CEN/TS 17434:2020
(Main)Ambient air - Determination of the particle number size distribution of atmospheric aerosol using a Mobility Particle Size Spectrometer (MPSS)
Ambient air - Determination of the particle number size distribution of atmospheric aerosol using a Mobility Particle Size Spectrometer (MPSS)
This document describes a standard method for determining particle number size distributions in ambient air in the size range from 10 nm to 800 nm at total concentrations up to approximately 10^5 cm^-3 with a time resolution of a few minutes. The standard method is based on a Mobility Particle Size Spectrometer (MPSS) used with a bipolar diffusion charger and a Condensation Particle Counter (CPC) as the detector. The document describes the performance characteristics and minimum requirements of the instruments and equipment to be used, and describes sampling, operation, data processing and QA/QC procedures, including calibration.
Außenluft - Bestimmung der Partikelanzahlgrößenverteilung des atmosphärischen Aerosols mit einem Mobilitäts-Partikelgrößenspektrometer (MPSS)
Dieses Dokument beschreibt ein Standardverfahren zur Ermittlung von Partikelanzahlgrößenverteilungen in Außenluft im Größenbereich von 10 nm bis 800 nm bei Gesamtkonzentrationen bis etwa 10^5 cm^−3 mit einer zeitlichen Auflösung von wenigen Minuten. Das Standardverfahren beruht auf einem Mobilitäts-Partikelgrößen¬spektrometer (MPSS), das mit einem bipolaren Diffusionsauflader sowie einem Kondensations¬partikelzähler (CPC) als Detektor betrieben wird. Dieses Dokument legt die Leistungskenngrößen und Mindestanforderungen an zu verwendende Geräte und Ausrüstung fest und beschreibt Probenahme, Betrieb, Datenverarbeitung und QA/QC Maßnahmen, einschließlich Kalibrierung.
Air ambiant - Détermination de la distribution granulométrique de particules d’un aérosol atmosphérique à l’aide d’un spectromètre de granulométrie à mobilité électrique (MPSS)
Le présent document décrit une méthode normalisée de détermination des distributions granulométriques de particules dans l’air ambiant dans la gamme de tailles allant de 10 nm à 800 nm à des concentrations totales allant jusqu’à environ 10^5 cm^-3 avec une résolution temporelle de quelques minutes. La méthode normalisée repose sur un spectromètre de granulométrie à mobilité électrique (MPSS) associé à un chargeur à diffusion bipolaire et à un compteur de particules à noyaux de condensation (CPC) pour la détection. Le présent document décrit les caractéristiques de performance et les exigences minimales relatives aux instruments et au matériel à utiliser, ainsi que les procédures de prélèvement, d’utilisation, de traitement des données, et d’assurance qualité et de contrôle qualité, y compris l’étalonnage.
Zunanji zrak - Določevanje spektra velikosti delcev atmosferskih aerosolov s spektrometrom na osnovi mobilnosti (MPSS)
General Information
Overview
CEN/TS 17434:2020 specifies a standard method for measuring the particle number size distribution of atmospheric aerosol in ambient air using a Mobility Particle Size Spectrometer (MPSS). The method covers particle diameters from 10 nm to 800 nm, at total number concentrations up to approximately 10^5 cm^-3, with a typical time resolution of a few minutes. The procedure uses an MPSS equipped with a bipolar diffusion charger and a Condensation Particle Counter (CPC) detector, and defines instrument performance, sampling, data processing and QA/QC requirements.
Key Topics and Requirements
- Measurement principle: Mobility-based size classification (MPSS) combined with CPC detection and bipolar charging.
- Size & concentration range: 10 nm–800 nm; concentrations up to ~10^5 cm^-3; short time resolution (minutes).
- Sampling & conditioning: Requirements for inlet design, aerosol drying, dilution systems and minimising losses.
- Instrument performance: Minimum MPSS design criteria and test procedures covering:
- Aerosol flow rate and flow condition checks
- Particle size range and calibration accuracy
- Accuracy of integrated number concentration and size distribution
- Background (false) concentration and leak checks
- Data processing & corrections:
- Data inversion from mobility to size distributions
- Corrections for diffusion losses and CPC detection efficiency
- Delay time adjustments and uncertainty estimation
- Quality assurance / quality control (QA/QC):
- Calibration and maintenance schedules (flows, CPC, sensors)
- Routine checks (false background, leak tests)
- Measurement uncertainty guidance
- Supporting guidance: Normative and informative annexes on bipolar charge distribution, particle diffusion loss calculations, dilution system design, laminar flow, and data reporting formats (Level 0–2).
