Hydrogen deployment is projected to expand in energy transition scenarios to decarbonize hard-to-electrify end uses. Hydrogen is an indirect climate forcer, and increased hydrogen production and use may lead to an increase in hydrogen emissions, which could occur during production, delivery, and/or final consumption. At the same time, when hydrogen deploys in the energy system, other energy carriers such as liquid fuels, natural gas, coal, and electricity would be displaced, affecting both CO2 and non-CO2 emissions, including CH4, SO2, NOx, CO, NMVOC, and BC. To our knowledge, the full suite of potential climate forcing changes from hydrogen deployment has not been examined in existing studies, in part because it requires combining information from different fields. This study addresses this gap by using a well-known integrated assessment model (GCAM) to combine (1) credible hydrogen deployment scenarios that illustrate which energy carriers could be displaced by hydrogen; (2) information about hydrogen emission rates and emission factors of other climate forcers by technology, sector, region and time; and (3) a simple climate model capable of translating all relevant emissions, including hydrogen emissions, into changes in climate forcing. Across all scenarios considered, when compared to a scenario without hydrogen deployment for energy, we find that reduced forcing from CO2 emissions dominates all other forcing changes. In addition, the net forcing change excluding CO2 and methane, as well as the net indirect forcing change from CO, NOx, NMVOC, and H2 is negative and small relative to the total forcing change. These results raise important questions for technology and policy assessment regarding the treatment of indirect and aerosol effects.
How to cite: O'Rourke, P., Mignone, B. K., Binsted, M., Chapman, B. R., Clifton, O. E., Dorheim, K., Kyle, P., and Smith, S. J.: Changes in climate forcing from hydrogen deployment as a decarbonization strategy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21824, https://doi.org/10.5194/egusphere-egu25-21824, 2025.
Investments in “clean” hydrogen as an alternative to fossil fuels are driven by anticipated climate benefits. However, most climate impact assessments of hydrogen pathways overlook or underestimate important climate-warming emissions (i.e., hydrogen, methane) and impacts over time. Moreover, hydrogen is often evaluated against conventional fossil fuels without considering alternative decarbonization options, which limits the ability to inform decision-making effectively. This study evaluates the greenhouse gas emissions mitigation potential of 31 well-to-use hydrogen pathways (renewable- and grid-based electrolytic hydrogen and fossil fuel-based hydrogen with carbon capture and sequestration [CCS]) and 14 other alternative pathways (direct electrification, electro-fuels, and CCS) to replace conventional fossil fuels for eleven use cases across various economic sectors. We aim to quantify the effect of hydrogen and methane emissions on the climate benefits of decarbonization pathways and provide guidance on where to deploy hydrogen for maximum climate benefits. Preliminary results show that, across all use cases, hydrogen and methane emissions can considerably reduce the near-term climate benefits of a decarbonization pathway, with an average of a 3% and 12% reduction for every 1% of hydrogen and methane emitted, respectively. Renewable electricity-based pathways (direct electrification, hydrogen, and electro-fuels) consistently offer greater climate benefits than pathways that involve fossil fuel and CCS, but their deployment should consider the efficiency of utilizing renewable electricity. For use cases where direct electrification is available (i.e., light-duty vehicles, buses, trucks, and home heating), it is the most efficient option to reduce climate-warming emissions. Hydrogen and electro-fuels can achieve comparable benefits but demand around 1.4-7 times the renewable electricity capacity. Therefore, they should be reserved for use cases where electrification is limited (i.e., ship, aircraft, industrial heat, power) and where hydrogen serves as a feedstock (i.e., fertilizer, steel, refinery). In these cases, additional renewable capacity buildout is required to avoid diverting resources from other essential decarbonization strategies and inadvertently increasing system level emissions.
How to cite: Sartzetakis, S., Esquivel-Elizondo, S., Rettig, I., and Sun, T.: Comparative Greenhouse Gas Impact Assessment of Well-to-Use Hydrogen and Other Alternative Pathways Across 11 Use Cases, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13708, https://doi.org/10.5194/egusphere-egu25-13708, 2025.
Hydrogen is expected to be a key contributor to the energy transition. It represents an energy carrier solution for some sectors that are difficult to decarbonize such as industrial processes or long-distance transport. The hydrogen market is therefore likely to expand rapidly in the coming decades. However, hydrogen has an indirect impact on climate, with an estimated GWP100 around 11.6 ± 2.8 (Sand, 2023). It is thus important to understand how much hydrogen is emitted to the atmosphere during its economic lifecycle (from production, to transport, storage and end-use), as well as design systems to safely minimize the emissions. Frameworks regulating hydrogen emissions are expected in the near future and UK Low Carbon Hydrogen standard already requires measuring, monitoring and reporting hydrogen emissions from hydrogen production facilities.
