Urban areas as important sources of industrial and transport emissions, have a key impact on the atmospheric greenhouse gas trends. In order to study these emissions we collected atmospheric air samples at the HUN-REN Institute for Nuclear Research (ATOMKI) of Debrecen, Hungary, in three different seasons (winter, spring and summer). Sampling was done to reflect differences between weekdays and weekends and between morning and afternoons. For this study we collected at least 23 samples each season. We compared carbon dioxide (CO2) concentration and radiocarbon (14C) results with observations from the Hungarian ICOS (Integrated Carbon Observation System) regional background station. Within the project, stable isotope analysis was performed at Utrecht University while CO2 mole fraction and 14C were measured at ATOMKI.
The results show that depleted δ13C and Δ14C values observed during morning hours -especially winter- may indicate fossil fuel emission sources. On the other hand, summer shows enriched isotopic values because of the stronger biogenic uptake. We analyzed strong correlations between δ¹³C and Δ¹⁴C values in winter, compared to weaker correlations in spring, suggesting that isotopic signals may be influenced by different processes depending on the season. The findings provide important information in the field of carbon isotopic measurements that could simplify distinguishing between CO2 sources or understanding seasonal shifts between biogenic and anthropogenic sources.
Project number C2295145 has been implemented with the support provided by the Ministry of Culture and Innovation of Hungary from the National Research, Development and Innovation Fund, financed under the KDP-2023 finding scheme.
How to cite: Baráth, B. Á., Varga, T., Major, I., Bán, S., Barcza, Z., Haszpra, L., Röckmann, T., van Es, J., van der Veen, C., and Molnár, M.: A comprehensive carbon isotopic analysis of seasonal carbon dioxide variability from an urban environment in Hungary, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16416, https://doi.org/10.5194/egusphere-egu25-16416, 2025.
The hydroxyl radical (OH) serves as a primary sink for CH4 in the atmosphere and plays an important role in interpreting the global CH4 budget. Changes in the OH trend have recently been proposed as a potential explanation for the renewed increase of CH4 and the simultaneous decrease in δ13C(CH4) since 2007. In this work, we introduce comprehensive numerical sensitivity simulations to explore the impact of temporal OH variations on the globally averaged CH4 mixing ratio and δ13C(CH4) signature. We apply the state-of-the-art global chemistry-climate model EMAC and use a simplified approach to simulate methane loss. Our simulations apply different OH fields, including climatologically described and transient OH fields, and assume moderate changes in the CH4 tropospheric lifetime. We also consider methane isotopologues and the kinetic isotope effects in physical and chemical processes. The setup uses recent CH4 emission inventories and accounts for regional differences in the isotopic signatures of individual emission source categories. Our results suggest that the influence of an OH reduction on the global δ13C(CH4) is rather small and does not explain the observed trend in CH4. Additionally, we examine the impact of the latitudinal OH distribution on the relative contribution of different emission source categories to the global CH4 rise and the global mean surface δ13C(CH4).
How to cite: Nickl, A.-L., Jöckel, P., Winterstein, F., and Schmidt, A.: Numerical simulation of the impact of atmospheric OH variability on the global mean δ13C(CH4) trend., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16768, https://doi.org/10.5194/egusphere-egu25-16768, 2025.
The δ18O signature of atmospheric CO2 can be used as a tracer for estimating gross primary production (GPP), however, this method requires having detailed knowledge of δ18O signatures of numerous water reservoirs and isotopic fractionation associated with transfer processes, which are highly variable due to the complexity of the hydrological cycle. Simultaneous measurements of δ18O-CO2 and δ17O-CO2 can simplify this requirement, since variations in δ17O are, for most processes, strongly correlated with variations in δ18O. Thus, it is possible to combine measurements of δ18O-CO2 and δ17O-CO2 into a tracer that removes the mass-dependent fractionations related to the hydrological cycle, known as the ‘triple oxygen isotope excess’ (Δ17O). Variability in Δ17O only depends weakly on the oxygen isotope signatures of soil and leaf water and should therefore in principle be a more direct tracer for GPP than variations in δ18O alone.
We present a 2.5-year record (2021-2024) of atmospheric δ13C-CO2, δ18O-CO2, δ17O-CO2, Δ17O, and CO2 mole fraction measurements at Weybourne Atmospheric Observatory on the north Norfolk coast in the UK (52º 57’ N, 1º 07’ E). Measurements are made in-situ every 4 minutes using a tuneable infrared laser direct adsorption spectroscopy (TILDAS) dual-laser analyser from Aerodyne Research Inc. We present observed atmospheric variability in Δ17O on seasonal, diurnal, and synoptic timescales, and report the measurement system short-term repeatability and reproducibility.
