Top 3 most polluted countries in the world

Emerging nations around the world are often heralded for their fast growth but we don't often hear about the downsides of that rapid development.

The World Health Organization (WHO) recently released a report on air quality in countries around the globe, on which we based a list of the ten most polluted countries. Almost all the worst offenders are either major oil and gas producers, or emerging economies that are growing rapidly.

The WHO study looked at air quality in 91 countries, measured by the amount of PM10 particles per cubic meter. PM10 particles are particles of 10 micrometers or less that can cause diseases and infections. According to the WHO, PM10 levels above 20 micrograms per cubic meter can cause health risks. The top ten most polluted countries have PM10 levels from six times to14 times that level.

So, which countries have the world's worst air quality?

3. Pakistan = Pollution level: 198 ug/m3

Pakistan's air pollution is nearly ten times higher than levels considered dangerous by the WHO.

Political instability, corruption and a lack of government measures to curb carbon emissions have led to a cloak of thick smoke over major cities like Karachi, Lahore and Islamabad. In 2008, a government study revealed that every car in Pakistan, regardless of its age, generates 25 percent more carbon than one in the U.S.

Karachi, Pakistan's biggest city has a capacity for only 700 vehicles per hour, but according to the study, there are more than 11,000 vehicles per hour on the roads. The city, which already has more than half the country's 3.5 million vehicles, adds up to 400 new cars a day.

Water pollution from raw sewage and industrial waste has also become a major problem in the country. In addition, Pakistan's water supply is evaporating so quickly that it will become a "water-famine" country by the end of this decade, according to the country's Centre for Research and Security Studies.

2. Botswana = Pollution level: 216 ug/m3

It might seem strange that a country with a population of only 2 million people, and the largest proportion of land under conservation in the world, is the second most polluted nation in the world. But, that is the case of Botswana, 80 percent of which is covered by the Kalahari Desert.

The country was one of the poorest nations in Africa at the time of its independence from Britain in 1966. Today, Botswana is one of the world's fastest growing economies, and the largest producer of diamonds. The country has transformed itself into a middle-income economy with an annual average growth rate of about 9 percent, according to The World Bank. Mineral revenues account for about 40 percent of government revenues.

With growing wealth, the southern African nation has experienced widespread environmental damage. Wild fires and pollution from the mineral industry are the main sources of the country's poor air quality. Copper smelting for example has been blamed for sulfur dioxide and nickel emissions.

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.