According to a World Health Organisation report, Delhi is no longer the world's most polluted city and is ranked 11th in the most polluted cities list. However, four Indian cities – Gwalior, Allahabad, Patna, and Raipur are among the top 10 most polluted cities. The highest PM2.5 levels were recorded in Iran's Zabol (217), followed by India's Gwalior (176).