Cl Total sulfur dioxide: For the purposes of this standard, it is the sulfur dioxide that is found in the free state, and that which is found to be part of inorganic and organic compounds. C-2 Free sulfur dioxide. For the purposes of this standard, it is the sulfurous anhydride that is found in the free state, plus the sulfurous anhydride that is found in the state of mineral combinations such as sulfurous acid, acid sulfites and neutral sulfites. C-3 Combined sulfur dioxide: For the purposes of this standard, it is the difference between total sulfur dioxide and free sulfur dioxide.