SIST EN ISO 21258:2010

SLOVENSKI STANDARD
01-november-2010
(PLVLMHQHSUHPLþQLKYLURY'RORþHYDQMHPDVQHNRQFHQWUDFLMHGLGXãLNRYHJD
PRQRNVLGD125HIHUHQþQDPHWRGDQHGLVSHU]LYQDLQIUDUGHþDPHWRGD,62

Stationary source emissions - Determination of the mass concentration of dinitrogen
monoxide (N2O) - Reference method: Non-dispersive infrared method (ISO 21258:2010)
Emissionen aus stationären Quellen - Bestimmung der Massenkonzentration von
Distickstoffmonoxid (N2O) - Referenzverfahren: Nicht-dispersives Infrarot-Verfahren
(ISO 21258:2010)
Émissions de sources fixes - Détermination de la concentration massique de protoxyde
d'azote (N2O) - Méthode de référence: Méthode infrarouge non dispersive (ISO
21258:2010)
Ta slovenski standard je istoveten z: EN ISO 21258:2010
ICS:
13.040.40 (PLVLMHQHSUHPLþQLKYLURY Stationary source emissions
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 21258
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2010
ICS 13.040.40
English Version
Stationary source emissions - Determination of the mass
concentration of dinitrogen monoxide (N2O) - Reference
method: Non-dispersive infrared method (ISO 21258:2010)
Émissions de sources fixes - Détermination de la Emissionen aus stationären Quellen - Bestimmung der
concentration massique de protoxyde d'azote (N2O) - Massenkonzentration von Distickstoffmonoxid (N2O) -
Méthode de référence: Méthode infrarouge non dispersive Referenzverfahren: Nicht-dispersives Infrarot-Verfahren
(ISO 21258:2010) (ISO 21258:2010)
This European Standard was approved by CEN on 19 May 2010.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2010 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21258:2010: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
This document (EN ISO 21258:2010) has been prepared by Technical Committee ISO/TC 146 "Air quality" in
collaboration with Technical Committee CEN/TC 264 “Air quality” the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by December 2010, and conflicting national standards shall be withdrawn
at the latest by December 2010.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 21258:2010 has been approved by CEN as a EN ISO 21258:2010 without any modification.

INTERNATIONAL ISO
STANDARD 21258
First edition
2010-06-15
Stationary source emissions —
Determination of the mass concentration
of dinitrogen monoxide (N O) —
Reference method: Non-dispersive
infrared method
Émissions de sources fixes — Détermination de la concentration
massique de protoxyde d'azote (N O) — Méthode de référence:
Méthode infrarouge non dispersive

Reference number
ISO 21258:2010(E)
©
ISO 2010
ISO 21258:2010(E)
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ii © ISO 2010 – All rights reserved

ISO 21258:2010(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Symbols and abbreviated terms .5
5 Principle.6
6 Description of the automated measuring equipment.6
6.1 General .6
6.2 Sampling line components.7
6.3 Analyser equipment .8
6.4 Responsibilities .8
7 Performance criteria and determination of the performance characteristics.9
7.1 Performance criteria.9
7.2 Determination of the performance characteristics and measurement uncertainty .10
7.3 Establishment of the uncertainty budget.10
8 Measurement procedure.11
8.1 Sampling location.11
8.2 Sampling point(s) .11
8.3 Choice of the measuring system .11
8.4 Setting of the analyser on site .12
9 Ongoing quality control.13
9.1 General .13
9.2 Frequency of checks.13
10 Evaluation of the method in the field .14
11 Expression of results.14
12 Test report.15
Annex A (informative) Schematic diagram of a typical analyser .16
Annex B (normative) Procedures for determination of the performance characteristics during the
general performance test.17
Annex C (informative) Example of assessment of compliance of NDIR method for N O with
requirements on emission measurements .20
Annex D (informative) Results of comparison tests.27
Annex E (informative) Leak test procedures.30
Bibliography.32

ISO 21258:2010(E)
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 body interested in a subject for which a technical committee has been
established has the right 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.
International 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 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 21258 was prepared by Technical Committee ISO/TC 146, Air quality, Subcommittee SC 1, Stationary
source emissions.
iv © ISO 2010 – All rights reserved

