Drayage Truck Emissions at the Port of Oakland
In 2010, the California Air Resources Board (ARB) began to implement a drayage truck emission control regulation at sea ports and rail yards in an effort to reduce the high levels of air pollutants traditionally found in neighborhoods adjacent to these areas. At the Port of Oakland, this resulted in an accelerated diesel particle filter (DPF) retrofit and truck replacement program—part of the port's Comprehensive Truck Management Program (CTMP). Given the time and expense that truckers, the port, and ARB devoted to this effort, the participants were keen to find out what level of effect it is having on truck emissions.
Researchers from Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California, Berkeley (UCB) were able to supply the answer. Independent of the port and ARB, Thomas Kirchstetter, of Berkeley Lab's Environmental Energy Technologies Division (EETD), and Timothy Dallman and Professor Robert Harley of UCB, began measuring emissions from drayage trucks driving to the Port of Oakland in November 2009, before the regulation took effect. They compared these baseline data to new data that they gathered in June 2010, and published their paper describing this work—"Effects of Diesel Particle Filter Retrofits and Accelerated Fleet Turnover on Drayage Truck Emissions at the Port of Oakland"—in Environmental Science and Technology in October 2011.
Addressing a Health Concern of Neighborhoods Adjacent to Ports
Heavy-duty diesel trucks emit significant quantities of fine particulate matter (PM2.5), black carbon (BC, a component of particulate matter), and oxides of nitrogen (NOx). While all of these emissions can affect health, exposure to diesel PM, in particular, is associated with a variety of adverse health effects, and can lead to cardiovascular and respiratory diseases, as well as lung cancer.
Diesel engines in newer vehicles are much cleaner in terms of emissions than the older ones, but as of late 2008, 17% of drayage trucks entering the Port of Oakland still had 1993 or older model engines, and only 6% were 2004 vintage or newer. Waiting for those vehicles to turn over to newer, less-polluting models would mean that another generation of neighborhood residents would be exposed to high levels of pollutants from those vehicles before the problem improved.
The ARB drayage truck regulation addressed this issue by implementing a ban on 1993 and older engine model years, diesel particle filter (DPF) retrofit requirements for more recent engines, and incentives to replace older trucks with 2007-plus model-year trucks that meet the most stringent exhaust PM emission standards. These combined activities are expected to reduce PM emissions from drayage trucks much more rapidly than what could be achieved by relying on natural fleet-turnover; by 2014 the program is estimated to reduce PM emissions from the state drayage truck fleet 86% from 2007 baseline levels.
Mobile Lab Enables Site-Specific Emissions Capture
To determine whether these benefits were being achieved, Kirchstetter, Dallman, and Harley set up a mobile laboratory loaned from the Bay Area Air Quality Management District (BAAMD) on an overpass above a main freeway leading to the port.
The team measured truck emissions in November 2009, and then again in June 2010 after it was estimated that approximately 95% of the retrofit work required by the initial phase of the drayage truck rule had been completed. A video camera recorded the trucks passing, so that the team could verify when individual trucks passed the site. Instrumentation measured PM2.5, BC, and NOx, as well as carbon dioxide (CO2), from which the team quantified the rate at which passing trucks emitted pollutants in terms of grams of pollutant emitted per kilogram of fuel burned.
Truck Emissions Reductions Confirmed
Emissions of the measured pollutants were markedly lower in June 2010, after the implementation of the drayage truck rule, than they were in November 2009, before the rule was implemented. On average, BC emission factors for trucks at the port decreased 50% with an associated three-fold increase in the fraction of very low-emitting trucks (Figure 2a). This improvement, realized in only seven months, is comparable to a similar BC reduction seen in a nearby traffic tunnel over the course of nine years, from 1997 to 2006, where truck emissions were reduced through natural modernization of the truck fleet as opposed to the program of accelerated clean up at the Port.
Information from the port and the BAAQMD on the composition of the drayage truck fleet at the Port of Oakland suggests how these improvements came about. By 2010, as a result of the truck rule, the fleet was composed of: 0% of trucks with pre-1994 model year engines (down from 17% in 2008), 53% of model year 1994-2003 truck engines retrofitted with DPFs, and 14% of trucks with 2007 and newer model year engines already equipped with a particle filter (up from only 2% in 2008). Trucks with 2004-2006 model year engines made up 33% of the fleet (up from 4% in 2009). Emissions are expected to decline even more as future retrofit and replace deadlines are reached and the fleet of drayage trucks continues to modernize.
The PM2.5 emission factors also show a shift toward lower emissions—in this case, showing a five-fold increase in the number of trucks with no measureable PM2.5 emissions, resulting in a substantial decrease in PM2.5 emissions over the study period. The NOx emission factor also decreased, by about 40% over the study period. Prior work has shown that DPF systems alone have little to no impact on total NOx emissions, so the improvement is probably the result of older engines being replaced by 2004 and newer engines at the Port of Oakland—from 6% in 2008 to 47% in 2010.
Building on Success
The study verified a substantial positive impact from the retrofit and accelerated truck replacement program in the communities surrounding the Port of Oakland where truck activity is high. Benefits include substantial reductions in exhaust emissions of BC and NOx from trucks operating in the vicinity.
"When we presented our study to the Alameda Board of Supervisors, the reception was good," recalls Kirchstetter. " The supervisors thanked us and so did some of the truckers who attended. The study showed that their efforts have really made a difference."
The first study is just the initial step of a larger effort. "We were back taking measurements at the same spot in November 2011," says Kirchstetter, "and we're going back again in several months. Our newer measurements include the size and number concentration of the PM emissions, and instead of just measuring total NOx, we're differentiating between nitric oxide and nitrogen dioxide."
The more recent measurements may be used to confirm the earlier results, but more important, data from the expanded measurements will provide more granular information for those studying health effects at the port.
For more information, contact:
- Thomas Kirchstetter
- (510) 486-5319
Dallmann, Timothy R., Robert A. Harley, and Thomas W. Kirchstetter. "Effects of Diesel Particle Filter Retrofits and Accelerated Fleet Turnover on Drayage Truck Emissions at the Port of Oakland." Environ. Sci. Technol. 2011, 45 (24). 10773-10779.