Loosely packed electrically conductive material is retained within a tube of dielectric material. A sheath of electrically conductive material surrounds the tube. A pair of electrodes, adapted to be connected to a source of high voltage are electrically connected to the material and the sheath, respectively, to generate corona discharge between the material and the tube and between elements of the material to transform oxygen molecules in a gas passing through the material in the tube into ozone to produce an ozone enriched outflow of gas.