No abstract

The generation and distribution of electricity comprises nearly 40% of U.S. CO(2), emissions, as well as large shares of SO(2), NO(x), small particulates, and other toxins. Thus, correctly accounting for these electricity-related environmental releases is of great importance in life cycle assessment of products and processes. Unfortunately, there is no agreed-upon protocol for accounting for the environmental emissions associated with electricity, as well as significant uncertainty in the estimates. Here, we explore the limits of current knowledge about grid electricity in LCA and carbon footprinting for the U.S. electrical grid, and show that differences in standards, protocols, and reporting organizations can lead to important differences in estimates of CO(2) SO(2), and NO(x) emissions factors. We find a considerable divergence in published values for grid emissions factor in the U.S. We discuss the implications of this divergence and list recommendations for a standardized approach to accounting for air pollution emissions in life cycle assessment and policy analyses in a world with incomplete and uncertain information.

ivIn 2005, there were approximately 50,000 diesel powered public transit buses operating in the United States, consuming over 500 million gallons of fuel annually. The Clean Air Act identifies diesel powered motor vehicles, including transit buses, as significant sources of several criteria pollutants which contribute to ground level ozone formation or smog. The effects of air pollution in urban areas are often more significant due to congestion and can lead to respiratory and cardiovascular health impacts. Life cycle assessment has been utilized in the literature to compare conventional gasoline powered passenger cars with various types of electric and hybrid powered alternatives; however, no similarly detailed studies exist for mass transit buses.LCA results from this study indicate that the use phase, consisting of diesel production/combustion for the conventional bus and electricity generation for the electric bus, dominates most impact categories; however, the effects of battery production are significant for global warming, carcinogenics, ozone depletion, and ecotoxicity. There is a clear connection between the mix of power generation technologies and the preference for the diesel or electric bus. With the existing U.S. average grid, there is a strong preference for the conventional diesel bus over the electric bus when considering global warming impacts alone. Policy makers must consider regional variations in the electricity grid prior to recommending the use of battery electric buses to reduce CO 2 emissions. This study found that the electric bus was preferable in only eight states including Washington and Oregon. Improvements in battery technology reduce the life cycle impacts from the electric bus, but the electricity grid makeup is the dominant variable.