justed on the basis of the U.S. Energy Information Administration’s Annual Energy Outlook, which reports historical mixes as well as future forecasts (EIA 2006, 2009a).

Mobile6.2

To evaluate heavy-duty vehicle emissions, EPA’s Mobile6.2 on-road emissions modeling tool was used (EPA 2009). Unlike GREET, Mobile6.2 is designed to evaluate the many different conditions under which vehicles may operate, and not feedstock production, fuel production, or vehicle-manufacturing life-cycle emissions. Mobile6.2 heavy-duty vehicle operational emission factors were used in combination with GREET feedstock and fuel production factors to create life-cycle inventories for several different vehicle classes.

GREET does not evaluate ammonia emissions, so Mobile6.2 is used to capture this pollutant for both light- and heavy-duty vehicles. Ammonia emissions, which result in secondary particle formation, were determined by Mobile6.2 for a set of vehicles that overlap with the vehicle and fuel combinations evaluated in GREET. Ammonia emissions were estimated for the vehicle operation component only; they were not estimated for the feedstock, fuel, and vehicle manufacturing components.

THE EMISSIONS MODELING PROCESS

Model Framework

The emissions model utilized GREET to generate feedstock, fuel production, operation, and vehicle-manufacturing factors for light-duty vehicles and Mobile6.2 to generate operational factors for heavy-duty vehicles. GREET feedstock and fuel production factors were applied to the heavy-duty vehicle Mobile6.2 operational factors, as described later in this appendix. For all vehicles, energy inputs, CO2, CH4, N2O, VOC, CO, NOx, PM10, PM2.5, and SOx emissions are determined for the life-cycle components. APEEP county unit damages are based on emissions of VOCs, NOx, PM2.5, and SOx.

GREET Temporal Boundaries

GREET can evaluate vehicles and life-cycle processes from 1990 through 2020. The tool has many time series for engines, turbines, and critical parameters that capture changes in efficiencies, emissions, and other parameters (for example, ethanol yields from corn and fuel sulfur levels) historically and up to 2020. GREET also makes the assumption that fleet age is 5 years. When evaluating life-cycle emissions in a year, GREET as-



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