Abstract: A apparatus for controlling the amount of polluting substances within a fluid such as the exhaust gas of an internal combustion engine, wherein the polluted fluid passes through a corona-producing chamber having spaced conductive members biased by an alternating electrical potential which effect elimination or conversion of the harmful substances within the exhaust through a series of chemical reactions. Prior to passing through the corona-producing chamber, the exhaust gas is mixed with air or other oxygen containing substance to create an ozone field and other chemical reactants within the chamber to reduce the amount of various contaminants of the polluted gas. The corona-producing member is provided with a plurality of corona-emitting elements which cause an intense corona discharge to occur within the chamber.