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Regulatory Issues FAQ

Where is the regulatory use of air quality models defined?

Visit the "Appendix W to Part 51 Guideline" on Air Quality Models at Appendix W for Federal regulations. Back to top of page.

Who determines the regulatory use of models?

Appendix W designates the U.S. EPA Regional Office as the arbiter of Federal regulatory use:  “The Regional Administrator has the authority to select models that are appropriate for use in a given situation.” (3.3.a). Back to top of page.

Is AERMOD-HPC suitable for regulatory use?

Appendix W defines the terminology of "preferred" and "alternate" model. As a clarification, on December 11, 2007, the U.S. EPA released a memorandum indicating that proprietary versions of EPA regulatory models cannot have the status of a "preferred" model (http://www.epa.gov/scram001/Clarification%20on%20Reg.%20Status%20of%20Prop.%20Versions%20of%20AERMOD.pdf). In this reading AERMOD-HPC falls under the official designation of an "alternate" model because it is proprietary.   Alternate models are still suitable for regulatory use, however, their use and acceptability is determined by U.S. EPA Regional Offices.  This is accomplished via modeling protocols or other formal communications concerning the modeling approach proposed for the project. The use of an alternate model requires equivalence demonstrations to show that it may be "treated for all practical purposes as the preferred model" (Appendix W, paragraph 3.2 2c).  HiCLAS1 is currently contacting EPA Regional Modelers to determine the scope of the model equivalence demonstration. Back to top of page.

Has AERMOD-HPC demonstrated equivalence to AERMOD?

AERMOD-HPC does not modify the underlying science of the model and equivalence testing is on-going at HiCLAS1 using a Model Equivalence Database (MED). The MED includes test cases provided by the U.S. EPA (where publicly available), by HiCLAS1 customers, and from our own work. This MED is applied to show that AERMOD-HPC gives equivalent results to those of U.S. EPA’s AERMOD. Details are available at the Model Equivalence Demonstration page (click MEDlist tab at left). These pages are updated as the MED is expanded. Back to top of page.

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Last modified:  04/15/2009