In late 2019, users of AirVisual in Vietnam noted their concern that Hanoi had been at no. 1 on AirVisual’s “major city ranking” at certain times over the course of several weeks.

If your city’s at the top of the major city ranking, this does not mean that it’s the world’s no. 1 polluted city.

The “major city ranking” currently consists of around 90 major global cities. Any city can top the live ranking at any given time, as happened with London and even San Francisco last year.

How is the IQAir AirVisual major city ranking generated? Click here for details on how AirVisual curates the “major city ranking” in order to make it relevant to AirVisual users.

AirVisual also publishes a separate annual world ranking in partnership with Greenpeace. The latest report, published in March 2019, showed that Hanoi was not in the world’s top 200 most polluted cities in 2018.

The AirVisual Platform is transparent about where its data is sourced from and how it’s published. In order to calculate Hanoi air quality, AirVisual uses data from the governmental Hanoi Environmental Monitoring Portal and from the US embassy to report real-time air pollution levels.

In the AirVisual app and on the website, the source of the data is always published in order to ensure full transparency to our users. If you are unsure about the data, please refer to the source and contact IQAir to report a problem.

Why is the major city ranking important?

IQAir AirVisual believes that awareness of pollution levels is what leads to change.

That’s what happened in Beijing: when people realized how serious air pollution was in the city of Beijing, they pushed the government to implement stronger environmental policies – as a result, Beijing pollution has dropped dramatically.