Dhaka, the densely populated capital of Bangladesh, ranked first among the world’s most polluted cities on Thursday morning.

At 9:20 am, Dhaka recorded an air quality index (AQI) score of 257 and classified it as ‘very unhealthy’ as reported by IQAir.

Cairo in Egypt, Kolkata in India, Ulaanbaatar in Mongolia, and Hanoi in Vietnam occupied the second, third, and fourth spots on the list, with AQI scores of 223, 222, and 199 respectively.

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.

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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.