How does urban form influence PM2.5 concentrations: Insights from 350 different-sized cities in the rapidly urbanizing Yangtze River Delta region of China, 1998–2015

Abstract Although PM2.5 poses a serious threat to public health, the role of urban form in influencing concentrations of this air pollutant is unresolved. Ridge regression was employed to investigate relationships between satellite-derived estimates of PM2.5 concentrations and the urban form of 350 cities in the rapidly urbanizing Yangtze River Delta (YRD) of eastern China. The cities were stratified by population into small ( 1,000,000), and urban circularity, fragmentation, and compactness were measured from 1998 to 2015. Circularity was not a statistically significant predictor of PM2.5 concentrations, except for maxima in large cities. Although fragmentation was strongly negatively correlated with mean and maximum PM2.5 concentrations for all cities, compactness was positively associated with mean and maximum PM2.5 concentrations only in small and medium-sized cities. Urban form thus had a relatively stronger impact on PM2.5 concentrations in cities that were not yet large. After controlling for population, land area, and climate, more sprawled cities had lower PM2.5 concentrations than their more spatially compact counterparts. These findings indicate that planning agencies in the YRD should encourage moderately scattered and polycentric urban development rather than compact, monocentric growth.