California Air Resources Board

Principal Investigator/Author: Thomas Kirchstetter

Contractor: University of California, Berkeley

Contract number: 12-315

Project Status: Completed

Relevant CARB programs: Diesel Vehicles, Heavy-Duty Low NOx, Mobile Source Emissions Research Program  

Topic areas: Air Pollution, On-Road Heavy-Duty Vehicles, Research

Research Summary:

California Air Resources Board (CARB) regulatory programs have targeted emissionsreductions of particulate matter (PM) and oxides of nitrogen (NOX) from heavy-dutyvehicles (HDVs) over the past decade, and real-world emissions measurements ofthe current fleet are essential for evaluating the efficacy of the programs. Emissionsof PM, NOX, particles, and gas-phase nitrogen species from HDVs at the CaldecottTunnel (Oakland, CA) were quantified in 2014, 2015, and 2018 via a plume capturesampling method and matched to license plates. As diesel particulate filter (DPF)penetration increased to 91 percent and selective catalytic reduction (SCR) to59 percent, black carbon (BC) emissions decreased by 79 percent, and NOXemissions decreased by 57 percent. Issues with DPFs were identified in a smallnumber of "high-emitters," with 3.8 and 3.2 percent of the fleet emitting half offleet-averaged BC in 2014 and 2018, respectively (a relative decrease of 16 percent).NOX emissions were less skewed, with the fleet portion contributing half of all NOX, decreasing from 20.1 to 14.2 percent over that same time period. Fleet-averaged BCemissions decreased from 0.41 to 0.18 g/kg fuel over these four years, while NOXdecreased from 16.3 to 13.2 g/kg fuel. NOX emissions from SCR-equipped vehiclesat this site were still broadly higher than predicted based on certification standards.

Keywords: emission reductions, particulate matter (PM), oxides of nitrogen (NOx), heavy duty vehicles (HDVs), fleet, Caldecott Tunnel, plume capture, diesel particulate filter (DPF), selective catalytic reduction (SCR), black carbon (BC

Final Report: Please email research@arb.ca.gov to request the Final Report generated by this research contract.