World's Most Polluted Countries

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 to 14 times that level.

So, which countries have the world's worst air quality? Click ahead to find out.