Dhaka has topped the list of cities worldwide with the worst air quality for the second consecutive day.

With an air quality index (AQI) score of 182 at 8:55am today, the air was classified as 'unhealthy'.

An AQI between 151 and 200 is considered 'unhealthy' while 201-300 is 'very unhealthy', and 301+ is considered 'hazardous', posing severe health risks to residents.

Qatar's Doha, Vietnam's Hanoi and India's Mumbai occupied the second, third and fourth spots on the list, with AQI scores of 174, 173 and 170, respectively.

The AQI, an index for reporting daily air quality, informs people how clean or polluted the air of a certain city is and what associated health effects might be a concern for them.

The AQI in Bangladesh is based on five 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.

As per World Health Organization (WHO), air pollution kills an estimated seven million people worldwide every year, mainly due to increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer, and acute respiratory infections.