Sulfur dioxide (SO2) is removed from carbon dioxide feed gas comprising SO2 as a contaminant by maintaining the carbon dioxide feed gas at an elevated pressure in contact with an alkaline sorbent for a period of time sufficient to react said alkaline sorbent with SO2. Where NOx, oxygen (O2) and water are also present, not only is the rate of reaction with the sorbent increased, but also additional SO2 is removed by conversion to sulfuric acid, and NOx is removed as nitric acid. The method has particular application in the removal of SO2 and NOx from flue gas produced by oxyfuel combustion of a hydrocarbon or carbonaceous fuel.