EN 14211:2005

SLOVENSKI STANDARD
01-september-2005
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Ambient air quality - Standard method for the measurement of the concentration of
nitrogen dioxide and nitrogen monoxide by chemiluminescence
Luftqualität - Messverfahren zur Bestimmung der Konzentration von Stickstoffdioxid und
Stickstoffmonoxid mit Chemilumineszenz
Qualité de l'air ambiant - Méthode normalisée pour le mesurage de la concentration en
dioxyde d'azote et en monoxyde d'azote par chimiluminescence
Ta slovenski standard je istoveten z: EN 14211:2005
ICS:
13.040.20 Kakovost okoljskega zraka Ambient atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 14211
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2005
ICS 13.040.20
English version
Ambient air quality - Standard method for the measurement of
the concentration of nitrogen dioxide and nitrogen monoxide by
chemiluminescence
Qualité de l'air ambiant - Méthode normalisée pour le Luftqualität - Messverfahren zur Bestimmung der
mesurage de la concentration en dioxyde d'azote et Konzentration von Stickstoffdioxid und Stickstoffmonoxid
monoxyde d'azote par chimiluminescence mit Chemilumineszenz
This European Standard was approved by CEN on 10 December 2004.
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 Central Secretariat 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 Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 14211:2005: E
worldwide for CEN national Members.

Contents
Page
Foreword.4
1 Scope .5
2 Normative references .5
3 Terms and definitions .6
4 Symbols and abbreviated terms .10
5 Principle.12
5.1 General.12
5.2 Measuring principle.13
5.3 Type approval test .13
5.4 Field operation and quality control.14
6 Sampling equipment .14
6.1 General.14
6.2 Sampling location.14
6.3 Sample inlet and sampling line .14
6.4 Particulate filter.15
6.5 Control and regulation of sample flow rate .15
6.6 Sampling pump for the manifold.15
7 Analyser equipment .16
7.1 General.16
7.2 Converter .16
7.3 Ozone generator .16
7.4 Reaction chamber.17
7.5 Optical filter .17
7.6 Detector .17
7.7 Ozone removal device.17
7.8 Sampling pump for the analyser.17
7.9 Residence time inside the analyser.17
8 Type approval of nitrogen dioxide and nitrogen monoxide analysers .17
8.1 General.17
8.2 Relevant performance characteristics and performance criteria .18
8.3 Design change .20
8.4 Procedures for determination of the performance characteristics during the laboratory test .21
8.5 Determination of the performance characteristics during the field test.32
8.6 Expanded uncertainty calculation for type approval.36
9 Field operation and ongoing quality control .36
9.1 General.36
9.2 Suitability evaluation.37
9.3 Initial installation.38
9.4 Ongoing quality control .38
9.5 Calibration of the analyser.40
9.6 Checks .41
9.7 Maintenance .44
9.8 Data handling and data reports.44
10 Expression of results .45
11 Test reports and documentation.45
11.1 Type approval test .45
11.2 Field operation .45
Annex A (normative) Calculation of residence times for a maximum allowable NO increase in the
sampling line [ISO 13964] .47
Annex B (normative) Test of lack of fit.48
Annex C (informative) Sampling equipment.50
Annex D (informative) Sampling on microscale [2] .52
Annex E (informative) Types of chemiluminescence analysers.53
Annex F (informative) Manifold testing equipment.56
Annex G (normative) Type approval.57
Annex H (normative) Calculation of uncertainty in field operation at the hourly limit value .76
Annex I (normative) Calculation of uncertainty in field operation at the annual limit value .82
Bibliography.92

Foreword
This document (EN 14211:2005) has been prepared by 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 September 2005, and conflicting national standards shall be withdrawn at the
latest by September 2005.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark,
Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
1 Scope
This document specifies a continuous measurement method for the determination of the concentration of nitrogen
dioxide and nitrogen monoxide present in ambient air based on the chemiluminescence measuring principle. This
document describes the performance characteristics and sets the relevant minimum criteria required to select an
appropriate chemiluminescence analyser by means of type approval tests. It also includes the evaluation of the
suitability of an analyser for use in a specific fixed site so as to meet the Directives data quality requirements and
requirements during sampling, calibration and quality assurance.
