Sulfur dioxide (chemical formula: SO2), also known as sulfite anhydride, is the most common sulfur oxide, the main component of sulfuric acid feedstock gas. Sulfur dioxide is a colorless gas with a strong pungent odor and is one of the main pollutants in the atmosphere. The gas is emitted during volcanic eruptions, and sulfur dioxide is also produced in many industrial processes. Because coal and petroleum often contain sulfur compounds, sulfur dioxide is produced when burned. When sulfur dioxide dissolves in water, it forms sulfite (the main component of acid rain).