ISO 21258:2010(E)
Introduction
Dinitrogen monoxide (N O, also known as nitrous oxide) is an important greenhouse gas with a global
warming potential 310 times that of carbon dioxide (CO ). N O is of both natural and anthropogenic origin.
2 2
Increased emissions of N O have been observed, for example, in the exhaust gas of combustion processes
using nitrogenous fuels at temperatures below 900 °C, and in the reduction of NO using the selective non-

x
catalytic reduction (SNCR) process, in particular when urea is used. There is considerable uncertainty over
current N O emissions, which is reflected in the wide range of emission factors cited. The largest uncertainties
are for emissions from natural and agricultural sources, which are difficult to measure accurately. In the past,
emissions from stationary sources such as coal-fired plants and industry were overestimated due to a serious
artefact in the grab-sampling methodology used to measure emissions. N O is involved in the EU emission
trading scheme along with CO and methane (CH ).
2 4
Improved measurement techniques are helping to reduce uncertainties in emission estimates. Improved
measurement techniques are also a prerequisite for accurate information on N O and its potential role in the
enhanced greenhouse effect.
INTERNATIONAL STANDARD ISO 21258:2010(E)

Stationary source emissions — Determination of the mass
concentration of dinitrogen monoxide (N O) — Reference
method: Non-dispersive infrared method
1 Scope
This International Standard specifies a method for sampling, sample conditioning and determination of
dinitrogen monoxide (N O) content in the flue gas emitted from ducts and stacks to atmosphere. It sets out the
non-dispersive infrared (NDIR) analytical technique, including the sampling system and sample gas
conditioning system.
This International Standard is a reference method for periodic monitoring and for calibration, adjustment or
control of automatic monitoring systems permanently installed on a stack.
This reference method has been successfully tested on a sewage sludge incinerator where the N O
concentration in the flue gas was up to about 200 mg/m .
2 Normative references
The following referenced documents are indispensable for the application 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 9169:2006, 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
ISO/IEC Guide 98-3:2008, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
influence quantity
quantity that is not the measurand but that affects the result of the measurement
[ISO/IEC Guide 98-3:2008, B.2.10]
3.2
interference
negative or positive effect upon the response of the measuring system, due to a component of the sample that
is not the measurand
ISO 21258:2010(E)
3.3
interferent
interfering substance
substance present in the air mass under investigation, other than the measurand, that affects the response
[ISO 9169:2006, 2.1.12]
3.4
lack of fit
systematic deviation within the range of application between the measurement results obtained by applying
the calibration function to the observed response of the measuring system measuring reference materials and
the corresponding accepted value of such reference materials
NOTE 1 Lack of fit may be a function of the measurement result.
[ISO 9169:2006, 2.2.9]
NOTE 2 The expression “lack of fit” is often replaced in everyday language for linear relations by “linearity” or “deviation
from linearity”.
3.5
measurand
particular quantity subject to measurement
[ISO/IEC Guide 98-3:2008, B.2.9]
3.6
performance characteristic
one of the quantities assigned to equipment in order to define its performance
NOTE Performance characteristics can be described by values, tolerances, or ranges.
3.7
reference gas
gaseous mixture of stable composition used to calibrate the reference measuring system and which is
traceable to national or international standards
3.8
reference method
measurement method taken as a reference by convention, which gives the accepted reference value of the
measurand
3.9
repeatability in the laboratory
precision under repeatability conditions in the laboratory
NOTE 1 Repeatability can be expressed quantitatively in terms of the dispersion characteristics of the results. In this
International Standard, the repeatability is expressed as a value with a level of confidence of 95 %.
[1]
NOTE 2 Adapted from ISO 3534-2:2006 , 3.3.5.
3.10
repeatability conditions in the laboratory
observation conditions where independent test results are obtained with the same method on identical test
items in the same test or measuring facility by the same operator using the same equipment within short
intervals of time in the laboratory
NOTE 1 Repeatability conditions in the laboratory include:
⎯ the same measurement procedure at the same laboratory;
2 © ISO 2010 – All rights reserved

