Research Projects

Project at a Glance

Title: Impact of reformulated fuels on particle and gas-phase emissions from motor vehicles.

Principal Investigator / Author(s): Kirchstetter, Thomas W & Robert Harley

Contractor: UC Berkeley

Contract Number: 95-330

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


A major air pollution control strategy in California in the 1990s has been the reformulation of gasoline and diesel fuel to reduce vehicle emissions. A multi-year field study was conducted in northern California at the Caldecott tunnel to assess the impact of reformulated fuels on vehicle emissions, and to provide an updated characterization of gas and particle- phase emissions from on-road vehicles.

The introduction of reformulated gasoline (RFG) in California led to large changes in gasoline composition. The combined effects of RFG and fleet turnover between summers 1994 and 1997 were large decreases in exhaust emissions of carbon monoxide (CO), non-methane organic compounds (NMOC) and nitrogen oxides (NOx). Although it was difficult to separate the fleet turnover and RFG contributions to these changes, it was clear that the effect of RFG was greater for NMOC than for NOx. The effects of RFG on emissions of toxic organics such as benzene and formaldehyde and on the mass and reactivity of evaporative VOC emissions were significant.

Per unit mass of fuel burned, heavy-duty diesel trucks emit about five times the NOx, 25 times more fine particle (PM2) mass and 15-20 times the number of fine particles compared to light-duty vehicles. Results of this study suggest that diesel vehicles in California are responsible for nearly half of NOx emissions and greater than three quarters of exhaust fine particle emissions from on-road motor vehicles. Diesel trucks were found to be the major source of lower molecular weight polycyclic aromatic hydrocarbons (PAH), but light-duty gasoline vehicles were found to be an important source of some higher molecular weight PAH. Size-resolved measurements were made to determine the distribution of particulate PAH across the ultrafine and accumulation size modes.


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

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