NOx/SOx Secondary NAAQS

More on the NOx/SOx Secondary NAAQS

Oxides of sulfur (SOx) and oxides of nitrogen (NOx) are criteria pollutants under the national ambient air quality standards (NAAQS) of the Clean Air Act. Primary (i.e. health-based) NAAQS for SOx and NOx were set recently.

However, near the end of October 2009, the DC Circuit Ct granted EPA’s request to modify its schedule for review of the secondary (i.e. based on environmental effects) NAAQS for these pollutants. EPA’s goal in requesting more time was to facilitate its ability to set an “ecologically relevant” NAAQS for nitrogen and sulfur loading using an indicator that would not specify air quality but environmental impact levels.

One of EPA’s targets in this effort is to regulate “reactive nitrogen,” including ammonia and ammonium, even though it does not have the authority to do so given the fact that the chemical formula for ammonia is NH3 and is not an oxide of anything. Similarly, the chemical formula for ammonium is NH4.

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