The densely populated capital of Bangladesh continues to dominate the list of world cities with the worst air quality. 

On Wednesday, Dhaka occupied the second position in the list. The city's air quality index (AQI) was recorded at 213 at 10.48am, which is considered 'poor' or  'very unhealthy'.

India’s Delhi and Kolkata occupied the first and third spots, with AQI scores of 478 and 191, respectively, in the latest list of world cities with the worst air quality.

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.

AQI, an index for reporting daily air quality, is used by government agencies to inform people how clean or polluted the air of a certain city is, and what associated health effects might be a concern for them.

Also read: Bangladeshis lose over 1.8 years of lifespan to air pollution: Scientists

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 during winter and improves during monsoon.

A report by the Department of Environment (DoE) and the World Bank in March 2019 pointed out that the three main sources of air pollution in Dhaka "are brick kilns, fumes from vehicles and dust from construction sites".

With the advent of winter, the city’s air quality starts deteriorating sharply due to the massive discharge of pollutant particles from construction works, rundown roads, brick kilns and other sources.

Also read: Dhaka’s air quality still ‘unhealthy’ despite rain

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.

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.