Hydrogen has been proposed as a low polluting alternative transportation fuel that could help improve urban air quality. This research examines the potential impact of introducing a hydrogen-based transportation system on urban ambient air pollutant concentrations. This study considers two scenarios, where significant numbers of new hydrogen vehicles are added to a constant number of gasoline vehicles. In our scenarios hydrogen fuel cell vehicles are introduced in Sacramento, California at market penetrations of 9% and 20%. From a life cycle analysis (LCA) perspective, considering all the emissions involved in producing, transporting, and using hydrogen, this research compares three hypothetical natural gas to hydrogen pathways: (1) on-site hydrogen production; (2) central hydrogen production with pipeline delivery; and (3) central hydrogen production with liquid hydrogen truck delivery. With geographic considerations in Sacramento County, California, the spatial layout of each pathway step (such as the natural gas to hydrogen conversion plant, refueling stations or onsite production stations, truck delivery routes, etc.) will be determined using GIS data and relevant real-world engineering/economic data. Using a Gaussian plume dispersion model, the incremental pollution levels due to each ydrogen pathway scenario will be estimated.
For comparison purposes, conventional petroleum (both gasoline and diesel) pathways and advanced petroleum pathways with evolved vehicle technologies will be examined as well in the research. Hydrogen and fuel cell vehicle scenarios will be compared with the scenarios of petroleum and low emissions vehicles (LEVs) or ultra-low emissions vehicles (ULEVs), from the perspective of lifecycle air quality impacts. Common sense tells that vehicle operation accounts for the majority of gasoline/diesel pathways’ emissions and, therefore, plays an important role in leading to urban pollution. The California mobile emission inventory model, EMFAC2007, will be used to estimate regional emissions from conventional and advanced vehicle operation. An hourly, gridded emission inventory model, DTIM4, will be run to disaggregate the regional total emissions into finer grid cells to address spatial differences of emissions, which is important to the subsequent air quality model. Prior to this, real-world transportation networks and activities will be extracted from a travel forecasting model, SACMET. Thus, impacts of gasoline/diesel vehicle operation on urban air quality can be determined.
It would be interesting to quantitatively compare hydrogen pathways with petroleum pathways in terms of the resulting changes in air quality. That would also be of meaningful implications and helpful for policymakers to think about hydrogen, a promising alternative transportation fuel.
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