City-scale health benefits from experimental results at the tree canopy level: Insights from a nature-based solution case study

Nature-based solutions, such as urban parks, play a crucial role in mitigating air pollution in cities while offering significant health benefits. However, a knowledge gap remains in understanding how vegetation-mediated pollutant removal translates into city-scale air quality improvements and health outcomes. This study uses a green area in Turin, Italy, as a case study, applying different approaches to assess the ecosystem services it provides. Different approaches based on, or inspired to, i-Tree Eco model were used to estimate the amount of particulate matter (PM) removed by trees, while scanning electron microscopy with X-ray spectroscopy (SEM/EDX) was employed to measure PM deposition on leaves. Based on these findings, the air quality improvement was evaluated under different scenarios. The corresponding reduction in disease burden -including conditions such as stroke and type 2 diabetes- at the city level was quantified using the Urban and Transport Planning Health Impact Assessment (UTOPHIA) tool. Results showed that while modelling and experimental approaches produced comparable estimates for fine particulate matter (PM2.5), discrepancies were observed for coarse particles (PM₁₀), influencing the projected health outcomes. A detailed analysis of the applied methodologies, including parameter interdependencies, provides valuable insights into their influence on estimated outcomes. These findings can contribute to improving future approaches for translating local air quality data into city-scale policy decisions.