The short answer
Read five things together: the AQI number, category, update time, reporting area, and primary pollutant. Then use the health guidance for that pollutant and the people involved. A number without its pollutant, place, and time can be incomplete or misleading.
Start here
- Confirm that the displayed place or reporting area is relevant to you.
- Check when the value was updated and whether it is current or forecast.
- Read both the AQI number and its category text.
- Identify the primary pollutant before choosing health or activity guidance.
What the AQI reports
The U.S. Air Quality Index converts measured pollutant concentrations to one scale for communicating outdoor air quality and health concern. Higher values mean greater pollution and greater health concern.
The overall reported AQI is the highest pollutant-specific index available for the reporting area and period. That pollutant is often called the primary or critical pollutant.
Read the display in this order
Check the city, ZIP code, reporting area, or monitor. A regional value is not a measurement at the home.
Find the update time. Do not use an old value as the current condition.
Current describes recently observed conditions. Forecast predicts later air quality. Neither substitutes for the other.
Read both. Color alone is not enough, especially when the information is heard or colors cannot be distinguished.
Find which pollutant produced the highest available index before choosing the applicable health guidance.
Current and forecast answer different questions
AirNow's current AQI uses NowCast calculations for ozone and particle pollution. It combines several recent monitor readings and gives more weight to recent hours when conditions are changing. It is current information, but it is not an instantaneous sensor at the home.
A forecast helps plan the day and may identify a better or worse period. Check the current value again before a long or strenuous activity when pollution is elevated or changing.
Do not call every particle reading smoke
Wildfire smoke is one source of PM2.5, but fine particles also come from vehicles, power generation, industrial processes, wood burning, and other combustion. An elevated PM2.5 AQI does not establish its cause by itself.
Use official fire, plume, local air-agency, or emergency information before labeling the condition wildfire smoke. A nearby fire also does not prove that the air at the home is currently unhealthy.
Use the result
- Open the health message for the category and primary pollutant.
- Check whether anyone involved is in that pollutant's sensitive groups.
- Decide whether to shorten, lighten, move, or reschedule outdoor activity.
- Check again if conditions, the activity, or official guidance changes.
What changes this answer
General guidance becomes a personal decision through these details.
Official monitor, map, forecast, temporary sensor, or lower-cost sensor, each with a different geographic basis.
Observation update, NowCast period, forecast period, and how quickly conditions are changing.
Ozone, particles, carbon monoxide, nitrogen dioxide, and sulfur dioxide do not have identical implications.
Sensitive groups, symptoms, work, activity intensity, and an individual care plan change what happens next.
Where this guidance stops
- Outdoor AQI does not measure indoor air quality.
- Monitor coverage varies, and an area may have no current value for some pollutants.
- This guide explains the reading. It does not diagnose whether symptoms were caused by air pollution.
Sources
Consequential guidance is checked against the linked source material.
- AirNow. AQI Basics. Checked September 4, 2026.
- AirNow. Using the Air Quality Index. Current, forecast, and NowCast guidance. Checked September 4, 2026.
- AirNow. Fire and Smoke Map Information. Checked August 28, 2026.
- U.S. Environmental Protection Agency. Communicating Air Quality Conditions: The Air Quality Index. Updated September 30, 2025. 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.