To ensure the quality and transparency of reported emissions, Equinor started a project in 2023 to develop and test a method to measure emissions from industrial sites. The instrument chosen was a modified mass spectrometer to allow measurements of small concentrations of hydrogen (<1ppm), with a high precision to detect only minor enhancements (~10ppb) above atmospheric background levels. As the performance of the instrument was very encouraging, 2024 was dedicated to trying to quantify emissions from a point source or an industrial site using the tracer ratio method. The selection of tracer was guided by Equinor’s safety and sustainability principles adapted to the purposes of this study. Results of small-scale tests, large-scale validation and real-life experiments will be presented.
How to cite: Roudot, M., Krohl, V., Mikoviny, T., Piel, F., Sobolev, N., and Wisthaler, A.: Refining Hydrogen Emission Measurements: Methodological Insights and Pilot Findings , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6850, https://doi.org/10.5194/egusphere-egu25-6850, 2025.
Hydrogen has emerged as a key contender for decarbonizing hard-to-abate sectors, as it has the advantage of emitting no direct carbon dioxide emissions during combustion. However, modeled indirect climate warming impacts from additional hydrogen in the atmosphere have raised questions about its role in achieving net-zero energy transitions. Here we will present findings from two complementary modeling efforts that evaluated the climate implications of hydrogen emissions, and the life cycle impacts across various applications.
The first model effort evaluated emissions in 23 net-zero scenarios from prominent U.S. economy-wide studies, estimating the magnitude of hydrogen emissions relative to residual energy-related carbon dioxide and methane emissions. The model was used to evaluate the potential impact of hydrogen emissions relative to emissions reductions and carbon dioxide removal strategies needed for net-zero scenarios. Then the model was used to estimate energy-related hydrogen and methane emissions rates and global warming potentials with the best available data in literature. Modeling results indicated that hydrogen emissions ranged from 0.02–0.15 GtCO2e/year (using GWP100), with higher emissions in scenarios featuring increased hydrogen production. Despite these emissions, the calculated climate impacts represent less than 15% of combined hydrogen, methane, and carbon dioxide emissions in most scenarios. These impacts can be largely abated through reductions in residual CO2 emissions or enhanced carbon dioxide removal. More specifically, residual CO2 emissions would need to be reduced by 1-25% in scenarios allowing fossil fuels and 32-98% in scenarios restricting fossil fuels to abate the warming effect of H2 emissions.
The second modeling effort involved a life cycle assessment (LCA) of electrolysis and steam methane reforming, highlighting that production methods and feedstock emissions are the dominant factors influencing life cycle emissions, rather than hydrogen leakage. Comparisons of hydrogen-based and fossil fuel-based systems revealed greenhouse gas emission reductions in steel production (800–1400 kgCO2e per tonne of steel) when hydrogen is used in direct reduction steel manufacturing (producing iron from iron ore without melting) rather than fossil fuels in blast furnaces, as well as in heavy-duty transportation (0.1–0.17 kgCO2e per tonne-km of cargo). Importantly, decarbonization potential of hydrogen varies by application, with steel production consistently showing emissions reductions, while benefits in heavy-duty transportation depend on the hydrogen production pathway.
These findings underscore the importance of advancing hydrogen emissions measurement, mitigation strategies, and tailored application areas to maximize its potential climate benefits while addressing indirect warming impacts.
How to cite: Moore, C., Nasta, A., Goita, E., Beagle, E., and Webber, M.: Modeling Climate Impacts of Hydrogen Transition Pathways, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12419, https://doi.org/10.5194/egusphere-egu25-12419, 2025.
With a possible transition toward a hydrogen-based economy as an alternative to fossil fuels, concerns arise regarding the environmental impacts of hydrogen emissions. Although hydrogen has no direct radiative forcing, it indirectly contributes to global warming through its interactions with atmospheric components such as methane, ozone, and water vapor. This impact has not been assessed in the SSP scenarios or in the broader AR6 scenario database.
This study integrates a comprehensive hydrogen budget into the OSCAR compact Earth system model, focusing on its sources, sinks, and chemical interactions, to assess its potential climatic impacts under the main SSP scenarios of ScenarioMIP. We evaluated key anthropogenic sources such as fossil fuel combustion, biomass burning, and leakage from hydrogen infrastructure. We parameterised secondary sources such as methane and VOC oxidation. The major sinks, atmospheric oxidation by hydroxyl radicals and soil uptake by bacteria, were modelled using simplified equations calibrated against outputs from complex process-based models.
With our approach, the hydrogen and methane cycles are fully interacting during transient simulations. Our simulations quantify the influence of hydrogen emissions on methane lifetime, tropospheric ozone, and stratospheric water vapor, which combined amount to a slight increase in radiative forcing. Under a leakage rate of 1.8%, the global temperature impact remains minor, altering predictions by a few hundredths of a degree, while a higher leakage rate of 10% amplifies the effect but hardly reaches one tenth of a degree in any scenario. The quantitative impact of hydrogen emissions in terms of global temperature exhibits a widely differing profile across scenarios, strongly influenced by the IAMs’ assumptions regarding future use of hydrogen and by the scenarios’ own emissions of methane.
Although these estimates of the climatic impact of hydrogen are not entirely negligible, especially in low-warming scenarios for which every fraction of a degree counts, our findings suggest that correcting the absence of its quantification in the AR6 scenario database would not lead to a drastic reclassification of these scenarios, which should be reassuring for policy-makers.
