Estimates of emissions from hydrogen transportation fueling infrastructure and vehicles.

Implication statement: Hydrogen is being presented and adopted as a carbon-free alternative to traditional fossil fuels in the transportation sector. Carbon emissions from hydrogen production have been well characterized, but hydrogen emissions themselves interfere with chemical processes that serve to check concentrations of atmospheric greenhouse gases. Recent published analyses suggest a 100-year global warming potential of approximately 10 for hydrogen, so that direct hydrogen emissions are of concern in quantifying climate change benefits. This is similar to concerns that methane emissions diminish the benefits of natural gas as a low carbon fuel. Our review and study have gathered the scattered literature and data relevant to hydrogen emissions, employed analogies from natural gas deployment, and derived realistic estimates of hydrogen emissions for the pump-to-wheels (PTW) transportation sector. Our results demonstrate that losses depend on the type and scale technology in place and can be substantial as a percentage. The results should be combined with existing upstream climate change emissions for hydrogen production and upstream distribution to improve quantitative assessment of the net environmental benefit offered by hydrogen in the transportation sector. This in turn should guide future investment and policy decisions. A direct implication of the results is that effort should be made to abate pump-to-wheels hydrogen emissions through adoption of best technology and practice, through improvement of hydrogen recovery, and through sizing of fueling infrastructure that is appropriate for vehicle fleet size.