AirNow + wildfire smoke — when AQI is a real-time tool

Real-time vs. historical AirNow

Real-time AirNow updates AQI hourly from monitoring stations across the country. During smoke events, it's the source of truth for 'should I go outside?' decisions.

Historical AirNow goes back to 1997 for some sites. zipradar pulls 5-year averages for context — useful for 'is this normal?' comparisons.

What stations measure

EPA-certified Federal Reference / Equivalent Method (FRM/FEM) instruments. Highest accuracy.

EPA-coordinated Continuous PM monitors. Slightly less accurate but real-time.

PurpleAir community sensors (since 2020): not EPA-certified but increasingly integrated into AirNow's 'Fire and Smoke Map'. Higher coverage, lower per-sensor accuracy.

Wildfire smoke mode

When fires affect multiple states, EPA switches AirNow to 'Fire and Smoke Map' mode showing real-time PM2.5 from all source types.

This is when AQI 200+ readings become common. Sensitive groups should follow the AirNow alerts; everyone should reduce outdoor exposure.

Where AirNow leaves gaps

Rural areas often have no station within 50 miles. zipradar shows the distance to the nearest station so you know.

Localized pollution sources (a specific factory, a wood-stove neighborhood) can produce hyperlocal spikes invisible to AirNow.

Indoor air is not measured. If you have a HEPA purifier, it can keep your indoor AQI well below outdoor.