AQI and Asthma: What Air Quality Numbers Mean

You can’t lower your city’s Air Quality Index, but you can lower how much polluted air you breathe. The AQI is the EPA’s daily color-coded scale for air pollution. Once you know what each level means, you can plan workouts, trips and time outdoors around it, and keep the air inside your home cleaner on bad days.

This guide explains the AQI categories, which pollutants matter most for asthma, and what to do at each level, indoors and out. For more, see our indoor air quality guides.

Jump to: Quick answer · The AQI scale · Pollutants measured · Outdoors on bad days · Cleaner air indoors · Travel and summer plans · FAQ

Contents hide

1 Quick answer

2 The AQI scale

3 What the AQI measures

4 Outdoors on high-AQI days

5 Keep indoor air cleaner on bad days

6 Travel and summer plans

7 Frequently asked questions

7.1 What AQI level is bad for asthma?

7.2 How can I reduce my AQI exposure at home?

7.3 Does the AQI include pollen?

7.4 Is it safe to exercise when the AQI is over 100?

7.5 Where can I check the AQI?

8 Sources

9 Share this post

Quick answer

The AQI runs from 0 to 500. Up to 100 is generally satisfactory; 101 and above is unhealthy, first for sensitive groups, then for everyone.
People with asthma are a sensitive group. At 101 or more, follow your asthma action plan and keep quick-relief medicine handy (EPA).
Ozone and particle pollution (including wildfire smoke) are the pollutants that most often drive bad AQI days.
Check AirNow.gov or the free AirNow app for current readings and forecasts.
Indoors on smoky days: close windows, avoid candles and wood fires, and run a HEPA air cleaner sized for the room.

The AQI scale

AQI	Color	Level	What it means
0 to 50	Green	Good	Air pollution poses little or no risk.
51 to 100	Yellow	Moderate	Acceptable, but there may be a risk for people unusually sensitive to air pollution.
101 to 150	Orange	Unhealthy for sensitive groups	Sensitive groups may have health effects; the general public is less likely to be affected.
151 to 200	Red	Unhealthy	Some of the general public may have health effects; sensitive groups may have more serious effects.
201 to 300	Purple	Very unhealthy	Health alert: increased risk for everyone.
301 and up	Maroon	Hazardous	Health warning of emergency conditions.

Source: AirNow AQI basics. An AQI of 100 generally matches the national short-term air quality standard for that pollutant.

What the AQI measures

The EPA calculates an AQI for five major pollutants regulated by the Clean Air Act:

Ground-level ozone, which forms in sunlight and peaks on hot, sunny days. See ozone and asthma.
Particle pollution, including fine particles (PM2.5) from vehicles, power plants, industry, woodstoves and wildfires, and coarse particles (PM10) from road dust and grinding.
Carbon monoxide
Sulfur dioxide
Nitrogen dioxide

The AQI does not include pollen. Check a pollen forecast separately; our pollen avoidance guide explains how.

Outdoors on high-AQI days

The EPA’s air quality guides for ozone and particle pollution give this advice for sensitive groups, including people with asthma:

AQI 101 to 150: make outdoor activities shorter and less intense, take more breaks, and watch for coughing or shortness of breath. Follow your asthma action plan and keep quick-relief medicine handy.
AQI 151 to 200: avoid long or intense outdoor activities; consider rescheduling or moving them indoors.
AQI 201 and up: avoid all physical activity outdoors.

Other tips from the guides: for ozone, exercise in the morning when levels are lower; for particles, exercise away from busy roads. And in extreme heat, don’t stay in a hot home with the windows closed; go somewhere with air conditioning or a cooling center.

Keep indoor air cleaner on bad days

The EPA notes that when particle levels are high outdoors, they can be high indoors too. To keep them lower:

Close windows and doors when outdoor air is bad.
Don’t add particles: skip candles, smoking, fireplaces and wood stoves.
Use a HEPA filter in your heating and cooling system if it can take one, or a portable air cleaner.
Size the air cleaner to the room. The EPA’s indoor air filtration fact sheet suggests a clean air delivery rate (CADR) of at least two-thirds of the room’s area in square feet, run continuously.
Choose a CARB-certified model and avoid ionizers and ozone generators, which can add ozone.

Humidity control matters too, since damp air feeds dust mites and mold; see humidity control for allergies. For choosing a purifier, read the problems with cheap air purifiers.

Travel and summer plans

Check the forecast for your destination on AirNow before and during your trip, especially in wildfire season.
Pack enough asthma medicine, including quick-relief inhalers, and bring your asthma action plan.
In the car, keep windows up on bad air days and change the cabin air filter on schedule.
Plan outdoor activities flexibly so you can move them to a better day or time.

Allergies can complicate travel too; see apps for tracking pollen and air quality.

This guide is general information, not medical advice. Read our medical disclaimer.

Frequently asked questions

What AQI level is bad for asthma?

At 101 and above, “unhealthy for sensitive groups,” people with asthma should make outdoor activities shorter and less intense and keep quick-relief medicine handy. Some very sensitive people may notice symptoms in the moderate range (51 to 100).

How can I reduce my AQI exposure at home?

Close windows, avoid candles, smoking and wood fires, and use a HEPA filter in your HVAC system or a portable HEPA air cleaner sized for the room.

Does the AQI include pollen?

No. It covers ozone, particle pollution, carbon monoxide, sulfur dioxide and nitrogen dioxide. Check pollen forecasts separately.

Is it safe to exercise when the AQI is over 100?

If you have asthma, keep it shorter and less intense, take breaks and watch for symptoms. Above 150, avoid long or intense outdoor exercise, and above 200, avoid outdoor activity altogether.