There is no single AQI number that makes outdoor air equally safe for everyone. In the U.S., the smoke-related AQI runs from Good (0–50) to Hazardous (301+); as the category worsens, reduce outdoor activity and spend more time in filtered indoor air. People at higher risk should take precautions earlier. Check AirNow’s Fire and Smoke Map and local alerts again before heading outside, because smoke can change during the day.
What the wildfire smoke AQI measures
The Air Quality Index (AQI) turns measured pollution into color-coded categories, health messages and recommended actions. The AQI system covers five major pollutants regulated under the Clean Air Act; it is not an index of wildfire smoke alone. During wildfire events, AirNow’s Fire and Smoke Map reports particle pollution—the key pollutant in smoke—and pairs readings with health guidance.
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The category is more useful than treating a single reading as a universal safe-or-unsafe switch. It communicates escalating health concern and advice, but personal risk varies. Someone with asthma, for example, may need to limit exposure at a reading that another person tolerates without noticeable symptoms. Use the category guidance together with your health needs, local alerts and changing conditions.
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What each AQI number and category means
AirNow’s U.S. Fire and Smoke Map Version 4 help page lists these ranges. The colors and category names below are the map’s particle-pollution categories for smoke events.
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| AQI range | Category | Practical interpretation |
|---|---|---|
| 0–50 | Good | Air quality is in the lowest concern category on this scale. Continue to check conditions if smoke is nearby or changes are expected. |
| 51–100 | Moderate | Concern is higher than in the Good range. People who are unusually sensitive to air pollution may notice effects and should use their own health needs to guide exposure. |
| 101–150 | Unhealthy for Sensitive Groups | People in sensitive groups should reduce exposure and modify activity. |
| 151–200 | Unhealthy | Everyone should limit prolonged or heavy exertion and limit time outdoors. |
| 201–300 | Very Unhealthy | Everyone should avoid prolonged or heavy exertion and stay indoors, preferably in filtered air. |
| 301 and above | Hazardous | Everyone should avoid outdoor activity and stay indoors, preferably in filtered air. |
These are escalating categories, not guarantees that a particular person will or will not have symptoms. The most important change as the reading rises is that advice applies to more people and calls for stronger exposure reduction.
Is AQI 150 safe to go outside?
AQI 150 is at the top of the Unhealthy for Sensitive Groups range. It is not a blanket declaration that outdoor air is safe for everyone: people in sensitive groups should reduce exposure and modify activity. At 151, the reading enters the Unhealthy category, where the guidance broadens to everyone, who should limit prolonged or heavy exertion and time outdoors.
If you are near a category boundary, do not base a decision on one point alone. Check the latest map reading and local health or emergency alerts, and consider whether you are in a group that needs to act earlier.
When to stay indoors during wildfire smoke
Follow the action advice for the current category rather than relying on one threshold for all situations. As smoke worsens, scale back activity in stages:
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- Unhealthy for Sensitive Groups (101–150): If you are in a sensitive group, reduce exposure and modify activity.
- Unhealthy (151–200): Everyone should limit time outdoors and avoid prolonged or heavy exertion.
- Very Unhealthy (201–300): Everyone should stay indoors, preferably in filtered air, and avoid prolonged or heavy exertion.
- Hazardous (301+): Everyone should avoid outdoor activity and stay indoors, preferably in filtered air.
At lower categories, a sensitive person may still need to take precautions. Conversely, the advice does not mean a brief necessary trip at a high reading has the same exposure as hours of outdoor work; reduce exposure as much as practical and follow any local emergency instructions.
How to check smoke levels near you
Use AirNow’s Fire and Smoke Map for current particle-pollution conditions and health recommendations, and pay attention to local public-health and emergency alerts. AirNow describes its AQI NowCast as using shorter averaging periods when pollution changes rapidly, such as during a wildfire. That makes current readings useful during a changing smoke event, but it does not remove the need to check again as conditions evolve.
- Open the AirNow Fire and Smoke Map and check the reading for your location, not just the nearest city or a regional headline.
- Read the category and its health advice together. A number without its category can obscure the recommended action, especially near a boundary.
- Check the map again before outdoor activity and as conditions change. AirNow Version 4 documentation includes daily history and an indicator showing whether air quality is stable, improving or worsening.
