SIST-TS CEN/TS 18073:2025

SLOVENSKI STANDARD
01-januar-2025
Zunanji zrak - Določanje koncentracije delcev. ki se lahko usedajo na površino
pljuč (LDSA) z uporabo monitorjev aerosolov na podlagi difuzije in naboja
Ambient air - Determination of lung deposited surface area (LDSA) concentration using
aerosol monitors based on diffusion charging
Außenluft - Bestimmung der lungendeponierbaren Oberflächenkonzentration (LDSA) mit
Aerosolmonitoren auf Basis der Diffusionsaufladung
Air ambiant - Détermination de la concentration en surface spécifique des particules
pouvant se déposer dans les poumons (LDSA) à l’aide de moniteurs d’aérosols basés
sur la charge par diffusion
Ta slovenski standard je istoveten z: CEN/TS 18073:2024
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 18073
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
September 2024
TECHNISCHE SPEZIFIKATION
ICS 13.040.20
English Version
Ambient air - Determination of lung deposited surface area
(LDSA) concentration using aerosol monitors based on
diffusion charging
Air ambiant - Détermination de la concentration en Außenluft - Bestimmung der lungendeponierbaren
surface spécifique des particules pouvant se déposer Oberflächenkonzentration (LDSA) mit
dans les poumons (LDSA) à l'aide de moniteurs Aerosolmonitoren auf Basis der Diffusionsaufladung
d'aérosols basés sur la charge par diffusion
This Technical Specification (CEN/TS) was approved by CEN on 5 August 2024 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, Türkiye 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
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 18073:2024 E
worldwide for CEN national Members.

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 Particle size metrics . 7
3.3 Particle concentration metrics . 7
4 Principle . 8
4.1 Physical principles . 8
4.2 Physiological principles . 8
5 Function . 9
5.1 General. 9
5.2 Inertial separator. 10
5.3 Diffusion charger . 10
5.4 Ion trap . 13
5.5 Charge measurement . 14
6 Interpretation of the current . 15
7 Sampling and conditioning . 16
7.1 General. 16
7.2 Sampling . 17
7.3 Humidity conditioning . 17
8 DCAM design criteria, performance criteria and test procedures . 18
8.1 DCAM design and performance criteria . 18
8.2 Test procedures for DCAM performance criteria . 18
8.2.1 Actual flow rates . 18
8.2.2 Calibration curve . 19
8.2.3 Calibration factor . 20
9 Measurement procedure . 20
9.1 Measurement planning . 20
9.2 Environmental operating conditions . 21
9.3 Initial installation . 21
9.4 Function testing . 21
9.5 Data processing and reporting . 21
10 Interfering factors and error sources . 22
10.1 Ambient conditions . 22
10.2 Contamination and wear . 22
11 Maintenance . 22
12 Measurement uncertainty . 23
12.1 Introduction . 23
12.2 Summary of method . 23
12.3 Sources of uncertainty . 23
12.3.1 General . 23
12.3.2 Step 2: Determination of the calibration factor . 23
12.3.3 Step 3: Sampling of particles . 24
12.3.4 Step 4: Charging of particles . 25
12.3.5 Step 5: Measurement of current . 25
12.3.6 Step 6: Calculation of LDSA concentration . 25
Annex A (informative) Flow arrangements . 26
A.1 Flow rate attributes . 26
A.2 Instruments with single flow charger . 26
A.3 Instruments using a mixing type charger . 27
Annex B (informative) Input parameters and numerical data for the ICRP model . 29
Bibliography . 31

European foreword
This document (CEN/TS 18073:2024) 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.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
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, Türkiye and the
United Kingdom.
