Mono- and polycentric urban spatial structure and PM2.5 concentrations: Regarding the dependence on population density.

City planners are increasingly drawn to the possibilities of transforming urban spatial structure as an important strategy for reducing air pollution. This paper addresses mixed findings in the existing literature through reliable methodology and heterogeneity tests. We examined the effects of spatial mono- and polycentricity on PM 2.5 concentrations using spatial econometric models based on a three-year panel of data for cities at, or above, the prefecture in China. We found that population density had a robust moderating effect. That is, all else being equal, PM 2.5 concentrations are lower when low-density cities have a strong-monocentric spatial structure and when high-density cities are polycentric. We estimated the population density threshold at which point the relationship between structure and density changes at about 160 persons/km.2 Our findings can serve as a possible criterion for differentiating low- and high-density cities in China and guide policymakers in planning optimal urban structures to mitigate air pollution. • The spatial centralization index and spatial concentration index are used together to quantify polycentricity. • PM 2.5 lower when low-density cities have strong-monocentric spatial structure. • Densely populated cities can reduce PM 2.5 concentrations using a polycentric structure. [ABSTRACT FROM AUTHOR]