REAL-WORLD EMISSIONS OF MERCURY FROM AUTOMOBILES: THE 1998 FORT McHENRY TRAFFIC TUNNEL STUDY

Gerald J. Keeler *, J. Timothy Dvonch, James A. Barres, (The University of Michigan Air Quality Laboratory, Ann Arbor, MI 48109-2029, USA); Matthew S. Landis (USEPA-National Exposure Research Laboratory, Research Triangle Park, NC 27711, USA); Robert K. Stevens (Florida Dept. of Environmental Protection at USEPA, Research Triangle Park, NC 27711, USA).

A relative data gap exists worldwide for both magnitudes and speciation of mercury (Hg) emissions from many anthropogenic source types, including mobile sources. As part of the overall project objective to develop a comprehensive trace element and organic automotive emission source profile, measurements of Hg were made during the Ft. McHenry Traffic Tunnel Study, conducted in Baltimore, MD in September 1998.

As part of this study, measurements of total particulate mercury (TPM), fine particulate (FPM), total gaseous mercury (TGM), and reactive gaseous mercury (RGM) were collected concurrently at three locations. Two of these locations included traffic tubes #3 and #4, which are the northbound lanes of I-95 as the interstate passes under Baltimore Harbor. As part of the expected breakdown in vehicle types passing through the two tubes, heavy duty trucks, trailers, etc. were concentrated in traffic tube #4 (primarily diesel emissions). Light duty and passenger vehicles made up the vast majority of traffic in tube #3 (primarily gasoline emissions). The third sampling location included the rooftop of the building housing the Tunnel Authority personnel, which rests above the traffic tubes. This site was designed to quantify local ambient air that may serve as a background of the air which enters the traffic tubes. A total of 10 sampling periods were conducted with measurements made at all 3 sampling locations.

Results indicated consistent increases of TGM in each tunnel with respect to the ambient background location, with increases of 0.6 ng/m3 and 0.8 ng/m3 in tubes #4 and #3, respectively. Consistent increases were also observed for FPM in each tunnel with respect to the background location, with increases of 41 pg/m3 and 39 pg/m3 in tubes #4 and #3, respectively. However, no clear increases of TPM or RGM were observed in either traffic tube with respect to the background location.