The potential transition to a hydrogen-based economy, requires a comprehensive understanding of hydrogen's atmospheric behaviour for well-informed decision-making. Among the uncertainties surrounding the atmospheric fate of hydrogen, the chemical processes governing its formation and transformation are pressing.

This study employs STOCHEM-CRI, a global 3D tropospheric chemical transport model, to explore the chemical uncertainty associated with atmospheric hydrogen. The primary objective is to improve our understanding of the hydrogen distribution, sources, and sinks on a global scale. Addressing the significant role of formaldehyde (HCHO) as a chemical source, we update its photolysis parameterisation in accordance with recent recommendations (JPL 2020 and IUPAC 2013) and assess its variability. Furthermore, we evaluate the atmospheric burden of HCHO as a function of its sources to identify key photochemical contributors to the present hydrogen budget.

The study undertakes preliminary studies of the major sink of atmospheric hydrogen, namely uptake by soil, to gauge its impact. Through a meticulous examination of model outputs against observational data, various scenarios are systematically assessed for their ability to accurately replicate global hydrogen distribution and seasonal variations.

Preliminary results show updates to the photochemical parameters of HCHO significantly reduce the hydrogen burden by between 50 and 90 ppb globally. This is namely due to updates to the quantum yield of the molecular (H2 producing) photolysis channel which varies significantly when compared to previous recommendations. There is limited variation between the two updates (JPL 2020 and IUPAC 2013) of up to 5 ppb. Additionally, minor updates relating to the temperature dependence of the soil sink result in significant improvement in the models replication of observational data, including seasonal variation.

How to cite: Holland, R., Khan, M. A. H., and Shallcross, D.: Understanding and quantifying chemical uncertainties in the hydrogen budget, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3142, https://doi.org/10.5194/egusphere-egu24-3142, 2024.

Accurate modelling of tropospheric ozone is crucial for understanding its climate and health effect, yet the uncertainty associated with natural ozone precursor emissions such as lightning and soil NO_x is often overlooked. Here we apply a global chemical transport model, GEOS-Chem High Performance, to explore this uncertainty.

The modelled present-day tropospheric ozone burden, under low to high natural NO_x emissions levels (set to align with the current literature’s range), varies from 285 to 373 Tg; primarily attributed to lightning NO_x uncertainty. Such a range far exceeds the ozone difference driven by anthropogenic emissions between the two most disparate SSP scenarios in 2050 (33 Tg). Ozone’s sensitivity to natural emissions is the highest around the tropical upper troposphere where ozone’s climate effect is also large, and would be even higher if anthropogenic emissions were reduced along the SSP1-2.6 pathway. At the surface, global mean warm-season ozone ranges from 32.4 to 38.8 ppbv, mainly due to soil NO_x. This especially introduces large ozone uncertainties in southern hemisphere regions such as the Amazon and Australia.

We also examine ΔO₃-anthro, the ozone change driven by anthropogenic emissions changes up-to 2050. We found that with respect to tropospheric ozone burden, ΔO₃-anthro shows limited differences between high and low natural emission levels (~13%), implying that the estimate of future changes in ozone radiative forcing is subject to less uncertainty from uncertain natural emissions than the present-day ozone radiative forcing itself. However, ΔO₃-anthro related to the surface ozone exposure metric shows significant contrasts with different natural NO_x emissions. The largest difference exceeds 5 ppbv (~50%) in regions such as Europe, North America, eastern China, and India. We hence stress that extra care needs to be taken when using individual models to assess ozone health risks in these densely populated regions as highly uncertain natural emissions will produce a presently unconstrained error.

How to cite: Ye, X., Wang, X., Li, D., Griffiths, P., Archibald, A., and Zhang, L.: Uncertainties in tropospheric ozone changes due to natural precursor emissions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4434, https://doi.org/10.5194/egusphere-egu24-4434, 2024.

