Research Projects

Project at a Glance

Project Status: complete

Report Published July 1998:

Title: Evaluation of factors that affect diesel exhaust toxicity.

Principal Investigator / Author(s): Norbeck, Joseph M

Contractor: UC Riverside

Contract Number: 94-312

Research Program Area: Emissions Monitoring & Control, Health & Exposure

Topic Areas: Mobile Sources & Fuels, Toxic Air Contaminants


Diesel exhaust has been designated by the International Agency for Research on Cancer as a probable human carcinogen and is undergoing evaluation as a potential toxic air contaminant under the California Air Resources Board's (CARB's) air toxics program. Diesel exhaust comprises a complex mixture of hundreds of particle bound and vapor phase compounds. Extensive literature exists on the relationship between diesel fuel parameters and emissions of criteria pollutants; however, little is known about the impact of these fuel changes on the complex speciation of the gas-phase, semi-volatile, and particle-phase components and specifically on emissions of toxic components present in diesel exhaust. This study was designed to provide this information.

In 1991, CARB instituted regulatory efforts to reduce emissions of total hydrocarbons (THC), carbon monoxide (CO), oxides of nitrogen (NOx), and particulate matter (PM) from diesel fuel (CARB, 1988; 1991). The regulations took effect October 1, 1993. These regulations were based on a review of the available data regarding the impact of fuel properties on these emissions. The regulation limits the maximum sulfur content to 0.05 percent, the minimum cetane index to 40, and the maximum aromatic content to 10 percent. Because these changes could require fuel refiners to make major capital investments, CARB has allowed fuel producers the option of developing less costly alternatives with a higher aromatic content, if equivalent emissions can be demonstrated (CARB, 1988).

To evaluate the emissions impact of these regulations a team of researchers from UC Riverside College of Engineering Center for Environmental Research and Technology (CE-CERT) and Statewide Air Pollution Research Center (SAPRC), as well as the Department of Environmental Toxicology at UC Davis, conducted testing on three diesel fuels: a pre-1993 fuel, a low aromatic fuel, and alternative formulation blend, henceforth referred to as reformulated fuel. Emission testing was conducted at the Los Angeles County Metropolitan Transportation Authority (LACMTA) emission test facility. The test bed was a Cummins L10, six-cylinder inline, turbocharged, four-stroke direct injected diesel engine rated at 310 Bhp @ 1600 RPM. The engine was tested over the heavy-duty transient test cycle. Multiple samples were collected for each of the three fuels over a four-week test interval. A total of 47 test cycles (7 cold and 40 hot) were run with the pre-1993 diesel fuel, 23 test cycles (4 cold and 19 hot) were run with the low aromatic fuel and 39 test cycles (5 cold and 34 hot) were run with the reformulated diesel blend.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

Stay involved, sign up with ARB's Research Email Listserver