Dhaka, March 31 -- Dhaka, the densely populated capital of Bangladesh, ranked 4th among the world's most polluted cities on Tuesday morning, recording an Air Quality Index (AQI) of 171 at 08:45 am.

Today's air was classified as 'unhealthy', referring to a serious health threat, according to the AQI index.

Delhi of India, Chiang Mai Thailand, and Kinshasa of Democratic Republic of the Congo occupied the first three spots on the list, with AQI scores of 228, 22o and 171, respectively.

AQI levels of 101-150 are 'unhealthy for sensitive groups', 151-200 is 'unhealthy', 201-300 is 'very unhealthy', and readings above 301 are considered 'hazardous', posing severe health risks.

The AQI, which reports daily air quality, informs residents how ...