What AQI Is Safe for Outdoor Exercise?

The same AQI that is harmless on a walk to the mailbox matters a great deal during a tempo run or a hard ride, because exercise multiplies how much air you move through your lungs. This guide gives you the cutoffs by intensity and by who you are, using the EPA's Air Quality Index categories, so you can decide in ten seconds whether today's workout stays outside.

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QUICK ANSWER

What AQI is safe for exercising outside?

Healthy adults can exercise outdoors normally when the AQI is 100 or below. From 101 to 150 (Unhealthy for Sensitive Groups), healthy adults can usually continue at moderate effort, while people with asthma, heart disease, children and older adults should shorten or ease their workout. From 151 to 200 (Unhealthy), everyone should reduce intensity and duration. Above 200, move the workout indoors.

  • ✓0 to 50 (Good): any activity, any intensity, for everyone.
  • ✓51 to 100 (Moderate): normal training; unusually sensitive people watch for symptoms.
  • ✓101 to 150 (USG): sensitive groups ease up or go indoors; healthy adults keep it moderate.
  • ✓151 to 200 (Unhealthy): everyone shortens and lightens; skip intervals and long efforts.
  • ✓201 and up: exercise indoors.

Frequently asked questions

What AQI is safe for exercising outside?▾

An AQI of 0 to 50 (Good) is safe for everyone at any intensity. At 51 to 100 (Moderate), healthy adults can train normally while unusually sensitive people watch for symptoms. At 101 to 150 (Unhealthy for Sensitive Groups), people with asthma, heart disease, children and older adults should shorten or ease outdoor workouts; healthy adults can usually continue with moderate effort. Above 150, everyone should reduce intensity and duration, and above 200 exercise indoors.

Why does exercise make air pollution worse for you?▾

Hard exercise raises your breathing rate several times over, and you tend to breathe through your mouth, bypassing the nose's filtering. That means more pollution reaches deep into the lungs per minute than at rest. The EPA specifically defines "prolonged or heavy exertion" as the activity to reduce when the AQI rises for this reason.

Is it better to exercise in the morning or evening when air quality is bad?▾

It depends on the pollutant. Ozone is lowest in the early morning and peaks mid-to-late afternoon, so on summer ozone days the morning is best. Fine particles from smoke or winter inversions are often worst overnight and in the early morning, so on those days midday or afternoon may be cleaner. Check the current reading and dominant pollutant on your city page before heading out.

Does a mask help when exercising in bad air quality?▾

A well-fitted N95 respirator filters fine particles effectively, but it also adds breathing resistance, and it does nothing for ozone. It is a reasonable option for a walk or easy effort during smoke, not a substitute for moving a hard workout indoors when the AQI is Unhealthy.

Why Exercise Changes the Math

At rest an adult breathes roughly 6 to 8 liters of air per minute. During vigorous exercise that can rise many-fold, and most of it comes in through the mouth rather than the nose, which normally traps some larger particles. The result is that a runner or cyclist inhales far more pollution per hour than a bystander in the same air, and it penetrates deeper. This is why the EPA's AQI cautionary statements talk specifically about “prolonged or heavy exertion” rather than simply being outdoors. The advice below applies that framework to common activities.

The Exercise AQI Chart

AQILight (walking, easy yoga, golf)Moderate (jogging, casual cycling, hiking)Vigorous (tempo runs, intervals, team sports)
0 to 50 GoodGoGoGo
51 to 100 ModerateGoGoGo; sensitive people watch for symptoms
101 to 150 USGGo; sensitive groups take breaksHealthy adults OK; sensitive groups shorten or go indoorsHealthy adults ease to moderate; sensitive groups indoors
151 to 200 UnhealthyKeep it shortShorten; consider indoorsIndoors
201 to 300 Very UnhealthyAvoidIndoorsIndoors
301+ HazardousStay insideStay insideStay inside

“Sensitive groups” here means what the EPA means: people with asthma or other lung disease, people with heart disease, children and teenagers, older adults, pregnant people, and outdoor workers with long exposures. If that is you, read your column one row up.

Adjust for the Pollutant, Not Just the Number

Ozone days (hot, sunny, summer)

Ozone is lowest at dawn and climbs through the afternoon, typically peaking between mid-afternoon and early evening. A morning workout on an ozone alert day can be in Good air even when the forecast peak is orange. Ozone irritates the airways directly, so coughing, chest tightness or a scratchy throat mid-workout are signals to stop. Masks do not filter ozone.

Particle days (smoke, winter inversions)

PM2.5 does not follow a clean daily curve. Wildfire smoke can arrive at any hour and hang for days; winter inversions are often worst overnight and in the early morning, improving by early afternoon. Check the live reading rather than assuming. Fine particles are the pollutant that a fitted N95 can meaningfully reduce, and the one where indoor air with a HEPA filter is a genuine refuge. Our wildfire smoke guide covers the specifics.

Activity-Specific Guides

We maintain detailed guides for individual activities that go into duration, terrain and typical intensity: running, cycling, hiking, walking, and kids' sports. The full list is on the activities page.

Protect Yourself Outdoors

Gear for exercising in poor air

If you're heading out for a workout while the air is poor, a home purifier won't help you out on the road. Two pieces of gear actually protect you where you'll be breathing hardest:

N95 / KN95 mask

Wear a mask when exercising in poor air — a snug N95/KN95 filters the PM2.5 and wildfire smoke that mouth-breathing drives deep into your lungs. (Masks do little against ozone, a gas.)

Shop N95 / KN95 Masks on Amazon →
Portable air-quality monitor

Check the air where you actually are — a pocket PM2.5 monitor reads your street, trail or field, which can be far worse (or better) than the nearest official station miles away.

Shop Portable AQ Monitors on Amazon →

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A Simple Decision Routine

  1. Check the current AQI and dominant pollutant on your city page, not yesterday's forecast.
  2. Find your row in the chart above, moving up one row if you are in a sensitive group.
  3. Time it: mornings for ozone, whenever the reading is lowest for particles.
  4. Downgrade the effort before you cancel: an easy 30 minutes at AQI 130 is a very different exposure from 60 minutes of intervals.
  5. Stop for symptoms such as coughing, wheezing, chest tightness, unusual fatigue or shortness of breath beyond what the effort explains.

For what each AQI band means for health more broadly, see our guide to the AQI scale. If you have asthma, the asthma and air quality guide covers medication timing and warning signs in more depth.