Interpreting the relationship between urban forests and air quality: Horizontal and vertical investigations utilizing unmanned aerial vehicles

Abstract

Urban forests play a crucial role in regulating air pollutants, but their net impact on air quality remains a subject of debate. To address this issue, this study conducted observations of PM_2.5 and SO₂ concentrations vertically and horizontally above forests and streets using an unmanned aerial vehicle system during low-pollution and high-pollution days. The vertical air purification by urban forests were analyzed in conjunction with the horizontal distribution of PM_2.5 and SO₂ and their correlation with microclimatic factors. Results showed that PM_2.5 purification by urban forests increased from noon to afternoon on low-pollution days, while there was no significant difference in PM_2.5 concentrations at 0–30 m between forests and streets on high-pollution autumn days. During high-pollution autumn days, urban forests obstructed the deposition of PM_2.5 into the forests when atmospheric PM_2.5 concentrations increased. Additionally, forests appeared to trap SO₂, leading to a negative effect on SO₂ concentrations in the afternoon.