Area Designations for the 2024 Revised Secondary Annual Sulfur Dioxide National Ambient Air Quality Standard

This memorandum provides information on the schedule and process for initially designating areas for the 2024 Revised Secondary Annual Sulfur Dioxide (SO₂) National Ambient Air Quality Standard (NAAQS). In addition, this memorandum identifies important factors that the EPA intends to evaluate in making area designations and nonattainment area boundary decisions for this standard. 

• Initial Area Designations for the 2024 Revised Secondary Annual Sulfur Dioxide National Ambient Air Quality Standard (Revised January 16, 2025) (pdf) (1.26 MB)