The present invention relates to a gas cleaning system for cleaning a gas stream containing carbon dioxide and sulfur dioxide, said gas cleaning system comprising: a pre-conditioning section (3); a CO2 removal stage (5); and a post-conditioning section (4); said pre-conditioning section comprising at least two gas-liquid contacting devices (19,20) arranged upstream of the CO2 removal stage (5) with respect to the flow direction of the gas; and said post-conditioning section comprising at least two gas-liquid contacting devices (30,31) arranged downstream of the CO2 removal stage with respect to the flow direction of the gas. The present invention further relates to a method for cleaning a gas stream containing carbon dioxide and sulfur dioxide, said method including removing, at least partly, carbon dioxide from the gas stream in a carbon dioxide removal step by bringing the gas stream into contact with a liquid comprising ammonia; contacting the gas stream with liquid in at least two steps upstream of the carbon dioxide removal step; and contacting the gas stream with liquid in at least two steps downstream of the carbon dioxide removal step.