Applications and Users
This Technical Specification is intended for:
- Atmospheric researchers studying aerosol dynamics, nucleation and size-resolved particle concentrations.
- Environmental monitoring laboratories and national air quality networks conducting ambient aerosol monitoring.
- Air quality networks and projects integrating data into systems such as ACTRIS, EMEP and GAW (Annex G guidance).
- Instrument manufacturers and service providers who design, test or calibrate MPSS systems.
- Regulators and consultants requiring standardized, traceable particle number size distribution measurements for health and policy assessment.
Related integration and value
- Enables harmonised, comparable particle number size distribution data across monitoring sites.
- Supports trend analysis, exposure assessment and model evaluation by providing well-documented measurement and QA/QC procedures.
- Annexes provide practical calculation examples (diffusion losses, dilution uncertainty) and data reporting templates for network compatibility.
Keywords: MPSS, particle number size distribution, ambient air, aerosol, CPC, bipolar diffusion charger, aerosol sampling, QA/QC, calibration, diffusion losses.
Frequently Asked Questions
CEN/TS 17434:2020 is a technical specification published by the European Committee for Standardization (CEN). Its full title is "Ambient air - Determination of the particle number size distribution of atmospheric aerosol using a Mobility Particle Size Spectrometer (MPSS)". This standard covers: This document describes a standard method for determining particle number size distributions in ambient air in the size range from 10 nm to 800 nm at total concentrations up to approximately 10^5 cm^-3 with a time resolution of a few minutes. The standard method is based on a Mobility Particle Size Spectrometer (MPSS) used with a bipolar diffusion charger and a Condensation Particle Counter (CPC) as the detector. The document describes the performance characteristics and minimum requirements of the instruments and equipment to be used, and describes sampling, operation, data processing and QA/QC procedures, including calibration.
This document describes a standard method for determining particle number size distributions in ambient air in the size range from 10 nm to 800 nm at total concentrations up to approximately 10^5 cm^-3 with a time resolution of a few minutes. The standard method is based on a Mobility Particle Size Spectrometer (MPSS) used with a bipolar diffusion charger and a Condensation Particle Counter (CPC) as the detector. The document describes the performance characteristics and minimum requirements of the instruments and equipment to be used, and describes sampling, operation, data processing and QA/QC procedures, including calibration.
CEN/TS 17434:2020 is classified under the following ICS (International Classification for Standards) categories: 13.040.20 - Ambient atmospheres. The ICS classification helps identify the subject area and facilitates finding related standards.
You can purchase CEN/TS 17434:2020 directly from iTeh Standards. The document is available in PDF format and is delivered instantly after payment. Add the standard to your cart and complete the secure checkout process. iTeh Standards is an authorized distributor of CEN standards.
Standards Content (Sample)
SLOVENSKI STANDARD
01-junij-2020
Zunanji zrak - Določevanje spektra velikosti delcev atmosferskih aerosolov s
spektrometrom na osnovi mobilnosti (MPSS)
Ambient air - Determination of the particle size spectra of atmospheric aerosol using a
Mobility Particle Size Spectrometer (MPSS)
Außenluft - Bestimmung des Partikelgrößenspektrums des atmosphärischen Aerosols
mit einem Partikelgrößenmobilitätsspektrometer (MPSS)
Air ambiant - Détermination de la distribution granulométrique de particules d’un aérosol
atmosphérique à l’aide d’un spectromètre de granulométrie à mobilité électrique (MPSS)
Ta slovenski standard je istoveten z: CEN/TS 17434:2020
ICS:
13.040.20 Kakovost okoljskega zraka Ambient atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
CEN/TS 17434
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
April 2020
TECHNISCHE SPEZIFIKATION
ICS 13.040.20
English Version
Ambient air - Determination of the particle number size
distribution of atmospheric aerosol using a Mobility
Particle Size Spectrometer (MPSS)
Air ambiant - Détermination de la distribution Außenluft - Bestimmung der
granulométrique de particules d'un aérosol Partikelanzahlgrößenverteilung des atmosphärischen
atmosphérique à l'aide d'un spectromètre de Aerosols mit einem Mobilitäts-
granulométrie à mobilité électrique (MPSS) Partikelgrößenspektrometer (MPSS)
This Technical Specification (CEN/TS) was approved by CEN on 22 December 2019 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to
submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS
available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in
parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.
