1. Mongolia
Pollution level: 279 ug/m3

Mongolia is the world’s most polluted country and also home to one of the world’s most polluted cities — Ulaanbaatar.

The city of 1.2 million accounts for about 45 percent of Mongolia’s population. During the coldest months of the year — December to February — Ulaanbaatar’s horizon is completely hidden behind a thick grey-brown smoky haze.

The country’s main sources of pollution are its traditional coal-fuelled stoves and boilers used for heating and cooking, as well as congested traffic and old cars. Heating is essential for the survival of its people for about eight months of year. The country uses everything from coal, wood to refuse, such as black tar-dipped bricks and old car tires to fuel stoves and boilers. Ulaanbaatar’s dry climate and severe windstorms further worsen its dangerous levels of airborne dust.

Rapid urbanization has also been a major factor behind the country’s pollution problem. Ulaanbaatar’s population has expanded by 70 percent over the last 20 years with the city’s infrastructure unable to keep up with growth. With an air pollution level 14-times higher than the WHO’s standard threat level, the number of premature deaths, chronic bronchitis and respiratory related hospital admissions are on a rapid rise. The government has been trying to mitigate the problems by introducing measures such as cleaner coal-based fuel and modern stoves to address its pollution crisis.