The method is applicable to the determination of the concentration of nitrogen dioxide present in ambient air from
3 3
0 µg/m to 500 µg/m . This concentration range represents the certification range for NO for the type approval test.
3 3
NOTE 1 0 µg/m to 500 µg/m of NO corresponds to 0 nmol/mol to 261 nmol/mol of NO .
2 2
The method is applicable to the determination of the concentration of nitrogen monoxide present in ambient air
3 3
from 0 µg/m to 1 200 µg/m . This concentration range represents the certification range for NO for the type
approval test.
3 3
NOTE 2 0 µg/m to 1 200 µg/m of NO corresponds to 0 nmol/mol to 962 nmol/mol of NO.
The method covers the determination of ambient air concentrations of nitrogen dioxide and nitrogen monoxide in
zones classified as rural areas, urban-background areas and traffic-orientated locations.
NOTE 3 Lower ranges may be used for measurement systems applied at rural locations monitoring Ecosystems.
The results are expressed in µg/m (at 293 K and 101,3 kPa).
When the standard is used for other purposes than the EU Directive, the range and uncertainty requirements need
not apply.
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.
ENV 13005, Guide to the expression of uncertainty in measurement
EN ISO 14956, Air quality — Evaluation of the suitability of a measurement procedure by comparison with a
required measurement uncertainty (ISO 14956:2002)
ISO 6142, Gas analysis — Preparation of calibration gas mixtures — Gravimetric method
ISO 6143, Gas analysis — Comparison methods for determining and checking the composition of calibration gas
mixtures
ISO 6144, Gas analysis — Preparation of calibration gas mixtures — Static volumetric method
ISO 6145 (all parts), Gas analysis — Preparation of calibration gas mixtures using dynamic volumetric methods
ISO 13964:1998, Air quality — Determination of ozone in ambient air — Ultraviolet photometric method
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
3.1
ambient air
outdoor air in the troposphere, excluding workplace air
3.2
sample gas temperature
temperature at the sample inlet outside the monitoring station
3.3
availability of the analyser
fraction of the total time period for which usually valid measuring data of the ambient air concentration is available
from an analyser
3.4
certification range
concentration range for which the analyser is type approved
3.5
calibration
comparison of the analyser response to a known gas concentration with a known uncertainty
3.6
combined standard uncertainty
calculation result of combining the uncertainties determined from all performance characteristics specified in this
document according to the prescribed procedures given in this document
3.7
converter efficiency
degree of conversion of NO present in the sample gas into NO, given as a percentage
3.8
coverage factor
numerical factor used as a multiplier of the combined standard uncertainty in order to obtain an expanded
uncertainty
3.9
designated body
body which has been designated for a specific task (type approval tests and/or QA/QC activities in the field) by the
competent authority in the Member States
NOTE It is recommended that the designated body is accredited for the specific task according to EN ISO/IEC 17025.
3.10
expanded uncertainty
quantity defining an interval about 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
NOTE for the purpose of this document the expanded uncertainty is the combined standard uncertainty multiplied by a
coverage factor k = 2 resulting in an interval with a level of confidence of 95 %

As stated in the relevant EU legislation.
3.11
fall time
difference between the response time (fall) and the lag time (fall)
3.12
independent measurement
individual measurement that is not influenced by a previous individual measurement by separating two individual
measurements by at least four response times
3.13
individual measurement
measurement averaged over a time period equal to the response time of the analyser
3.14
influence quantity
quantity that is not the measurand but that affects the result of the measurement (VIM 2.7), either an interferent
influence quantity (i.e. the concentration of a substance in the air under investigation that is not the measurand), or
an external influence quantity (i.e. a quantity that is not the measurand nor the concentration of a substance in the
air mass under investigation)
NOTE Examples are:
 presence of interfering gases in the flue gas matrix (interferent influence quantity);
 temperature of the surrounding air (external influence quantity);
 atmospheric pressure (external influence quantity);
 pressure of the gas sample (external influence quantity).

