A device useful for separating gaseous pollutants, such as sulphur dioxide, from a gas by means of an absorption liquid is disclosed. The device includes a horizontal apertured plate mounted between an inlet and an outlet arranged for passage of a gas containing a gaseous pollutant therethrough. On an upper surface of the horizontal apertured plate is a flowing layer of absorption liquid. The separation of the gaseous pollutant from the gas is adjustable by varying the thickness of the flowing layer of absorption liquid by moving a throttle means to a position that provides the desired amount of resistance to the following layer of absorption liquid.