As the world comes to terms with its carbon addiction, an inevitable transition from burning of fossils fuels to other energy sources will occur. This transition will require new mechanisms to move and store energy, with one possibility being hydrogen. Increasing use of hydrogen as an energy vector will lead to additional release of hydrogen to the atmosphere due to the unintended release of hydrogen during its manufacture, transport, storage, and use. Possibilities for hydrogen use include shipping, land transport, electricity use and distribution.

The effect of increased concentrations of atmospheric H₂ (molecular hydrogen), NH₃ (ammonia) and CH₃OH (methanol) on atmospheric constituents, and subsequently climate, are not well quantified and may become significant as the hydrogen economy grows. Here, the ACCESS-UKCA global composition-climate model is used to simulate the impacts of increased fluxes (and hence increases in concentration) of NH₃ and CH₃OH on key climate-relevant atmospheric constituents such as OH (hydroxyl), and O₃ (ozone).

In ACCESS-UKCA, we find that a modest increase of emissions of NH₃ and CH₃OH results in regionally and locally significant increases in these species. The subsequent impacts on atmospheric oxidative capacity are globally negligible for the scenario tested, however there are locally significant differences. These local and regional effects may impact air quality, and merit further investigation.

One significant uncertainty is the size of the contribution that hydrogen will make to the energy mix in the future, both regionally and globally. Thus it is difficult to specify the changes in emissions that are necessary to conduct these kinds of simulations. This uncertainty is a fundamental constraint on our ability to understand the impact on atmospheric composition of a transition to a hydrogen-based economy.