Secondary National Ambient Air Quality Standards (NAAQS) for Nitrogen Dioxide (NO2) and Sulfur Dioxide (SO2)
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Rule Summary
In 2012, EPA decided to retain the current secondary NAAQS for NO2 and 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
Related Rules
Primary National Ambient Air Quality Standard for Sulfur Dioxide
Primary National Ambient Air Quality Standards for Nitrogen Dioxide
Scientific and Technical Documents Supporting the secondary NAAQS for SO2 and NO2