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 the ambient air for the following criteria pollutants: Particulate matter, lead, sulfur dioxide, ozone, nitrogen dioxide, and carbon monoxide. This rule making will update the air quality standards for particulate matter with a diameter of 2.5 microns or less (PM2.5) and 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. This rule making will consider updates to the cause or contribute threshold values, also known as significant impact levels, and associated provisions used in the permitting of proposed new or modified sources of air pollution.

Reasons Why Rules on this Subject may be Needed and What They Might Accomplish: Chapter 173-476 WAC, Ambient air quality standards: Amendments are needed to align the state ambient air quality standards with the National Ambient Air Quality Standards (40 C.F.R. Part 50) for PM2.5 and sulfur dioxide. In March 2024, the Environmental Protection Agency (EPA) lowered the maximum allowable level of PM2.5 from 12 micrograms per cubic meter of air to nine micrograms per cubic meter of air. For sulfur dioxide, amendments are needed to reflect a new secondary annual standard of 10 parts per billion adopted by EPA in December 2024.

Chapter 173-400 WAC, General regulations for air pollution sources: Amendments are needed to update the cause or contribute threshold values to align with updated EPA-recommended values. In 2013, ecology adopted threshold values which aligned with EPA-recommended values for most, but not all, of the criteria pollutants. EPA has since revised some recommended values and now updates are needed to align with the EPA recommendations. Ecology may also consider other changes including adopting cause or contribute threshold values for the criteria pollutants for which ecology did not previously adopt threshold values and making changes to provisions related to the cause or contribute values. The amendments are intended to align with EPA recommendations, but could vary depending on the rule development and community engagement processes.

Other Federal and State Agencies that Regulate this Subject and the Process Coordinating the Rule with These Agencies: Local air permitting authorities also regulate new or modified sources of air pollution. Ecology has discussed the use of cause or contribute values in the new source review process and will continue to work with local authorities as we develop the rule.

Interested parties can participate in the decision to adopt the new rule and formulation of the proposed rule before publication by contacting Linda Kildahl, Department of Ecology, Air Quality Program, 300 Desmond Drive S.E., Lacey, WA 98503, phone 360-706-3038, Washington relay service or TTY call 711 or 877-833-6341, email linda.kildahl@ecy.wa.gov, rule making website or air quality rule and state implementation plan updates distribution list [contact agency for URLs].

Additional comments: Interested parties can stay informed about the rule making and public involvement opportunities as described above. Ecology will extend an offer for government-to-government consultation with tribal governments during each phase of rule development.