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Air Quality

The Commission has long worked to address air management issues, with a specific focus on ensuring that Commission transportation plans and programs “conform” to air quality standards.

Air Quality Management

The Federal Clean Air Act (CAA) requires the U.S. Environmental Protection Agency (EPA) to set national ambient air quality standards (NAAQS) for six criteria pollutants considered harmful to public health and the environment. These pollutants include carbon monoxide, lead, nitrogen dioxide, particulate matter, ozone, and sulfur dioxide.


Nonattainment and Maintenance Areas

Areas not meeting the NAAQS for one or more of the criteria pollutants are designated as “nonattainment” areas by the EPA. Areas previously in nonattainment that subsequently meet the NAAQS are called “maintenance” areas.

Within Southeastern Wisconsin, the EPA has designated these nonattainment and maintenance areas.


State Implementation Plans

Federal law also requires states to prepare implementation plans for air quality (SIP) to identify how the NAAQS in nonattainment areas will ultimately be met. In Wisconsin, this is the responsibility of the Wisconsin Department of Natural Resources. The attainment demonstration included in the SIP takes into account many different emission source sectors.


Determining Conformity

In nonattainment and maintenance areas, the CAA requires that the fiscally constrained MPO plan and transportation improvement program (TIP) conform with the mobile source emissions budgets included in the SIP. The Commission, as the MPO for Southeastern Wisconsin, periodically prepares a conformity demonstration of the plan and TIP. Commission transportation planning models and the EPA MOVES model are used to produce estimates of mobile source emissions and demonstrate conformity.

This air quality assessment report documents the most recent conformity determination of the year 2050 fiscally constrained transportation system and regional transportation improvement program.


Air Quality Improvement

In recent years, the combination of local controls and offsets implemented in and outside the Region, along with national vehicle emissions control requirements, have resulted in a significant improvement in ambient air quality. Projections of future emissions indicate a continued decline in precursor emissions and improvement in air quality.