Dynamic evolution of PM2.5 removal by urban forests during rapid urbanization: From forest landscape pattern dominance to impervious surfaces

Long-term exposure to PM_2.5 (fine particulate matter with an aerodynamic diameter <2.5 μm) causes serious harm to human health. Urban forests have the potential to effectively mitigate PM_2.5 in the air. However, with the progress of urbanization, the layout, structure, and functions of urban forests have evolved, and the impact of these transformations on their PM_2.5 removal capacity remains to be fully explored. Our study used a dry deposition model to simulate the dynamics of PM_2.5 removal by forests in Changchun City during rapid urbanization and identified the drivers. We found that the urban forest cover increased from 18.09% in 2000 to 24.59% in 2020. Although 12% of the urban forest was converted into impervious surfaces, the overall coverage still showed an increase, mainly due to the conversion of other land types, including cropland and wetland. Rapid urbanization also had a significant impact on the configuration of urban forests, as urban forest patches have become more fragmented, with simpler shapes. The PM_2.5 removal of urban forests has gradually declined, affecting 45.50% of the urban area. The total PM_2.5 removal amount decreased from 793 t yr⁻¹ to 528 t yr⁻¹. Urban forest landscape patterns primarily influenced the PM_2.5 removal capacity, accounting for 72%. As impervious surfaces increased, the capacity was reduced, and the influence of landscape patterns weakened. This study confirmed the significant impact of urbanization on the PM_2.5 removal capacity of urban forests, which gradually surpassed the regulatory effect of landscape patterns. These findings provide valuable theoretical support for urban environment and planning, and guide the development of effective air quality improvement policies.