As a mild cold wave is sweeping across the country, Dhaka's air quality has been marked "unhealthy".

With an air quality index (AQI) score of 175 at 9:29am today, Dhaka ranked 5th on the list of cities worldwide with the worst air quality.

India's Delhi and Kolkata and Pakistan's Karachi and Lahore occupied the first four spots, with AQI scores of 243, 212, 212, and 195 respectively.

An AQI between 151 and 200 is considered "unhealthy" while 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 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.