Abstract: A decomposition device and a method for decomposing gases with soot or other harmful substances has a processing station using dielectrically hindered discharge. The device has at least two electrodes, one of which is a porous and gas permeable electrode. In order to decompose the gas containing harmful substances, the gas is first introduced into a processing station in which the gas is subjected to plasma processing involving an alternate voltage supply, and from which the gas is let out. The gas is introduced through one end of the processing station formed by the two electrodes.