Abstract: Stack gases containing sulfur dioxide and other pollutant gases and particulate matter are passed through a horizontally extending chamber wherein the stack gases are sprayed by a liquid reagent. The liquid spray droplets move across the cross-sectional flow area of the stack gases and scrub the stack gases thereby removing a substantial portion of the pollutant gases and particulate matter therefrom. The resultant liquid slurry which might otherwise collect in the chamber is washed therefrom by the spray and drains downwardly from the chamber for discharge thereby preventing plugging of the chamber.