Why is the US Air Quality Index used in the ranking?

IQAir’s live major city air quality rankings, available for both the most polluted cities and cleanest cities, are based on the Air Quality Index (AQI), with users able to select between
U.S. AQI⁺ or CN AQI⁺. The rankings display real-time updates, with U.S. AQI⁺ providing hourly updates, offering a more immediate reflection of current air quality compared to traditional 24-hour averages used by platforms like AirNow.
The U.S. AQI⁺ system, widely recognized for its simplicity and health-based approach, measures key pollutants like PM2.5, PM10, ozone, and others. The AQI value reflects the concentration of the most dominant pollutant, ensuring that the health risk presented is always the highest relevant to the current conditions. Users can also switch to CN AQI⁺,
which follows China’s national standards, offering flexibility depending on regional relevance.
For PM2.5, U.S. AQI defines air as “Good” when concentrations are below 9 µg/m³, while the World Health Organization (WHO) recommends a more stringent guideline of 5 µg/m³ for annual exposure to minimize health risks. This difference reflects the WHO’s stricter health focus, based on the latest research into air pollution risks.
The flexibility in IQAir’s platform, allowing users to toggle between U.S. AQI⁺ and CN AQI⁺, ensures that the rankings offer a comprehensive and real-time view of global air quality, accommodating the specific needs and preferences of users around the world.

For more information on how the US AQI and city rankings relate, please follow the link below:
https://www.iqair.com/us/newsroom/why-is-the-us-air-quality-index-used-in-the-ranking