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The United States Environmental Protection Agency (U.S. EPA) is implementing the national ambient air quality standards (NAAQS) for ozone.

Ground-level ozone is a gas that is formed by the reaction of volatile organic compounds and oxides of nitrogen in the atmosphere in the presence of sunlight. On October 1, 2015, the U.S EPA adopted a new, more stringent 8-hour ozone standard that is set at 0.070 parts per million (or 70 part per billion). The final rule for the 2015 8-hour ozone National Ambient Air Quality Standard (NAAQS) was published October 26, 2015.

On November 16, 2017, U.S. EPA established initial air quality designations for the 2015 ozone NAAQS. The U.S. EPA finalized attainment/unclassifiable designations for Texas without including nonattainment designations or a designation for the San Antonio area.

On July 17, 2018, the U.S. EPA signed a notice for the final designations of the 8 counties comprising the San Antonio area. The U.S. EPA is finalizing a marginal nonattainment designation for San Antonio (Bexar County), which becomes effective on September 24, 2018 (60 days from the publication of the final designation in the federal register on July 25, 2018). The surrounding counties of San Antonio (Atascosa, Bandera, Comal, Guadalupe, Kendall, Medina, and Wilson) will be designated as attainment or unclassifiable. With this action, EPA has completed the initial designations for the 2015 ozone NAAQS for all areas of Texas.