The National Physical Laboratory (NPL) is the UK's National Measurement Institute and is a world-leading centre of excellence in developing and applying the most accurate measurement standards, science and technology available. For more than a century, NPL has developed and maintained the nation's primary measurement standards. These standards underpin an infrastructure of traceability throughout the UK and the world that ensures accuracy and consistency of measurement. Hydrogen is used extensively in industry and is, on a small scale, already sold commercially as a zero emission fuel for busses and passenger cars. In the near future hydrogen use will expand in the UK and abroad as new zero emission fuels are needed to heat homes and power cars, busses, HGVs, trains, ships and aeroplanes. When it's used to fuel vehicles, the hydrogen needs to be very pure, as even trace amounts of impurities can impact the vehicles performance (performance loss, shorter range or lifetime). NPL is a world leader in measuring impurities in hydrogen and offers a commercial service where NPL scientists will fill gas bottles with hydrogen and then check the hydrogen for impurities in a laboratory using sophisticated and sensitive instruments. This service is already used by refuelling station operators to periodically check that the hydrogen they sell commercially meets required standards. Unfortunately, the process is expensive, slow to return results and generally won't be suitable when there are 1000's of refuelling stations across the UK and Europe (expected before 2030). A better approach is needed. In this project NPL will develop new low-cost sensors that will detect any impurities that could damage a fuel cell but won't be able to tell exactly what the impurity is. These sensors will be left running at a refuelling station, continuously taking small samples from the station's hydrogen supply. NPL scientists will then only need to take a sample back to the laboratory for a full analysis when a problem is detected. Refuelling station operators will also be able to know immediately (through an app or online service) if there is a problem with the hydrogen they are selling and act as necessary. This innovative solution is a huge improvement over current R&D aiming at only measuring 13 impurities individually. This project and the new sensors it will develop will therefore lead to lower priced zero emission fuels and provide consumers with greater confidence that the fuel they are buying is pure.