The Nord Stream subsea pipeline leaks in September 2022 resulted in an unprecedented amount of methane to be released to the atmosphere. However, the total amount emitted remains ambiguous, reflected in a wide range of pipeline volumetric estimates (bottom-up) and measurement-based (top-down) emissions estimates.

To derive a conclusive estimate of emissions, the United Nations Environment Programme’s International Methane Emissions Observatory (UNEP’s IMEO) has brought together a multitude of research groups spanning several disciplines to synthesise, contextualise and, where possible, reanalyse modelled emissions estimates. In this presentation, we present new pipeline rupture emission rate simulations and compare them with various top-down quantification approaches applied to the Nord Stream pipeline leaks. We show that our simulated bottom-up

emissions are reconciled with airborne, satellite and tall tower estimates over various points throughout the emission event, indicating our cumulative total is a robust estimate of emissions.

UNEP’s IMEO’s approach of synthesising and reanalysing existing data from all available sources assists in overcoming the methodological limitations of the individual approaches and provides a more holistic quantification of methane emissions from the Nord Stream pipeline leaks. This approach demonstrates how sharing data generated from various disciplines and quantification platforms can be used to overcome key assumptions when modelling and quantifying emissions. More generally, this study highlights the benefits of applying diverse measurement approaches to quantifying methane emissions in support of reduction commitments such as the Global Methane Pledge.

Affiliations

1-20 listed in Authors' Affiliations section

21. Deutscher Wetterdienst, Frankfurter Strasse 135, 63067 Offenbach, Germany

22. National Centre for Earth Observation, STFC Rutherford Appleton Laboratory (RAL), Chilton, UK

23. Remote Sensing Group, STFC Rutherford Appleton Laboratory, Chilton, UK

24. Technische Universität Braunschweig, Institute of Flight Guidance, Braunschweig, Germany

25. Enagás Transporte SAU, Madrid, Spain

26. GHGSat Inc., Montreal, Canada

27. Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

28. National Centre for Earth Observation, University of Leicester, Leicester, UK

29. School of Physics and Astronomy, University of Leicester, Leicester, UK

30. School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, United States

31. Key Laboratory of Coastal Environment and Resources of Zhejiang Province, School of Engineering, Westlake University, Hangzhou, Zhejiang Province, 310030, China

How to cite: Harris, S. and Schwietzke, S. and the Nord Stream Co-Authors: Synthesis of methane emissions estimates from the Nord Stream subsea pipeline leaks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20489, https://doi.org/10.5194/egusphere-egu24-20489, 2024.

Within the framework of the Oil and Gas Methane Partnership 2.0 (OGMP 2.0), initiated by the United Nations Environment Programme (UNEP), companies in the Oil and Gas (O&G) sector have committed to monitor and to reduce their methane (CH₄) emissions. Presently, more than 120 companies have joined OGMP 2.0 covering operations in 70 countries around the world, one of which is Oman. Methane is one of the most potent greenhouse gases after carbon dioxide and the focus of worldwide initiatives to combat global warming. This includes UNEP’s International Methane Emissions Observatory (IMEO), which focuses on improved data collection and delivery not only from O&G, but also from other emission sectors including waste. According to Oman’s latest Biennial Update Report, the solid waste sector is the second largest CH₄ emitter behind the O&G sector and represents 15% of Oman’s CH₄ emissions. However, until now, no sector-specific measurement-based studies on such emissions exist for Oman.

Here, we present a novel measurement study, supported and funded by UNEP´s IMEO. The approach involves measuring CH₄ emissions from both O&G installations and landfills using the unique helicopter-towed probe HELiPOD equipped with in situ CH₄ instrumentation complemented by mobile ground-based CH₄ measurements. Quantifications of CH₄ mass fluxes from individual sources or clusters can be provided from these measurements. The methodology was deployed during the METHANE-To-Go-Oman field experiment lasting from November to December 2023 in collaboration with partners from the O&G and waste industry in Oman. Within four weeks, more than 70 flight hours were successfully flown with a helicopter in the northern and southern parts of Oman, which required a complex setup. For each of the 26 flights, different flight strategies were implemented depending on the wind situation at the probed sites, which was characterized by a continuously running wind lidar. The HELiPOD probe (weight 325 kg, length 5 m) was equipped with a sensor system measuring the 3D wind vector and in situ instrumentation (Picarro G2401-m and Licor-7700) to measure CH₄ with a high precision (1 ppb) and temporal resolution (up to 40 Hz), which is necessary for a precise calculation of the CH₄ mass flux. An initial overview of the measurements is presented focusing on a showcase from a landfill.

By comparing our collected data (top-down approach) with methane mass flux estimates provided by the industry (bottom-up approach), we aim to assist the involved companies and related governments in prioritizing their methane emission mitigation actions and policies for future endeavours.

