Can Changes in Urban Form Affect PM_2.5 Concentration? A Comparative Analysis from 286 Prefecture-Level Cities in China

It is crucial to the sustainable development of cities that we understand how urban form affects the concentration of fine particulate matter (PM_2.5) from a spatial–temporal perspective. This study explored the influence of urban form on PM_2.5 concentration in 286 prefecture-level Chinese cities and compared them from national and regional perspectives. The analysis, which explored the influence of urban form on PM_2.5 concentration, was based on two types of urban form indicators (socioeconomic urban index and urban landscape index). The results revealed that cities with high PM_2.5 concentrations tended to be clustered. From the national perspective, urban built-up area (UA) and road density (RD) have a significant correlation with PM_2.5 concentration for all cities. There was a significant negative correlation between the number of patches (NP) and the average concentration of PM_2.5 in small and medium-sized cities. Moreover, urban fragmentation had a stronger impact on PM_2.5 concentrations in small cities. From a sub-regional perspective, there was no significant correlation between urban form and PM_2.5 concentration in the eastern and central regions. On the other hand, the influence of population density on PM_2.5 concentration in northeastern China and northwestern China showed a significant positive correlation. In large- and medium-sized cities, the number of patches (NP), the largest patch index (LPI), and the contagion index (CONTAG) were also positively correlated with PM_2.5 concentration, while the LPI in small cities was significantly negatively correlated with PM_2.5 concentration. This shows that, for more developed areas, planning agencies should encourage moderately decentralized and polycentric urban development. For underdeveloped cities and shrinking cities, the development of a single center should be encouraged.