Four of them are in Iran

Atta Kenare / AFP / Getty Images Young Arab Iranians swim in the Karoon river in Ahwaz, Iran, July 21, 2003.

A day after the World Health Organization published a report linking air pollution to lung cancer, Quartz has put together a list of the most polluted cities in the world, based on data from the same organization. While the list originally came out this Spring, it’s an important reminder given the recent health news.

At the top? The city of Ahwaz, in Western Iran. With a population of more than three million, it is also the capital of the Khuzestan Province, which produces most of Iran’s oil. Like the other cities in the WHO’s top ten, it is a center of heavy industry.

Here are the ten most polluted cities, ranked by the amount of airborne particles less than 10 micrometers in diameter per cubic meter of outdoor air:

1. Ahwaz, Iran

2. Ulaanbaatar, Mongolia

3. Sanandaj, Iran

4. Ludhiana, India

5. Quetta, Pakistan

6. Kermanshah, Iran

7. Peshawar, Pakistan

8. Gaborone, Botswana

9. Yasouj, Iran

10. Kanpur, India

[Quartz]