Particulate matter accumulation and capture efficiency by urban trees in Mbeya city, Tanzania: implications for air quality and eco-city sustainability
摘要
Urban air pollution is a pressing challenge in rapidly growing cities, yet the capacity of urban trees to mitigate suspended particulate matter (SPM) remains poorly understood in developing countries. This study evaluated the capacity for accumulation and capture efficiency of selected trees in Mbeya City, Tanzania, and analyzed associated trace elements. The study revealed significant variations in SPM accumulation among trees and particle size classes, with Eriobotrya japonica recording the highest PM₁₀ accumulation (0.82 mg/cm²) and Persea americana exhibiting the highest PM₂.₅ accumulation (0.76 mg/cm²). On average, trees at experimental sites showed higher SPM accumulation (0.52 mg/cm²) compared to control sites (0.07 mg/cm²). In terms of capture efficiency, E. japonica demonstrated the highest efficiency for PM₁₀ (17.57%), while P. americana showed the highest for PM₂.₅ (22.10%), indicating high capture capacities. Trace element analysis of the accumulated SPM revealed species-specific variations. Carica papaya exhibited the highest concentrations of Fe (198.06 mg/kg), Cd (5.99 mg/kg), and Cr (8.38 mg/kg), whereas Mangifera indica showed the highest Pb levels (179.41 mg/kg). P. americana recorded the highest Cu (2.12 mg/kg), E. japonica exhibited the highest Ni (110.03 mg/kg), and Annona reticulata had the highest Zn concentration (27.81 mg/kg). Trace element concentrations were significantly higher in samples from experimental sites compared to control sites. The elevated levels are likely associated with vehicular emissions. Therefore, city managers and policymakers should prioritize the integration of high-performing tree species such as Eriobotrya japonica, Persea americana, Carica papaya, Azadirachta indica, and Tectona grandis into urban greening and roadside planting programs to enhance air quality and promote eco-city sustainability.