Sulfurous acid is a chemical compound with the formula H₂SO₃. It is formed when sulfur dioxide (SO₂) dissolves in water. This weak acid is colorless and has a pungent smell, often associated with burnt matches. Sulfurous acid is used in various industrial processes, including the production of sulfites and as a preservative in food and beverages. In nature, sulfurous acid can be found in volcanic gases and is a component of acid rain. It plays a role in the sulfur cycle, which is essential for the environment. However, exposure to sulfurous acid can be harmful, causing irritation to the eyes and respiratory system.