A molecule can pass from the electronic initial condition to an electronic excited condition by absorption of energy. During the transition the absorbed energy can be emitted again to an energetically lower-lying condition. On the one hand it can happen in form of heat (non-radiative deactivation) and, on the other hand, by the emission of light (luminescence). Chemoluminescence means light which is emitted by excitation of a chemical reaction. It is being used in the analysis of nitrogen gases. Nitrogen monoxide reacts with ozone to excited nitrogen dioxide. The emitted light is amplified and measured by a photomultiplier. In order to analyze nitrogen dioxide, it has to be reduced with a catalyst to nitrogen monoxide. Then it can be detected as described above. If all nitrogen oxides should be measured in a sample gas stream, the content of nitrogen monoxide has to be measured first. This measurement is carried out without a catalyst. Subsequently, the gas stream will be passed through the catalyst, what will reduce the nitrogen dioxide to NO and the sum of NO and NO2 (NOx) will be determined. Nitrogen oxides increase especially during the burning process so that this method of analysis is applied in the combustion gas analysis of power plants, in the automotive industry as well as in environmental technologies. Chemoluminescence is one of the measurement principle made available in the ecom-J2Knpro TECH.