What does AQI mean?
AQI stands for Air Quality Index, a scale from 0 to 500 that reports how clean or polluted the air is. An AQI of 100 generally matches the level of the short-term national air quality standard, and values at or below 100 are generally thought of as satisfactory.
Action level Worth checking
- Why you are seeing it
- It appears in weather apps, on news reports and on air quality maps, usually as a number with a color.
- Why it matters
- The number and its category show how the air compares with the national standard, which helps you decide whether to pay closer attention to the guidance for your area.
- What should I do?
- Find the category and color for the number you are looking at.
- Read the guidance that comes with the reading for your area on AirNow or from your local health department.
- If you have a health condition, ask your doctor what readings matter for you.
- A common misunderstanding
- The AQI is not a percentage and not a score out of 100: it is a scale from 0 to 500, and the line at 100 is where the air stops being generally satisfactory.
The six categories
| Color | Category | AQI values |
|---|---|---|
| Green | Good | 0 to 50 |
| Yellow | Moderate | 51 to 100 |
| Orange | Unhealthy for Sensitive Groups | 101 to 150 |
| Red | Unhealthy | 151 to 200 |
| Purple | Very Unhealthy | 201 to 300 |
| Maroon | Hazardous | 301 and higher |
Why 100 is the line
For each pollutant, an AQI value of 100 generally corresponds to an air concentration that equals the level of the short-term national ambient air quality standard for protection of public health. AQI values at or below 100 are generally thought of as satisfactory, and when values are above 100, air quality is considered unhealthy.
A simple example
Three readings
An AQI of 42 is in the Good category (0 to 50).
An AQI of 100 is the top of the Moderate category, the value that generally matches the short-term national standard.
An AQI of 135 is in the Unhealthy for Sensitive Groups category (101 to 150).
Using the number
- Look at the category and its color first; the number places you inside it.
- Check the reading for your own area, because an AQI reading is for a particular place.
- For what to do about a reading, follow the guidance given with it on the AirNow site or from your local health department.