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AirHistory

Fact-Checking Policy

Last updated: June 2026

Every number on airhistory.org is meant to be traceable to a primary public record. This policy describes where our facts come from and how we check them before they are published.

Primary sources only

AirHistory builds its pages from the EPA Air Quality System (AQS). We do not republish second-hand summaries, scraped aggregations, or unattributed figures. Each page cites the dataset it draws from and links back to the source so any reader can verify a figure independently.

No invented numbers, no synthetic data

If a value is not present in the underlying public data, it does not appear on airhistory.org. We never fabricate statistics to fill a gap, and we never use model-generated estimates in place of reported figures. Where the data is genuinely missing, we say so rather than guess.

How figures are verified

  • Faithful processing. Data is fetched directly from the source, then transformed with documented, repeatable code — not hand-transcribed, where transcription errors would creep in.
  • Source-of-truth checks. Derived values (rankings, grades, composite scores) are computed from the source fields using stated formulas, so the inputs to any number remain auditable. 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.
  • Sanity bounds. Cross-cutting totals and outliers are checked against known ranges to catch unit errors, duplicates, and mis-scaled values before they reach a page.
  • Dating. Every dataset page carries a “Last updated” date so readers know how current a figure is.

The limits of what we check

AirHistory verifies that our pages faithfully represent the EPA Air Quality System (AQS). We do not independently audit the issuing agency’s collection methods, and we cannot guarantee the source itself is free of error. Source records may be incomplete, reported late, or restated after publication. We treat the primary record as authoritative and follow its corrections — always verify a consequential figure against the original source before acting on it.

Found an error?

Tell us and we will fix it. See our Corrections Policy for how to report an issue and what happens next, and our Editorial Policy for how our content is produced.