ISO 21258:2010(E)
⎯ the same operator;
⎯ the same measuring instrument used under the same conditions;
⎯ the same location;
⎯ repetition over a short period of time.
[1]
NOTE 2 Adapted from ISO 3534-2:2006 , 3.3.6.
3.11
repeatability in the field
precision under repeatability conditions in the field
NOTE 1 Repeatability can be expressed quantitatively in terms of the dispersion characteristics of the results. In this
International Standard the repeatability under field conditions is expressed as a value with a level of confidence of 95 %.
[1]
NOTE 2 Adapted from ISO 3534-2:2006 , 3.3.5.
3.12
repeatability conditions in the field
observation conditions where independent test results are obtained with the same method on identical test
items in the same test or measuring facility by the same operator using the same equipment within short
intervals of time in the field
NOTE 1 Repeatability conditions in the field include:
⎯ the same measurement procedure;
⎯ two sets of equipment, the performance of which fulfils the requirements of the reference method, used under the
same conditions;
⎯ the same location;
⎯ implemented by the same laboratory;
⎯ typically calculated on short periods of time in order to avoid the effect of changes of influence parameters.
[1]
NOTE 2 Adapted from ISO 3534-2:2006 , 3.3.6.
3.13
reproducibility in the field
precision under reproducibility conditions in the field
NOTE 1 Reproducibility in the field can be expressed quantitatively in terms of the dispersion characteristics of the
results. In this International Standard the reproducibility under field conditions is expressed as a value with a level of
confidence of 95 %.
[1]
NOTE 2 Adapted from ISO 3534-2:2006 , 3.3.10.
NOTE 3 Results are usually understood to be corrected results.
3.14
reproducibility conditions in the field
observation conditions where independent test results are obtained with the same method on identical test
items in different test or measurement facilities with different operators using different equipment in the field
NOTE 1 Reproducibility conditions in the field include:
⎯ the same measurement procedure;
ISO 21258:2010(E)
⎯ several sets of equipment, the performance of which fulfils the requirements of the reference method, used under the
same conditions;
⎯ the same location;
⎯ implemented by several laboratories.
[1]
NOTE 2 Adapted from ISO 3534-2:2006 , 3.3.11.
3.15
residence time in the measuring system
time period for transportation of the sampled gas from the inlet of the probe to the inlet of the measurement
cell
3.16
response time
time interval between the instant when a stimulus is subjected to a specified abrupt change and the instant
when the response reaches and remains within specified limits around its final stable value, determined as the
sum of the lag time and the rise time in the rising mode, and the sum of the lag time and the fall time in the
falling mode
[ISO 9169:2006, 2.2.4]
3.17
span gas
gas or gas mixture used to adjust and check a specific point on the response line of the measuring system
NOTE This concentration is often chosen around 80 % of full scale.
3.18
uncertainty (of measurement)
parameter, associated with the result of a measurement, that characterises the dispersion of the values that
could reasonably be attributed to the measurand
[ISO/IEC Guide 98-3:2008, B.2.18]
3.19
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
[ISO/IEC Guide 98-3:2008, 2.3.1]
3.20
combined standard uncertainty
standard uncertainty of the result of a measurement when that result is obtained from the values of a number
of other quantities, equal to the positive square root of a sum of terms, the terms being the variances or
covariances of these other quantities weighted according to how the measurement result varies with changes
in these quantities
[ISO/IEC Guide 98-3:2008, 2.3.4]
3.21
expanded uncertainty
quantity defining an interval around the result of a measurement that may be expected to encompass a large
fraction of the distribution of values that could reasonably be attributed to the measurand
[ISO/IEC Guide 98-3:2008, 2.3.5]
NOTE In this International Standard, the expanded uncertainty is calculated with a coverage factor of k = 2, and with
a level of confidence of 95 %.
4 © ISO 2010 – All rights reserved

