Prediction of pollutants dispersion patterns around two adjacent urban road tunnels

Road tunnels have recently become prevalent in urban areas of China. In areas adjacent to these tunnels, air quality and human health are important public health concerns. As such, assessing pollutant dispersion and decay rates around tunnel portals in the surrounding environment is an important field of study. This study established a three-dimensional computational fluid dynamics (CFD) model containing two adjacent urban road tunnels, to estimate pollution dispersion characteristics outside the tunnels. The results indicate that, when pollutants were exhausted from the portals only, crossflow between the two adjacent tunnels was quite severe. The highest carbon monoxide (CO) concentration was nearly 50?ppm, exceeding the 10?ppm limit National Standard in China for 1?h exposure when exhaust shafts are absent. When shafts exhausted 80% of the pollutants from the tunnel portal, crossflow between the adjacent tunnels decreased to 10-50% of that without shafts. The simulation results demonstrate that the combination of shafts and portals was an effective and energy-saving strategy to exhaust pollution from adjacent super-long urban road tunnels. These findings increase our fundamental understanding and provide guidelines for evaluating pollutant exposure risk around tunnel portals, the design of tunnel exhaust shafts, and environmental planning purposes in urban environments.