Mechanisms of Ventilation in Real Street Canyon: The Bologna iSCAPE Case Study

Traffic induced emissions have been commonly addressed as major source for air pollution in cities. Gases and particulate matter resulting from the combustion processes are the main components of these emissions, but also pneumatic abrasion, brake discs consumption and road dust resuspension contribute to air quality deterioration. The presence of dense built up areas limits the efficacy of atmospheric winds to disperse pollutants, enhancing near ground concentrations. It is known that tree planting in urban street canyons influences pollutants dispersion and exchange with the free atmosphere by affecting wind ventilation at street and neighborhood levels. Nevertheless, the actual quantification of tree influence depends on different and mutual interacting factors: synoptic meteorological conditions, wind stress at the top of the canyon, geometry of the street canyon and vegetation. Within the recently EU-funded project iSCAPE, the role of vegetation in street canyons has being analyzed in real street canyons in the city of Bologna (Italy). Specifically, multi-levels of turbulent fluxes are being measured during summer 2017 in two typical street canyons in combination with ground level concentration measurements. Data interpretation is assisted by Computational Fluid Dynamics (CFD) modelling to extract the key mechanisms of ventilation in typical Italian cities. Results are sought for extension to other European cities that are characterized by low synoptic conditions and similar morphological structures.