In this series of reactions, sulfur dioxide (SO2) is first oxidized to sulfur trioxide (SO3), which then reacts with potassium hydrogensulfate (KHSO4) to form potassium sulfate (K2SO4) and barium sulfate (BaSO4) simultaneously.

Overall reaction:
2SO2 + O2 → 2SO3
3SO3 + KHSO4 → K2SO4 + BaSO4