Lingering heavy smog in Beijing has kept many people indoors and shun outdoor activities, and an orange alert - the second highest – was issued by the National Meteorological Center, but some have no choice but to stay outside because of their jobs. Traffic policeman Ren Yongjie wears a mask while guiding traffic on a smoggy day in Beijing, Feb 24, 2014. To ensure traffic safety amid the haze, the city has assigned more officers on its roads. [Photo/Xinhua]