EN 14212:2005

SLOVENSKI STANDARD
01-september-2005
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Ambient air quality - Standard method for the measurement of the concentration of
sulphur dioxide by ultraviolet fluorescence
Luftqualität - Messverfahren zur Bestimmung der Konzentration von Schwefeldioxid mit
Ultraviolett-Fluoreszenz
Qualité de l'air ambiant - Méthode normalisée pour le mesurage de la concentration de
soufre par fluorescence U.V.
Ta slovenski standard je istoveten z: EN 14212:2005
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 14212
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2005
ICS 13.040.20
English version
Ambient air quality - Standard method for the measurement of
the concentration of sulphur dioxide by ultraviolet fluorescence
Qualité de l'air ambiant - Méthode normalisée pour le Luftqualität - Messverfahren zur Bestimmung der
mesurage de la concentration de SO2 par fluorescence UV Konzentration von Schwefeldioxid mit Ultraviolett-
Fluoreszenz
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 14212:2005: 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 .9
5 Principle.12
5.1 General.12
5.2 Measuring principle.13
5.3 Type approval test .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 Selective traps for interfering agents .16
7.3 Optical assembly .16
7.4 Pressure measurement .16
7.5 Flow rate indicator.16
7.6 Sampling pump for the analyser.17
7.7 Internal span source.17
8 Type approval of sulphur dioxide UV fluorescence analysers .17
8.1 General.17
8.2 Relevant performance characteristics and performance criteria .17
8.3 Design changes .19
8.4 Procedures for determination of the performance characteristics during the laboratory test .19
8.5 Determination of the performance characteristics during the field test.30
8.6 Expanded uncertainty calculation for type approval.33
9 Field operation and ongoing quality control .34
9.1 General.34
9.2 Suitability evaluation.34
9.3 Initial installation.36
9.4 Ongoing quality control .36
9.5 Calibration of the analyser.38
9.6 Checks .38
9.7 Maintenance .41
9.8 Data handling and data reports.42
10 Expression of results .42
11 Test reports and documentation.42
11.1 Type approval test .42
11.2 Field operation .42
Annex A (normative) Calculation of lack of fit.44
Annex B (informative) Sampling equipment.46
Annex C (informative) Sampling on micro-scale [2] .48
Annex D (informative) Schematic diagram of a fluorescence analyser.49
Annex E (informative) Manifold testing equipment .50
Annex F (normative) Type approval .51
Annex G (normative) Calculation of uncertainty in field operation at the hourly limit value .73
Annex H (normative) Calculation of uncertainty in field operation at the annual limit value.86
Bibliography.103

Foreword
This document (EN 14212:2005) 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 sulphur
dioxide present in ambient air based on the ultraviolet fluorescence measuring principle. This document describes
the performance characteristics and sets the relevant minimum criteria required to select an appropriate ultraviolet
fluorescence 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 for use.
The method is applicable to the determination of the mass concentration of sulphur dioxide present in ambient air
3 3
from 0 µg/m to 1 000 µg/m sulphur dioxide. This concentration range represents the certification range for the
type approval test.
3 3
NOTE 1 0 µg/m to 1 000 µg/m of SO corresponds to 0 nmol/mol to 376 nmol/mol of SO .
2 2
NOTE 2 Lower ranges may be used for measurement systems applied at rural locations monitoring Ecosystems.
The method covers the determination of ambient air concentrations of sulphur dioxide in zones classified as rural
areas, urban-background areas and traffic-orientated locations.
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 14956:2002, 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
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
calibration
comparison of the analyser response to a known gas concentration with a known uncertainty
3.5
certification range
concentration range for which the analyser is type approved
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
coverage factor
numerical factor used as a multiplier of the combined standard uncertainty in order to obtain an expanded
uncertainty
3.8
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.
3.9
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 %
3.10
fall time
difference between the response time (fall) and the lag time (fall)

)
As stated in the relevant EU legislation.
3.11
independent measurement
individual measurement that is not influenced by a previous individual measurement by separating two individual
measurements by at least four response times
3.12
individual measurement
measurement averaged over a time period equal to the response time of the analyser
3.13
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).

