ARB Research Seminar

This page updated July 16, 2013

On-Road Measurement of Light-Duty Gasoline and Heavy-Duty Diesel Vehicle Emissions

Robert A. Harley, Ph.D., Department of†Civil and Environmental Engineering, University of California, Berkeley

May 08, 2009
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


Emissions from light-duty (LD) gasoline and heavy-duty (HD) diesel vehicles were measured at the Caldecott tunnel in the San Francisco Bay area in summer 2006, with comparisons to results from previous years at the same site made to quantify emission trends over time. LD vehicle emissions of nitrogen oxides, volatile organic compounds, carbon monoxide, and particulate matter (PM) continue to decline over time due to fleet turnover effects and improved emission control technologies on new vehicles.

Some  effects of the switch from methyl-tert butyl ether (MTBE) to ethanol in California gasoline were observed. Substantial reductions in HD diesel truck emissions of PM were also observed between 1997 and 2006. The distributions of black carbon (soot) and ultrafine particle number emissions from individual diesel trucks were measured as part of this study, and sub-populations of high-emitting trucks were identified. NOx from HD trucks has been decreasing more slowly than for LD vehicles over the last decade, with the result that the relative importance of diesel engines as a source of NOx emissions in California has increased dramatically.

Diesel engines are also an important source of direct emissions of aldehydes, which are malodorous, toxic, and reactive in the atmosphere. Exhaust emissions of ammonia from LD vehicles used to be negligible, then increased with the adoption of three-way catalytic converters, and appear to have declined since 1999 as carbon monoxide emissions and air/fuel ratio for LD vehicles have been brought under better control.

Speaker Biography

Robert A. Harley Ph.D., is a Professor in the Department of Civil and Environmental Engineering at the University of California, Berkeley, where he has been on the faculty since 1993.  Dr. Harley's research focuses on air quality and sustainable transportation; he is an author of 60 papers published in peer-reviewed scientific journals. Professor Harley currently serves as Environmental Engineering faculty group leader (2007-09).  Dr. Harley is also Deputy Department Head for Atmospheric Sciences in the Environmental Energy Technologies Division of Lawrence Berkeley National Laboratory, a U.S. Department of Energy science lab located adjacent to campus.  Dr. Harley received the National Science Foundation's young investigator (CAREER) award in 1996, as well as a visiting scientist fellowship (1999-2000) at the University of Colorado/NOAA Aeronomy Lab in Boulder. Professor Harley served for 3 years as Vice Chair of the Civil and Environmental Engineering Department at Berkeley (2001-04), chairing committees that were responsible for undergraduate curriculum and graduate student admissions.  Professor Harley holds a bachelor's degree in Engineering Science (Chemical Engineering option) from the University of Toronto; and both M.S. and a Ph.D. degree in Environmental Engineering Science from the California Institute of Technology (Caltech).

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