An apparatus for generating ozone inside packaged articles comprises an electrode assembly in which coplanar electrodes are supported along a contact surface. The electrodes are solid state conductive electrodes. These electrodes may be interdigitated and/or arranged with uniform spacing therebetween along a portion of their length. Where the electrodes are straight they may be parallel, but other shapes can also be evenly spaced. In some examples the electrodes are partially insulated and partially exposed. In some examples the electrodes are embedded/potted in an insulator to exclude air spaces from around the electrodes.