3.14
interference
response of the analyser to interferents
3.15
interferent
component of the air sample, excluding the measured constituent, that effects the output signal
3.16
lack of fit
maximum deviation of the average of a series of measurements at the same concentration from the linear
regression line
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
long-term drift
difference between zero or span readings over a determined period of time (e.g. period of unattended operation)
3.22
monitoring station
enclosure located in the field in which an SO analyser has been installed in such a way that its performance and
operation comply with the prescribed requirements
3.23
parallel measurement
two measurements from different analysers, sampling from one and the same sampling manifiold starting at the
same time and ending at the same time
3.24
performance characteristic
one of the parameters assigned to equipment in order to define its performance
3.25
performance criterion
limiting quantitative numerical value assigned to a performance characteristic, to which conformance is tested
3.26
period of unattended operation
time period over which the drift is within the performance criterion for long-term drift
3.27
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.
3.28
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 1 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.
NOTE 2 In this document the reproducibility under field conditions is expressed as a value with a level of confidence of 95 %
3.29
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
3.30
response time (fall)
response time to a negative step change
NOTE The response time (fall) is the sum of the lag time (fall) and the fall time.
3.31
response time (rise)
response time to a positive step change
NOTE The response time (rise) is the sum of the lag time (rise) and the rise time.
3.32
rise time
difference between the response time (rise) and the lag time (rise)
3.33
sampled air
ambient air that has been sampled through the sampling inlet and sampling system
3.34
sampling inlet
entrance to the sampling system where ambient air is collected from the atmosphere
3.35
short-term drift
difference between zero or span readings at the beginning and end of a 12 h period
3.36
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
[ENV 13005]
3.37
surrounding temperature
temperature of the air directly surrounding the analyser (temperature inside the monitoring station or laboratory)
3.38
type approval
decision taken by a designated body that the pattern of an analyser conforms to the requirements as laid down in
this document
3.39
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
3.40
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 SO concentration of the applied gas;
C average concentration of the measurements at sampling gas pressure P
P1 1;
C average concentration of the measurements at sampling gas pressure P
P2 2;
C concentration of the reference standard;
R
C concentration of site standard;
s
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
e
D difference sample/calibration port ;
sc
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 reproducibility under field conditions;
f
r absolute reproducibility in the field;
f,abs
r repeatability standard deviation;
i
r repeatability at concentration c ;
l,ct t
r repeatability at zero;
l,z
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 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 surrounding air temperature at the laboratory (K);
l
t two-sided Students t-factor at a confidence level of 0,05, with n-1 degrees of freedom;
n-1, 0,05
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 S02 zero
V minimum voltage V (V) specified by the manufacturer;
1 min
V maximum voltage V (V) specified by the manufacturer;
2 max
V voltage obtained when the reference standard is injected;
r
V voltage obtained when the site standard is injected;
s
V voltage obtained when zero gas is injected;
z
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 (µmol/mol);
ct t
X averaging effect;
av
x average of the measurements using the calibration port;
c
X influence quantity of H O with concentration 19 mmol/mol;
H2O,z,ct 2
X influence quantity of H S with concentration 10 nmol/mol;
H2S,z,ct 2
x the ith measurement;
i
influence quantity of the interferent at concentration c (µmol/mol);
X
t
int,ct
X influence quantity of the interferent at zero (µmol/mol);
int,z
X lack of fit (largest residual from the linear regression function);
l
X influence quantity of NH with concentration 10 nmol/mol;
NH3,z,ct 3
X influence quantity of NO with concentration 500 nmol/mol;
NO,z,ct
X influence quantity of NO with concentration 200 nmol/mol;
NO2,z,ct 2
X influence quantity of sampling gas pressure;
Psg
x
average of the measurements using the sample port (µmol/mol);
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 influence quantity of m-xylene with concentration 1 µmol/mol;
xl,z,ct
X difference between the readings of the recent zero check and the most recent calibration;
z
(x ) the ith measurement result of analyser 1, mathematically corrected for zero and span drift;
1,f i
(x ) the ith measurement result of analyser 2 at the same time as the measurement of analyser 1,
2,f i
mathematically corrected for zero and span drift;
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 concentration of sulphur dioxide in ambient air by
means of ultraviolet fluorescence. The requirements, the specific components of the ultraviolet fluorescence
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 combined expanded uncertainty
of the measurement method. In this combined expanded uncertainty calculation the actual values of the various
performance characteristics of a type approved analyser and the site-specific conditions at the monitoring station
are taken into account. The combined 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
UV (ultraviolet) fluorescence is based on the emission of light by SO molecules excited by UV radiation when they
return to their ground state:
The first reaction step is:
*
SO + hν → SO (1)
2 2
* ’
Then in the second step the excited SO molecule returns to its ground state, emitting an energy hν according to
the reaction:
* ’
SO → SO + hν (UV) (2)
2 2
The intensity of the fluorescence radiation is proportional to the number of SO molecules in the detection volume
and is therefore proportional to the concentration of SO .
