High-Resolution LES-Based Air Quality Modeling Over Munich: Evaluation of Model Performance, and Pollution Drivers

Air pollution is a critical issue, particularly in urban areas, making the monitoring and understanding of the  air pollutant’s sources essential. Urban regions are often very heterogeneous due to the complexity of buildings, roadways, vegetation, and various emission sources. Governments prioritize these areas to implement intervention measures aimed at addressing air pollution, as urban regions are both major sources of pollution and densely populated. Therefore, simulating the dispersion of air pollutants at high spatial and temporal resolution is crucial for understanding pollution sources and evaluating different intervention measures.

In this context, we have set up the Large-Eddy Simulation (LES)-based air quality model, PALM-4U (Parallelized Large-Eddy Simulation Model for Urban), over Munich, Germany. The goal is to simulate meteorology and concentrations of air quality relevant species at high spatial (10 meters) and temporal (10 minutes) resolution across the city. The model uses high-resolution static parameters (e.g., building height, vegetation height), dynamic meteorological variables from the WRF model (with a 400-meter resolution) for boundary conditions, and a high-resolution emission inventory (100 meters). The boundary conditions for air quality species were obtained from CAMS model ensemble outputs. 

We compared the simulated meteorology and air pollutant concentrations with data from an extensive measurement campaign conducted in August 2023 for selected days. The results showed good agreement for wind speed (Mean Bias (MB) = 0.23 m/s, Pearson correlation coefficient (R) = 0.86) and wind direction (MB = 35°, R = 0.83). The PALM-4U model overestimated NO₂ concentrations by 0.82 ppb (+15.5 %), underestimated O₃ concentrations by 4.5 ppb (-13.7 %) and overestimated PM₁₀ concentrations by 1.4 µg m^-3 (+11.7 %), although it accurately captured the diurnal variations. Sensitivity analysis revealed that the boundary conditions from the mesoscale model have a significant impact on the modeled air quality concentrations.

This model setup will be further utilized to evaluate the effectiveness of various measures, such as low-speed zones, low-emission zones, and the extent of electric vehicle adoption required to achieve safe air pollution levels within Munich.