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Lifecycle Analysis of Air Quality Impacts of Hydrogen and Gasoline Transportation Fuel Pathways

Abstract

Hydrogen has been proposed as a low-polluting alternative transportation fuel. This dissertation analyzes the lifecycle air quality impacts of hydrogen and gasoline use in light duty vehicles, including impacts from fuel production, delivery, and vehicle use. The analysis is conducted for various scenarios in Sacramento, California, for four pollutants: CO, NOx, VOC, and PM10. Three natural gas-based hydrogen supply pathways are considered: onsite hydrogen production via small-scale steam methane reforming (SMR), central SMR production with gaseous hydrogen pipeline delivery, and central SMR production with liquid hydrogen truck delivery. Four gasoline pathway scenarios, as compared to hydrogen pathways, are also investigated in the study. A new method is developed using travel demand model data to estimate air quality impacts of gasoline fleet operations, regression analysis is used to explore the relationship between lifecycle precursor emissions and secondary ozone formation for each hydrogen supply pathway, and a Gaussian atmospheric dispersion model is used to analyze ambient impacts.

The centralized/pipeline hydrogen pathway and the onsite hydrogen production pathway reduce pollution the most. The centralized hydrogen production with liquid truck delivery is the least clean option among the three means of hydrogen supply. The examined gasoline pathway, even with advanced new gasoline vehicles, would lead to much higher ambient concentrations of pollutants than the hydrogen pathways, producing 273 times greater CO, 88 times greater VOC, 8 times greater PM10, and 3.5 times greater NOx concentrations than those caused by the centralized/pipeline hydrogen pathway, assuming the same size vehicle population. The study also estimates the potential impacts of the above hydrogen pathways on secondary ozone air quality. The results indicate that adding a significant number of hydrogen fuel cell vehicles (FCVs) to the region would have a very small impact on secondary ozone pollution; in fact, it does not necessarily increase the peak ozone concentration, and may even cause it to decrease in some cases. The results show that advanced gasoline vehicle technologies significantly reduce air quality impacts of light duty vehicles, but hydrogen vehicle technologies provide still greater benefits, reducing the contribution of light duty vehicles to ambient air pollutant concentrations to near-zero.

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