You’ve seen the number on the news when there’s wildfire smoke: “AQI 180.” But what is the AQI actually measuring, and at what point should you change your plans?
Six pollutants, one number
The US Air Quality Index (AQI) is run by the EPA. It takes six pollutants - PM2.5, PM10, ozone, NO₂, SO₂, and CO - calculates a sub-index for each, and reports the worst one as the overall AQI on a 0–500 scale. SafeInhale shows you that headline number and which pollutant is driving it.
The two that matter most for day-to-day health are usually:
- PM2.5 - fine particles (smoke, combustion) small enough to reach deep into your lungs.
- Ozone - ground-level ozone that builds up on hot, sunny afternoons.
The categories
SafeInhale uses the official EPA categories and colors - no invented scale:
- 0–50 · Good (green) - air is satisfactory.
- 51–100 · Moderate (yellow) - fine for most; unusually sensitive people should watch out.
- 101–150 · Unhealthy for Sensitive Groups (orange) - people with asthma, heart, or lung conditions may feel effects.
- 151–200 · Unhealthy (red) - everyone may start to notice; sensitive groups more so.
- 201–300 · Very Unhealthy (purple) - health alert.
- 301+ · Hazardous (maroon) - emergency conditions.
When to actually change plans
At AQI 101–150, sensitive groups should consider making outdoor activity shorter and less intense, taking additional breaks, watching for symptoms, and following their asthma action plan.
At AQI 151–200, everyone should consider reducing prolonged or heavy outdoor activity, with additional caution for sensitive groups. On smoke days, a well-fitting N95 can reduce exposure to particle pollution, including smoke particles, but it does not protect against harmful gases.
See your current AQI and primary pollutant on the pollen & air page.
Informational only - not medical advice.