3.15
interference
response of the analyser to interferents
3.16
interferent
component of the air sample, excluding the measured constituent, that effects the output signal
3.17
lag time
time interval from the instant at which a step change of sample concentration occurs at the inlet of the analyser to
the instant at which the output reading reaches a level corresponding to 10 % of the stable output reading
3.18
lag time (fall)
lag time for a negative step change
3.19
lag time (rise)
lag time for a positive step change
3.20
limit value
level fixed on the basis of scientific knowledge, with the aim of avoiding, preventing or reducing harmful effects on
human health and/or the environment as a whole, to be attained within a given period and not to be exceeded once
attained
3.21
lack of fit
maximum deviation of the average of a series of measurements at the same concentration from the linear
regression line
3.22
long term drift
difference between zero or span readings over a determined period of time (e.g. period of unattended operation)
3.23
monitoring station
enclosure located in the field in which an NO analyser has been installed to monitor nitrogen monoxide and
x
dioxide concentrations in such a way that its performance and operation complies with the prescribed requirements
3.24
parallel measurement
measurements from different analysers, sampling from one and the same sampling manifold starting at the same
time and ending at the same time
3.25
performance characteristic
one of the parameters assigned to equipment in order to define its performance
3.26
performance criterion
limiting quantitative numerical value assigned to a performance characteristic, to which conformance is tested
3.27
period of unattended operation
time period over which the drift is within the performance criterion for long term drift
3.28
repeatability (of results of measurement)
closeness of the agreement between the results of successive individual measurements of the same measurand
carried out under the same conditions of measurement [1]
NOTE These conditions are called laboratory repeatability conditions and include:
- the same measurement procedure;
- the same observer;
- the same analyser, used under the same conditions;
- at the same location;
- repetition over a short period of time.
3.29
reproducibility under field conditions
closeness of the agreement between the results of simultaneous measurements with two analysers in ambient air
carried out under the same conditions of measurement
NOTE These conditions are called field reproducibility conditions and include:
- the same measurement procedure;
- two identical analysers, used under the same conditions;
- at the same monitoring station;
- the period of unattended operation.
3.30
residence time inside the analyser
time period for the sampled air to be transported from the inlet of the analyser to the reaction chamber for the
NO-channel
3.31
residence time in the sampling system
time period for the sampled air to be transported from the sampling inlet (of the sampling system) to the inlet of the
analyser
3.32
response time
time interval from the instant at which a step change of sample concentration occurs at the inlet of the analyser to
the instant at which the output reading reaches a level corresponding to 90 % of the stable output reading
3.33
response time (fall)
response time to a negative step change
NOTE Response time (fall) is the sum of the lag time (fall) and the fall time.
3.34
response time (rise)
response time to a positive step change
NOTE Response time (rise) is the sum of the lag time (rise) and the rise time.
3.35
rise time
difference between the response time (rise) and the lag time (rise)
3.36
sampled air
ambient air that has been sampled through the sampling inlet and sampling system
3.37
sampling inlet
entrance to the sampling system where ambient air is collected from the atmosphere
3.38
short-term drift
difference between zero or span readings at the beginning and end of a 12 h period
3.39
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
[ENV 13005]
3.40
surrounding temperature
temperature of the air directly surrounding the analyser (temperature inside the monitoring station or laboratory)
3.41
total residence time
sum of the residence time in the sampling system and the residence time inside the analyser
3.42
type approval
decision taken by a designated body that the pattern of an analyser conforms to the requirements as laid down in
this document
3. 43
type approval test
examination of two or more analysers of the same pattern which are submitted by a manufacturer to a designated
body including the tests necessary for approval of the pattern
3.44
uncertainty (of measurement)
parameter associated with the result of a measurement that characterises the dispersion of the values that could
be attributed to the measureand
4 Symbols and abbreviated terms
For the purposes of this document, the following symbols and abbreviated terms apply.
