Clarification on the Use of AERMOD Dispersion Modeling for Demonstrating Compliance with the NO2 National Ambient Air Quality Standard
Abstract
This memorandum clarifies the applicability of current guidance in the Guideline on Air Quality Models (40 CFR Part 51, Appendix W) for modeling NO2 impacts in accordance with the prevention of significant deterioration (PSD) permit requirements to demonstrate compliance with the new 1-hour NO2 standard and the existing annual standard. The guidance provided here supplements the June 28, 2010, and March 1, 2011, guidance memorandums by providing further clarification and guidance on the application of Appendix W for the 1-hour NO2 standard. The primary purpose of this memorandum was to provide an assessment of the appropriateness of the new ARM2 NOx speciation method and to provide guidance on its application and acceptance as an alternative Tier 2 modeling approach under Appendix W. A number of other NO2-related modeling issues for regulatory purposes with the AERMOD air quality model were also addressed.