WAC 173-476-110. Ambient air quality standards for PM-2.5

(1) Standards for PM-2.5. (a) The three-year average of the annual arithmetic mean concentration of PM-2.5 must not exceed 12.0 μ g/m 3 . (b) The three-year average of the ninety-eighth percentile twenty-four-hour average concentration of PM-2.5 must not exceed 35 μ g/m 3 . (2) Measurement method. The levels of PM-2.5 in the ambient air must be measured by: (a) A FRM based on 40 C.F.R. Part 50, Appendix L and designated according to 40 C.F.R. Part 53; or (b) A FEM designated according to 40 C.F.R. Part 53. (3) Interpretation method. The interpretation method found in 40 C.F.R. Part 50, Appendix N must be used.