Data sources & attribution

Every number on WildfireWindow comes from one of the five public feeds below. This page states what each one is, how often it updates, what it is good for, and where it falls down — because a source you cannot see the limits of is not really attributed.

AirNow — U.S. EPA and NOAA

What it is: the official U.S. air-quality reporting system, aggregating regulatory-grade monitors run by state, local and tribal agencies. What we take: current observations and next-day forecasts by latitude/longitude. Cadence: observations are hourly; we cache them for 10 minutes and forecasts for 60. Why it is our display truth: AirNow computes the official AQI. We never show a self-computed value that disagrees with it for the same monitor.

Limitations: coverage is a monitor network, not a grid. Rural areas can be tens of miles from the nearest instrument, and a reported value is for a reporting area, not your street. Observations are hourly, so during a fast-moving plume the most recent published figure can lag reality. airnow.gov

OpenAQ

What it is: an open aggregator of air-quality measurements from around the world. What we take: raw pollutant concentrations, used for redundancy where AirNow is thin. Licence: CC BY 4.0. Limitations: it aggregates sources of varying quality, and a station appearing in OpenAQ is not necessarily a regulatory-grade instrument. Where OpenAQ and AirNow disagree for a U.S. location, AirNow wins. openaq.org

NOAA HMS — Hazard Mapping System

What it is: smoke plume polygons drawn by NOAA analysts from satellite imagery, classified light, medium or heavy. Cadence: updated through the day, with a manual analysis step. Limitations: these are overhead plumes. A heavy polygon over your city means smoke in the air column, which is not the same as smoke at ground level — the two decouple regularly, and this is the single most misread product in wildfire reporting. Ground truth is the monitor reading, not the polygon. NOAA OSPO

NASA FIRMS — active fire detections

What it is: thermal anomaly detections from the VIIRS instrument at roughly 375 m resolution. Cadence: per satellite overpass, a few times daily. Limitations: a detection is a hot pixel, not a mapped fire perimeter — one incident produces many detections, and cloud cover hides fires entirely between passes. Agricultural burns, flares and industrial heat sources also register. Detections are not authoritative for incident status; InciWeb is. We acknowledge the use of data from NASA's Fire Information for Resource Management System (FIRMS), part of NASA's Earth Science Data and Information System (ESDIS). firms.modaps.eosdis.nasa.gov

National Weather Service — active alerts

What it is: official watches, warnings and advisories, filtered by us to air-quality events. Cadence: as issued. Limitations: alerts are issued by local forecast offices on their own thresholds, so the boundary between an alerted and an un-alerted county is administrative, not atmospheric. No alert does not mean clean air. weather.gov

How they combine

The AQI you see is AirNow's for U.S. monitors, computed on the 2024 EPA breakpoints with the NowCast method — see how we calculate AQI. Fire and smoke layers are context around that number, never a substitute for it. When a source is unreachable the affected element says so explicitly rather than falling back to a stale value.

Last reviewed 2026-07-15.