Introduction
There is growing recognition of the importance of aerosol particles with diameters D < 1 µm for human
health as well as for their effects on climate. While usually the mass concentration of airborne particles
is quantified both in the environment and at the workplace, various studies have shown the relevance of
the number and surface area concentration to their health effects. Correlations between the incidence of
respiratory diseases and the number concentrations of airborne particles are, e.g. given in [1]. It was
shown that the effects on health due to inhaled particles correlate better with the particle surface area
dose than with the particle mass dose [2] or the particle number dose [3]. To describe the air quality in
terms of dust load, it therefore appears advisable to supplement the parameters of mass concentration
(for PM and PM , see EN 12341 [4]), particle number concentration and number size distribution
10 2,5
(see EN 16976 [5] and CEN/TS 17434 [6]) with measurements of further metrics, e.g. particle surface
area concentration as a health-relevant metric.
For the measuring device required for the implementation of the measuring method described in this
document, the designation “electrical aerosol monitor based on diffusion charging” abbreviated to DCAM
(Diffusion-Charger-based Aerosol Monitor) is introduced.

1 Scope
This document specifies a process for the electrical diffusion charging of aerosols with subsequent
measurement of particle charge. With the aid of this method, it is possible to determine the lung-
deposited surface area (LDSA) concentration of particles in ambient air. Depending on the design of the
electrical diffusion charger, the LDSA of particles in the size range of approximately 20 nm to
approximately 300 nm is measurable.
Furthermore, this document specifies design criteria for LDSA measuring aerosol monitors as well as
performance criteria and the associated test procedures. The performance criteria depend on the
application and they are more stringent when the instrument is operated in an air quality monitoring
station.
In the determination of the LDSA concentration, the share of geometric particle surface area
concentration is determined that can be deposited in the alveolar region of the human lung. Typical
particle surface area concentrations with alveolar deposition measured in urban areas range from
2 3 2 3
5 µm /cm to 50 µm /cm .
Instruments based on this measurement principle can be designed to be very compact with a low power
consumption. This makes them ideally suited for hand-held measurements, other forms of mobile
application or to measure personal exposure. On the other hand, they can be easily adapted to serve as a
stationary instrument in air quality monitoring stations.
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:
— 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
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: EN 16976:2024] [5]
3.1.2
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] [7]
3.1.3
number size distribution
frequency distribution of the particle number concentration as a function of particle size
[SOURCE: EN 16976:2024] [5]
3.2 Particle size metrics
3.2.1
equivalent diameter
diameter of the sphere with defined characteristics which behaves under defined conditions in exactly
the same way as the particle being described
[SOURCE: ISO 27891:2015] [7]
3.2.2
aerodynamic diameter
3 –3 –3
diameter of a sphere of density ρ = 10 kg·m = 1 g·cm with the same terminal velocity due to
gravitational force in calm air as the particle, under the prevailing conditions of temperature, pressure
and relative humidity within the respiratory tract
[SOURCE: ISO 13138:2012] [8]
3.2.3
Stokes diameter
diameter of a spherical particle which at the same velocity relative to a medium experiences the same
drag force as the particle to be described
3.3 Particle concentration metrics
3.3.1
particle number concentration
number of particles related to the unit volume of the carrier gas
[SOURCE: ISO 27891:2015] [7]
3.3.2
particle surface area concentration
total surface area of all dispersed particles per unit of volume of the carrier gas
3.3.3
lung-deposited surface area concentration
LDSA concentration
particle surface area concentration per unit volume of air, weighted by the deposition probability in the
lung
[SOURCE: ISO 16000-34:2018] [9]
4 Principle
4.1 Physical principles
This method combines the particle-size-dependent electrical diffusion charging of particles with
subsequent measurement of the electrical current caused by the charged particles. In this process, gas
ions of a single polarity are attached by diffusion to the aerosol particles. The mean particle charge n
c
resulting from this diffusion charging is a function of particle size D (Stokes diameter) and can be
p
approximated with Formula (1):
x
nD() k⋅ D (1)
cp c p
Here, the coefficient k and exponent x are empirically determined quantities that are dependent on the
c
particle size range concerned and specific to a charger type. For pure diffusion chargers, various studies
have shown that, for particles of diameter < approx. 400 nm, the exponent x ranges from 1,1 to 1,4 (e.g.
[10 to 12]).
