Controlled-Release Experiment to Optimize Emission Quantification of H₂ Point Sources

The global energy transition is expected to increase atmospheric hydrogen concentrations through fugitive emissions during production, transport, storage, and use, with loss rates potentially reaching up to 10% of total hydrogen production. This is of concern since atmospheric H₂ oxidation lengthens methane's lifetime, enhances tropospheric ozone, and increases stratospheric water vapor, making hydrogen an indirect greenhouse gas. Until recently, climate-relevant H₂ emissions, producing downwind enhancements below 1 μmol mol^-1 (ppm), were undetectable due to the lack of sensitive measurement techniques. Using our multiplatform active AirCore sampler with a newly developed high-resolution Agilent 8890 GC-PDHID system capable of simultaneously measuring H₂ (±2 ppb), CH₄ (±0.5 ppb), and CO₂ (±0.3 ppm), we built upon our previous work and further optimize our sampling and emission estimation method through controlled H₂ release experiments using an 8 kW electrolyzer emitting 1.1 ± 0.1 m³ h^-1 (1.65 ± 0.15 g min^-1 under standard atmospheric conditions). We investigate the role of different sampling conditions (i.e. sampling duration and plume coverage) on the accuracy of emission quantification. From a total of 14 downwind profiles collected using both UAV and ground-based sampling, we derived a weighted mean hydrogen emission rate of 0.94 ± 0.06 m³ h^-1, with uncertainty driven by plume coverage, data resolution and spacing, and wind variability. The observed H₂ plume behavior closely matches that of tracers such as CH₄, indicating that established methane measurement strategies are transferable to hydrogen point sources. Our work facilitates future H₂ emission measurements by demonstrating the versatility and accessibility of our proposed measurement method.