BEIJING, CHINA - JANUARY 31:  A little tourist wearing the PM2.5 mask walk on the Tiananmen Square during severe pollution on January 31, 2013 in Beijing, China. Heavy smog that has choked Beijing for the last five days weakened slightly on Thursday due to a light rainfall, although the capital's air remains heavily polluted. The haze choking many Chinese cities covers a total area of 1.43 million square kilometers, the China's Ministry of Environmental Protection said Wednesday.  (Photo by Feng Li/Getty Images)