Air pollution is one of the leading causes of death around the world. Therefore you may be curious: “What are the least polluted cities in the world?” Smart Air analyzed 2020 air pollution data from 540 major cities in the world to create the 2020 ranking of the “25 Least Polluted Cities in the World”. So, which cities had the cleanest air?
Rankings: 25 Most Polluted Cities in the World
1. Zurich, Switzerland
2. Hobart, Australia
3. Reykjavik, Iceland
4. Turku, Finland
5. Tallinn, Estonia
6. Trondheim, Norway
7. Tampere, Finland
8. Uppsala, Sweden
9. Launceston, Australia
10. Bergen, Norway
11. Edinburgh, Scotland
12. Funchal, Portugal
13. Oulu, Finland
14. Honolulu, US
15. Halifax, Canada
16. Calgary, Canada
17. Glasgow, Scotland
18. Vancouver, Canada
19. Winnipeg, Canada
20. Stockholm, Sweden
21. Adelaide, Australia
22. Saint Petersburg, Russia
23. Surrey, Canada
24. Helsinki, Finland
25. Vantaa, Finland
Analysis
Of the 25 least polluted cities in the world with the best air quality, Nordic countries (Finland, Sweden, Norway, Iceland) dominated the rankings. 10 out of the 25 cities with the best and cleanest air were Nordic countries. Finland topped the list with 5 cities in the top 25. Canada also had a great showing, matching Finland by also having 5 cities ranking in the top 25 cleanest air cities.
Even though these are some of the cities with the best air quality in the world, each city experienced times during 2020 where pollution was over the WHO recommended limit. This shows how serious air pollution is all across the world. There is also research that even little amounts of pollution such as those typically present in these least polluted cities can have an impact on health.
Below is a pollution heat map from the WHO. WHO research shows that over 92% of people in the world are breathing unsafe air with high air pollution levels.

How Air Pollution Was Measured to Find Least Polluted Cities in World
There are various pollutants (both particles and gases) that can be found in the air. One of the most commonly tracked pollutants are very small, fine particles called PM2.5.
These small pollutants are under 2.5 micrograms in width and considered to be one of the more dangerous pollutants due to their ability to enter deep into the lungs and bloodstream. The above rankings of the least polluted cities in the world were ranked based on their 2020 average PM2.5 pollution levels.
Open Data
As part of Smart Air’s open data pledge, the raw PM2.5 AQI 2020 world pollution data used for the rankings of the world’s least polluted cities are openly available to download from the link below:
Download 2020 World Major Cities Air Quality Rankings
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