Microclimate and air quality investigation in historic hilly urban areas: Experimental and numerical investigation in central Italy

Outdoor environmental comfort strongly affects the quality of life and depends on local microclimate phenomena. However, impact of local boundaries is still weakly studied in hilly urban historical layouts. Local microclimate variability and its influence on pedestrians’ comfort in selected hilly historical urban areas with varying local boundaries in term of vegetation, surface materials, urban density, and air quality, is investigated. To this aim, a field monitoring is carried out during summer in hilly dense built environment and numerical analysis is performed. Monitoring campaigns show how higher density and surface roughness in the urban historical area reduce daily temperature fluctuation up to 3 °C, with higher night temperatures. Temperature discrepancies up to 5 °C are detected compared to suburban greener area. Moreover, inverse correlation between sky-view factor and nighttime cooling is registered, with mean temperature variation up to 6.6 °C. Numerical analysis shows different thermal comfort conditions within the same district, due to different local boundaries in terms of sky-view factor and surface materials properties. Maximum Predicted Mean Vote difference of 0.6 is detected in the same area. Findings demonstrate how impact of local boundaries needs to be accurately investigated, when analyzing quality of outdoor urban environment, to realistically predict citizens’ outdoor thermal conditions.