A non-thermal plasma cell having an annulus of a dielectric material, such as ceramic, formed from a continuous wall of material, the continuous wall having apertures therein, a pair of annular air-permeable electrodes mounted on opposing sides of the wall of the dielectric, and optionally an air gap provided between each electrode and the wall over at a least part of the circumference of the wall. The thickness of the dielectric material is substantially greater than the thickness of the electrodes, which may comprise metal foils.
