The impact of urban block typology on pollutant dispersion

Block typology is a central component for urban planning and a key element to represent the urban form, which affects the airflow. Therefore, the aim of this work consists of investigating the impact of different urban block typologies in urban pollutant dispersion. Five typologies derived from real cities were investigated using the computational fluid dynamics technique: single-block, detached buildings, central courtyard, inner courtyards, and row. The numerical simulations were performed using URANS (Unsteady Reynolds-Averaged Navier-Stokes) equations and the κ−ω SST model to represent the turbulence effects. The model was validated using wind tunnel experimental data. Urban air quality was assessed using five parameters: mean age of air, net escape velocity, pollutant concentration at pedestrian level, and pollutant mass fluxes towards the urban canopy and outwards from it. The results showed that the single-block typology revealed an average pollutant concentration at pedestrian height 80% lower than that estimated in the detached building typology, which presented the highest concentration, probably due to the highest aspect ratio associated with permeable facades. Further, the higher the wind velocity, the lower the mean age of air. Finally, the unbuilt areas’ disposition within the block proved to be the more important parameter influencing the pollutant dispersion. •The local ventilation performance strongly depends on block typology.•The canyon aspect ratio alone isn’t enough to analyze street ventilation.•The unbuilt areas disposal into the block is a key factor for pollutant dispersion.•The porosity in the crosswind direction increases the pollutant concentration.•Openings in the wind direction were more effective for the pollutant dispersion.