This rule establishes initial air quality designations for certain areas in the United States, including areas of Indian country, for the 2015 primary and secondary national ambient air quality standards (NAAQS) for ozone. On November 6, 2017, the Environmental Protection Agency (EPA) designated about 85 percent of the country as attainment/unclassifiable and three counties as unclassifiable. In this action, the EPA is designating all remaining areas, except for eight counties in the San Antonio, Texas metropolitan area. Areas are being designated as either nonattainment, attainment/unclassifiable, or unclassifiable. Areas designated as nonattainment are also being classified by operation of law according to the severity of their air quality problems. The classification categories are Marginal, Moderate, Serious, Severe, and Extreme. In addition, five nonattainment areas in California are being voluntarily reclassified to a higher classification.