Composition of light-duty motor vehicle exhaust particulate matter in the Denver, Colorado area

A study to characterize particulate matter emissions from 195 in-use gasoli ne and diesel passenger vehicles was conducted during the summer of 1996 an d the winter of 1997 in the Denver, Colorado region. Vehicles were tested a s received on chassis dynamometers using the Federal Test Procedure (FTP) U rban Dynamometer Driving Schedule (UDDS). Both PM-10 and regulated emission s were measured for each phase of the UDDS. Approximately 88% of the PM-10 collected was carbonaceous material, of which the average organic fraction was 0.7 for gasoline vehicles and 0.4 for diesel vehicles. This suggests th at the organic carbon (OC) to elemental carbon (EC) split may be useful in separating light-duty gasoline from diesel PM emissions. Sulfate emission r ates averaged 0.45 and 3.51 mg/mi for gasoline and diesel vehicles, indicat ing that the EPA's mobile emissions model overpredicts sulfate emission rat es. Elements identified by X-ray fluorescence averaged between 3 and 9% of the PM-10 mass. Polynuclear aromatic hydrocarbon (PAH) profiles developed m ay help distinguish between gasoline and diesel vehicles in source apportio nment studies. Total PAH emissions, however, were not a good candidate as a tracer of gasoline PM emissions. Hopane and sterane emissions were very si milar across the fleet and may be useful tracers for mobile source PM emiss ions. Overall, emission rates varied significantly with vehicle classificat ion and driving condition, suggesting that a single profile representing th e entire fleet will need to carefully reflect the local fleet composition a nd the local weighting of cold, hot, and hot-stabilized emissions.