No single AQI (air quality index) number makes outdoor exercise safe or unsafe, because how much pollution you breathe in also depends on how hard and how long you go. A healthy adult can train normally up to an AQI of 100, cut back on long or hard efforts above 150, and take exercise indoors above 200. Sensitive groups should ease off earlier, above 100.
No single AQI number turns outdoor exercise from safe to unsafe. The reality is that this is a complicated decision, and a single number oversimplifies. What matters is how much pollution you actually take in. That depends on how dirty the air is, how hard you're breathing, and how long you stay out, so a hard, long workout pulls in far more than an easy walk at the same reading.1 Exercising makes you breathe harder and deeper, and more of what's in the air ends up in your lungs.23
The index does still give you a workable ladder. At or below 100, the air is generally satisfactory4, and a healthy adult can train as usual. From 101 to 150, the orange band, people with heart or lung disease, older adults, and children are told to cut back on long or hard exertion, though the general public is less likely to be affected.14
At 151 and up, anyone active outdoors can start to feel it.1 In that Unhealthy range, 151 to 200, cut back on long or hard activities and take more breaks.45 By Very Unhealthy, 201 to 300, avoid the long, hard efforts and move them indoors.45 At 301 and above, skip outdoor activity altogether.45
Stopping altogether isn't the point. Going easier or shorter when pollution is high cuts the amount you breathe in.1 Slow a run to a jog, or trade an hour for thirty minutes. Let your body have the final say too: dirty air can bring on coughing, chest tightness, wheezing, or shortness of breath2, any of which means ease off or head inside, whatever the number reads.
When in doubt, take the exercise indoors. Don't let a bad air day stop you from staying healthy.
Sources
- [1] Patient Exposure and the Air Quality Index. Accessed August 7, 2026. https://www.epa.gov/pmcourse/patient-exposure-and-air-quality-index
- [2] Health Effects of Ozone in the General Population. Accessed August 7, 2026. https://www.epa.gov/ozone-pollution-and-your-patients-health/health-effects-ozone-general-population
- [3] Air Quality and Outdoor Activity Guidance for Schools. Accessed August 7, 2026. https://document.airnow.gov/air-quality-and-outdoor-guidance-for-schools.pdf
- [4] U.S. EPA (AirNow). Air Quality Index (AQI) Basics. Accessed August 6, 2026. https://www.airnow.gov/aqi/aqi-basics/
- [5] Air Quality Guide for Particle Pollution. Accessed August 7, 2026. https://www.airnow.gov/sites/default/files/2023-03/air-quality-guide-for-particle-pollution_0.pdf
About the author
Dr. Colin Little
MD, FAWM, Chief Medical Officer, GOES Health
- Board Certified Emergency Physician
- Fellow of the Academy of Wilderness Medicine (FAWM)
- Wilderness Medicine Fellowship, University of Utah
- Emergency Medicine Residency and Chief Resident, Stanford / Kaiser
- Doctor of Medicine, University of Arizona College of Medicine – Phoenix