ISO 21258:2010(E)
3.22
uncertainty budget
list of sources of uncertainty and their associated standard uncertainties, compiled with a view to evaluating a
combined standard uncertainty associated with a measurement result
[6]
[ISO/TS 21748:2004 , 3.13]
3.23
zero gas
gas or gas mixture used to establish the zero point on a calibration curve within a given concentration range
[4]
[ISO 12039:2001 ]
4 Symbols and abbreviated terms
γ measured concentration of N O at actual oxygen concentration
a 2
γ concentration of N O on dry basis
d 2
γ normalized concentration of N O
n 2
γ measured concentration of N O on wet basis
w 2
grand mean of measured N O concentration
γ
ϕ measured water vapour content, as a percentage volume fraction
H O,m
ϕ measured oxygen content, as a volume fraction, in the waste gas
O ,m
ϕ reference oxygen content, as a volume fraction
O ,ref
C coefficient of variation of repeatability

V,r
C coefficient of variation of reproducibility

V,R
C coefficient of variation of the standard uncertainty

V,u
k coverage factor
n number of test results
PFA perfluoroalkoxy
PTFE polytetrafluoroethylene
QA quality assurance
QC quality control
s standard deviation of level j
j
s repeatability standard deviation
r,j
s reproducibility standard deviation
R,j
u standard uncertainty
u(γ ) combined uncertainty of the measured concentration of N O
N O 2
U(γ ) expanded uncertainty of the measured concentration of N O
N O 2
ISO 21258:2010(E)
5 Principle
This International Standard describes a reference method for sampling, sample conditioning, and determining
N O content in the flue gas emitted from ducts and stacks to atmosphere by means of a continuous analyser
using non-dispersive infrared method. A number of performance characteristics with associated minimum
performance criteria are given for the analyser and details of the uncertainty of the method are presented.
Requirements and recommendations for quality assurance and quality control of field measurements are
given.
6 Description of the automated measuring equipment
6.1 General
A representative volume of flue gas is extracted from the emission source for a fixed period of time at a
controlled flow rate. Dust present in the volume sampled is removed by filtration before the sample is
conditioned and passes to the analytical instrument. Figure 1 shows a typical arrangement of a complete
measuring system for N O.
Key
1 gas sampling probe
2 primary filter
3 heating (for use as necessary)
4 sampling line (heated as necessary)
5 sample cooler with condensate separator
6 sample pump
7 secondary filter
8 needle valve
9 flow meter
10 N O analyser
11 output
12 inlet for zero and span gas (preferably in front of the nozzle) to check the complete system
13 inlet for zero and span gas to check the conditioning system and N O analyser
14 inlet for zero and span gas to check the converter and N O analyser
15 valve
16 converter for CO oxidation
Figure 1 — Example of the installation of measuring devices
6 © ISO 2010 – All rights reserved

ISO 21258:2010(E)
6.2 Components of the sampling apparatus
6.2.1 Sampling probe
The sampling probe shall be made of suitable, corrosion-resistant material, e.g. stainless steel. The probe
shall be heated to avoid condensation occurring in its interior; it shall also be cooled by an air or water jacket
when sampling very hot gases. Nonetheless, it shall not be cooled below the acid dew-point. The probe
diameter shall be appropriately sized to provide a flow rate that meets the requirements of the analysers.
6.2.2 Primary filter
The filter shall be made of ceramic or sintered metal with 10 µm pore size. The filter shall be heated above the
water or acid dew-point.
6.2.3 Sampling line
The sampling line shall be made of polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) or stainless steel.
The lines shall be operated 15 °C above the dew-point of condensable substances (generally the water or
acid dew-point). The tube diameter should be appropriately sized to provide a flow rate that meets the
requirements of the analysers, under selected line length and the degree of pressure drop in the line as well
as the performance of the sampling pump used.
6.2.4 Sample cooler or permeation drier
The sample cooler or permeation drier shall be used to separate water vapour from the flue gas. The dew-
point shall be sufficiently below the ambient temperature. A cooling temperature of 2 °C to 5 °C is suggested.
Sufficient cooling is required for the volume of gas being sampled and the amount of water vapour that it
contains. The cooler and the sample treatment procedure is important to prevent artefact formation of N O
from NO and SO dissolved in the condensate, and thus minimize a source of error in the results.
2 2
6.2.5 Sampling pump
A gas-tight pump is used to withdraw a continuous sample from the duct through the sampling system. This
may be a diaphragm pump, a metal bellows pump, an ejection pump or other pumps. The pump shall be
constructed of corrosion-resistant material. The performance of the pump shall be such that it can supply the
analyser with the gas flow required. In order to reduce the residence time in the sampling line and the risk of
physicochemical transformation of the sample, the gas flow can be greater than that required for the analytical
units.
6.2.6 Secondary filter
The secondary filter is needed to remove the remaining particulate material, in order to protect the pump and
the analyser. A filter that retains particles greater than 1 µm is recommended. Acceptable materials are PTFE
or borosilicate glass. The size of the filter shall be determined from the sample flow required and the
manufacturer's data on the flow rate per unit area.
6.2.7 Flow controller and flow meter
The flow controller and flow meter are used to set the required flow. They shall be constructed of corrosion-
resistant material.
6.2.8 Converter
The converter is an oxidation catalyst tube, which may be needed for pretreatment of the sample gas. The
converter oxidizes CO in the sample gas into CO which can be corrected for later, in order to decrease the

