Urban climate and pollution feedbacks in high resolution WRF-CHEM experiments.

The interactions between urban climate and air pollution are complex and bidirectional. On one hand, urban characteristics, such as the heat island effect and  higher surface roughness, modify local circulations and can enhance the accumulation of pollutants under certain conditions. On the other hand, atmospheric pollutants, such as aerosols or green house gases, can alter radiative and thermodynamic processes, affecting air temperature, cloud formation, and atmospheric stability.  However, the knowledge on these feedbacks is still scarce. In this context, high resolution coupled atmosphere-chemistry models can help to understand better these interactions.  

We present a set of high-resolution (1km)  WRF-Chem simulations over several large and medium-sized European cities to investigate the impact of urban areas on local meteorology and air quality, as well as the interactions between pollutants and urban climate modification. The experiments include idealized configurations removing and including urban areas, and activating and deactivating anthropogenic emissions. The comparison among the experiments permit as to identify the relative role of each factor in the generation of the urban climate.  The results show that the model is capable of reproducing the Urban Heat Island (UHI) effect and capturing its influence on local circulations. When urban emissions are introduced through the atmospheric chemistry module, average impacts on meteorological variables are generally modest. However, under specific weather conditions, typically characterized by weak winds and overcast skies, urban emissions can significantly alter local atmospheric dynamics. On the other hand, the results indicate that a full inclusion of the city morphological features enhances the pollution urban island.