SIST-TS CEN/TS 18086:2025
(Main)Workplace exposure - Direct-reading low-cost particulate matter sensors for measuring airborne NOAA - Guidelines for application
Workplace exposure - Direct-reading low-cost particulate matter sensors for measuring airborne NOAA - Guidelines for application
This document gives guidelines on the use, calibration and evaluation of low-cost optical particulate matter sensor modules and systems for workplace exposure assessments.
This document is based on extensive laboratory and workplace tests for airborne NOAA.
This document is particularly aimed at engineered NOAA at workplaces and the sensors’ applicability for process control of NOAA-producing plants via airborne particle concentration measurements in workplace air.
NOTE This document is also applicable to other airborne particles included in some of the tests during the prenormative research.
Exposition am Arbeitsplatz - Direkt anzeigende kostengünstige Feinstaubsensoren zur Messung luftgetragener NOAA - Leitlinen für den Einsatz
Exposition sur les lieux de travail - Capteurs de matière particulaire à lecture directe et à faible coût pour le mesurage des NOAA en suspension dans l’air - Lignes directrices pour l’application
Le présent document donne des lignes directrices relatives à l’utilisation, à l’étalonnage et à l’évaluation des systèmes et des modules de capteurs optiques d’aérosol à faible coût destinés à l’évaluation de l’exposition sur les lieux de travail.
Il s’appuie sur des essais exhaustifs en laboratoire et sur les lieux de travail pour les NOAA en suspension dans l’air.
Il traite en particulier des NOAA produits sur les lieux de travail et de l’applicabilité des capteurs au contrôle de processus des sites de production de NOAA par le biais de mesurages de la concentration de particules en suspension dans l’air sur les lieux de travail.
NOTE Le présent document est aussi applicable à d’autres particules en suspension dans l’air, y compris lors de certains essais au cours des recherches prénormatives.
Izpostavljenost na delovnem mestu - Nizkocenovni senzorji z direktnim odčitavanjem za merjenje lebdečih nanopredmetov ter njihovih agregatov in aglomeratov (NOAA) - Smernice za uporabo
Ta dokument podaja smernice za uporabo, umerjanje in vrednotenje nizkocenovnih optičnih senzorskih modulov in sistemov za ocenjevanje izpostavljenosti na delovnem mestu.
Ta dokument temelji na obsežnih preskusih za lebdeče nanopredmete ter njihove agregate in aglomerate (NOAA) v laboratoriju in na delovnem mestu.
Ta dokument je zlasti namenjen za namensko proizvedene lebdeče nanopredmete ter njihove agregate in aglomerate na delovnih mestih ter uporabnost senzorjev za nadzor procesov v obratih za proizvodnjo lebdečih nanopredmetov ter njihovih agregatov in aglomeratov z merjenjem koncentracije delcev v zraku na delovnem mestu.
OPOMBA: Ta dokument se uporablja tudi za druge lebdeče delce, vključene v nekaterih preskusih med prednormativno raziskavo.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-januar-2025
Izpostavljenost na delovnem mestu - Nizkocenovni senzorji z direktnim
odčitavanjem za merjenje lebdečih nanopredmetov ter njihovih agregatov in
aglomeratov (NOAA) - Smernice za uporabo
Workplace exposure - Direct-reading low-cost particulate matter sensors for measuring
airborne NOAA - Guidelines for application
Exposition am Arbeitsplatz - Direkt anzeigende kostengünstige Feinstaubsensoren zur
Messung luftgetragener NOAA - Leitlinen für den Einsatz
Exposition sur les lieux de travail - Capteurs de matière particulaire à lecture directe et à
faible coût pour le mesurage des NOAA en suspension dans l’air - Lignes directrices
pour l’application
Ta slovenski standard je istoveten z: CEN/TS 18086:2024
ICS:
13.040.30 Kakovost zraka na delovnem Workplace atmospheres
mestu
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
CEN/TS 18086
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
November 2024
TECHNISCHE SPEZIFIKATION
ICS 13.040.30
English Version
Workplace exposure - Direct-reading low-cost particulate
matter sensors for measuring airborne NOAA - Guidelines
for application
Exposition sur les lieux de travail - Capteurs de matière Exposition am Arbeitsplatz - Direkt anzeigende
particulaire à lecture directe et à faible coût pour le kostengünstige Feinstaubsensoren zur Messung
mesurage des NOAA en suspension dans l'air - Lignes luftgetragener NOAA - Leitlinen für den Einsatz
directrices pour l'application
This Technical Specification (CEN/TS) was approved by CEN on 23 September 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 18086:2024 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Symbols and abbreviations . 9
4.1 Symbols . 9
4.2 Abbreviations . 9
5 Measurement principle of low-cost PM sensors . 10
