EPA has released a policy document titled “Policy Assessment for the Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur,” in which the agency suggests revising the secondary national ambient air quality standards (NAAQS) for oxides of nitrogen and sulfur.

The document proposes adding a standard based on maintaining an acid-neutralizing capacity in the environment in a range between 20 and 70 microequivalents per liter and recommends retaining the existing standards while adding the joint acidification standard. For sulfur dioxide, the current secondary standard is 0.5 parts per million (ppm), averaged over three hours. For nitrogen dioxide, the current secondary standard is 0.53 ppm, averaged annually. All areas of the country current meet those standards, according to EPA. The agency says it intends to issue a proposed rule for the new NAAQS in July 2011, with a final rule to follow by March 2012. The document is part of EPA’s periodic review of the air quality standards for the two pollutants. See 76 Fed. Reg. 4,694 (January 26, 2011).