FprEN 16980-1

Photocatalysis - Continuous flow test methods - Part 1: Determination of the degradation of nitric oxide (NO) in the air by photocatalytic materials

This document specifies a method for assessing the performance of photocatalytic inorganic materials contained in cement mortars and/or limes or ceramic-based matrices, paints or materials deposited as thin films or coatings on a variety of substrates for the photocatalytic abatement of nitric oxide in the gas phase. This method does not apply to the assessment of samples to be applied with flow perpendicular to the surface or flow permeating the surface itself as polymeric and paper filters, honeycomb structures and suchlike.
The performance for the photocatalytic sample under test is evaluated by measuring the degradation rate of nitric oxide (NO) using the method specified herein. The photocatalytic abatement rate is calculated from the observed rate by eliminating the effects of mass transfer. The intrinsic photocatalytic abatement rate is an intrinsic property of the material tested and makes it possible to distinguish the photocatalytic activities of various products with an absolute scale defined with physical and engineering meaning.
For the measurements and calculations described in this document the concentration of nitrogen oxides (NOx) is defined as the stoichiometric sum of nitric oxide (NO) and nitrogen dioxide (NO2).

Photokatalyse - Prüfverfahren mit kontinuierlichem Durchfluss - Teil 1: Bestimmung des Abbaus von Stickstoffmonoxid (NO) aus der Luft durch photokatalytische Werkstoffe

Dieses Dokument legt ein Verfahren zur Bewertung der Leistung von photokatalytischen anorganischen Werkstoffen fest, enthalten in Zementmörtel und/oder Kalken oder aus Keramik bestehenden Grund-substanzen, Farben oder Werkstoffen, die als dünne Filme oder Beschichtungen auf einer Vielzahl von Trägerwerkstoffen für die photokatalytische Minderung von Stickstoffmonoxid in der Gasphase vorkommen. Dieses Verfahren gilt weder für die Bewertung von Proben, die mit einem Fluss senkrecht zur Oberfläche verwendet werden, noch für Proben, wie Polymer  und Papierfilter, Wabenstrukturen und dergleichen, bei denen der Fluss die Oberfläche durchdringt.
Die Leistung für die zu prüfende photokatalytische Probe wird durch die Messung der Abbaugeschwindigkeit von Stickstoffmonoxid (NO) mithilfe des hier festgelegten Verfahrens bewertet. Die photokatalytische Minderungsgeschwindigkeit wird aus dem beobachteten Wert berechnet, indem die Auswirkungen des Stoff¬übergangs abgezogen werden. Die intrinsische photokatalytische Minderungsgeschwindigkeit ist eine intrinsische Eigenschaft des untersuchten Werkstoffs und macht es möglich, die photokatalytischen Aktivitäten verschiedener Produkte in einem absoluten Maßstab, bestimmt im physikalischen und technischen Sinn, zu unterscheiden.
Für die in diesem Dokument beschriebenen Messungen und Berechnungen, wird die Konzentration von Stickoxiden (NOx) als die stöchiometrische Summe von Stickstoffmonoxid (NO) und Stickstoffdioxid (NO2) definiert.

Photocatylyse - Méthode d’essai en flux continu - Partie 1 : Détermination de la dégradation du monoxyde d’azote (NO) dans l’air par des matériaux photocatalytiques

Le présent document décrit une méthode d’évaluation de la performance des matériaux inorganiques photocatalytiques contenus dans les mortiers de ciment et/ou les chaux ou dans les matrices à base de céramique, les peintures ou les matériaux déposés sous forme de films minces ou de revêtements sur une variété de substrats pour la dégradation photocatalytique du monoxyde d’azote en phase gazeuse. Cette méthode ne doit pas être appliquée à l’évaluation des échantillons devant être utilisés avec un flux perpendiculaire à la surface ou traversant la surface, comme les filtres polymères et papier, les structures en nid d’abeille et autres éléments similaires.
La performance de l’échantillon photocatalytique étudié est évaluée en mesurant la vitesse de dégradation du monoxyde d’azote (NO) à l’aide de la méthode décrite ici. La vitesse de dégradation photocatalytique est calculée à partir de la vitesse observée en éliminant les effets du transfert de masse. La vitesse intrinsèque de dégradation photocatalytique est une propriété intrinsèque du matériau soumis à l’essai et elle permet de distinguer les activités photocatalytiques de divers produits au moyen d’une échelle absolue définie par des caractéristiques physiques et mécaniques.
Pour les mesurages et les calculs décrits dans le présent document, la concentration en oxydes d’azote (NOx) est définie comme la somme stœchiométrique du monoxyde d’azote (NO) et du dioxyde d’azote (NO2).

