Bangladesh, June 29 -- After being in the 'good' category for some days, Dhaka's air quality slipped to the 'moderate' zone on Wednesday.

With an air quality index (AQI) score of 84 at 9.30am, the densely populated metropolis ranked 12th in the list of world cities with the worst air quality.

Pakistan's Lahore, Saudi Arabia's Riyadh and the UAE's Dubai occupied the first three spots in the list, with AQI scores of 177, 157 and 154, 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.

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