DIFFERENCES IN THE CARBON COMPOSITION OF SOURCE PROFILES FOR DIESEL-POWERED AND GASOLINE-POWERED VEHICLES

Filter samples of diesel-fueled heavy-duty and gasoline-fueled light-duty vehicle exhaust were acquired under controlled conditions associated with the State of Arizona's motor vehicle inspection and maintenance program. Samples of a mixture of emissions from these vehicles were also acquired at roadside sites. These samples were analysed for mass, elements, ions, and carbon. The carbon which evolved at temperatures of 120, 250, 450, and 550-degrees-C in a pure helium atmosphere, and at temperatures of 550, 700, and 800-degrees-C in a 2% oxygen-98% helium (by volume) atmosphere was measured with a flame ionization detector. The fraction of carbon which evolved at 700-degrees-C in the 2% oxygen atmosphere was found to be nearly 10-times as abundant (as a fraction of PM2.5 mass emissions) in the heavy-duty diesel-fueled vehicle emissions relative to the light-duty gasoline-fueled vehicle emissions. The organic carbon which evolved at 120-degrees-C was twice as abundant in diesel exhaust. The fraction of carbon which evolved at 550-degrees-C in an oxidizing atmosphere was twice as abundant in gasoline-fueled vehicle exhaust as it was in diesel exhaust. These differences in relative composition may be sufficient to allow diesel- and gasoline-fueled vehicle exhaust contributions to be distinguished from each other in ambient samples through the use of receptor models.