Fotokataliza - Metode preskušanja kontinuiranega pretoka - 1. del: Ugotavljanje razgradnje dušikovega oksida (NO) v zraku z materiali fotokatalize

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN 16980-1:2020
01-junij-2020
Fotokataliza - Metode preskušanja kontinuiranega pretoka - 1. del: Ugotavljanje
razgradnje dušikovega oksida (NO) v zraku z materiali fotokatalize

Photocatalysis - Continuous flow test methods - Part 1: Determination of the degradation

of nitric oxide (NO) in the air by photocatalytic materials

Photokatalyse - Prüfverfahren mit kontinuierlichem Durchfluss - Teil 1: Bestimmung des

Abbaus von Stickstoffmonoxid (NO) aus der Luft durch photokatalytische Werkstoffe

Photocatalyse - Méthodes d'essai en flux continu - Partie 1 : Mesure de la dégradation

du monoxyde d'azote (NO) dans l'air par un matériau photocatalytique
Ta slovenski standard je istoveten z: prEN 16980-1
ICS:
13.040.20 Kakovost okoljskega zraka Ambient atmospheres
25.220.20 Površinska obdelava Surface treatment
oSIST prEN 16980-1:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 16980-1:2020
DRAFT
EUROPEAN STANDARD
prEN 16980-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2020
ICS 13.040.20; 87.040; 87.060.20; 91.100.10 Will supersede CEN/TS 16980-1:2016
English Version
Photocatalysis - Continuous flow test methods - Part 1:
Determination of the degradation of nitric oxide (NO) in
the air by photocatalytic materials

Photocatalyse - Méthodes d'essai en flux continu - Photokatalyse - Prüfverfahren mit kontinuierlichem

Partie 1 : Mesure de la dégradation du monoxyde Durchfluss - Teil 1: Bestimmung des Abbaus von

d'azote (NO) dans l'air par un matériau Stickstoffmonoxid (NO) aus der Luft durch

photocatalytique photokatalytische Werkstoffe

This draft European Standard is submitted to CEN members for parallel enquiry. It has been drawn up by the Technical

Committee CEN/TC 386.

If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN 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-CENELEC

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, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are

aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without

notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 16980-1:2020 E

worldwide for CEN national Members.
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Contents Page

European foreword ....................................................................................................................................................... 3

1 Scope .................................................................................................................................................................... 4

2 Normative references .................................................................................................................................... 5

3 Terms, definitions and abbreviations ..................................................................................................... 5

3.1 Terms and definitions ................................................................................................................................... 5

3.2 Abbreviations ................................................................................................................................................... 5

4 Principle ............................................................................................................................................................. 7

5 Interferences .................................................................................................................................................... 7

6 Apparatus ........................................................................................................................................................... 7

6.1 General ................................................................................................................................................................ 7

6.2 Gas mixture preparation system ............................................................................................................... 7

6.3 Illumination and measuring system: ....................................................................................................... 8

7 Sample preparation ..................................................................................................................................... 14

7.1 Precaution....................................................................................................................................................... 14

7.2 Sample characteristics ............................................................................................................................... 14

7.3 Conditioning ................................................................................................................................................... 14

8 Measurement of concentrations ............................................................................................................. 15

8.1 General ............................................................................................................................................................. 15

8.2 Measurement of the initial concentration of nitrogen oxides before entering the

photochemical reactor ............................................................................................................................... 15

8.3 Conversion without sample ...................................................................................................................... 15

8.4 Conversion in the dark and in the presence of sample .................................................................. 16

8.5 Conversion under illumination in the presence of sample ........................................................... 16

9 Calculation of photocatalytic degradation rate ................................................................................. 17

9.1 The observed rate of photocatalytic degradation ............................................................................ 17

9.2 Intrinsic rate of photocatalytic transformation ................................................................................ 18

10 Optional part .................................................................................................................................................. 18

10.1 Conversion under illumination in the presence of sample at different fan speeds ............. 18

10.2 Calculation of photocatalytic degradation rate at different fan speeds ................................... 19

11 Acceptability ranges of main test parameters ................................................................................... 20

