Buildings are blanketed by sand and dust in Lanzhou, capital of northwest China's Gansu Province on March 9, 2013.
Pollution is such a menace in Lanzhou that the government even considered bulldozing an adjacent mountain to allow fresh air into its toxic bowl. The city in northwestern China is situated in a narrow curved valley, a landscape that prevents air from flowing freely. Pollution is also exacerbated by huge dust storms kicked up by the Gobi Desert. In 2011, the World Health Organization reported that Lanzhou had the worst air quality in China.