oSIST prEN 16976:2023
(Main)Ambient air - Determination of the particle number concentration of atmospheric aerosol
Ambient air - Determination of the particle number concentration of atmospheric aerosol
This European Standard specifies a standard method for determining the particle number concentration in ambient air in a range up to about 107 cm–3 for averaging times equal to or larger than 1 min. The standard method is based on a Condensation Particle Counter (CPC) operated in the counting mode and an appropriate dilution system for concentrations exceeding the counting mode range. It also defines the performance characteristics and the minimum requirements of the instruments to be used. The lower and upper sizes considered within this document are 10 nm and a few micrometres, respectively. This document describes sampling, operation, data processing and QA/QC procedures including calibration parameters.
Außenluft - Bestimmung der Partikelanzahlkonzentration des atmosphärischen Aerosols
Dieses Dokument beschreibt ein Standardverfahren zur Bestimmung der Partikelanzahlkonzentration in Außenluft im Bereich bis etwa 107 cm−3 für Mittelungszeiten von mindestens 1 min. Das Standardverfahren basiert auf einem im Zählmodus betriebenen Kondensationspartikelzähler (en: Condensation Particle Counter, CPC) mit geeignetem Verdünnungssystem für Konzentrationen, die den Bereich des Zählmodus überschreiten. Weiterhin werden Leistungskenngrößen und Mindestanforderungen für geeignete Geräte definiert. Die in diesem Dokument betrachteten unteren und oberen Partikelgrößen sind 10 nm bzw. einige Mikrometer. Dieses Dokument beschreibt Probenahme, Betrieb des Geräts, Datenverarbeitung und QA/QC-Maßnahmen, einschließlich der Kalibrierparameter.
Air ambiant Détermination de la concentration en nombre de particules de l'aérosol atmosphérique
Le présent document décrit une méthode normalisée de détermination de la concentration en nombre de particules dans l'air ambiant sur une plage allant jusqu'à 107 cm–3 environ, pour des durées de calcul des moyennes supérieures ou égales à 1 min. La méthode normalisée repose sur l’utilisation d’un compteur de particules à noyaux de condensation (CNC) fonctionnant en mode comptage et d’un système de dilution approprié pour les concentrations en dehors de la plage du mode comptage. Il définit également les caractéristiques de performance et les exigences minimales relatives aux instruments à utiliser. Les tailles de particules minimale et maximale considérées dans le présent document sont, respectivement, de 10 nm et quelques micromètres. Le présent document décrit le prélèvement, le fonctionnement, le traitement des données et les procédures d'assurance qualité et de contrôle qualité, y compris les paramètres d'étalonnage.
Zunanji zrak - Določevanje številčne koncentracije delcev atmosferskih aerosolov
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
oSIST prEN 16976:2023
01-junij-2023
Zunanji zrak - Določevanje številčne koncentracije delcev atmosferskih aerosolov
Ambient air - Determination of the particle number concentration of atmospheric aerosol
Außenluft - Bestimmung der Partikelanzahlkonzentration des atmosphärischen Aerosols
Air ambiant Détermination de la concentration en nombre de particules de l'aérosol
atmosphérique
Ta slovenski standard je istoveten z: prEN 16976
ICS:
13.040.20 Kakovost okoljskega zraka Ambient atmospheres
oSIST prEN 16976:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
3.1 Aerosol properties. 6
3.2 Instrument performance . 7
3.3 Flow rates . 7
4 Atmospheric aerosol . 8
5 Description of the method . 8
5.1 Sampling and conditioning . 8
5.1.1 Sampling . 8
5.1.2 Drying . 10
5.1.3 Dilution . 10
5.2 Determination of the number concentration with a CPC . 10
5.2.1 Condensation growth . 10
5.2.2 Optical detection . 12
6 CPC performance criteria and test procedures . 13
6.1 General. 13
