Modeling the Influence of Traffic Infrastructure Changes on Air Quality in Prague with the LES Model PALM

Large-eddy simulation (LES) models provide valuable high-resolution information for air quality applications in urban environments. By capturing turbulence and transport processes at fine scales, LES enables detailed investigations of urban challenges like heat islands and air pollution dispersion. However, applying LES in urban planning has faced several challenges. Past studies have shown LES to be highly sensitive to input data quality, including model parameters and boundary conditions. Compared to lower-resolution models, LES is also computationally expensive, often limiting applications to individual case studies. This work presents the TURBAN project, in which the LES model PALM was used for a series of modeling experiments in Prague, Czech Republic, focusing on extreme events – namely heatwaves and poor air quality episodes. Initial simulations tested PALM's sensitivity to boundary conditions from different regional models, finding ICON provided optimal driving data. Evaluation against observations from a dedicated measurement campaign then assessed PALM performance in six three-day episodes of heat-wave and/or poor air quality conditions. Finally, PALM was applied to scenarios exploring the air quality impacts of planned traffic infrastructure changes in a heavily trafficked area of Prague. These scenarios examine a proposed connection between the northern and eastern sections of the city’s inner and outer ring roads. The integrated evaluation and application of PALM provides essential insights into using LES for understanding complex interactions of urban planning, thermal comfort, and air pollution.