With an air quality index (AQI) score of 186 at 9:03 am on Saturday, Dhaka’s air ranked as worst among cities around the world.

India’s Delhi and Nepal’s Kathmandu occupied the next two spots, with AQI scores of 176 and 172, 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.

AQI, an index for reporting daily air quality, is used by government agencies to inform people how clean or polluted the air of a certain city is, and what associated health effects might be a concern for them.

In Bangladesh, the AQI is based on five criteria pollutants -- Particulate Matter (PM10 and PM2.5), NO2, CO, SO2 and Ozone.

Also read: Dhaka’s air quality ‘unhealthy’ this morning

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

Air pollution consistently ranks among the top risk factors for death and disability worldwide.

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