6.2 General requirements for the CPC . 13
6.3 Test conditions . 14
6.4 Performance characteristics and criteria . 14
6.5 Test procedures . 15
6.5.1 Calibrated flow rate . 15
6.5.2 Number concentration measurement range . 15
6.5.3 Number concentration detection limit . 15
6.5.4 Calibration factor . 15
6.5.5 Instrument-specific assessment of linearity and slope of response . 16
6.5.6 Detection efficiency curve at low particle size . 16
6.5.7 Upper particle size detection limit . 17
6.5.8 Zero count rate . 17
6.5.9 Response time . 17
6.5.10 Dependence of flow rate on supply voltage. 17
6.5.11 Accuracy of temperature and pressure sensor calibration . 17
6.5.12 Effect of failure of mains voltage . 17
7 Performance criteria and test procedures for the sampling and conditioning system
. 18
7.1 General requirements . 18
7.2 Performance characteristics and criteria . 18
7.3 Diffusion losses . 18
7.4 Relative humidity. 19
7.5 Dilution . 19
7.5.1 Dilution factor . 19
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7.5.2 General criteria for dilution systems . 19
7.6 Primary sampling flow . 20
8 Measurement procedure . 20
8.1 Measurement planning . 20
8.2 Environmental operating conditions . 20
8.3 Initial installation . 20
8.4 Initial checks on site . 21
8.5 Data processing and reporting . 21
9 Quality control, quality assurance and measurement uncertainty . 21
9.1 General . 21
9.2 Frequency of calibrations, checks and maintenance . 22
9.2.1 General . 22
9.2.2 Maintenance of CPC . 22
9.2.3 Calibration of linearity . 22
9.2.4 CPC zero check . 23
9.2.5 Number concentration check . 23
9.2.6 Check of the actual flow rate . 23
9.2.7 Temperature and pressure sensor calibration . 23
9.2.8 CPC internal diagnostics. 23
9.2.9 Sample system maintenance . 23
9.2.10 Relative humidity sensor . 24
9.2.11 Dilution factor (where applicable) . 24
9.2.12 Leak check . 24
9.3 Measurement uncertainty . 24
9.3.1 General . 24
9.3.2 CPC plateau detection efficiency . 25
9.3.3 CPC detection efficiency drift . 25
9.3.4 Flow determination . 25
9.3.5 Correction to standard temperature and pressure . 25
9.3.6 Diffusion losses in the sampling system . 25
9.3.7 Dilution factor (where applicable) . 26
9.3.8 Calculation of overall uncertainty . 26
Annex A (normative) Determination of diffusion losses in sampling lines . 27
Annex B (informative) Example of the calculation of diffusion losses in a sampling system
. 29
Annex C (informative) Data reporting . 32
Annex D (informative) Uncertainty calculation (example) . 34
Annex E (informative) Atmospheric aerosols . 36
Annex F (informative) Dilution systems. 39
Annex G (informative) Laminar flow . 46
Annex H (informative) Coincidence correction . 47
Annex I (informative) Results of an experimental comparison of different CPCs . 49
Bibliography . 54
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European foreword
This document (prEN 16976:2023) has been prepared by Technical Committee CEN/TC 264 “Air
quality”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede CEN/TS 16976:2016.
In comparison with the previous edition, the following technical modifications have been made:
— 1: The lower limit of the measured particle size range is set to be 10 nm and thus identical to MPSS
(Mobility Particle Size Spectrometers) measurements (see CEN/TS 17434). In air quality monitoring
networks where MPSS will be used for determining the particle size distribution a CPC may be used
for QA purposes for the MPSS data.
— 3: The parameter “calibration factor” was introduced and defined. The terms and definitions for the
various flow rates were revised and rearranged.
— 5.1.2: Aerosol diffusion dryer based on silica is excluded, because diffusion losses are too high with
this type of dryer.
— 6.2: Coincidence correction shall be applied. No other correction factors shall be applied unless a
correction for the analysed flow rate is necessary.
