Comparing Lifetime Emissions of Natural Gas and Conventional Fuel Vehicles: An Application of the Generalized ANCOVA Model

摘要

New regulations and incentives are encouraging the use of clean, alternative fuel vehicles (AFVs) in urban areas. These vehicles are seen as one option for reducing air pollution from mobile sources. However, because of the limited number of AFVs on the road, little is known about actual lifetime emissions characteristics of in-use AFVs. This study describes the use of a generalized analysis of covanance model to evaluate and compare the emissions from natural gas vehicles with emissions from reformu- lated gasoline vehicles. The model describes fleet-wide emissions deterioration while also accounting for indi- vidual vehicle variability within the fleet. This ability to measure individual vehicle variability can then be used to provide realistic bounds for the emissions deteriora- tion in individual vehicles and the fleet as a whole. In order to illustrate the use of the model, the carbon mon- oxide, oxides of nitrogen (NOx), non-methane hydrocar- bon (NMHC), and carbon dioxide emissions characteristics of a fleet of dedicated natural gas Dodge Ram vans and a fleet of dedicated reformulated gasoline Dodge Ram vans operating in the U.S. government fleet are explored.