Bangladesh’s capital Dhaka ranked worst in the Air Quality Index (AQI) on Monday morning.    The city had a score of 190 at 8am, indicating that the air quality was ‘unhealthy’.    When the AQI value is between 150 and 200, everyone may begin to experience health effects.   China’s Shenzhen and India’s Delhi occupied the second and third spots in the list of cities with the worst air quality with AQI scores of 189 and 183 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.   In Bangladesh, the AQI is based on five criteria pollutants – Particulate Matter (PM10 and PM2.5), NO2, CO, SO2 and Ozone (O3).   The Department of Environment has also set national ambient air quality standards for these pollutants. These standards aim to protect against adverse human health impacts.   Dhaka has long been grappling with air pollution. Its air quality usually improves during monsoon.