To convert the charge transport by the particles into a measurable electrical current, the particles can be
deposited either directly on a conductive electrode (e.g. by an electric field) or transported in the gas-
borne state into a Faraday cup. If the particles are deposited on a filter within the Faraday cup, current
flows onto the electrically isolated, metal Faraday cup (electrostatic induction) to compensate for the
charge introduced into the cup. Alternatively, the charging process can be switched on and off at a certain
frequency. This gives rise to charged “aerosol packets” that generate a pulse of current on entering and
leaving the Faraday cup.
In all cases the very small electrical currents (< 1 pA) are converted with electrometer amplifiers into a
voltage that represents the method’s output signal and can be further processed by a data acquisition
system.
Diffusion charging shows only little dependence on the ambient conditions of temperature and pressure
and on particle material [13]. The relative humidity can indirectly affect the charging process if it results
in a change in particle size.
4.2 Physiological principles
Only a portion of the inhaled particles is deposited in the lung, the remainder being exhaled. Particles are
deposited in the lung principally because of their Brownian motion (diffusional deposition), the blocking
effect (interception deposition) and particle inertia (impaction deposition). Particle inertia is not relevant
in the considered size range from approx. 20 nm to approx. 300 nm. With increasing particle size,
diffusional deposition declines, while interception and impaction deposition increase. Thus, the lung
deposition efficiency is the particle-size-dependent ratio of the quantity of particles deposited in the lung
to the total quantity of inhaled particles.
Figure 1 shows the deposition efficiency in the alveolar region of the human lung calculated using KDEP
[14], an open source implementation of the ICRP (International Commission on Radiological Protection)
model [15]. The curve represents an average for male and female individuals with nose breathing and
the activity pattern “member of the public”. Spherical particles with a density of 1 500 kg/m were used
as model for the atmospheric aerosol. Numerical results of the calculation can be found in Annex B. Owing
to the size dependences of the separation mechanisms in the respiratory tract, this yields a characteristic
curve with an efficiency maximum at approx. 20 nm and an efficiency minimum at approx. 300 nm. Since
impaction deposition predominates above this minimum, the efficiency becomes additionally dependent
on particle density. The Figure also illustrates that, in the size range from approx. 20 nm and approx.
300 nm, the alveolar deposition curve shows a slope, which on the double logarithmic scale employed is
−0,9
D
almost constant and proportional to (compare the dot-dashed straight line). If the particle surface
P
=
2 −0,,9 11
area dependent on the square of particle diameter is weighted with this ratio, this yields D ⋅=D D
PP P
. For certain parameters of the charging process, this corresponds to the relationship for the mean
particle charge given in 4.1, so an interpretation of the signal as the lung-deposited surface area
concentration is possible.
Figure 1 — Efficiency η of particle deposition in the alveolar region of the human lung as a
function of particle diameter D (conforming to [15]; parameters given above)
P
5 Function
5.1 General
In an electrical aerosol monitor based on diffusion charging (DCAM), particles, after passing through an
inertial separator, if necessary, are electrically charged in a diffusion charger. Excess ions are then
removed in an ion trap and the particle charges are measured. Depending on the charging characteristics,
the measured current is proportional to the particle diameter concentration or to the lung-deposited
surface area concentration. Figure 2 shows a general schematic of a DCAM.
Key
1 inertial separator (optional)
2 diffusion charger
3 ion trap
4 charge detector
Figure 2 — Schematic of an electrical aerosol monitor based on diffusion charging (DCAM)
5.2 Inertial separator
The useful measurement range of a DCAM has an upper limit at about 300 nm. As alveolar deposition
increases above this diameter (see Figure 1), the LDSA of larger particles is increasingly underestimated
by the instrument. To avoid internal soiling of the instrument by larger particles an inertial separator
(preferably a cyclone) may optionally be used at the inlet of the instrument. For most atmospheric
situations, where the aerosol particle number size distribution is dominated by fine and ultrafine
particles, this is not necessary, because the number concentration of particles larger than the upper size
limit of the instrument is rather small. Only in the vicinity of sources for coarse particles (e.g. sea salt,
desert dust, industrial dust emissions) the use of an inertial separator is recommended.
