As part of the Gasoline/Diesel PM Split Study, relatively large fleets of gasoline vehicles 53 and diesel vehicles 34 were tested on a chassis dynamometer to develop chemical source profiles for source attribution of atmospheric particulate matter in California's South Coast Air Basin. Gasoline vehicles were tested in cold-start and warm-start conditions, and diesel vehicles were tested through several driving cycles. Tailpipe emissions of particulate matter were analyzed for organic tracer compounds, including hopanes, steranes, and polycyclic aromatic hydrocarbons. Large intervehicle variation was seen in emission rate and composition, and results were averaged to examine the impacts of vehicle ages, weight classes, and driving cycles on the variation. Average profiles, weighted by mass emission rate, had much lower uncertainty than that associated with intervehicle variation. Mass emission rates and elemental carbon/organic carbon (EC/OC) ratios for gasoline vehicle age classes were influenced most by use of cold-start or warm-start driving cycle (factor of 2-7). Individual smoker vehicles had a large range of mass and EC/OC (factors of 40 and 625, respectively). Gasoline vehicle age averages, data on vehicle ages and miles traveled in the area, and several assumptions about smoker contributions were used to create emissions profiles representative of on-road vehicle fleets in the Los Angeles area in 2001. In the representative gasoline fleet profiles, variation was further reduced, with coldstart or warm-start and the representation of smoker vehicles making a difference of approximately a factor of two in mass emission rate and EC/OC. Diesel vehicle profiles were created on the basis of vehicle age, weight class, and driving cycle. Mass emission rate and EC/OC for diesel averages were influenced by vehicle age (factor of 2-5), weight class (factor of 2-7), and driving cycle (factor of 10 -20). Absolute and relative emissions of molecular marker compounds showed levels of variation similar to those of mass and EC/OC.

The detailed chemical composition of particulate matter emissions from four non-smoking gasoline powered motor vehicles were measured using three different driving conditions: a cold-cold start Unified Driving Cycle (UDC), a hot UDC, and a steady state cruise driving cycle. The cold-cold start UDC tests were performed with a cold-cold start temperature of 0• C, which is significantly lower than the 24• C cold start temperature widely used for motor vehicle testing. Each vehicle was operated over three cold-cold UDC cycles, three hot UDC cycles, and a steady state driving cycle comprised of 2 hours at 100 kilometers per hour (kph) plus 1 hour at 50 kph. Particulate matter emissions were characterized for elemental carbon (EC), organic carbon (OC), sulfate ions, nitrate ions, ammonium ions, and organic compounds using gas chromatography mass spectrometry (GCMS). Mass emissions rates for the test vehicles using both the hot UDC and steady state driving cycles ranged from <0.1 to 1.3 mg km −1 , while the average cold-cold UDC cycle emissions ranged from 1.0 to 7.1 mg km −1 for the four vehicles. The cold-cold start UDC emissions averaged 5-30 times higher than the hot start UDC emissions. EC was an important contributor to the particulate matter emissions for the cold-cold start UDC emissions. Speciation of the organic compounds in the particulate matter emissions demonstrates differences in the composition of the organic aerosol emissions for the different driving cycles. The results of the present study demonstrate the important impact of cold-cold start temperature and driving conditions.

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