Life Cycle Air Pollution Damages of Petroleum and Natural Gas Pathways for Powering Light-Duty Vehicles and Heavy-Duty Vehicles

Motivation. The negative environmental externalities (such as air pollutants and climate change) from energy use are primary challenges to the sustainability of human society. The National Research Council (NRC) (2010) found... [ view full abstract ]

Motivation. The negative environmental externalities (such as air pollutants and climate change) from energy use are primary challenges to the sustainability of human society. The National Research Council (NRC) (2010) found large air pollution damages associated with on-road vehicles, totaling $56 billion. Since 2010, a number of studies have examined the air pollution damages of petroleum fuels and alternative fuels in U.S. We found that recent studies focused on passenger cars, and relied on the GREET model for their emission estimates. The common attributes in these studies, while enabling comparative analysis between the different studies, have some limitations. Specifically, these studies ignored vehicle segments other than passenger cars, and used a single source of emissions data and a specific marginal damage model without testing the alternatives. In this paper, we estimated air pollution damages of petroleum and natural gas pathways for different vehicles types and addressed the robustness of the findings with different emissions data and marginal damage estimates used.

Method. We estimated air pollution damages from criteria air pollutants (CAPs) emitted over the life cycle (well-to-wheel) of vehicles. The functional unit of the study is one vehicle mile traveled. We considered five vehicle types: passenger cars, sports utility vehicles (SUVs), transit buses, local-haul tractor-trailers, and long-haul trucks. We evaluated five fuel pathways: conventional petroleum fuels (gasoline or diesel), CNG, LNG, natural gas-based electricity, and electricity from the current U.S. grid. Behavioral changes in driving patterns that may occur when petroleum fuels are replaced are not considered. Two spatialized emissions inventories were built using emissions data from the GREET model and the National Emission Inventory as well as peer-review studies. Compared to existing literature, this paper relies on the most recent data to reflect the changing U.S. energy landscape. We followed the “damage function approach” and used the marginal damage for each CAP in each county reported by two state-of-art models (AP2 and EASIUR). We used a consistent Value of a Statistical Life and the same dollar across comparison studies.

Results. We found that battery electric vehicles (BEVs) with increased penetrations of natural gas-based electricity achieve the lowest damages for passenger cars, SUVs, and transit buses; while CNG, LNG high-pressure direct-ignition (HPDI) and diesel hybrid-electric trucks each achieve lowest damages for trucks in different parts of the U.S. Our work showed that spatial differences in marginal damages of SO2 and NOx lead to different rankings of fuel pathways in the Rocky Mountain, western Texas, and New England. While we found large differences in emissions factors of oil refineries from two emissions sources, key findings on the rank of vehicle pathways remained robust.

Significance. This work advances the existing research on the environmental impacts of transportation fuel pathways by rigorously comparing the impact of two emissions data and the impact of two state-of-the-art marginal damage models on the rank of fuel pathways based on their life cycle air pollution damages. Our work calls for better data collection on CAP emissions from key energy facilities and continued advancement on marginal damage estimates.