Sustainable hydrogen has emerged in recent years as a promising contributor in clean energy transitions for its potential to help decarbonize multiple sectors. Scholars are increasingly envisioning numerous uses for cleanly-produced hydrogen, including industrial heat, energy storage, or grid-balancing demand response. Recent work, however, has indicated that hydrogen might itself be an indirect greenhouse gas, with hydrogen emissions potentially increasing warming and therefore offsetting its expected climate benefits. As we begin a national build out of clean hydrogen infrastructure, it is vital to understand potential sources and magnitudes of hydrogen emissions along the supply chain so we can prepare for and address these issues at the outset, instead of having to mitigating these impacts through retrofits down the line. This grant funds the preliminary stages of a major research project by the Environmental Defense Fund (EDF) to conduct a multi-sector, collaborative hydrogen emissions field measurement campaign to better quantify hydrogen emissions across the full hydrogen value chain. Led by Ramón Alvarez, Associate Chief Scientist at EDF, and working closely with partners at West Virginia University and Transport Energy Strategies, EDF will collect hydrogen emissions data from real-world hydrogen fueling stations, including both gaseous and liquid fueling infrastructure, and vehicles, focusing primarily on heavy-duty vehicles like trucks, buses, and forklifts. The team will deploy two new measurement devices, a hydrogen full-flow sampling system, to be used for hydrogen emissions measurement at fueling stations, and the hydrogen portable emissions measurement system, to be used for vehicle emissions testing. These measurement devices will integrate a fine-resolution hydrogen sensor that will allow the project team to measure hydrogen emissions at concentrations that are too low to be a safety concern—and thus are below the measurement threshold of existing sensors—but that, collectively, might aggregate to have climate impacts. The team will use their results to develop some of the first estimates of hydrogen emissions in the transportation sector. In addition to publishing their findings in scholarly journals, EDF will release a publicly available hydrogen emission inventory, which will include the team’s field campaign results and will continue to be expanded as EDF’s larger hydrogen campaign progresses and expands.