6 Usability of low-cost sensors for monitoring NOAA concentrations in workplaces . 12
7 Calibration and adjustment of low-cost PM sensors . 13
7.1 General. 13
7.2 Laboratory calibration and adjustment . 16
7.2.1 General. 16
7.2.2 Particle size dependence of sensor reaction . 16
7.2.3 Calibration and adjustment for polydisperse aerosols . 20
7.3 Comparability of sensors . 26
7.4 On site calibration in workplaces . 27
8 Interfering factors and error sources . 29
Annex A (informative) Sampling convention for different mass concentration fractions . 31
Annex B (informative) Calibration of low-cost PM sensors with monodisperse particles –
Results from prenormative research . 33
Annex C (informative) Calibration of low-cost PM sensors with polydisperse particles –
Results from prenormative research . 37
Annex D (informative) Workplace measurements – Results from prenormative research . 47
Annex E (informative) Measurement principle of low-cost PM sensors . 58
Bibliography . 64
European foreword
This document (CEN/TS 18086:2024) has been prepared by Technical Committee CEN/TC 137
“Assessment of workplace exposure to chemical and biological agents”, 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.
This document has been prepared under a standardization request addressed to CEN by the European
Commission.
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 implement this European Standard: 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
The production and use of engineered nano-objects and their agglomerates and aggregates (NOAA) has
increased over the recent years, as well as the concerns related to their potential adverse health effects.
The measurement of nano-objects is particularly difficult because of the small size of the particles and
small relative mass in comparison with other contaminants. Human exposure to NOAA is most likely to
occur in workplaces, where they are produced, processed and handled in large quantities or over long
periods of time. Continuous monitoring of such workplaces would improve exposure assessment,
especially in cases where the exposure pattern is very inhomogeneous and large, and fluctuating
background concentrations are present.
There has been an increased interest in the use of low-cost particulate matter (PM) sensors in different
areas. Up to now, exposure concentrations are measured only during limited time periods and with
limited spatial resolution, using expensive bulky static measurement and sampling equipment and/or
direct reading personal monitors and personal samplers. In contrast, due to their low-costs and small
size, the low-cost PM sensors allow for:
— the setting up of dense measurement networks in workplaces to monitor dust concentrations with
high spatio-temporal resolution;
— use as personal monitors;
— use to produce information on the efficiency of process controls of NOAA-production facilities, the
background and the far field.
Therefore, due to the lower costs compared with established scientific grade instruments, more devices
can be employed for in total lower costs. The main purpose of such sensor networks is to estimate
exposure levels in workplaces. At the time of writing this document, low-cost PM sensors should not be
considered for any compliance measurements, because they cannot replace reference measurements
e.g. with samplers for the respirable fraction. They should rather be considered as complementary to
reference measurements. However, this limitation can become obsolete in the future, when new
generations of low-cost PM sensors overcome the shortcomings of today’s sensors. They can thus be
applied as an indicator for exposure, as a warning system or to identify potential particle sources, e.g. as
a permanent implementation of a Tier 1 exposure assessment (EN 17058 [1]). Individual threshold
values may be defined to implement and/or initiate control measures.
The low-cost PM sensors available are based on measuring the light scattered by airborne particles,
which depends on particle size, shape and refractive index. To calibrate the sensors for the
determination of particle mass concentrations, average values for these properties, as well as for the
effective particle density, must be assumed. The sensors are typically calibrated for use in ambient air
monitoring. However, the particle properties assumed in the calibration for ambient use can be very
different from those of particles encountered in workplaces. Due to the wide diversity of particle
properties in workplace air, a single generalizable calibration for different workplaces is not feasible. In
addition, measurement artefacts, e.g. stemming from relative humidity, can be different in workplace
and atmospheric measurements.
