Coal fires used to beat the bitter cold of Mongolian winters blanket capital city Ulaanbaatar with smog in the winter, the BBC's Roger Hearing finds, when he meets residents from the Ger District.

Typical sanitation is makeshift and in the form of latrines, says Choikhand Janchivlamdan, a sanitation expert at the Green Initiative. This can lead to the spread of disease. Lost livestock due to harsh winters and a desire for better education is leading people to the city, she says. As people move to the city from the countryside, the problem gets worse as no new sewage systems are built.

Tserenbat Namsrai, Mongolia's environment minister, plans to introduce smokeless fuel in a bid to combat pollution and introducing more electric heating.

Robert Ritz, a US professor who lives in the city, says PM2.5 particulates - that's atmospheric particulate matter that have a diameter of less than 2.5 micrometres - kill thousands of people per year.