More Thoughts on SO2 NAAQS

The public comment period for U.S. EPA’s draft dispersion modeling guidance for the 1-hour sulfur dioxide (SO2) National Ambient Air Quality Standard (NAAQS) is open until December 2, 2011. Since the guidance will lead to a significant and complicated undertaking in performing dispersion modeling for a wide range of facilities, it is anticipated that many states and industrial facilities will submit comments, many of which will focus on determining which facilities should be included in the modeling 

demonstration. U.S. EPA’s timing on processing comments and submitting a final guidance document needs to allow for the preparation and state submittal of dispersion modeling by June 2013. Most state agencies are still digesting the guidance and

preparing comments, and many are awaiting final guidance before formalizing which facilities will be modeled and how the modeling will look. ALL4 has been involved with strategic modeling in preparation for the NAAQS implementation process. Ambient air

boundaries (the distance between modeled sources and receptors), building downwash,

and topography have all been observed to result in substantial differences in modeled concentrations when comparing facilities against one another (specific facilities will all have a unique combination of factors driving modeled concentrations).

Stay tuned for more updates in December and beyond on the status of U.S. EPA’s NAAQS modeling guidance.