Dhaka's air quality remained in the "hazardous" zone Friday morning, reports UNB.

With an air quality index (AQI) score of 335 at 9:10am, the capital ranked first in the list of world cities with the worst air quality.

An AQI between 151 and 200 is considered "unhealthy," 201 to 300 "very unhealthy” and 301 to 400 is considered "hazardous”, posing serious health risks to residents.

India’s Delhi, Pakistan’s Lahore and Afghanistan’s Kabul occupied the second, third and fourth spots in the list, with AQI scores of 302, 213 and 188, respectively.

In Bangladesh, the AQI is measured 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 a factor increasing a person's chances of developing heart disease, chronic respiratory diseases, lung infections and cancer in several studies.