Dhaka's air quality continued to be in the 'very unhealthy' zone this morning.

With an air quality index (AQI) score of 252 at 9:54am, Dhaka ranked 3rd on the list of cities worldwide with the worst air quality.

India's Kolkata and Delhi and Pakistan's Karachi occupied the first, second and fourth spots with AQI of 302, 255 and 195, respectively.

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.

Meanwhile, an AQI between 101 and 200 is considered 'unhealthy', particularly for sensitive groups.

In Bangladesh, the AQI is based on five criteria pollutants -- Particulate Matter (PM10 and PM2.5), NO2, CO, SO2 and Ozone.

Dhaka has long been grappling with air pollution issues. Its air quality usually turns unhealthy in winter and improves during the monsoon.

As per the World Health Organization (WHO), air pollution kills an estimated seven million people worldwide every year, largely as a result of increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer and acute respiratory infections.