This dataset represents the historical Air Quality Control Regions (AQCRs) established under the Clean Air Act. AQCRs were originally designated by the U.S. Environmental Protection Agency (EPA) to group contiguous areas with similar air pollution characteristics for air quality planning and management purposes. The 1970 Clean Air Act directed the EPA to establish AQCRs to support implementation of the National Ambient Air Quality Standards (NAAQS). States were required to develop State Implementation Plans (SIPs) describing how they would monitor, control, and reduce criteria pollutants within each designated AQCR. Historically, AQCRs were classified as either attainment areas, where air quality met federal standards, or nonattainment areas, where standards were not met.

Although the EPA now designates attainment and nonattainment status primarily at the county or sub-county level, AQCRs remain an important geographic framework for state air quality planning, emissions inventory development, and air pollution transport modeling.

Data Development

No official GIS boundary dataset exists for the original AQCR designations because the AQCR program predates modern GIS technology. This GIS layer was developed in 2026 using official AQCR definitions published in Title 40, Code of Federal Regulations (CFR), Part 81.  AQCR boundaries were delineated by interpreting regulatory descriptions and using county and administrative boundary datasets, primarily contemporary but historical when available.

Users should consult the Electronic Code of Federal Regulations (eCFR) for authoritative area definitions:

https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-81

Data Limitations

EPA has made every effort to ensure the accuracy of this GIS boundary layer. However, because the dataset was reconstructed from regulatory descriptions using mostly modern boundary files, some AQCR boundaries may not precisely reflect the original geographic extents established at the time of designation. Changes to county boundaries, administrative areas, or source reference datasets may result in minor differences between this GIS representation and the original AQCR definitions.

This layer is intended to support mapping, planning, analysis, and historical reference. For regulatory, legal, or official purposes, users should rely on the AQCR descriptions contained in 40 CFR Part 81 as published in the eCFR.

Source

Air Quality Control Region definitions contained in Title 40, Code of Federal Regulations (CFR), Part 81: https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-81