A availability of the analyser
a
Av average concentration of the measurand during the field test
b sensitivity coefficient of the analyser to sample gas pressure change
gp
b sensitivity coefficient of the analyser to sample gas temperature change
gt
b sensitivity coefficient of the analyser to surrounding air temperature change
st
b sensitivity coefficient of the analyser to electrical voltage change
V
C NO concentration of the applied gas
C average concentration of the measurements at sampling gas pressure P1
P1
C average concentration of the measurements at sampling gas pressure P2
P2
C average concentration of the measurements at span level at the beginning of the drift period
s,1
C average concentration of the measurements at span level at the end of the drift period
s,2
c test gas concentration
t
C average concentration of the measurements at sample gas temperature T
T1 1
C average concentration of the measurements at sample gas temperature T
T2 2
C average concentration reading of the measurements at voltage V
V1 1
C average concentration reading of the measurements at voltage V
V2 2
C average concentration of the measurements at zero at the beginning of the drift period
z,1
C average concentration of the measurements at zero at the end of the drift period
z,2
av
average of at least four independent measurements during the constant concentration period (t )
c
C
const
av
average of at least four independent measurements during the variable concentration period (t )
v
C
var
average difference of parallel measurements
d
f
d the ith difference in a parallel measurement
f,i
D long-term drift at span concentration c
l,s t
D long-term drift at zero
l,z
D short-term drift at span level
s,s
D short-term drift at zero
s,z
D difference sample/calibration port
sc
E converter efficiency
conv
E sample system collection efficiency
ss
F response factor in concentration units per voltage output of the analyser
r
P sampling gas pressure P
1 1
P sampling gas pressure P
2 2
R mean analyser response to the test gas directly sampled by the analyser
d
R mean analyser response to the test gas via the sample manifold
m
s repeatability standard deviation at zero
r,z
s repeatability standard deviation at concentration c
r,ct t
s reproducibility standard deviation under field conditions
r,f
s repeatability standard deviation
l
T surrounding air temperature
T surrounding air temperature at the laboratory
l
T sample gas temperature T
1 1
T sample gas temperature T
2 2
t relative difference between response time (rise) and response time (fall)
d
t response time (fall)
f
t response time (rise)
r
t time period of the field test minus the time for calibration, conditioning and maintenance
t
t total time period with validated measuring data
u
t whole number of t and t pairs
V NO zero
V minimum voltage V (V) specified by the manufacturer
1 min
V maximum voltage V (V) specified by the manufacturer
2 max
average of measurements
x
x first average of the measurements at T just after calibration
1 l
x average of the measurements at zero
z
x second average of the measurements at T just before calibration
2 l
x average of the measurements at concentration c
ct t
X averaging effect
av
x average of the measurements using the calibration port
c
X influence quantity of CO with concentration 500 µmol/mol
CO2,z,ct 2
X influence quantity of H O with concentration 19 mmol/mol
H2O,z,ct 2
x the ith measurement
i
influence quantity of the interferent at concentration c
X
t
int,ct
X influence quantity of the interferent at zero
int,z
X largest residual from the linear regression function at concentrations higher than zero
l
X residual from the linear regression function at zero concentration
l,z
X influence quantity of NH with concentration 200 nmol/mol
NH3,z,ct 3
X influence quantity of O with concentration 200 nmol/mol
O3,z,ct 3
x average of the measurements using the sample port
s
X difference between the readings of two consecutive span checks
s
x average of the measurements at T or T
T min max
X difference between the readings of the recent zero check and the most recent calibration
z
(x ) the ith measurement result of analyser 1;
1,f i
(x ) the ith measurement result of analyser 2 at the same time as the measurement of analyser 1;
2,f i
Z reading of the first zero check
Z reading of the second zero check
∆P measured pressure drop induced by the manifold pump
m
∆R change in the analyser’s response due to the influence of the pressure drop induced by the manifold
a
pump, expressed as a percentage
5 Principle
5.1 General
This document describes the method for measurement of the concentrations of nitrogen dioxide and nitrogen
monoxide in ambient air by means of chemiluminescence. The requirements, the specific components of the
chemiluminescence analyser and its sampling system are described. A number of performance characteristics with
associated minimum performance criteria are given for the analyser. The actual values of these performance
characteristics for a specific type of analyser shall be determined in a so-called type approval test for which
procedures have been described. The type approval test comprises a laboratory and a field test. The selection of a
type approved analyser for a specific measuring task in the field is based on the calculation of the expanded
uncertainty of the measurement method. In this expanded uncertainty calculation the actual values of various
performance characteristics of a type approved analyser and the site-specific conditions at the monitoring station
are taken into account (see 9.6). The expanded uncertainty of the method shall meet the requirements of the (EU)
legislation. Requirements and recommendations for quality assurance and quality control are given for the
measurements in the field (see 9.4).
