The aim of this study is to investigate the problems caused by discharge of polluted air from tunnels into the environment with a specific focus on residential areas. In city tunnels, portal or stacks, pollutant management is a big challenge. Nowadays, air quality management, particularly in urban tunnels, is considered as a part of the ventilation system design. The goal is to see the environmental impacts beforehand. From environmental aspects, preventive measures are required either inside or outside the tunnel in some cases. Niayesh tunnel in Tehran is taken as a case for proving the objectives presented in this study. Concentration of carbon monoxide at the vicinity of the portals is calculated using the proper dispersion simulation. The results of dispersion modeling for the assumed worst case of ventilation can help to understand the environmental impact of ventilation. The worst traffic emissions for a congested traffic scenario,are selected as an emission source for dispersion modeling. According to the traffic condition and fleet composition, the crucial emission extracted from the tunnel is carbon monoxide. Therefore, the performed simulation only focuses on carbon monoxide dispersion modeling. From the other side, carbon monoxide is taken as a demonstration pollutant, because it is inert and chemical reactions can be neglected in short-term considerations. A lagrangian model composed of Graz Lagrangian Model and Graz Mesoscale Model is used for flow-field and dispersion calculations.
- The study indicated that environmental impact of the discharged carbon monoxide from the Niayesh tunnel is in standard level.
- According to the distance of the buildings from the portals, the effects of emitted carbon monoxide from the Niayesh tunnel on the surrounding residential areas can be ignored
- The obtained results are only valid for carbon monoxide with the assumed emission and traffic conditions in the mentioned tunnel.
- The longitudinal ventilation system is found sufficient for the Niayesh tunnel with the current traffic conditions, and portal air quality management is not required
- In the case of increase in traffic to more than two lanes or change of fleet composition, another redundant system (air exchange station) might be required.