ISO 7935:2024

International
Standard
ISO 7935
Second edition
Stationary source emissions —
2024-02
Determination of the mass
concentration of sulfur dioxide
in flue gases — Performance
characteristics of automated
measuring systems
Émissions de sources fixes — Détermination de la concentration
en masse de dioxyde de soufre — Caractéristiques de
performance des systèmes de mesurage automatiques
Reference number
© ISO 2024
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 4
4.1 Symbols .4
4.2 Abbreviated terms .5
5 Principle . 5
6 Description of the automated measuring systems . 5
6.1 Sampling and sample gas conditioning systems .5
6.2 Analyser equipment .6
7 Performance characteristics and criteria . 6
7.1 Performance criteria .6
7.2 Determination of the performance characteristics .7
7.2.1 Performance test .7
7.2.2 Ongoing quality control .7
8 Selection and installation procedure . 7
8.1 Choice of the measuring system .7
8.2 Sampling .8
8.2.1 Sampling location .8
8.2.2 Representative sampling .8
8.3 Calculation of conversion from volume to mass concentration for SO .8
9 Quality assurance and quality control procedures . 8
9.1 General .8
9.2 Frequency of checks.9
9.3 Calibration, validation and measurement uncertainty .9
10 Test report . 10
Annex A (informative) Extractive SO measurement systems .11
Annex B (informative) In situ SO measurement systems .20
Annex C (normative) Operational gases .24
Annex D (normative) Procedures for determination of the performance characteristics .25
Annex E (informative) Examples of the results for the assessment of SO AMS — SO
2 2
measurement .33
Annex F (informative) Calculation of uncertainty of measurement of SO .37
Bibliography .43

iii
Foreword
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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This document was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 1, Stationary
source emissions.
This second edition cancels and replaces the first edition (ISO 7935:1992), which has been technically
revised.
The main changes are as follows:
— the structure and the components have been updated to be similar to the latest editions of e.g. ISO 10849
(measurement of nitrogen oxides), ISO 12039 (measurement of CO, CO and O ), ISO 17179 (measurement
2 2
of NH ), ISO 13199 (measurement of total VOC), ISO 25140 (measurement of CH ), ISO 21258 (measurement
3 4
of N O);
— Clause 3 has been revised with the addition or deletion and change in terms and definitions;
— a new analytical technique has been added (laser spectroscopic technique or tunable laser spectroscopy)
for measurement of SO ;
— the performance characteristics and criteria as well as QA/QC procedures have been changed to
harmonize with latest ISO standards;
— examples of performance test results and the results of uncertainty calculation have been added for SO
measurement.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Sulfur dioxide (SO ) can arise in considerable quantities from combustion of fossil fuels used for energy
generation, industrial activities processing sulfur or sulfur containing material, and from combustion of
sulfur containing waste. The waste gas from these processes, containing sulfur dioxide, is usually discharged
into the ambient atmosphere, via a duct or a chimney.
For evaluating the mass concentration of sulfur dioxide present in the waste gas of stationary source
emissions, a number of highly developed methods of integrated sampling and subsequent determination by
chemical analysis and automated measuring systems are available.

v
International Standard ISO 7935:2024(en)
Stationary source emissions — Determination of the mass
concentration of sulfur dioxide in flue gases — Performance
characteristics of automated measuring systems
1 Scope
This document specifies a method for the determination of sulfur dioxide (SO ) in flue gases of stationary
sources and describes the fundamental structure and the key performance characteristics of automated
measuring systems.
The method allows continuous monitoring with permanently installed measuring systems of SO emissions.
This document describes extractive systems and in situ (non-extractive) systems in connection with a range
of analysers that operate using, for example, the following principles:
— non-dispersive infrared absorption (NDIR);
— Fourier transform infrared (FTIR) spectroscopy;
— laser spectroscopic technique or tunable laser spectroscopy (TLS);
— non-dispersive ultraviolet absorption (NDUV);
— differential optical absorption spectroscopy (DOAS).
Other equivalent instrumental methods can be used provided they meet the minimum performance
requirements specified in this document. The measuring system can be validated with reference materials,
according to this document, or comparable methods.
Automated measuring system (AMS) based on the principles listed above has been used successfully in this
application for the measuring ranges as shown in Annex E.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 9169, Air quality — Definition and determination of performance characteristics of an automatic measuring
system
ISO 14956, Air quality — Evaluation of the suitability of a measurement procedure by comparison with a
required measurement uncertainty
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IE
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