This document 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 document describes the performance characteristics and sets the relevant minimum criteria required to select an appropriate chemiluminescence analyser by means of type testing. 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 nitrogen dioxide for type testing. 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 nitrogen monoxide for the type testing. NOTE 1 It is possible to use other ranges depending on the levels present in ambient air. NOTE 2 When this document is used for purposes other than for measurements required by Directive2008/50/EC, the ranges and uncertainty requirements possibly do 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, traffic-orientated locations and locations influenced by industrial sources. The results are expressed in µg/m3 (at 20 °C and 101,3 kPa). NOTE 3 500 µg/m3 of nitrogen dioxide corresponds to 261 nmol/mol of nitrogen dioxide at 20 °C and 101,3 kPa. 1 200 µg/m3 of nitrogen monoxide corresponds to 962 nmol/mol of nitrogen monoxide at 20 °C and 101,3 kPa. This document contains information for different groups of users. Clause 5 to Clause 7 and Annex B and Annex 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 testing of NOx analysers. These sections contain information about: — type testing conditions, test procedures and test requirements; — analyser performance requirements; — evaluation of the type testing results; — evaluation of the uncertainty of the measurement results of the NOx analyser based on the type testing results. Clause 9 to Clause 11 and Annex F and Annex 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. This document represents an evolution of earlier editions (EN 14211:2005 and EN 14211:2012). It is advisable that when equipment is procured it complies fully with this document. NOTE 4 Type testing performed prior to the publication of this document for the purpose of demonstrating equivalence are still valid. NOTE 5 Analysers type tested prior to the publication of this document remain valid for use for regulated monitoring purposes.