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ON-ROAD EMISSION SAMPLING OF A HEAVY DUTY DIESEL VEHICLE FOR POLYCHLORINATED DIBENZO-P-DIOXINS AND POLYCHLORINATED DIBENZOFURANS
Citation:
Ryan*, J V. AND B K. Gullett*. ON-ROAD EMISSION SAMPLING OF A HEAVY DUTY DIESEL VEHICLE FOR POLYCHLORINATED DIBENZO-P-DIOXINS AND POLYCHLORINATED DIBENZOFURANS. ENVIRONMENTAL SCIENCE & TECHNOLOGY 34(21):4483-9, (2000).
Description:
The first known program to characterize mobile heavy diesel vehicle emissions for polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) during highway and in-city driving routes was successfully conducted. 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 related to driving conditions. Extensive care was taken to ensure high data quality including modifying measurement methodologies to ensure valid sample collection, sampling large volumes to improve analyte detection, minimization of background contaminant levels, replicate measurements, and closely understanding and scrutinizing the quality of analytical data. Analytical results from five tests showed significant yields of PCDDs/Fs. The average emission factor obtained from this work was 0.029 nanogram (ng) international toxic equivalency/kilometer (I-TEQ/km). The upper limit of the 95% confidence interval provides an estimated emission factor of 0.106 ng I-TEQ/km. Based on these values and 1993 diesel truck travel estimates, the projected U.S. annual emissions from on-road diesel vehicles are 4.4g I-TEQ/yr with a 95% confidence upper bound of 16.1 g I-TEQ/yr. Target analyte non-detects were minimal and resulted in little impact on the calculation of I-TEQ levels. No discernable difference in emissions was observed as a function of driving route. Analysis of the tractor operating parameter data showed no clear relationship between TEQ or total PCDD/F emissions and carbon monoxide or total hydrocarbon emissions. The large variation in emissions, even from similar driving routes, suggests that more definitive characterization of heavy duty diesel fleet emissions is required to improve the confidence of these estimates and to determine the primary causal factors for PCDD/F formation.