Emission rates of regulated pollutants from on-road heavy-duty diesel vehicles

Emissions from heavy-duty diesel (HDD) vehicles are affected by many factors. Changes in engine technology, operating mode, fuel properties, vehicle speed and ambient conditions can have significant effects on emission rates of regulated species. This paper presents the results of on-road emissions testing of 11 HDD vehicles (model years 1996–2000) over the ARB Four Phase driving schedule and the urban dynamometer driving schedule (UDDS). Emission rates were found to be highly dependent on vehicle operating mode. Per mile NOx emission rates for vehicle operation at low speeds, in simulated congested traffic, were three times higher per mile emissions then while cruising on the freeway. Comparisons of NOx emission factors to EMFAC baseline emission factors were within 5–40% for vehicles of various model years tested over the UDDS. A comparison of NOx emission factors for a weighted average of the ARB four phase driving schedule yielded values within 17–57% of EMFAC values. Generally, particulate matter (PM) emission rates were lower than EMFAC values.