Dhaka's air was very unhealthy on Friday morning.

With an Air Quality Index (AQI) score of 166 at 9:37am, Dhaka ranked fifth on the list of cities worldwide with the worst air quality.

Thailand’s Chiang Mai, Nepal’s Kathmandu, China’s Beijing and Myanmar’s Yangon occupied the first four spots on the list, with AQI scores of 210, 183, 171 and 166, respectively.

An AQI score between 150 and 200 is unhealthy, between 201 and 300 is very unhealthy, while a reading of 301+ is hazardous, posing serious health risks to residents.

In Bangladesh, AQI scores are based on five criteria 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.

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

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.