an apparatus and process for removing acidic gases and nox from flue gases produced by utility and industrial plants . the process and apparatus convert nox , and particularly nitric oxide , to nitrogen dioxide , which is then reacted to form a valuable byproduct . the process generally entails contacting a flue gas with a scrubbing medium to absorb acidic gases from flue gas and produce an intermediate flue gas . the intermediate flue gas is then cooled to cause nitric oxide present therein to be oxidized to form nitrogen dioxide , which is then absorbed from the flue gases to produce a nitrogen dioxide - containing solution and a scrubbed flue gas . the nitrogen dioxide in the nitrogen dioxide - containing solution is then reacted with ammonium hydroxide to form ammonium nitrate as a valuable byproduct .