How to cite: Gasser, T. and Baudouin, G.: Modelling the Climatic Impact of Hydrogen Emissions in SSP scenarios, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3587, https://doi.org/10.5194/egusphere-egu25-3587, 2025.
Atmospheric hydrogen sources and sinks vary greatly with latitude and season. In particular, the major sink is deposition into soils for which there is a strong seasonality and inter-hemispheric asymmetry. However, it is understood that there is a positive global warming potential (GWP) when hydrogen is oxidised in the atmosphere.
We have formulated a conceptual model based on hydrogen fluxes that were calculated in a comprehensive atmospheric chemistry simulation as part of the HECTER project. We have used this model to extensively probe the sensitivities of the GWP and distribution of hydrogen to the time of year of emissions and their latitude, and to asymmetries in the atmosphere’s oxidising capacity. Examining these sensitives helps us to understand the discrepancies between different atmospheric chemistry models and with observations, and to further constrain uncertainties in the hydrogen GWP.
How to cite: Tardito Chaudhri, A. and Brown, M.: Conceptual Experiments to Deepen our Understanding of Sensitivities in the Hydrogen Distribution and its Impacts., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2918, https://doi.org/10.5194/egusphere-egu25-2918, 2025.
The widescale global use of Hydrogen (H2) fuel may result in increasing concentrations of atmospheric H2 gas as a result of diffuse operational leakage. While H2 is not a direct greenhouse gas (GHG), it does exhibit secondary GHG effects and influences several important atmospheric chemistry reactions which could have cascading environmental effects. The dominant process of H2 removal from the atmosphere is uptake by soils; however, this removal mechanism is poorly understood and the fate and impact of increased H2 emissions on the soil sink remain highly uncertain. In order to better understand future impacts of increased H2 concentrations we need to understand current uptake rate of a range of different soils. Models require more information and data to improve the simulation of microbial processes in soils that dominate the global sink of atmospheric H2. Over the past year, we have carried out H2 flux measurements from a number of soils, both in the field (grasslands, arable, forests and peatland soils in the UK) as well as under controlled laboratory conditions, by completing several controlled incubation experiments with soil from the UK and abroad. These studies have provided important information regarding the impact that soil moisture, soil pH, temperature and other soil properties have on H2 fluxes in soils. Our studies highlight that both physical (e.g. soil aeration) and microbial (e.g. pH and temperature) parameters strongly influence the microbial uptake of H2 in soil types, with large differences in fluxes observed between different soil types under relatively similar environmental conditions.
How to cite: Cowan, N., Hanlon, M., Bezanger, A., Dean, J., Meisel, O., Forster, G., Mills, G., Garrard, N., Nemitz, E., and Drewer, J.: Investigating the drivers of microbial H2 uptake: a summary of measured fluxes from a range of soil types and locations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18281, https://doi.org/10.5194/egusphere-egu25-18281, 2025.
Hydrogen fuel can help decarbonize the economy, but hydrogen leakage has indirect climate consequences. Atmospheric oxidation of hydrogen by hydroxyl radicals (OH) increases methane, ozone, and stratospheric water vapor concentrations. Current global 3-D atmospheric chemistry models estimate a global warming potential for hydrogen of 12 ± 3 over a 100-year horizon (GWP-100), but the models overestimate global OH concentrations and underestimate OH reactivity (OHR). These OH biases cause overestimates of the responses of methane and ozone to hydrogen. Here, we compare the hydrogen GWP-100 calculated from the standard GEOS-Chem model and a modified GEOS-Chem model where OH and OHR biases are corrected with missing organic emissions and a terminal OH sink over continents. The hydrogen GWP-100 from the standard GEOS-Chem model agrees with previous studies, but the modified GEOS-Chem model is 20% lower. Better understanding of the factors controlling global OH concentrations and OHR is needed for hydrogen GWP estimates.
How to cite: Yang, L., Jacob, D., Lin, H., Dang, R., Bates, K., East, J., Travis, K., Pendergrass, D., and Murray, L.: Assessment of Hydrogen’s Climate Impact Is Affected by Model OH Biases, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1429, https://doi.org/10.5194/egusphere-egu25-1429, 2025.
Hydrogen export from Iceland to Teesside, UK, presents a promising opportunity to decarbonize the industrial sector in Teesside. Hydrogen export to Teesside involves storage in containers, transportation via trucks to Reykjavík port, and shipping to Teesside via Rotterdam. Leveraging Iceland's abundant renewable energy resources, including geothermal and hydropower, hydrogen production achieves high full load hours (FLH) compared to intermittent renewables in other countries. Excess electricity in Iceland, which cannot be sold to neighboring countries due to geographic isolation, can be acquired at competitive prices for hydrogen production. Notably, this pricing advantage may reduce hydrogen costs below those of conventional fossil fuels, even when considering the relatively low energy efficiency of hydrogen production processes. This excess energy is particularly available during periods of intense snow and ice melt in summer, further enabling high FLH for hydrogen production.
