Section 096-110-3 - Sulfur Dioxide Ambient Air Quality StandardsA. The primary ambient air quality standard for sulfur oxides measured as sulfur dioxide is a 1-hour average concentration of 75 ppb. The primary sulfur dioxide standard is met when the 99th percentile 1-hour daily maximum concentration averaged over 3 years, as determined in accordance with 40 CFR Part 50 Appendix T, is less than or equal to 75 ppb.B. The secondary ambient air quality standard for sulfur oxides measured as sulfur dioxide is a maximum 3-hour concentration of 0.5 ppm. The secondary sulfur dioxide standard is met when the second-highest 3-hour average per calendar year, as determined in accordance with 40 CFR Part 50 , Appendix A, is less than or equal to 0.5 ppm.06- 096 C.M.R. ch. 110, § 3