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 (NO_x), 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 NO_x, 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.

Air quality issues caused by nitrogen dioxide (NO₂) have become increasingly serious in Chinese cities in recent years. As important urban green infrastructure, urban forests can mitigate gaseous nitrogen pollution by absorbing NO₂ through leaf gas exchange. This study investigated spatiotemporal variations in the NO₂ removal capacity of urban forests in Beijing city from 2014–2019, based on the i-Tree Eco deposition model. The results show that the annual removal capacity of administrative districts within Beijing city ranged from 14,910 to 17,747 tons, and the largest capacity (2684 tons) was found in the Fangshan district. The annual removal rate of NO₂ by urban forests in administrative districts within Beijing was estimated at between 0.50–1.60 g/m², reaching the highest (1.47 g/m²) in the Mengtougou district. The annual average absorption of NO₂ by urban forests can account for 0.14–2.60% of annual total atmospheric NO₂ and potentially reduce the NO₂ concentration by 0.10–0.34 µg/m³ on average. The results of a principal component analysis suggest that the distribution of urban forests in Beijing is not optimized to maximize their NO₂ removal capacity, being higher in suburban areas and lower in urban areas. This study provides insights into botanical NO₂ removal capacity in Beijing city to mitigate atmospheric N pollution, addressing the key role of urban forests in improving human wellbeing.