EPA Air Quality System daily AQI for every US county since 2015. Per county × day: 0-500 Air Quality Index, category (Good/Moderate/Unhealthy/Hazardous), defining pollutant (PM2.5/Ozone/NO2/SO2/CO/PM10), defining monitor site, count of reporting monitors. Joins with epa_pollutant_emissions on county FIPS to cross-reference daily air quality against annual stationary-source releases. Powers /county-aqi/{fips} canonical pages and daily-history queries.
The listed URL identifies a referenced source; it does not by itself document the ingestion endpoint. Referenced source URL: https://aqs.epa.gov/aqsweb/airdata/download_files.html. Source-specific terms apply. US federal employee-authored works are generally public domain under 17 USC 105; non-federal and third-party material retains source terms. Free or keyless access does not alter source terms. Metadata and normalization authored by MORVS (AI Analytics LLC) are CC0 only where expressly stated.