This rule establishes the initial air quality designations for certain areas in the United States (U.S.) for the 2010 primary sulfur dioxide (SO<INF>2</INF>) National Ambient Air Quality Standard (NAAQS). The Environmental Protection Agency (EPA) is designating the areas as either nonattainment, unclassifiable/attainment, or unclassifiable, based on whether the areas do not meet the NAAQS or contribute to a nearby area that does not meet the NAAQS; meet the NAAQS; or cannot be classified on the basis of available information as meeting or not meeting the NAAQS, respectively. The designations are based on the weight of evidence for each area, including available air quality monitoring data and air quality modeling. The Clean Air Act (CAA) directs areas designated nonattainment by this rule to undertake certain planning and pollution control activities to attain the SO<INF>2</INF> NAAQS as expeditiously as practicable. This is the second round of area designations for the 2010 SO<INF>2</INF> NAAQS.