Urban greenness and heavy PM_2.5 events in China: A national long-term panel study on burden, severity, and...

Evidence suggests connections between urban greenness and PM_2.5, yet most studies rely on city- or regional-scale designs or short time windows, often overlooking PM_2.5 pollution events (PEs) and the dynamics within those events. Using a 2000-2022 panel of built-up areas in 371 Chinese cities, we examined associations of total greenness (NDVI) and tree cover with annual PE burden, severity, and PM_2.5 accumulation and dispersion during PEs. Higher NDVI and tree cover were generally associated with lower annual PE burden and severity. Per 1-SD increase in NDVI, heavy PEs (≥75 μg/m³) were 1.7% fewer, PE days were 2.9% fewer, and cumulative intensity was 3.0% lower; event duration and mean intensity were also lower. Tree cover showed smaller associations, with 0.3% fewer PEs, 0.6% fewer PE days, and 0.2% lower cumulative intensity, and less stable results for extremely heavy PEs (≥150 μg/m³) and regional analyses. Within events, NDVI showed limited associations with accumulation or dispersion, whereas tree cover was associated with 0.4-0.7% greater magnitudes and faster rates of both accumulation and dispersion, suggesting steeper event trajectories. PE associations with greenness were weaker than those with meteorological and emission-related factors and varied by region, especially in the Sichuan Basin and Pearl River Delta. These findings suggest that urban greening may complement source-oriented strategies for mitigating PM_2.5 PE burden and severity, but greenspace design should be tailored to regional context, emission-related factors, and meteorological conditions, with attention to the composition and spatial arrangement of tree canopy and other vegetation types.