Run as usual when the Air Quality Index (AQI) shows Good or Moderate. Shorten your run in orange, avoid hard outdoor miles in red, and move indoors in purple and maroon. Running raises your inhaled dose because you breathe much harder. Sensitive runners need earlier cutoffs, and everyone needs a local, current reading.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- What the six AQI colors mean
- When should you change your run?
- Why does running raise your dose?
- How can you pick cleaner air?
- What helps when smoke is high?
What the six AQI colors mean
The U.S. EPA defines six AQI levels from 0 to 500, with Good at 0–50 in green and Hazardous at 301-plus in maroon, as explained in the AQI Basics page. Moderate is 51–100 in yellow. Unhealthy for Sensitive Groups is 101–150 in orange.
Unhealthy is 151–200 in red, and Very Unhealthy is 201–300 in purple. For fine particles, the U.S. EPA tightened breakpoints in its 2024 PM2.5 fact sheet. Good is now 0–9.0 micrograms per cubic meter. Moderate is 9.1–35.4, orange is 35.5–55.4, red is 55.5–125.4, and purple is 125.5–225.4.
When should you change your run?
The U.S. EPA advises sensitive groups to shorten exertion or do less intense activity at 101–150, as detailed in its particle-pollution guide. At 151–200, everyone should avoid long or intense outdoor activity.
Sensitive groups include people with asthma, heart or lung disease, older adults, children, and pregnant people. At 201–300, reschedule the run or move it indoors. At 301-plus, avoid all outdoor physical activity. Use this quick match for particle pollution:.
- 0–100: normal training for most runners
- 101–150: sensitive runners shorten, slow down, or go indoors
- 151–200: all runners skip long or hard outdoor sessions
- 201-plus: move indoors or rest
Why does running raise your dose?
Exercise sharply increases how much air you pull into your lungs. CDC notes intense exercise can mean inhaling 10–20 times more air than at rest. A marathon study also measured sharply higher PM1, PM2.5, and PM10 deposition rates during the race.
Dose changes performance even before you feel sick. Collegiate and marathon analyses found each extra 1 microgram per cubic meter of PM2.5 added seconds per 5K and roughly 25–32 seconds per marathon. A Munich modeling study put the tipping point near 55 micrograms per cubic meter for a 60-minute moderate run.
How can you pick cleaner air?
Ozone often peaks in the early-to-mid afternoon. New York health officials and EPA ozone guidance advise checking AirNow.gov or NowCast before running. Shift runs to before 10 a.m. or after 7 p.m.
on high-ozone days. Route choice also matters. Run away from heavy traffic when you can. Choose parks, side streets, or trails over busy roads. Move the workout indoors on high-pollution days.
What helps when smoke is high?
When smoke is high, EPA puts staying indoors first, then limiting exertion and filtering indoor air. Close windows and doors. Run an air cleaner or air conditioner on recirculate if available.
Skip hard indoor workouts that still leave you breathing hard. A properly fitted NIOSH-approved N95 or P100 can reduce fine-particle inhalation outdoors. Surgical, dust, and cloth masks do not. AQI is location- and pollutant-specific and can spike within hours in smoke, so pair the nearest NowCast or Fire and Smoke Map reading with symptoms like cough, chest tightness, or unusual fatigue.