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This action will establish the initial air quality designations for all areas of the United States 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 is contained in CAA section 107. Under the schedule, states and Tribes are to submit their designation recommendations no later than 1 year from promulgation of the revised NAAQS. EPA is required to notify states and Tribes of any modifications that EPA intends to make to their recommendations no later than 120 days prior to promulgation of the designations. EPA must make the designations no later than 2 years from the February 2024 promulgation of the revised NAAQS. However, EPA may extend that date by up to 1 year if EPA has insufficient information to complete the designations in 2 years.