To avoid an influence on the particle number size distribution below 300 nm the particle penetration at
300 nm should be larger than 90 %.
For battery operated versions of a DCAM it is possible that the internal pump is not designed to cope with
the additional pressure drop across the separator. For a DCAM operated stationary in an air quality
monitoring station the inlet of the sampling system (e.g. a PM sampling inlet) may be used as a separator.
5.3 Diffusion charger
In a diffusion charger, ions of the same polarity are generated by means of corona discharge. In the
particle charging zone, both the ions and the particles are subject to Brownian motion, i.e. to diffusion, by
means of which the ions attach to particles and electrically charge them.
The mean number of elementary charges on particles after diffusion charging depends on particle size
and ion properties. Further important factors are particle dwell time, ion concentration and the degree
of mixing of ions and particles in the charger. Furthermore, size-dependent particle loss can possibly
occur in the charger owing to the effect of the electric field on already charged particles. Additional effects
of space-charge and mirror charge are taken into account in the calibration process.
By modifying the dwell time and/or ion concentration in the charger or the ionizer (i.e. the aerosol or
ionizer flow rate and/or corona voltage), the exponent x in Formula (1) can be varied within certain
limits. The coefficient k depends on the device type and design. To convert the measured currents into
c
the respective measures of concentration, calibration factors are required.
With a corona charger, free gas ions of the same polarity are generated by corona discharge [16]. To this
end, a strongly inhomogeneous field is generated between a corona electrode and a counter electrode.
Typical configurations can be a thin corona wire (see Figure 3) or a pointed corona needle in combination
with a flat or cylindrical counter electrode. In the vicinity of the corona, electrons are accelerated to a
speed high enough to knock electrons out of air molecules by colliding with them and to thus generate
positive ions and free electrons.
A corona discharge also causes the formation of ozone as a by-product. A corona discharge with positive
polarity produces significantly less ozone than a corona discharge with negative polarity [17; 18], so,
corona chargers are typically designed with positive polarity. The positive corona discharge is also more
stable, and thus easier to regulate. The amount of ozone formed in positive corona chargers is typically
below the odour threshold (ca. 100 µg/m ), and, if at all, even smaller amounts will be released from the
device, as the ozone reacts easily with any surface in the instrument. Health-relevant ozone
concentrations are not released from such devices. Care shall only need to be taken if ozone-sensitive
measurements are carried out in the direct vicinity of a diffusion charger.
If the corona electrode has a positive potential in relation to the counter electrode, the electrons move
rapidly to the corona electrode and the positive ions to the counter electrode.
Figure 3 shows the principle of a single flow charger. Here, the aerosol (4) flows through a duct. In an
ionizer chamber located to the side of this duct and separated from this duct by a tightly meshed, metal
grid (3), there is a thin wire, e.g. made of tungsten (2), retained by insulators to which a high voltage U
C
is applied. The purpose of the grid is to screen off the electric field generated by the corona wire. Applied
to it is a low grid voltage U that generates a low field strength E in the aerosol duct. Only a small share
G
of the positive ions generated by corona discharge penetrate the grid, move in the aerosol duct under the
influence of this field transversely to the direction of flow and attach to the aerosol particles in the
process. The field strength is so weak that the attachment process is dominated by diffusion.
Figure 4 shows the example of a mixing type charger.
Key
1 insulator
2 Corona electrode (e.g. wire, tip)
3 grid
4 aerosol (aerosol flow rate Q )
A
5 charged aerosol
Figure 3 — Example of a single flow charger
Key
1 aerosol (aerosol flow rate Q )
A
2 mixing/charging chamber
3 air (ionizer flow rate Q )
I
4 adsorption filter
5 particle filter
6 insulator
7 Corona needle
8 charged aerosol
Figure 4 — Example of a mixing type charger
In this configuration, the ions are generated at the tip of a corona needle held by an insulator (7) to which
a high voltage U is applied. An air flow (ionizer flow rate Q ; 3), which has been cleaned in an adsorption
C I
filter (4) and a particle filter (5), transports these ions into a mixing chamber (2). The aerosol (1) flows
from the opposite side into this mixing chamber and is mixed turbulently with the cleaned air flow and
the ions it contains. In this process, the ions attach to the particles by diffusion.
