EPA To Announce Secondary Standard for SOx and NOx

July 6, 2011

By court order, EPA is scheduled to announce by July 12, 2011, its proposed secondary standards for oxides of nitrogen and sulfur (NOx and SOx).

In contrast with primary standards, which are designed to protect human health, secondary standards are established to protect the environment. In the case of NOx and SOx, some of the primary targets include reduced aquatic and terrestrial acidification, and reduced nitrogen deposition on land and water.

The Clean Air Scientific Advisory Committee, EPA's independent advisor on technical issues, is concluding that the current standards, and their form, are inadequate to protect the environment. CASAC provides suggestions for what a new standard might be, offering possible insights into how the proposed standards may be crafted.

Among industry organizations that have an interest in these standards are:

Among sources for comment from an environmental advocacy perspective are:

After public comment and agency review of the proposed standards, a final rule is expected by the court-ordered date of March 20, 2012.

The proposed standards should be available at:

An updated primary standard for NOx was announced Jan. 22, 2010. For more information:

An updated primary standard for SO2 (which serves as an indicator for SOx) was announced June 2, 2010. For more information: