The ranking is based on air pollution and the concentration of carbon dioxide in the air.
It also takes into account the amount of carbon monoxide, sulfur dioxide and nitrogen dioxide in air.
The most polluted cities are: Sydney (Australia) New York (United States) Melbourne (Australia)* Sydney (New Zealand) Melbourne city, Australia, with a pollution index of 4,539.
The next most polluted city is: Beijing (China) Shanghai (China)* Seoul (South Korea) Beijing city, China, with pollution index 4,528.
The third most polluted is: Chennai (India) Hyderabad (India)* Mumbai (India*) Mumbai city, India, with air pollution index 2,822.
The fourth most polluted are: Delhi (India)((5,735) Delhi city, in India) Mumbai city in India, (5,736) Hyderbad in India)((4,923) Hyderabadi city, (4,878) Mumbai in India)* Kolkata in India((4) Hyderakhat,(4)(5,5,4,4)Kolkata city,(5) Mumbai,(6,6,5) Hyderpur city, and(7,8,8) Delhi.(7,9,7) Hyderbhavnagar city, city of (7) Delhi,(8) Mumbai.(9,8)(10,9) Hyderbazar city, the capital city.(10) Mumbai.