Skip to main content
U.S. flag

An official website of the United States government

Here’s how you know

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

HTTPS

Secure .gov websites use HTTPS
A lock (LockA locked padlock) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

    • Environmental Topics
    • Air
    • Bed Bugs
    • Chemicals and Toxics
    • Climate Change
    • Emergency Response
    • Environmental Information by Location
    • Environmental Justice
    • Greener Living
    • Health
    • Land, Waste, and Cleanup
    • Lead
    • Mold
    • Pesticides
    • Radon
    • Science Topics
    • Water Topics
    • A-Z Topic Index
    • Laws & Regulations
    • By Business Sector
    • By Topic
    • Compliance
    • Enforcement
    • Guidance
    • Laws and Executive Orders
    • Regulations
    • Report a Violation
    • Environmental Violations
    • Fraud, Waste or Abuse
    • About EPA
    • EPA Administrator
    • Organization Chart
    • Staff Directory
    • Planning, Budget, and Results
    • Jobs and Internships
    • Headquarters Offices
    • Regional Offices
    • Lab and Research Centers
Sulfur Dioxide (SO2) Pollution
Contact Us

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

Secondary National Ambient Air Quality Standards (NAAQS) for Nitrogen Dioxide (NO2) and Sulfur Dioxide (SO2)
Basic Information
Federal Register Citations
  • 77 FR 20218
  • 76 FR 46084
Docket Numbers
  • EPA-HQ-OAR-2007-1145

On this page:

  • Rule Summary
  • Rule History
  • Additional Resources

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

Fact Sheets and Additional Information Regarding the 2012 Decision to Retain the Secondary NAAQS for NO2 and SO2

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

  • Sulfur Dioxide Home
  • Sulfur Dioxide Basics
  • Setting & Reviewing SO2 Standards
  • Primary SO2 Standard Regulatory Actions
  • Secondary NO2 and SO2 Standard Regulatory Actions
  • Implementing SO2 Standards
  • Primary SO2 Standard Implementation Actions
  • SIP Checklist Guide
  • SIP Training Presentations and Assistance
  • SO2 Measurement and SIP Data
  • Other Criteria Air Pollutants
Contact Us to ask a question, provide feedback, or report a problem.
Last updated on April 5, 2022
United States Environmental Protection Agency

Discover.

  • Accessibility
  • Budget & Performance
  • Contracting
  • EPA www Web Snapshot
  • Grants
  • No FEAR Act Data
  • Plain Writing
  • Privacy
  • Privacy and Security Notice

Connect.

  • Data.gov
  • Inspector General
  • Jobs
  • Newsroom
  • Open Government
  • Regulations.gov
  • Subscribe
  • USA.gov
  • White House

Ask.

  • Contact EPA
  • EPA Disclaimers
  • Hotlines
  • FOIA Requests
  • Frequent Questions

Follow.