Controlled-release experiment to optimize emission quantification of H2 point sources

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.