How to cite: Huntrieser, H., Förster, E., Pätzold, F., Bretschneider, L., Maier, N., Necki, J., Bartyzel, J., Jagoda, P., Witschas, B., Roiger, A., Lampert, A., (be´ah), O. E. S. H. C., and Lunt, M.: First Initiative in the Arabian Peninsula to Measure Methane Emissions from the Oil & Gas and Waste Sector by a Helicopter Probe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14711, https://doi.org/10.5194/egusphere-egu24-14711, 2024.

Atmospheric methane (CH₄) concentrations have more than doubled since the beginning of the industrial age, making CH₄ the second most important anthropogenic greenhouse gas after carbon dioxide (CO₂). The oil and gas (O&G) sectors are one of the major anthropogenic CH₄ sources accounting for 22% of global anthropogenic CH₄ emissions. The METHANE-To-Go Africa (MTGA) scientific aircraft campaign in September 2022 was conducted as part of UNEP’s International Methane Emissions Observatory (IMEO). During the campaign, we conducted the first large scale methane measurements of the O&G sector in West Africa. The study provides an initial empirical understanding of the magnitude and location of emissions in this important but previously unobserved source region. The emissions of O&G facilities were determined using an aircraft-based mass balance method.

The entire emissions of the Angolan offshore O&G sector and the liquid natural gas (LNG) plant were observed to be in the range of emissions reported by the Angolan operators. This is much less than the estimates from scientific emission inventories like EDGAR and CAMS-GLOB-ANT.

For the regional scale emission estimates, the Angolan O&G facilities are aggregated in blocks, a local operator-wise separation of assets. Most blocks have low emissions of methane. We observed medium emissions at one block and high emissions at two blocks. These three blocks are close to the coast, in shallow water, and the facilities are generally older than further out at sea.

Often the emissions of individual facilities or groups of facilities could be discerned from the mass balance flights. We deduced emission estimates for 31 individual facilities and 10 groups of facilities. The emission estimates on different days are consistent for all facilities, showing little temporal variation. The generally older shallow-water facilities show higher emissions than the deep and ultra-deep water facilities, which have a higher oil production.

The additional trace gases CO₂, SO₂, NO_y and aerosol particles were also observed from the aircraft. This data is used to further investigate the source of CH₄ emissions: flaring, fugitives, venting, or burning of fuel gas. The CH₄-CO₂ ratio indicates that most CH₄ emissions result from fugitives and venting, not flaring. Ten different flare exhaust plumes were sampled at close distance. The flaring observations will be further analyzed including information on gas composition from the operators.

Overall, this study gathered a unique dataset in its coverage providing extraordinarily comprehensive measurements of the CH₄ emissions from the O&G industry off the coast of West Africa.

How to cite: Fiehn, A., Eckl, M., Bräuer, T., Pühl, M., Dapurkar, N., Gottschaldt, K.-D., Aufmhoff, H., Eirenschmalz, L., Neumann, G., Sakellariou, F., Sauer, D., Ventura, G., Cadete, W., Zua, D., Xavier, M., Correia, P., and Roiger, A.: Aircraft-based mass balance estimate of methane emissions from the offshore oil industry in Angola, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18796, https://doi.org/10.5194/egusphere-egu24-18796, 2024.

Ambitious methane (CH₄) emissions mitigation represents one of the most effective opportunities to slow the rate of global warming.  The oil and gas (O&G) sector, a significant source of CH₄ emissions, offers technically feasible and cost-effective emission mitigation options. Romania, a key O&G producer within the EU, with the second highest reported CH₄ emissions from the energy sector in 2020 can play an important role towards the EU’s emission reduction targets. Based on UNFCCC data, during the period 1990-2019, one of the largest reductions in fugitive CH₄ emissions from O&G were observed in Romania. However, the concentrated reduction in mostly a single year raises questions about the true extent of emission reductions. The Romanian Methane Emissions from Oil and Gas (ROMEO) project aimed to characterize CH₄ emissions related to onshore O&G production in Romania at a component, facility, and basin scale using a variety of both ground- and airborne-based measurement techniques. In the first phase in 2019 in the southern main oil production region, measured emissions were characterised by heavily skewed distributions, with 10% of the sites accounting for more than 70% of total emissions. Integrating the results from all site-level quantifications, we derive a central estimate of 5.4 kg h^–1 site^-1 of CH₄ (3.6 – 8.4, 95% confidence interval) for oil production sites. Aircraft quantifications from mass balance flights and raster flights, combined with atmospheric modelling, confirm these high emission rates. Based on the site-level results, we estimate a total of 120 ktons CH₄ yr^–1 (range: 79 - 180 ktons yr^–1) from oil production sites in our studied areas. This is approximately 2.5 times higher than the reported emissions from the entire Romanian oil production sector for 2020. During the second phase in 2021, targeting the Transylvanian gas production basin, more emitting sites are observed, but the emission rates per gas production site are lower than those from the oil production sites in the oil production region. Based on the source level characterization, up to three quarters of the detected emissions from oil production sites are related to operational venting. In 2021, following reported repairs by operators to address open vents, additional aircraft flights using a remote sensing method targeting the southern oil production region detected fewer emitting oil production sites. However, there is large uncertainty surrounding the exact magnitude of emissions below the method’s high detection threshold. Additionally, high emissions were observed from large vent stacks that had not been detected with the ground-based measurements in 2019. Our results suggest massive mitigation potential in Romania's O&G production infrastructure by capturing gas and minimizing operational venting and leaks. By synthesizing the findings and data collected across different spatial and temporal scales during the ROMEO campaigns, we can gain better understanding and valuable insights into the true magnitude and distribution of CH₄ emissions from Romania's O&G sector. The results of this data integration can allow us to fill critical gaps of missing information and address discrepancies between existing emission inventories and empirical estimates.

