California Air Resources Board

Principal Investigator/Author: Gary Bishop

Contractor: University of Denver

Contract Number: 17RD015

Project Status: Completed

Relevant CARB Programs: Mobile Source Emissions Inventory, Advanced Clean Cars, Zero Emission Vehicle

Topic Areas: Light-Duty Vehicle Research, Advanced Technology & Low Carbon Transit

Research Summary:

A sixteen-year record of on-road emission measurements at a West Los Angeles site (La Brea Ave. and I-10) was continued with an additional data collection campaign in May of 2018. During this campaign, the University of Denver collected 19,259 emission measurements of carbon monoxide (CO), carbon dioxide, hydrocarbons (HC), nitric oxide (NO), ammonia (NH3), and nitrogen dioxide (NO2) from light and medium-duty vehicles. Since 1999, the CO mean emissions have decreased by 84% (70.3 to 11 g/kg), the HC mean emissions by 79% (7.0 to 1.5 g/kg), and the NO mean emissions by 76% (6.6 to 1.6 g/kg). These decreases have happened despite an older fleet (8.9 years) now than before the 2008 recession. Over this same time, the 99th percentiles have dropped by more than a factor of three for CO and HC (773 to 212 gCO/kg of fuel and 93 to 31 gHC/kg of fuel) and a factor of 1.6 for NO (53 to 32 gNO/kg of fuel). However, during recent campaigns, the reductions in the 99th percentiles have leveled out for HC and may be slowing for CO, which will likely slow future emissions reductions despite gradual electrification of the fleet.

Keywords: on-road emissions, light-duty vehicles (LDV), medium-duty vehicles, carbon monoxide (CO), carbon dioxide, hydrocarbons (HC), nitric oxide, ammonia, nitrogen dioxide (NO2), emission reduction