With an air quality index (AQI) score of 171 at 8:50 am on Thursday, Dhaka ranked 4th in the list of cities worldwide with the worst air quality, reports UNB.

Thailand’s Chiang Mai, India’s Delhi and Pakistan’s Lahore occupied the first three spots, with AQI scores of 245, 197, and 173 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.