4 The record articles

New Secondary NAAQS Avoided For Now

Posted: May 4th, 2012

Author: All4 Staff 

U.S. EPA announced on March 20, 2012 that the secondary National Ambient Air Quality Standards (NAAQS) for nitrogen oxides (NOX) and sulfur oxides (SOX) will be retained as they currently exist:

  • NOX:  0.053 parts per million (ppm) on an annual average; and
  • SOX: 0.5 ppm on a three (3) hour average not to be exceeded more than once per year.

While primary NAAQS are promulgated to be directly protective of human health, secondary NAAQS are in place to protect the physical environment (e.g., vegetation).  A direct evaluation of the secondary NAAQS levels is required for a new permitting project that triggers Prevention of Significant Deterioration (PSD) major permitting requirements.  The recent promulgation of extremely stringent 1-hour primary NAAQS levels for NO2 and SO2 has shifted permitting focus away from the current secondary standards because compliance with the 1-hour primary NAAQS levels all but assures compliance with the secondary standards.  However, U.S. EPA was also considering the promulgation of “multi-pollutant” secondary NAAQS that would consider NOX and SOX concentrations together as a single standard.  Such a multi-pollutant rule could muddle permitting projects that are located near Federal Class I areas or that trigger permitting requirements for just NOX or SOX.  Multi-pollutant NOX and SOX standards could also serve as a precedent for other future ambient standards that are tied to atmospheric chemistry.  For now, U.S. EPA is not pursuing the multi-pollutant concept until more information can be gathered, and the 1-hour primary NAAQS levels will remain the primary drivers that dictate the feasibility and design of new projects.


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