— 6.3: All tests are carried out only at one temperature (between 20 °C and 30 °C).
— 6.4: Table 1: Criteria for several performance characteristics were changed, the performance
characteristic “calibration factor” was included.
— 6.5: Some of the test procedures have been revised, a test procedure for the calibration factor was
added.
— 7.2: Two dilution factors are necessary: one for reducing the concentration, an additional one for
drying.
— 7.5: The method of using tracer gas for the determination of the dilution factor of a dilution system
has been removed. General criteria for dilution systems were added.
— 9.2: The test “Determination of low size cut-off” was removed, the “Number concentration check”
was substantially revised.
— Annex E: The ambient particle number concentration values were updated.
— Annex F: An example of the design of a dilution system and an example for the calculation of the
uncertainty of the dilution factor have been added.
— Annex H: The new Annex “Coincidence correction” was added.
— Annex I: The new Annex “Results of an experimental comparison of different CPCs” was added.
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Introduction
There is a growing awareness of the significance of aerosol particles with diameters of D < 1 µm for
human health as well as for their climatic impact. To assess air quality, it appears necessary to
supplement gravimetrically determined mass concentrations such as PM2,5 and PM10 with a
measurement of the particle number concentration. Since ultrafine particles with diameters of D < 0,1 µm
make an almost insignificant contribution to the mass of atmospheric aerosol particles, they can best be
detected with counting measuring methods of sufficient sensitivity.
As particle measurement instrumentation allows determining either the particle number concentration
or the particle number size distribution two documents are established:
— one dealing with the determination of the single parameter number concentration (a measure of
“total” number concentration, this document)
— one dealing with the determination of number concentration within a limited number of size ranges
(CEN/TS 17434).
Clauses 5 and 6 contain general information about the method and the expected properties of the aerosol
to be measured.
Clause 7 sets out the performance criteria for CPCs. Specifically, these are the relevant performance
characteristics of CPC instruments (without any sampling system), the respective criteria that shall be
met, and a description of how the tests shall be carried out. In general, these tests are expected to be
carried out by test houses or CPC manufacturers rather than users and could form the basis for type
testing of CPCs in future.
Clause 8 sets out the performance criteria and test procedures for the sampling and conditioning system
(e.g. dilution). These may be applied by manufacturers of sampling systems, test houses or users
(network operators).
Clause 9 sets out requirements for the installation, initial checks and calibrations, and operation of a CPC
and sampling system at a monitoring site, including routine maintenance, data processing (including use
of QA/QC data) and reporting. In general, these will be the responsibility of users (network operators),
though calibrations requiring test aerosols shall only be carried out by suitably qualified laboratories.
Clause 10 sets out Quality Assurance and Quality Control procedures, i.e. the ongoing checks and
calibrations that are required on the CPC and sampling system during operation at a monitoring site. It is
expected that these will be the responsibility of users (network operators), though calibrations requiring
test aerosols shall only be carried out by suitably qualified laboratories. The main sources of
measurement uncertainty are described.
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1 Scope
This document describes a standard method for determining the particle number concentration in
7 –3
ambient air in a range up to about 10 cm for averaging times equal to or larger than 1 min. The standard
method is based on a Condensation Particle Counter (CPC) operated in the counting mode and an
appropriate dilution system for concentrations exceeding the counting mode range. It also defines the
performance characteristics and the minimum requirements of the instruments to be used. The lower
and upper sizes considered within this document are 10 nm and a few micrometres, respectively. This
document describes sampling, operation, data processing and QA/QC procedures including calibration
parameters.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 27891:2015, Aerosol particle number concentration — Calibration of condensation particle counters
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1 Aerosol properties
3.1.1
particle
small piece of matter with defined physical boundary
Note 1 to entry: The phase of a particle can be solid, liquid, or between solid and liquid and a mixture of any of the
phases.