How to cite: Stavropoulou, F., Vinković, K., Korbeń, P., Schmidt, M., Jagoda, P., Necki, J. M., Maazallahi, H., Brunner, D., Kuhlmann, G., Delre, A., Scheutz, C., Schwietzke, S., Zavala-Araiza, D., Chen, H., and Röckmann, T. and the ROMEO team: High potential for CH4 emission mitigation from oil infrastructure in one of EU's major production regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11142, https://doi.org/10.5194/egusphere-egu24-11142, 2024.

Accurate and frequent measurement-based inventories of methane emissions from the upstream oil and gas (UOG) industry are crucial to developing and implementing effective regulations and achieving sustainable mitigation.  Recent advances in the analysis of large-scale survey data have enabled measurement-based basin/jurisdiction-level methane inventories from remote surveys of UOG infrastructure.  Treating like facility or well types as strata within a larger sample and leveraging analytics that consider measurement uncertainties, probabilities of detection, empirical (non-smooth) source distributions, and sample size effects, specific conclusions can be derived in the context of measurement sensitivities and uncertainties.  These analyses provide useful insights to regulators and industry, including but not limited to the individual contributions of equipment types to overall methane emissions.  However, a priori design and optimization of surveys to cost-effectively derive measurement-based inventories and ensure survey coverage can achieve acceptable levels of uncertainty remains a key challenge. 

Here, we present an analysis of data from extensive aerial LiDAR and ground-based surveys of UOG facilities in Western Canada to provide much-needed guidance on source- and facility-specific sampling protocols for the UOG industry.  Insights into the temporal intermittency and variability of source rate magnitudes are derived using a statistically robust method that considers the quantification accuracy and probability of detection function of the aerial instrument.  Results provide important context regarding the required survey coverage of aerially detectable sources (greater than approximately 1 kg/h) to support the development of accurate inventories, defensible frequencies of regulated inspections, and alternative leak detection and repair programs. 

How to cite: Johnson, M., Conrad, B., and Tyner, D.: Aerial Survey Sample Size Requirements for Robust Methane Inventories in the Upstream Oil and Gas Industry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20389, https://doi.org/10.5194/egusphere-egu24-20389, 2024.

UNEP's Methane Alert and Response System (MARS) is a satellite-based system for the detection and mitigation of methane emissions around the world. As part of the International Methane Emissions Observatory (IMEO), MARS is the first global system connecting satellite methane detection to transparent notification processes intended to trigger mitigation efforts. MARS harnesses state-of-the-art satellite data to identify major emissions, activate its partners to notify relevant stakeholders, and support and track progress toward mitigation.

During the year-long pilot phase, more than 600 plumes from the energy sector were detected with high-resolution satellites, and more than a hundred were notified. In December 2023, MARS entered the nominal phase with the launch of a data portal including information about the plumes detected and notified by MARS. In its current form, MARS is focused on the detection of strong point sources (~>1 ton/h) from the oil and gas production sector, but the system is expected to develop and integrate observations from new satellites as they become available and extend to the notification of smaller sources, also from other sectors such as coal mining, waste, or agriculture.

In this contribution, we will provide a brief overview of the MARS satellite-based plume detection and monitoring system, with the updates made since the launch of the nominal phase. Furthermore, we will describe some examples of real source detection and notification efforts and discuss the next steps planned for MARS in 2024.

How to cite: Irakulis-Loitxate, I., Randles, C., Watine-Guiu, M., Mateo-García, G., Vaughan, A., Demeter, M., Cifarelli, C., Guanter, L., Maasakkers, J. D., Aben, I., de Jong, T. A., Sharma, S., Groshenry, A., Peyle, Q., Benoit, A., and Caltagirone, M.: UNEP's Methane Alert and Response System (MARS): current status, new developments and case studies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16048, https://doi.org/10.5194/egusphere-egu24-16048, 2024.

Methane (CH₄) is an important anthropogenic greenhouse gas and its rising concentration in the atmosphere contributes significantly to global warming. A comparatively small number of highly emitting persistent methane sources is responsible for a large share of global methane emissions. Methane sources often show large uncertainties regarding their emissions or locations, especially at local scales, making their detection and quantification inevitable to support mitigating climate change.

