The short answer
The Air Quality Index (AQI) is a public communication tool that summarizes air pollution levels into a single number and color category. It is useful for planning, but it is not a personal medical measure. Two people with similar lung conditions can respond differently to the same AQI reading. Use it as one input, alongside your own symptoms and your clinician's guidance.1
What the AQI measures
The AQI is calculated from several pollutants, including fine particulate matter (PM2.5), ground-level ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide. On wildfire smoke days, PM2.5 is usually the dominant contributor. The index runs from 0 to 500, grouped into categories from "Good" to "Hazardous."
| AQI range | Category | General guidance |
|---|---|---|
| 0–50 | Good | Air quality is considered satisfactory. |
| 51–100 | Moderate | Acceptable, though sensitive individuals may notice effects. |
| 101–150 | Unhealthy for sensitive groups | People with lung conditions may consider reducing outdoor exertion. |
| 151–200 | Unhealthy | Everyone may begin to experience effects; sensitive groups more so. |
| 201+ | Very unhealthy to hazardous | Significant risk; public health advisories typically issued. |
Limits of the AQI
The AQI is designed for populations, not individuals. A few limitations are worth knowing:
- Readings come from monitoring stations, which may be some distance from your home.
- Indoor air can differ substantially from outdoor air, depending on your building.
- The index does not account for individual sensitivity or medical history.
- Short-term peaks within a day may not be reflected in a daily average.
- Smoke composition varies by what is burning and how far it has traveled.
Because of these limits, the AQI is best treated as a rough guide rather than a personal threshold. Your own symptoms are also data.2
Practical planning
On smoke days, common suggestions in public health guidance include:
- Checking the local AQI before planning outdoor activity.
- Shifting exercise indoors or postponing it when air quality is poor.
- Keeping windows closed when outdoor air is smoky.
- Using a well-fitted mask (such as an N95 or KN95) when outdoors if needed.
- Paying attention to symptoms rather than relying only on the number.
These are general suggestions. What is right for you depends on your situation, and your care team may have specific guidance. Our article on Cold Air, Humidity, and Changing Weather covers related environmental factors.
Indoor air on smoke days
Indoor air is not automatically cleaner than outdoor air. Smoke particles can enter through open windows, doors, and gaps. A few practical measures are often discussed:
- Keeping windows and doors closed while outdoor air is smoky.
- Using a portable air cleaner with a HEPA filter, if available.
- Running an air conditioner on recirculate mode rather than pulling in outdoor air.
- Avoiding activities that add indoor particles — frying, candles, vacuuming without a HEPA filter.
For a room-by-room review of indoor air, see our guide The Home Air Review.
What to discuss with your care team
- At what AQI level would you suggest I limit outdoor activity?
- Are there specific symptoms I should watch for on smoke days?
- Should I adjust my action plan during wildfire season?
- Would a portable air cleaner be worth considering for my home?
- Is there anything in my current medicines I should review before smoke season?
Sources
- U.S. Environmental Protection Agency. Air Quality Index (AQI) Basics.
- Centers for Disease Control and Prevention. Wildfire Smoke and Your Health.
- American Lung Association. Wildfires and Lung Health.
- National Heart, Lung, and Blood Institute. COPD: Living With COPD.