4 The record articles

More Stringent SO2 NAAQS Finalized by U.S. EPA

Posted: June 27th, 2010

Author: All4 Staff 

U.S. EPA has announced the promulgation of a new 1-hour National Ambient Air Quality Standard (NAAQS) for sulfur dioxide (SO2). The new 1-hour NAAQS level is 75 parts per billion (ppb) measured as the three year average of the 99th percentile daily 1-hour maximum concentration. The new 1-hour NAAQS is a primary standard that replaces the existing annual and 24-hour SO2 NAAQS levels. The NAAQS will become effective in August 2010, at which point any future construction permit applications or applications that are still under state or U.S. EPA review for major new sources or major modifications will need to address compliance with the 1-hour NAAQS level (i.e., there is no “grandfathering” of existing construction permit applications). 

The new NAAQS is extremely restrictive due to the stringency of the NAAQS level and the short-term nature of the standard. The NAAQS level is lower than the recently promulgated 1-hour NO2 NAAQS (75 ppb versus 100 ppb) and is measured in a manner that will capture more peak concentrations (99th percentile versus 98th percentile). In areas that will be in attainment with the new SO2 NAAQS, the new standard will make demonstrating NAAQS compliance for Prevention of Significant Deterioration (PSD) construction permits and Title V renewals extremely difficult where required. Some areas will eventually be designated as nonattainment areas with respect to the new NAAQS, at which point Lowest Achievable Emission Rate (LAER) requirements that have not historically been addressed for SO2 will need to be implemented for major new sources or major modifications. Proactively planning for the impacts of the new NAAQS is critical (see ALL4’s May 2010 4 The Record article for guidance). 


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