A full life cycle assessment (LCA) was performed to evaluate the environmental impacts, using secondary data from the ecoinvent database and primary data obtained through research. Additionally, a tool was developed to assess environmental impacts for any transportation chain, ensuring the flexibility and applicability of the analysis. Logistic chains for hydrogen transport, encompassing storage, trucking, and shipping, were identified and validated in collaboration with local stakeholders. Utilizing Polymer Electrolyte Membrane Electrolysis (PEM-EC) and Iceland’s renewable electricity grid mix, hydrogen production emits 13–21 times less greenhouse gases compared to grid-based production in countries like Austria and Belgium.
Transportation of green hydrogen, including liquefaction, storage, and shipping, contributes 25–36% of the carbon footprint for export scenarios but remains a small fraction of the overall emissions compared to grid-based production in fossil-intensive electricity grids. Notably, liquefaction accounts for 81% of the transportation phase’s footprint. Environmental breakeven analyses reveal that Iceland's hydrogen supply chain can offset the emissions of alternative grid-based production within three years, or less than one year when relying solely on geothermal power.
Our results demonstrate the feasibility of establishing a low-emission hydrogen supply chain to support Teesside's industrial decarbonization. Aligning with IEA recommendations, such efforts promote the development of a global green hydrogen infrastructure. Iceland’s renewable energy potential, competitive pricing of excess electricity, and robust logistics planning position it as a pivotal player in the transition to cleaner industrial operations. As an outlook, Iceland plans to further develop its renewable energy infrastructure, increasing its capacity for green hydrogen production and export in the future [2].
[1] Vilbergsson K.V., Dillman K., Emami N., Ásbjörnsson E.J., Heinonen J., D. C. Finger, Can remote green hydrogen production play a key role in decarbonizing Europe in the future? A cradle-to-gate LCA of hydrogen production in Austria, Belgium, and Iceland, International Journal of Hydrogen Energy, Volume 48, Issue 46, 2023, Pages 17711-17728, ISSN 0360-3199, https://doi.org/10.1016/j.ijhydene.2023.01.081
[2] Cabalzar U., Blumer L., Fluri R., Zhang X., Bauer C., Finger D., Bach C., Frank E., Bordenet B., C. Stahel, (2021) Projekt IMPEGA - Import von strombasiertem Gas, Aqua & Gas, 6, 40-45, Schweizerischer Verein des Gas- und Wasserfaches
How to cite: Finger, D. C., Costa, D. A., Bjarnhéðinn, G., Arackal Narayanan, J., Thoppurathu Varghese, R., Hmaimid, Z., and Ahmed, T.: Green Hydrogen from Iceland: A Clean Energy Pathway to Decarbonizing Teesside’s Industry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9572, https://doi.org/10.5194/egusphere-egu25-9572, 2025.
Hydrogen has been identified as an essential energy carrier for a future low-carbon economy. However, recent studies have highlighted the indirect impact of hydrogen emissions on climate change, emphasizing the necessity of quantifying hydrogen emissions. It is within this framework that the NHyRA project is being carried out. The European consortium of 14 entities of NHyRA aims to assess potential current and future hydrogen emissions throughout its entire chain value (from production to end uses), develop methods to detect and measure these emissions and provide an inventory where to collect these measurements in addition to validated data that already exist in the literature.
This work will focus on the potential hydrogen emission sources from a water electrolysis system. Among existing hydrogen production methods, water electrolysis is a promising technology for converting and storing electricity, making it interesting for harnessing intermittent and fluctuating renewable energy sources. Furthermore, several European countries are implementing challenging development plans regarding the capacity of installed electrolysers. Understanding the various factors that can influence the amount of hydrogen released by this technology before it is deployed on a large scale is crucial to minimizing its environmental impact and then adopting effective mitigation strategies on the technology, e.g., new components or control strategies.
Herein, we first introduce the fundamentals of water electrolysis, and we present the typical overall design of an electrolysis system, which includes the electrolysis stack and all the auxiliaries needed for its proper work, i.e. the so-called “balance of plant”. We then proceed to qualitatively present and categorize the main potential emission sources. We start with the “Vented emissions”, which are emissions needed for the system's proper operation. The analysis includes the description of the main mechanisms that may lead to these types of hydrogen released to the vent, like physical phenomena (e.g. Hydrogen crossover) or emissions coming from a process step (e.g. Hydrogen vented after a purification unit until the quality required for fuel cell application is reached or related to Start-up/shut down procedures). Last, we present the “fugitive emissions”, which include all uncontrolled emissions that come from connections that are not perfectly sealed or permeation phenomena related.
As a conclusion of the work, we present a methodology to estimate the amount of hydrogen released considering also different operational conditions. Finally, to put all these different types of emissions in perspective, we perform a preliminary assessment of the emissions that would happen for a specific PEM electrolysis system for different power supply configurations.
How to cite: Lefranc, O., Clavreul, J., Guzzini, A., Piras, P., Saccardi, A., Saccani, C., and Pellegrini, M.: Preliminary results of the characterization of the hydrogen emissions from a water electrolysis plant at pilot scale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12198, https://doi.org/10.5194/egusphere-egu25-12198, 2025.
