Poster session
We invite contributions covering:
- Assessment of methane emission reduction approaches
- Novel and emerging methane mitigation approaches, including emissions destruction and atmospheric removal
- Measurement and verification of mitigation effectiveness
- The role of methane mitigation in future climate scenarios
As a potent greenhouse gas that has increased in abundance in recent years, methane is an important target for mitigation. Enhancing the chemical loss of methane by adding chlorine to the atmosphere has been proposed by some as a potential method for atmospheric methane removal. Chlorine is known to have a wide range of impacts in the atmosphere, therefore a rigorous assessment of the potential unintended impacts that could arise from atmospheric chlorine addition is required.
Here, the Frontier Research System for Global Change version of the University of California Irvine Chemical Transport Model (FRSGC/UCI CTM) was used to investigate the efficacy and unintended consequences of atmospheric chlorine addition for methane removal. A range of scenarios were designed with varying chlorine emissions magnitudes and spatial distributions to assess how much chlorine is needed, where the most efficient areas to release the chlorine could be, and how the unintended impacts vary with these amounts and locations.
Using an idealised distribution with chlorine emissions (as Cl2) evenly distributed over the global oceans, we find that atmospheric chlorine addition produces a complex response on the methane lifetime. In broad agreement with previous modelling work, we find a global emission magnitude that is below a threshold of ~100 Tg Cl2/year would increase the methane lifetime and thus not be effective. Below this threshold, the additional chlorine results in enough tropospheric ozone destruction to reduce methane loss via hydroxyl radicals more than the increased loss via chlorine radicals. Above ~100Tg Cl2/year, the additional chlorine begins to decrease the methane lifetime, and chlorine becomes a more important sink of methane.
Other scenarios tested include concentrating chlorine emissions over specific ocean basins (e.g. Pacific, Atlantic) and in different latitude bands, such as the tropics. The response of methane under these and other scenarios, along with the unintended impacts of chlorine addition on air quality (e.g. ground level ozone) and the wider environment, will be discussed.
How to cite: Vest, K., Hossaini, R., Wild, O., and O'Connor, F.: Modelling the Enhancement of Methane Oxidation through the Addition of Chlorine, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8097, https://doi.org/10.5194/egusphere-egu26-8097, 2026.
Increased natural methane emissions make the Global Methane Pledge’s goal of cutting the total atmospheric methane burden harder to achieve. Methane’s 2020-2022 surge has faded, but current growth is still rapid. Cutting emissions is feasible: rapid advances are being made in direct practical methods to quantify and reduce agricultural methane emissions worldwide [Nisbet et al. 2025. Practical paths towards quantifying and mitigating agricultural methane emissions. Proc Royal Soc A 481]. Location, identification, quantification, and distinction between different specific sources are all becoming better, though often multiple emitters such as manure pools, animal housing, biodigesters and landfills are co-located. Top targets include cutting emissions from manure stores, biodigesters, and waste. In some cases agricultural methane can be used to generate electricity. New technology may make it possible to destroy methane in livestock barns. Emissions from crop waste and food waste in heaps and landfills, a major source of air pollution in Africa and South Asia, can be sharply and quickly reduced. Controlling biomass burning is an urgent priority in South Asia and tropical Africa, where rural crop waste burning is widespread, despite the damaging impact on public health. To date, tropical countries have paid little attention to methane, but they have the skills and resources to make significant reductions in agricultural emissions.
How to cite: Nisbet, E.: Mitigating Agricultural Methane Emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22360, https://doi.org/10.5194/egusphere-egu26-22360, 2026.
The successful mitigation of anthropogenic methane (CH₄) emissions hinges on the development of technologies that are not only effective but also economically viable at an industrial scale. Building upon previous lab-scale success, this study presents the scaling of an in-situ Methane Eradication Photochemical System (MEPS). The system is built into a shipping container, where air is drawn from a cattle barn and mixed with Cl₂ before entering a 5.5 m³ photochemical chamber. Here, the Cl₂ is photolyzed into chlorine radicals which oxidize CH₄ to CO and CO₂. The treated air is then passed through a scrubber to remove HCl and residual Cl₂. This scaled system was evaluated with airflows ranging from 250 to 1200 m³/hr across various methane concentrations.
The results indicate consistent and robust performance, validating the system's scalability. At relatively high methane concentrations (89 ppm), the system achieved a specific power of 0.33 kWh/gCH₄ and an apparent quantum yield (AQY) of 5.68% at a flow of 243 m³/hr. Performance was maintained at concentrations of 44 ppm under high-flow conditions (1122 m³/hr), yielding a specific power of 0.53 kWh/gCH₄ and an AQY of 2.3%. Furthermore, the system showed promise against challenging low concentrations (10 ppm at 970 m³/hr), with a specific power of 2.2 kWh/gCH₄.
The successful demonstration of low energy consumption across this range of flow rates and methane levels confirms the scalability of the technology. The possibility of scaling this to a level where it will effectively remove methane from cattle barns seems promising. Ongoing improvements, including the installation of a larger ventilation system, are underway to better understand the operational limits and expand the system's capabilities before scaling for commercialization can happen.