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.
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. CEN/TS 17434:2020 E
worldwide for CEN national Members.
Contents Page
European foreword . 5
Introduction . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Symbols and abbreviations . 8
5 Atmospheric aerosol . 8
6 Description of the method . 10
6.1 Sampling and conditioning . 10
6.1.1 Sampling . 10
6.1.2 Aerosol Drying . 11
6.2 Determination of particle number size distribution with an MPSS . 12
6.2.1 Physical principle . 12
6.2.2 Particle charging . 12
6.2.3 Mobility analysis. 12
6.2.4 Data inversion . 16
6.2.5 Correction for particle losses due to diffusion . 16
6.2.6 Correction for CPC detection efficiency . 16
7 MPSS performance criteria and test procedures . 17
7.1 MPSS design and performance criteria . 17
7.2 Test procedures for MPSS performance criteria . 18
7.2.1 Actual aerosol flow rate . 18
7.2.2 Particle size range . 18
7.2.3 Particle size calibration accuracy . 19
7.2.4 Accuracy of integrated particle number concentration . 19
7.2.5 False background number concentration . 19
7.2.6 Flow condition . 19
7.2.7 Accuracy of the particle number size distribution. 20
8 Performance criteria and test procedures for the sampling and conditioning system . 20
8.1 General requirements . 20
8.2 Performance characteristics and criteria . 20
8.3 Particle losses due to diffusion . 21
8.4 Relative humidity . 21
8.5 Dilution factor . 21
8.6 Primary sampling flow . 22
9 Measurement procedure . 22
9.1 Measurement planning . 22
9.2 Environmental operating conditions . 22
9.3 Initial installation . 22
9.4 Initial checks on site. 22
9.5 Data reporting . 23
10 Quality control, quality assurance and measurement uncertainty . 24
10.1 General . 24
10.2 General operating procedures . 24
10.3 Frequency of calibrations, checks and maintenance . 24
10.3.1 General . 24
10.3.2 Aerosol flow rate calibration (MPSS) . 25
10.3.3 Aerosol flow rate calibration (CPC) . 25
10.3.4 Humidity, temperature and pressure sensors calibration . 26
10.3.5 CPC calibration . 26
10.3.6 Delay time check . 26
10.3.7 Mean false background concentration check (CPC) . 26
10.3.8 Leak check . 26
10.3.9 Sampling system maintenance . 26
10.3.10 Humidity sensor calibration . 26
10.3.11 Dilution factor calibration (where applicable) . 26
10.3.12 Leak check . 26
10.4 Measurement uncertainty . 27
Annex A (normative) Bipolar charge distribution . 28
Annex B (normative) Calculation of particle losses due to diffusion . 30
B.1 General equations and constants . 30
B.2 Particle losses due to diffusion in straight tubes of circular cross section . 31
B.3 Particle losses due to diffusion in a MPSS . 32
Annex C (informative) Example of the calculation of particle losses due to diffusion in a
sampling system . 33
C.1 Description of the sampling system . 33
C.2 Air properties and diffusion coefficient . 34
C.3 Losses in the primary sampling tube . 34
C.4 Particle losses due to diffusion in the secondary sampling tube and the MPSS . 35
C.5 Overall sampling losses . 36
Annex D (informative) Example of an MPSS design . 37
Annex E (informative) Dilution system . 39
E.1 Background . 39
E.2 Criteria for dilution systems . 39
E.3 Design example of a dilution system . 39
E.4 Operating parameters of a dilution system . 40
E.5 Example for the calculation of the uncertainty of the dilution factor . 42
Annex F (informative) Laminar flow . 45
Annex G (informative) Data reporting . 46
G.1 Motivation . 46
G.2 Level 0 (annotated raw data) . 47
G.3 Level 1 (data processed to final physical property, potential corrections applied,
original temporal resolution) . 47
G.4 Level 2 (hourly averages, including measures of variability) . 47
G.5 Implementation in ACTRIS / EMEP / GAW . 47
G.6 Data and Metadata Included in Level 0 . 48
G.6.1 Data . 48
G.6.2 Metadata . 49
G.6.3 Flags . 51
G.7 Data and Metadata Included in Level 1 . 51
G.7.1 Data . 51
G.7.2 Metadata . 51
G.7.3 Flags . 54
G.8 Data and Metadata Included in Level 2 . 54
G.8.1 Data . 54
G.8.2 Metadata . 55
G.8.3 Flags . 57
Annex H (informative) Atmospheric aerosols in Europe . 58
H.1 General . 58
H.2 Mean concentrations . 58
H.3 Examples of measurements. 59
Bibliography . 62
European foreword
This document (CEN/TS 17434:2020) has been prepared by Technical Committee CEN/TC 264 “Air
quality”, the secretariat of which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
According to the CEN/CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to announce this Technical Specification: 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 the United
Kingdom.
