Regulated emissions from 21 in-use heavy-duty diesel vehicles were measured on a heavy-duty chassis dynamometer via three driving cycles using a low-sulfur diesel fuel. Emissions of particulate matter (PM), nitrogen oxides (NO x ), carbon monoxide (CO), total hydrocarbon (THC), and PM sulfate fraction were measured. For hot start tests, emissions ranged from 0.30 to 7.43 g/mi (mean 1.96) for PM; 4.15−54.0 g/mi (mean 23.3) for NO x ; 2.09−86.2 g/mi (mean 19.5) for CO; and 0.25−8.25 g/mi (mean 1.70) for THC. When emissions are converted to a g/gal basis, the effect of driving cycle is eliminated for NO x and largely eliminated for PM. Sulfate comprised less than 1% of the emitted PM for all vehicles and test cycles. A strong correlation is observed between emissions of CO and PM. Cold starting at 77 °F produced an 11% increase in PM emissions. Multivariate regression analyses indicate that in-use PM emissions have decreased at a slower rate than anticipated based on the stricter engine certification test standards put into effect since 1985. NO x emissions do not decrease with model year for the vehicles tested here. Smoke opacity measurements are not well correlated with mass emissions of regulated pollutants.

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