The primary and secondary ambient air quality standards for sulfur dioxide (SO2), chemical abstracts service registry number (CAS #) 7446-09-5, shall be as follows:

1. (a) The primary ambient air quality standard for SO2 shall be 75 parts per billion (ppb), 1-hour average concentration; and
2. (b) The secondary ambient air quality standard for SO2 shall be 0.5 parts per million (ppm), 3-hour average concentration.

Source. #120, eff 8-31-73; ss by #721.3, eff 12-7-75; ss by #1717, eff 2-19-81; ss by #2332, eff 4-29-83; ss by #2938, eff 12-27-84; ss by #5033, eff 12-27-90; ss by #6227, eff 4-25-96; ss by #8054, eff 2-28-04; ss by #10173, eff 9-1-12; ss by #13382, eff 5-25-22