This Regulatory Impact Analysis (RIA) provides illustrative estimates of the incremental costs and monetized human health benefits of attaining a revised short‐term Sulfur Dioxide (SO2) National Ambient Air Quality Standard (NAAQS) within the current monitoring network of 488 SO2 monitors. Because this analysis only considers counties with an SO2 monitor, the possibility exists that there may be many more potential nonattainment areas than have been analyzed in this RIA.

This RIA chiefly serves two purposes. First, it provides the public with an estimate of the costs and benefits of attaining a new SO2 NAAQS. Second, it fulfills the requirements of Executive Order 12866 and the guidelines of OMB Circular A‐4. 1 These documents present guidelines for EPA to assess the benefits and costs of the selected regulatory option, as well as one less stringent and one more stringent option. As stated above, we chose 50 ppb as an analytic lower bound, and 150 ppb as an upper bound. (We chose 50 ppb as an analytic lower bound before decisions were made about either the proposed range, or the range for requesting public comment.)

• Regulatory Impact Analysis (RIA) for the Proposed Revision to the Sulfur Dioxide (SO2) National Ambient Air Quality Standards (NAAQS) (PDF)(168 pp, 3 MB, November 16, 2009)