AbstractOxides of nitrogen are present in the effluent gases from nitric acid and nylon intermediates plants and if released in sufficient quantity they could be objectionable owing to their intensive reddish‐brown color and to their corrosive and poisonous nature. A paper study showed that the oxides of nitrogen could be reduced by absorption in an alkaline solution. Based on pilot plant tests, a large fume abatement unit was designed, installed, and operated in a satisfactory manner to reduce the concentration of the oxides of nitrogen. In 1956, the color of the combined effluent gases was practically eliminated when a more economic waste ammonia‐caustic liquor replaced the dilute caustic scrubbing solution and finely dispersed ammonium salts were removed in a Venturi scrubber. The method may be used to eliminate the objectionable brownish‐red color of effluent gases leaving a nitric acid