This study follows the approach used by other studies (Unnasch 1989 and 1996, Wang 1999, DeLuchi 1991, and Balles 1992). Emissions are estimated for steps in the fuel production and distribution process. This study relies on both process-specific analyses, using emission factors for fuel-cycle steps, and emission inventories or aggregate data. The report is organized along the modular approach that was used to calculate emissions.
Other than combustion and fugitive emissions associated with fuel production and distribution and vehicle CO2 emissions, no other environmental impacts, are considered in this report. In order to consider the total emissions from fuel production and distribution, exhaust and evaporative emissions need to be added to the fuel-cycle emissions in this study. Only emissions from fuel production equipment are considered in this study. Emissions associated with the production of equipment, facilities, or vehicles have not been included in this report. Spills and upsets are only considered when they are part of routine operations. For example, the probability-weighted emissions from fuel tanker shipment spills are not considered, but average emissions from vehicle fueling spills are counted.
1.5 Report Organization
Section 2 outlines the basic assumptions regarding fuel compositions and fuel properties used in the study. It also discusses NMOG speciation data for fuel, fuel vapor, and exhaust emission. Section 3 presents an overview of the fuel production scenarios for each fuel. The geographical area where fuels are produced and distributed are identified so transportation and distribution emissions can be accounted for. Emission rates for equipment that are used in the production and distribution of fuels are presented in Section 4. A data base approach was used to relate the mix of equipment, storage, and transportation modes in Section 3 with emission rates in Section 4. Section 5 discusses the trends in vehicle fuel economy and the likely fuel economy for diesel, LPG, and methanol fuel cell vehicles. The fuel-cycle calculation procedure is discussed in Section 6. The results per unit of fuel produced are presented in Section 7. A final series of calculations relates vehicle fuel economy with emissions per unit of fuel to show the fuel-cycle emissions on a gram per mile basis.