Simulation and Evaluation of Pollutant Dispersion from Urban Tunnel Ventilation Shafts

This paper presents a case study on the evaluation of pollutant dispersion from urban tunnels using simulation-based approaches. In urban tunnel design, understanding the environmental impact of tunnel emissions is crucial. Specifically, this study focuses on the dispersion of pollutants, particularly carbon monoxide, at the middle air exchange station and its exhaust shaft. The study provides valuable insights into the environmental impact of tunnel emissions and contributes to ensuring that standard tunnel design and ventilation systems meet the required standards for minimizing pollution and maintaining a safe and sustainable urban environment. Comprehensive analysis and simulation models, including the Graz Lagrangian Model and the Graz Mesoscale Model, were utilized for the study. The research demonstrates that carbon monoxide concentrations decrease to negligible levels (below one ppm) within a 100 m distance from the ventilation shafts. The annual average concentration of carbon monoxide within a range of up to 30 m remained below ten ppm, and since there are no specific facilities in the vicinity of the shaft, there is no cause for concern. Additionally, in terms of daily maximum concentrations, under specific atmospheric stability conditions and particular weather patterns, the maximum carbon monoxide concentration extends up to a distance of 60 m, remaining below 20 ppm, and then dissipates beyond that distance. It is important to note that these results were observed at elevations of 20 to 30 m above ground level. Below those levels, carbon monoxide concentrations in all considered scenarios are extremely low and can be disregarded. The study highlights that the implemented ventilation systems effectively mitigate pollutant dispersion in the urban tunnel. The results demonstrate that carbon monoxide emissions are well below the acceptable limits, ensuring the safety of nearby residential and office buildings, hospitals, green areas, and parks. The research findings provide valuable insights for informed decision-making in tunnel design, emphasizing the importance of appropriate ventilation systems and construction methods to minimize the environmental impact of tunnel emissions.