Sulfur dioxide, SO2, is a colorless gas or liquid with a strong, choking odor. It is produced from the burning of fossil fuels (coal and oil) and the smelting of mineral ores (aluminum, copper, zinc, lead and iron) that contain sulfur. Sulfur dioxide dissolves easily in water to form sulfuric acid. Sulfuric acid is a major component of acid rain. Acid rain can damage forests and crops, change the acidity of soils, and make lakes and streams acidic and unsuitable for fish. Sulfur dioxide also contributes to the decay of building materials and paints, including monuments and statues.