Dhaka's air quality remained in the "unhealthy" zone this morning.

With an air quality index (AQI) score of 196 at 9:15am, the capital ranked second in the list of world cities with the worst air quality.

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

India's Delhi, Chile's Santiago, Poland's Krakow occupied the first, third and fourth spots in the list, with AQI scores of 206, 178 and 175, 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 heart disease, chronic respiratory diseases, lung infections and cancer, according to several studies.