An updated assessment of fine particle emissions from light- and heavy- duty vehicles is needed due to recent changes to the composition of gasoline and diesel fuel, more stringent emission standards applying to new vehicles sold in the 1990s, and the adoption of a new ambient air quality standard for fine particulate matter (PM2.5) in the United States. This paper reports the measurement of emissions from vehicles in a northern California roadway tunnel during summer 1997. Separate measurements were made of uphill traffic in two tunnel bores: one bore carried both light-duty vehicles and heavy- duty diesel trucks, and the second bore was reserved for light-duty vehicles. Ninety-eight percent of the light-duty vehicles were gasoline-powered. In the tunnel, heavy-duty diesel trucks emitted 24, 37, and 21 times more fine particle, black carbon, and sulfate mass per unit mass of fuel burned than light-duty vehicles. Heavy-duty diesel trucks also emitted 15-20 times the number of particles per unit mass of fuel burned compared to light-duty vehicles. Fine particle emissions from both vehicle classes were composed mostly of carbon; diesel-derived particulate matter contained more black carbon (51 ± 11% of PM2.5 mass) than did light-duty fine particle emissions (33 ± 4%). Sulfate comprised only 2% of total fine particle emissions for both vehicle classes. Sulfate emissions measured in this study for heavy-duty diesel trucks are significantly lower than values reported in earlier studies conducted before the introduction of low-sulfur diesel fuel. This study suggests that heavy-duty diesel vehicles in California are responsible for nearly half of oxides of nitrogen emissions and greater than three-quarters of exhaust fine particle emissions from on-road motor vehicles.
Bibliographical noteFunding Information:
The authors thank Rex Ganding, Linsey Marr, and Brett Singer of UC Berkeley; Pablo Cicero, Chas Cowell, Bart Croes, Bill Davis, Samantha Kwan, Brian Oxley, and Jim Pederson of the California Air Resources Board; Gary Kendall and Mike Traverse of the Bay Area Air Quality Management District; and Anthony Hansen of Magee Scienti"c. We also thank Caltrans sta! at the Caldecott tunnel. This research was supported by the California Air Resources Board (Contract 95-330).
- Black carbon
- Organic carbon
- Reformulated gasoline
- Tunnel study