Mr. Karl Brooks Regional Administrator U.S. EPA, Region VII 11201 Renner Boulevard Lenexa, KS 66219 Dear Mr. Brooks: This is inresponse to your August 19, 2014 letter regarding designations for the 2012 annual fine particulate matter (PM2 .5) National Ambient Air Quality Standard (NAAQS) of 12 micrograms per cubic meter (μg!m\ The letter states the U.S. Environmental Protection Agency (EPA) intends to designate the City ofSt. Louis and St. Louis, St. Charles, Franklin, and Jefferson Counties as "unclassifiable" andthe rest ofthe state "attainment/unclassifiable." We are concerned that an "unclassifiable" status may leave the St. Louis area open to a future nonattainment area designation when the issues with Illinois' PM2.s monitoring data are resolved. In ourDecember 10, 2013 submission, we recommended the entire State ofMissouri be designated "attainment/unclassifiable" for the 2012 annual PM2.s NAAQS. Ourrecommendation considered that all Missouri monitors were in compliance with this standard based on 2010-2012 ambient monitoring data. It also relied on our technical evaluation ofmonitoring, emissions, and meteorological data demonstrating that Illinois sources, not Missouri sources, were the primary contributors to violating monitors located onthe Illinois side ofthe St. Louis area. We stand by our recommendationthat the entire State ofMissouri be designated "attainment/unclassifiable" for the 2012 annual PM2 .5 NAAQS. All Missouri monitors continue to be in compliance ofthis standard based on 2011-2013 data and annual PM2 .5 design values are trending downward. Though quality-assurance issues preclude the use ofIllinois PM2 .5 monitoring data to determine a violation ofthe NAAQS, the general conclusions from our analysis still stand. Our evaluation ofmeteorological patterns and general trends data onhigh and low PM2.s days support the conclusion that localized sources in Illinois are the primary contributors to the monitors ofconcern onthe Illinois side ofthe St. Louis area. We also have comments on a statement in EPA's Illinois Technical Support Document (TSD) indicating that ifthe Illinois portion ofthe St. Louis area is determined to be violating the 2012 PM2.s NAAQS, EPA would likely find the contributing area to be the same as the area contributing to violations ofthe previous 1997 PM2 .5 NAAQS of 15 μg/m3• The 1997 PM2 .5 standard boundary designation process is not comparable to the current process because one of Missouri's monitors in the St. Louis urban core was in violation ofthat standard at the time. 

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### Mr. Karl Brooks Page Two Consequently, our designation effort for the 1997 standard focused on evaluating Missouri sources' contribution to the violating Missouri monitor and recommending an appropriate nonattainment area boundary. The Air Program cautions against applying conclusions from the previous PM2.5 

### designation effort to the current process because Missouri does not have any monitors violating the 2012 PM2.5 

### NAAQS. We appreciate the valuable assistance EPA Region 7 staffhas provided thus far and look forward to continuing to work with you and your staffthroughout the rest ofthe process. Ifyou have any questions regarding this letter, please contact Ms. Wendy Vit, Air Quality Planning Section Chief, Air Pollution Control Program at P.O. Box 176, Jefferson City, MO 65102 or by telephone at (573) 751-4817. Thank you for your consideration. Sincerely, AIR POLLUTION CONTROL PROGRAM

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cc: Missouri Air Conservation Commission File# 2012-PM-l Annual Designation Recommendation

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