To achieve a charge that is as reproducible as possible, the ion flow can be measured and kept constant
by modifying the corona voltage in both configurations.
5.4 Ion trap
In the flow downstream from the diffusion charger, there are not only charged particles but also free ions.
So that downstream charge measurement exclusively registers the particle charges and not the ion
charges, the ions are separated in an ion trap. An electrostatic separator is used for this purpose, which
can have a variety of designs, e.g. two parallel plate electrodes or two coaxially arranged electrodes. If
only a weak electric field is generated between the electrodes, this will mainly remove the highly mobile
ions and the charged particles only to a negligible extent.
5.5 Charge measurement
Figure 5 shows two different configurations for measurement of the charges transported by the charged
particles.
Figure 5 — Configurations for the measurement of charge transport
a) Faraday cup with separator
b) Faraday cup without separator
c) Transimpedance amplifier
d) Amplifier output voltage for the Faraday cup with separator
e) Amplifier output voltage for the Faraday cup without separator
In both configurations, a Faraday cup (a, b) is used as a charge detector, which is connected to the
inverting input of an electrometer amplifier (transimpedance amplifier, c). This input, with this circuitry
variant, is practically at ground potential. Since this amplifier has an extremely high input resistance, the
current flows via the feedback resistor R to the amplifier output. Given a high resistance value of typically
R = 10 Ω, a current of I = 1 pA is converted into an amplifier output voltage U = –1 V. If it is assumed
that voltages up to approximately U = –1 mV are still measurable, this corresponds to a lower detection
limit for the current of approximately I = 1 fA.
If the particles transported into the Faraday cup are separated in a fibre filter (a), the charges transported
by the particles no longer leave the Faraday cup. The outcome of this is that charges with the opposite
sign flow by induction via the transimpedance amplifier to the Faraday cup, which, given a constant
aerosol concentration, also yields a constant output voltage of the electrometer amplifier over time (d).
If the Faraday cup is operated without a particle separator and particle charging is switched on and off at
a certain frequency (b), individual “packets” of charged particles are obtained in the continuous aerosol
flow that generate a pulse in the induced current on entering and leaving the Faraday cup [19]. As shown
in Figure 5, the pulses produced by the charged particles entering and leaving the Faraday cup have
opposite signs (e). The frequency at which the individual charged aerosol packets are generated by
switching on the charger has to be adapted to the dwell time dictated by the flow rate and geometry of
the Faraday cup so that only one charge packet is present in the Faraday cup at any time. The signal’s
amplitude (difference in voltage between the maximum value of the positive pulse and the minimum
value of the negative pulse (also known as the peak-to-peak value)) is evaluated here. This value is not
affected by any DC voltage drift of the electrometer amplifier.
To keep the effect of external electric fields on the highly sensitive current measurement as small as
possible, the entire configuration in all cases is enclosed by further metallic shielding.
The currents resulting from the particle charge are very small, and usually < 100 fA for ambient air
measurements. The electrometers employed should therefore have a low noise level, e.g.

fA
05,
≤ 1 fA⋅ s alternative expression : 1 so that the lower detection limit is low.


Hz

The zero of the electrometer drifts due to the ambient and operating conditions. The zero setting of the
electrometer is therefore regularly, e.g. hourly, and automatically checked and corrected. Excepted from
this is the variant using a Faraday cup without a separator. Since in this case only the signal amplitude
(the AC component) is determined to measure the current, zero drift is irrelevant.
6 Interpretation of the current
The surface area concentration deposited in the alveolar region corresponds to the surface area size
distribution of the particles in an aerosol, weighted with the associated lung deposition curve (see
Figure 1) and integrated over particle size. In the range from 20 nm to 300 nm, separation in the alveolar
−0,9 1,1
D D
region is roughly proportional to , thus yielding a proportionality to for the lung-deposited
P P
surface area (see 4.2). The unit for lung-deposited surface area concentration conventionally used is
2 3
µm /cm .
