India’s Delhi and Nepal's Kathmandu occupied the first and third spots in the list, with AQI scores of 282 and 179, respectively.

An AQI score between 151 and 200 is considered ‘unhealthy'. AQI between 201 and 300 is said to be 'very unhealthy' while a reading of 301 to 400 is considered 'hazardous' and can pose serious health risks to residents.

In Bangladesh, the AQI is measured 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.

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.