Hydrogen (H2) provides an alternative to fossil fuel use during the transition to net zero emissions. However, the climate impacts of a H2 economy are dependent on its production method and leakage rates during production, transport, and storage. H2 acts as an indirect greenhouse gas through its impacts on methane (CH4), tropospheric ozone, and stratospheric water vapor. H2 reacts with hydroxyl radicals (OH), the primary sink of CH4, thereby causing the CH4 lifetime to increase. The climate impacts of H2 are not well constrained, largely due to uncertainties in the H2 soil sink, which accounts for ~75% of atmospheric H2 loss.
Here, we develop a two-box model of the CH4–CO–OH–H2 scheme based on the work of Prather (1994). We improve the conventional four-equation system and incorporate data from UK Earth System Model (UKESM1) simulations to generate time-varying OH production and parameterize impacts of nitrogen oxides (NOx) on the system. We evaluate the CH4 lifetime under various H2 leakage rates and SSP scenarios to quantify impacts of changes in carbon monoxide (CO), CH4, volatile organic compounds, and NOx. As the H2 soil sink dominates uncertainty in the H2 budget, we perform a Monte Carlo analysis of uncertainties in H2 soil deposition and quantify impacts on the CH4 lifetime. We estimate the indirect global warming potential of H2 under each scenario relative to both CH4 and CO2 and propose H2 leakage rates required for climate benefits under various SSP scenarios.
How to cite: Dressel, I., Archibald, A., Brown, M., Warwick, N., and Griffiths, P.: Quantifying climate implications of a future hydrogen economy using a two-box model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7461, https://doi.org/10.5194/egusphere-egu25-7461, 2025.
Alternate energy carriers to fossil fuels are needed to mitigate climate change, of which hydrogen is one candidate if generated sustainably. Atmospheric hydrogen indirectly contributes to greenhouse warming by extending methane lifetime, and increasing stratospheric water vapour and tropospheric ozone. Its main sinks are oxidation with OH, and dry deposition via microbial soil uptake. The latter accounts for approximately 50−90% of the sink and is poorly constrained under present day conditions, with very limited studies on its future evolution. The soil sink is a large source of uncertainty in quantifying hydrogen’s climate impact and the H2 global warming potential (GWP).
This work uses an offline hydrogen deposition scheme to perform the first multi-model assessment of deposition velocities driven by physical climate data from 5 models from the Coupled Model Intercomparison Phase 6 project. Deposition values from historical data are compared to observations, and deposition velocities from 4 future scenarios (2015−2100) are assessed. We find hydrogen soil uptake increases over the century, with larger increases under scenarios with stronger climate forcing, leading to shorter hydrogen soil lifetimes. A large discrepancy (20%) between models is attributed to differences in soil moisture and soil porosity, and results in a variation of 33% in the hydrogen GWP under present day condition, with a maximum decrease of 5.3% by the end of the century.
How to cite: Brown, M., Archibald, A., and Warwich, N.: Future Hydrogen Soil Deposition: Multi-model assessment of hydrogen deposition and lifetime, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8383, https://doi.org/10.5194/egusphere-egu25-8383, 2025.
A result of the global energy transition is an expected increase in atmospheric hydrogen, due to fugitive H2 emissions during production, transport, storage and usage. Loss rates are predicted to be up to 10% of the total hydrogen production. The oxidation of hydrogen in the atmosphere leads to the lengthening of the lifetime of methane, enhanced tropospheric ozone production, and increased stratospheric water vapor levels, thereby acting as an indirect greenhouse gas. Until recently, small but climate-relevant hydrogen emissions leading to atmospheric hydrogen concentrations < 1 ppm downwind of emissions sources remained undetected. However, with our newly developed and demonstrated method using an ‘active’ AirCore sampler combined with a Gas Chromatographic system (GC-system) with a Pulsed Discharge Helium Ionization Detector (PDHID), we can detect atmospheric hydrogen emissions with a precision of <2 ppb. The ‘active’ AirCore is an atmospheric sampling system consisting of a long narrow tube (in the shape of a coil) in which atmospheric air samples are collected using a pump during the sampling experiment, in this way preserving a profile of the trace gas of interest along the measurement trajectory. Here, we present first result of a controlled-release experiment to optimize our emission quantification of H2 point sources. As a point source we used a 8 kW electrolyser releasing a constant flow of 1.1 ± 0.1 m3 of hydrogen per hour through a small vent which refers to 1.65 ± 0.15 g min-1 (under standard atmospheric conditions). For our experiments we deployed a newly developed high resolution Agilent 8890 GC-PDHID system that is able to measure H2 (< 2 ppb), CH4 (< 0.5 ppb) and CO2 (< 0.3 ppm), combined with an ‘active’ AirCore as a sampling tool. During our field experiments we deployed two different sampling methods downwind of the plume; the active AirCore was either taken on ground or flown with an UAV up to 35 m altitude. The active AirCore system with a sample volume of 4.1 L, was filled to an end-pressure of up to 1.6 bar over the course of about 2 hours of sampling resulting in up to 200 discrete H2 samples on the new GC-PDHID system. As a control measurement and source apportionment along the measurement trajectory, another sampling technique was involved which uses dried and vacuumized 2.5 L glass flasks to collect discrete samples. The glass flasks samples were further analyzed by Cavity Ring Down Spectroscopy (Picarro G2401) on mole fractions of CO2, CH4, CO, for comparison to the GC-PDHID results. We present first results of our field experiments visualizing the cross sections of the downwind plume up to ~35 m altitude and using these results to optimize our inverse Gaussian plume model. Further work will focus on expanding the inventory of other fugitive hydrogen sources along the hydrogen value chain.
