Jiang Zhen, his wife Zhang Fang and their children Doudou (2nd R) and Dudu (2nd L) pose with a portable device that measures air quality and an air purifier in the children's room, on the second day after China's capital Beijing issued its second ever “red alert” for air pollution, in Beijing, China, December 20, 2015. (Photo by Kim Kyung-Hoon/Reuters)
