According to the WHO (World Health Organization), the captial of Iran - Ahvaz is the most polluted city in the world in 2011 with 372 micrograms air pollutants per cubic meter. It is followed by Ulaan Baatar in Mongolia with 279 micrograms per cubic meter. The third most polluted city is another Iranian city - Sanandaj with 254 micrograms per cubic meter.

Two Chinese cities Linfen and Tianying were mentioned by Times in 2007 as the most polluted cities in the world. The type of pollutants are coal and particulars caused by industrial emissions and automobile. Four years later, none of the Chinese cities were listed in the top 10 polluted cities in 2011.