Why can sulfur dioxide gas from modern copper smelters be used to make sulfuric acid?

Sulfur dioxide gas produced during modern copper smelting is a valuable byproduct that can be converted into sulfuric acid because it serves as a chemical precursor to sulfur trioxide ($S{O}_3$).1

In modern flash or bath smelting processes, the concentrate is reacted with oxygen or oxygen-enriched air, which generates a gas stream with a high concentration of sulfur dioxide. This gas is captured and processed using the contact process. In this industrial method, the sulfur dioxide is oxidized—typically in the presence of a catalyst—to form sulfur trioxide, which is then combined with water to produce sulfuric acid.234

Capturing this gas is an essential environmental and industrial practice, as it prevents the release of sulfur dioxide, a harmful pollutant, while simultaneously providing a source of sulfuric acid that is often reused within the metallurgical operations themselves.142