Alternative Demonstration Approach for the 2024 Secondary Sulfur Dioxide National Ambient Air Quality Standard under the Prevention of Significant Deterioration Program
On December 10, 2024, the Environmental Protection Agency (EPA) revised the secondary sulfur dioxide (SO2) National Ambient Air Quality Standard (NAAQS) from a 3-hour average standard to an annual average standard set at 10 parts per billion (ppb), averaged over 3 consecutive years. Under the Prevention of Significant Deterioration (PSD) program, any permit issued on and after the effective date of the new secondary annual SO2 NAAQS for construction at a stationary source that increases SO2 emissions in significant amounts will need to be supported by a demonstration that the increased emissions from the proposed major stationary source or major modification will not cause or contribute to violation of that standard. The EPA’s regulations specify air quality models and requirements for applying such models to make this demonstration for the pollutants subject to NAAQS. The EPA has also provided recommendations in regulations and guidance memoranda that permit applicants and reviewing authorities may follow to make this showing. Permit applicants and reviewing authorities can use these existing resources to make the required showing for the new secondary annual SO2 NAAQS, but these parties may need to take additional steps and collect additional data to do so in certain circumstances. To help facilitate implementation of the new secondary annual SO2 NAAQS under the PSD program without these additional burdens, the EPA developed a streamlined, alternative PSD demonstration approach.