Chapters 173-476 and 173-400 WAC – Air Quality Standards and Impact Levels
We are starting rulemaking to update:
- Chapter 173-476 WAC, Ambient Air Quality Standards — This chapter establishes the ambient air quality standards in Washington to comply with Title I of the federal Clean Air Act. It establishes maximum acceptable levels in ambient air for criteria pollutants (carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, sulfur dioxide).
- Chapter 173-400 WAC, General Regulations for Air Pollution Sources — This chapter establishes standards and rules to control and prevent pollution from air contaminant sources.
With this rulemaking, we intend to update:
- Air quality standards for particulate matter with a diameter of 2.5 microns or less (PM2.5) and sulfur dioxide (SO2).
- "Cause or contribute" threshold values (also known as significant impact levels) and associated provisions used in permitting proposed new or modified sources of air pollution.
- Administrative and other amendments to clarify language or otherwise improve air quality regulations.
Rulemaking timeline
Announcement phase (CR-101)
Filing date:
Nov. 19, 2025
Announcement documents
Rule development phase
Nov. 19, 2025 – Fall 2026Public input & involvement
We plan to hold stakeholder meetings in Winter/Spring 2026. We will update this page with meeting specifics. To get updates about these meetings and this rulemaking, join our email list.
This rulemaking will include an environmental justice assessment, as required by the Healthy Environment for All Act (the HEAL Act, RCW 70A.02.060). We want to engage with communities and Tribes to hear their input and related environmental justice concerns. To get updates about these meetings and this rulemaking, join our email list.
Related links
Contact information
Linda Kildahl
Rulemaking Lead
linda.kildahl@ecy.wa.gov
360-706-3038
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Accessibility
To request ADA accommodation for disabilities, or printed materials in a format for the visually impaired, contact Ecology's ADA Coordinator by email at ecyadacoordinator@ecy.wa.gov, or call 360-407-6831. People with impaired hearing may call Washington Relay Service at 711. People with speech disability may call TTY at 877-833-6341.