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The U.S. Environmental Protection Agency (EPA) Proposes to Retain NOx and SOx Secondary National Ambient Air Quality Standards (NAAQS)


On August 1, 2011, EPA published a proposed rule retaining the secondary NAAQS for oxides of nitrogen (NOx) and sulfur (SOx).  The secondary standards are intended to protect against damage to the environment from certain air pollutants.  As with many other standards, EPA was forced to promulgate this standard after being sued by an environmental group for its failure to review the standard within the statutory framework.

The current secondary standard is 0.053 ppm for NO2, averaged over one year, and 0.5 ppm for SO2, averaged over three hours.  While keeping these standards, EPA added an additional secondary standard, which is identical to the health-based primary standard set by the agency in 2010.  The secondary standard for NO2 is now 100 ppb averaged over one hour and 75 ppb averaged over one hour for SO2.  EPA stated that it has explored the possibility of developing a multi-pollutant standard to address deposition-related effects from these pollutants, but that it did not yet have enough data to set a new multi-pollutant standard.  EPA is planning a five year field pilot program to collect and analyze data designed to inform the next review of the NAAQS for NOx and SOx.  EPA expects to issue a final rule on these proposed secondary standards by March 2012 in accordance with a court imposed deadline.

To view a complete PDF of the Third Quarter 2011 issue of the Air Quality Letter, click HERE.


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