The TROPOspheric Monitoring Instrument (TROPOMI) onboard on the Sentinel-5 Precursor (S5P) satellite, launched in October 2017, provides measurements of the column-averaged dry-air mole fraction of atmospheric methane (XCH₄) with a daily global coverage and a high spatial resolution of up to  km², enabling the detection and quantification of localized methane sources.

We developed a fully automated algorithm to detect regions with persistent methane enhancement and to quantify their emissions using a monthly XCH₄ TROPOMI dataset from the years 2018-2021, generated with the WFM-DOAS retrieval algorithm, developed at the University of Bremen. The detection process comprises several steps, including an analysis of the monthly dataset, where we first characterize each region by several quantities, such as the number of months in which the region shows a methane enhancement, and then marking the regions that fulfill the defined persistence criteria. We detect more than 200 potential persistent source regions (PPSRs), which account for about 20 % of the total bottom-up emissions. By comparing the PPSRs in a spatial analysis with anthropogenic and natural emission databases we attribute one of the following source types to each detected region: coal, oil and gas, other anthropogenic sources (such as landfills or agriculture), wetlands, or unknown. Many of the detected regions are well-known methane source regions, like large oil and gas fields (e.g., Permian Basin in the USA, Galkynish and Dauletabad in Turkmenistan), coal mining areas (e.g., Bowen Basin in Australia, Upper Silesia Coal Basin in Poland), regions including large urban cities (Dhaka in Bangladesh, Mumbai in India, Rio de Janeiro in Brazil) or wetland areas (e.g., Pantanal in Brazil, Sudd in South Sudan).

In this presentation, the algorithm and some results, including a global overview of the detected regions and a more detailed analysis for some of the regions, are presented.  

How to cite: Vanselow, S., Schneising, O., Buchwitz, M., Bovensmann, H., Boesch, H., and Burrows, J. P.: Automated detection of regions with persistently enhanced methane concentrations using Sentinel-5 Precursor satellite data , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10722, https://doi.org/10.5194/egusphere-egu24-10722, 2024.

Methane super emitters are gaining importance for methane emission mitigation due to initiatives like the EPA’s Super Emitter Response Program. In addition, a variety of new methane plume-mapping sensors are coming online (e.g., Carbon Mapper/Planet Tanager, EnMAP, PRISMA, EMIT, GHGSat, MethaneSat). These sensors all have the capability to map and measure super emitters, therefore it is critical that we have robust methods to characterize the performance of individual sensors and to combine observations from multiple sensors. In this study we use coincident data from the EMIT instruments and an airborne imaging spectrometer to demonstrate the performance of EMIT and to test methods for multi-sensor observations. We use these data to constrain a Probability of Detection (POD) model for EMIT. We demonstrate that under favorable conditions the 90% probability of detection for EMIT is 700 kg/hr and the 10% probability of detection is 275 kg/hr. We also offer a new framework for how sensors with dramatically different detection limits, such as an airborne imaging spectrometer and EMIT, can be combined to accurately measure persistence and emission rates for individual sources that are observed by multiple instruments. 

How to cite: Ayasse, A., Cusworth, D., and Duren, R.: Coincident Airborne and Satellite Acquisitions of Methane Plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11178, https://doi.org/10.5194/egusphere-egu24-11178, 2024.

How to cite: Yuvaraj, R., Lauvaux, T., Ciais, P., Bonne, J.-L., Joly, L., Groshenry, A., and Ba, A.: High-resolution modelling of methane plumes: validation and sensitivity experiments to explore UAV and satellite observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18958, https://doi.org/10.5194/egusphere-egu24-18958, 2024.

Methane is one of the most powerful greenhouse gases that has contributed to about a third of the 2010-2019 global warming relative to the pre-industrial times in 1850-1900. The Upper Silesian Coal Basin in southern Poland is one of the strongest anthropogenic methane (CH₄) emitters in Europe, with emissions ranging from 228 to 339 ktCH₄yr^-1. In that region, ventilation shafts and drainage stations used in coal mines are the main sources of CH₄ emissions, of which the mass flows and their sources of uncertainties can be assessed using an adapted version of the Integrated Mass Enhancement (IME) method.

This challenge can be tackled using observations from Fabry-Perot imaging Short Wave InfraRed (SWIR) spectrometers onboard of the GHGSat aircraft and GHGSat satellite constellation. GHGSat acquisitions were made in June and July 2022 during a campaign including other measurements and which was partially funded in the framework of UNEP’s International Methane Emissions Observatory. The GHGSat level-2 data provide full-swath CH₄ concentration estimations and filtered CH₄ plumes with spatial resolutions < 1.1 m on a swath width < 0.75 km for the aircraft, and < 28 m on a swath width < 12 km for the satellites, both featuring a spectral resolution of 0.1 nm. Furthermore, another version of the methane plumes was generated through a Z-test filter.