5.2 Measuring principle
Chemiluminescence is based on the reaction of nitrogen monoxide with ozone. In a chemiluminescence analyser
air is sampled through a filter (to prevent contamination of the gas conveying system, especially the optical
components of the analyser) and fed at a constant flow rate into the reaction chamber of the analyser, where it is
mixed with an excess of ozone for the determination of nitrogen monoxide only. The emitted radiation
(chemiluminescence) is proportional to the number of nitrogen monoxide molecules in the detection volume and
thus proportional to the concentration of nitrogen monoxide. The emitted radiation is filtered by a selective optical
filter and converted into an electric signal by a photomultiplier tube or a photodiode.
For the determination nitrogen dioxide, the sampled air is fed through a converter where the nitrogen dioxide is
reduced to nitrogen monoxide and analysed in the same way as previously described. The electrical signal
obtained from the photomultiplier tube or photodiode is proportional to the sum of concentrations of nitrogen
dioxide and nitrogen monoxide. The amount of nitrogen dioxide is calculated from the difference between this
concentration and that obtained for nitrogen monoxide only (when the sampled air has not passed through the
converter).
Chemiluminescence is the emission of light during a chemical reaction. During the gas-phase reaction of NO and
ozone light with an intensity proportional to the concentration of NO is produced when electrons of the excited NO
molecules decay to lower energy states.
This chemiluminescence method is based on the reaction
NO + O3 → NO2* + O2 (1)
NO2* → NO2 + hν (2)
*
Excited nitrogen dioxide (NO ) emits radiation in the near infrared region (600 nm to 3 000 nm) with a maximum
centered around 1 200 nm. For the determination of nitrogen dioxide, the nitrogen dioxide present in sampled air is
converted to nitrogen monoxide in a converter as a result of the reaction:
converter (catalyst)
NO → NO (3)
The NO is then analysed according to the reactions (1) and (2).
The concentrations of nitrogen dioxide and nitrogen monoxide are directly measured in volume/volume units (if the
analyser is calibrated using a volume/volume standard), since the emitted radiation from the chemiluminescence
reaction is proportional to the concentration of nitrogen monoxide in volume/volume units. The final results for
reporting are expressed in µg/m using standard conversion factors (see Clause 10).
5.3 Type approval test
The type approval test is based on the evaluation of performance characteristics determined under a prescribed
series of tests. In this document test procedures are described for the determination of the actual values of the
performance characteristics for at least two analysers in a laboratory and two analysers in the field. A designated
body shall perform these tests. The evaluation for type approval of an analyser is based on the calculation of the
expanded uncertainty in the measuring result based on the numerical values of the tested performance
characteristics and compared with a prescribed maximum uncertainty.
The type approval of an analyser and subsequent QA and QC procedures provide evidence that the defined
requirements concerning data quality laid out in relevant EU directives can be satisfied.
Appropriate experimental evidence shall be provided by
 type approval tests performed under conditions of intended use of the specified method of measurement, and
 calculation of expanded uncertainty of results of measurement by reference to ENV 13005.
5.4 Field operation and quality control
Prior to the installation and operation of a type approved analyser at a monitoring station, a expanded uncertainty
calculation shall be performed with the actual values of the performance, obtained during the type approval tests,
and the site-specific conditions at that monitoring station. This calculation shall be used to demonstrate the
suitability of a type-approved analyser under the actual conditions present at that specific monitoring station.
