Bangladesh's capital Dhaka topped the list of cities with the worst air in the Air Quality Index (AQI) on Friday morning.
It had an AQI score of 412 at 08:46 am. The air was classified as 'hazardous'.
Mongolia's Ulaanbaatar and Nepal's Kathmandu occupied the second and third spots in the list of cities with the worst air quality with AQI scores of 247 and 187 respectively.
An AQI score is between 301 and 500 implies health warnings of emergency conditions and the entire population is more likely to be affected.
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.