Changes refer to updates made to the 2018 World Air Quality Report PDF and complete ranking. Changes include recategorization of selected locations within Europe under different city groupings.
To see more historical rankings, see the link below:
https://www.iqair.com/us/us/world-most-polluted-cities
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Keywords: AirVisual, World air quality (AQI) ranking, changelog, 2018, world air report, world air