Dhaka's air quality is in the “unhealthy” zone Saturday morning.

With an air quality index (AQI) score of 155 at 8:53am Saturday, Dhaka ranked 6th in the list of cities worldwide with the worst air quality.

India's Delhi, Pakistan's Lahore and China's Beijing occupied the first three spots in the list, with AQI scores of 203, 168 and 163, respectively.

An AQI between 101 and 150 is considered “unhealthy”, AQI between 201 and 300 is said to be “very unhealthy”, while a reading of over 301 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.

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.