A study to characterize particulate matter emissions from 195 in-use gasoline and diesel passenger vehicles was conducted during the summer of 1996 and the winter of 1997 in the Denver, Colorado region. Vehicles were tested as received on chassis dynamometers using the Federal Test Procedure (FTP) Urban Dynamometer Driving Schedule (UDDS). Both PM-10 and regulated emissions 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 that the organic carbon (OC) to elemental carbon (EC) split may be useful in separating light-duty gasoline from diesel PM emissions. Sulfate emission rates averaged 0.45 and 3.51 mg/mi for gasoline and diesel vehicles, indicating that the EPA's mobile emissions model overpredicts sulfate emission rates. Elements identified by X-ray fluorescence averaged between 3 and 9% of the PM-10 mass. Polynuclear aromatic hydrocarbon (PAH) profiles developed may help distinguish between gasoline and diesel vehicles in source apportionment studies. Total PAH emissions, however, were not a good candidate as a tracer of gasoline PM emissions. Hopane and sterane emissions were very similar across the fleet and may be useful tracers for mobile source PM emissions. Overall, emission rates varied significantly with vehicle classification and driving condition, suggesting that a single profile representing the entire fleet will need to carefully reflect the local fleet composition and the local weighting of cold, hot, and hot-stabilized emissions.

One hundred three in-use vehicles identified as high hydrocarbon and/or carbon monoxide emitters by remote sensing and roadside visual, underhood checks during a 1995 South Coast Air Quality Management District program were tested on the IM240 cycle using a transportable dynamometer. Seventy-one of these vehicles were repaired as part of the program and were retested. Seventeen vehicles in the fleet initially emitted visible smoke from the tailpipe and were classified as "smokers". The fleet ranged in age from 6 to 22 years, with a median age of 12.3 years. Exhaust HC, CO, NO x , and particulate emissions (PM-10) were measured. PM-10 mass and the elemental and carbonaceous composition of the particulate matter were determined. The average fleet PM-10 emission rate was 0.138 g/mi, while the average emission rate for smokers was 0.395 g/mi. It was concluded that the casual observation of smoking vehicles was not very successful in identifying high PM-10 emitting vehicles. The particulate matter composition was primarily carbonaceous, with a variable distribution between the elemental and organic carbon fractions, and showed no significant difference in the percent organic carbon fraction between smokers and non-smokers. The PM composition differed, on average, between pre-repair and post-repair samples. The effect of the California Smog Check repair program on PM emission rates could not be evaluated due to concerns regarding the effect of vehicle conditioning on these measurements.

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