Commuters take a public bus in Beijing, Oct 18, 2016. The worst air pollution so far this winter began moving into Beijing on Dec 16 and is expected to last for over five days. The city issued its first red alert for air pollution on Dec 15 and emergency measures have been taken to tackle the smog. The severe smog blanketing northern regions covered more than 750,000 square kilometers by Saturday. [Photo/VCG]