This European Standard specifies a continuous measurement method for the determination of the concentrations of nitrogen dioxide and nitrogen monoxide present in ambient air based on the chemiluminescence measuring principle. This standard describes the performance characteristics and sets the relevant minimum criteria required to select an appropriate chemiluminescence 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 [1] and requirements during sampling, calibration and quality assurance for use.The method is applicable to the determination of the concentration of nitrogen dioxide present in ambient air up to 500 µg/m3. This concentration range represents the certification range for NO2 for the type approval test.The method is applicable to the determination of the concentration of nitrogen monoxide present in ambient air up to 1 200 µg/m3. This concentration range represents the certification range for NO for the type approval test.NOTE 1It is possible to use other ranges depending on the levels present in ambient air. NOTE 2When this European 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 nitrogen dioxide and nitrogen 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 µg/m3 (at 20 °C and 101,3 kPa).NOTE 3500 µg/m3 of NO2 corresponds to 261 nmol/mol of NO2 at 20 °C and 101,3 kPa. 1 200 µg/m3 of NO corresponds to 962 nmol/mol of NO at 20 °C and 101,3 kPa.This standard contains information for different groups of users.Clauses 5 to 7 and Annexes B and C contain general information about the principles of NOx measurement by chemiluminescence analyser and sampling equipment.Clause 8 and Annex E are specifically directed towards test houses and laboratories that perform type-approval testing of NOx 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 NOx analyser based on the type-approval test results.Clauses 9 to 11 and Annexes F and G are directed towards monitoring networks performing the practical measurements of NOx 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.