Based on its review of the air quality criteria for ozone (O<INF>3</INF>) and related photochemical oxidants and national ambient air quality standards (NAAQS) for O<INF>3</INF>, EPA is making revisions to the primary and secondary NAAQS for O<INF>3</INF> to provide requisite protection of public health and welfare, respectively. With regard to the primary standard for O<INF>3</INF>, EPA is revising the level of the 8-hour standard to 0.075 parts per million (ppm), expressed to three decimal places. With regard to the secondary standard for O<INF>3</INF>, EPA is revising the current 8- hour standard by making it identical to the revised primary standard. EPA is also making conforming changes to the Air Quality Index (AQI) for O<INF>3</INF>, setting an AQI value of 100 equal to 0.075 ppm, 8- hour average, and making proportional changes to the AQI values of 50, 150 and 200.