For cleaning a flow of used air from a spray booth wherein articles are lacquered, a duct is provided with a first constriction where the flow of used air is brought into contact with washing fluid so as to wet lacquer particles in the used air. Downstream of the first constriction a guide conduit, which has a bend therein deflects the flow of used air and the washing fluid. The guide conduit is provided with a second constriction and after the flow of used air and the washing fluid have been deflected they pass through the second constriction, which is narrower than the first. Turbulence is thus created and the washing fluid is atomized and intimately mixed with the used air.