An air quality alert is an official notice that the air in your area contains pollutants at levels that may be harmful to your health. It is issued by government agencies — the Environmental Protection Agency at the national level, and state or local air quality agencies — when pollution reaches certain thresholds. The alert usually includes the main pollutant of concern, the affected area, and how long the condition is expected to last. What you do about it depends on your health, your age, and how long you plan to be outside.
What Is an Air Quality Alert and What Triggers One?
An air quality alert is triggered when measured pollution levels reach thresholds set by the EPA. These thresholds are based on the Clean Air Act, which requires the agency to set National Ambient Air Quality Standards for six common pollutants.
Those six pollutants are:
- Ground-level ozone — formed when sunlight reacts with emissions from vehicles, industry, and other sources
- Particulate matter (PM2.5 and PM10) — tiny particles from smoke, dust, vehicle exhaust, and industrial processes
- Carbon monoxide — mostly from vehicle exhaust
- Sulfur dioxide — from burning fossil fuels, especially coal
- Nitrogen dioxide — from vehicles and power plants
- Lead — from industrial sources and older paint
When monitors detect one or more of these pollutants at or above the standard, the local agency issues an alert. The alert may last hours or days depending on weather patterns and pollution sources.
Ground-level ozone alerts are most common on hot, sunny days with little wind. Particulate matter alerts often happen during wildfires, dust storms, or periods of stagnant air in winter. The type of alert tells you what you are breathing and how to respond.
How Do You Read the Air Quality Index?
The Air Quality Index, or AQI, is a color-coded scale that runs from 0 to 500. It translates pollutant concentrations into a single number so the public can quickly understand the health risk.
Here is how the categories break down:
| AQI Range | Category | Color | Meaning |
|---|---|---|---|
| 0–50 | Good | Green | Air quality is satisfactory |
| 51–100 | Moderate | Yellow | Acceptable, but some pollutants may concern sensitive people |
| 101–150 | Unhealthy for Sensitive Groups | Orange | Sensitive groups may feel effects |
| 151–200 | Unhealthy | Red | Everyone may begin to feel effects |
| 201–300 | Very Unhealthy | Purple | Health alert; everyone at greater risk |
| 301–500 | Hazardous | Maroon | Emergency conditions |
An air quality alert is typically issued when the AQI is forecast to reach 101 or higher — the “Unhealthy for Sensitive Groups” level. Some agencies issue alerts at lower levels depending on local conditions and the specific pollutant.
One thing many people miss: the AQI is not a measure of a single pollutant. It reflects whichever pollutant is highest at that moment. So an AQI of 120 could be driven by ozone on a summer afternoon or by PM2.5 from wildfire smoke. The health implications differ.
Who Is Most at Risk During an Air Quality Alert?
Some people face higher risk from polluted air than others. The EPA and the Centers for Disease Control and Prevention identify these groups as most vulnerable:
- People with asthma or other chronic lung conditions
- People with heart disease
- Older adults
- Children and teenagers, whose lungs are still developing
- Pregnant women
- People who work or exercise outdoors
For these groups, even short exposure to elevated pollution can trigger symptoms. Asthma attacks, chest tightness, coughing, and shortness of breath are common responses. People with heart conditions may experience chest pain, palpitations, or fatigue.
Children breathe more air per pound of body weight than adults and their airways are narrower. That combination makes them more susceptible to pollution-related irritation and inflammation.
If you are in a sensitive group, an air quality alert is a signal to adjust your day. It is not a reason to panic, but it is a reason to pay attention.
What Should You Do When an Air Quality Alert Is Issued?
The right response depends on the AQI level, your health status, and how long you plan to be outside. Here are the general steps public health agencies recommend.
Check the current AQI and forecast. Use AirNow.gov or your local air quality agency’s website or app. Conditions can change quickly, especially during wildfire season.
Limit outdoor exertion. Exercise makes you breathe faster and deeper, pulling more pollution into your lungs. On orange or red alert days, move workouts indoors or postpone them. This matters most for sensitive groups, but everyone benefits from reducing heavy outdoor activity when the AQI is high.
Keep windows and doors closed. If you have air conditioning, run it with the fresh-air intake closed and the filter clean. If you do not have air conditioning and it is hot outside, seek a cooling center or public building with filtered air.
Use a portable air cleaner if you have one. Units with HEPA filters can reduce indoor particulate levels. The evidence for portable air cleaners is strongest for particulate matter, not for gases like ozone.
Avoid other sources of indoor pollution. Do not burn candles, use a fireplace, or run a gas stove without ventilation. Vacuuming can stir up particles — if you must vacuum, use a HEPA-filter vacuum.
Wear a mask if you must be outside. A well-fitting N95 or KN95 respirator can reduce inhalation of fine particles. Note that cloth masks and surgical masks are not designed to filter PM2.5. Masks offer little protection against ozone or other gases.
Follow medication plans. If you have asthma or another lung condition, keep your rescue inhaler with you and follow your healthcare provider’s instructions. Do not change your medication routine without talking to your doctor.
Do Air Quality Alerts Actually Protect Your Health?
The short answer is yes — alerts are designed to give people time to reduce exposure. But the evidence on how well they work in practice is more nuanced than you might expect.
Research consistently shows that short-term exposure to elevated PM2.5 and ozone is associated with increased emergency room visits for asthma and cardiovascular events. That link is well established. What is less clear is how consistently people change their behavior in response to alerts.
Some studies suggest that awareness of air quality alerts is lower than public health agencies assume. People who are not in sensitive groups may ignore alerts entirely. Others may not know what specific actions to take.
The alerts themselves do not clean the air. They give you information. What you do with that information is what affects your exposure. If you stay indoors with filtered air on a red alert day, you reduce your exposure. If you go for a run, you do not.
How Can You Reduce Your Exposure Long-Term?
Air quality alerts are short-term events, but the underlying pollution is often a long-term issue. Here are steps that can help over time.
- Support local air quality monitoring and clean air policies
- Reduce your own contributions — drive less, avoid burning wood or trash
- Use high-efficiency filters in your home HVAC system
- Seal gaps around windows and doors if you live in a high-pollution area
- Check the AQI before planning outdoor activities, especially in summer
If you live in an area with frequent alerts — parts of California, the Southwest, or regions downwind of industrial sources — consider making indoor air filtration a permanent part of your home setup. The EPA has published guidance on choosing and using air cleaners.
For people with asthma or heart disease, talk with your healthcare provider about an action plan for high-pollution days. This is not a reason to live in fear. It is a reason to have a plan.
Frequently Asked Questions
What does an air quality alert mean?
An air quality alert means pollution levels in your area are high enough to potentially harm health, especially for sensitive groups. The alert tells you which pollutant is elevated and how long the condition may last.
At what AQI level should I stay indoors?
There is no single threshold that applies to everyone. The EPA recommends that sensitive groups reduce outdoor exertion when the AQI reaches 101 or higher, and everyone should consider limiting outdoor activity when the AQI exceeds 150.
Do masks help during an air quality alert?
A well-fitting N95 or KN95 respirator can reduce your exposure to fine particles like PM2.5. Cloth and surgical masks are not designed to filter these particles, and masks offer little protection against gases such as ozone.
How long do air quality alerts usually last?
Alerts can last from a few hours to several days, depending on weather and pollution sources. Wildfire-related alerts may persist until the fire is contained or winds shift.
