Impact of urban space on PM2.5 distribution: A multiscale and seasonal study in the Yangtze River Delta urban agglomeration

Despite concerted efforts in emission control, air pollution control remains challenging. Urban planning has emerged as a crucial strategy for mitigating PM2.5 pollution. What remains unclear is the impact of urban form and its interactions with seasonal changes. In this study, based on the air quality monitoring stations in the Yangtze River Delta urban agglomeration, the relationship between urban spatial indicators (building morphology and land use) and PM2.5 concentrations was investigated using full subset regression and variance partitioning analysis, and seasonal differences were further analysed. Our findings reveal that PM2.5 pollution exhibits different sensitivities to spatial scales, with higher sensitivity to the local microclimate formed by the three-dimensional structure of buildings at the local scale, while land use exerts greater influence at larger scales. Specifically, land use indicators contributed substantially more to the PM2.5 prediction model as the buffer zone expanded (from an average of 2.41% at 100 m range to 47.30% at 5000 m range), whereas building morphology indicators displayed an inverse trend (from an average of 13.84% at 100 m range to 1.88% at 5000 m range). These results underscore the importance of considering building morphology in local-scale urban planning, where the increasing building height can significantly enhance the dispersion of PM2.5 pollution. Conversely, large-scale urban planning should prioritize the mixed use of green spaces and construction lands to mitigate PM2.5 pollution. Moreover, the significant seasonal differences in the relationship between urban spatial indicators and PM2.5 pollution were observed. Particularly noteworthy is the heightened association between forest, water indicators, and PM2.5 concentrations in summer, indicating the urban forests may facilitate the formation of volatile compounds, exacerbating the PM2.5 pollution. Our study provides a theoretical basis for addressing scale-related challenges in urban spatial planning, thereby fostering the sustainable development of cities.