Dhaka, the densely populated capital of Bangladesh topped the list of cities around the world with the worst air quality for the third consecutive day.

With an air quality index (AQI) score of 166 at 9:50am today, Dhaka ranked first among cities with the most polluted air. The air was classified as "unhealthy", according to the air quality and pollution city ranking.

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.

United Arab Emirates Dubai, South Korea's Incheon and India's Delhi occupied the second, third and fourth spots in the list, with AQI scores of 161, 159 and 158, 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.