Nitrogen oxides are nitric oxide (NO) and nitrogen dioxide (NO2). NO2 is water-soluble and since by higher temperatures combustion gases do exceed the dew point, the following factors favouring an accurate NOx measurement -besides the measurement principle itself- are to be considered:
- Gas transport (as quick and residue-free as possible)
- Cooling and drying of the gas to eliminate humidity
- Calibration of the measuring sensors
From the measurement technique point of view, a NOx measurement (value calculated out of a NO and NO2 measurement) is to clearly differentiate from an NOx calculation (calculation of NO2 value via approximation formula out of the NO measurement result).