Bangladesh's capital Dhaka ranked third worst in Air Quality Index (AQI) on Monday morning.

The air quality of Dhaka was classified as very unhealthy as it had an AQI score of 279 at 8:34am.

Afghanistan's Kabul and India's Delhi were the worst and second worst cities on the list with scores of 353 and 295 respectively.

When the AQI value is between 201 and 300, the entire population is likely to be affected. Active children and adults, and people with respiratory diseases are advised to avoid all outdoor exertion in this situation.

The AQI is a tool for reporting daily air quality of any city or country. It tells how clean or polluted the air is, and what associated health effects might be a concern for public. The AQI focuses on health effects that one might experience within a few hours or days after breathing polluted air.

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.

Bangladesh's overcrowded capital has been grappling with air pollution for a long time. The quality usually improves during monsoon.