In  the atmosphere, this pungent gas becomes a major component of acid  rain.
As a solid it forms the white areas on Jupiter's moon, Io; on  Earth it's usually a gas. Naturally occurring in volcanic gases  and the waters of some warm springs, it's a byproduct of the  smelting of iron and copper pyrite, as well as coal burning. In  the atmosphere, this pungent gas becomes a major component of acid  rain. For ten points, name this acid anhydride of sulfurous acid.
As a solid it forms the white areas on Jupiter's moon, Io; on  Earth it's usually a gas.
{sulfur dioxide} or {SO2}