Wash. Rev. Code § 70A.15.2540
The rules and regulations hereafter adopted by an authority under the provisions of this chapter shall supersede the existing rules, regulations, resolutions and ordinances of any of the component bodies included within said authority in all matters relating to the control and enforcement of air pollution as contemplated by this chapter: PROVIDED, HOWEVER, That existing rules, regulations, resolutions and ordinances shall remain in effect until such rules, regulations, resolutions and ordinances are superseded as provided in this section: PROVIDED FURTHER, That nothing herein shall be construed to supersede any local county, or city ordinance or resolution, or any provision of the statutory or common law pertaining to nuisance; nor to affect any aspect of employer-employee relationship relating to conditions in a place of work, including without limitation, statutes, rules or regulations governing industrial health and safety standards or performance standards incorporated in zoning ordinances or resolutions of the component bodies where such standards relating to air pollution control or air quality containing requirements not less stringent than those of the authority.
RCW 70A.15.2540