A day after the World Health Organization published a report linking air pollution to lung cancer, the business news website Quartz has put together a list of the most polluted cities in the world, of which four are in Iran. Dust, mostly originating from Iraq, is one of the prime factors behind the pollution in these Iranian cities.

Based on data compiled by the WHO, Quartz republished a list, which originally came out this spring, which should be regarded as an important warning, given the reports on the link between air pollution and lung cancer.

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

The Iranian cities of Sanandaj, Kermanshah and Yasouj are also included in the list, and like Ahwaz, all continue to suffer heavy dust storms, mostly coming from neighboring Iraq.

The ten most polluted cities in the world, ranked by the amount of airborne particles less than 10 micrometers in diameter per cubic meter of outdoor air, are: Ahwaz of Iran, Ulaanbaatar of Mongolia, Sanandaj of Iran, Ludhiana of India, Quetta of Pakistan, Kermanshah of Iran, Peshawar of Pakistan, Gaborone of Botswana, Yasouj of Iran, and Kanpur of India.