Modeling of carbon monoxide dispersion around the urban tunnel portals

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.