Many global climate and Earth system models that participated in CMIP6 did not include fully interactive chemistry mechanisms mainly due to the large associated computational cost of these schemes. A number of studies have recently highlighted the potential importance of enhanced aerosol-chemistry-climate coupling and associated feedbacks for the anthropogenic effective radiative forcing (ERF) of a number of key climate forcing agents such as aerosols (Thornhill et al., 2021), methane (O’Connor et al., 2022) and ozone. The different levels of complexity in both aerosol and chemistry schemes in CMIP6 models has been highlighted as a leading contributor to the large inter-model diversity in the ERF of aerosols and trace gas species (Thornhill et al., 2021). To this end, as part of the EU Horizon project, ESM2025, advanced stratospheric-tropospheric chemistry schemes have been developed and implemented in 2 ESMs, CNRM-ESM and NorESM2, for the first time. Dedicated experiments have been conducted to determine the pre-industrial (1850) to present-day (2014) ERF with these updated models and the UKESM1.1 model, to assess the impact of fully interactive chemistry on the ERF of key forcing agents. In UKESM1.1, which already includes interactive chemistry, the interactive chemistry scheme is switched off and run with a much-simplified aerosol-chemistry mechanism driven by prescribed oxidant fields. We argue the improved realism of representing these aerosol-chemistry-climate interactions is essential for improved cross-model consensus on the magnitude of anthropogenic ERFs of aerosol and key trace gas species.

References:

Thornhill et al., Effective radiative forcing from emissions of reactive gases and aerosols – a multi-model comparison, Atmos. Chem. Phys., 21, 853–874, https://doi.org/10.5194/acp-21-853-2021, 2021.

O’Connor et al., Apportionment of the pre-industrial to present-day climate forcing by methane using UKESM1: The role of the cloud radiative effect. Journal of Advances in Modeling Earth Systems, 14, e2022MS002991. https://doi.org/10.1029/2022MS002991, 2022.

How to cite: Mulcahy, J., Cussac, M., Olivie, D., Nabat, P., Michou, M., and Lathiere, J.: Quantifying the role of interactive chemistry on the anthropogenic effective radiative forcing in Earth System Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20693, https://doi.org/10.5194/egusphere-egu24-20693, 2024.

Context: Increasing use of hydrogen (H₂) across the economy is currently seen as an important strategy for decarbonization of fossil fuel-dependent sectors. Energy scenarios, especially those aiming at net-zero GHG emission targets, project that surplus electricity produced from renewable sources, such as solar and wind, will be converted and stored as H₂ by electrolysis. The use of pure hydrogen would require the replacement or significant modification of some of the infrastructure (e.g. steel pipelines) and end-use appliances (e.g. combustion engines) by H₂-dedicated equipment (e.g. PE/PVC pipelines, fuel cells); in fact, many sectors are already moving towards these solutions. However, hydrogen can also be blended into natural gas and used in the same applications. The combustion of such blends enables reduction of carbon intensity in several sectors without significant technological retrofits. However, hydrogen combustion under lean air conditions leads to higher thermal formation of nitrogen oxides (NOx), when compared to natural gas. The amount depends on the burner type, load and hydrogen blending ratio. While NOx emissions pose a direct risk to human health and act as a precursor to the O₃ and particulate matter, deployment of H₂ would also result in direct leakages to atmosphere and associated climate impacts.

Objective: This study seeks to quantify and evaluate the potential NOx increases in the European Union (EU27) countries due to the combustion of hydrogen blended with natural gas.

Methodology: We use GAINS model framework to conduct this analysis assuming that hydrogen combustion will mostly take place in the buildings, industry (boilers and furnaces) and power generation sectors. The exclusion of the transport sector is justified by the predominant use of hydrogen in fuel cell vehicles, which do not contribute to NOx formation. Since hydrogen blends will be used in the same devices as currently natural gas, existing abatement technologies as well as their adoption rates are kept across all sectors and regions.