12 Test report ...................................................................................................................................................... 21

Annex A (informative) Typical trend of NO, NO and NO concentrations during a
2 x

photocatalytic test at nominal fan speed ............................................................................................. 23

Annex B (informative) Typical trend of NO, NO and NO concentrations during a
2 x

photocatalytic test using different fan speeds ................................................................................... 24

Annex C (informative) Example of test for the control of mass transfer conditions ........................ 25

Annex D (informative) Typical Ohmic response of the fan ........................................................................ 26

Bibliography ................................................................................................................................................................. 27

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European foreword

This document (prEN 16980-1:2020) has been prepared by Technical Committee CEN/TC 386

“Photocatalysis”, the secretariat of which is held by AFNOR.
This document is currently submitted to the CEN Enquiry.
This document will supersede CEN/TS 16980-1:2016.
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1 Scope

This document describes a method for assessing the performance of photocatalytic inorganic materials

contained in cement mortars and/or limes or ceramic-based matrices, paints or materials deposited as

thin films or coatings on a variety of substrates for the photocatalytic abatement of nitric oxide in the gas

phase. This method is not suitable for the assessment of samples to be applied with flow perpendicular

to the surface or flow permeating the surface itself as polymeric and paper filters, honeycomb structures

and suchlike.

The performance for the photocatalytic sample under test is evaluated by measuring the degradation rate

of nitric oxide (NO) using the method described herein. The photocatalytic abatement rate is calculated

from the observed rate by eliminating the effects of mass transfer. The intrinsic photocatalytic abatement

rate is an intrinsic property of the material tested and makes it possible to distinguish the photocatalytic

activities of various products with an absolute scale defined with physical and engineering meaning.

For the measurements and calculations described in this document the concentration of nitrogen oxides

(NO ) is defined as the stoichiometric sum of nitric oxide (NO) and nitrogen dioxide (NO ).

x 2
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2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

CEN/TS 16599:2014, Photocatalysis —Irradiation conditions for testing photocatalytic properties of

semiconducting materials and the measurement of these conditions

EN ISO 9169, Air quality — Definition and determination of performance characteristics of an automatic

measuring system (ISO 9169)

ISO 7996, Ambient air — Determination of the mass concentration of nitrogen oxides — Chemiluminescence

method
3 Terms, definitions and abbreviations
3.1 Terms and definitions

For the purposes of this document, the following terms, definitions and abbreviations apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

• ISO Online browsing platform: available at https://www.iso.org/obp
• IEC Electropedia: available at http://www.electropedia.org/
3.1.1
concentration of nitrogen oxides
stoichiometric sum of nitric oxide (NO) and nitrogen dioxide (NO )

Note 1 to entry: For grade 999 nitrogen or air: the purity of the gas should be equal at least to 99,9 %.

3.1.2
photocatalyst

catalyst able to produce, upon absorption of light, chemical transformations of the reaction partners

Note 1 to entry: The excited state of the photocatalyst repeatedly interacts with the reaction partners forming

reaction intermediates and regenerates itself after each cycle of such interactions.

3.1.3
photocatalytic materials

materials in which or on which the photocatalyst is added by coating, impregnation, mixing, etc

3.2 Abbreviations
CSTR Continuous Stirred-Tank Reactor
C concentration at reactor inlet
OUT,DARK

C concentration of NO and NO at reactor outlet under stable conditions in the dark (no

illumination)
OUT, light

concentration at reactor outlet under stable conditions with illumination (lamp on)

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concentration of NO at reactor inlet
concentration of NO at reactor inlet
OUT,DARK
concentration of NO at reactor outlet under stable conditions in the dark (no
illumination) without sample
OUT,DARK
concentration of NO at reactor outlet under stable conditions in the dark (no
illumination) without sample
OUT,DARK
concentration of NO at reactor outlet under stable conditions in the dark (no
NO,S
illumination) in presence of sample
OUT,DARK
concentration of NO at reactor outlet under stable conditions in the dark (no
NO ,S
illumination) in presence of sample
OUT, LIGHT

concentration of NO at reactor outlet under stable conditions with illumination (lamp

on) without sample
OUT, LIGHT

concentration of NO at reactor outlet under illumination of sample measured at fan

NO,0
speed at nominal voltage V
OUT, LIGHT

concentration NO at reactor outlet under illumination of sample measured at fan speed