Therefore:
F = k ×c (3)
SO
where
F is the intensity of fluorescence radiation;
k is the factor of proportionality;
c is the concentration of SO .
SO
Before entering the fluorescence analyser the air sample is passed through a filter in order to exclude interferences
caused by contamination with particles.
The sampled air is scrubbed to remove any interference by aromatic hydrocarbons that may be present. A
hydrocarbon scrubber device is used to achieve this.
The sampled air is then introduced into a reaction chamber, where it is irradiated by UV light in the wavelength
range between 200 nm and 220 nm. The UV fluorescent light emitted in the wavelength range of
240 nm to 420 nm, is optically filtered and then converted to an electrical signal by a UV detector, for example, a
photomultiplier tube.
The response of the analyser is proportional to the number of SO molecules in the reaction chamber. Therefore,
temperature and pressure either have to be kept constant, or, if variation of these parameters occurs, the
measured values have to be corrected.
The concentration of sulphur dioxide is directly measured in volume/volume units if the analyser is calibrated using
a volume/volume standard. 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. These tests
shall be performed by a designated body. 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 characteristics, 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 fluorescence analyser at a monitoring station, a single sampling inlet 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 uncertainty of the measurement; to minimise this contribution to the uncertainty,
performance criteria for the sampling equipment and sampling conditions are given in the following subclauses.
NOTE In Annex B different arrangements of the sampling equipment are schematically presented.
6.2 Sampling location
The location where the ambient air is sampled and analysed is not specified, as this depends on the measurement
requirements (such as measurements in e.g. a rural area or an urban-background area).
NOTE For guidance on sampling points on a micro-scale, see Annex C.
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 rain water into the sampling system is
prevented. The sampling line shall be as short as practicable to minimise the residence time.
The material of the sample inlet as well as the sampling line (or system) may 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 sulphur dioxide due to losses shall be less than 2 %
NOTE 1 This value may be achieved when the quality assurance and quality control recommendations are followed (see
Clause 9).
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 due to the sampling line including the particulate filter shall be such that it
causes less than 1 % of the output signal of the analyser.
In the case where a sampling manifold is used, an additional pump is necessary with sufficient capacity to meet the
sampling requirements stated in the previous subclauses (see also Annex B).
Depending on the location of the particulate filter in the sampling system (see 6.4) the sampling line may be
contaminated by deposition of dust. This may induce losses of SO in the sampling line. The sampling system shall
be cleaned (as stated in 9.4.2) 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 of measured SO concentrations. Both sampling line and filter shall be conditioned with
ambient air for a period of at least 30 min at the nominal sampling 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 (8.5.6) and during field operation (11.2.3). Conditioning mayalso be done in the laboratory before
installing, in the sampling system.
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 SO .
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 and borosilicate glass.
The particulate filter shall be changed periodically depending on the dust loading at the sampling site (as indicated
in 9.4.2). During this filter change the filter housing shall be cleaned. Overloading of the particulate filter may cause
loss of sulphur 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.
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 B). 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 that a flow alarm system is installed. An example of a sampling
manifold is given in Annex B.
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
A schematic diagram of a UV fluorescence analyser is given in Annex D.
UV fluorescence analyser consists of the principal components which are described in 7.2 to 7.6.
