Effects of Tunnel Exhaust on Ambient Carbon Monoxide Levels: A Comparative Study of Ambient Monitoring Data with Wind Tunnel Dispersion Simulation for the Dewey Square Tunnel in the Boston Downtown Area

摘要

The two-way Dewey Square Tunnel (DST) built in the 1950's as part of Interstate 93 (I-93), was recently reconfigured to a one-way tunnel serving the Central Artery (I-93) south-bound traffic. The 2,400 feet long DST is longitudinally ventilated, such that the in-tunnel vehicular exhaust is pushed through the exit portal by the piston action effect created by the moving vehicles. In order to determine the effects of the exhaust plume leaving the tunnel portal in the wake of exiting traffic, carbon monoxide (CO) monitors were installed along a sidewalk which runs parallel to the downstream section of the tunnel portal, and inside the tunnel approximately 100 feet from its exit portal. These monitors collected hourly data for a period of five months during 2005. In addition, a physical simulation study was performed to evaluate the effects of tunnel emissions on the existing environment, the proposed commercial building development immediately downstream and adjacent to the tunnel portal, and the associated sidewalks. This paper provides the description and results of the CO monitoring program, the findings of the wind tunnel tests, and a comparison of air quality impacts determined by both the monitoring program and the wind tunnel testing. When compared to the ambient CO monitoring levels, the results indicated that the wind tunnel results under predicted the high CO levels recorded at the closest monitoring site and over predicted those at the farther sites, with an overall over prediction in the order of approximately 10 percent for the highest measured levels at any of the sidewalk locations.