ISO 15900:2020

INTERNATIONAL ISO
STANDARD 15900
Second edition
2020-10
Determination of particle size
distribution — Differential electrical
mobility analysis for aerosol particles
Détermination de la distribution granulométrique — Analyse de
mobilité électrique différentielle pour les particules d'aérosol
Reference number
ISO 15900:2020(E)
©
ISO 2020

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ISO 15900:2020(E)

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© ISO 2020
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ISO 15900:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 4
5 General principle . 5
5.1 Particle size classification with the DEMC . 5
5.2 Relationship between electrical mobility and particle size . 6
5.3 Measurement and data inversion . 7
5.4 Transfer function of the DEMC . 8
5.5 Charge distribution function . 9
5.5.1 General. 9
5.5.2 Charge distribution function for radioactive bipolar charge conditioners . 9
5.5.3 Charge distribution functions for other bipolar and unipolar charge
conditioners .10
5.6 Particle losses in the DMAS .11
5.7 Effects due to non-spherical particles.11
5.8 Measurement of particle sizes below 10 nm .11
5.9 Traceability of measurement results .11
6 System and apparatus .13
6.1 General configuration .13
6.2 Components .14
6.2.1 Pre-conditioner .14
6.2.2 Charge conditioner .14
6.2.3 DEMC .15
6.2.4 Aerosol particle detector .15
6.2.5 System controller, data acquisition and analysis .15
7 Measurement procedures .16
7.1 Setup and preparation of the instrument .16
7.1.1 General.16
7.1.2 Aerosol pre-conditioning: Adapting the aerosol to be measured to the
requirements of the DMAS .16
7.1.3 Aerosol pre-conditioning: Separation of large particles .16
7.1.4 Charge conditioning .17
7.1.5 DEMC: Flows .17
7.1.6 DEMC: Voltage .18
7.1.7 DEMC: Temperature and pressure .18
7.1.8 Particle detection: CPC . . .18
7.1.9 Particle detection: FCAE .18
7.1.10 Data acquisition .18
7.2 Pre-measurement checks.18
7.2.1 General.18
7.2.2 Overall DMAS check .19
7.2.3 Data acquisition check .19
7.3 Measurement .19
7.4 Maintenance .19
8 Periodic tests and calibrations .20
8.1 Overview .20
8.2 Zero tests .21
8.2.1 General.21
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ISO 15900:2020(E)

8.2.2 Particle detector zero test .21
8.2.3 Overall DMAS zero test with inlet filter .21
8.2.4 Overall DMAS zero test with DEMC voltage set to 0 V .21
8.3 Flow rate tests .21
8.4 Voltage calibration .22
8.5 Charge conditioner test .22
8.6 Calibration for size measurement .22
8.6.1 General.22
8.6.2 Purpose of calibration .22
8.6.3 Particle size standards .22
8.6.4 Dynamic DMAS particle size calibration procedure .23
8.6.5 Static DMAS particle size calibration procedure .24
8.7 Size resolution test .28
8.8 Number concentration calibration .28
9 Using a DEMC at a fixed voltage to generate particles of a chosen size .29
9.1 General .29
9.2 Multiply-charged particles .30
9.3 Size calibration with certified spheres .30
9.4 Sheath flow .30
9.5 Slip correction (if applicable) .31
9.6 Voltage (if applicable) .31
9.7 Calculation of overall uncertainty .31
10 Reporting of results .31
Annex A (informative) Charge conditioners and charge distributions .33
Annex B (informative) Particle detectors .44
Annex C (informative) Slip correction factor .48
Annex D (informative) Data inversion .51
Annex E (informative) Cylindrical DEMC .67
Annex F (informative) Example certificate for a DMAS particle size calibration .72
Annex G (informative) Good practice for measurements at particle sizes below 10 nm .75
Annex H (informative) Examples for overall system tests .77
Annex I (informative) Comparison of different approaches to calculate diffusion loss in
laminar tube flow.83
Annex J (informative) Corrections for effects due to non-spherical particles.87
Bibliography .88
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ISO 15900:2020(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 24, Particle characterization including
sieving, Subcommittee SC 4, Particle characterization.
This second edition cancels and replaces the first edition (ISO 15900:2009), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— subclauses on particle losses due to Brownian diffusion, effects due to non-spherical particles, and
measurement of particles below 10 nm have been added in Clause 5;
— traceability diagrams for DEMC and DMAS have been added in Clause 5;
— calibration for size measurement in Clause 8 has been refined;
— Clause 9 for “Using a DEMC at a fixed voltage to generate particles of a chosen size” has been added;
— Annex D for “Data inversion” has been rewritten completely;
— Annex F for “Example certificate for a DMAS particle size calibration” has been added;
— former Annex G for “Uncertainty” in the previous edition has been deleted;
— new Annex G for “Good practice for measurements at particle sizes below 10 nm” has been added;
— Annex H for “Examples for overall system tests” has been added;
— Annex I for “Comparison of different approaches to calculate diffusion loss in laminar tube flow” has
been added;
— Annex J for “Corrections for effects due to non-spherical particles” has been added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO 15900:2020(E)

