Wildfire season generally runs through summer and fall, reaching its height between early July and early September. Beyond the direct damage, wildfires emit a blend of pollutants that may reach communities far from the source.

Wildfires are not the sole factor affecting outdoor air. The American Lung Association notes that power plants, vehicle emissions, climate shifts, other disasters and household or industrial energy use all contribute.

As of 2026 the ALA states that 44 percent of Americans, or 152.3 million people, live in counties with unhealthy air pollution levels.

Whether a nearby wildfire or a hazy day raises concerns, the US Air Quality Index, or AQI, offers a reliable way to check conditions. The index is often visible in weather apps and can trigger alerts when levels worsen. A dedicated site, AirNow, also provides detailed readings.

How the AQI measures air cleanliness

The EPA uses the AQI to report air conditions, and the scale runs from zero to 500 with color coding. On AirNow users can enter a zip code or city to view current and forecast values, the main pollutant and trends over 24 hours, seven days or 30 days.

Five pollutants regulated under the Clean Air Act are tracked: particle pollution, ozone, carbon monoxide, nitrogen dioxide and sulfur dioxide. Monitors across the country supply the data.

Cities above 350,000 residents must issue daily AQI reports. Ozone readings cover an eight-hour window while particle pollution uses a 24-hour average.

Six AQI categories explained

The index uses six colors to show risk levels, especially for ozone and particle pollution, the two pollutants that most affect health:

Green (0 to 50): Air quality is rated good with minimal health risk.

Yellow (51 to 100): Conditions are moderate, yet unusually sensitive individuals may notice effects.

Orange (101 to 150): Air can be unhealthy for sensitive groups though most people remain unaffected.

Red (151 to 200): Everyone may feel health impacts, with greater risk for sensitive groups.

Purple (201 to 300): Very unhealthy air raises the chance of problems for all residents.

Maroon (301 and higher): Hazardous levels mean everyone faces elevated risk.

Sensitive groups include those with heart or lung conditions, children, older adults, pregnant individuals and outdoor workers.

Steps to take during poor air quality

When the AQI reaches unhealthy ranges, follow these guidelines for ozone and particle pollution:

Yellow/moderate: Sensitive people should shorten outdoor time and skip vigorous activity. Stop and rest if coughing or breathing becomes difficult.

Orange/unhealthy for sensitive groups: Sensitive individuals should limit outdoor exertion and rest often. People with asthma should keep medication ready and follow their plan. Those with heart disease should call a doctor if shortness of breath or unusual fatigue occurs.

Red/unhealthy: Sensitive groups should avoid extended or intense outdoor activity and move plans indoors or to morning hours when ozone is lower. Everyone else should cut back on long outdoor efforts and consider morning timing.

Purple/very unhealthy: Sensitive groups must skip all outdoor activity. Seek air-conditioned spaces such as libraries or cooling centers during extreme heat.

Maroon/hazardous: All outdoor physical activity should be avoided. Move to air-conditioned indoor areas if heat is severe, and keep asthma medication accessible.

Face mask guidance

The ALA advises a properly fitted N95 or KN95 mask, not cloth or dust masks, for necessary outdoor time during poor air quality.

Improving air inside the home

Stay indoors with windows and doors closed. Use an air conditioner on recirculate mode during hot weather or visit public cooling centers. Avoid exhaust fans that vent outside.

Run a HEPA air purifier to reduce indoor pollutants. An air quality monitor can reveal whether indoor conditions are also a concern on high-AQI days.