Dhaka has ranked the second on the list of cities with the worst air quality today with an AQI score of 258 at 10:58am.

The air was classified as "very unhealthy", with such air quality persisting for the past few days, according to the Air Quality Index.

Pakistan's Lahore, India's Delhi and Nepal's Kathmandu occupied the first, second and fourth spots in the list, with AQI scores of 271, 219 and 188 respectively.

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.