Introduction
Differential electrical mobility classification and analysis of airborne particles has been widely used
to measure a variety of aerosol particles ranging from nanometre-size to micrometre-size in the gas
phase. In addition, the electrical mobility classification of charged particles can be used to generate
mono-disperse particles of known size for calibration of other instruments. One notable feature of these
techniques is that they are based on simple physical principles. The techniques have become important
in many fields of aerosol science and technology, e.g. aerosol instrumentation, production of materials
from aerosols, contamination control in the semiconductor industry, atmospheric aerosol science,
characterization of engineered nanoparticles, and so on. However, in order to use electrical mobility
classification and analysis correctly, several issues, such as the slip correction factor, the ion-aerosol
attachment coefficients, the size-dependent charge distribution on aerosol particles and the method
used for inversion of the measured mobility distribution to the aerosol particle size distribution, need
due caution.
There is, therefore, a need to establish an International Standard for the use of differential electrical
mobility analysis for classifying aerosol particles. Its purpose is to provide a methodology for adequate
quality control in particle size and number concentration measurement with this method.
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INTERNATIONAL STANDARD ISO 15900:2020(E)
Determination of particle size distribution — Differential
electrical mobility analysis for aerosol particles
1 Scope
This document provides guidelines and requirements for the determination of aerosol particle number
size distribution by means of the analysis of electrical mobility of aerosol particles. This measurement
is usually called “differential electrical mobility analysis for aerosol particles”. This analytical method
is applicable to particle size measurements ranging from approximately 1 nm to 1 µm. This document
does not address the specific instrument design or the specific requirements of particle size distribution
measurements for different applications but includes the calculation method of uncertainty. In this
document, the complete system for carrying out differential electrical mobility analysis is referred to as
DMAS (differential mobility analysing system), while the element within this system that classifies the
particles according to their electrical mobility is referred to as DEMC (differential electrical mobility
classifier).
NOTE This document does not include technical requirements and specifications for the application of DMAS,
which are defined in application specific standards or guidelines, e.g. for road vehicle applications (ISO/TC 22),
environmental measurements (ISO/TC 146) or nanotechnologies (ISO/TC 229).
2 Normative references
There are no normative references in this document.
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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
aerosol
system of solid and/or liquid particles suspended in gas
3.2
attachment coefficient
attachment probability of ions and aerosol particles
3.3
bipolar charging
process which attains a conditioned charge distribution of both positive and negative charges on
aerosol particles
3.4
bipolar charge conditioner
device which attains a conditioned charge distribution of both positive and negative charges on aerosol
particles
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ISO 15900:2020(E)