These observations were complemented with local wind profile and plume profile observations to estimate the effective wind speed that accounts for the effects of turbulent diffusion in the plume dissipation. This was achieved using two instruments from the University of Heidelberg: a wind lidar measuring the wind profile up to 200 m height at a sampling rate of ~8 seconds and a hyperspectral SWIR camera featuring a 1 min scanning time, a spatial resolution of 0.8 m and a spectral resolution of 7 nm. Since local wind profile measurements are rarely accessible, this study attempted to find a relationship between the effective wind speed for the methane plumes of that region as a function of the wind speed at 10 m height from the ERA5-Land reanalysis (spatial resolution of 9 km and temporal resolution of 1 h).

Finally, a comparison is performed between the methane mass flow estimations derived from GHGSat satellites and aircraft observations with coinciding mass flow estimation from the CH₄ safety sensors located inside four of the same ventilation shafts (data collected by AGH University of Kraków) and the hyperspectral camera in June and July 2022. Moreover, another comparison is done with data acquired from a helicopter towed probe (HELiPOD) operated by the DLR and the Technical University of Braunschweig over one of the same shafts in June 2022. While bottom-up inventories may have delays of a few years before being available and require a certain level of trust, satellites can solve these issues through a faster top-down approach but still with relatively high uncertainties and multiple sources. The findings presented in this study can help to quantify the level of contribution from the different sources of uncertainties with high resolution data.

How to cite: Taupin, Q., Schüttemeyer, D., Girard, M., Knapp, M., Butz, A., Swolkień, J., Field, R., Huntrieser, H., Förster, E., and Kuhlmann, G.: Quantifying anthropogenic methane emissions and their uncertainties using very high spatial and spectral resolution satellite and airborne data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11333, https://doi.org/10.5194/egusphere-egu24-11333, 2024.

As we are risking to exceed the 1.5-degree target in the next decade, effective measures to cut back greenhouse gas emission are necessary. With this in mind, the global community expressed the necessity to shift away from fossil fuels at COP 28 for the first time in its history. During this transition process, millions of oil and gas wells will be abandoned. However, recent studies found substantial methane emissions from old abandoned wells for example in the USA and Canada. Hence, the establishment of a proper abandonment procedure is necessary. To achieve this, further research of the current situation of abandoned wells in different countries, reasons for well integrity failure and best abandonment practices are inevitable. So far, only about a dozen countries have measured data on methane emissions and even less include it in their yearly greenhouse gas inventory. Germany has about 20,000 abandoned wells, which are generally plugged and buried, however, it is unclear, whether they are emitting methane or not.

Here, we present an overview of two years of closed-chamber methane emission measurements at 59 onshore oil and gas wells in Northern Germany, covering both abandoned exploration and production wells. As the majority of well sites showed no methane leakage, we focus on two oil fields (“Steimbke Nord” and “Nienhagen (-Elwerath)”) with sample sites that showed minor methane emissions of up to ~540 nmol m^-2 s^-1. Based on a combination of soil gas hydrocarbon concentrations (methane, ethane, and propane) and isotopic methane compositions, we were able to link the methane emissions at three well sites at “Steimbke-Nord” to regionally occurring natural methanogenesis in the overburden (peat). One well at “Nienhagen (-Elwerath)”, however, was characterized by high δ¹³C-CH₄ and a composition of higher hydrocarbons, typical for oil-associated gases and/or biodegraded oil. We will discuss two possible emission sources: (1) well integrity failure and (2) microbial degradation of oil residues from an old oil spill or a drilling mud pit. Furthermore, we will examine the mitigation potential of microbial methane oxidation for methane emissions to the atmosphere. In summary, our data demonstrates the complexity of emission studies on buried abandoned wells and underlines the necessity for a combination of soil gas sampling and flux measurements.

How to cite: Jordan, S. F. A., Schlömer, S., Krüger, M., and Blumenberg, M.: Methane emissions at buried abandoned wells in Northern Germany: sampling strategies, pitfalls, and silver linings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8005, https://doi.org/10.5194/egusphere-egu24-8005, 2024.

Methane (CH₄) is the second most important anthropogenic greenhouse gas (GHG), and its emissions reduction has been identified as an essential mitigation target to slow down climate change. According to inventories, fossil fuel production and usage account for roughly 17% of the global CH4  emissions, of which approximately 33% originate from coal mining. Accurate identification of coal mining-related CH₄ sources and quantification of their annual emission rate is needed for corporate reporting requirements, national inventory verification, and the development of CH₄ mitigation strategies.

A previous study estimated CH₄ emissions for six coal mines in the Bowen Basin in Queensland, Australia, using TROPOMI satellite measurements. It covered a sub-area of the Bowen Basin, where coal is mined at over 40 active mining locations distributed over 60,000 km². The study showed a significant discrepancy compared to inventory estimates by a factor of 7 during 2018 and 2019.