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 PM or PM with a measurement
10 2.5
of the particle number concentration. Since ultrafine particles with diameters of D < 0,1 µm make an
almost insignificant contribution to the mass concentration 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 Technical Specifications have been established:
— one dealing with the determination of the single parameter number concentration (a measure of
“total” number concentration (CEN/TS 16976)),
— one dealing with the determination of number concentrations within a limited number of size ranges
(this document).
Clauses 5 and 6 contain general information about the method and the expected properties of the aerosol
particles to be measured.
Clause 7 sets out the performance criteria for MPSSs. Specifically, these are the relevant performance
characteristics of MPSS 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 MPSS manufacturers rather than users, and could form the basis for type
approval of MPSSs in future.
Clause 8 sets out the performance criteria and test procedures for the sampling and conditioning system.
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 an
MPSS 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 MPSS and sampling system during operation at a monitoring site. It
is expected that these will be the responsibility of users (network operators). The main sources of
measurement uncertainty are described, but it is not possible in this document to quantify the overall
measurement uncertainty for data reported following the method.
1 Scope
This document describes a standard method for determining particle number size distributions in
ambient air in the size range from 10 nm to 800 nm at total concentrations up to approximately
5 –3
10 cm with a time resolution of a few minutes. The standard method is based on a Mobility Particle
Size Spectrometer (MPSS) used with a bipolar diffusion charger and a Condensation Particle Counter
(CPC) as the detector. The document describes the performance characteristics and minimum
requirements of the instruments and equipment to be used, and describes sampling, operation, data
processing and QA/QC procedures, including calibration.
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 16976:2016, Ambient air — Determination of the particle number concentration of atmospheric
aerosol
ISO 15900, Determination of particle size distribution — Differential electrical mobility analysis for aerosol
particles
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 http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp/ui
3.1
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
[SOURCE: CEN/TS 16976:2016]
3.2
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
[SOURCE: CEN/TS 16976:2016, modified]
3.3
number size distribution
frequency distribution of the particle number concentration represented as a function of the logarithm
of particle size, such that the area under the distribution between two sizes is the number concentration
of that size range
3.4
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]
3.5
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.
–3
Note 2 to entry: The usual unit is cm .
[SOURCE: ISO 27891:2015, modified]
4 Symbols and abbreviations
CPC Condensation Particle Counter
DMA Differential Mobility Analyser
HEPA High Efficiency Particulate Air
MPSS Mobility Particle Size Spectrometer
PSL Polystyrene Latex
QA/QC Quality Assurance / Quality Control
5 Atmospheric aerosol
Atmospheric aerosols are strongly dependent on their local and regional sources. Especially, the size
distributions 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 [1].
Due to these different formation processes the size distribution of the atmospheric aerosol shows three
to four different modes which schematically are sketched in Figure 1.
