A recently completed program was developed to evaluate ultra-low sulfur diesel fuels and passive diesel particle filters (DPF) in several different truck and bus fleets operating in Southern California. The primary test fuels, ECD and ECD-1, are produced by ARCO, a BP company, and have less than 15 ppm sulfur content. A test fleet comprised of heavy-duty trucks and buses were retrofitted with one of two types of catalyzed diesel particle filters, and operated for one year.As part of this program, a chemical characterization study was performed in the spring of 2001 to compare the exhaust emissions using the test fuels with and without aftertreatment. A detailed speciation of volatile organic hydrocarbons (VOC), polycyclic aromatic hydrocarbons (PAH), nitro-PAH, carbonyls, polychlorodibenzo-p-dioxins (PCDD) and polychlorodibenzo-p-furans (PCDF), inorganic ions, elements, PM10, and PM2.5 in diesel exhaust was performed for a select set of vehicles. The testing was carried out on four diesel vehicles and two compressed natural gas (CNG) vehicles, using a representative California diesel fuel, ECD-1, and ECD, all with and without DPFs. One diesel vehicle was also tested with Fischer-Tropsch (F-T) diesel fuel. The CNG vehicles were tested using motor vehicle-grade compressed natural gas.Results presented in this paper provide vehicle emissions profiles for total particulate matter (TPM), PM10 and PM2.5, inorganic ions, elements, and VOCs. Ethene, C2-C5 olefins, BTEX, and benzene have been highlighted due to their high reactivity or toxicity for the diesel and CNG vehicles. Additional speciated exhaust emissions will be published in a future paper.The TPM and particle-bound element emissions are greatly reduced on vehicles equipped with aftertreatment devices and the CNG vehicles. The DPFs effectively reduce the light olefins and EC/OC. Emissions of particle-bound inorganic ions are very low for all vehicles, regardless of fuel/aftertreatment.