To further verify satellite estimates and improve knowledge of the distribution, persistence, and strength of emissions of this mining region, the Bowen Basin CH₄ Mapping (BBCMap) Campaign was conducted in September-October 2023, funded by and performed in collaboration with UNEP's International Methane Emissions Observatory. During this campaign, two HK36 Eco-Dimona research aircraft carrying complementary sensing instrumentation were deployed. The MAMAP2D-Light (Methane Airborne MAPper 2D – Light) imaging spectrometer for estimating atmospheric CH₄ and CO₂ column anomalies and a lidar for topography scans were deployed on one DIMONA HK36 research aircraft, while the second identical aircraft was equipped with an in-situ payload consisting of an LGR OA-ICOS gas analyser for simultaneous measurements of atmospheric CH₄, CO₂, and water vapor concentrations, a turbulence probe for wind statistics, and a bag sampler for collecting multiple gas samples during each flight for later 13C isotope analyses in the laboratory. This two-aircraft strategy allowed coordinated measurements of CH₄ emissions from different coal mines with both remote sensing and in-situ instruments and simultaneous wind measurements, which is essential for deriving a robust flux estimate.

During the campaign, 39 flights were conducted, covering approximately 33 mines across roughly 20,000 km², focussing on the northern part of the Bowen Basin. Preliminary MAMAP2D-Light measurements of atmospheric CH₄ column anomalies and emission estimates for both open-cut and underground coal mines will be presented and discussed.

How to cite: Borchardt, J., Krautwurst, S., Gerilowski, K., Huhs, O., Schindewolf, J., Bovensmann, H., Kumm, M., McGrath, A., Chakravarty, S., Junkermann, W., Hacker, J., Bai, M., Kelly, B. F. J., Harris, S., Field, R., Bösch, H., and Burrows, J. P.: BBCMap 2023: Assessing methane emissions from open-cut and underground coal mining in eastern Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17580, https://doi.org/10.5194/egusphere-egu24-17580, 2024.

Satellite-based detection of methane (CH₄) point sources is crucial in identifying and mitigating anthropogenic emissions of CH₄, a potent greenhouse gas. Previous studies have indicated the presence of CH₄ point source emissions from coal mines in Shanxi, China, an important source region with large CH₄ emissions, but a comprehensive survey has remained elusive. This study aims to conduct a survey of CH₄ point sources over Shanxi's coal mines based on observations of the Advanced HyperSpectral Imager (AHSI) on board the Gaofen-5B satellite (GF-5B/AHSI) between 2021 and 2023. The spectral shift in center wavelength and change in full-width-half-maximum (FWHM) are estimated for all spectra channels, which are used as inputs for retrieving the enhancement of column-averaged dry-air mole fraction of CH₄ (ΔXCH₄) using a matched-filter based algorithm. Our results show that the spectral calibration on GF-5B/AHSI reduced estimation biases of emission flux rate by up to 5.0%. We applied the flood-fill algorithm to automatically extract emission plumes from ΔXCH₄ maps. We adopted the integrated mass enhancement (IME) model to estimate the emission flux rate values from each CH₄ point source. Consequently, we detected CH₄ point sources in 32 coal mines with 93 plume events in Shanxi province. The estimated emission flux rate ranges from 857.67 ± 207.34 kg·h^-1 to 14333.02 ± 5249.32 kg·h^-1. The total emission flux rate reaches 13.26 t·h^-1 in Shanxi, assuming all point sources emit simultaneously. Our results show that wind speed is the dominant source of uncertainty contributing about 84.84% to the total uncertainty in emission flux rate estimation. Interestingly, we found a number of false positive detections due to solar panels that are widely spread in Shanxi. This study also evaluates the accuracy of wind fields in ECMWF ERA5 reanalysis by comparing with ground-based meteorological station. We found large discrepancy, especially in wind direction, suggesting incorporating local meteorological measurements into the study CH₄ point source are important to achieve high accuracy. The study demonstrates that GF-5B/AHSI possesses capabilities for monitoring large CH₄ point sources over complex surface characteristics in Shanxi. 

How to cite: He, Z., Zeng, Z., Gao, L., and Liang, M.: A survey of methane point source emissions from coal mines in Shanxi province of China using AHSI on board Gaofen-5B, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1632, https://doi.org/10.5194/egusphere-egu24-1632, 2024.

Urban areas are at the forefront of climate change impacts, with cities being responsible for ~75% of global GHG emissions. Methane, a GHG 80 times more potent than CO₂, is significantly emitted from a range of urban sources including biogenic (e.g., landfills, drainage channels, and wetlands) and abiogenic (e.g., transportation, compressor stations, and oil and gas leaks). The real-time monitoring and precise identification of methane sources are crucial for targeted mitigation and the development of climate-resilient urban planning.

While mobile methane analyzer systems for monitoring methane have been deployed in European and North American cities, their use in densely populated tropical megacities with inferior infrastructure, like Dhaka, Bangladesh, is limited. This limitation obstructs a comprehensive understanding and mitigation of methane emissions on a global scale. Dhaka stands as the world's seventh most populous city, is acutely vulnerable to the impacts of climate change, and contends with extreme air pollution, ranking within the most polluted 1% of cities globally. Satellite imagery has persistently revealed a dense methane cloud above Dhaka, but the precise sources and extent of these emissions remain largely uncharted. Moreover, the potential methane sources in Dhaka may vary from those in other cities. Identifying and measuring these specific sources is imperative for formulating effective mitigation strategies.

