Definition

SO2 is a dense, colorless, toxic, non-flammable, reactive gas composed of one sulfur atom bonded to two oxygen atoms. It has a suffocating, unpleasant, strong, distinct odour similar to a matchstick being struck. It is an acidic, erosive gas that reacts easily with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid, and sulfate particles.