NO ,0
nominal voltage V
F Flow
F fan flow at i applied potential (i = 0..n)
v,i
I irradiance
LED light emitting diodes
MM molecular mass
P pressure in atmosphere
PTFE Polytetrafluoroethylene
R ideal gas constant
RH gas relative humidity at 25 °C inside the reactor
dark
conversion of NO in the dark
dark
conversion to NO in the dark
PHOTO
conversion of NO under illumination without sample
NO,lamp
total
conversion of NO measured at each fan flow F
v,i
NO ,i
total
conversion to NO measured at each fan flow F
2 v,i
NO ,i
photo NO abatement rate at each fan flow F
v,i
NO,i
photo NO photocatalytic production rate at each fan flow F
2 v,i
NO ,i
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photo NO abatement rate corresponds to NO abatement rate minus NO photocatalytic
x 2
NO ,i
production rate

photoCAT NO photocatalytic degradation rate intrinsic to the surface of the material, after

removing the mass transfer limitations

photoCAT NO photocatalytic degradation rate intrinsic to the surface of the material, after

removing the mass transfer limitations
UV-A ultraviolet with wavelength (λ) situated between 315 nm and 400 nm (IUPAC)
V0 fan nominal operating potential (in Volt)
V fan minimum operating potential (in Volt) set by the manufacturer
min
S Sample
T temperature in Kelvin
t time to reach the stability of NO concentration
stab
UV UltraViolet
Vr Reactor net volume
4 Principle

The method consists in measuring the photocatalytic abatement of nitric oxide (NO) by photocatalytic

materials as specified in Clause 1 using a Continuous Stirred-Tank Reactor (CSTR) with flow tangential

to the sample. Information on the theory is reported in the specialized literature (Minero et al. 2013). The

residual NO and NOx concentration at the CSTR outlet is measured by a chemiluminescence analyser

(ISO 7996).

The photocatalytic activity test is carried out using chromatographic grade air, also obtained by mixing

pure gases, to which NO is added in such an amount as to simulate a high degree of air pollution. The NO

concentration is set to (0,50 ± 0,05) ppmv.
5 Interferences

The measurement’s interferences are reported in the technical specifications of the chemiluminescence

analyser. As what is measured are all species that can be converted by reduction to NO, NO concentration

is here defined as [NO ] = [NO ]-[NO]. For interferences on chemiluminescence detection, see Winer et al.

2 x
(1974).
6 Apparatus
6.1 General
The test apparatus shall consist of the following main components.
6.2 Gas mixture preparation system
The system used for preparing the reaction mixture is shown in Figure 1.

The mass flow controllers, calibrated and traceable, shall ensure a maximum flow consistent with that

needed for a correct test execution. To ensure the necessary accuracy, the flow shall not exceed 90 % of

the rated full scale.

As an example, to obtain the gas mixture only gases of chromatographic grade or higher purity shall be

used. Instead of dry air cylinders, two separate cylinders of pure N and O can be used at the inlet of

2 2
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mass-flow controllers, adjusted so as to produce a mixture consisting of 20,8 % of O and 79,2 % of N .

2 2
The NO concentration to flow #1 is set to (0,50 ± 0,05) ppmv.

a) Relative humidity is set by regulating the b) Relative humidity is set by regulating the

flow to U, which is downstream to F pressure before U and F
Key
S source of nitric oxide NO diluted in N
1 2

S2 cylinder of air (chromatographic grade) or, alternatively, individual cylinders of N2 and O2

(chromatographic grade)
F flow controller with mass-flow controllers (2 or 3)
P pressure regulators with low-pressure manometers
U humidifier maintained at controlled temperature
F#1 flow entering the reactor
Figure 1 — Gas mixture preparation system

The humidification of the gas mixture can be obtained with two different configurations:

a) using two mass flow controllers regulating the flow to U, as in Figure 1 left;

b) using one mass flow controller regulating the pressure on U, as in Figure 1 right.

