Northern China is choking under the worst air pollution episode of this year. A total of 23 cities have been under air pollution "red alert," including Beijing which launched a smog red alert for the first time this winter. The air pollution red alert measures cause significant disruption to life in Beijing and surrounding areas, with a strict limitation on numbers of cars on the road and school and business closures.

From 4pm on Dec 21 to 10:30am on Dec 22, the smoggy skies were completely transformed in less than 24 hours as 'airpocalypse' ends. This timelapse video, filmed from the top of one of Beijing's tallest building, shows the smog leaving Beijing.