Search

Although PM 2.5 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 PM 2.5 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 (<500,000), medium-sized (500,000–1,000,000), and large (>1,000,000), and urban circularity, fragmentation, and compactness were measured from 1998 to 2015. Circularity was not a statistically significant predictor of PM 2.5 concentrations, except for maxima in large cities. Although fragmentation was strongly negatively correlated with mean and maximum PM 2.5 concentrations for all cities, compactness was positively associated with mean and maximum PM 2.5 concentrations only in small and medium-sized cities. Urban form thus had a relatively stronger impact on PM 2.5 concentrations in cities that were not yet large. After controlling for population, land area, and climate, more sprawled cities had lower PM 2.5 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. • We measured urban form by "circularity", "fragmentation", and "compactness". • We quantified the impact of urban form on PM 2.5 for different-sized cities in the YRD. • We compared the impact of urban form on air quality in China and the US. • We proposed optimized urban form characteristics to mitigate PM 2.5 pollution. [ABSTRACT FROM AUTHOR]

Planned urban form has become an important strategy to improve air quality in urban agglomerations (UAs), especially pollution due to PM 2.5 , but the influencing mechanisms are not yet clear. This study explores the relationship between four metrics of urban form (size, fragmentation, shape, and dispersion) as determined by analysis of remotely sensed images at 30-m resolution and PM 2.5 concentrations in 19 Chinese UAs. The influence of level of urban development and season is examined. Five control variables, including population density, temperature, precipitation, wind speed, and the normalized difference vegetation index (NDVI) are selected for use in multiple linear regression models. Size, fragmentation, and shape of urban form, but not dispersion, were found to have significant effects on PM 2.5 concentrations of different urbanization-level UAs. Urban size and fragmentation have stronger impacts on PM 2.5 concentrations in UAs with lower urbanization levels while urban shape has a greater impact in higher-level UAs. In terms of seasonal variation in all UAs, urban form is more pronouncedly associated with PM 2.5 concentrations during spring and autumn than summer and winter. Urban size and fragmentation are positively associated with PM 2.5 concentrations whereas urban shape and dispersion are on the contrary. The relationships between urban form and PM 2.5 uncovered here underscore the importance of urban planning as a tool to minimize PM 2.5 pollution. Specifically, local government should encourage polycentric urban form with lower fragmentation in urban agglomerations. UAs with lower urbanization levels should control the disordered expansion of construction land and higher-level UAs should promote the mix of green land and construction land. Moreover, measures to control air pollution from anthropogenic activities in spring, autumn and winter are likely to be more effective in decreasing PM 2.5 concentrations in UAs. • The urban form was measured by urban size, fragmentation, shape, and dispersion. • Effect of urban form on PM 2.5 concentrations varies with urbanization levels of urban agglomerations. • Seasonally, urban form has a stronger effect on PM 2.5 concentrations in spring and autumn. • Polycentric urban form with lower fragmentation should be encouraged in urban agglomerations for reducing PM 2.5 pollution. [ABSTRACT FROM AUTHOR]