influence of the interferent.
ISO 21258:2010(E)
The converter uses a mixture of manganese and copper oxides which can oxidize CO to CO at 120 °C. Since
it has been confirmed that the decomposition of N O begins at temperatures higher than 300 °C, no effect of
the converter on the measured N O concentration has been found. The converter efficiency shall be such that
the performance criteria given in Table 1 shall be met.
6.3 Analyser equipment
The gas analysers use, as the measurement principle, the absorption of infrared radiation (IR) by the
component measured in characteristic wavelength ranges. The analysers operate according to the non-
dispersive IR method (NDIR), while the selectivity of measurement is achieved by the radiation detector which
is filled with the component to be measured. A schematic diagram of a typical analyser is given in Figure A.1.
Special attention should be given to CO and CO interference, since for detection of N O the absorption at
2 2
around 4,5 µm is usually used, while CO has its absorption at 4,5 µm to 4,7 µm and CO has its absorption at
4,3 µm. The CO interference can be excluded by using the converter (see 6.2.8). The CO sensitivity requires
determination with CO test gases. During real operation, CO requires simultaneous measurement to yield
2 2
data for real-time correction of the N O readings. In many instruments, this CO interference correction is
2 2
done automatically through a CO channel.
Since it can interfere with the measurement and lead to condensation in the analyser, water vapour present in
the sampled gas is condensed in a gas cooler before the gas enters the analyser. Note that the presence of
water droplets can affect the analysis of N O, since the solubility of N O in water is 1,2 g/l (at 20 °C,
2 2
101,3 kPa).
6.4 Responsibilities
6.4.1 General
The reference method shall comply with the performance criteria specified in Table 1. These performance
criteria are allocated to the responsibilities specified in 6.4.2 to 6.4.4.
6.4.2 General performance test
The manufacturer of the measuring system shall prove, in a general performance test, that the relevant
performance criteria listed in Table 1 are fulfilled by the instrument type.
6.4.3 Ongoing quality assurance and quality control in the laboratory
The user of the measuring system shall prove, during regular laboratory tests within the ongoing QC
programme, that the relevant performance criteria listed in Table 1 are fulfilled.
6.4.4 Quality assurance during operation in the field
The user of the measuring system shall check, during field operation, that the relevant performance criteria
listed in Table 1 are fulfilled.
8 © ISO 2010 – All rights reserved

