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Environmental degradation caused by rapid urbanization is a pressing global issue. However, little is known about how urban changes operate and affect environments across multiple scales. Focusing on China, we found urbanization was indeed massive from 2000 to 2015, but it was also very uneven, exhibiting high internal city dynamics. Urban areas in China as a whole became less green, warmer, and had exacerbated PM2.5 pollution. However, environmental impacts differed in newly developed versus older areas of cities. Adverse impacts were prominent in newly urbanized areas, while old urban areas generally showed improved environmental quality. In addition, regional environmental issues are emerging as cities expand, connect and interact to form urban megaregions. To turn urbanization into an opportunity for, rather than an obstacle to, sustainable development, we must move beyond documenting urban expansion to understand the environmental consequences of both internal city dynamics and the formation of urban megaregions. [ABSTRACT FROM AUTHOR]

China's policy on atmospheric pollution is changeable in recent years. The single‐year estimated population exposure to air pollution is widely used in China where has the largest population and the heaviest fine particulate (PM2.5) pollution worldwide. However, the single‐year estimate introduces considerable uncertainty and loses consideration on multiyear cumulative exposure, thus may underestimate the burden of disease and mislead decisions regarding environmental conservation. We thus estimate the cumulative population exposure to PM2.5 pollution from 2000 to 2015. Areas with PM2.5 > 35 μg/m3 within China's territory increased from an average of 39% (2000–2005) to 42% (2006–2015), causing 471.6 million population at 58.8 × 104 km2 were exposed to 16 years' cumulative exposure to PM2.5 > 35 μg/m3. The migrant population contributed a major proportion of the increased population exposure, especially in East China's rapidly urbanizing areas. Cumulative population exposure to air pollution would provide a better understanding on the long‐term health risk and may suggest to a long, stable, and effective environmental protection regulation and policy should be carried out in China. Key Points: A multiyear frequency‐based cumulative PM2.5 risk was estimated in ChinaThe 471.6 million population on 1,588,000 km2 were exposed to 16 year's cumulative PM2.5 pollutionThe migrant population contributed a major proportion of the increased population exposure, especially large in East China's urban area [ABSTRACT FROM AUTHOR]

Objective To investigate multicontaminant air pollution in Chinese cities, to quantify the urban population affected and to explore the relationship between air pollution and urban population size. Methods We obtained data for 155 cities with 276 million inhabitants for 2014 from China's air quality monitoring network on concentrations of fine particulate matter measuring under 2.5 μm (PM2.5), coarse particulate matter measuring 2.5 to 10 μm (PM10), nitrogen dioxide (NO2), sulfur dioxide (SO2) and ozone (O3). Concentrations were considered as high, if they exceeded World Health Organization (WHO) guideline limits. Findings Overall, 51% (142 million) of the study population was exposed to mean annual multicontaminant concentrations above WHO limits -- east China and the megacities were worst affected. High daily levels of four-contaminant mixtures of PM2.5, PM10, SO2 and O3 and PM2.5, PM10, SO2 and NO2 occurred on up to 110 days in 2014 in many cities, mainly in Shandong and Hebei Provinces. High daily levels of PM2.5, PM10 and SO2 occurred on over 146 days in 110 cities, mainly in east and central China. High daily levels of mixtures of PM2.5 and PM10, PM2.5 and SO2, and PM10 and SO2 occurred on over 146 days in 145 cities, mainly in east China. Surprisingly, multicontaminant air pollution was less frequent in cities with populations over 10 million than in smaller cities. Conclusion Multicontaminant air pollution was common in Chinese cities. A shift from single-contaminant to multicontaminant evaluations of the health effects of air pollution is needed. China should implement protective measures during future urbanization. [ABSTRACT FROM AUTHOR]