Low-cost PM sensors exist with different levels of complexity, resulting in different wealth of
information, ranging from a voltage output as a measure for the total particle concentration, via
different size-integrated fractions of the mass and/or number concentration to number size
distributions with high size resolution. The focus of this document is on those sensors that are able to
deliver size-integrated number and/or mass concentrations in different size fractions. Most low-cost
PM sensors were originally developed for ambient air quality monitoring and are thus calibrated
following ambient sampling conventions, e.g. for PM and PM (US EPA 40 CFR part 62 [2] and 40
2,5 10
CFR part 53 [3], respectively), which are not identical with the sampling conventions for workplaces,
e.g. for the respirable or thoracic fraction according to EN 481 (see Annex A).
The methods and procedures described in this document apply to the sensor modules only and not to
complete devices, based on these. Sensor modules are considered to be low-cost, if their prices are at
least 10 to 100 times lower than the prices of established instruments of comparable type, e.g. those
described in CEN/TR 16013-2 [4] and CEN/TR 16013-3 [5].
1 Scope
This document gives guidelines on the use, calibration and evaluation of low-cost optical particulate
matter sensor modules and systems for workplace exposure assessments.
This document is based on extensive laboratory and workplace tests for airborne NOAA.
This document is particularly aimed at engineered NOAA at workplaces and the sensors’ applicability
for process control of NOAA-producing plants via airborne particle concentration measurements in
workplace air.
NOTE This document is also applicable to other airborne particles included in some of the tests during the
prenormative research.
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.
EN 481, Workplace atmospheres — Size fraction definitions for measurement of airborne particles
EN 1540, Workplace exposure — Terminology
ISO 27891, Aerosol particle number concentration — Calibration of condensation particle counters
ISO 21501-1, Determination of particle size distribution — Single particle light interaction methods —
Part 1: Light scattering aerosol spectrometer
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1540 and the following 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
adjustment of a measuring system
set of operations carried out on a measuring system so that it provides prescribed indications
corresponding to given values of a quantity to be measured
[SOURCE: ISO/IEC Guide 99:2007, 3.11 [6]]
3.2
advanced aerosol photometer
measurement device that combines a photometric measurement of light scattered by a cloud of
particles inside a measurement volume to determine total number and/or mass concentrations with
spectrometric features to distinguish between concentrations in different particle size fractions
3.3
aerodynamic aerosol classifier
AAC
measurement device that size-classifies airborne particles according to the aerodynamic diameter
based on classification of the particle relaxation time
3.4
aerosol photometer
measurement device that determines particle size-integrated number or mass concentrations by
measuring the integral intensity of light scattered by a cloud of particles inside a measurement volume
Note 1 to entry: Photometers can only be calibrated for known particle size distributions.
3.5
calibration
operation that, under specified conditions, in a first step, established a relation between the quantity
values with measurement uncertainties provided by measurement standards and corresponding
indications with associated measurement uncertainties and, in a second step, uses this information to
establish a relation for obtaining a measurement result from an indication
[SOURCE: ISO/IEC Guide 99:2007, 2.39]
Note 1 to entry: In practice, a calibration is often done in conjunction with a later adjustment.
3.6
condensation particle counter
CPC
measurement device that determines in real-time the number concentration of airborne particles
ranging from few nm up to several µm in size in a limited range of concentration, but does not
discriminate between particles of different sizes or origin
3.7
mobility particle size spectrometer
MPSS
measurement device that determines number size distributions of airborne submicron particles based
on electrical mobility analysis
3.8
optical aerosol spectrometer
measurement device that determines number size distributions of airborne particles by measuring the
intensity of light scattered by individual particles inside a small measurement volume as a measure for
the particle size and counting the number of scattered light pulses as a measure for the number
concentration
Note 1 to entry: CEN/TR 16013-2 [4] also refers to Optical Aerosol Spectrometers as Optical Particle Counters.
