Dhaka, the overcrowded capital city of Bangladesh, topped the list of cities with the worst air quality with an Air Quality Index score of 179 on Sunday morning.
The air was classified as unhealthy, according to the air quality and pollution city ranking.
An AQI between 151 and 200 is considered unhealthy, 201-300 is very unhealthy and 301-400 is considered hazardous, posing severe health risks to residents.
India's Delhi, Indonesia's Jakarta and Kuwait's Kuwait City occupied the second, third and fourth spots on the list, with AQI scores of 159, 159 and 154, 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.
According to the 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.