The gas mixture preparation system shall ensure a relative humidity of (40 ± 5) % inside the CSTR

reactor. The relative humidity shall be measured either inside the reactor R (Figure 2) or immediately at

its outlet on flow 2 of Figure 2 by means of a hygro-thermometer.
6.3 Illumination and measuring system:
6.3.1 General:
The light source arrangement and the measuring system are shown in Figure 2.
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Key
R reaction chamber, Continuous Stirred-Tank Reactor (CSTR) type
V fan
A power supply of fan V
N NO/NO2 chemiluminescence analyser
E processing/logging unit
L illumination system
1, 2, 3, 4 flow paths, with valves and tubing
Figure 2 — Illumination, reaction and measuring system

All parts of the test apparatus, including connections and pipes, which come into contact with the nitric

oxide mixture shall be made of chemically inert materials. For pipes and connections PTFE is

recommended. The pipes of paths 1, 2, 3, 4 and the related connections shall have an outer diameter of

6 mm (1/4”) and inner clearance of at least 4 mm to avoid overpressures that may affect the gas

concentration inside the reactor.

Temperature shall be measured and recorded inside the reactor during the test or immediately at its

outlet on flow 2 by means of a hygro-thermometer. The gas temperature inside the reaction chamber

shall be (25 ± 5) °C.
6.3.2 Illumination system L:

The illumination source shall consist of any lamp able to excite the photocatalyst (quartz mercury vapor

lamps, UV-A fluorescent lamps, Xenon lamps, LEDs, lamps consisting of a metal vapor element combined

with tungsten incandescence elements, etc.) as specified in the Technical Specification CEN/TS 16599.

The illumination system shall provide an average irradiance to the test sample surface within the range

of wavelengths that are mostly adsorbed by the photocatalyst, equal to (10,0 ± 5 %) W/m .

The geometry of the illumination system shall be such that uniform illumination of the sample surface is

ensured. The illumination is considered uniform if 5 independent measurements performed on the

surface (one in centre position and the other four in positions perpendicular to each other and next to

the edge of the sample) show a percentage variation compared to the average value of less than 10 %.

The control of the uniformity of illumination and average irradiance shall be repeated each time the

system geometry changes (position of the lamp or any filters or reflectors, sample position, etc.).

Irradiance shall be measured by placing a radiometric sensor inside the reaction chamber in the same

position occupied by the sample in order to measure real irradiance at its surface. A second measuring

sensor for the control of source stability can be positioned outside the reaction chamber, provided that it

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has been calibrated with a reference radiometric sensor placed inside the reactor. Irradiance can be

measured continuously during the test or, alternatively, just before the beginning of the test and

immediately after its conclusion. The irradiance values shall be measured only after the lamp intensity

has stabilized as a result of its warming-up (typically 10 min after being turned on). The irradiance value

as measured shall be recorded as average value in the test report.

The radiometer used for the measurement shall have been previously calibrated by means of a

spectroradiometer, which in turn has been previously calibrated by means of standard sources.

In order to avoid decomposition by direct photolysis of NO, the integrated irradiance at λ < 340 nm shall

be less than 0,5 W/m . The direct NO photolysis rate shall be checked by performing the test using the

empty reactor, where standard NO concentration (0,5 ppmv) is introduced and the reactor outlet

concentration is measured according to 8.3, a). For example, in the case of a photocatalyst consisting of

pure TiO , the illumination system that uses a medium-pressure mercury lamp shall be such as to ensure

the surface of the sample receives a UV irradiance (λ < 400 nm) mainly composed of the line at 365 nm

of mercury, and an integrated irradiance for λ < 340 nm of less than 0,5 W/m .

The spectrum of the lamp used shall be acquired and reported in the test report, because the analysis

result depends significantly on the lamp type used.
6.3.3 Reaction chamber R:
A schematic of the reaction chamber is given in Figure 3.
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Dimensions in millimetres
Key
1, S sample 4 inflow
2 fan
3 outflow
3A gas output (alternative)

Figure 3 — Top view of the CSTR reaction chamber, with dimensional details and indication of

flows for thorough mixing and location of the sampling point

Other dimensional details of the reaction chamber with related sample positions are also shown in the

Figures 4 and 5 below.

