This European Standard describes the chemiluminescence method, including the sampling and the gas conditioning system, to determine the NO/NO2/NOX concentrations in flue gases emitted from ducts and stacks to atmosphere. This European Standard is the Standard Reference Method (SRM) for periodic monitoring and for calibration or control of Automatic Measuring Systems (AMS) permanently installed on a stack, for regulatory or other purposes such as calibration. To be used as the SRM, the user shall demonstrate that the performance characteristics of the method are better than the performance criteria defined in this European Standard and that the overall uncertainty of the method is less than ± 10 % relative at the daily Emission Limit Value (ELV). NOTE When the chemiluminescence method is the measurement principle used for AMS, reference should be made to EN 14181 and other relevant standards provided by CEN TC 264. An Alternative Method to this SRM may be used provided that the user can demonstrate equivalence according to the Technical Specification CEN TS 14793, to the satisfaction of his national accreditation body or law. This SRM has been evaluated during field tests on waste incineration, co-incineration and large combustion installations. It has been validated for sampling periods of 30 min in the range of 0 mgNO2/m3 1300 mgNO2/m3 for large combustion plants and 0 mgNO2/m3 - 400 mgNO2/m3 for waste incineration, according to emission limit values (ELVs) laid down in the following Council Directives: Council Directive 2001/80/EC on the limitation of emissions of certain pollutants into the air from large combustion plants; Council Directive 2000/76/EC on waste incineration plants. The ELVs for NOx (NO + NO2) in EU directives are expressed in mgNO2/m3, on dry basis, at a reference value for O2 and at the reference conditions (273 K and 101,3 kPa).