ISO 21258:2010(E)
Table 1 — Relevant performance criteria of the analyser and the measuring system criteria to be
evaluated during the general performance test and by means of ongoing QA-QC in laboratory tests
and during field operation
Performance characteristic Performance criterion
Response time u 200 s × × ×
u 2 % of upper limit of the lowest
Detection limit ×  ×
measuring range used
u 2 % of upper limit of the lowest
Lack of fit × × ×
measuring range used
u 2 % of upper limit of the lowest
Zero drift in 24 h × × ×
measuring range used
u 2 % of upper limit of the lowest
Span drift in 24 h × × ×
measuring range used
u 2 % of upper limit of the lowest
Sensitivity to atmospheric pressure ×  ×
measuring range used for 2 kPa
Sensitivity to sample volume flow or
a
— ×  ×
sample pressure
u 2 % of upper limit of the lowest
Sensitivity to ambient temperature ×  ×
measuring range used per 10 °C
Sensitivity to electric voltage u 2 % of the range per 10 V ×  ×
u 6 % of upper limit of the lowest
b
Interferents × × ×
measuring range used
Losses and leakage in the sampling
u 2 % of the measured value  × ×
line and conditioning system
Standard deviation of repeatability in u 2 % of upper limit of the lowest
c
× × ×
laboratory at zero measuring range used
Standard deviation of repeatability in u 2 % of upper limit of the lowest
c
× × ×
laboratory at span level measuring range used
a
The tested volume flow range or pressure is defined in the manufacturer's recommendations.
b
Interferents that shall be tested are at least those given in Table 2.
c
Only one of the two values shall be included in the calculation: the first possibility is to choose the repeatability standard deviation
obtained from laboratory tests corresponding to the closest concentration to the actual concentration in stack, or the higher standard
deviation of repeatability or coefficient of variation of repeatability independently of the concentration measured in stack.
7 Performance criteria and determination of the performance characteristics
7.1 Performance criteria
Table 1 gives an overview of the relevant performance characteristics and performance criteria of the analyser
and measurement system to be evaluated on three levels, during general performance test, by means of
ongoing QA-QC during laboratory tests, and during field operation. In the rightmost column, values included in
the calculation of the expanded uncertainty are indicated.
Performance test
QA-QC in laboratory
Field operation
Term for evaluating
uncertainty
ISO 21258:2010(E)
The upper limit of the lowest measuring range used should be set according to the application, so that the
measurement values lie within 20 % to 80 % of the analyser range.
7.2 Determination of the performance characteristics and measurement uncertainty
7.2.1 Performance test
The performance characteristics of the method shall be determined during the general performance test. The
values of the performance characteristics determined shall meet the performance criteria specified in Table 1.
The procedures for the determination of these performance characteristics are specified in Annex B.
The ambient conditions applied during the general performance test have to be documented.
7.2.2 Ongoing quality control
The user shall check specific performance characteristics during ongoing operation of the measuring system
with a frequency specified in Table 3.
The measurement uncertainty during field application shall be determined by the user of the measuring
system in accordance with applicable national or International Standards. It can be determined by a direct or
[5]
by an indirect approach for uncertainty estimation as described in ISO 20988 . The uncertainty of the
measured values under field operation is not only influenced by the performance characteristics of the
analyser itself but also by uncertainty due to:
a) sampling line and sample conditioning system;
b) site specific conditions;
c) reference gases used.
7.3 Establishment of the uncertainty budget
An uncertainty budget shall be established to determine if the analyser and its associated sampling system
fulfils the requirements for a maximum allowable expanded uncertainty. This uncertainty budget shall be
drawn up according to the procedures specified in ISO 14956 or ISO/IEC Guide 98-3 requirements, taking into
account all the relevant characteristics included in calculation of expanded uncertainty given in Table 1.
The principle of calculation of the expanded uncertainty is based on the law on propagation of uncertainty laid
down in ISO/IEC Guide 98-3 requirements as listed.
⎯ Determine the standard uncertainties for each value included in the calculation of the budget uncertainty
by means of laboratory and field tests, and in accordace with ISO/IEC Guide 98-3 requirements.
⎯ Calculate the uncertainty budget by combining all the standard uncertainties in accordance with
ISO 14956, including the uncertainty of the reference gas and taking variations range of influence
quantities and interferents of the specific site conditions into account. These conditions are sometimes
unknown. In this case, default values defined in Table 2 shall be applied.
⎯ Values of standard uncertainty less than 5 % of the maximum standard uncertainty can be discarded.
⎯ Calculate the expanded uncertainty.

