An estimated 7,000 people, many of them wearing air masks and gas masks underneath thick winter hats, braved temperatures that fell below minus 20 degrees Celsius (minus 4 Fahrenheit). Standing in the city's central Sukhbataar Square, they held black balloons and protest signs. One banner read: "Wake up and smell the smog."
Ulaanbaatar is one of the world's coldest capitals, and more than half of the city's 1.3 million residents rely on burning raw coal, plastic, rubber tires and other materials to stay warm and cook meals in their homes. In impoverished neighborhoods that ring the city, known as ger districts, many herders and others live in traditional round tents without heating, leaving them to burn polluting fuels.
Want to lift people out of dire poverty and lessen pollution? In some parts of the world, traditional fuels are the answer.