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Ranking of the most polluted big cities in the world in April 2021

We have prepared our own ranking of cities with the highest levels of air pollution in April 2021. What regions of the world turned out to be the “worst” when it comes to the quality of air?

To prepare the ranking, we used data developed by a team of scientists from the European Commission, who distinguished, using satellite and demographic data, areas of uniform, dense development for cities. The summary of the administrative border and the area of ​​compact development is presented below using Krakow as an example.

The application of the above-mentioned areas avoids the problems caused by the course of administrative borders.

From the dataset, we chose cities larger than 500,000 inhabitants (which is approximately 1,000 areas). Out of these 1,000 urban areas, we chose those with at least 4 measurement points (including Airly, PurpleAir sensors and state stations). The use of at least 4 sensors allowed for better sampling and the possibility to reject outliers (erroneous).

In order to eliminate outliers (erroneous) data from outside our network, the observations were rejected based on the interquartile range.

The ranking of the most polluted large cities in the world for April 2021 is below:

20. Kraków, Poland  – 27,2 (mean CAQI for April 2021)

19. Katowice, Poland – 27,2

18. Yogyakarta, Indonesia – 28,4

17. Bangkok, Thailand – 28,9

16. Łódź, Poland – 29,1

15. Nur-Sultan, Kazakhstan – 29,3

14. Bishkek, Kirgistan – 29,9

13. Accra, Ghana – 30,4

12. Beirut, Lebanon – 30,5

11. Monterrey, Mexico– 30,6

10. Hong Kong, China – 31,6

9. Kuwait City, Kuwait – 33,9

8. Guadalajara, Mexico – 38,9

7. Milan, Italy – 42,8

6. Jakarta, Indonesia – 47,2

5. Mexico City, Mexico – 48,9

4. Yangon, Myanmar – 50,3

3. Bengaluru, India – 56,6

2. Ho Chi Minh City, Vietnam – 60,8

1. Delhi, India – 61,7

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