Dhaka's air quality turned ‘very unhealthy’ on Friday morning, with an Air Quality Index (AQI) score of 203 at 8:40am.
With this score, the capital ranked fourth among the world's most polluted cities, according to the AQI scale.
A ‘very unhealthy’ air quality level means everyone, regardless of their health condition, may experience more serious health effects or discomfort from air pollution. Even short-term exposure can affect anyone.
Pakistan's Lahore topped the list with an AQI score of 456, followed by India's Delhi with 251 and Kolkata with 221.
On Thursday, Dhaka ranked fifth among the world's most polluted cities, recording an AQI score of 174 at 10:25am.
According to the AQI scale, readings of 101-150 are considered unhealthy for sensitive groups, while scores of 151-200 indicate unhealthy air quality. Readings of 201-300 are classified as very unhealthy, while scores above 301 are considered hazardous and pose serious health risks.
The AQI measures daily air quality and indicates pollution levels and their potential effects on public health.
In Bangladesh, air quality is assessed based on five major pollutants: particulate matter (PM10 and PM2.5), nitrogen dioxide (NO2), carbon monoxide (CO), sulphur dioxide (SO2) and ozone.
The World Health Organization estimates that air pollution causes around seven million deaths worldwide each year, mainly from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer and acute respiratory infections.