Rapid urbanization is intensifying air pollution across cities worldwide, with fine particulate matter (PM2.5) emerging as one of the most hazardous pollutants to public health. While urban trees are widely recognized for their role in air purification, particularly through pollutant absorption and filtration, most existing studies rely on predictive models such as i-Tree Eco and rarely incorporate direct field-based validation of PM2.5 exposure levels for urban residents. A critical gap remains in understanding the actual distribution of health-threatening PM2.5 concentrations and the localized effectiveness of urban vegetation in mitigating these pollutants. This study addresses this gap by assessing PM2.5 pollution levels and evaluating the particulate matter absorption capacity of urban trees in two street alleys with contrasting tree canopy cover (TCC) in Warsaw, Poland. The research was conducted in two phases: first, PM2.5 concentrations were monitored using dust sensors during peak and post-peak traffic periods; second, the i-Tree Eco model was employed to quantify pollutant uptake by trees at each site. The findings indicate that exceedances of the WHO PM2.5 air quality standard (15 μg/m³) occurred 1.5 times more frequently on streets with only 6% tree canopy cover (TCC), compared to streets with more than 30% TCC. Moreover, the site with optimal TCC, trees demonstrated over 14-fold greater effectiveness in PM2.5 removal. Furthermore, the model has been shown to be statistically significant, meaning that one of the predictors, TCC or DBH, has a significant impact on PM2.5 removal levels. These findings highlight the critical role of tree canopy density in enhancing urban air quality and suggest that sole reliance on modeled estimations without ground-level data may significantly underestimate residents’ exposure to PM2.5. By integrating in-situ pollution monitoring with ecosystem service modeling, this study provides a more accurate assessment of urban trees' capacity to mitigate air pollution. The findings underscore the need for data-driven urban greening policies and offer actionable insights for improving air quality in cities like Warsaw.
Kais et al. (Sat,) studied this question.