Key
1 Nucleation mode I Ultrafine particles
2 Aitken mode II Fine particles
3 Accumulation mode III Coarse particles
4 Coarse mode
Figure 1 — Schematic representation of the different modes of the size distribution of
atmospheric aerosols (mode height not to scale)
Particles in the nucleation mode are mainly produced by photochemical reactions and by mixing
processes from gaseous precursors. If supply of gaseous precursors persists, they grow rapidly by
condensation so that their size is shifted into the Aitken mode. Combustion processes contribute particles
directly to the Aitken mode. The size of the particles in the Aitken mode increases mainly by cloud
processing, condensation and coagulation, so that they are shifted into the accumulation mode. Particles
in the coarse mode are mainly produced by mechanical processes like the abrasion and resuspension of
mineral dust, dispersion of sea salt as particles and emission of pollen and other biological material. Both
the accumulation and the coarse mode particles are often not clearly recognizable in the number
distribution but contribute substantially to the mass distribution.
Besides these definitions used in the field of atmospheric physics there are the health and regulatory
definitions of fine, ultrafine and coarse particles. The size ranges associated with these terms are also
given in Figure 1.
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 (coarse mode).
Anthropogenic emissions in this size range play a minor role on a global scale. Submicrometer natural
aerosols consist mainly of marine sulphate, biogenic organics, and wildfire carbonaceous particles.
Submicrometer anthropogenic aerosols are complex mixtures of primary and secondary particles,
consisting mainly of sulphate, 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, continental or urban aerosols can contain a few thousand up to one million particles
per cubic centimetre. The number concentration of the anthropogenic aerosols over land, especially in
urban areas is dominated by particles in the size range smaller than 0,1 µm. Major sources for high
particle number concentrations in this size range are regional new particle formation due to
homogeneous nucleation and local combustion processes. Average background concentrations in an
urban area are several tens of thousands of particles per cubic centimetre.
For details see Annex H.
6 Description of the method
6.1 Sampling and conditioning
6.1.1 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 shall 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 shall 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 affecting the exposure of humans (e.g. traffic) calls for much lower sampling
heights (1,5 m to 4 m above the ground, see Directive 2008/50/EC [2]).
The design of the aerosol inlet 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 MPSS. Steps shall be taken to avoid soiling of the sampling lines by particles larger than
10 µm. PM10 or PM2.5 inlets can be used for this purpose (see Figure 2).
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 particle losses due to diffusion to walls, it is necessary to sample the aerosol with the aid of a
pump at a primary flow rate (Q ) much higher than the secondary flow rate (Q ). The instrument
tot MPSS
should sample isoaxially in the central area from this volumetric flow via a secondary sampling tube that
is as short as possible. The flow in the primary sampling tube should be laminar in order to prevent
additional particle loss due to turbulence. Ideally, a Reynolds number of about Re = 2000 shall be aimed
for (see 8.2) to minimize losses due to diffusion.
The particle losses due to diffusion in the sampling system shall be determined and corrected (see
Annex C).
Key
1 PM sampling inlet
2 Primary sampling tube
3 Secondary sampling tube
Figure 2 — Basic design of the aerosol intake port
The aerosol inlet and the sampling 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.
6.1.2 Aerosol Drying
Aerosols with a high relative humidity (mist in extreme cases) should be dried, as the size of hydrophilic
particles (particles containing salts or water-soluble organic material) is strongly dependent on the
relative humidity due to hygroscopic growth. Ambient air may increase its relative humidity considerably
when cooled down in an air-conditioned environment. The requirement is to keep the relative humidity
of the sample flow at the MPSS inlet lower than 40 % [3]. The relative humidity at the inlet of the MPSS
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 three recommended methods to dry the aerosol:
— Aerosol diffusion dryer based on silica;
TM
— Membrane dryer (e.g. Nafion dryer);
— Dilution with dry particle-free air. In this case, the exact dilution ratio shall be known in order to
calculate the correct concentrations. The minimum requirement with respect to accuracy of the
dilution factor is given in 8.2, the operation principle of a suitable dilution system is presented in
Annex G.
Heating is not recommended as this may change the aerosol (significant evaporation of semi-volatile
compounds above 40 °C).
6.2 Determination of particle number size distribution with an MPSS
6.2.1 Physical principle
Mobility particle size spectrometers consist of a sequential setup of a bipolar diffusion charger, a
Differential Mobility Analyser (DMA), and a Condensation Particle Counter (CPC). By setting different
voltages in the DMA, particles of different electrical mobility are selected and their particle number
concentration can be measured. Ramping or stepping the voltage yields an electrical particle mobility
distribution, which can later be inverted into a particle number size distribution (ISO 15900).
