ARB Research Seminar

This page updated January 29, 2020

Measurements Show a Cleaner On-Road Vehicle Fleet: High Emitters Increasingly Important

Photo of Gary Bishop Ph.D.

Gary Bishop, Ph.D.

February 13, 2020
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Research Project


As the results of this on-road vehicle emission measurement project suggest, the light-duty vehicle fleet as a whole, as well as its highest-emitting portions, has become cleaner; and the highest emitters are responsible for increasingly large portions of the fleet emissions.

This project used roadside remote sensing device (RSD) to measure on-road light- and medium-duty vehicle exhaust emissions at the ramp from southbound South La Brea Avenue to eastbound Interstate-10 in West Los Angeles of California. During a six-day campaign in spring 2018, the project collected around 20,000 measurements of fuel-based emission rates of carbon monoxide (CO), hydrocarbons (HC), nitric oxide (NO), nitrogen dioxide (NO2), ammonia (NH3), and sulfur dioxide (SO2). The project extends a historical measurement record at the same location since 1999. The results show that, between 1999 and 2018, fleet fuel-based emissions have decreased by 84% for CO, 79% for HC, and 76% for NO. Over the same period, the 99th percentile emission rates have decreased by 73% for CO, 67% for HC, and 40% for NO. The highest 1% measurements in 2018 contributed to 38% of total CO emissions from all measurements (up from 14% in 1999), 43% of total measured HC emissions (up from 17% in 1999), and 27% of total measured NO emissions (up from 10% in 1999). During the three most recent campaigns (in 2013, 2015, and 2018), the 99th percentile HC emission rates appear to have leveled out and the reductions of the 99th percentile CO emission rates may be slowing, which could slow future fleet emission reductions despite the gradual electrification of the fleet.

Speaker Biography

Gary Bishop has been a Research Scientist with the Department of Chemistry and Biochemistry at the University of Denver since 1987, working with Professor Donald Stedman and his group. The group has specialized in developing spectroscopic instrumentation capable of remotely detecting vehicle exhaust. The group has used these instruments to measure light-duty vehicle fleets in more than 21 countries and in more than 30 United States locations. In addition, the group has used these instruments to measure heavy-duty diesel trucks and commercial aircraft in London, snowmobiles in Yellowstone National Park, and line-haul locomotives in Nebraska. This work has resulted in 10 patents and more than 50 peer reviewed journal publications. He holds a Ph.D. degree in bio-physical chemistry from the University of Colorado at Boulder.

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