Greenery as a mitigation strategy to urban heat and air pollution: a comparative simulation-based study in a densely built environment.

The urban heat island and the urban air pollution concentration are two major climate-change-related phenomena affecting the built environment worldwide. This paper aims to verify the potential effect of different mitigation measures through a simulation study. In detail the present study focuses on the analysis of the environmental impacts of urban vegetation, such as green facades, vertical greenery, and green pavements. After an extensive screening of the literature review, an investigation of the impact of the most common built environment design variables in a defined case study led to the definition of a typical urban canyon was tested. The results show that the presence of trees in a street canyon could reduce the air temperature peaks by 5-10 °C, while the high-level vegetation canopies can lead to a deterioration in air quality with a PM concentration increasing by 1.2-1.5%. Instead, using low-level green infrastructure improves the air quality conditions on the sidewalk, reducing the NOx in the range of 10-20%. The analyzed high-level greenery generated an air temperature reduction effect on a street level ranging from 8 to 12°C. The present work contributes to clarifying the potential mitigation effect of green infrastructure in a densely built environment, where the risk of increasing temperatures and air pollutants is foreseen to be more intense in the coming years.