Chapters 173-476 and 173-400 WAC – Air Quality Standards and Impact Levels
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.
Rulemaking timeline
Announcement phase (CR-101)
Filing date:
Nov. 19, 2025
Announcement documents
Rule development phase
November 19, 2025 – September 23, 2026Public input & involvement
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.
Public comment periods (informal)
Closed: April 15, 2026, 12:01 a.m. – May 17, 2026, 11:59 p.m.
Read comments.
Closed: June 3, 2026, 12:01 a.m. – June 28, 2026, 11:59 p.m.
Read comments.
Rulemaking meetings
| Date | Meeting information | Location |
|---|---|---|
| Wednesday, April 15, 2026 10 a.m. – 11 a.m. |
Agenda Presentation Draft rule language 173-476 Draft rule language 173-400 |
|
| Tuesday, June 9, 2026 10 a.m. – 11 a.m |
Agenda Presentation Draft rule language 173-476 (same as previous draft) Draft rule language 173-400 |
webinar recording |
1 Webinar information:
Register for each webinar to get your meeting ID and passcode.
To hear the webinar better or to call in only, use your phone (instead of the computer) to call 253‑215‑8782.
Rule proposal phase (CR-102)
Sept. 24, 2026
- Proposal notice – CR-102 form
- Proposed rule language
- Preliminary Regulatory Analyses
- SEPA Determination of Nonsignificance (DNS) and Environmental Checklist
Comment period
Comments are accepted September 24, 2026, 12 a.m. – November 17, 2026, 11:59 p.m. We accept comments in the following ways:
-
Attend a public hearing online (webinar): November 10, 2026, 10 a.m.
- Mail to: Linda Kildahl
Department of Ecology
Air Quality Program
P.O. Box 47600
Olympia, WA 98504-7600
Public hearing
Date/Time: November 10, 2026, 10 a.m. online (webinar)
Location: online (webinar)
Register for the webinar to get your meeting ID and passcode.
To hear the webinar better or to call in only, use your phone (instead of the computer) to call 253‑215‑8782.
Agenda: Presentation, question-and-answer session, followed by public hearing
Accessibility: To ask for ADA accommodation, email Linda Kildahl, call 360‑407‑6831, or dial 711 (relay service).
Related links
Contact information
Linda Kildahl
Rulemaking Lead
linda.kildahl@ecy.wa.gov
360-706-3038
Stay informed
Join our email list
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.