1. (1) Standard for sulfur oxides (measured as sulfur dioxide).

   1. (a) Annual. The annual average concentration for sulfur oxides in the ambient air must not exceed 0.02 ppmv in a calendar year.
   2. (b) Twenty-four-hour. The twenty-four-hour average concentration for sulfur oxides in the ambient air must not exceed 0.14 ppmv more than once per calendar year. The twenty-four-hour averages must be determined from successive nonoverlapping twenty-four-hour blocks starting at midnight each calendar day.
   3. (c) Three-hour. The three-hour average concentration for sulfur oxides in the ambient air must not exceed 0.5 ppmv more than once per calendar year. The three-hour averages must be determined from successive nonoverlapping three-hour blocks starting at midnight each calendar day.
   4. (d) One-hour. The three-year average of the annual ninety-ninth percentile of the daily maximum one-hour average concentrations for sulfur oxides in the ambient air must not exceed 75 ppbv.

2. (2) Measurement method. The levels of sulfur oxides must be measured as sulfur dioxide by:

   1. (a) A FRM based on 40 C.F.R. Part 50, Appendix A-1 or A-2; or
   2. (b) A FEM designated according to 40 C.F.R. Part 53.

3. (3) Interpretation methods.

   1. (a) The annual arithmetic mean is based on the average of hourly data. To be used in calculating the annual average, the hourly data must be at least seventy-five percent complete in each calendar quarter of the year.
   2. (b) The interpretation method for the twenty-four-hour average found in 40 C.F.R. Part 50.4(d) must be followed.
   3. (c) The interpretation method for the three-hour average found in 40 C.F.R. Part 50.5(c) must be followed.
   4. (d) The interpretation method for the one-hour average found in 40 C.F.R. Part 50, Appendix T must be followed.

4. (4) Rounding of values.

   1. (a) The annual arithmetic mean and twenty-four-hour averages must be rounded to two decimal places. Fractional parts equal to or greater than 0.005 ppmv must be rounded up.
   2. (b) The three-hour standard averages must be rounded to one decimal place. Fractional parts equal to or greater than 0.05 ppmv must be rounded up.
5. (5) Sunset provision. The ambient standards in WAC 173-476-130 (1)(a) and (b) are no longer applicable in a specific area one year after the effective date of the EPA's designation of attainment status of that area for the standard in WAC 173-476-130 (1)(d) and 40 C.F.R. 50.17.

[Statutory Authority: Chapter 70.94 RCW. WSR 13-24-010 (Order 12-05), § 173-476-130, filed 11/21/13, effective 12/22/13.]