OS1 7996 International Standard Ambient air --- Determination of the mass concentration of nitrogen oxides --- Chemiluminescence method Air ambiant - Détermination de la concentration en masse des oxydes d'azote - Methode par chimiluminescence First edition 1985-12-15 UDC 614.71 : 543.272.32 Ref. No. ISO 7996-1985 (E) Descriptors : air, quality, chemical analysis, determination of content, nitrogen oxides. Copyright International Organization for Standardization Price based on 9 pages ed without license from IHS Not for Resale Foreword ISo (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through IsO technical committees. Each member the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with IsO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting. International Standard ISO 7996 was prepared by Technical Committee ISO/TC 146, Air quality. Users should note that all International Standards undergo revision from time to time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. International Organization for Standardization, 1985 Printed in Switzerland ted without license from IHSs Not for Resale ISO 7996-1985 (E) INTERNATIONAL STANDARD Ambient air --- Determination of the mass concentration of nitrogen oxides s - Chemiluminescence method Scope and field of application The electric signal obtained is proportional to the total amount of nitrogen oxides, and the nitrogen dioxide contribution is This International Standard specifies a chemiluminescence calculated from the difference between this value and that ob- method for the determination of the mass concentration of tained for nitrogen monoxide only -- when the air sampie does nitrogen oxides present in ambient air. not pass through the converter. The method is applicable to the determination of the mass con- Analysers may be of the dual or cyclic type. In the dual type, centration of nitrogen monoxide present in ambient air up to the air flow is divided into two streams, one passing directly to approximately 12,5 mg/m3 and of nitrogen dioxide up to the reaction chamber and the other via the converter. There are approximately respectively 1] at 25 °℃ and 19 mg/m3 two reaction chambers and one or two detectors respectively 101,3 kPa. monitoring the nitrogen monoxide and nitrogen oxides content of the air sample. In the cyclic type analyser, there is only one For interferents, see 6.6. reaction chamber and detector and the output alternates between nitrogen monoxide and total nitrogen oxides measure- ments, i.e. the air sample alternately bypasses or passes 2 References through the converter. - Preparation of calibration gas mix- ISO6142,Gasanalysis tures -- Weighing methods. 1so 6144, Gas analysis - Preparation of calibration gas mix- 4 Reactions tures -- Static volumetric methods. Luminescence is a characteristic of many substances from Iso 6349, Gas analysis - Preparation of calibration gas mix- which light is emitted when they are excited. This phenomenon tures - Permeation method. is called chemiluminescence when produced as a result of a chemical reaction. Iso 6711, Gas analysis - Checking of calibration gas mixtures by a comparison method. This chemiluminescence method is based on the reaction NO + 03 → NO2 + 02 3 Principle NO′ → NO2 + h v Passage of the air sample through a filter (to prevent mat- operation of the chemiluminescence analyser) at a constant Excited nitrogen dioxide emits radiation centred around the f