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

An updated assessment of fine particle emissions from light- and heavy-duty vehicles is needed due to recent changes to the composition of gasoline an d diesel fuel, more stringent emission standards applying to new vehicles s old in the 1990s, and the adoption of a new ambient air quality standard fo r 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 traff ic 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 vehicl es. 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 f ine particle, black carbon, and sulfate mass per unit mass of fuel burned t han 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 ca rbon (51 +/- 11% of PM2.5 mass) than did light-duty fine particle emissions (33 +/- 4%). Sulfate comprised only 2% of total fine particle emissions fo r 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 s tudy suggests that heavy-duty diesel vehicles in California are responsible for nearly half of oxides of nitrogen emissions and greater than three-qua rters of exhaust tine particle emissions from on-road motor vehicles. (C) 1 999 Published by Elsevier Science Ltd. All rights reserved.