Dhaka's air quality continued to be in the 'unhealthy' zone on Monday morning.

With an air quality index (AQI) score of 159 at 9 am, Dhaka ranked 13th in the list of cities around the world with the worst air quality.

An AQI between 101 and 200 is considered 'unhealthy', particularly for sensitive groups.

Read more: Dhaka ranks 5th worst in Air Quality Index

Pakistan’s Lahore, India’s Delhi and Kolkata occupied the first three spots in the list, with AQI scores of 454, 226 and 187, respectively.

An AQI between 201 and 300 is said to be 'poor', while a reading of 301 to 400 is considered 'hazardous', posing serious health risks to residents. In Bangladesh, the AQI score is based on five kinds of 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.

Read more: Dhaka's air quality continues to be 'unhealthy'

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.