The densely populated capital of Bangladesh continues to dominate the list of cities with the worst air quality in the world. On Wednesday, Dhaka was ranked the world's second-most polluted city, as its air quality index (AQI) was recorded at 194 at 9.54am. Russia’s Krasnoyarsk and Pakistan’s Lahore occupied the first and third spots, with AQI scores of 290 and 182, respectively. An AQI between 101 and 200 is considered 'unhealthy', particularly for sensitive groups. Similarly, an AQI between 201 and 300 is said to be 'poor', while a reading of 301 to 400 is considered 'hazardous', posing serious health risks to residents. Read: Unauthorized production of lead acid batteries endanger environment, say experts 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.