is supported on a cylindrical dielectric rod 40 within the tube 20 the mesh 38 is wrapped about the rod 40 and provides a sliding fit within the interior of the tube 20 the interweaving of the mesh 38 provides voids through which the gas may pass from the inlet 30 along the interior of the tube to an outlet 42 in the opposite end fitting 14 a ground electrode 44 is formed on the outer surface of the tube 20 from a conductive epoxy coating typically the electrode 44 is a silver filled epoxy such as that available from chomerics div of parker hannifin corp of wolburn me the ground electrode 44 is connected through cable 46 to a ground terminal 48 provided in the fitting 14 in operation oxygen bearing gas typically air or air enriched with oxygen is fed through the inlet 30 and along the interior of the tube 20 to the outlet 42 power is supplied from the power supply 36 to the electrode 38 to generate an alternating electric field between the electrodes 38 44 as the gas passes the electrode a portion of the oxygen in the gas is converted to ozone and passing through the outlet 42 the heat generated is removed by water flowing through the inlet 24 and through the chamber 22 to the outlet 25 the water is in intimate contact with the ground electrode 44 and thus provides an efficient heat removal during operation the close fit of the grid between the rod 40 and the tube 20 promotes.