Data Sources & Limitations

AirNow (EPA)

Stage 1 uses data from AirNow, the U.S. Environmental Protection Agency's real-time air quality reporting system. AirNow aggregates data from thousands of federal, state, and local monitoring stations across the country.

How AQI is calculated

The Air Quality Index (AQI) is a standardized scale from 0 to 500, defined by the EPA. It measures concentrations of five major pollutants: ground-level ozone, particle pollution (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. The AQI value reported for a location is the highest value among all measured pollutants at that time.

What “Reporting Area” means

AirNow reports air quality for a reporting area — which may cover a city, county, or multi-county region — rather than your exact ZIP code or street address. If the nearest monitor is several miles away, conditions at your location may differ from what is shown. Highly localized sources of pollution (traffic, industry, wildfires close by) may not be reflected in the reported AQI.

Data freshness

AirNow monitoring stations typically update hourly. BreathCount caches responses for up to 1 hour to reduce API load. If a reading is more than 1 hour old, a stale data warning is displayed. For rapidly changing conditions (wildfire smoke, weather events), always check AirNow directly.

Known limitations

• AQI readings represent a monitoring station or reporting area, not your exact location.
• Data may be unavailable for rural ZIP codes or areas without nearby monitors.
• AirNow data does not capture hyper-local pollution events (e.g., a fire one block away).
• Forecasted and modeled data (when used) carry additional uncertainty compared to observed readings.
• BreathCount is for informational purposes only and is not medical advice. Consult a healthcare provider for guidance specific to your health condition.

Attribution

Air quality data is provided by AirNow (U.S. EPA). BreathCount is not affiliated with or endorsed by the EPA.