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Summary of Seattle-Tacoma Puget Sound Area Ozone 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)).


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

Improvements to existing Motor Vehicle Inspection and Maintenance Program (within the current statutory authority of the Department of Ecology) including upgrade to Acceleration Simulation Mode (ASM1) test procedure.

Mandatory reduction in gasoline volatility.

EPA Effective Date

November 25, 1996