The analyzer uses ozone (O3) which reacts with the nitric oxide (NO) in the sample stream, yielding an excited state of NO2 (NO2*) plus oxygen (O2). Excited NO2* will return to a more stable ground state, and in the process, produces a chemiluminescent light, the intensity of which is proportional to the concentration of NO that was converted into NO2 within the reaction chamber. A photodiode detector is used to measure the light and reports out a ppmv NO value.
In order to produce a total NOx signal, the sample is first routed through an internal converter that turns any NO2 in the sample into NO. This stream is then subjected to O3 gas and the resultant reaction is now directly proportional to the total NOx concentration. The analyzer then makes an internal calculation, deriving the final NO2 concentration from the NOx converter efficiency.