Sulfurous acid (also
sulphurous acid) is the
chemical compound with the
formula H
2SO
3. There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase. The conjugate bases of this elusive acid are, however, common anions,
bisulfite (or hydrogen sulfite) and
sulfite. Sulfurous acid is an intermediate species in the formation of
acid rain from sulfur dioxide.