Northeastern Illinois does not attain national ambient air quality standards for certain pollutants. It is classified as a marginal non-attainment area for the 8-hour ozone standard, and a non-attainment area for the annual fine particulate matter (PM2.5) standard. The region must implement a transportation program which will help to reduce levels of these pollutants to national standards.
Nonattainment areas are designated by the US Environmental Protection Agency (US EPA) based, in part, on recommendations from the Illinois Environmental Protection Agency (IEPA). IEPA's recommendation follows US EPA guidelines for identifying nonattainment areas. This includes not just monitor data, but also emissions data, urbanization patterns, meteorology, and so on. Technical information on this process can be found on the IEPA website.
Nonattainment areas are established independent of metropolitan planning organization or metropolitan planning area boundaries. For example, the northeastern Illinois nonattainment area includes two counties in northwest Indiana, and a small area of southeast Wisconsin. The Northwestern Indiana Regional Planning Commission and Southeastern Wisconsin Regional Planning Commission handle conformity requirements for those two areas.
As part of the transportation planning and programming process, CMAP staff evaluates the impact of proposed transportation activities on the region's air quality. This evaluation, called a conformity analysis, is submitted to IEPA and US EPA for their review before a long-range regional transportation plan or Transportation Improvement Program (TIP) is approved. The conformity analysis must demonstrate that the emissions resulting from the plan or TIP meet the requirements of (i.e., "conform to") the regulations governing air quality.
Some individual transportation projects must be evaluated for local air quality impacts, commonly called a "hot spot analysis." Projects that are subject to hot spot analysis are called, "projects of air quality concern." They involve significant levels of diesel vehicle traffic, or are identified in a PM2.5 or PM10 State Implementation Plan as a localized air quality concern. Hot spot analysis is conducted by the agency implementing the project as part of the environmental assessment process.
Interagency consultation is required under the transportation conformity rule, as described in 40 CFR 51.402. In the northeastern Illinois region, these procedures are addressed through the Tier II Consultation process. Decisions made through this interagency consultation process guide the MPO in making conformity determinations.