The reaction chamber shall be built with NO inert materials, i.e. glass, polymethylmethacrylate or other

inert plastic materials. The chamber shall be gas-tight. On top, the chamber shall be provided with a flat

window that is transparent to the light emitted by the illumination system and vertically incident to the

sample. This flat window, transparent to the wavelengths used (e.g. made up of borosilicate glass for

λ ≥ 340 nm) shall be 3 mm to 4 mm thick to ensure sufficient strength and also removable to allow for

sample positioning.
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Dimensions in millimetres
Key
HAC holes for air circulation
HF hole for a fan with Φ = 60 mm
1 top window
2 fan 60 mm nominal
3 gas outlet
4 gas inlet
Figure 4 — Side view (back of fan side) of the CSTR reactor
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Dimensions in millimetres
Key
3 gas outlet
h distance to the surface of the sample
S sample
th sample on the support, any thickness, max 50mm
max

Figure 5 — Side view (fan front side) of reactor CSTR, with indications of sample position

The reaction chamber shall comply with the dimensions shown in Figures 3 to 5. Considering the volumes

3 3

occupied by internal barriers, fan, sample and sample support, the total net volume is 2,8 dm to 3,5 dm .

This volume is not critical. The gas flow is maintained constant throughout the whole test, and shall be

3 −1

equal to 1,6 dm min . It shall be at least 20 % higher than the sampling flow of the NO/NO analyser.

The max flow variation allowed is 10 %.

The fan ensures perfect mixing inside the reaction chamber. The fan is placed inside the reactor on a

support having a hole with diameter equal to the fan aperture and axial to the fan axis. The support has

lateral holes that ensure full air mixing inside the chamber. The fan shall provide nominal flows of 70 m

h at the nominal supply voltage V .

Fans with external dimensions of 60 mm × 60 mm and thickness from 25 mm to 35 mm are suitable for

this purpose. The fan flow shall be varied by varying the supply voltage by an appropriate power supply

of continuous variable output voltage (see A of Figure 2).
6.3.4 NO/NO analyser

The analyser shall be calibrated according to the procedures described in ISO 7996 or according to

EN ISO 9169. The instrument's calibration can be performed using NO and/or NO mixtures at a known

and certified concentration of either grade 999 nitrogen or air. For the measurement range adopted

during calibration, at least 4 standard gas mixtures shall be analysed, supported by the related calibration

certificates, with different NO contents in N (or in any other inert gas) with concentrations equal to

approx. 0,2 ppmv, 0,4 ppmv, 0,6 ppmv, 0,8 ppmv.

Alternatively, the concentrations needed to check the analyser calibration can be generated starting from

a single gas cylinder with certified NO concentration and with the help of a calibrated flow controller

provided with calibration certificates for mass-flow controllers.

Adjustments and calibrations shall be always carried out when the measuring device is under steady

conditions.
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By comparing the measured NO concentration values and the related certified values it is possible to

obtain, for each concentration level, the corresponding analyser calibration condition, which can be

expressed in table form, as a calibration curve or a response factor.

If calibration provides a linear response as nitrogen oxide concentrations vary within the calibration

range, then a single level measurement can be adopted during the control of the instrument calibration

condition. The frequency of such control operations depends on the accuracy level desired in accordance

with the time drift of the instrumental signal typical of each NOx-analyser.
7 Sample preparation
7.1 Precaution
Samples shall be eventually preconditioned following the supplier advices.
7.2 Sample characteristics

The samples being analysed shall have a surface area of (64 ± 6) cm . For larger samples, use a mask. The

surface area value shall be carefully assessed being a parameter necessary for the normalization of the

test result.

The sample shall be positioned on a support made of borosilicate glass, polytetrafluoroethylene (PTFE)

or ceramic material that is not photocatalytically active, paying attention that its surface is as close as

possible to the level of the fan rotation axis and central to the free space between fan and reactor wall in

the lateral direction (see Figure 5). As to distance tolerances, the sample surface can be at a distance of

30 mm to 50 mm from the internal base, that is 60 mm to 40 mm from the inner surface of the upper

transparent window of the reactor. This means that the sample shall have a maximum usable thickness

of 50 mm. Solid samples of 50 mm thickness can be positioned in the reaction chamber without any

support.

The geometric surface area exposed to the gas flow can be square, rectangular or circular, provided that

the illumination uniformity conditions are met (see 6.3.2). The sample width in axial direction should not

exceed 120 mm. Typically a cylindrical sample has a surface area of (64 ± 6) cm (±10 %).

The required surface area can be achieved by combination of various samples, provided that they are

coplanar and the resulting surface meets the specifications above.

The surfaces of the tested sample other than those exposed orthogonally to the incident lightbeam, shall

be isolated from gas containing nitric oxide by means of a coating of commercial silicones, paraffin waxes,

inert polymer films or composite materials. The test shall be performed only after these protective films

have completely dried. All coatings shall withstand irradiance conditions for at least 6 h, shou

...