3.5
charging
processes that leave aerosol particles with size dependent specific distributions of unipolar or bipolar
electrical charges
3.6
charge conditioner
device (or component of a DMAS) which establishes a known conditioned size dependent charge
distribution on aerosol particles which are passed through it
3.7
charge distribution function
mathematical and/or empirical description of a conditioned particle size dependent charge distribution
3.8
condensation particle counter
CPC
instrument that measures the particle number concentration of an aerosol
Note 1 to entry: The sizes of particles detected are usually smaller than several hundred nanometres and larger
than a few nanometres.
Note 2 to entry: A CPC is one possible detector for use with a DEMC.
Note 3 to entry: In some cases, a condensation particle counter may be called a condensation nucleus counter (CNC).
3.9
conditioned charge distribution
distribution of unipolar or bipolar electrical charges on aerosol particles defined by a charge
distribution function, which is in a steady state for a sufficiently long period of time in an aerosol
instrument downstream of a unipolar or bipolar charge conditioner
3.10
critical mobility
instrument parameter of a DEMC (3.11) that defines the electrical mobility of aerosol particles that exit
the DEMC in aerosol form, which may be defined by the geometry, sample and sheath flow rates, and
electrical field intensity
Note 1 to entry: Particles larger or smaller than the critical mobility migrate to an electrode or exit with the
excess flow and do not exit from the DEMC in aerosol form.
3.11
differential electrical mobility classifier
DEMC
classifier able to select aerosol particles according to their electrical mobility and pass them to its exit
Note 1 to entry: A DEMC classifies aerosol particles by balancing the electrical force on each particle with its
aerodynamic drag force in an electrical field. Classified particles are in a narrow range of electrical mobility
determined by the operating conditions and physical dimensions of the DEMC, while they can have different sizes
due to difference in the number of charges that they have.
Note 2 to entry: Another common acronym for the DEMC is DMA.
3.12
differential mobility analysing system
DMAS
system to measure the size distribution of submicrometre aerosol particles consisting of a charge
conditioner, a DEMC, flow meters, a particle detector, interconnecting plumbing, a computer and
suitable software
Note 1 to entry: Another common acronym for the DMAS is MPSS (mobility particle size spectrometer).
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3.13
electrical mobility
ratio of migration velocity (3.18) to electrical field for particles and ions in a gas
3.14
equivalent diameter
d
diameter of a sphere with defined characteristics which behaves under defined conditions in exactly
the same way as the particle being described
Note 1 to entry: Particle diameter (or simply diameter) used throughout this document always refers to the
electrical mobility equivalent diameter, which defines the size of charged particles with the same electrical
mobility or the same terminal migration velocity in still air under the influence of a constant electrical field.
3.15
Faraday cup aerosol electrometer
FCAE
electrometer designed for the measurement of electrical charge concentration carried by an aerosol
Note 1 to entry: A Faraday cup aerosol electrometer consists of an electrically conducting and electrically grounded
cup as a guard to cover the sensing element that includes aerosol filtering media to capture charged aerosol
particles, an electrical connection between the sensing element and an electrometer circuit, and a flow meter. An
FCAE measures electrical current ranging from about one femtoampere (fA) to about ten picoamperes (pA).
3.16
Knudsen number
Kn
ratio of gas molecular mean free path to the radius of the particle, which is an indicator of free molecular
flow versus continuum gas flow
3.17
laminar flow
gas flow with no temporally or spatially irregular activity or turbulent eddy flow
3.18
migration velocity
steady-state velocity of a charged airborne particle within an externally applied electric field
3.19
particle diameter
electrical mobility equivalent diameter
Note 1 to entry: Also, just called diameter.
3.20
plateau detection efficiency
mean detection efficiency of a CPC in the size range which is not biased by particle size
[SOURCE: ISO 27891:2015, 3.27, modified — term “plateau efficiency” has been changed to "plateau
detection efficiency.]
3.21
Reynolds number
Re
dimensionless number expressed as the ratio of the inertial force to the viscous force
Note 1 to entry: For example, applied to an aerosol particle or a tube carrying aerosol particles
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3.22
slip correction
S
C
dimensionless factor used to correct the drag force acting on a particle for non-continuum effects that
become important when the particle size is comparable to or smaller than the mean free path of the gas
molecules
3.23
Stokes's drag
drag force acting on a particle that is moving relative to a continuum fluid in the creeping flow limit
(low Reynolds number)
3.24
transfer function
ratio of particle concentration at the outlet of a DEMC to the particle concentration at the inlet of the DEMC
Note 1 to entry: It is normally expressed as a function of electrical mobility.
3.25
unipolar charge conditioner
device which attains a conditioned charge distribution of either positive or negative charges on aerosol
particles
3.26
unipolar charging
process which attains a condition
...