Why do I see different AQI numbers between IQAir and other platforms?
It’s common to see different AQI values for the same location on platforms like IQAir, AirNow, and others. These differences occur due to several factors, including the AQI system used, the frequency of data updates, and the sources from which the data is aggregated. Below are the key reasons why these discrepancies exist:
Different AQI systems (U.S. AQI vs. U.S. AQI⁺)
IQAir uses U.S. AQI⁺, which is a more real-time version of the U.S. Environmental Protection Agency’s (EPA) AQI. While both systems rely on the same pollutant thresholds and guidelines, U.S. AQI⁺ applies hourly updates for more real-time data, as opposed to the traditional 24-hour averages used by AirNow and some other platforms. This results in a more immediate reflection of current air quality conditions. You can find more detailed information about the EPA's system in their Technical Assistance Document.
In addition to U.S. AQI⁺, IQAir also offers CN AQI⁺, based on China’s national air quality standards, which provides another perspective for users monitoring air quality globally.
Differences in pollutants reported
Another reason AQI values may differ between platforms is that they may report a different subset of pollutants from the same monitoring station. For example, one platform may include more pollutants, such as sulfur dioxide (SO₂) or nitrogen dioxide (NO₂), while another may only report particulate matter (PM2.5) and ozone (O₃) for the same location. The AQI number displayed is typically based on the dominant pollutant (the highest AQI value at that moment), so variations in which pollutants are included can cause discrepancies.
It may be worth checking that you are comparing identical stations across the two platforms, and ensuring they are reporting the same pollutants at any given time.
Differences of data sources
IQAir doesn’t just rely on one source of data. It combines information from official governmental reference stations, its own IQAir AirVisual monitors, and some low-cost monitors from other manufacturers. This means that while IQAir may show data from a nearby government station, other platforms could be showing data from regional government sources that might have slightly different readings due to variations in how pollutants are measured or aggregated.
For example, if you are comparing IQAir’s data to a regional government website, the differences may arise from the fact that the website focuses solely on its own official stations, while IQAir provides a broader dataset by incorporating additional low-cost sensor data to give a more detailed picture of local air quality.
Last update time
The timing of data updates plays an important role in AQI differences. IQAir updates its data hourly, but other platforms may update more or less frequently. For instance, some sources may refresh data every 10 minutes, while others might aggregate data over a longer period. A slight delay in updates or different averaging periods can lead to noticeable variations in AQI values.
This discrepancy is especially common when comparing platforms that pull from the same data source but at different intervals. For example, you might see different AQI numbers on IQAir’s platform versus another platform that updates its data more or less frequently.
Differences in pollutant aggregation periods
The way different platforms aggregate and display AQI data can also vary, especially in terms of pollutant averaging periods. IQAir’s U.S. AQI⁺ is based on hourly averages for all pollutants, providing more immediate updates on current air quality. By contrast, platforms like AirNow use the original U.S. AQI system, which applies longer averaging periods, such as 24-hour averages for particulate matter (PM2.5).
Users of the IQAir platform and the IQAir AirVisual app can easily switch between U.S. AQI⁺ and CN AQI⁺. However, other air quality platforms may use entirely different AQI systems or even custom calculations. It’s important to review the specific definitions and methods used by each platform when comparing AQI values.