On-road measurement of "ne particle and nitrogen oxide emissions from light- and heavy-duty motor vehicles

An updated assessment of "ne particle emissions from lightand 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 "ne particulate matter (PM 2.5 ) 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 tra$c 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 "ne 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 PM 2.5 mass) than did light-duty "ne particle emissions (33$4%). Sulfate comprised only 2% of total "ne particle emissions for both vehicle classes. Sulfate emissions measured in this study for heavy-duty diesel trucks are signi"cantly 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 "ne particle emissions from on-road motor vehicles. ( 1999 Published by Elsevier Science Ltd. All rights reserved.