Sulfur dioxide (SO2) is a colorless gas, identifiable by its pungent odor and very irritating to the mucous membranes (respiratory tract and eyes) from 1 ppm! Although corrosive and harmful , it is above all a toxic gas classified R23 and R34, i.e. toxic by inhalation and responsible for burns. Finally, it is very reactive with many solvents (alcohol, toluene), but especially with water to form sulfuric acid (H2SO4), SO2 is also the primary factor in acid rain.