How to cite: Westra, I., Scheeren, H. A., Penninga, M. J., van Heuven, S. M. A. C., and Meijer, H. A. J.: Controlled-release experiment to optimize emission quantification of H2 point sources, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9443, https://doi.org/10.5194/egusphere-egu25-9443, 2025.
In the coming decades, hydrogen infrastructure is expected to expand significantly as our energy supply moves towards net-zero carbon emissions in response to anthropogenic climate change. However, whilst hydrogen itself is not a greenhouse gas, it causes indirect warming. It reacts with other trace gases in the atmosphere, resulting in increased concentrations of tropospheric methane and ozone, and stratospheric water.
This project aims to quantify parts per billion (ppb) level concentration variations in mobile measurements of atmospheric hydrogen in the UK, enabling small leaks to be detected. Molecular hydrogen can be difficult to contain due to its small size and tendency to leak from storage. Reducing gas analysers require frequent calibration and are generally not portable. Furthermore, hydrogen is not IR active, and therefore cannot be measured using the same techniques as other mobile analysers.
We are redeveloping an off-the-shelf cavity ring-down spectroscopy (CRDS) analyser to be used for mobile measurements. The instrument contains a catalyst which converts molecular hydrogen within sample gases into water vapour that is measured using CRDS. Due to this measurement method, gases in the analyser must be dried prior to injection. The instrument is regularly flushed with dry nitrogen (N2), and ambient air and calibration standards are passed through a drying inlet that we have designed to reduce moisture within the sample gas. This inlet consists of a flow meter followed by a Nafion dryer, Drierite and magnesium perchlorate; the sample passes through a moisture detector before injection. The air is dried further by an internal drier within the instrument.
Local data will be compared to both continuous and flask measurements taken with the gas chromatography and reducing gas photometer instrument in our laboratory. After this, we will conduct field campaigns at industrial sites across the UK that are likely to be emitting molecular hydrogen.
A precise, accurate mobile analyser allows for accurate measurements of fugitive emissions from the industrial sector and better constraint of models and hydrogen’s source inventory. The analyser also allows for measurements in remote locations, and could be extremely beneficial in the search for natural hydrogen. This project allows for improvement in our understanding of hydrogen’s impact on the climate and energy sector.
How to cite: Standen, I., Fisher, R., France, J., Lowry, D., Lanoisellé, M., and Nisbet, E.: Development of Instrumentation for Mobile Measurements of Hydrogen Emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9950, https://doi.org/10.5194/egusphere-egu25-9950, 2025.
This programme examines the climate and air quality implications of transitioning from fossil fuels to hydrogen-based energy systems. It comprises three independent projects – ELGAR, HECTER and COSH-AIR – that investigate various aspects of hydrogen usage and its effects on the atmosphere. The research explores future global and UK energy scenarios, focusing on the development of hydrogen infrastructure and the potential for fugitive hydrogen emissions. It also examines the role of microbial soil processes in removing atmospheric hydrogen, as well as the impacts of hydrogen deployment on climate and air quality. This overview will provide a summary of the research undertaken and the insights gained throughout the programme.
How to cite: Warwick, N., Archibald, A., Dodds, P., Nemitz, E., ApSimon, H., and Drewer, J. and the Hydrogen Environmental Impacts Team: The UK Environmental Impacts of Hydrogen Energy Programme, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10785, https://doi.org/10.5194/egusphere-egu25-10785, 2025.
With the proposed increased use of hydrogen energy, a more accurate representation of the atmospheric hydrogen budget is crucial to evaluating potential climate impacts. To this end, we extend the study by Sand et al. (2023), where five different chemical models were used to calculate the global warming potential of hydrogen. A box-model (SimpleH2 model) has been developed using those model results to calculate how atmospheric hydrogen concentrations and hydrogen isotopic compositions change for different sources and sinks. The sources included in the model are anthropogenic sources, biomass burning, nitrogen fixation (over land and ocean), photochemical production in the atmosphere, and geological sources. The two sinks are soil uptake and oxidation by OH. In this study, we will simulate the box model with different combinations of sources and sinks (both in terms of concentrations and isotopic values) to evaluate the feasibility of those inputs, focusing on the contributions of different geological sources and soil sinks. For example, adding a geological source of 20 Tg/year with an isotopic composition of -600 per mil and increasing the soil uptake by 20 Tg/year, will modify the isotopic composition of atmospheric H2 (to ~10 per mil) far from the observed range. These provide us with useful constraints that can be tested in future measurement campaigns.
