The short answer
There is no single AQI that is safe for every person and every activity. At 0 to 50, no AQI-related change is generally needed. From 51 to 100, unusually sensitive people may need to shorten or reduce activity. At 101 and above, sensitive groups should make changes. At 151 and above, everyone should reduce exposure. At 301 and above, everyone should avoid outdoor physical activity. Always check which pollutant is driving the AQI, who is involved, and how long and strenuous the activity will be.
Start here
- Confirm whether the AQI is current or forecast and note its time and reporting area.
- Identify whether ozone or particle pollution is driving the reading.
- Use the more protective guidance for anyone in a sensitive group.
- Choose the smallest useful change: shorten, reduce intensity, move, or reschedule.
Start with the activity, not the color
A short walk and a long run do not create the same exposure. Before changing a plan, identify how long people will be outside, how hard they will be breathing, whether a cleaner and cooler indoor location exists, and whether anyone involved needs the sensitive-group guidance.
Longer activity means more time breathing polluted air. Strenuous activity makes a person breathe faster and more deeply. Official guidance does not give one universal number of safe minutes, so change the duration, intensity, timing, or location instead of treating a time limit as a guarantee.
Who may need an earlier change
For ozone, sensitive groups include people with lung disease such as asthma, children and teenagers, older adults, and people who are active outdoors, including outdoor workers.
For particle pollution, sensitive groups include people with heart or lung disease, older adults, children and teenagers, outdoor workers, and people whose exposure or health risk is increased by social and economic conditions. EPA clinical guidance also identifies people with diabetes as a sensitive group.
Someone who knows that pollution causes symptoms may need to change activity at a lower AQI. Follow an individual asthma or medical action plan when one exists.
Use the pollutant-specific action
No AQI-related change is generally needed for ozone or particles. Other hazards can still change the plan.
A person who is unusually sensitive should consider making the activity shorter or less intense and watch for symptoms. Others can generally continue.
Sensitive groups should make long or strenuous activity shorter or less intense and take more breaks. For ozone, consider moving activity to the morning after checking the forecast.
Sensitive groups should avoid long or strenuous activity and consider moving or rescheduling it. Everyone else should reduce long or strenuous activity and take more breaks.
Sensitive groups should avoid all outdoor physical activity. Everyone else should avoid long or strenuous outdoor activity and move or reschedule it when possible.
Everyone should avoid outdoor physical activity. Sensitive groups should remain indoors and keep activity low in a location that is also safe for temperature and other hazards.
Make the smallest effective change
- Shorten the time outside.
- Walk instead of run, use lighter work, or add rest periods.
- For ozone, consider a morning time after checking the current forecast.
- Move to a location with suitable cooling and particle control.
- Reschedule or cancel when the category calls for avoiding the activity or no safer setting is available.
Watch conditions and people
Check again if the activity lasts several hours, the sky or smoke changes, an alert arrives, or the forecast shows a change during the planned time.
Stop and follow the person's care plan if symptoms develop. Severe breathing or heart symptoms need urgent help according to local emergency guidance, regardless of the displayed AQI.
Moving indoors is not protective if the indoor place is dangerously hot. When heat and pollution overlap, a cooled public building, cooling center, or another air-conditioned place with particle control may be safer.
What not to rely on
- Do not use the color without the AQI number and category text.
- Do not infer the pollutant from the AQI category.
- Do not invent an exact safe number of outdoor minutes.
- Do not treat being indoors as sufficient when the building is hot, smoky, or poorly ventilated.
- Do not use a stale value as the current condition.
What changes this answer
General guidance becomes a personal decision through these details.
Its number, category, time, reporting area, and whether it is current or forecast.
Ozone and particle pollution have overlapping but not identical activity guidance.
Age, health, pregnancy, outdoor work, symptoms, and individual care plans can change the threshold.
Duration, intensity, time of day, and whether a genuinely safer location is available.
Where this guidance stops
- This guide does not diagnose pollution-related illness or replace an individual medical or asthma action plan.
- Official local health instructions, emergency alerts, and workplace requirements take precedence when they are more specific.
- An indoor alternative must also be safe for heat, ventilation, and other hazards.
Sources
Consequential guidance is checked against the linked source material.
- AirNow. Air Quality Guide for Ozone. EPA-452/F-23-001, February 2023. Checked September 4, 2026.
- AirNow. Air Quality Guide for Particle Pollution. EPA-452/F-23-002, February 2023. Checked September 4, 2026.
- AirNow. Air Quality and Outdoor Activity Guidance for Schools. Checked August 28, 2026.
- AirNow. Your Health. Checked September 4, 2026.
- U.S. Environmental Protection Agency. Patient Exposure and the Air Quality Index. Ozone guidance. Checked August 28, 2026.
- U.S. Environmental Protection Agency. Patient Exposure and the Air Quality Index. Particle-pollution guidance. Checked August 28, 2026.
General information, not advice tailored to you or a guarantee of safety. You are responsible for decisions about your safety. Follow current directions from local authorities. Read the safety disclaimer.