Response Mechanisms of Air Quality Index (AQI) Spatiotemporal Dynamics in Shandong Province: A Perspective of Vegetation Greenness and Ecological Efficiency

The spatiotemporal dynamics of the Air Quality Index (AQI) and its response to vegetation regulation require further investigation. Using multi-source data from 2020 in Shandong Province, China, this study analyzed the effects of vegetation greenness (NDVI, LAI, EVI), ecological efficiency (Net Primary Productivity, NPP), and landscape structure on AQI within 3 km grids. Monthly correlation analyses revealed that AQI peaks in January (125.09), June (99.01), and December (105.81). PM2.5, O3, and PM10 were the primary pollutants in winter, summer, and spring/autumn, respectively. Vegetation showed a significant purifying effect from June to September. NPP (r = −0.83) was more effective in mitigating air pollution than greenness-related indices (r = −0.48). Pollution mitigation was enhanced by vegetation patches with complex shapes and dispersed configurations. During the non-growing season, the vegetation alleviating effect weakened considerably, and a decoupling between greenness and ecological efficiency occurred. This decoupling was associated with a stronger positive correlation between population density and AQI. The findings highlight the importance of seasonal vegetation dynamics and landscape optimization for regional air quality management.