[SOURCE: ISO 27891:2015, modified]
3.1.2
aerosol
multi-phase system of solid and/or liquid particles suspended in a gas, ranging in particle size from
0,001 µm to 100 µm
3.1.3
number size distribution
frequency distribution of the particle number concentration represented as a function of particle size
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3.1.4
particle number concentration
number of particles related to the unit volume of the carrier gas
Note 1 to entry: For the exact particle number concentration indication, information on the gaseous condition
(temperature and pressure) or the reference to a standard volume indication is necessary.
[SOURCE: ISO 27891:2015]
3.2 Instrument performance
3.2.1
coincidence error
error that occurs with counting measuring methods when two or more particles are counted
simultaneously as a single particle
Note 1 to entry: Coincidence error is related to particle number concentration, flow velocity through the sensing
zone and size of sensing zone.
3.2.2
detection efficiency
ratio of the particle number concentration determined by the measuring instrument to the reference
particle number concentration of the aerosol at the instrument's inlet
Note 1 to entry: The detection efficiency depends on particle size and may depend on particle number
concentration.
3.2.3
calibration factor
model- or instrument-specific ratio between the reference FCAE reading and the CPC count rate, both
converted to particle number concentration
3.3 Flow rates
3.3.1
actual flow rate
volumetric flow rate of an individual instrument, measured at its inlet under the actual air conditions
3.3.2
nominal flow rate
volumetric flow rate which a specific CPC model is designed for and which is indicated on the instrument
specification sheet by the manufacturer
Note 1 to entry: The actual flow rate of individual instruments may differ from the nominal flow due to
manufacturing tolerances.
3.3.3
calibrated flow rate
actual flow rate at the time of calibration documented on a calibration certificate
3.3.4
analysed flow rate
volumetric flow rate which is used for instrument internal calculation of the particle number
concentration
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4 Atmospheric aerosol
Atmospheric aerosols are strongly dependent on their local and regional sources. Especially, the size
distribution in number and mass, as well as the size-resolved chemical composition are highly variable.
Aerosol particles are either emitted directly (primary aerosols) or formed by nucleation and
condensation from pre-cursor gases (secondary aerosol). Combustion processes lead to both primary
and secondary aerosols.
Mass-wise, the global direct emission of aerosol particles is dominated by sea salt, biological material as
well as by desert and volcanic dust. These particles are generally larger than 1 µm. Anthropogenic
emissions in this size range play a minor role on a global scale. Submicrometer natural aerosols consist
mainly of marine sulfate, biogenic organics, and wildfire carbonaceous particles. Submicrometer
anthropogenic aerosols are complex mixtures of primary and secondary particles, consisting mainly of
sulfate, nitrate, organics, and elemental carbon.
Particle number concentrations of atmospheric aerosols cover several orders of magnitude. While
remote marine or free tropospheric aerosols have number concentrations as low as tens or a few hundred
per cubic centimetre, anthropogenically influenced aerosols can contain a few thousand up to one million
particles per cubic centimetre. The number concentration of the anthropogenic aerosol over land,
especially in urban areas is dominated by particles in the size range smaller than 0,1 µm. Major sources
for high number concentrations in this size range are regional new particle formation and local
combustion processes. Average background concentrations in an urban area are several thousands of
particles per cubic centimetre.
For details see Annex E.
5 Description of the method
5.1 Sampling and conditioning
5.1.1 Sampling
The measurement of atmospheric aerosols will always necessitate sampling and the transport of the
sample to the measuring instrument. Moreover, in certain cases the sample has to be processed in terms
of temperature, relative humidity, and particle concentration in order to adapt the aerosol to the
measuring instrument's permissible operating conditions.
The information given on this issue in this document refers to stationary ambient monitoring sites. For
mobile applications (e.g. measurements from aircraft), additional considerations have to be taken into
account.
The measuring instruments shall be accommodated in a protected environment in controlled conditions
(temperature 20 °C to 30 °C).