3.9
optical equivalent diameter
diameter of a spherical particle with known refractive index that causes the same scattering light
intensity as the particle under investigation
3.10
PM
x
particulate matter suspended in air which is small enough to pass through a size-selective inlet with a
50 % efficiency cut-off at x μm aerodynamic diameter
[SOURCE: EN 12341:2023, 3.1.16] [7]
Note 1 to entry: Commonly measured PM fractions are PM , PM , PM and PM . PM is nearly identical with
x 1 2,5 4 10 4
the respirable fraction.
3.11
reference measurement instrument
instrument that is calibrated against a traceable method and that is designated for the calibration of
other measurement devices of a given kind in a given organization
3.12
sensor module
sensor and signal processing algorithms that determine number concentration and/or mass
concentration and/or size distribution of airborne particles, based on the measurement of light
scattered by particles
Note 1 to entry: Sensor modules are considered to be low-cost if prices are at least 10 to 100 times lower than
established instruments of the same type.
3.13
sensor
individual sensor
physical unit that produces a signal related to the concentration of particulate matter in air
Note 1 to entry: The low-cost PM sensors available at the time of writing this document were all based on light
scattering. This document might not be applicable to sensors working on a different measurement principle.
3.14
sensor network
set of multiple connected sensors or sensor systems that are spatially distributed to monitor particulate
concentrations in a workplace with spatiotemporal resolution
3.15
sensor system
single integrated set of hardware that uses one or more sensor modules to produce a signal related to
the concentration of particulate matter in air that can supply real time measurements
Note 1 to entry: Sensor systems contain many common components in addition to the basic sensing or analytical
element that is used for detection. Common core components and functions can include:
— sensing detector (the actual sensor);
— sampling capability (generally active sampling for PM);
— power systems, which may include batteries;
— analogue to digital conversion;
— signal processing;
— local data storage;
— data transmission;
— enclosure.
4 Symbols and abbreviations
4.1 Symbols
a Slope of linear fit curve [-]
3 3
b
y-intercept of linear fit curve [1/m or kg/m ]
C
Number concentration [1/m ]
N
C
Mass concentration [kg/m ]
m
C Cunningham slip correction factor [-]
c
d Particle diameter, at which instrument reaches 50 % detection efficiency [m]
d Aerodynamic equivalent diameter [m]
ae
d Mobility equivalent diameter [m]
mob
d Optical equivalent diameter [m]
opt
d Particle diameter [m]
p
I Light intensity [cd]
m Refractive index [-]
Regression coefficient [-]
R
α Scattering parameter [-]
ϕ Aperture angle [rad]
λ Wavelength of light [m]
η Detection efficiency [-]
ρ
Unit density [1000 kg/m ]
ρ
Effective particle density [kg/m ]
eff
ρ
Particle density [kg/m ]
p
Θ Detection angle [rad]
4.2 Abbreviations
AAC Aerodynamic Aerosol Classifier
APS Aerodynamic Particle Sizer
CPC Condensation Particle Counter
DEHS Di-Ethyl-Hexyl-Sebacate
DEMC Differential Electrical Mobility Classifier
ELPI Electrical Low Pressure Impactor
LCS Low-Cost Sensor
LOQ Limit of quantification
MPSS Mobility Particle Size Spectrometer
NOAA Nano-objects, their agglomerates and aggregates
OAS Optical Aerosol Spectrometer
PM Particulate Matter
PSL Polystyrene Latex
TEOM Tapered Element Oscillating Microbalance
TiO Titanium dioxide
5 Measurement principle of low-cost PM sensors
The available low-cost PM sensors are based on the measurement of light, scattered by particles inside
a measurement volume, illuminated by a light source, within the sensor. The light-scattering sensors
can be categorized in three sub-categories:
a) Spectrometers;
b) Photometers;
c) Advanced photometers.
In a spectrometer, individual particles are transported with a flow through the measurement volume.
To ensure that at most a single particle is present inside the measurement volume, its size shall be
small. Each individual particle causes a light pulse, whose intensity is determined with a photo-detector
as a measure for the particle size. The pulses are furthermore counted and classified based on their
height in order to obtain the number size distribution of the particles, based on the optical equivalent
diameter (CEN/TR 16013-2 [4]). Mass size distributions are calculated from the number size
distributions, by assuming the particles’ refractive indices, shapes and densities, which often depend on
the particle size. Different number and mass (PM ) size fractions can be obtained from the
x
corresponding size distributions by weighting them with the required sampling convention (see
Annex A) and integration over the particle size.
