Guide
Is it safe to run or exercise in smog?
Last reviewed 4 Nov 2026 · DanixSoft
Exercise outdoors when the AQI is 100 or less. From 101 to 150, people with asthma, heart or lung conditions should move indoors and everyone else should keep it lighter. Above 150, move every workout indoors: during hard exercise you breathe many times more air, and more of it through the mouth, so more fine particles reach the lungs.
By AQI level
| US AQI | Outdoor exercise |
|---|---|
| 0–50 | Go for it. |
| 51–100 | Fine for most; unusually sensitive people go easier. |
| 101–150 | Sensitive groups indoors; others shorter and lighter, with breaks. |
| 151–200 | Indoors for everyone. |
| 201+ | Indoors, and keep it light if the room air is not filtered. |
Pick the cleanest hours
In winter smog the air is often worst late in the evening and through the night, when the ground cools and a lid of warm air traps pollution near the surface, and it usually eases in the early afternoon, when the sun mixes the air. That is a common pattern, not a rule: check the hourly chart on your city’s page, which marks the cleanest hour in the next 24 hours.
If you must train outside
- Keep it shorter and easier than usual, and stop if you get chest tightness, wheezing or unusual breathlessness.
- Stay away from main roads; traffic adds pollution right where you breathe.
- A well-fitted N95/KN95 helps for walking; it is hard to breathe through during hard running.
- Indoor gyms are only better if the air inside is filtered or the doors and windows stay shut.