The ChemiLuminescence effect is used to measure the reaction between ozone and nitrogen oxide. A molecule can pass of the electronic ground state to an electronic excited state through energy absorption. The absorbed energy can be emitted in the transition to an energetically lower state again.
This happens on the one hand in form of heat (non-radiative deactivation) and on the other by the emission of light (luminescence).
Nitrogen oxides arise in particular during combustion, thats why this analysis method finds application in the exhaust gas measurement technology of
power plants, in the automotive industry as well as in environmental technology.
Chemiluminescence refers to light which is emitted after excitation of a molecule during a chemical reaction. It is being used in the analysis of nitrogen gases.
Nitrogen monoxide reacts with ozone to excited nitrogen dioxide.
The subsequently emitted light (proportional to the NO-concentration) is measured and amplified by a photomultiplier.
In order to analyse higher nitrogen oxides, they have to be reduced with a catalyst (NOX-converter) to nitrogen monoxide.
NO + O3 → NO2* + O2
NO2* → NO2 + hν (luminescence)
If all nitrogen oxides should be measured in a single sample gas stream, the content of nitrogen monoxide must be measured first.
This measurement is carried out without the catalyst. Subsequently, the gas stream is passed over the catalyst and thus all nitrogen oxides
(e.g. NO2) are reduced to NO.
The content of all nitrogen oxides is measured and the calculated difference between NO2 and NOX measurement indicates the concentrations of both components.
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