On May 27, 2008, the 8-hour ozone standard changed from 0.084 ppm to 0.075 ppm. This change triggered an attainment designation process by which Missouri submitted recommendations to EPA outlining proposed area boundaries and classifications. Missouri recommended that counties in the Kansas City and St. Louis metropolitan areas, as well as Ste. Genevieve and Perry counties south of St. Louis, be designated nonattainment areas under the new 0.075 ppm standard.
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