In a photometer, the light scattered by a cloud of particles inside the measurement volume is measured
(CEN/TR 16013-3 [5]). The measurement volume of a photometer is much larger than that of a
spectrometer. A photometer cannot distinguish particle sizes and only delivers size-integrated
information. Only for stable particle size distributions and compositions, the total light intensity
measured by a photometer is proportional to the total particle mass and number concentration.
Photometers usually report the mass concentration of one PM fraction by assuming the (constant)
x
particle number size distribution, refractive indices, particle shapes and densities.
Advanced photometers use a combination of a photometer and a spectrometer. The size of the
measurement volume is usually in-between the sizes in spectrometers and photometers. An advanced
photometer measures a photometric signal of a cloud of particles as an offset and a measure for the
overall concentration. In addition, individual peaks sticking out of the offset signal are detected. These
peaks stem from the typically rather low number of large particles, which, however, have a strong
contribution to the mass concentration. These peaks are counted and classified based on their heights
in order to differentiate between different size fractions [8]. Advanced photometers are thus able to
deliver mass concentrations in more than one different size fraction. Some advanced photometers also
deliver estimates of the number concentration in different size fractions.
Most available low-cost PM sensors apply the advanced photometric or photometric principle due to
their lower complexity compared with the spectrometric principle. Whereas the overall measurement
principles of the low-cost PM sensors are identical to the ones used in established, scientific grade
measurement devices, there are some differences. For example, most low-cost sensors do not use a
particle free sheath flow to protect the optics from fouling, which can have an effect on the
measurement accuracy, longterm stability and durability.
The sensors typically provide the measurement results in terms of particle mass concentrations in one
or more size fractions (PM ) and in some cases also as particle number concentrations in one or more
x
size fractions. It shall be noted that the intensity of light, scattered by particles depends on multiple
particle properties, but not the particle mass and thus a bespoke calibration is needed in order to
determine mass concentrations (see Clause 6). A detailed description of the measurement principle of
the three sensor categories is provided in Annex E.
Advantages and disadvantages of the three sensor categories are listed in Table 1.
Table 1 — Advantages and disadvantages of low-cost PM sensors
Advantages Disadvantages
— No fan needed — Signal not exclusively proportional to mass
concentration, specific calibration needed
— Lowest cost
— Dependent on particle size distribution,
— Wide concentration range refractive indices, shapes, but not particle
density
— Fast response to changes inside
measurement volume — Slow dynamic response without forced flow
through measurement volume
— Easy data handling (single data point per
time step) — Single value for total light scattered only, no
particle size differentiation
— Delivers concentrations in different size — Size fractions pre-defined by manufacturer and
fractions not freely selectable
— Can deliver both number and mass — Signal not exclusively proportional to number or
concentrations mass concentration, but dependent on particle
size distribution, refractive indices and shapes
— Quick response to dynamic size
distribution and concentration changes — Output relies on the typically undisclosed
manufacturer calibration and algorithms
— Lower costs compared with spectrometers
— Delivers particle number size distributions — Not suitable for particle sizes below
approximately 0,3 µm
— Size-integrated number and mass
concentrations can be calculated for any — Not suitable for high concentrations; upper
size fraction within measurement range concentration limit due to coincidence error
(depending on measurement volume)
— Suitable for low concentrations; lower
limit depending on measurement volume — Signal not exclusively proportional to mass
concentration
— Quick response to dynamic size
— More expensive than photometers and advanced
Spectrometer Advanced photometer Photometer
distribution and concentration changes photometers
— Signal proportional to number
concentration
Figure 1 provides a decision tree for the choice of an appropriate sensor type, depending on the
anticipated sensor application.
