Quantifying the Scaling Effects of Urban Green Infrastructure on Air Quality and Greenhouse Gas Dynamics: Insights from a Multi-Site Evaluation in Athens, Greece

Urban green infrastructure (GI) provides a promising nature-based solution to mitigate urban air pollution, particularly fine particulate matter (PM), yet its quantifiable impacts across diverse urban settings remain insufficiently explored. This study investigates pollutant dynamics in Athens, Greece, a Mediterranean megacity characterized by high anthropogenic emissions and sparse green cover. A two-week monitoring campaign was conducted at four urban locations with vegetation density ranging from 5% to 100%. Concentrations of PM2.5, PM10, NO2, CO2, O3, and VOCs were measured and analyzed using statistical approaches including ANOVA, ANCOVA, and regression models to normalize meteorological influences. Results showed consistent decreases in primary pollutants (PM2.5, PM10, NO2, VOCs, CO2) with increasing vegetation cover, while O3 exhibited the expected inverse pattern due to reduced NO titration. Diurnal analyses revealed sharp peaks in PM and other pollutants during morning and evening rush hours in low vegetation corridors, contrasted with flatter profiles in greener sites. These findings demonstrate that even modest increases in green cover can dampen traffic-related pollution surges, reduce daily variability, and lower human exposure. The study highlights GI as a scalable and cost-effective strategy for particulate matter reduction and sustainable urban air quality improvement.