NOTE In ISO standardization the terms DMAS (Differential Mobility Analysing System) and DEMC (Differential
Electrical Mobility Classifier) are used for MPSS and DMA, respectively. A bipolar diffusion charger is termed charge
conditioner in ISO standardization.
6.2.2 Particle charging
Before the aerosol particles enter the DMA, they are brought to a bipolar charge equilibrium using a
bipolar diffusion charger. This bipolar charge equilibrium can be described theoretically [4] (for data on
particle charging probabilities as a function of particle size as well as for simplified methods to calculate
these data see Annex A). Positive and negative ions are produced continuously in this bipolar diffusion
charger, for instance by a radioactive or a soft X-ray source. The radioactive sources used in field
85 63 241 210
observation include e.g. Kr, Ni (beta emitters), Am and Po (alpha emitters).
To achieve a bipolar charge equilibrium, the particle number concentration should be significantly lower
7 −3
than the equilibrium ion pair concentration, which is estimated to be approximately 10 cm . As more
charges are attached to large particles than small ones, the upper concentration limit depends on the
particle number size distribution of the aerosol, so that no definitive value for the maximum
concentration can be given. The recommended upper limit for the total particle number concentration
5 −3
entering the MPSS is 10 cm .
6.2.3 Mobility analysis
A DMA is usually built in the shape of a cylindrical capacitor (see Figure 3). The charged polydisperse
aerosol is injected at a flow rate Q through an annular slit close to the outer electrode into the DMA and
A
then merged with the particle-free sheath air flow Q .
S
Key
1 Polydisperse aerosol flow rate
Outer electrode; radius r Q
o A
2 Annular inlet slit Sheath air flow rate
Q
S
3 Mobility-selected aerosol flow rate
Inner electrode; radius r Q
i M
4 Annular exit slit Excess air flow rate
Q
E
U Voltage L Effective length
Figure 3 — Principle of a DMA
All flows have to be strictly laminar. Due to the voltage applied between the inner and outer electrode,
charged particles move perpendicular to the direction of flow either to the inner or, for the opposite sign
of charge, to the outer electrode. The ratio of the particle velocity v to the electric field E is defined as
E
the electric mobility of the particle according to Formula (1):
ne⋅⋅ C D
v ( )
P
E
Z
P
E 3πη⋅⋅ D
P
(1)
Where
Z is the electrical mobility of a charged particle;
P
n is the number of elementary charges carried by the particle;
−19
e
is the elementary charge ( e 1,602⋅ 10 C );
C(D ) is the Cunningham slip correction factor (see Annex B);
P
η is the dynamic gas viscosity;
D is the particle diameter.
P
The electrical particle mobility depends primarily on the number of elementary charges on the particle
(proportional) and on particle diameter (inversely), but also on the dynamic gas viscosity, particle shape,
Cunningham slip correction factor, and hence also indirectly on temperature and pressure of the gas
flowing inside the DMA (ISO 15900). The smaller the particle diameter and the higher the number of
charges, the larger is the electrical particle mobility.
NOTE The Cunningham slip correction is often just called slip correction.
As the dimensions of the inlet and exit slit as well as the flow rates of the polydisperse and mobility-
selected aerosol flows are not indefinitely small, not only particles with one specific mobility will enter
the exit slit but also particles with a slightly larger or smaller mobility. To describe this behaviour, a
transfer function can be used, which gives the probability for a particle of a given mobility to enter the
exit slit at a given voltage or nominal mobility (see Figure 4). For the required case, that QQ= and
SE
QQ= this transfer function can be approximately represented by a triangle with a height of 1.
AM
Key
T Transfer function
Z Electrical mobility
P
* Mean electrical particle mobility
Z
P
ΔZ Half-width of the transfer function
P
Figure 4 — DMA transfer function
=
==
By knowing the dimensions of the DMA (length and radii of the inner and outer electrode) and the flow
rates inside the DMA, one can calculate the voltage between the electrodes corresponding to the mean
*
electrical particle mobility Z (see Formula (2)).
