This European Standard specifies the standard reference method (SRM) based on the infra-red (IR) absorption principle. It includes the sampling and the gas conditioning system, and allows the determination of the carbon monoxide CO in flue gases emitted to the atmosphere from ducts and stacks. This European Standard specifies the characteristics to be determined and the performance criteria to be fulfilled by measuring systems using the IR measurement method. It applies for periodic monitoring and for the calibration or control of automatic 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 (AM) to the SRM by application of prEN 14793. This European Standard has been validated during field tests on waste incineration, co-incineration and large combustion plants and on a recognized test bench. It has been validated for CO concentrations with sampling periods of 30 min in the range of 0 mg/m3 to 400 mg/m3 for large combustion plants and 0 mg/m3 to 740 mg/m3 for waste and co-incineration. Directive 2010/75/EC lays down emission values which are expressed in mg/m3, on dry basis at a specified value of oxygen and at standard conditions of 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.