Pollutant concentrations were measured at high time resolution in the exhaust plumes of more than a thousand drayage trucks as they drove toward the Port on a major access road. Emission factors were matched to data from a statewide drayage truck registry, including engine make, model year, and installed emission control equipment. Between 2009 and 2013, California's Drayage Truck Regulation led to near-universal use of DPFs (diesel particulate filters) on Port trucks.

The study found that:

• Fleet-average emission factors decreased by 76 ± 22% and 53 ± 8% for black carbon (BC) and oxides of nitrogen (NO_x), respectively.

• Direct emissions of nitrogen dioxide (NO₂) increased, and consequently the NO₂/NO_x emission ratio increased from 0.03 ± 0.02 to 0.18 ± 0.03.

• DPF-equipped trucks had substantially lower BC and higher NO₂ emission factors than trucks without DPFs.

• The newest trucks equipped with both DPFs and selective catalytic reduction (SCR) systems for NO_x control had the lowest average emission factors for BC and ultrafine particles (UFP), and an average NO₂ emission factor that was about equal to that of the Port truck fleet that was on the road in 2009 before recent emission regulations took effect.

• The median age of truck engines declined from 11 to six years, and the percentage of trucks equipped with diesel particulate filters increased from 2% to 99%.

The study findings occurred over a relatively short time. Comparable emissions reductions could normally take up to a decade through gradual replacement of old trucks or natural fleet turnover.

In this case, the improvements are attributed to the ARB’s Drayage Truck Regulation and to the Comprehensive Truck Management Program at the Port of Oakland, which require vehicle owners serving the port to clean up their trucks by either replacing them with newer models or installing diesel particulate filters (DPFs).

Adopted in 2007, the ARB’s Drayage Truck Regulation requires all trucks serving major California ports and intermodal rail yards to be registered and upgraded according to a staggered implementation schedule.

By 1 Jan 2023, all class 7 and 8 diesel-fueled drayage trucks must have 2010 or newer engines. Currently, pre-2007 model year (MY) trucks cannot serve the ports. All 2007-2009 MY trucks are compliant through 2022.

Dr. Harley will elaborate on these results during an ARB-hosted research seminar and webcast open to the public at 1:30 pm (PDT) on Thursday, 18 June.

Resources

• Robert Harley, “On-Road Measurement of Emissions from Heavy-Duty Diesel Trucks: Impacts of Fleet Turnover and ARB’s Drayage Truck Regulation” Final Report Contract No. 09-340