A submicron filter assembly (24) is added to an exhaust gas controlled destruction and oxidation unit (10). Controlled destruction and oxidation unit (10) treats exhaust gas from at least one semiconductor wafer fabricating reactor. The submicron filter (24) filters submicron particles out of the treated exhaust gas to prevent visible plumes from forming in wafer fab exhaust systems (stacks). The controlled destruction and oxidation unit (10) and submicron filter assembly (24) are ideally suited for use at the point of generation of the exhaust gases. In one embodiment of the invention, the submicron filter assembly comprises an electrostatic filter (26). The electrostatic filter (26) includes a positively charged first grid (28) and a grounded second grid (30). The second grid may include a mist screen for removing particulate build-up. In another embodiment of the invention, the submicron filter assembly (36) comprises a mist eliminator (38) and a HEPA filter (40).