Dhaka's air worst polluted in the world Wednesday morning

World cities with most air pollution on Wednesday morning.

Dhaka, Jan 11 -- The densely populated capital of Bangladesh has once again topped the list of world cities with the worst air quality.

The capital's air quality index (AQI) was recorded at 259 at 9.55am on Wednesday.

China's Chengdu and Chongqing occupied the next two spots, with AQI scores of 212, and 206, respectively.

An AQI between 151 and 200 is said to be ‘unhealthy’ while 201 and 300 is considered ‘very unhealthy’, and 301 to 400 is ranked 'hazardous', posing serious health risks to residents.

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.

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. - UNB