When winter descends on Ulaanbaatar, Mongolia, the air turns foul. Here in the world’s coldest capital city, residents light open fires of coal or wood to heat their uninsulated houses. Soot fills the skies, and people don face masks to ward off smog so thick it can hide buildings a few hundred metres away. “White clothing becomes grey after a few hours,” says Munkhmandakh Myagmar, executive director of the Press Institute of Mongolia.
The city is one of the most polluted in the world, according to the World Health Organization (WHO) — and estimates suggest that particulate air pollution causes one-tenth of the city’s deaths. But information about the extent of that pollution is limited and hard to find.