Under the Federal Clean Air Act, if a state an area 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. Hall County is a part of a 20-county area that has been designated as nonattainment for the 8-hour Ozone standard, and part of a 22-county area designated as nonattainment for the Fine Particle Particulate Matter (PM 2.5) standard. Areas that are designated nonattainment or previously designated nonattainment for the 8-hour ozone and PM2.5 standards must show (through a process known as transportation conformity) that their transportation activities will not conflict with State air quality goals for that area.



Eventually, as part of the state’s SIP, the Georgia Environmental Protection Division (EPD) will 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. States do not have submit SIPs with MVEBs immediately after nonattainment designations so in the interim, conformance for GHMPO's LRTP and TIP to air quality standards is being shown by a comparison of future year emissions to a 2002 baseline of emissions.

Because Hall County is but a small portion of the overall nonattainment areas, the GHMPO coordinates 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 aligns its various review and approval schedules with those of the ARC whenever possible.



For more general information on the Clean Air Act and the air quality issue, click here to read the EPA’s 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" here.