Pro WeatherUnderstanding Air Quality Index: AQI vs EAQI
If you have a Davis AirLink sensor, your station measures the same thing: the concentration of particulate matter in the air. But there are two different ways to translate that raw measurement into an air quality index: the US EPA AQI and the European EAQI.
They use the same data but present it very differently, which causes confusion. This guide explains the difference and how to choose which one to display on your weather site.
The raw measurement
Both indices start from the same raw measurement: the concentration of PM2.5 (particles smaller than 2.5 micrometres) in the air, measured in micrograms per cubic metre (µg/m³). This is the particle size that is small enough to enter the lungs and bloodstream, making it the most health-relevant measure.
The AirLink sensor uses a laser particle counter to measure PM1, PM2.5, and PM10 simultaneously. The raw PM2.5 value is the same regardless of which index you choose to display.
US EPA AQI
The Air Quality Index used by the United States Environmental Protection Agency breaks PM2.5 concentrations into six categories:
| AQI Range | Level | Colour | Health concern |
|---|---|---|---|
| 0–50 | Good | Green | Little to no risk |
| 51–100 | Moderate | Yellow | Acceptable for most |
| 101–150 | Unhealthy for Sensitive Groups | Orange | Sensitive groups affected |
| 151–200 | Unhealthy | Red | General health effects |
| 201–300 | Very Unhealthy | Purple | Widespread effects |
| 301–500 | Hazardous | Maroon | Emergency conditions |
The AQI scale is designed to be intuitive: 100 is roughly the national standard, and higher numbers represent increasing health risk. The breakpoints between categories are set by regulation and differ for PM2.5, PM10, ozone, and other pollutants.
European EAQI
The European Air Quality Index, published by the European Environment Agency (EEA), works differently from the US AQI. Instead of a single 0–500 number, it sorts air quality into six named bands, and the overall rating is set by whichever pollutant is worst. For PM2.5, the bands (hourly concentrations in µg/m³) are:
| Band | PM2.5 (µg/m³) | Colour |
|---|---|---|
| Good | 0–10 | Cyan |
| Fair | 10–20 | Green |
| Moderate | 20–25 | Yellow |
| Poor | 25–50 | Red |
| Very Poor | 50–75 | Dark red |
| Extremely Poor | 75+ | Purple |
Because the EAQI reports a band rather than a number, it is read as a category, not compared on a 0–100 scale. The European thresholds are stricter at the cleaner end than the US ones, so the same air can land in a worse-sounding band. For example, a PM2.5 reading of 30 µg/m³ falls in the EAQI "Poor" band, while on the US scale the same reading is around 90 AQI, which is still only classed as "Moderate." The two systems can describe identical air in very different language, which is why showing the right one for your audience matters.
Which one should you use?
The answer depends on your audience:
- Use EPA AQI if your site serves a US audience. It matches what people see on US weather apps, news, and government services.
- Use EAQI if your site serves a European audience. It is the standard used by the European Environment Agency and displayed on European weather services.
- Display both if your audience is mixed or if you want to be comprehensive. Some sites show both indices side by side, which helps visitors understand the difference.
Pro Weather supports both standards. You can choose which one your site displays, and the colour-coded panel updates automatically based on your AirLink readings.
Why it matters
Air quality data is most useful when your audience understands what they are looking at. Showing the wrong index for your region leads to confusion: a European visitor used to the EAQI's named bands might read a US AQI number as healthier than their own scale would call it, or vice versa.
By choosing the right index for your audience, you make your air quality data immediately useful rather than requiring visitors to learn an unfamiliar scale.
See your air quality on your site
If you have a Davis AirLink sensor, Pro Weather displays your air quality data with the correct colour coding, index value, and health recommendations. The panel is updated every 10 minutes alongside your other weather data. Start your Pro Weather site and your air quality readings will appear automatically.