Spatial Analysis of Air Quality Impacts from Using Natural Gas for Road Transportation

The negative environmental externalities from energy use are primary challenges to the sustainability of human society. The NRC report on the Hidden Costs of Energy found that “in 2005, the vehicle sector produced $56 billion in health and other nonclimate-change damages”, most of which are associated with petroleum use. In this paper, we analyze the benefits of different pathways for using natural gas in the transportation sector with regards to reduced non-climate change environmental and health externalities in each county in the United States. For this analysis we focus on light-duty and heavy-duty on-road vehicles (passenger vehicle, transit bus, and tractor trailer), which account for more than 75% of transportation energy consumption. Our analysis addresses non-climate change environmental and health externalities from criteria air pollutants (CAP) emitted throughout the life cycle of natural gas-based fuels, from energy extraction to vehicle driving. The emissions inventory is built based on recent publications of emission sources. For damage estimations and valuations, we follow the “damage function approach” and use the marginal damages from the AP2 model and EASIUR model. We consider gasoline (for light duty vehicles) or diesel (for heavy-duty vehicles) internal combustion engine vehicles as the baseline vehicles, and we assess the benefits of natural gas pathways as the reduced externalities compared to those from petroleum use. The functional unit is one vehicle mile traveled (VMT) for light-duty vehicles, and one short ton of cargo moved over one mile (ton-mile) for heavy-duty vehicles. We find that battery electric vehicles (BEV) powered with natural gas electricity and compressed natural gas (CNG) have 80% and 15% lower median damages than gasoline passenger vehicles. If charged with grid-average electricity, BEVs have a 20% higher median damage than gasoline. CNG-SI and LNG-HPDI trucks both have a 45% lower median damages compared to conventional diesel trucks. Looking across regions, we find that urban areas are likely to achieve larger benefits than rural areas due to larger population densities. Los Angeles and San Francisco Bay Area, for example, stand out as regions where larger reduction benefits could happen. The use of natural gas in road transportation sector to reduce environmental damages are possible but the benefits are contingent on how natural gas is used and where to replace petroleum fuels. We find that vehicle tailpipe emissions are the largest contributor of damages from trucks while feedstock extraction, fuel production, and vehicle operation play important roles in causing damages from passenger vehicles.