About AirHistory
Clean air, measured at your doorstep.
What we do
AirHistory tracks decades of U.S. air-quality monitor readings so residents, journalists, and researchers can see how clean the air actually is where they live, work, and send their kids to school.
We focus on U.S. air quality and pollution monitoring. Every page on airhistory.org is built from the EPA Air Quality System (AQS), cited and linkable so readers can trace any number back to its source.
Who runs this
AirHistory is built and maintained by the AirHistory Team. We're a small group working on making public U.S. air quality and pollution monitoring data easier for non-specialists to read. If you have a correction, a data tip, or a question about how a number was derived, the contact email below reaches us directly.
Who this is for
AirHistory is built for parents, public-health researchers, local reporters, and anyone with asthma or allergies who wants an honest look at their air.
Why this exists
Public data on U.S. air quality and pollution monitoring is technically free, but practically locked behind file formats, acronyms, and paywalled dashboards. AirHistoryexists to close that gap: take the raw federal and public-sector data, and turn it into pages a normal person can read in thirty seconds.
How we work
- Primary source only. We pull from the EPA Air Quality System (AQS) and cite the exact dataset and version on every page.
- No invented numbers. If a figure is not in the underlying public data, it does not appear on airhistory.org. We never generate synthetic statistics to fill gaps.
- Methodology, in plain English. We aggregate EPA AQS monitor-by-monitor readings into annual averages for ozone, PM2.5, PM10, NO2, SO2, CO, and lead, then compute county- and state-level trends over the full reporting history. Pages surface both the raw EPA AQI and plain-English day counts in each AQI bucket so readers can skip the jargon.
- Refreshed on a schedule. Refreshed from the EPA AQS API roughly every four months, tracking the cadence at which EPA closes out each reporting quarter.
- Corrections welcome. Readers flag issues all the time. When the source fixes a record, AirHistory follows.
Known limitations
AQS data lags real-world readings by several months because states run quality checks before submitting monitor data to EPA, and not every county has a monitor — rural counties are often represented by the closest upwind monitor rather than a local one.
Why decades of EPA AQS data deserves a dedicated home
The U.S. Environmental Protection Agency maintains the Air Quality System (AQS), the federal repository of every air-pollution monitor reading collected by state and tribal agencies since the 1980s. AQS captures hourly and daily readings for ozone, fine particulate matter (PM2.5), coarse particulate (PM10), nitrogen dioxide, sulfur dioxide, carbon monoxide, and lead across thousands of monitors nationwide. The dataset is comprehensive, but its presentation is built for atmospheric scientists rather than for residents trying to understand the air at their own address.
AirHistory closes that gap. Every county page consolidates the monitors in that county into a single readable picture: annual-average PM2.5 and ozone, day counts in each Air Quality Index bucket, the multi-decade trend line, and an honest note when the county has thin monitor coverage or relies on a regional monitor several miles away. The data is the same EPA data that was always available; what the site contributes is the structure that makes the data answer the questions a homeowner, parent, or local reporter actually has.
How the pipeline pulls EPA data
The pipeline runs against the EPA AQS API on a quarterly cadence aligned to EPA’s own quality-assurance release calendar. Each pull touches every monitor in every state with reporting activity in the most recent quarter, computes the annual rolling averages and AQI day counts, and merges the result into the county-level pages.
A practical detail: state and tribal air-quality agencies submit data to EPA on a delay, typically three to six months after the readings are taken, so that on-the-ground errors can be cleaned up before the data hits the federal record. AirHistory always shows the as-of date for the most recent monitor reading, so a reader can see how current the data actually is for any given county.
Where AQS data has limits worth knowing
Three things to know. First, monitor coverage is uneven. Counties with major metros have dense monitor networks; rural counties often have only one or two monitors, or none at all. Pages for under-monitored counties flag this explicitly and use the nearest upwind monitor as a regional proxy.
Second, AQS captures regulated pollutants only. Wildfire-smoke episodes show up in the PM2.5 readings but the underlying source is not always attributable; haze events from agricultural burning or distant fires can produce alarming-looking PM2.5 readings that are very different in source from urban combustion-related particulate.
Third, AQS lags real time. For real-time AQI, EPA runs the AirNow program separately. AirHistory is designed for the historical-trend question, not for what is the AQI right now; for that, AirNow is the better reference and we link to it from every county page where applicable.
Independence
AirHistory is an independent publication. We are not funded, owned, or directed by any of the agencies, companies, or organizations that appear in our data. Hosting is paid for by advertising — see our Privacy Policy for details — and we do not take paid placements, sponsored rankings, or "remove-my-entry" fees.
History
AirHistory launched in 2025 as part of a small portfolio of independent public-data sites. It has been maintained and updated continuously since.
Contact
Tips, corrections, data-partnership questions, and press inquiries: hello@airhistory.org. More options on our contact page.