Dhaka's air quality was ranked second worst in the world this morning.

With an air quality index (AQI) score of 251 at 9:03am, Dhaka's air was categorised as 'very unhealthy'.

An AQI between 101 and 200 is considered 'unhealthy', particularly for sensitive groups while an AQI between 201 and 300 is said to be 'very unhealthy'.

India's Delhi and Kolkata and Pakistan's Lahore occupied the first, third and fourth spots on the list, with AQI scores of 303, 238 and 230, respectively.

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.