Research Projects

Project at a Glance

Title: Measuring real-world emissions from the on-road passenger car fleet

Principal Investigator / Author(s): Stedman, Donald and Gary Bishop

Contractor: University of Denver

Contract Number: 12-303

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels, Monitoring


Carbon Monoxide (CO), Hydrocarbon (HC), Nitric Oxide (NO), Nitrogen Dioxide (NO2), and Ammonia (NH3) emissions from motor vehicles are important sources that contribute to urban air pollution. This contract extends a nine-year record of on-road emission measurements using remote sensing device (RSD) systems at a west Los Angeles location with two additional data collection campaigns in the spring of 2013 and 2015. The contractor collected 27,247 (2013) and 22,124 (2015) emission measurements of CO, carbon dioxide (CO2), HC, NO, NH3 and NO2 from light- and medium-duty vehicles. Fuel-based mass emission rates of those pollutants were calculated. The results show that, between 1999 and 2015, fleet emissions have decreased by 82 percent for CO, 81 percent for HC, and 71 percent for NO. These decreases have happened despite the fact that fleet average age has increased by two years as a result of the decreased vehicle sales during the 2008-2009 recession. Over the same period of time, the 99th percentile emission rates have dropped by 67 percent for CO, 74 percent for HC, and 36 percent for NO. There are concerns however, that the reductions in the 99th percentiles may be leveling out which could also stall future fleet average emissions reductions. These data sets were also used to document that 2009 and newer Volkswagen and Audi diesel vehicles had excessive on-road NO and NO2 emissions.


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