Bangladesh’s capital Dhaka ranked second worst in the Air Quality Index (AQI) on Monday morning.   Dhaka had an AQI score of 168 at 08:09am. The air was classified as ‘unhealthy’.   Thailand’s Chiang Mai and Mongolia’s Ulaanbaatar occupied the first and third spots in the list of cities with worst air quality with AQI scores of 198 and 165 respectively.   When the AQI value is between 151 and 200, every city dweller, particularly members of sensitive groups, may begin to experience adverse health effects.   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.   In Bangladesh, the AQI is based on five criteria pollutants – Particulate Matter (PM10 and PM2.5), NO2, CO, SO2 and Ozone (O3).   Dhaka has long been grappling with air pollution. Its air quality usually improves during monsoon.