Since diffusion chargers can be designed in a way that their charging efficiency in the particle size range
1,1
D
concerned is roughly proportional to , the current caused by the charged particles is proportional to
P
the lung-deposited surface area concentration. By using suitable calibration factors, it is thus possible to
calculate the surface area concentration deposited in the alveolar region from the total measured current.
Figure 6 shows, as an example, the nominal characteristic. Clearly evident is the match within ± 30 % in
the size range of 20 nm ≤ D ≤ 300 nm, as well as the positive deviations for particles smaller than 20 nm
P
and the negative deviations for particles greater than 300 nm.
Key
X particle diameter DP in nm
Y normalized alveolar LDSA/normalized charging efficiency
1 alveolar LDSA
2 charging efficiency
3 ±30 % uncertainty
Figure 6 — Normalized alveolar LDSA concentration and normalized charging efficiency
with ±30 % uncertainty range; the curves are normalized to the function value at 100 nm
7 Sampling and conditioning
7.1 General
A range of DCAM devices are available which typically take the form of either hand-held devices (for
mobile operation) or fixed-location devices (e.g. for operation in air quality monitoring stations). This
Clause provides some general guidance on sampling and conditioning of atmospheric aerosols prior to
measurement by a DCAM, primarily for fixed-location devices. The requirements cannot necessarily be
met by hand-held devices.
If the DCAM is operated in an air quality monitoring network, its sampling system has to fulfil the
requirements of this network (e.g. ACTRIS [20]).
2 3
The upper limit of the LDSA concentration is in the order of at least 10 000 µm /cm . This corresponds
6 –3
to number concentrations of about 10 cm even for the largest particles in the measurement range.
Thus, for practically all atmospheric aerosol concentrations no dilution of the aerosol is necessary.
7.2 Sampling
Sampling should be representative for different particle sizes regardless of the direction and velocity of
the wind. This however is not a critical condition for the small particles (< 300 nm) measured by a DCAM.
The sampling location chosen depends on the measurement task being undertaken. If undisturbed
atmospheric aerosol is to be measured, the air intake should be 5 m to 10 m above ground level, but
buildings, vegetation, or the topography of the terrain can make an even higher sampling point necessary.
By contrast, the measurement of aerosols close to the source (e.g. traffic) requires much lower sampling
points (1,5 m to 4 m above the ground, see Directive 2008/50/EC [21]).
If an external intake port and sampling lines are used, they shall be made of a conductive, corrosion-
resistant material with a low surface roughness (e.g. stainless steel) and be electrically earthed. This
prevents chemical changes to the aerosol and particle losses due to electrostatic effects. Where possible,
the sampling tubes should be vertical and contain no bends. Flexible tubing of electrically conductive
material may also be used for small connections or short distances, but the length of flexible tubing should
be below 50 cm and the tube material shall not emit gases that might influence the ion production in the
charger of the DCAM. For handheld devices, sampling is performed directly via the instrument’s inlet, so
no internal intake port is required.
To reduce diffusion losses in long sampling lines, it can be necessary to sample air using a pump with a
primary flow rate much higher than the sampling flow rate (either the aerosol flow rate or the sum of the
aerosol flow rate and the ionizer flow rate; see Annex A) of the DCAM. The DCAM should sample isoaxially
from the central area of this primary flow via a short secondary sampling tube. 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 2000 shall be achieved.
The diffusion losses in total the sampling system for the smallest relevant particle size of 20 nm shall be
less than 20 %. The diffusion losses may be calculated theoretically [5].
If a DCAM is to be operated over longer periods of time, especially when at a remote location, steps shall
be taken to avoid soiling of the sampling lines by particles larger than 10 µm. For this purpose, a PM
inlet to the sampling system can be used (see 5.2).
