This European Standard specifies the standard reference method (SRM) based on the chemiluminescence principle for the determination of the nitrogen oxides (NOx) in flue gases emitted to the atmosphere from ducts and stacks. It includes the sampling and the gas conditioning system, as well as the analyser. This European Standard specifies the characteristics to be determined and the performance criteria to be fulfilled by portable automated measuring systems (P-AMS) based on this measurement method. It applies for periodic monitoring and for the calibration or control of automated measuring systems (AMS) permanently installed on a stack, for regulatory or other purposes. This European Standard specifies criteria for demonstration of equivalence of an alternative method to the SRM by application of EN 14793:2017. This European Standard has been validated during field tests on waste incineration, co-incineration and large combustion installations and on a recognized test-bench. It has been validated for sampling periods of 30 min in the range of 0 mg/m3 to 1300 mg/m3 of NOx for large combustion plants and 0 mg/m3 to 400 mg/m3 of NOx for waste incineration, according to emission limit values (ELV) laid down in the Directive 2010/75/EU. The ELV for NOx (NO + NO2) in EU Directives is expressed in mg/m3 of NO2 on a dry basis, at a specified value for oxygen and at standard conditions (273 K and 101,3 kPa). NOTE The characteristics of installations, the conditions during field tests and the values of repeatability and reproducibility in the field are given in Annex A.