Onitsha tops the list of World's most polluted cities

You will be surprise to know that the world's most polluted city isn't Beijing or Delhi.

According to a new report from the World Health Organization, the pollution in megacities like Beijing China, Delhi India and a host of others are actually only a tip of the iceberg and the cities with the worse case of pollution in the world is probably in Iran and Nigeria.

The World's Health Organization studied air qualities of the cities and the size of particles found in the air. Generally, a lot of attention is placed upon particles of a PM2.5 size, which is around one-30th the size of a human hair. These particles are particularly worrying because they have the ability to enter lungs and blood tissue and cause serious health problems.

However, you can also measure larger particles in the air. At PM10, the particles are coarser, though they can still be inhaled and cause health problems.

Based on PM2.5 Zabol in Iran comes out on top and based on PM10 Nigeria's Onitsha, a city of half-a-million people on the Niger River, is atop this list. The city has been known for its rapid growth and gridlock, though some locals were apparently still surprised that it appeared so high on the list. See more data below: