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1、 Reference number ISO 10498:2004(E) ISO 2004 INTERNATIONAL STANDARD ISO 10498 First edition 2004-06-01 Ambient air Determination of sulfur dioxide Ultraviolet fluorescence method Air ambiant Dosage du dioxyde de soufre Mthode par fluorescence dans lultraviolet ISO 10498:2004(E) PDF disclaimer This P
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6、. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2004 All rights reserved ISO 10498:2004(E) ISO 2004 All rights reserved iii Foreword ISO (the International Organization for S
7、tandardization) 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 body interested in a subject for which a technical committee has been established has the ri
8、ght to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Internationa
9、l Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as
10、an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO
11、 10498 was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 3, Ambient atmospheres. INTERNATIONAL STANDARD ISO 10498:2004(E) ISO 2004 All rights reserved 1 Ambient air Determination of sulfur dioxide Ultraviolet fluorescence method 1 Scope This International Standard describe
12、s an ultraviolet fluorescence method for sampling and determining sulfur dioxide (SO2) concentrations in the ambient air using automatic analysers. This International Standard is applicable to the determination of sulfur dioxide mass concentrations of a few micrograms per cubic metre to a few millig
13、rams per cubic metre or, expressed in terms of volume fraction, from a few microlitres per cubic metre to a few millilitres per cubic metre. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited
14、applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 4219, Air quality Determination of gaseous sulfur compounds in ambient air Sampling equipment ISO 6142, Gas analysis Preparation of calibration gas mixtures Gravimetric method ISO 6
15、144, Gas analysis Preparation of calibration gas mixtures Static volumetric method ISO 6145-1, Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 1: Methods of calibration ISO 6145-4, Gas analysis Preparation of calibration gas mixtures using dynamic volumetri
16、c methods Part 4: Continuous syringe injection method ISO 6145-6, Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 6: Critical orifices ISO 6349, Gas analysis Preparation of calibration gas mixtures Permeation method ISO 6767, Ambient air Determination of th
17、e mass concentration of sulfur dioxide Tetrachloromercurate (TCM)/pararosaniline method ISO 9169, Air quality Definition and determination of performance characteristics of an automatic measuring system 3 Principle of analysis The UV fluorescence method is not an absolute measurement method. Therefo
18、re, the instrument shall be calibrated regularly, using calibration gas diluted with air whose O2 and N2 content is close to normal atmospheric concentrations. It is also sensitive to pressure and temperature. This measurement technique is subject to less chemical interference than other techniques
19、available at present (see Annex A). However, the ISO 10498:2004(E) 2 ISO 2004 All rights reserved following compounds can affect the determination of sulfur dioxide: hydrogen sulfide, aromatic hydrocarbons, nitric oxide, water, and low molecular mass mercaptans. In individual cases where high concen
20、trations of various pollutants are present, it is recommended that their effect on the response of the analyser be determined (see Annex A for typical interference factors). The UV fluorescence method is based on the fluorescent emission of light by SO2 molecules previously excited by UV radiation.
21、The first reaction step is: SO2 + h(UV) SO2* Then in the second step, the excited SO2* molecule returns to the original ground state, emitting a photon of energy h according to the reaction: SO2* SO2 + h The intensity of the fluorescent radiation is proportional to the number of SO2 molecules in the
22、 detection volume, and is therefore proportional to the molar concentration of SO2. Therefore: I = kSO2 where I is the intensity of fluorescent radiation; k is the factor of proportionality; SO2 is the molar concentration of SO2. The air sample flows into the inlet of the analyser, where it is scrub
23、bed to remove any interference by aromatic hydrocarbons that may be present. A hydrocarbon scrubber device usually accomplishes this. Then the air sample flows into a reaction chamber, where it is irradiated by UV radiation with a wavelength in the range of 200 nm to 220 nm. The fluorescent light, i
24、n the wavelength range of 240 nm to 420 nm, is optically filtered and then converted to an electrical signal by a detector, for example a photomultiplier tube. The response of the analyser is proportional to the number of SO2 molecules in the reaction chamber. Therefore, temperature and pressure eit
25、her have to be kept constant or, if variation of these parameters is expected, the measured values have to be corrected. For this UV fluorescence method to yield accurate concentration measurements, it must be calibrated against some primary standard (see 4.2). 4 Reagents and materials 4.1 Zero air
26、Zero air used in the calibration of the analyser should not contain a concentration of SO2 detectable by the analyser under calibration. The concentration of O2 in the zero air shall be within 2 % of that in normal air (20,9 %). ISO 10498:2004(E) ISO 2004 All rights reserved 3 4.2 SO2 calibration ga
27、s mixtures 4.2.1 Primary calibration method One of the following equivalent methods for primary calibration shall be used: static volumetric dilution (ISO 6144); permeation tube sources (ISO 6349); tetrachloromercurate method (TCM) (ISO 6767); gravimetric preparation of gas mixtures in combination w
28、ith various dilution systems (ISO 6142, ISO 6145-1, ISO 6145-4, ISO 6145-6). Several methods for generating SO2 calibration gas standard mixtures are proposed (see 4.2.2). Whichever method is chosen, it is recommended that it be compared periodically against another independent traceable calibration
29、 method. The range of SO2 calibration concentrations chosen shall be between 10 % to 90 % of the SO2 concentration range in use. 4.2.2 Transfer-standard calibration methods Other methods to prepare calibration standard gases may also be used, if they are comparable to one or more of the methods ment