After the installation of the approved analyser at the monitoring station its correct functioning shall be tested.
Requirements for quality assurance and quality control are given for the operation and maintenance of the
sampling system, as well as for the analyser, to ensure that the uncertainty of subsequent measurement results
obtained in the field is not compromised.
6 Sampling equipment
6.1 General
Depending on the installation of the chemiluminescence analyser at a monitoring station, a single sampling line for
the analyser may be chosen. Alternatively sampling can take place from a common sampling inlet with a sampling
manifold to which other analysers and equipment may be attached. Conditions and layout of the sampling
equipment will contribute to the uncertainty of the measurement; to minimise this contribution to the expanded
uncertainty, performance criteria for the sampling equipment are given in the following subclauses.
NOTE In Annex C different arrangements of the sampling equipment are schematically presented.
6.2 Sampling location
The location where the ambient air shall be sampled and analysed is not specified as this depends strongly on the
category of a monitoring station (such as measurements in e.g. a rural area or background area).
NOTE For guidance on sampling points on a micro scale, see Annex D.
6.3 Sample inlet and sampling line
A specific method for sampling or sampling equipment is not described. It is acceptable that the equipment fulfils
the following minimum requirements.
The sample inlet shall be constructed in such a way that ingress of rainwater into the sampling line (or system) is
prevented. The sampling line shall be as short as practical to minimise the residence time.
The material of the sample inlet as well as the sampling line (or system) can influence the composition of the
sample. In practice, the best materials such as polytetrafluoroethylene (PTFE), perfluoro-ethylene-propylene (FEP),
borosilicate glass or stainless steel shall be used. Copper or copper-based alloys, shall not be used. The influence
of the sampling system on the measured concentrations of nitrogen monoxide and nitrogen dioxide due to losses
shall be less than 2 %.
NOTE 1 This value may be achieved when the quality assurance and quality control recommendations (see Clause 9) are
followed.
NOTE 2 The sample line may be moderately heated to avoid condensation. Condensation may occur in the case of high
ambient temperature and/or humidity.
The influence of the pressure drop along the sampling line including the particulate filter shall be such that it causes
less than 1 % of the signal output of the analyser.
As O is generally present in the sampled air, a change in concentrations of NO and NO will occur due to the
3 2
reaction of NO with O in the sampling line. In order to avoid a significant change in the concentrations of NO and
NO the residence time in the sampling system from the sampling inlet to the inlet of the analyser shall be < 5 s.
The increase in the nitrogen dioxide can be calculated by the formula given in Annex A.
In the case where a sampling manifold is used, an additional pump is necessary with sufficient capacity to fulfil the
sampling requirements stated in the previous subclauses (see also Annex C).
Depending on the location of the particulate filter in the sampling system (see 6.4), the sampling line can be
contaminated by deposition of dust. This can induce losses of NO in the sampling line(s). The sampling system
shall be cleaned (as stated in 9.4.1) with a frequency which is dependent on the site-specific conditions.
The sampling line manifold and filter shall be conditioned (at initial installation and after each cleaning) to avoid
temporary decrease in the measured NO and NO concentrations. Both sampling line and filter shall be conditioned
with ambient air for a period of at least 30 min at the nominal sample flow rate. The concentration measured during
these periods shall not be included in the calculation of data capture, hourly and annual averages.
These conditioning periods shall not be included in the calculation of the availability of the analyser during the type
approval test (8.5.7) and during field operation (11.2.3). Conditioning may also be done in the laboratory before
installing.
6.4 Particulate filter
A particulate filter shall be placed in the sample line before the inlet of the analyser. This particulate filter shall
retain all particles likely to alter the performance of the analyser. It shall be made of PTFE. The material of the filter
housing shall be chemically inert to nitrogen monoxide and nitrogen dioxide. Copper or copper-based alloys shall
not be used.
NOTE 1 A pore size of the filter of 5 µm usually fulfils this requirement.
NOTE 2 Suitable materials for the filter housing are for example PTFE, stainless steel, or borosilicate glass.
