Air Quality

Federal Clean Air Act


Under the Federal Clean Air Act, if an area within a state fails to meet any of the National Ambient Air Quality Standards (NAAQS), the state must develop a State Implementation Plan (SIP) to demonstrate how pollution will be cleaned up. Until 2013, Hall County was a part of a 20-county area that was designated as nonattainment for the 8-hour ozone standard. Until 2016, Hall County was a part of a 22-county area designated as nonattainment for the Fine Particle Particulate Matter (PM 2.5) (PDF) standard. Areas that were designated nonattainment for the 8-hour ozone and PM2.5 standards must show (through a process known as transportation conformity) that their transportation activities would not conflict with State air quality goals for that area.
Cars going over a bridge on the highway with a 45 mph speed sign

Designated Maintenance Area


Hall County, subsequently, had been designated as part of a 20-county area, 8-hour ozone maintenance area. In addition, Hall County has been designated as part of a 22-county particulate matter 2.5 maintenance area. A maintenance area classification requires conformity to transportation budgets for 20 years once the region is designated as attainment. Because Hall County was but a small portion of the overall nonattainment areas, the GHMPO coordinated closely with the Atlanta Regional Commission (ARC) which functions as the Atlanta MPO and has the technical staff to carry out the modeling necessary to demonstrate air quality conformity for entire area. As part of this coordination, the GHMPO aligned its various review and approval schedules with those of the ARC whenever possible.

As of 2013, the Atlanta region demonstrated attainment to the 1997 ozone standard, which allowed Hall County to be removed from the nonattainment area. As of October 2016, the PM2.5 national ambient air quality standard has been revoked for the Atlanta maintenance area, Hall County included, meaning there is no longer a requirement to demonstrate transportation conformity to that particular standard. 
The Plan
As part of the state's SIP, the Georgia Environmental Protection Division (EPD) has set Motor Vehicle Emissions Budgets (MVEBs) for the designated nonattainment pollutants and their precursors. The GHMPO's Long Range Transportation Plan (LRTP) and Transportation Improvement Program (TIP) are evaluated in the context of these emissions budgets, and must be determined in conformance under the air quality standards.

The most recent version of the approved Conformity Determination Report (CDR) (PDF) includes both Atlanta region and Hall County projects.
A bridge over the water
More Information
For more general information on the Clean Air Act and the air quality issue, read the EPAs Plain English Guide to the Clean Air Act. Additionally, for more general information on transportation conformity, refer to "Transportation Conformity: A Basic Guide for State and Local Officials."