7.2 Selective traps for interfering agents
One or more selective traps shall be used before the fluorescence cell to remove interfering gases such as
aromatic hydrocarbons.
These selective traps shall not retain any SO , and shall be changed regularly in accordance with the
manufacturer's instruction manuals.
If high concentrations of H S are expected in the ambient air, a selective scrubber should be used.
7.3 Optical assembly
The optical assembly consists of a UV lamp, a fluorescence cell, a reference sensor and a UV detector.
The UV lamp emission may be pulsed electronically or mechanically in order to enable synchronous detection and
amplification of the signal. The lamp shall have a stabilised power supply to ensure a stable emission of light. An
optical filter is used to restrict the wavelengths to a range which allows excitation of the sulphur dioxide molecule
and minimizes the interferences due to water vapour, aromatic hydrocarbons or nitrogen monoxide. This filter shall
remove radiation at wavelengths longer than 600 nm, to minimize any interference produced by the UV
fluorescence of unsaturated hydrocarbons, which radiate at these wavelengths.
The reference sensor in the extension of the beam path behind the reaction chamber checks the constancy of the
UV lamp and is used to correct the fluorescence signal or to control the UV lamp.
The fluorescence cell shall be made of material inert to SO and UV radiation. The cell shall be heated to a
constant temperature above the water vapour dew point to avoid water condensation, and to minimise temperature
changes. An optical trap in the fluorescence cell shall be used to prevent reflection of the UV radiation.
The UV detector, for example a photomultiplier tube, detects the fluorescence light emitted by the SO molecules in
the fluorescence cell. A selective optical filter placed in front of the photomultiplier tube reduces the signal due to
scattering of incident light.
The optical assembly shall be placed in a heated temperature-controlled enclosure.
7.4 Pressure measurement
The output signal of the analyser is proportional to the density of SO (number of SO molecules) present in the
2 2
reaction chamber and depends on the pressure in the chamber. Variations of internal pressure shall be measured
and the signal corrected.
7.5 Flow rate indicator
A flow rate indicator shall be included in the analyser.
NOTE It is recommended that the flow rate be kept constant by means of a flow controller.
7.6 Sampling pump for the analyser
The sampling pump is situated at the outlet of the analyser, and draws the sample through the analyser. It can be
separate or part of the analyser. In any case it shall be capable of operating within the specified flow requirements
of the manufacturer of the analyser and pressure conditions required for the reaction chamber.
NOTE If the use of the UV lamp produces ozone, it is recommended to vent this ozone outside the monitoring station and
away from the sampling inlet. A suitable charcoal filter may be used for trapping ozone.
7.7 Internal span source
Some analysers are equipped with an internal span source. This span source shall not be used for calibration
purposes. The concentrations generated by this internal span source may be used for functional tests only.
8 Type approval of sulphur dioxide UV fluorescence analysers
8.1 General
The determination of the concentration of sulphur dioxide in ambient air has to fulfil the requirement of a maximum
uncertainty in the measured values, which is prescribed by EU legislation. In order to achieve an uncertainty less
than (or equal to) this required uncertainty, the analyser has to fulfil all the criteria for a number of performance
characteristics, which are given in this document. The values of the selected performance characteristics shall be
evaluated by means of laboratory and field tests. By combining the values of the selected performance
characteristics in an uncertainty calculation, a judgement can be made whether or not the analyser meets the
criterion of maximum uncertainty prescribed by EU legislation.
This process of assessment (type approval test) of the values of the performance characteristics comprises
laboratory and field tests and the calculation of the expanded uncertainty. At least two analysers shall be tested in
the laboratory and two analysers of the same type shall be tested during the field test. All tested analysers are
required to pass.
A designated body shall perform the type approval tests. The type approval shall be awarded by or on behalf of the
competent authority.
NOTE It is recommended that the designated body for the type approval test is accredited for these activities according to
EN ISO/IEC 17025.
8.2 Relevant performance characteristics and performance criteria
The performance characteristics which shall be determined during a laboratory and field test, and their related
performance criteria are given in Table 1.
The determination of the value of the performance characteristics stated in Table 1 shall be performed by a
designated body
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