Expected Results: We expect the results of this study will allow us a better understanding of hydrogen impacts in terms of pollutant emissions. While the paper asserts that the findings are unlikely to influence the development or viability of future hydrogen economies in Europe, it acknowledges the importance of the analysis in revealing potential emissions trends and identifying local or country-specific trade-offs. The emphasis on existing regulations and emission control strategies in Europe provides context for the limited air quality impacts expected on the overall trajectory of hydrogen adoption. Moreover, these preliminary results could lead to relevant insights regarding expected H₂ fugitive emissions which may impact climate mitigation targets and economical viability. 

How to cite: Brito, T., Höglund-Isaksson, L., Rafaj, P., Sander, R., and Klimont, Z.: Analysis of trade-offs from the use of hydrogen blended with natural gas in the European Union, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10187, https://doi.org/10.5194/egusphere-egu24-10187, 2024.

A shift in our energy production is crucial to the control of global warming. This will occur as fossil fuels are phased out, following legislation created to reach the targets set out in the Paris Agreement. One of the possible sources for a low carbon energy landscape is renewable hydrogen. Whilst hydrogen represents an alternative energy store, it can leak from the system. Understanding the fate of leaked hydrogen is vital to quantify the implications of this energy transition. This study uses the atmospheric version of the United Kingdom Earth System Model to analyse the impact of hydrogen on the atmosphere. The model indicates that increased atmospheric hydrogen leads to an increase in tropospheric ozone concentrations. Ozone is a greenhouse gas and therefore there is an indirect atmospheric warming due to hydrogen emission through ozone. Understanding the relationship between hydrogen and the chemical ozone budget is therefore required to dissect how this warming occurs. We find that hydrogen increases ozone production, governed by the increased flux through the reaction of HO₂ with NO. Future atmospheric nitrogen oxide concentrations are expected to decrease in the coming decades, under most climate scenarios. Understanding the relationship between hydrogen and background NO_x concentrations is therefore crucial in determining the mechanisms of how hydrogen is expected to impact future atmospheres. We use the model to calculate the tropospheric global warming potential of hydrogen and how this is altered by changing background NO_x. We find that this tropospheric GWP will stay relatively constant alongside decreases in ground level anthropogenic NO_x.

How to cite: Bryant, H., Stevenson, D., Heal, M., and Sand, M.: The Impacts of Hydrogen on Tropospheric Ozone and their Modulation by Background NOx, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10918, https://doi.org/10.5194/egusphere-egu24-10918, 2024.

Using hydrogen as an alternate fuel source could lead to lower carbon emissions if sourced from renewable energies. However, it can act as an indirect greenhouse gas by extending the lifetime of methane and causing stratospheric water vapour to increase. The global production and loss of hydrogen in the atmosphere are important in order to quantify its lifetime and, by extension, its global warming potential. The main sinks for hydrogen are loss through chemical reactions with OH and biological soil uptake, the latter of which accounts for approximately 80% loss and, on average, has an error range of +/-40%. Due to the wide potential range of deposition velocities and its large global impact on hydrogen, this introduces a major uncertainty to the overall hydrogen budget.

Previously in the UK Chemistry and Aerosol model (UKCA), the soil uptake of hydrogen was fixed temporally and depended on land type, following the scheme by Sanderson et al. (2003). We have implemented the deposition scheme from Paulot et al. (2021) into UKCA in order to better represent the uptake of hydrogen. A wide range of soil parameters are used in the updated scheme: soil moisture, temperature, snow depth, soil carbon content, soil type, and soil saturation content, which allow for a more diverse and dynamic range of deposition velocities. These results from UKCA are evaluated against previous global hydrogen budgets and verified against hydrogen observations from the National Oceanic and Atmospheric Administration.

The calculation of hydrogen deposition velocity onto soil is independent of atmospheric hydrogen, and, as a result, can be calculated offline. We use data from CMIP6 simulations as inputs to calculate a range of global hydrogen deposition velocities across multiple future projections using a range of different deposition models. The different uncertainties associated with models (hydrogen deposition and climate models) natural variation, and future scenarios can be isolated. Fluctuations in deposition and variation through time can be analysed to assess the which factors have the greatest contribution to the hydrogen deposition velocity uncertainty.

