The U.S. Air Quality Index (AQI) and the World Health Organization (WHO) air quality guidelines both aim to inform the public about health risks related to air pollution, but they differ significantly in their thresholds, particularly for particulate matter (PM2.5).
The U.S. AQI, used by platforms like AirNow and IQAir's U.S. AQI⁺ (which is based on hourly data aggregation), categorises PM2.5 concentrations below 9 μg/m³ as "Good." In contrast, the WHO's 2021 guidelines recommend an annual average of 5 μg/m³ for PM2.5 to minimise long-term health risks. While the WHO acknowledges that no level of air pollution is completely safe, their guideline is considered the authoritative global benchmark for reducing exposure to PM2.5 over time.
This means that while the U.S. AQI⁺ may reflect real-time hourly concentrations, the same levels could still exceed the WHO's stricter annual guideline. Despite these differences, both systems emphasise public health protection and offer essential guidance on reducing exposure to harmful air pollutants.
See the U.S. air quality index for PM2.5 concentrations below for a clear comparison between the U.S. AQI and the WHO guideline. Again, note the significantly higher threshold in the "good" category listed below:
Also see this chart for reference to PM2.5, AQI, and additional pollutants in the revised WHO guideline:
For more information on how this information is gathered click the link below:
What is the air quality index (AQI)?
