Evaluating ambient air quality at exit portals of the Central Artery/Tunnel
- Rowan Williams Davies and Irwin Inc., Guelph, Ontario (Canada)
Full transverse ventilation, with supply and exhaust ducts parallel to the roadway, is the main ventilation approach used on the Central Artery/Tunnel project in Downtown Boston, Massachusetts. However, longitudinal ventilation, in which exhaust air is discharged at the tunnel exit, has been adopted for many of the entrance and exit ramps of the proposed tunnel. In the case of exit ramps, the exhaust fumes are discharged to the outside air, causing a local increase in airborne pollutants. As a result, the feasibility of longitudinal ventilation for these ramps depended in part on whether or not applicable ambient air quality requirements would be met. Physical modeling in a boundary layer wind tunnel was used to predict the dispersion of the exit ramp emissions and evaluate the impact on ambient air quality. Maximum 1-hour, 24-hour and annual average pollutant concentrations at sensitive receptors were predicted by combining the wind tunnel data with five years of hourly meteorological data and background pollutant concentration data for the Boston area. Three levels of analysis were developed in order to streamline the process of evaluating each exit ramp tunnel. At the first level, the pollutant contribution from the given tunnel portal was combined with the measured background pollutant concentration for the study area. At the third level, modeled contributions from traffic on local surface streets, other nearby exit ramps and/or ventilation buildings of the proposed tunnel system were also included. If emissions from a tunnel portal failed to meet the State ambient air quality requirements at any level of analysis, the analysis was discontinued and the tunnel was deemed unsuitable for longitudinal ventilation. The study results showed that nitrogen dioxide was the limiting pollutant.
- OSTI ID:
- 351681
- Report Number(s):
- CONF-970677--
- Country of Publication:
- United States
- Language:
- English
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