P
r
o
Q ⋅ ln
S
r
i
U=
*
2π⋅ ZL⋅
P
(2)
Where
U is the voltage;
Q is the sheath air flow rate;
S
r is the radius of the outer electrode;
o
r is the radius of the inner electrode;
i
*
is the mean electrical particle mobility;
Z
P
L is the length of the electrode.
The width of the triangle 2·ΔZ , which gives the mobility resolution of the DMA depends on the ratio of
P
the flow rates Q and Q and is given by in Formula (3).
A S
Q
A *
2⋅∆ZZ⋅
PP
Q
S
(3)
Where
Z is the electrical mobility of a charged particle;
P
Q is the polydisperse aerosol flow rate;
A
Q is the sheath air flow rate;
S
*
is the mean electrical particle mobility;
Z
P
ΔZ is the half-width of the transfer function.
P
The particle number concentration in this sample flow is measured by a CPC. The electrical particle
mobility distribution is determined measuring the particle number concentration at various different
voltages covering the entire electrical particle mobility range to be investigated.
This can be done by increasing or decreasing the voltage stepwise and waiting after each step until a
stable number concentration reading is obtained. For a typical number of 32 mobility values this leads to
a measurement time in the order of 10 min. For faster measurements, the voltage can be either increased
(upscan) or decreased (downscan), or both, continuously over a period of only a few minutes (scanning
method). In this case, it is essential to know the transport time (delay time) of the particles in the system
to relate the number concentration readings to the corresponding voltages.
The range of voltages necessary to cover the whole mobility range reaches from a few volts for particles
of 10 nm diameter up to 10 kV for particles of 800 nm diameter. A high voltage power supply with an
output voltage range of 0 V to 10 kV normally is less accurate at the lower end of this range. This means
that the voltages used to measure particles in the range of 10 nm to 20 nm may differ by about 20 % from
the nominal value leading to comparable errors in the determination of particle size.
=
6.2.4 Data inversion
Particles will enter the DMA with a range of positive and negative charges, and many of the smaller
particles will be uncharged. Particles of more than one size can have the same electrical mobility
depending on the number of elementary charges on each particle. Determining the particle number size
distribution therefore requires a data inversion process that takes account of the size-dependent
charging probabilities [5].
A significant number concentration of particles larger than the upper size limit of the MPSS, carrying large
numbers of elementary charges, cause large errors in this process. A pre-separator at the DMA inlet shall
be used in such cases. The pre-separator may be omitted for most atmospheric applications, if the size
range of the MPSS extends up to 800 nm or more. The reason is that the atmospheric particle number
size distribution declines very steeply towards larger particle sizes, making the contributions of multiple
charged particles much less important. Sensitivity tests have shown that multiple charges on particles
larger than 800 nm diameter are only important in the case of exceptional amounts of these large
particles, such as at kerbside, semi-arid and coastal sites. These exceptional circumstances will usually
be apparent from the lack of a steep decline in particle number concentration at sizes less than 800 nm.
6.2.5 Correction for particle losses due to diffusion
Particles losses due to diffusion increase with decreasing particle size. They depend on the geometry of
the flow paths and on the flow rates. For simple tubes of circular cross section particle losses due to
diffusion can be calculated theoretically (see Annex B). For more complex geometries, these losses shall
be determined experimentally. From these experimental results an equivalent length for the investigated
geometry can be derived, which is the length of a simple tube having the same losses. Based on this
equivalent length, particle losses due to diffusion can then again be calculated, depending on the particle
sizes and flow rates.
The secondary sampling tube together with the different parts of an MPSS (dryer, diffusion charger, DMA,
and the connecting lines in between) can add up to an equiv
...
