The effect of urbanization on environmental pollution in rapidly developing urban agglomerations

China is experiencing a rapid urbanization that is unprecedented in human history. This has significantly improved the well-being of residents, but has also caused serious environmental problems in the Beijing-Tianjin-Hebei urban agglomeration (BTHUA). Therefore, the study constructed the indexes of urbanization and environmental pollution based on the existing literature, used the analytic hierarchy process, entropy method and the principle of minimum information entropy to obtain the subjective, objective and comprehensive weights of the evaluation indexes respectively, and took BTHUA as an example to study the effects of urbanization elements and subsystems on environmental pollution from 2000 to 2015 by using geographically and temporally weighted regression model. This study reached the following conclusions. (1) The urbanization index increased rapidly from 0.157 in 2000 to 0.438 by 2015. National policies have significant impacts on environmental protection in urban agglomerations. (2) The service industry level, fiscal revenue, resident income, education level, Internet application were factors that reduced environmental pollution. The urbanization rate, population agglomeration, economic development, industrial development, urban construction, and transportation construction were factors that aggravated environmental pollution. (3) The impacts of urbanization on environmental pollution fluctuated periodically, with the period of fluctuation being consistent with China's five-year plan. National policy has significantly promoted the coordinated development of urbanization and environmental protection, although there was a lag effect. The effects of the trends in population, economic, social, spatial, and comprehensive urbanization factors on environmental pollution were basically the same, but the degree of each effect differed. (4) Urbanization improved the environmental quality in mountainous areas, but aggravated the degree of local environmental pollution in plains and coastal areas. The rate of urbanization of urban agglomerations differed, with the rate of urbanization lagging behind in mountainous areas, whereas it was excessive in plains and coastal areas.