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This action will establish the initial air quality designations for all areas of the U.S. under the 2024 revised primary annual fine particle (PM2.5) National Ambient Air Quality Standards (NAAQS). Designations of attainment, nonattainment, or unclassifiable are based upon air quality monitoring data and other relevant information pertaining to the ambient air quality in the affected area, including whether an area contributes to a violation of the standard in a nearby area. The schedule and process for designations are contained in CAA section 107. Under the schedule, states and Tribes are to submit their designation recommendations no later than one year from promulgation of the revised NAAQS. The EPA is required to notify states and Tribes of any modifications that the EPA intends to make to their recommendations no later than 120 days prior to promulgation of the designations. The EPA must make the designations no later than two years from the February 2024 promulgation of the revised NAAQS. However, the EPA may extend that date by up to one year if the EPA has insufficient information to complete the designations in two years.