The CEN/TS 17434:2020 standard provides a comprehensive framework for the determination of particle number size distributions in ambient air, focusing on particles within the size range of 10 nm to 800 nm. Its scope is particularly relevant for environmental monitoring and air quality assessment, where understanding atmospheric aerosol characteristics is crucial. One of the strengths of this standard is its detailed methodological approach that builds upon the use of a Mobility Particle Size Spectrometer (MPSS) paired with a bipolar diffusion charger and a Condensation Particle Counter (CPC). This combination ensures high accuracy in measuring particle concentrations, with the capability to detect levels up to approximately 10^5 cm^-3, thus enhancing the understanding of aerosol dynamics in the atmosphere. Moreover, the document outlines performance characteristics and sets minimum requirements for the instruments and equipment involved. This establishes a solid foundation for ensuring consistency and reliability in measurements across different studies and applications. The inclusion of comprehensive QA/QC procedures, as well as guidance on sampling, operation, and data processing, further supports the credibility of the results obtained through this method. The time resolution of a few minutes allows for real-time monitoring, which is pertinent for both research and regulatory purposes, making the CEN/TS 17434:2020 increasingly relevant in the context of public health and environmental protection. Overall, this standard serves as an essential tool for researchers, policymakers, and environmental professionals seeking to assess atmospheric conditions accurately and efficiently.
CEN/TS 17434:2020 표준 문서는 대기 중 입자 수 크기 분포를 측정하기 위한 방법을 제시하고 있으며, 이는 10nm에서 800nm 크기 범위의 입자를 대상으로 총 농도가 약 10^5 cm^-3까지 측정할 수 있습니다. 이 표준의 주요 강점 중 하나는 이동 입자 크기 분광기(Mobility Particle Size Spectrometer, MPSS)를 기반으로 하여, 양극 확산 충전기(bipolar diffusion charger)와 응축 입자 계수기(Condensation Particle Counter, CPC)를 조합하여 신뢰성 높은 측정을 수행할 수 있다는 점입니다. 이 문서는 사용해야 할 기기 및 장비의 성능 특성과 최소 요구 사항을 상세히 설명하고 있어, 대기 질 분석에 있어 매우 실용적입니다. 특히 샘플링, 운영, 데이터 처리, 품질 보증(QA) 및 품질 관리(QC) 절차를 포함하여, 측정의 정확성을 높이는 데 중점을 두고 있습니다. 이는 사용자가 기준을 준수하며 일관된 결과를 얻을 수 있도록 지원합니다. CEN/TS 17434:2020 표준의 적합성은 대기 오염 모니터링 및 연구에서 매우 중요한 요소로, 입자 물질의 크기 분포를 정량적으로 분석할 수 있다는 점에서 대기 중 미세먼지 측정 및 관리에 기여합니다. 이는 대기 과학, 환경 정책 개발 및 공공 건강 보호와 같은 다양한 분야에서 그 중요성이 더욱 부각되고 있습니다. 표준의 전반적인 구조와 상세한 절차는 연구자와 실험실 기술자가 대기 중 입자 크기 분포를 효과적으로 분석하는 데 필요한 신뢰할 수 있는 지침을 제공하므로, 입자 분석 관련 분야에서 큰 가치를 지니고 있습니다.
CEN/TS 17434:2020は、大気中のエアロゾルの粒子数サイズ分布をMobility Particle Size Spectrometer（MPSS）を用いて定量化するための標準化文書であり、特に10 nmから800 nmの粒子サイズ範囲を対象としています。この標準の範囲は、空気中の微小粒子の研究や環境モニタリングにおいて非常に重要であり、環境政策や健康リスク評価における基礎データを提供します。 この標準の強みは、MPSSとバイポーラ拡散充電器、冷却粒子カウンター（CPC）を使用することで、粒子数の高精度な測定を可能にしている点です。特に、前述の機器を組み合わせることで、約10^5 cm^-3の総濃度までの粒子を数分単位で測定できるため、動的な大気環境の理解に貢献します。さらに、標準では機器の性能特性や最低要件が明確に記載されており、実施者が適切な機器を選定し、信頼性の高いデータを得る手助けをしています。 また、サンプリング、操作、データ処理、QA/QC手順、キャリブレーションについても詳細に説明されており、これによって実際の測定プロセスにおける一貫性と再現性が保証されます。このような包括的なアプローチは、研究者や技術者にとっての実用的なガイドラインとなり、規格の信頼性を高めています。 CEN/TS 17434:2020は、環境科学や公衆衛生、さらには政策提言に不可欠なデータ収集手段を提供するため、今後の研究や実務においてもその関連性はますます高まるでしょう。この標準は、大気の粒子数サイズ分布を理解し、環境問題に対処するための重要なツールです。
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...