[Effects of Urban Expansion and Changes in Urban Characteristics on PM_2.5 Pollution in China]

Study of the influence of China's rapid urbanization and changing urban characteristics on urban ecology is of profound significance for the sustainable development of cities. The results of this study found that such changes have had a profound effect on PM_2.5 concentrations. To explore the effects of urbanization on air quality (especially on PM_2.5) we used indicators of population expansion, economic expansion, and urban geographical to represent levels of urban expansion, and used population density, urban CI, ISC, NDVI, and a night light index to indicate urban space characteristics. The strength of correlations between urban space characteristics and PM_2.5 pollution were as follows:night light index > CI > population density > ISC > urban geographical expansion ≥ population expansion>NDVI. The highest correlation coefficient was between PM_2.5 and the night light index, which was 0.77. During 2010-2015, the total contribution of urban expansion, urban characteristics, and spatial heterogeneity was 80.30%. The contribution of changes in urban characteristics was 55.00% and the contribution of spatial heterogeneity was 25.60%, both of which were above the contribution of basic urban characteristics in 2010, which was 5.70%. From 2000 to 2010, the contribution of changes in urban spatial characteristics to changes in PM_2.5 concentrations was 39.30% and the contribution of the heterogeneity of urban spatial characteristics was 14.90%, both of which were higher than the contribution of basic urban characteristics in 2000, which was 3.70%. The results indicated that as urban transformation and development continue, green ecological cities should fully consider urban spatial layouts and the associated changes in urban spatial characteristics, minimize damage to the ecological environment from urban construction, and they should realize low-carbon and green development.