India’s Delhi, Kazakhstan’s Astana and Pakistan’s Lahore occupied the first three spots on the list

FILE PHOTO: Dhaka city air pollution Mehedi Hasan/Dhaka Tribune

With an air quality index (AQI) score of 158 on Wednesday morning, Dhaka ranked fourth on the list of cities worldwide with the worst air quality for the second consecutive day.

India's Delhi, Kazakhstan's Astana and Pakistan's Lahore occupied the first, second and third spots, with AQI scores of 204, 173 and 160, respectively.

An AQI between 151 and 200 is considered unhealthy, between 201–300 is very unhealthy and 301–400 is hazardous, posing severe health risks to residents.

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.

The AQI in Bangladesh is based on five pollutants: particulate matter (PM10 and PM2.5), NO2, CO, SO2 and ozone.

Dhaka has long been grappling with air pollution issues. Its air quality usually turns unhealthy in winter and improves during the monsoon.

As per the World Health Organization (WHO), air pollution kills an estimated seven million people worldwide every year, mainly due to increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer and acute respiratory infections.