This European Standard specifies a continuous measurement method for the determination of the concentration of carbon monoxide present in ambient air based on the non-dispersive infrared spectroscopic measuring principle. This standard describes the performance characteristics and sets the relevant minimum criteria required to select an appropriate non-dispersive infrared spectroscopic analyser by means of type approval tests. It also includes the evaluation of the suitability of an analyser for use in a specific fixed site so as to meet the data quality requirements as specified in Annex I of Directive 2008/50/EC and requirements during sampling, calibration and quality assurance for use. The method is applicable to the determination of the mass concentration of carbon monoxide present in ambient air up to 100 mg/m 3 carbon monoxide. This concentration range represents the certification range for the type approval test. NOTE 1 Other ranges may be used depending on the levels present in ambient air. NOTE 2 When the standard is used for other purposes than for measurements required by Directive 2008/50/EC, the ranges and uncertainty requirements may not apply. The method covers the determination of ambient air concentrations of carbon monoxide in zones classified as rural areas, urban-background areas and traffic-orientated locations and locations influenced by industrial sources. The results are expressed in mg/m 3 (at 20 °C and 101,3 kPa). NOTE 3100 mg/m 3 of CO corresponds to 86 µmol/mol of CO. This standard contains information for different groups of users. Clauses 5 to 7 and Annexes B, C and D contain general information about the principles of carbon monoxide measurement by non-dispersive infrared spectroscopic analyser and sampling equipment. Clause 8 and Annex E are specifically directed towards test houses and laboratories that perform type-approval testing of carbon monoxide analysers. These sections contain information about: Type-approval test conditions, test procedures and test requirements; Analyser performance requirements; Evaluation of the type-approval test results; Evaluation of the uncertainty of the measurement results of the carbon monoxide analyser based on the type-approval test results. Clauses 9 to 11 and Annex F are directed towards monitoring networks performing the practical measurements of carbon monoxide in ambient air. These sections contain information about: Initial installation of the analyser in the monitoring network and acceptance testing; Ongoing quality assurance/quality control; Calculation and reporting of measurement results; Evaluation of the uncertainty of measurement results under practical monitoring conditions.