30、ioned in 4.2.1. Although any of the primary calibration methods may be used as transfer standards, in practice, it is easier to use a laboratory-calibrated permeation source or cylinder of SO2. The latter can be used either directly (with cylinders containing 0,1 mg/m3 to 10,0 mg/m3 of SO2 in air),
31、or with appropriate quantitative dilution (using cylinders containing ten to several hundred milligrams of SO2 per cubic metre of air). Gas cylinders containing SO2 standards shall be made of an inert material or have been passivated to ensure concentration stability of 3 % for the period of use exp
32、ected. Cylinders containing low concentrations shall be checked regularly against primary standards. 4.2.3 Operational (field) span check To aid in the quality control of the routine operation of the analyser on-site, span checks may be performed regularly (preferably daily, but at least weekly). Fo
33、r example, an internal permeation device may form an integral part of the apparatus, or an external calibrated cylinder, with appropriate dilution if necessary, may be used. The operation of the span check is controlled by valves, either manually or by remote control. The described span-check system
34、 is suitable for quality control in routine operations (see for example ISO 6879), to verify that the analyser is operating correctly, but may not be suitable for proper calibration as described in 4.2.1. The span-check system should regularly be compared to a laboratory-based calibration system as
35、described in 4.2.1. 5 Apparatus 5.1 Sampling line The sampling line and its residence time shall be as short as practical. This line shall be of a material which is chemically inert to SO2, such as fluorocarbon polymer or glass, in accordance with ISO 4219. If any doubt exists as to the inertness of
36、 the sampling line, calibration gases shall be used to test the complete sampling train. If water is expected to condense in the sampling line (when humid ambient air is drawn into a cool measurement environment), auxiliary heating of the sampling line will be necessary. ISO 10498:2004(E) 4 ISO 2004
37、 All rights reserved 5.2 Sample inlet filter for particulate matter The particulate matter filter at the sample inlet shall remove particles which could interfere with the correct operation of the analyser. It shall not remove any SO2, and consequently the filter and its support shall be made from i
38、nert material, such as fluorocarbon polymer. It is recommended to install the filter at the inlet of the sampling line leading to the instrument in order to prevent contamination of the sampling component by ambient particulate matter. NOTE A fluorocarbon polymer filter of 5 m pore size has been fou
39、nd to be effective (see ISO 4219). Monthly replacement of filters loaded with particulate matter is generally sufficient. Depending on the concentration of suspended particulate matter in ambient air, the filter may need to be replaced more frequently. 5.3 Analyser for measuring SO2 by UV fluorescen
40、ce (see Figure 1). The main components are described below. Key 1 sample 8 modulator 2 sampling inlet filter 9 optical outlet filter 3 selective traps for interfering agents 10 photomultiplier tube 4 reaction chamber 11 compensation pressure flowrate 5 optical inlet filter 12 pump 6 optical trap 13
41、exhaust 7 UV lamp 14 synchronous electronic amplification a Expressed as ml/m3. Figure 1 Schematic diagram of a UV fluorescence SO2 analyser ISO 10498:2004(E) ISO 2004 All rights reserved 5 5.3.1 Selective traps for interferents One or more selective traps should be used before the reaction chamber
42、to remove interfering gases such as aromatic hydrocarbons. These selective traps shall not retain any SO2 and shall be changed in accordance with manufacturers instruction manuals and existing national requirements. If high concentrations of H2S are expected in the ambient air, a selective scrubber
43、for H2S should be used. 5.3.2 Optical assembly and fluorescence cell The UV lamp emission may be pulsed electronically or mechanically for synchronous detection and amplification of the signal. The lamp shall have a stabilized power supply to ensure a stable emission of light. An optical filter is u
44、sed to restrict the wavelengths to a range that allows excitation of the SO2 molecule and yet minimizes the interference of water vapour, aromatic hydrocarbons or nitric oxide. The detector, for example the photomultiplier tube, detects the fluorescent light emitted by the SO2 molecules in the react
45、ion chamber. A selective optical filter placed in front of the detector reduces the signal due to scattering of the incident light. The reaction chamber shall be made of material inert to SO2 and UV radiation. The cell should be heated above the dewpoint to avoid water condensation and temperature f
46、luctuations. The optical trap of the chamber prevents reflection of the exciting UV radiation. The optical assembly should be placed in a heated enclosure. 5.3.3 Pressure regulator The output signal of the analyser depends on the density of SO2 (number of SO2 molecules) present in the reaction chamb
47、er, and is therefore proportional to the pressure in the reaction chamber. Variations of internal pressure shall be measured and the signal corrected or controlled by means of a regulator. The signal may have to be corrected also for external pressure and temperature fluctuations. Significant pressu
48、re corrections may be needed due to synoptic meteorological changes (up to 3 %) or by the altitude of the measurement site (about 10 % decrease in pressure for an 800 m rise in altitude). NOTE One of the main causes of a reduction in pressure in the reaction chamber is a pressure drop in the sample
49、line. 5.3.4 Flowrate controller and indicator It is recommended that the flowrate be kept constant by means of a flowrate controller. A flowrate indicator should be included in the instrument. 5.3.5 Air pump, which draws air through the analyser, at the end of the sample flow path. As the use of the UV lamp produces ozone, it is recommended to vent the analyser air through a suitable charcoal scrubber. -,-,- ISO 10498:2004(E) 6 IS