7.3 Humidity conditioning
In high humidity environments (including mist in extreme cases) the size of particles of hygroscopic
materials is strongly influenced by the humidity of the air [22]. Beyond that the condensation of water
vapour on the insulating elements of the Faraday cup would lead to a total malfunction of the highly
sensitive current measurement. For both reasons the relative humidity of the aerosol inside the
instrument shall not exceed 40 %.
The internal temperature of a DCAM normally is higher than the ambient temperature. In some
instruments the sensitive current measurement is stabilized by operating them at a controlled internal
temperature higher than the ambient temperature (e.g. 40 °C). Other instruments also show an increased
internal temperature due to the waste heat produced by electronic components. As the aerosol sample is
heated up to this internal temperature, its relative humidity decreases and water that might cover the
surface of particles is evaporated. Thus, in most cases, no external drying of the aerosol flow is necessary.
In case of doubt the relative humidity at the internal instrument temperature should be calculated from
the expected ambient aerosol humidity. Instruments without controlled heating can be equipped with an
external heating or drying to avoid problems.
If the DCAM is operated at a station of an air quality monitoring network, the regulations of this network
with respect to drying shall be followed.
8 DCAM design criteria, performance criteria and test procedures
8.1 DCAM design and performance criteria
Requirements for the DCAM design criteria are specified in Table 1, the requirements for the DCAM
performance criteria in Table 2.
Table 1 — DCAM design criteria
Component/parameter Requirement
Pre-separator (optional) Only required if the aerosol contains a significant contribution of
particles > approximately 300 nm. It may be an impactor or a cyclone
with sharp cut-off curve.
separation efficiency < 10 % at 300 nm
protection of instrument (responsibility of manufacturer)
Unipolar diffusion charger Needs to produce unipolar ions by corona discharge and charge the
particles by collision with ions with a charging efficiency
corresponding to the lung-deposited surface area of the aerosol
particles.
Ion trap Coaxial arrangement of cylindrical electrodes or parallel arrangement
of flat electrodes with a voltage applied between the two electrodes;
needs to expose mixture of charged particles and ions to a low electric
field to collect the highly mobile ions but leave particles airborne.
Charge measurement Highly sensitive electrometer; measurement range at least 1 fA to 1 pA;
0,5
noise level below 1 fA·s
Time resolution 1 s to 1 min
Table 2 — DCAM performance criteria
Performance criterion Requirement Sub-
clause
Actual flow rates ≤ 10 % deviation from nominal flow rates 8.2.1
Calibration curve (model-specific) independent of particle size between 20 nm 8.2.2
and 300 nm within a tolerance band ± 40 %
Calibration factor (instrument-specific) – 8.2.3

8.2 Test procedures for DCAM performance criteria
8.2.1 Actual flow rates
The aerosol flow rate for instruments with single flow charger and additionally the ionizer flow rate for
instruments with mixing type charger shall be measured with an external reference flow meter. The
reference flow meter shall measure with a relative expanded uncertainty (95 % confidence) of ≤ 2 % at
the controlled flow rate. At least 10 consecutive measurements shall be taken over a minimum period of
1 h. The mean of the measurement results shall be compared with the nominal flow rate, and the relative
difference shall meet the criterion in Table 2.
8.2.2 Calibration curve
The calibration curve of a DCAM is the plot of the calibration ratio R for different particle diameters as
C
a function of the particle diameter D . The calibration ratio is defined as the LDSA of a monodisperse
P
calibration aerosol divided by the instrument’s analogue output signal (normally a voltage). Figure 7
shows an example of the experimentally determined device characteristic for two different DCAMs.

Figure 7 — Calibration curve for two different DCAMs of the same type (example); R is the
C
calibration ratio, D the particle diameter
P
According to the considerations in 4.2 the calibration ratio should be nearly independent of particle size
in the size range between 20 nm and 300 nm. The real curves differ substantially from this theoretical
prediction. The horizontal lines confine a band of ±40 % around the horizontal part of the calibration
curves as required in Table 1.
The calibration curve shall be determined for a specific type of instrument experimentally using
monodisperse aerosols of at least eight different particle sizes in the size range between 20 nm and
300 nm. The calibration aerosol particles shall be compact and (nearly) spheric
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