Bangladesh's capital Dhaka ranked the third worst in the Air Quality Index (AQI) on Monday.
It had an AQI score of 175 at 09:10 am. The air was classified as 'unhealthy'.
Mongolia's Ulan Bator and South Thailand's Chiang Mai occupied the first and second spots in the list of cities with the worst air quality with AQI scores of 226 and 177 respectively.
A numerical value between 151 and 200 indicates that everyone may begin to experience health effects. Members of sensitive groups may experience more serious health effects.
Air quality between 201 and 300 is classified as 'very unhealthy'. If the score is between 301 and 500, then it is classified as 'hazardous'.
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.
In Bangladesh, the AQI is based on five criteria pollutants – Particulate Matter (PM10 and PM2.5), NO2, CO, SO2 and Ozone (O3).
The Department of Environment has also set national ambient air quality standards for these pollutants. These standards aim to protect against adverse human health impacts.
Dhaka has long been grappling with air pollution. Its air quality usually improves during monsoon.