5. The Oxides of Nitrogen If a nitrogen-oxygen mixture such as air is heated to over 1100 C, the nitrogen and oxygen will combine to form nitrogen oxide(no, no 2) The reaction that forms no does not depend directly on the fuel used The vital ingredients are only the nitrogen, the oxygen, and the high temperature The exhaust of an internal combustion engine running at high speed with out emission controls will contain about 4000 ppm of No. The exhaust of a coal-fired steam generator will have 200 to 1200 ppm of NO NO is a colorless gas, toxic in high concentrations, but its toxicity is generally considered to be minor compared to NO NO2 is also produced when NO reacts with O3 NO2 is reddish-brown gas that accounts for the brownish color of the familiar smog in cities5. The Oxides of Nitrogen If a nitrogen-oxygen mixture such as air is heated to over 1100oC, the nitrogen and oxygen will combine to form nitrogen oxide (NO, NO2 ). The reaction that forms NO does not depend directly on the fuel used. The vital ingredients are only the nitrogen, the oxygen, and the high temperature. The exhaust of an internal combustion engine running at high speed with out emission controls will contain about 4000 ppm of NO. The exhaust of a coal-fired steam generator will have 200 to 1200 ppm of NO. NO is a colorless gas, toxic in high concentrations, but its toxicity is generally considered to be minor compared to NO2 . NO2 is also produced when NO reacts with O3 . NO2 is reddish-brown gas that accounts for the brownish color of the familiar smog in cities