Dhaka's air quality was marked "unhealthy" this morning.

With an air quality index (AQI) score of 159 at 9:05am, Dhaka ranked 5th on the list of cities worldwide with the worst air quality.

India's Delhi, Nepal's Kathmandu and Indonesia's Medan occupied the first three spots in the list, with AQI scores of 177, 172 and 168, 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.

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.