15A NCAC 02D .0402 SULFUR OXIDES (a) The ambient air quality standards for sulfur oxides measured as sulfur dioxide are: (1) (2) (3) 80 micrograms per cubic meter (0.03 ppm) annual arithmetic mean, 365 micrograms per cubic meter (0.14 ppm) maximum 24-hour concentration not to be exceeded more than once per year, 1300 micrograms per cubic meter (0.5 ppm) maximum three-hour concentration not to be exceeded more than once per year. (b) Sampling and analysis shall be in accordance with procedures in Appendix A or A-1 40 CFR Part 50 or by a Federal Equivalent Method (FEM) designated in accordance with 40 CFR Part 53. (c) Applicability of the standards listed in Subparagraph (a)(1) and (2) of this Rule is in effect until one year after the effective date of initial designations under Section 107(d) of the Clean Air Act for the sulfur dioxide standard in Paragraph (d) of this Rule. (d) The primary one-hour annual ambient air quality standard for oxides of sulfur is 75 parts per billion (ppb, which is 1 part in 1,000,000,000), measured in the ambient air as sulfur dioxide. (e) The one-hour primary standard is met at an ambient air quality monitoring site when the three-year average of the annual (99th percentile) of the daily maximum one-hour average concentrations is less than or equal to 75 ppb, as determined in accordance with Appendix T of 40 CFR Part 50. History Note: Authority G.S. 143-215.3(a)(1); 143-215.107(a)(3); Eff. February 1, 1976; Amended Eff. September 1, 2011; July 1, 1984; December 1, 1976.