Development of a Hydrogen Portable Emissions Measurement System to Quantify Exhaust H2 Emissions from Fuel Cell Electric Vehicles

Portable emissions measurement systems (PEMS) have been key in determining real-world driving emissions from both light- and heavy-duty vehicles. PEMS enable the operator to quantify mass emissions and correlate those emissions to the fuel consumed or vehicle miles traveled. Mass-based emissions quantifications are enabled by the concurrent use of concentration sensors for species of concern along with methods to quantify the total exhaust flow rate. We developed a hydrogen (H2) PEMS system based on a review of the literature on fuel cell electric vehicles, expected gas concentrations, available H2 sensors, and flow measurement options. Our target accuracy was within ±15% over multiple orders of magnitude in mass-specific emissions rates. Early results from multiple trips of a single transit bus showed exhaust hydrogen emissions ranged from about 2.4 to 4.5 g/km or around 2.0–3.8% of their fuel. It is important to understand these and other emissions-associated fueling stations because H2 emissions can impact atmospheric chemistry and act as an indirect climate forcer. Furthermore, at current hydrogen prices, excessive losses discourage adoption of this transportation technology.