Dhaka has once again topped the list of world cities with the worst air quality.

With an air quality index (AQI) score of 251 at 8:53am yesterday, Dhaka ranked first in the list of cities with the worst air.

An AQI between 201 and 300 is said to be "very unhealthy", while a reading of 301 to 400 is considered "hazardous", posing serious health risks to residents.

India's Kolkata and Vietnam's Hanoi occupied the second and third spots in the list, with an AQI score of 201 and 192, respectively.

Dhaka air quality usually turns unhealthy in winter and improves during the monsoon.