Methods for detecting and quantifying hydrogen emissions over a wide range of temporal and spatial scales: a state-of-the-art review

Hydrogen (H 2 ) is currently used in several industrial sectors. However, due to its potential contribution to climate neutrality, the H 2 market is expected to expand to other sectors in the near future. H 2 emissions pose a concern due to their potential influence on methane`s atmospheric lifetime, therefore acting as an indirect greenhouse gas. Therefore, minimising H 2 emissions would reduce any environmental impact and enhance safety and efficiency of H 2 value chain. Adopting measures to mitigate H 2 emissions requires data that can be trusted and are truly representative of the emissions being monitored. Such data require validated methods based on robust metrological principles. Standard methods are needed to detect and quantify emissions over a wide range of mass or volumetric ranges, spatial and temporal scales, and emission source types across the H 2 value chain. In addition, many instruments and associated techniques are available on the (and near to) market for detecting H 2 leaks or measuring its concentration, but their suitability depends on how the instrument is deployed and its technological performance. To date, no publication reviewing these aspects is available in the literature. To cover this gap, the present paper will provide a foundation for the future development of H 2 monitoring methods. The essential constituents of a method will be defined, an overview of different monitoring techniques provided, followed by a discussion on future method development. Examples of such monitoring techniques covered are sniffers, acoustic imaging and tracer correlation. It should be feasible to develop methods to monitor emissions at component level in the near future, while further technical development is required for methods that cover larger spatial scales.