How to cite: Brown, M., Archibald, A., Abraham, L., Warwick, N., and Griffiths, P.: Modelling the Global Uncertainty of Hydrogen Deposition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16477, https://doi.org/10.5194/egusphere-egu24-16477, 2024.

Hydrogen fuel, a green transition option and a cleaner alternative to fossil fuels, has an indirect greenhouse impact through atmospheric reactions of “leaked” hydrogen. Sand et al., 2023 used six different chemistry-transport models (CTM) to estimate a Global Warming Potential over a 100-year time horizon (GWP-100) for hydrogen of 11.6 ± 2.8, in range with similar studies. In this study, we extend those analyses by investigating the atmospheric production and loss terms of hydrogen in the CTMs. Specifically, we compare formaldehyde (HCHO) and the hydroxyl radical (OH) concentrations. Then we develop a box model that can be used for quickly evaluating the impact of the different sources and sinks on atmospheric concentration and isotopic composition of H₂ from a global perspective.

Atmospheric production of hydrogen through photo-oxidation of methane and volatile organic compounds represents roughly 60% of the total production. To compare the atmospheric production in the models, we evaluate HCHO (produced during photo-oxidation). A preliminary comparison between the global mean model-derived tropospheric HCHO and TROPOMI-derived HCHO suggests that all models other than WACCM perform reasonably well. Generally, models tend to overestimate HCHO values over land and underestimate HCHO concentrations over the oceans. WACCM has very low HCHO values compared to TROPOMI and the other models.

The two primary removal mechanisms are soil uptake (65-85%), and atmospheric oxidation by hydroxyl radical (OH). Among the models, OsloCTM3 and WACCM have higher OH concentrations compared to GFDL, INCA and UKCA. Direct measurements of atmospheric OH concentrations are lacking due to the short lifetime of the OH radical. Therefore, we used CO and NO₂ concentrations as a proxy to evaluate the models. Compared to satellite values (TROPOMI for NO2 and MOPPIT for CO), models seem to generally overestimate NO₂ and underestimate CO. These results are discussed within the context of the OH radical and atmospheric lifetime of H₂.

Then we present a simple box model that is developed using CTM results for studying the atmospheric budget of H₂. Reconstructions of hydrogen concentrations using ice-core records from the South Pole over the last 150 years show an increase in H₂ concentration of ~200ppb, likely due to increased methane oxidation and anthropogenic emissions. We use time-varying emissions in our box model to replicate this time evolution since the pre-industrial period.

The box model also contains a framework for studying hydrogen isotopic composition. Each of the sources and removal processes of H₂ have distinct isotopic signatures. This allows for the evaluation of concurrent changes in atmospheric concentrations and hydrogen isotopic compositions for each source/sink contribution, leading to a more robust evaluation of the hydrogen budget in the atmosphere.

How to cite: Krishnan, S.: Atmospheric hydrogen budget: an evaluation using chemistry-transport models and a box model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16977, https://doi.org/10.5194/egusphere-egu24-16977, 2024.

Increased fugitive hydrogen in the stratosphere can promote chemical reactions that result in increased lifetimes and abundances of gases that have a harmful climate impact. It is therefore crucial to understand the significance of this effect, and thereon identify and mitigate potential leakage pathways within future hydrogen energy systems. Repurposing the existing high-pressure National Transmission System and low pressure local gas distribution networks for pure or blended hydrogen delivery throughout the UK, is a solution favoured by existing gas network operators. It minimises the necessary replacement of pipeline infrastructure by re-use of £30bn of already installed welded polythene pipe network and compatible assets, which will decrease associated transport costs. However, gaseous hydrogen can compromise mechanical properties of carbon steels, posing integrity concerns for pipelines and other network components. Considerable work has investigated the extent to which material integrity could affect the repurposing potential of existing infrastructure. By contrast, this study aims to quantify the ranges of anticipated increase in atmospheric hydrogen release upon conversion of existing UK gas networks for hydrogen delivery. Based on existing network architectures, provided by UK network operators, we identify the most likely locations for leakage within UK pipeline networks and present a static model to estimate potential fugitive hydrogen. Sensitivity analyses have been undertaken to assess the impact of emissions mitigation strategies, including polythene renewal in the Iron Mains Replacement Programme and replacement of wet compressor seals. Consequently, we can consider both physical leakage at joints and equipment, and permeation losses through pipe walls from natural gas leakage data. Our findings indicate that, while significant, the climate implications of determined theoretical rates of potential hydrogen leakage without mitigation are between 6.5 and 14 times less than those associated with current natural gas transport, based on respective GWP100s. It should be noted that we have considered only the potential emissions associated with pipeline transport, and have thus ignored the additional impact of embedded supply chain emissions.

