Dhaka ranked third on the list of cities worldwide with the worst air quality this morning.

Its air quality continued to be in the "unhealthy" zone with an air quality index (AQI) score of 173 at 9:09 am, according to the air quality index.

India's Delhi, Thailand's Chiang Mai occupied the first two spots on the list, with AQI scores of 197 and 182, respectively.

An AQI between 101 and 200 is considered "unhealthy", particularly for sensitive groups while an AQI between 201 and 300 is said to be "poor", while a reading of 301 to 400 is considered "hazardous", posing serious health risks to residents.

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.

Air pollution consistently ranks among the top risk factors for death and disability worldwide. Breathing polluted air has long been recognised as increasing a person's chances of developing a heart disease, chronic respiratory diseases, lung infections and cancer, according to several studies.

As per the World Health Organization (WHO), air pollution kills an estimated seven million people worldwide every year.