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Sulfur Dioxide (SO2) Pollution

Secondary National Ambient Air Quality Standards (NAAQS) for Nitrogen Dioxide (NO2) and Sulfur Dioxide (SO2)

Rule Summary

In 2012, EPA decided to retain the current secondary national ambient air quality standard (NAAQS) for nitrogen dioxide (NO2) and sulfur dioxide (SO2). The secondary NO2 standard is an annual arithmetic mean of 53 ppb. The secondary SO2 standard is 500 ppb averaged over three hours, not to be exceeded more than once per year.

Rule History

04/03/2012 – Final Decision to Retain the Secondary NAAQS for NO2 and SO2

08/01/2011 – Proposed Decision to Retain the Secondary NAAQS for NO2 and SO2

Additional Resources

Fact Sheets and Additional Information Regarding the 2012 Decision to Retain the Secondary NAAQS for Nitrogen Dioxide (NO2) and Sulfur Dioxide (SO2)

Related Rules

2010 Primary National Ambient Air Quality Standards (NAAQS) for Sulfur Dioxide

2010 Primary National Ambient Air Quality Standards (NAAQS) for Nitrogen Dioxide

Scientific and Technical Documents Supporting the secondary NAAQS for SO2 and NO2