Comment Period
Air Quality Standards and Impact Levels, Chapters 173-476 and 173-400 WAC
Proposed rulemaking – public comment period
Sept. 24, 2026, 12 a.m. - Nov. 17, 2026, 11:59 p.m. PT
We propose to update two rules:
- 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 propose 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.
Background
We write rules to implement and enforce state and federal environmental laws and rules. Ecology follows a three-phase process for rulemaking:
- Announcement and development
- Proposal
- Adoption
For each phase of the process, we update the rulemaking web page and notify interested parties. We also file notice in the Washington State Register. To learn more about Ecology’s rulemaking process, read the Frequently Asked Questions.
Comment online
- Use our online comment form
Comment by mail
Linda Kildahl
Washington Department of Ecology
Air Quality Program
P.O. Box 47600
Olympia, WA 98504-7600
Washington Department of Ecology
Air Quality Program
P.O. Box 47600
Olympia, WA 98504-7600
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