Measurements of Dioxin and Furan Emission Factors from Heavy-Duty Diesel Vehicles.

This note describes the results of a study of the on-road emissions of dioxins and furans from mobile sources. This work was performed in response to the U.S. Environmental Protection Agency's (EPA) draft document on dioxin reassessment, which used data from sources outside the United States to estimate an emission factor of 0.8 ng-TEQ/veh-mi for the U.S. fleet. The primary objective of this work was to measure on-road chlorinated dioxin and furan emission factors from in-use vehicles operating in the United States, with emphasis on heavy-duty vehicles. The experimental approach was to measure emissions in the Fort McHenry Tunnel in Baltimore, MD. All air entering and leaving the tunnel was sampled for concentrations of dioxins and furans (during 10 24-h sampling periods). The difference between the mass of material entering and the mass of material leaving the tunnel was taken to be the amount produced by the vehicles in transit. These measurements were combined with information on vehicle counts (obtained through videotapes) and tunnel length to determine average emission factors. For the limited range of vehicle operating conditions present in the tunnel experiment, the average heavy-duty diesel emission factor determined in this study was 0.28 ± 0.13 ng-TEQ/veh-mi, a factor of 3 lower than the EPA estimate.