Severe smog shrouds Hohhot, capital of North China's Inner Mongolia autonomous region on November 29, 2015. The city’s air quality index (AQI) hit 500 on Sunday. An AQI of over 300 is defined as "serious pollution" and an AQI between 201 and 300 is considered "heavy", according to China's standards. (Photo: China News Service/ Liu Wenhua)