10 © ISO 2010 – All rights reserved

ISO 21258:2010(E)
Table 2 — Default ranges of influence quantities and interferents to be applied
for the determination of the uncertainty budget
Variations range and default concentrations
Influence quantities and interferents
of interferents
Atmospheric pressure ±2 kPa
Sample volume flow variation In accordance with the manufacturer's recommendations
Ambient temperature ±15 °C
Power supply ±10 % of nominal supply voltage
CO 14 % volume
CO 300 mg/m
SO 200 mg/m
NO 250 mg/m
NOTE An example of the evaluation of an uncertainty budget is given in Annex C.
8 Measurement procedure
8.1 Sampling location
The sampling location chosen for the measurement devices and sampling shall be of sufficient size and
construction, that a representative emission measurement can be made that is suitable for the measurement
task. In addition, the sampling location shall be chosen with regard to safety of the personnel, accessibility and
availability of electrical power.
8.2 Sampling point(s)
It is necessary to ensure that the gas concentrations measured are representative of the average conditions
inside the flue gas duct. Therefore, the sampling points shall be selected so that the sample is as
representative as possible.
[3]
NOTE 1 The selection of sampling points for representative sampling is described, for example, in ISO 9096 and
[9]
EN 15259 .
If the flue gas is homogenous, sampling may be carried out at any point in the sampling plane. For larger
ducts, this point may be situated close to the sampling port provided that there is no disturbance of the flow or
concentration due to the influence of the sampling port.
NOTE 2 The homogeneity can be demonstrated with a continuous measurement of O or CO using a fixed and a
2 2
[9]
moving probe covering the sampling plane. The method is described in EN 15259 .
8.3 Choice of the measuring system
To choose an appropriate analyser, sampling line and sample conditioning unit, the following characteristics of
flue gases should be known before the field campaign:
a) temperature of exhaust gases;
b) humidity;
c) dust loading;
d) expected concentration range of N O;
ISO 21258:2010(E)
e) expected concentration of potentially interfering substances, including at least the four components listed
in Table 2.
The full scale of the selected analyser shall be 150 % to 300 % of the expected concentration. The full scale
should not be less than peak emission.
To avoid long response times, the sample line should be as short as possible. If necessary, a bypass pump
should be used. If there is a high dust loading in the sample gas, then an appropriate heated filter shall be
used.
Before conducting field measurements, the user shall verify that the analyser is functioning in accordance with
the required performance criteria fixed in this International Standard, and that the sampling line and
conditioning unit are in a good operational condition.
8.4 Setting of the analyser on site
8.4.1 General
The complete measuring system, including the conditioning unit, the sampling line, and the analyser, shall be
connected according to the manufacturer’s instructions. The nozzle of the probe is placed in the duct
according to 8.2.
The conditioning unit, sampling probe, filter, connection tube and analyser shall be stabilised at the required
temperature.
After pre-heating, the flow passing through the sampling system and the analyser shall be adjusted to the
chosen flow rate to be used during measurement. This flow shall be maintained at a constant level within
±10 % of the nominal flow rate.
When both the instrument and sampling system have been set up, the proper functioning of the instrument
and sampling system shall be checked. The results of these checks shall fulfil the requirements and limitations
as set out by the manufacturer of the instrument, as well as the requirements (such as materials used, and so
on) given by this International Standard. Compliance with the requirements of this International Standard shall
be documented.
Any data recording, data processing and telemetry system used in conjunction with the measuring system
shall be checked for proper functioning. If any components are changed, then these checks shall be repeated.
All checks shall be documented. The time resolution of the data recording system used to calculate the mean
values shall be less or equal to 10 s.
8.4.2 Preliminary zero and span check, and adjustments
8.4.2.1 Adjustment of the analyser
At the beginning of the measuring period, zero and span gases are supplied to the analyser directly, without
passing through the sampling system. Adjustments, as listed, are made until the correct zero and span gas
values are given by the data sampling system.
⎯ Adjust the zero value, if necessary.
⎯ Adjust the span, if necessary.
⎯ Finally, check zero again to see if there is no significant change (e.g. a change less than the standard
deviation of the repeatability at zero). If there is any problem, repeat the procedure.
12 © ISO 2010 – All rights reserved

ISO 21258:2010(E)
8.4.2.2 Check of the sampling system
Before starting the measurement, determine whether there is leakage in the sampling line by supplying zero
gas and span gas to the analyser through t
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