We have noticed some concern in Vietnam that Hanoi has been at no. 1 on AirVisual’s “major city ranking” at certain times over recent days.
We would like people to be aware that this does not mean that Hanoi is the world’s no. 1 polluted city. The “major city ranking” currently consists of around 90 major global cities.
At any one time, a city can top the live ranking, as happened with London and even San Francisco last year. Details on how we curate the “major city ranking” in order to make it relevant to people are here
We also publish a separate annual world ranking in partnership with Greenpeace. The report published in March showed that Hanoi was not in the world’s top 200 most polluted cities in 2018.
On our platform, we are transparent about where we get our data from and how we publish it. For calculating 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, we always publish the source of the data to be fully transparent to our users. If you are unsure about the data, please refer to the source and contact us to report a problem.
We believe that awareness of pollution levels is what leads to change. That’s what happened in Beijing: when people realized how serious the air pollution was, they pushed the government to implement stronger environmental policies. As a result, Beijing pollution has dropped dramatically.