AQI Over 100 Means Sensitive Groups Take Care, Check AirNow
When the Air Quality Index (AQI) is above 100, sensitive groups should take care: AirNow says an AQI of 101 to 150 is orange, “Unhealthy for Sensitive Groups,” when members of sensitive groups may experience health effects and the general public is less likely to be affected. The higher the AQI, the more air pollution and the greater the health concern.
The AQI is the US Environmental Protection Agency’s (EPA) index for reporting air quality. An AQI of 100 generally corresponds to the short-term national air quality standard for protecting public health; values at or below 100 are generally satisfactory, and above 100 the air is unhealthy, first for sensitive groups and then for everyone.
The six categories
AirNow explains (AirNow AQI basics):
| AQI | Color | Category | What it means |
|---|---|---|---|
| 0–50 | Green | Good | Air quality is satisfactory, and air pollution poses little or no risk |
| 51–100 | Yellow | Moderate | Acceptable, but there may be a risk for people who are unusually sensitive to air pollution |
| 101–150 | Orange | Unhealthy for Sensitive Groups | Members of sensitive groups may experience health effects; the general public is less likely to be affected |
| 151–200 | Red | Unhealthy | Some members of the public may experience health effects; sensitive groups may experience more serious effects |
| 201–300 | Purple | Very Unhealthy | Health alert: the risk of health effects is increased for everyone |
| 301 and higher | Maroon | Hazardous | Health warning of emergency conditions: everyone is more likely to be affected |
Which pollutants it covers
EPA sets an AQI for five major air pollutants regulated by the Clean Air Act:
- Ground-level ozone.
- Particle pollution (including PM2.5 and PM10).
- Carbon monoxide.
- Sulfur dioxide.
- Nitrogen dioxide.
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What this article did not check
- How to protect yourself when the AQI is unhealthy: AirNow has separate Activity Guides, which this article did not check.
- The current AQI where you live: this article doesn’t list live readings; check AirNow.
- Who counts as a sensitive group: this page doesn’t list them, and this article did not check.
Frequently asked questions
At what AQI should I start paying attention?
101 and up is orange, “Unhealthy for Sensitive Groups”; 151 and up is red, “Unhealthy,” when some members of the general public may also be affected.
What does an AQI of 100 mean?
It generally corresponds to the short-term national air quality standard for protecting public health; 100 or below is generally satisfactory.
What does the AQI measure?
Five major pollutants: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide and nitrogen dioxide.
What should I do when the air is bad?
AirNow points you to its Activity Guides; this article did not check what they say.
Sources and dates checked
All checked on 2026-10-31.
- AirNow, AQI Basics (no update date on the page):https://www.airnow.gov/aqi/aqi-basics/