June 20, 2013
From Singapore Haze, one of 18 photos. A woman wears a mask as the Singapore Central Business District is covered with haze Thursday evening, June 20, 2013. Singapore urged people to remain indoors amid unprecedented levels of air pollution Thursday as a smoky haze wrought by forest fires in neighboring Indonesia worsened dramatically. (AP Photo/Joseph Nair)

From Singapore Haze, one of 18 photos. A woman wears a mask as the Singapore Central Business District is covered with haze Thursday evening, June 20, 2013. Singapore urged people to remain indoors amid unprecedented levels of air pollution Thursday as a smoky haze wrought by forest fires in neighboring Indonesia worsened dramatically. (AP Photo/Joseph Nair)

January 30, 2013
From China’s Toxic Sky, one of 31 photos. The rooftops of Beijing’s Forbidden City, obscured by thick smog, in Beijing, China, on January 16, 2013. (Feng Li/Getty Images)

From China’s Toxic Sky, one of 31 photos. The rooftops of Beijing’s Forbidden City, obscured by thick smog, in Beijing, China, on January 16, 2013. (Feng Li/Getty Images)