Effectiveness of urban parks in reducing ambient PM10 through deposition and dispersion: towards greener cities
摘要
As the 'lungs of the city' and a refuge from pollutants, urban parks improve air quality by reducing ambient PM₁₀ through deposition and dispersion, particularly in major metropolises. This study evaluates the average relative reduction effect of urban parks on ambient PM10at the respiratory level (1.5 -2 m above ground) through deposition and dispersion, focusing on two widely planted tree species across the Middle East—oriental plane (Platanus orientalis L.) and white mulberry (Morus alba L.)—. These species are commonly used in urban green spaces due to their adaptability, broad canopy, and ability to withstand urban stressors. The research was conducted in Laleh Park, located in the heart of Tehran, one of the most polluted cities in the world. We developed a combined procedure integrating theoretical model (i.e., dry deposition flux) with both direct and indirect measurements of ambient PM10. We applied a dry deposition flux model using locally derived, seasonally adjusted deposition velocities for PM10 and PM2.5 on tree leaves, estimated through indirect measurements. Then, direct measurements taken inside and outside Laleh Park were used to disaggregate the park's effectiveness on ambient PM₁₀ into deposition and dispersion effects. The theoretical model showed that the park's trees contributed to a 10% total reduction in ambient PM10 at the respiratory level through deposition over the course of a year, with oriental plane trees accounting for a 9.3% reduction and white mulberry trees contributing an additional 0.7%. Direct measurements confirmed this finding, showing that the park's trees contributed to an average 10.4% reduction in ambient PM10 at the respiratory level through deposition over year. Furthermore, the dispersion of PM10 within the park accounted for an average 6.1% reduction in ambient PM10. Altogether, the combined effect of deposition and dispersion led to an average 16.5% reduction in ambient PM10 at the respiratory level inside the park. Elemental analysis of foliar deposits revealed elevated concentrations of Al and Pb, with enrichment factors of 110 and 7, respectively. The extremely high enrichment of Al and significant enrichment of Pb indicate strong anthropogenic contributions, likely from traffic-related sources. These findings highlight the potential for urban parks in cities like Tehran, to improve air quality, with implications for more effective urban planning. Further research is needed to assess the broader effectiveness of various types of urban green spaces (e.g., urban forests, parks, community gardens, and greenways) and plant species in mitigating different types of pollutants.