Role of urban vegetation in air phytoremediation: differences between scientific research and environmental management perspectives

Air pollutant removal by urban vegetation is perceived to be a key ecosystem service for mitigating air pollution. However, the effectiveness of air phytoremediation in cities requires more synthesis to inform environmental management. A Bayesian meta-analysis approach was used to quantify the effectiveness of the removal of typical air pollutants—particle matter (PM), nitrogen oxide (NOx), sulfur dioxide (SO2) and ozone (O3)—by synthesizing global field measurement studies. The results revealed that urban vegetation can mitigate the growth of air pollutant concentrations, with reduction rates of 16.5~26.7% for PM, 13.9~36.2% for NOx, and 20.5~47.8% for SO2. However, they failed to significantly mitigate ground-level O3, corresponding to an increase of 5.1~25.9%. The variability in effect sizes was mainly influenced by the distance to nearest highway, ambient concentration, relative humidity, and green coverage. A questionnaire survey conducted in Shenzhen city (China) showed that most environmental managers supposed positive impacts of urban vegetation on all four air pollutants, which was at odds with our findings with respect to O3. This study can inform the lessening of discrepancies between scientific research and environmental managers’ perceptions on how to improve air phytoremediation for urban air pollution mitigation in China and elsewhere.