Muguntuul Oyutan, 11, walks to school with her sister and friends in Ulaanbaatar, the capital of Mongolia. Mongolia is the world's most sparsely populated nation, and an increasing proportion of its citizens reside in the capital. Claire Harbage/NPR hide caption
Trucks churn up coal dust at the Tavan Tolgoi coal mine in the South Gobi desert. The Tavan Tolgoi deposit is estimated to possess 6.5 billion tons of coal, including high-grade coking coal — a product vital to the steel-making process. Claire Harbage/NPR hide caption
Rapid population growth in Ulaanbaatar, Mongolia, coupled with a household dependence on coal for heating and cooking has created perfect conditions for one of the most extreme cases of air pollution in the world. Claire Harbage/NPR hide caption
Herders bury animal carcasses in 2010 in Mongolia's Dundgovi province. A decade ago, an extreme winter — known in Mongolia as a dzud — claimed the lives of 22% of the nation's livestock and sped up migration from rural areas to urban centers. Jargal Byambasuren/Reuters hide caption