The sampling location depends on the measurement task. If the undisturbed atmospheric aerosol is to be
measured, air intake should take place 5 m to 10 m above the ground level. Buildings, vegetation, or the
topography of the terrain may make an even higher sampling point necessary. By contrast, the
measurement of aerosols close to the source (e.g. traffic) calls for much lower sampling points (1,5 m to
4 m above the ground, see Directive 2008/50/EC [1]).
The design of the intake port should permit representative sampling regardless of the direction of the
wind for a broad range of wind velocities. However, this is not a critical condition for the small particles
measured by the CPC. Steps shall be taken to avoid soiling of the sampling lines by particles larger than
10 µm. For this purpose, a PM10 or PM2,5 inlet can be used (see Figure 1). An inlet that removes particles
in the measurement range of the CPC (e.g. a commercial PM1 inlet) shall be avoided.
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Key
1 PM sampling inlet
2 Primary sampling tube
3 Secondary sampling tube
Figure 1 — Basic design of the aerosol intake port
The sample should ideally be fed via a vertical primary sampling tube without bends to the measuring
instruments. Since gas measuring methods have fundamentally different requirements regarding
sampling, gas and aerosol sampling should be conducted independently of each other.
To reduce diffusion loss, it is necessary to intake aerosol with the aid of a pump at a primary flow rate
(Q ) much higher than the secondary flow rate (Q ). The CPC should sample isoaxially in the central
tot CPC
area from this volumetric flow via a secondary sampling tube that is as short as possible. Flow in the
primary sampling tube should be laminar in order to prevent additional particle loss due to turbulence.
Ideally, a Reynolds number of Re ≤ 2000 shall be aimed for (see 7.2).
The diffusion losses in the sampling system for smallest relevant particle size of 10 nm shall be less than
25 % (see 7.2).
The intake port and lines shall be made of a conductive, corrosion-resistant material with a low surface
roughness (e.g. stainless steel) and electrically earthed. This prevents chemical changes to the aerosol
and particle losses due to electrostatic effects. Flexible tubing of electrically conductive material may also
be used for small connections or short distances. The length of flexible tubing should be below 50 cm.
The inlet and the flow-splitter of the sampling system shall be checked regularly to detect obstructions,
e.g. by insects, and cleaned, if necessary.
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5.1.2 Drying
Aerosols with a high relative humidity (mist in extreme cases) should be dried, as the size of particles of
hygroscopic materials is strongly influenced by humidity. The requirement is to keep the relative
humidity of the primary flow at the CPC inlet lower than 40 % (see 7.2). The relative humidity at the inlet
of the CPC shall be monitored.
With respect to the temperature conditions three cases are to be distinguished:
— In case the room temperature is higher than 22 °C no aerosol dryer is needed if the ambient dew
point temperature never exceeds 10 °C.
— If the dew point temperature is between 10 °C and the room temperature, the secondary flow shall
be dried.
— In case that the dew point temperature is above the room temperature, the primary flow shall be
dried before entering the room. Additional drying of the secondary flow may be necessary.
There are two recommended methods to dry the aerosol:
— Membrane dryer; preferably used to dry the secondary sampling flow.
— Dilution with dry particle-free air (see 5.1.3); preferably used to dry the primary sampling flow. In
this case the exact dilution ratio shall be known in order to calculate the correct concentrations.
5.1.3 Dilution
Dilution is applied either to reduce the number concentration of the ambient aerosol to the limits of the
CPC's measuring range or to reduce the humidity of the ambient aerosol. In both cases the dilution step
may introduce a high uncertainty which shall be estimated and specified in the report. Where dilution is
not required this step should be avoided. The minimum requirement with respect to accuracy of the
dilution factor for both cases is given in 7.2.
Preferably the CPC selected to measure at any particular site will have a concentration range in counting
mode that covers the expected concentrations. When this is not possible the sample shall be diluted with
particle-free air.
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