How to cite: Pickers, P., Forster, G., Kaiser, J., Marca, A., Manning, A., Paxton, R., and Arnold, T.: In-situ atmospheric measurements of CO2 polyisotopologues at Weybourne Atmospheric Observatory in the United Kingdom, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17599, https://doi.org/10.5194/egusphere-egu25-17599, 2025.
Bulk isotope ratios (δ13C-CH4 and δD-CH4) are used as tracers to help determine the contribution of methane (CH4) sources and sinks to the atmospheric burden. The multiply substituted (clumped) isotopologues are now potentially available as additional tracers to improve these distinctions in the global understanding of the CH4 budget. Measurement of Δ13CH3D and Δ12CH2D2, however, is more challenging than measurements of bulk isotopes and requires more advanced instrumentation. Our ongoing project, POLYGRAM (www.polygram.ac.uk), is developing the sampling strategy, sample preparation, mass spectrometry, and modelling work to begin monitoring these new isotopologue ratios.
Use of a custom-built automated preconcentrator is a key step in our approach during sample preparation, as HR-IRMS requires ultra-pure CH4 samples to measure the multiply substituted isotopologues. For ambient air studies we obtain 150 ml samples (1 bar) containing around 1% amount fraction of CH4, which can then be easily transported and further purified for final analysis. Importantly this separation technique is automated, free of liquid cryogen, and requires minimal manual intervention. We have also developed the system to be flexible and allow for preparation from any natural sources containing less than 1% CH4. We will present the validation of the method as well as a discussion to support the motivation for future development of monitoring Δ13CH3D and Δ12CH2D2 in the global atmosphere.
How to cite: Arnold, T., Defratyka, S., Gartside, A., Wilson, F., Rennick, C., Clog, M., and Chung, E.: Semi-automated separation of methane from ambient air for analysis of Δ13CH3D and Δ12CH2D2, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18216, https://doi.org/10.5194/egusphere-egu25-18216, 2025.
Recent progress in the field of laser spectroscopy has transformed the measurement of major greenhouse gases in the atmosphere, enabling real-time, in-situ field measurements of carbon dioxide (CO2) and methane (CH4) stable isotope ratios. These advancements provide critical insights into sources and sinks at local, regional, and global scales. These new measurement capabilities have generated an urgent demand for commutable isotopic gas reference materials for CO2 and CH4 at ambient amount fractions in air. Achieving the level of uncertainty required for such reference materials to effectively support climate mitigation efforts remains challenging. Furthermore, the reliance on individual calibration procedures by end-users has resulted in inconsistent data and hindered comparability across datasets. Addressing these challenges requires the development of new reference materials, improved validation protocols, and standardised calibration guidelines. This effort is essential to ensure traceability for field-deployable spectroscopic methods and traditional offline flask sampling techniques using mass spectrometry. The Metrology for Climate Action workshop, co-hosted by BIPM and WMO in 2022, underscored the critical need for an improved metrological support infrastructure to advance global comparability of greenhouse gas stable isotope ratio measurements. National Metrology Institutes (NMIs), Designated Institutes (DIs), and the WMO's Central Calibration Laboratory (CCL) were identified as key contributors in expanding the global network of certified reference material suppliers. This collaboration is crucial for providing the atmospheric measurement community with access to traceable isotopic greenhouse gas reference materials, thereby supporting the verification of emissions measurements. To address these demands, a new CCQM GAWG/IRWG joint Isotope Ratio Task Group was established in April 2023. This task group coordinates efforts among NMIs, DIs, and intergovernmental organisations to facilitate the development of a robust metrological support infrastructure for the accurate measurement of stable isotope ratios for atmospheric greenhouse gases and related applications. As part of its foundational activities, the task group recently submitted a comprehensive paper entitled “Developing Calibration and Measurement Capabilities for Atmospheric Methane Stable Isotope Ratios at NMIs/DIs: Metrology for Global Comparability.” This collaborative effort brought together experts from NMIs, DIs, academia, and intergovernmental organizations to provide key recommendations for advancing the measurement of CH4 stable isotope ratios. The paper also reviews the various elements that make up Calibration and Measurement Capabilities (CMC) to aid NMIs and DIs in developing their capabilities to support the atmospheric community's need for reliable stable isotope ratio measurements of CH4. This presentation will summarise the task group’s objectives, progress, and key recommendations. Additionally, it will provide a preliminary result from a global survey that is conducted in the first quarter of 2025, mapping the global capabilities for the measurement stable isotope ratio of CH4. Through fostering collaboration among diverse stakeholders, the task group aims to enhance global greenhouse gas data comparability and support effective climate action. We invite experts and organisations with a shared interest in this field to join us in this critical endeavour.