The particulate filter shall be changed periodically depending on the dust loading at the sampling site (as indicated
in 9.4.1). The filter housing shall be cleaned at least every six months. Overloading of the particulate filter may
cause loss of nitrogen dioxide by adsorption on the particulate matter and may increase the pressure drop in the
sampling line.
6.5 Control and regulation of sample flow rate
The sample flow rate into the analyser shall be maintained within the specifications of the manufacturer of the
analyser.
NOTE Flow rate into the chemiluminescence analyser is usually controlled by means of restrictors.
6.6 Sampling pump for the manifold
When a sampling manifold is used, a pump (or fan) is necessary for sampling ambient air and suction of the
sampled air through the sampling manifold. The inlet of the sampling pump (or fan) for the sampling manifold shall
be located at the end of the sampling manifold (see Annex C). The sampling pump or fan shall have sufficient
rating to ensure that all analysers connected to the manifold are supplied with the required amount of air and to
ensure that the residence time of a sample from inlet until entering the analyser is less than 5 s. To verify
functioning of this pump, it is recommended to install a flow alarm system. An example of a sampling manifold is
given in Annex C.
The influence of the pressure drop induced by the manifold sampling pump on the measured concentration shall be
< 1 %.
7 Analyser equipment
7.1 General
Generally three types of analysers are available:
a) dual type with two reaction chambers and one common photo multiplier or photodiode;
b) dual type with two reaction chambers each with a separate photo multiplier or photodiode;
c) single type with one reaction chamber (with one photo multiplier or photodiode).
In the dual types the airflow is divided into two streams, one passing directly to one of the reaction chambers for
measurement of the nitrogen monoxide content. The other stream is fed through the converter for conversion of the
nitrogen dioxide to nitrogen monoxide and then to the other reaction chamber for measurement of the total content
of nitrogen dioxide and nitrogen monoxide.
In the single analyser the air sample alternately bypasses or passes through the converter. This type of analyser
measures during a certain time period the amount of nitrogen monoxide and during the next time period the sum of
nitrogen dioxide and nitrogen monoxide concentrations.
NOTE 1 Schematic diagrams of typical analysers are given in Annex E, Figure E.1 and Figure E.2 (dual type) and Figure E.3
(single type).
NOTE 2 Some single type analysers do not fulfil the requirements for use at traffic-orientated locations, due to the rapid
fluctuations of the nitrogen dioxide and nitrogen monoxide concentrations. These rapid fluctuations may result in erroneous
determination of the NO2 concentrations, as these are the result of the subtraction of two consecutive readings (NOx and NO).
This averaging error is quantified in the type approval test. When an analyser passes this test, it can be installed at traffic-
orientated locations.
A chemiluminescence analyser consists of the principal components which are described in 7.2 to 7.8.
7.2 Converter
The converter converts nitrogen dioxide in the sampled air into nitrogen monoxide.
Most convertors use a heated furnace maintained at a constant temperature and are made of a material such as
stainless steel, copper, molybdenum, tungsten or spectroscopically pure carbon, other types are available, for
instance photolytic convertors. It shall be capable of converting at least 95 % of the nitrogen dioxide to nitrogen
monoxide. The conversion efficiency shall be checked according to 8.4.14. A mathematical correction for the NO
concentration shall be made when the converter efficiency is between 95 % and 100 %.
7.3 Ozone generator
Ozone is generated from oxygen either by ultraviolet radiation or by a high-voltage silent electric discharge. If
oxygen in ambient air is used for ozone generation by a high-voltage silent electric discharge, it is essential that the
air be thoroughly dried and filtered before entering the generator. If the ozone is generated from synthetic air of a
recognised analytical grade from a compressed gas cylinder, this synthetic air can be fed directly into the
generator. The concentration of ozone produced shall be sufficiently high to maintain the required lack of fit of the
analyser. Too low an ozone concentration will result in a non-linear response to the concentration of nitrogen
dioxide and nitrogen monoxide. The analyser shall fulfil the requirements for lack of fit as stated in 8.2.
WA
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