How to cite: Krishnan, S.: Constraining potential geological sources of atmospheric hydrogen using a box-model approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15596, https://doi.org/10.5194/egusphere-egu25-15596, 2025.
Given the significant role of volatile organic compounds (VOCs) on ozone formation, methane lifetime, atmospheric hydrogen formation, secondary organic aerosol formation, overall atmospheric chemistry, and both indirect and direct health impacts, their accurate representation in global atmospheric chemistry models is crucial. In this context, we introduce the Volatile Organic Compounds Model Intercomparison Project (VOCMIP) and invite atmospheric chemistry modeling groups to participate in this collaborative effort. VOCMIP aims to identify model consistencies and discrepancies, enhance parameterizations, and advance our understanding of VOC-related processes in the atmosphere. Global atmospheric chemistry model output will be compared to satellite data and in situ measurements from surface stations and aircraft campaigns for key VOCs. Special emphasis will be placed on formaldehyde (HCHO), examining its chemical sources and sinks, with a particular focus on its role in the atmospheric production of hydrogen.
How to cite: Myhre, G., Sand, M., Skeie, R., Krishnan, S., Sandstad, M., and Hodnebrog, Ø.: Volatile Organic Compounds Model Intercomparison Project (VOCMIP) , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16526, https://doi.org/10.5194/egusphere-egu25-16526, 2025.
Hydrogen (H2) is expected to become an increasingly important energy carrier during the energy transition. This will likely cause increased levels of atmospheric H2, due to unavoidable losses during the production, transport, storage, and usage of hydrogen. Multiple studies have shown that through interaction with the hydroxyl radical, global tropospheric and stratospheric composition could be impacted, however, a large uncertainty remains due to a lack of understanding of the global hydrogen budget.
For the first time, we present a comprehensive global hydrogen budget derived using a coupled H2-HD inversion framework embedded within the three-dimensional chemical transport model TM5. This budget is obtained using a global set of 178,640 H2 mole fraction measurements and 540 δD(H2) measurements, which are subsequently supplied to the CarbonTracker data assimilation system. Using its ensemble Kalman filter approach we estimate the magnitude and spatial distribution of monthly global hydrogen emissions, chemical production and losses for 2003–2023. To evaluate the robustness of our results, we compare optimized simulated hydrogen mole fractions with independent observational data from aircraft profiles collected during the IAGOS-CARIBIC, NOAA/ESRL, and ATom campaigns.
How to cite: Stroo, F., Peters, W., Hooghiem, J., Krol, M., Westra, I., and Meijer, H.: First coupled H2-HD inversion with a 3D chemical transport model (TM5): Constraining the global hydrogen budget, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17780, https://doi.org/10.5194/egusphere-egu25-17780, 2025.
Context: Expanding the use of hydrogen (H2) throughout the economy is widely regarded as a key approach to fossil fuel dependent decarbonizing sectors. However, recent studies have been showing that emissions of hydrogen to the atmosphere are indirectly associated with climate impacts, such as the prolonged lifetime of methane (CH4) as well as the formation of ozone (O3) and stratospheric water vapor (H2O). Despite hydrogen’s short atmospheric lifetime (4-7 years), the studies estimate that hydrogen atmospheric interactions could lead to a Global Warming Potential over 100 years (GWP-100) ranging from 6 to 18. Hydrogen emissions have two main sources: a) direct leakages from related appliances and infrastructure (eg.: electrolyzers, distribution networks, fuel cells); or b) incomplete combustion of fossil fuels or biomass due to poor oxygen supply, where carbon monoxide (CO) and H2 are formed.
Objective: This study aims to quantify historical hydrogen emissions from incomplete combustion from 1990 to 2020 and compare their CO₂-equivalent contribution. In addition, we evaluate the influence of policy measures on reducing these emissions.
Methodology and Data: The current work adopts the Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) model framework, which takes into account activity level (fuel consumption) by sector, emission factors and the application of control strategies for emissions abatement. We adopt historical fuel consumption from statistical data along with GAINS model’s assumptions. Hydrogen emission factors are derived from carbon monoxide (CO) emission factors by a conversion ratio estimated from the literature. Control strategies represent the countries’ regulations adopted over the period of 1990-2020.
Expected Results: As an indirect greenhouse gas, hydrogen emissions may not be as prominent as CO₂, CH₄, or N₂O, which are commonly monitored. Nevertheless, hydrogen leakage does occur and should be included in emissions inventories. Historical data and future projections could indicate consistent yearly reductions, largely driven by stricter control measures and policies—particularly vehicle standards aimed at reducing a variety of pollutants, including CO. The primary sources of hydrogen emissions from incomplete combustion are gasoline-fueled light-duty vehicles and biomass burning in the domestic sector, although sector-specific contributions may differ across countries.
