A fuel-based inventory for heavy-duty diesel truck emissions

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, on-road heavy-duty diesel trucks were estimated at the upper bound to emit 110 x 10(3) kg/day of nitrogen oxides (NOx) and 3.7 x 10(3) kg/day of fine black carbon (BC) particles. These upper bound values were 2.3 and 4.5 times, respectively, the corresponding predictions of 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 BC particle emissions on weekends may contribute to higher ambient ozone concentrations and higher organic carbon (OC) to 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.