How does metal ore smelting contribute to acid deposition?

Metal ore smelting contributes to acid deposition primarily through the release of sulfur dioxide ($S{O}_2$) gas. Many metal ores, such as those containing zinc, iron, and copper, are sulfide ores. During the smelting process, these ores are roasted—heated in the presence of air—which causes the sulfur in the ore to react with oxygen and form sulfur dioxide.123

Once emitted into the atmosphere, this sulfur dioxide reacts with water, oxygen, and other chemicals to form sulfuric acid. This acid then returns to Earth’s surface through acid deposition, which includes both wet forms like rain, snow, and fog, and dry forms such as acidic particles and gases. Because this process can transport acidity far from the original industrial source, smelting is recognized as a major anthropogenic cause of acid deposition, leading to significant environmental damage to forests, aquatic ecosystems, and building materials.241