Dhaka, Bangladesh’s densely populated capital, ranked second among the world’s most polluted cities on Thursday morning, recording an Air Quality Index (AQI) of 253 at 10:30 am.

The air was classified as ‘very unhealthy’, posing serious health risks, according to the AQI report of IQAir, a Swiss free real-time air quality monitoring platform.

Pakistan’s Lahore topped the list, while Kolkata, India, and Kathmandu, Nepal, ranked third and fourth with AQIs of 197 and 185, respectively.

By contrast, Batam and Medan in Indonesia recorded the world’s cleanest air with an AQI of 0.

According to the AQI scale, a reading between 50 and 100 is considered ‘moderate’, with generally acceptable air quality, though sensitive individuals should limit prolonged outdoor exertion.

AQI levels of 101–150 are ‘unhealthy for sensitive groups’, 151–200 is ‘unhealthy’, 201–300 is ‘very unhealthy’, and readings above 301 are considered ‘hazardous’, posing severe health risks.

The AQI, which reports daily air quality, informs residents how clean or polluted the air is and highlights potential health effects.

In Bangladesh, the AQI is calculated based on five key pollutants: particulate matter (PM10 and PM2.5), nitrogen dioxide (NO2), carbon monoxide (CO), sulfur dioxide (SO2), and ozone.

Dhaka has long struggled with air pollution. Air quality usually deteriorates in winter and improves during the monsoon season.

The World Health Organization (WHO) estimates that air pollution causes about seven million deaths worldwide each year, primarily from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer, and acute respiratory infections.