The U.S. Environmental Protection Agency compiles air quality monitoring data in the Air Quality System (AQS). Ambient air concentrations are measured at a national network of more than 4,000 monitoring stations and are reported by state, local, and tribal.
You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.- Air Quality System (AQS) Appendix B: Metadata (PDF)(2 pp, 103 K)