How to cite: Russell, H., Fogde, N., Bager, S., Weiss, N., McConville, A., Skifter Madsen, A., Feilberg, A., S. Johnson, M., and Krogsbøll, M.: Scaling a Methane Eradication Photochemical System for Agricultural Applications, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21983, https://doi.org/10.5194/egusphere-egu26-21983, 2026.
Interactions between iron-containing mineral dust and chloride-rich sea salt aerosols lead to the formation of iron(III) chloride salts, which initiate the photocatalytic release of molecular chlorine (Cl2) [1-5]. Photolysis of the chlorine generates reactive Cl radicals—potent atmospheric oxidants with substantial implications for the degradation of methane and other greenhouse gases. This catalytic chlorine production relies on the reoxidation of Fe(II) to Fe(III) through Fenton chemistry. To understand the photolytic chlorine production, the Fenton chemistry in these aerosols must be understood as well. This study presents experimental investigation and multiphase modeling of the dark chlorine production from the reaction of iron(III) chloride aerosols and H2O2. The experiments were performed in the 200 m3 European Photoreactor (EUPHORE) in Valencia, Spain. Measurements were collected with long-path FTIR, OPS, SMPS, PTR-MS, ACSM, Picarro G2108 and G2201-i as well as monitors for O3, NO, NO2, NOx, CO and HCHO. Furthermore, flask samples were collected for analysis of [CO], d13C-CO, [CH4], d13C-CH4 and VOCs at Utrecht University. Multiphase modeling of the experiment has been done through the integration of Fenton reactions and iron chloride chemistry into the kinetic multilayer model for Aerosol Dynamics, gas- and particle-phase chemistry in CHAMber environments (ADCHAM)[6]. A production was observed of 1.14 Cl2 molecules per Fe atom per hour and 4.33 H2O2 were consumed per Cl2 molecule produced. An inhibition of the chlorine production later in the experiment was observed and is under investigation.
This work is part of a project supported by the European Commission under the Horizon 2020 –Research and Innovation Framework Program through the ATMO-ACCESS Integrating Activity ATMO-TNA-7—0000000004 (GA N. 101008004)
[1] Chen et al. (2024) Environ. Sci. Technol., 58(28), 12585-12597
[2] Mikkelsen et al. (2024) Aerosol Research, 2, 31-47
[3] Wittmer et al. (2015) Environmental Chemistry, 12(4), 461-475
[4] Wittmer et al (2017) Journal of Atmospheric Chemistry, 74, 187-204
[5] van Herpen et al. (2023) PNAS, 120, 31
[6] Roldin et al. (2014) ACP, 14, 7953–7993
How to cite: Pennacchio, L., Mikkelsen, M., Brashear, C., Soler, R., Wood, E., Ródenas, M., Muñoz, A., van Herpen, M., Röckmann, T., Roldin, P., and Johnson, M.: Measurements and multiphase modeling of dark Fenton chlorine production from iron-salt aerosols at the European Photoreactor (EUPHORE), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15504, https://doi.org/10.5194/egusphere-egu26-15504, 2026.
Atmospheric oxidation enhancement (AOE) is a proposed category of methane removal that involves dispersing oxidizing agents to accelerate the natural oxidation of atmospheric methane. There is currently a lack of standardized metrics for assessing and comparing proposed AOE approaches. We present a quantitative assessment framework centered on conversion efficiency—the ratio of oxidized methane mass to dispersed material mass—to evaluate the feasibility of AOE approaches.
We propose two necessary but insufficient criteria: (1) climate beneficial (net carbon negative in CO₂e, accounting for methane oxidation and emissions from material production/transport), and (2) cost-effectiveness (cheaper than the social cost of methane, currently estimated to be ~$2000/tCH₄). These thresholds define minimum conversion efficiency requirements for each approach.
We apply this framework to two case studies: (1) iron salt aerosols (ISA), 40% FeCl₃ dispersed from marine vessels, and (2) hydrogen peroxide, 50% H₂O₂ dispersed from land-based towers. Drawing on published atmospheric modeling results and assumptions for material production costs and carbon intensities, we evaluate the conversion efficiencies that would be required to meet the climate beneficial and cost-effective criteria.
Conversion efficiency varies by location for both ISA and H₂O₂, with some deployment scenarios being climate detrimental. Critical uncertainties include regional variations in OH and Cl recycling rates and poorly constrained atmospheric loss pathways—uncertainties that could shift the conversion efficiency by orders of magnitude.
This proposed framework enables standardized comparisons and identifies priority research questions. Approaches failing to meet these criteria under optimistic assumptions suggest resources may be better allocated elsewhere, while those showing potential under plausible conditions merit deeper investigation. The goal is to provide a shared analytical foundation to help the community efficiently navigate the expanding solution space for atmospheric oxidation enhancement.
How to cite: Abernethy, S.: A framework for assessing atmospheric oxidation enhancement approaches, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8160, https://doi.org/10.5194/egusphere-egu26-8160, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 5
EGU26-18912 | Posters virtual | VPS3
Atmospheric Oxidation Enhancement with chlorine atoms: Efficiency, Plume Dynamics, and New Mechanistic InsightsTue, 05 May, 14:39–14:42 (CEST) vPoster spot 5