Headlamps make cold nights cozier, but leave the fuel-burning lanterns and stoves outside. Gopal Vijayaraghavan/Flickr hide caption

itoggle caption Gopal Vijayaraghavan/Flickr

Skyscrapers are obscured by heavy haze in Beijing on Jan. 13. Air pollution remains a serious — sometimes overwhelming — problem, but researchers say environmental technology is available to solve it. Ng Han Guan/AP hide caption

itoggle caption Ng Han Guan/AP

Men walk along a railway line in Beijing on Jan. 12, as air pollution reached hazardous levels. Wang Zhao/AFP/Getty Images hide caption

itoggle caption Wang Zhao/AFP/Getty Images