In October, the US Environmental Protection Agency (USEPA) approved revisions of Missouri's State Implementation Plan (SIP) for the following standards: 2008 Ozone National Ambient Air Quality Standards (NAAQS), 2010 Sulfur Dioxide (SO2) NAAQS, 2010 Nitrogen Dioxide (NO2) NAAQS, and 2012 Annual Particulate Matter with aerodynamic diameter less than 2.5 microns (PM2.5) NAAQS. Due to adverse comments during the comment period, the USEPA is withdrawing its approval of the above-referenced revisions. Based on review of comments, it can be assumed that the ruling was withdrawn due to Missouri failing to address adequate interstate transport provisions, as required per Prong 1 and Prong 2 of The Clean Air Act Section 110(a)(D)(i)(l). Missouri will need to revise and resubmit SIP revisions to the USEPA for future approval.
The following links provide documentation on each of the withdrawn rulings, as well as a copy of the SIP revisions: PM2.5 Ruling, NOx Ruling, Ozone Ruling, SO2 Ruling. Be on the lookout for new SIP revisions, and how they may affect your area.