How to cite: Nehrbass-Ahles, C. and Srivastava, A. and the CCQM GAWG/IRWG Joint Task Group on Stable Isotope Ratio Metrology for Atmospheric Source Apportionment (CCQM-GAWG-IRWG-TG-ISOTOP): Facilitating the development of a global measurement infrastructure for the measurement of stable isotope ratios for greenhouse gases source apportionment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18701, https://doi.org/10.5194/egusphere-egu25-18701, 2025.
The Arctic region plays a crucial role in the global methane (CH4) budget, as it is anticipated to contain substantial CH4 sources, such as (subsea) permafrost. The sparse network of land-based meteorological observation stations in the Arctic results in significant data gaps, particularly for marine sea-ice covered regions. Ship-based measurements can complement the land-based data enhancing our process understanding of the CH4 cycling in the Arctic including source-sink dynamics.
This study presents ship-borne observations of CH4 concentration and 𝜹13C-CH4 values continuously recorded in air near the ocean/ sea-ice surface with a Picarro G2132-i Isotope Analyzer during Leg 4 (June/July 2020) and Leg 5 (August/September 2020) of the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in the Central Arctic. Three approaches to filter contamination by local pollution sources on both time series were compared. Finally, the Pollution Detection Algorithm was applied to the raw data. A comparison with recordings from the closest land stations and their seasonal patterns suggests that the ship-borne data is more closely linked to dynamic changes in methane sources, sinks, and transport processes, rather than being solely driven by seasonality. To unravel underlying processes, which may contribute to variations in the ship-borne data, we employed a two-step approach. First, we defined air mass source areas and transport pathways within the Arctic Ocean boundary layer using five-day backward trajectories modelled with the LAGRANTO analysis tool and ERA5 wind field data. Second, we linked the observed variations to the air mass source regions by utilizing Keeling plot analysis and 𝜹13C-CH4 fingerprints.
Our analysis reveals that variations in the time series are related both to specific geographical source areas and to seasonally different distinct CH4 source strengths within certain source areas. The findings highlight the importance of considering air mass source areas and seasons to understand variations in CH4 concentration and 𝜹13C-CH4 values in the Arctic. The study highlights the need for further collection of ship-borne measurements of CH4 concentration and 𝜹13C-CH4 data to enhance process understanding and modelling approaches.
How to cite: Sellmaier, S., Damm, E., Sachs, T., Kirbus, B., Wiekenkamp, I., Rinke, A., Pätzold, F., Nomura, D., Lampert, A., and Rex, M.: Ship-borne atmospheric measurements during MOSAiC contribute to detect CH4 sources and transport pathways in the Arctic , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19640, https://doi.org/10.5194/egusphere-egu25-19640, 2025.
Atmospheric observations provide a reality check on the true efficacy of climate change mitigation policy. Methane (CH4) is a potent greenhouse gas (GHG) with multiple complex sources. Stable isotope ratio measurements for CH4 provide the fingerprints necessary to verify emissions by source type. The isoMET project focuses on improving ambient air CH4 isotope ratio monitoring capabilities both in the laboratory and field. This project also targets improvements in the quality of CH4 isotopic source signature information as well as modelling necessary to make top-down emissions estimates with sectorial attribution.
Here, we present a new metrological infrastructure, developed within the isoMET project, for a dataset for CH4 isotope source signature measurements. In addition, information on new state-of-the-art CH4 calibration reference materials, developed in the project, will be provided. Latest results from the project on analytical advances in high-resolution mass spectrometry and laser spectroscopy for doubly substituted isotopic species of CH4 (13CH3D, 12CH2D2) will be shown. In addition, we present results on laboratory and field intercomparison, demonstrating the capability of e.g. optical isotope ratio measurements (OIRS) for δ13C, δ2H, Δ13CH3D and Δ12CH2D2 measurements in CH4. Finally, the use of atmospheric chemistry transport modelling to direct the measurement strategy for optimal emissions estimation will be demonstrated.
References
[1] isoMET project available at: https://www.npl.co.uk/21grd04-isomet
[2] J. A. Nwaboh, J. Mohn, F. Mehr, T. Arnold, V. Ebert, CCQM GAWG-IRWG Workshop on Carbon Dioxide and Methane Stable Isotope Ratio Measurements, LATU (Uruguay), 2023
[3] Mehr Fatima, Javis Nwaboh, Joachim Mohn, Tim Arnold, and Volker Ebert, EGU 2024, EGU24-20560, https://doi.org/10.5194/egusphere-egu24-20560
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: Nwaboh, J., Mohn, J., Fatima, M., Kikaj, D., and Ebert, V.: Improvements in ambient CH4 isotope ratio measurements – the isoMET project, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20522, https://doi.org/10.5194/egusphere-egu25-20522, 2025.
