Variability of mobile source air toxic emissions factors with MOBILE6.2

This paper documents the ranges of mobile source air toxic (MSAT) emissions factors produced by the U.S. Environmental Protection Agency's MOBILE6.2 model because of changes in a variety of input parameters. These include calendar year, ambient temperature, fuel (gasoline) Reid vapor pressure (RVP), and vehicle speed. The variability of MSAT emissions factors is more than an order of magnitude. They are the most sensitive to changes in calendar year. For hydrocarbon-based MSATs (i.e., acetaldehyde, acrolein, benzene, butadiene, and formaldehyde), significant decreases in emissions factors can be realized by mitigating congested vehicle speeds. The variability is less for changes in temperature and changes in fuel RVP with moderate temperature. The emissions factors for diesel particulate matter change only as a function of calendar year and are not sensitive to changes in vehicle speed, temperature, or fuel RVP.