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Summary of Seattle-Tacoma Puget Sound Area 8-Hour Ozone 110(a)(1) Maintenance Plan


The Seattle-Tacoma Puget Sound Area was redesignated attainment for ozone on November 25, 1996.

Washington submitted an ozone maintenance plan on January 28, 1993, and EPA approved the plan on September 26, 1996 (61 FR 50438 (PDF)(6 pp, 189 K, About PDF)).

Washington submitted a second 10-year CO/ozone maintenance plan on December 17, 2003, and EPA announced its proposed approval of the plan on June 1, 2004 (69 FR 30847 (PDF)(6 pp, 164 K)).

On August 5, 2004, EPA approved the Central Puget Sound Area 2nd 10-year CO/ozone maintenance plan (69 FR 47365 (PDF)(2 pp, 143 K)).

On April 30, 2004 (69 FR 23858 (PDF)(95 pp, 537 K)), the EPA designated areas for the 1997 8-hour ozone standard and the Central Puget Sound area was designated attainment/unclassifiable. Subsequently, the EPA revoked the 1-hour ozone standard.

The EPA had also set forth requirements for antibacksliding purposes for areas that were designated attainment for the 1997 8-hour ozone standard if the area had previously been designated nonattainment for the 1-hour ozone standard. Areas like the Central Puget Sound area were required to submit a maintenance plan, under section 110(a)(1) of the Clean Air Act, to demonstrate the continued maintenance of the 1997 8-hour ozone standard for at least 10 years.

On January 10, 2008, the EPA received a section 110(a)(1) maintenance plan SIP submittal from Washington State to maintain the 1997 8-hour standard for ozone for the Central Puget Sound area which the EPA approved on May 2, 2014 (79 FR 25010 (PDF)(5 pp, 248 K)).


The plan relies on control strategies needed to assure attainment of the National Ambient Air Quality Standards (NAAQS) for ozone. The strategy focuses on vehicle Inspection and Maintenance Program in conjunction with the Federal Motor Vehicle Emissions Improvement Program.


  • WAC 173-422, Motor Vehicle Emission Inspection
  • PSCAA Regulation II

Contingency Measures

  • PSCAA Regulation I, Section 8.06, Outdoor Burning Ozone Contingency Measure
  • PSCAA Regulation II, Section 2.09, Oxygenated Gasoline Carbon Monoxide Contingency Measures and Fee Schedule
  • PSCAA Regulation II, Section 2.10, Gasoline Station Ozone Contingency Measure

EPA Effective Date

July 1, 2014