- Follow local alerts as well. Public authorities may give emergency instructions for your area that should take precedence over general guidance.
Wildfire smoke can vary over the course of a day. A morning reading should not be treated as a promise about afternoon conditions, and a daily history is context rather than a substitute for the current reading.
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Who should take precautions earlier
AirNow identifies several groups who may be more affected by smoke or need to be especially careful:
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- People with lung disease, including asthma or COPD.
- People with heart disease.
- Children and teenagers.
- Older adults, generally those 65 and older.
- Pregnant people.
- People with greater exposure, including outdoor workers.
- People with limited access to ways to reduce exposure.
If you have asthma or another lung condition, follow your clinician’s directions and your existing action plan. Contact a healthcare professional if symptoms worsen. People with heart or lung disease should not wait for the AQI to reach the Unhealthy category before considering exposure reduction; the category-specific guidance for sensitive groups begins at 101.
How to make indoor air cleaner
When staying inside, aim for a room with filtered air and as few particle sources as practical. A portable air cleaner is designed to serve a room or area, so choose one sized for the space where you will spend time. Avoid ozone-generating models, and, when practical, run the cleaner continuously at its highest fan speed.
Choose and use a portable air cleaner
- Check that the unit is intended for the size of the room or area you plan to use.
- Confirm replacement filters are available and consider their replacement cost, not only the unit’s purchase price.
- Consider noise at the fan speed you will actually use; a unit that is too disruptive may be harder to run continuously.
- Avoid ozone-generating devices.
- During smoke, run the unit continuously at the highest fan speed when practical.
These are selection criteria, not a comparative product test. The key practical question is whether the cleaner can serve the room you occupy and whether you can keep it running and maintain its filter.
Use central heating or cooling equipment carefully
If your home has central HVAC, AirNow advises using it to filter indoor air. Use a MERV-13-or-higher filter when appropriate for the system, choose suitable recirculation and fan settings, and close the fresh-air intake during smoke. Before changing a filter rating or setting, check that the filter’s physical dimensions and resistance are compatible with your equipment and follow the manufacturer’s guidance. A rating alone does not establish that a filter will work safely in every system.
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Reduce pollution made indoors
Smoke is not the only source of airborne particles. During a smoky period, avoid indoor activities that add pollution where possible, including frying, sweeping, vacuuming, and using gas, propane or wood-burning appliances. Keeping those sources down helps preserve the cleaner air you are trying to create.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to do if outdoor exposure is unavoidable
Reschedule strenuous exercise and outdoor tasks for a cleaner period if conditions improve. If you must work or travel outside, reduce the time exposed, take frequent breaks in cleaner indoor air, and use a properly fitting NIOSH-approved N95 respirator when appropriate. AirNow says N95 respirators can provide protection against wildfire smoke; cloth masks do not protect against it.
When choosing a respirator, focus on NIOSH approval, fit and appropriate use rather than appearance alone. A respirator that does not fit well cannot provide the intended protection. Follow the product’s instructions and applicable workplace requirements; outdoor workers should also follow their employer’s safety procedures and local guidance.
Balance smoke protection with heat safety
Keeping windows closed and spending time indoors can make a home too hot, particularly during a heat wave or when cooling is unavailable. A clean-air space must also be cool enough to remain safe. If your home becomes too hot, AirNow recommends seeking relief at a clean-air shelter, another air-conditioned building with good filtration, or with friends or family. Follow local emergency instructions when deciding where to go.
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Do not assume that staying in a hot room is the safer choice simply because outdoor air is smoky. If heat becomes unsafe, move to a cooler place where you can also reduce smoke exposure as much as possible.
Which air-quality scale should you use?
The ranges in this article are the U.S. AQI categories used in AirNow’s smoke guidance. AQI scales and public-health instructions can differ by country or jurisdiction. If you are outside the United States, use your local air-quality service and follow its category definitions rather than applying U.S. numbers as though they were universal.
AirNow’s advice here is grounded in U.S. EPA guidance, including the EPA’s June 2026 wildfire-smoke guide and factsheets, described by EPA as an interagency collaboration involving CDC, the U.S. Forest Service, California agencies and professional partners.
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