Mitigation impact of roadside trees on fine particle pollution

Area of Science:

• Environmental Science
• Urban Ecology
• Air Quality Management

Background:

• Fine particulate matter (PM2.5) from vehicle emissions poses significant health risks in urban areas, particularly near roadways.
• Istanbul faces declining air quality due to a rapid increase in non-electric vehicles, leading to elevated mortality rates linked to air pollution.
• Roadside vegetation is a potential strategy to mitigate urban air pollution and reduce public health risks.

Purpose of the Study:

• To investigate the effectiveness of roadside trees, specifically Mediterranean Cypress (Cupressus sempervirens), in mitigating vehicle-related PM2.5 and heavy metal (HM) pollution.
• To quantify the reduction in PM2.5 concentrations and pedestrian exposure to HMs under different tree planting scenarios.

Main Methods:

• Three experimental roadside conditions were established in Istanbul: no trees (C1), trees with gaps (C2), and dense trees (C3).
• PM2.5 samples were collected, and tree leaves were analyzed for heavy metal content.
• Pedestrian exposure to PM2.5 and HMs was calculated based on measured data.

Main Results:

• Dense roadside tree plantation (C3) reduced PM2.5 concentrations by 17%, reaching urban background levels.
• Significant removal of heavy metals was observed, with nickel concentrations decreasing from 26.4 ± 7.8 to 7.5 ± 2.4 μg/m³.
• Pedestrian exposure to heavy metals like cadmium and lead was reduced by over 50% in the dense tree scenario (C3).

Conclusions:

• Mediterranean Cypress trees are effective in significantly decreasing roadside PM2.5 and heavy metal pollution in dense traffic areas.
• Roadside tree plantations, especially dense configurations, are a crucial green infrastructure strategy for improving urban air quality and mitigating public health risks in cities like Istanbul.