Commenting open: September 24, 2026 12:00AM PT - November 17, 2026 11:59PM PT.

Public comment period: Rulemaking to amend Chapters 173-476 & 173-400 WAC

Ecology is seeking public comments on draft rule language for two air quality rules:


Chapter 173-476 WAC, Ambient Air Quality Standards. The amendments will:


  • Update air quality standards for fine particulate matter (PM2.5) and sulfur dioxide (SO2)


Chapter 173-400 WAC, General Regulations for Air Pollution Sources. The amendments will:


  • Update "cause or contribute threshold values," also called "significant impact levels" and associated provisions used to review proposed new or modified sources of air pollution


We are also proposing minor administrative changes or corrections.



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The comments you provide will help inform the final adopted rules.
 
Ecology will consider all comments received, revise the rules as necessary, and will respond to the comments in the Concise Explanatory Statement (CES). The CES will be published along with adoption of the rules.

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