Zabol in Iran is the most polluted city in the world according to the World Health Organization database. Gwalior and Allahabad are a close second and third. Patna and Raipur rank 6th and 7th. Totally, four Indian cities are among the world’s ten most polluted cities, 10 out top 20 are also in India.
Delhi has improved. Ahmedabad has stabilized and Patna has worsened. We have seen that Delhi has managed to arrest the declining air quality trend in 2015.