The Federal Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to set national ambient air quality standards (NAAQS) for six criteria pollutants (carbon monoxide, lead, nitrogen dioxide, particulate matter, ozone, and sulfur oxides) which are considered harmful to public health and the environment. Areas not meeting the NAAQS for one or more of the criteria pollutants are designated as “nonattainment” areas by the EPA. Within Southeastern Wisconsin, the EPA has designated a multi-state 2008 ozone nonattainment area which includes Kenosha County east of IH-94, and a single three-county PM2.5 maintenance area made up of Milwaukee, Racine, and Waukesha Counties. Areas designated as in nonattainment or maintenance of a criteria pollutant must demonstrate compliance with the NAAQS.
Federal law also requires that states prepare implementation plans for air quality (SIP) to identify how the NAAQS in the nonattainment area 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. SEWRPC becomes involved in the mobile source sector where the SIP provides emissions budgets for target future years. SEWRPC transportation planning models produce estimates of mobile source emissions. Federal law requires that in nonattainment and maintenance areas the planning agencies demonstrate that the mobile source emissions resulting from the modeling for transportation system activity in those target years “conform” to the budgets included in Wisconsin’s SIP. A report documenting the most recent conformity determination of the SEWRPC regional transportation plan and regional transportation improvement program may be found here. This conformity determination was made in July 2016. SEWRPC periodically updates that determination in accordance with Federal requirements.
Over the past decade, the combination of local controls and offsets implemented within and outside the Region, along with national vehicle emissions control requirements, have resulted in a significant improvement in ambient air quality within the Region as well as nationally, and projections of future emissions indicate a continued decline in precursor emissions and a continued improvement in air quality.