On-Road Emission Sampling of a Heavy-Duty Diesel Vehicle for Polychlorinated Dibenzo-p-dioxins and Polychlorinated Dibenzofurans

The first known program to characterize mobile heavy-duty diesel vehicle emissions for polychlorinated dibenzo- p -dioxins and polychlorinated dibenzofurans (PCDDs/Fs) during actual highway and in-city driving was successfully conducted. This technique enables a more representative measurement with reduced uncertainty than dynamometer testing or indirect tunnel emissions characterizations. The post-muffler exhaust of a diesel tractor hauling a loaded trailer was directly sampled with a modified EPA Method 23 train during on-road operation, and the measured PCDD/F emissions were related to driving conditions. The average emission factor obtained from this work was 0.029 ng international toxic equivalency (I-TEQ)/km. The upper limit of the 95% confidence interval provides an estimated emission factor of 0.106 ng I-TEQ/km. These data compare favorably to the limited data available in the literature. Target analyte nondetects were minimal and resulted in little impact on the calculation of I-TEQ levels. No statistical difference in emissions was observed as a function of driving route, largely as a result of the extreme variation in the two valid in-city tests. Analysis of the tractor emissions data showed no clear relationship between TEQ or total PCDD/F emissions and carbon monoxide or total hydrocarbon emissions.