In pursuit of this goal, we conducted a comprehensive ground-based mobile survey aimed to identify and quantify methane emissions in Dhaka, offering an intricate spatial and temporal emission profile of various urban sources. Using a human-propelled tri-wheeler equipped with a mobile gas analyzer system, we measured real-time CH₄ concentrations across ~1300 km during 38 surveys conducted in the winter and summer of 2023. The vehicle also featured a mobile weather station and GPS logger, recording plume locations alongside meteorological data. From the methane plumes identified, we directly measured methane flux from urban soils, drainages, wastewater channels, landfills, and wetlands. We created methane emission maps using spatial interpolation, determined plume characteristics with the Gaussian dispersion model, and computed emission rates from diverse urban sources using a flux calculation algorithm.

Preliminary findings show that average near-ground methane levels in Dhaka were 5.75 ppm (range: 2.04–309 ppm) in winter and 4.29 ppm (range: 2.05–230 ppm) in summer 2023, markedly surpassing the global background level of ~2.0 ppm, with frequent local spikes above 100 ppm. Our research reveals that in contrast to other global cities, biogenic sources are the dominant methane contributors in Dhaka, succeeded by gas leaks from pipelines and CNG stations. Urban wastewater channels and landfills emerge as the principal biogenic emitters, with substantial contributions from urban canals, wetlands, and soils in developed wetlands. Measurements at a major landfill indicated a methane emission rate of ~500 nmol.m^-2s^-1, and even the capped landfill a decade post-closure emit methane at notable rates (~9.4 nmol.m^-2s^-1), indicating they are the significant contributor of the methane cloud observed over Dhaka. These results emphasize the urgent need for targeted mitigation strategies that focus on the primary sources identified, to effectively tackle methane emissions in tropical megacities like Dhaka.

How to cite: Kayes, I., Halim, M. A., Wunch, D., and Thomas, S.: Demystifying the methane clouds over Dhaka, Bangladesh, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12408, https://doi.org/10.5194/egusphere-egu24-12408, 2024.

Scheutz¹, A. M. Fredenslund, P. Kjeldsen

¹Department of Environmental and Resource Engineering, Building 115, Technical University of Denmark, 2800 Kgs, Lyngby, Denmark.

Methane – a potent greenhouse gas - is emitted from several different treatment plants in the waste sector such as landfills, anaerobic digestion, composting, and wastewater treatment. Emissions vary in time and space and are highly dynamic. The sources are often complex consisting of many different unit processes at the treatment plant e.g. wastewater treatment plants and cover a large area e.g. landfills. Emission can thus occur from local point sources, leakages or hotspots. As an example, investigations have shown that for landfills emission rates can vary up to seven orders of magnitude within a few meters distance and that 50-70% of the total emission comes from a minor area (<5%) of the landfill. Quantification of these fugitive emissions are challenging, however measurement methods to identify local point sources and to quantify whole plant emissions are key in mitigating these direct emissions and documenting future reduction targets.

A well-established, validated, measuring method is the tracer gas dispersion method (TDM) which can quantify methane emissions at the facility level. The method relies on continuous, controlled release of a gaseous tracer at the source combined with downwind measurements of concentration of target gas (e.g. methane) and tracer gas (often acetylene). This method is well-established, validated, and has been used to quantify fugitive methane emissions from various sources such as landfills, composting plants, biogas plants, oil and gas, etc. The method has been applied at several facilities to determine emission rates, emission factors and mitigation efficiencies.

Three application cases will be presented:

• A landfill study focusing on determination of gas collection efficiencies and fulfillment of future reduction targets carried out at 23 Danish landfills.
• A landfill study presenting methane mitigation efficiencies of a new biocover technology implemented at 22 sites
• A biogas study quantifying methane emissions and losses at 69 Danish biogas plants

Combined the cases will illustrate how measurement can be used to determine emission rates, set emission reduction targets and document fulfillment.

References

Fredenslund, A.M., Gudmundsson, E., Falk, J.M., Scheutz, C., 2023. The Danish national effort to minimise methane emissions from biogas plants. Waste Management, 157, 15, 321-329.

Duan, Z., Kjeldsen, P., Scheutz, C. 2022. Efficiency of gas collection systems at Danish landfills and implications for regulations. Waste Management, 139, 269-278.

How to cite: Scheutz, C., Fredenslund, A., and Kjeldsen, P.: Methane emission quantification and reduction within the waste sector, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19967, https://doi.org/10.5194/egusphere-egu24-19967, 2024.

How to cite: McQuilkin, J., Ricketts, H., and Allen, G.: From novelty to norm: towards standardising drone quantification of gas emissions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-932, https://doi.org/10.5194/egusphere-egu24-932, 2024.

