This work characterized emission factors of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) from on-road sampling of three heavy duty diesel vehicles (HDDVs) under experimental conditions of city and highway driving; idling operation; high (>400 ppm) and low (<5 ppm) sulfur (S) fuels; and high mileage and rebuilt engine testing. Emission factors, homologue profiles, and isomer patterns were compared to determine whether the experimental conditions had an impact on PCDD/F emissions, or whether these conditions were uninfluential in determining a fleet-representative emission factor. For a single HDDV tested under conditions of a high mileage engine, a newly rebuilt engine, and the newly rebuilt engine with low S diesel fuel, emission factors were 0.023 (±0.022), 0.008 (±0.002), and 0.016 (±0.013) ng toxic equivalency (TEQ)/km, respectively. These results may infer some limited condition-specific differences in PCDD/F emissions, but these differences do not appear to have a significant effect on the HDDV emission factor. An older HDDV with mechanical fuel controls resulted in a single test value of 0.164 ng TEQIkm, significantly higher than all other results. Observed differences in emission factors, homologue profiles, and TEQ-related isomer patterns from this on-vehicle sampling and others' tunnel sampling suggest limitations in our present characterization of fleet PCDD/F emissions.
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