University of California Transportation Center

A fuel-based method for estimating heavy-duty diesel truck emissions is described. In this method, emission factors are normalized to fuel consumption; vehicle activity is measured by the amount of diesel fuel consumed. For the San Francisco Bay Area during summer 1996, heavy-duty diesel trucks were estimated to emit 100⋅103 kg/day of NOx and 6.4⋅103 kg/day of exhaust PM. These values were 2.1 and 1.8 times, respectively, the corresponding values predicted by California’s motor vehicle emission inventory model, MVEI 7G. Significant decreases in diesel truck activity and emissions, 70-80% below typical weekday levels, were observed in the Bay Area on weekends. Reductions in diesel NOx and black carbon (BC) particle emissions on weekends may contribute to higher ambient ozone concentrations and higher OC/BC ratios observed on weekends. Heavy-duty truck traffic peaks on weekdays during the middle of the day and falls off before the afternoon rush hour. Therefore, the diurnal pattern of heavy-duty truck travel may contribute to increases in ambient OC/BC ratios observed during late afternoon hours.