Discussion: While the expansion of a hydrogen economy may lead to higher emissions from direct leaks, hydrogen has also been released into the atmosphere through past and ongoing fuel combustion. Both sources must be taken into account to ensure these emissions do not undermine the expected benefits of a decarbonized, hydrogen-based economy. This underscores the importance of existing pollution-reduction policies and their co-benefits. Although control strategies have been effective in certain sector, such as transportation, emissions from domestic biomass burning remain difficult to manage and continue to pose challenges in developing countries. Finally, the overall effect of any strategy depends not only on its effectiveness but also on how future activities are distributed across different sectors.
How to cite: Brito, T., Höglund-Isaksson, L., Rafaj, P., Sanders, R., Pauls, A., Zhang, S., and Klimont, Z.: Evaluating Hydrogen Emissions from Incomplete Combustion: Historical Trends and the Role of Policy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18263, https://doi.org/10.5194/egusphere-egu25-18263, 2025.
Atmospheric hydrogen concentrations have been increasing in recent decades. Hydrogen is radiatively inert, but it is chemically reactive and exerts an indirect radiative forcing through chemistry that perturbs the concentrations of key species within the troposphere, including ozone. Using the atmospheric version of the United Kingdom Earth System Model, we analyse the impact of 10% increased surface concentrations of hydrogen on ozone production and loss. We also analyse the impact of this hydrogen in atmospheres with lower anthropogenic emissions of nitrogen oxides (80% and 30% of present-day anthropogenic surface emissions), as this is a likely outcome of the transition from fossil fuels towards cleaner technologies. In each case, we also assess the changes in hydroxyl radical concentration and hence methane lifetime and calculate the net impact on the hydrogen tropospheric global warming potential (GWP). We find that the hydrogen tropospheric GWP100 will change relatively little with decreases in surface anthropogenic NOx emissions (9.4 and 9.1 for our present day and 30% anthropogenic emissions, respectively). The current estimate for hydrogen GWP100 can therefore be applied to future scenarios of differing NOx, although this conclusion may be impacted by future changes in emissions of other reactive species.
How to cite: Stevenson, D. and Bryant, H.: Impacts of hydrogen on tropospheric ozone and methane and their modulation by atmospheric NOx, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19715, https://doi.org/10.5194/egusphere-egu25-19715, 2025.
Posters virtual: Wed, 30 Apr, 14:00–15:45 | vPoster spot 5
EGU25-19010 | Posters virtual | VPS3
Pre-normative research on hydrogen release assessmentWed, 30 Apr, 14:00–15:45 (CEST) | vP5.41
Hydrogen could play a crucial role in achieving climate neutrality by serving as an energy carrier for renewable sources, offering an alternative to traditional fossil fuels. However, researchers are investigating the impact of hydrogen emissions, as its leakage into the atmosphere poses a concern due to its potential to indirectly influence methane’s atmospheric lifetime and thereby extending its greenhouse effect. Therefore, minimising hydrogen emissions would reduce any potential environmental impact while enhancing safety and efficiency throughout the hydrogen value chain. Thus far, the literature lacks a verified data inventory on the amount of hydrogen emitted from the value chain. Little to no standardized data are present for many elements of the value chain. Otherwise, when present, efforts are still needed for their collection and validation in a unique inventory. The research community needs to address this by improving the capability to quantify small and large emissions and delivering validated methodologies and techniques for measuring or calculating them. An open-access and comprehensible user-friendly tool is urgently needed to better quantify the emissions from the whole hydrogen value chain. The pre-normative research on hydrogen release assessment (NHyRA) project is specifically designed to address these urgent needs. As a first step in this process, the project defined the hydrogen value chain, identifying its main components’ typical operative conditions and recognizing the potential sources of hydrogen emissions. The next step, the project is working to update an open-access first version of the hydrogen emissions inventory to serve as a reference for the scientific and industrial community. Therefore, by welcoming and validating any contribution of new data, including from outside the NHyRA Consortium, subsequent versions of the inventory will include a more significant amount of data for some of the archetypes (i.e. processes or equipment) in the hydrogen value chain section, to ensure consistent scenario analysis and provide mitigation action recommendations. Furthermore, the NHyRA Consortium experts have identified hydrogen detection and quantification techniques and instruments, covering those which are commercially available and emerging. In this regard, partners of the Consortium have identified three monitoring categories: Detection of emissions at the component level, Detection and quantification of emissions at the component level, and detection and quantification of emissions at the area/site level. Additionally, new or adequately adapted experimental, theoretical, and simulation methodologies will be validated to perform laboratory or in-field measurements to achieve the ambitious goal. Experimental tests will also be performed on the most critical elements of the hydrogen value chains by the partners of the Consortium. A complete picture of the hydrogen emission scenarios, applied on the middle (2030) and long (2050) term European hydrogen economy, will be developed to enable decision-makers to quantify the impact of hydrogen emissions in the energy system transition, identifying and prioritizing effective risk mitigation actions. Finally, the project will formulate recommendations for Standards and Technical Specifications.
How to cite: Connor, A., Guzzini, A., Holewa-Rataj, J., Piras, P., Claveul, J., Robino, M., and Kostereva, A.: Pre-normative research on hydrogen release assessment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19010, https://doi.org/10.5194/egusphere-egu25-19010, 2025.
