Proposed Revision to NO2 NAAQS Could Pose Problems Under PSD

In the July 2009 issue of 4 The Record, ALL4 included a summary of U.S. EPA’s announcement concerning a proposed new short-term (1-hour) National Ambient Air Quality Standard (NAAQS) for nitrogen dioxide (NO2).  The proposed standard will likely range between 150 µg/m3 and 188 µg/m3.  Relative to the current annual NO2 standard, it may be difficult to demonstrate compliance with the 1-hour NO2 NAAQS as part of an air quality modeling evaluation for the Prevention of Significant Deterioration (PSD) program.  The 1-hour NAAQS will be affected by short-term, worst case dispersion conditions, as well as peak hourly NOx emission rates.   

To illustrate the challenges that facilities may face in demonstrating compliance with the proposed NO2 NAAQS, ALL4 performed an air quality modeling evaluation utilizing the AERMOD air dispersion model and emissions from three different types of industrial facilities.  The evaluations included a typical pulp and paper facility, a cement facility, and a coal-fired utility boiler.  The following components were included in the evaluations:

• Maximum hourly NOx emission rates that would be expected for these industry types were included for all NOx emitting units at the example facilities, as would be required in a PSD air quality modeling NAAQS demonstration.
• Typical industrial building downwash impacts were considered in the model.
• Terrain surrounding the example facilities includes both simple and complex terrain (i.e., terrain above stack heights).
• Representative meteorological conditions for a one year period were used to model each example facility.

The peak predicted 1-hour NO2 concentrations resulting from the 1-hour NOx emissions from the pulp and paper, cement, and coal-fired utility facilities were 688, 278, and 717 µg/m3, respectively, which are all greater than the proposed NAAQS.  These example facilities serve as an indicator that demonstrating compliance with the 1-hour NAAQS may be difficult, and will require a level of strategy and data refinement beyond that which has traditionally been required to evaluate NOx emissions.