Canada is committed to reducing methane emissions by 50% below 2020 levels by 2030 in alignment with the Global Methane Pledge. The waste sector accounts for 23% of Canada’s methane emissions, and accurate estimations of current emissions from landfill sites are needed to guide mitigation efforts. In 2022, we conducted a cross-Canada aircraft-based methane measurement campaign in collaboration with Environment and Climate Change Canada (ECCC) and the UNEP’s International Methane Emission Observatory (IMEO). We used a Twin Otter equipped with high-speed gas analyzers and meteorological measurement sensors, which was flown in ascending loops, downwind transects, or both in combination, at 27 active and inactive municipal solid waste landfills in Ontario and Québec, Canada. Mass balance flux estimates were generated using the Top-Down Emission Rate Retrieval Algorithm. Additional mass balance measurements were made by Scientific Aviation using a similar approach based on Gauss’s theorem. A Gaussian dispersion model was used at other sites where conditions were unsuitable for mass balance. We were also able to compare some results to an independent truck-based measurement campaign of the same sites. Most mass balance measurements fell within a factor of ~3 with Greenhouse Gas Reporting Program data submitted by industry operators, showing reasonable correspondence within expected variability to atmospheric pressure changes and other weather variables.

The research indicated that aircraft estimates were consistently higher than those derived from trucks. This implies a possible underestimation in truck measurements, particularly during sunny, low-wind conditions when the thermal lift of landfill CH4 plumes is notable. On the other hand, Gaussian dispersion model estimates were higher and more variable than mass balance-based methane emission rate estimates. We also compared our mass balance estimates to a First Order Decay landfill model used by the Environment and Climate Change Canada Waste Reduction for planning purposes, and we found that the model often overestimated emissions. These measurement-based estimates contribute to a refined understanding of methane emissions from Canadian landfills and provide valuable data for regulatory planning purposes.

How to cite: Ghasemi, D., Fougère, C., Khaleghi, A., Stuart, J., Martino, R., Bourlon, E., and Risk, D.: Aerial Assessment of Methane Emissions from Canadian Landfills, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9675, https://doi.org/10.5194/egusphere-egu24-9675, 2024.

Agricultural greenhouse gas (GHG) release is the most dominant anthropogenic emission sector of methane (CH₄) and nitrous oxide (N₂O), therefore contribute significantly to global warming. However, there are large uncertainties in both, top-down and bottom-up emission estimates especially on the regional scale. Process models have difficulties to properly reproduce the complexity of the underlying GHG formation processes. In addition, the complicated measurement conditions, such as large areas, strong temporal variability and the spatial heterogeneity caused by the variety of agricultural emitters, makes measurements challenging. Hence the data situation is sparse. With regard to effective mitigation guidelines, observations with innovative measurement techniques are urgently needed in order to improve process-based models and therefore leading to a better understanding of agricultural GHG emissions.

Here we present first results of the in-situ aircraft campaign GHG Monitoring (GHGMon), which took place in June 2023 in the Netherlands, the world’s second largest exporter of agricultural products and thus one of the most prominent hotspots of associated N₂O and CH₄ emissions. The main objective of the campaign was to investigate agricultural emissions in this important source region and to provide a basis for the evaluation of bottom-up estimates. To this end, we setup a new eddy-covariance measurement system, based on a Quantum Cascade Laser Spectrometer and suitable for the direct and continuous airborne measurement of N₂O and CH₄ fluxes - to our knowledge, a novelty for N₂O. A total of 14 scientific research flights (45 hours) were conducted with the DLR research aircraft Cessna C208-B Grand Caravan to investigate the GHG fluxes of a variety of agricultural emitters under different meteorological conditions. The flight patterns were optimized for the eddy covariance measurement principle and to evaluate and optimize the new measurement system and to quantify this important source region. The gathered dataset will enable unique insights into the agricultural emissions of the Netherlands and will enable the evaluation of bottom-up emission estimates including process-based models.

We show that derived fluxes were consistent for repeated legs over the same target areas and during similar meteorological conditions, even on different days, indicating that our measurement approach is robust and reliable. In contrast, under different meteorological conditions, we observed different fluxes, e.g. N₂O fluxes after rainfall following on a drought period were multiple times larger than during the drought. There were also large differences measured between the emissions of diverse agricultural subsectors (cattle vs. crops vs. swine). Preliminary turbulent fluxes of 0 – 0.3 gm^-2d^-1(CH₄) and of 0 – 0.05 gm^-2d^-1(N₂O) where found during GHGMon, which in a next step will be compared to available inventories, such as the Netherlands national inventory. Our measurements demonstrate the usefulness of the airborne eddy covariance method to study agricultural N₂O and CH₄ emissions on a regional scale and to evaluate process models.

How to cite: Waldmann, P., Eckl, M., Gottschaldt, K.-D., Knez, L., Förster, E., Mallaun, C., Röckmann, T., Hutjes, R., Chen, H., Gerbig, C., Galkowski, M., Kiemle, C., and Roiger, A.: Quantifying agricultural CH4 and N2O emissions of the Netherlands using a novel airborne eddy-covariance measurements system: First results of the GHGMon campaign in June 2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19467, https://doi.org/10.5194/egusphere-egu24-19467, 2024.