We further propose a geospatial distribution of these potential hydrogen emissions across the UK network. The dataset could serve as a crucial input for future climate modelling to assess the impact of emission location dependency on hydrogen’s global warming potential and quantify the benefits of mitigating leakage in identified “hotspots”. 

How to cite: Peecock, A., Schewe, L., and Haszeldine, S.: Fugitive hydrogen emissions from a converted national UK network of methane pipelines – stratospheric climate impacts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19183, https://doi.org/10.5194/egusphere-egu24-19183, 2024.

Anthropogenic hydrogen emissions to the atmosphere have the potential to increase if there is a proliferation of hydrogen as a fuel in the future (Warwick et al., 2023).  It is well understood that atmospheric hydrogen has a positive indirect global warming potential (Ocko and Hamburg, 2022; Sand et al., 2023).  However, substantial uncertainty remains in evaluating this global warming potential, and how this value depends on the distribution of emissions.  Principally, the most appropriate surface deposition scheme to use in models remains unclear (Paulot et al., 2021).

Motivated by the observation that the seasonal variability of station hydrogen measurements (from Petron et al., 2023) can be well described as a function of latitude, we present an idealised latitude-height model for testing prototype deposition schemes.  We show how much of the key features of the seasonal variability can be captured with an illustrative benchmark deposition scheme, and finally how this model can be used to iteratively develop existing deposition schemes (e.g. Bertagni et al., 2021).

How to cite: Tardito Chaudhri, A. and Stevenson, D.: A Simple Approach for Atmospheric Hydrogen Modelling Based on the Seasonal Variability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6038, https://doi.org/10.5194/egusphere-egu24-6038, 2024.

Hydrogen and ammonia fuels are being explored as cleaner and sustainable energy alternatives to fossil fuels, due to their potential for decarbonization. The production of renewable energy-based hydrogen converted into green ammonia offers a more efficient solution for storing and transporting energy than gaseous hydrogen. However, both ammonia and hydrogen can indirectly lead to air pollution.

Ammonia, if leaking to the atmosphere, plays a role in forming secondary aerosols, generating particles like ammonium nitrate that add to fine particulate matter (particulate matter with diameter <2.5 micrometers; PM2.5). Additionally, the production of oxides of nitrogen (NO_X) gases during ammonia combustion contributes to tropospheric ozone formation and can influence aerosol abundance (as NO_X may lead to less aerosols and not necessarily more). Hydrogen, if leaked to the atmosphere, will impact tropospheric ozone and possible aerosols through a complex chain of chemical reactions.

Our research aims to assess the potential air quality effects of shifting to a hydrogen and ammonia-based economy.

Using simulations from the three-dimensional global chemical transport model (OsloCTM3), we are investigating the impacts of hydrogen and ammonia on key air quality parameters, with a specific focus on surface concentrations of ozone and PM2.5.

We will attempt to assess the benefits of this energy transition in relation to the reduction of atmospheric pollutants associated with fossil fuels. In the case of ammonia, we will compare air pollution impacts across different emission sectors. Future work will involve the analysis of chemistry-climate model simulations.

How to cite: Jouan, C., Hodneborg, Ø., and Skeie, R.: Impact of Hydrogen and Ammonia on Surface Air Pollution., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12262, https://doi.org/10.5194/egusphere-egu24-12262, 2024.