On thermal stratification in real street canyons with trees: Consequences for local air quality

This study analyses the effects of trees on local meteorology in a medium-size Mediterranean city (Lecce, IT) using field measurements and Computational Fluid Dynamics (CFD) simulations. Measurements were taken in two parallel street canyons with and without trees. Building façades and ground temperatures were estimated from infrared (IR) images, while flow and turbulence were measured by three ultrasonic anemometers. CFD simulations were performed by employing the Reynolds Stress Model (RSM). Overall the analysis shows that trees reduce the wind speed and alter the typical diurnal cycle of surface and air temperature within the canyon. In particular, the flow interaction with trees induces wind direction fluctuations below tree crowns and lower velocities which are expected to lead to larger pollutant and heat trapping in the lower part of the street canyon, especially in nocturnal hours.