This document specifies a continuous measurement method for the determination of the concentration of sulfur dioxide present in ambient air based on the ultraviolet fluorescence measuring principle. This document describes the performance characteristics and sets the relevant minimum criteria required to select an appropriate ultraviolet fluorescence 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 mass concentration of sulphur dioxide present in ambient air up to 1000 µg/m3. This concentration range represents the certification range for sulfur dioxide for 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 Directive 2008/50/EC, the ranges and uncertainty requirements possibly do not apply. The method covers the determination of ambient air concentrations of sulfur dioxide in locations classified as rural areas, urban-background areas, and for sampling influenced by traffic or industrial sources. The results are expressed in µg/m3 (at 20 °C and 101,3 kPa). NOTE 3 1 000 µg/m3 of SO2 corresponds to 376 nmol/mol of SO2. This document contains information for different groups of users. Clause 5 to Clause 7 and Annex C and Annex D contain general information about the principles of sulfur dioxide measurement by ultraviolet fluorescence analyser and sampling equipment. Clause 8 and Annex E are specifically directed towards test houses and laboratories that perform type testing of sulfur dioxide 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 sulfur dioxide 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 sulfur dioxide 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 the measurement results under practical monitoring conditions. This document represents an evolution of earlier editions (EN 14212:2005 and EN 14212:2012). 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.