Figure 1— Decision tree for the choice of a sensor type depending on purpose of its application
in a workplace
6 Usability of low-cost sensors for monitoring NOAA concentrations in
workplaces
Due to their low-costs, PM sensors can allow for establishing measurement networks with high density
to permanently monitor the spatio-temporal distribution of different dust fractions in workplaces. With
such networks, it is possible to keep track of when and where concentrations increase and can
therefore be a valuable indicator for potential particle leaks and areas of increased exposure. It shall,
however, be kept in mind that the sensors use a measurement principle, which is based on many
assumptions. Further, the possibilities for quality assurance, e.g. an inherent control of the sample flow
rate, are reduced and consequently the measurement uncertainty is higher compared to reference
instruments.
Therefore, low-cost sensor measurements shall not replace reference measurements for compliance
testing according to regulations.
The possibilities to monitor NOAA concentrations is limited due to the detectable particle size range of
the sensors. With optical light scattering devices like the PM sensors, particles with optical equivalent
sizes below approximately 0,3 µm cannot or not adequately be detected [9]. Nano-objects have by
definition a geometric size which at least in one dimension is smaller than 0,1 µm (ISO 80004-1 [10]).
Concentrations of single, unbound nano-objects can therefore normally not or not adequately be
measured with optical low-cost PM sensors. In contrast, if the nano-objects are present in agglomerated
or aggregated form, their sizes are often > 0,3 µm and thus detectable. Consequently, the usability of
optical low-cost PM sensors in workplaces at least during the production of NOAA is questionable.
However, they can be meaningfully applied during downstream use of NOAA, when agglomerated or
aggregated particles are to be monitored in air. Quantitative results are only possible if the particle size
distribution and chemical composition match the aerosol properties used for calibration.
7 Calibration and adjustment of low-cost PM sensors
7.1 General
The measurement of number or mass concentration with an optical low-cost PM sensor depends on
various particle and aerosol properties. The available low-cost PM sensors are typically factory-
calibrated for atmospheric aerosols and thus inherently assume mean values for these properties for
ambient particles. Depending on the particle and aerosol properties in the workplace to be investigated,
the factory calibration of a sensor can yield incorrect concentration values. For understanding the
applicability and the proper use of low-cost PM-sensors in workplaces, different types of calibrations
shall be applied. Depending on the outcome, either constant adjustment factors or adjustment functions
that take into account a potential offset or concentration dependence are determined, if necessary. For
the sensor adjustment, the measurement results are multiplied with the adjustment factor or function.
Adjustment factors therefore have no physical unit. If the photodetector signal, typically a voltage, is
accessible, a calibration factor or function can also be applied that relates the measured light intensity
dependent voltage to the corresponding particle concentration. In such cases, the calibration factor
1 µg
carries the unit for number concentrations and e.g. for mass concentrations.
m³⋅mV m³⋅mV
Figure 2 — Decision tree for the choice of an appropriate calibration method
Figure 2 provides a decision tree to select a proper calibration method, depending on the purpose of the
calibration. The different calibration and adjustment methods are described in the following. Due to the
lower quality assurance of the low-cost PM sensors compared with more expensive established,
scientific grade instruments, the inter-specimen variation of sensors of the same type can affect the
comparability of measurement data. If multiple sensors are used in the same workplace, the
comparability of the results from the sensors shall be checked before the measurements. If necessary,
an individual adjustment factor or function shall be determined per sensor specimen.
Any calibration requires the use of reference measurement instruments and/or particle size classifiers.
A list of suitable devices for the different metrics is provided in Table 2.
It is additionally recommended to regularly check the flow rate of the sensors. However, most flow
meters are not suitable, because they introduce a pressure drop that is too high to be overcome by the
fans used by the sensors to establish the sampling flow. Only flow meters with very low pressure drop,
e.g. bubble flow meters, shall be used. According to EN 482 bubble flow meters also provide the lowest
measurement uncertainty.
Table 2 — Overview of reference measurement instruments and size classifiers to be used for
calibration of low-cost PM sensors
Metric Instrument Size range Concentration Comments
range
11 3
Condensation Larger than Water based CPCs are not
Up to 3 × 10 1/m ,
Particle Counter 2,5 nm to 10 nm suitable for highly hydrophobic
depending on CPC
(CPC)
(d , depending on particles
model
(EN 16897 [11])
CPC model); upper
size limit not well
defined, mostly
between 1 µm and
10 µm
12 3
Optical Aerosol Larger than 0,1 µm OAS with very different
Up to 10 1/m ,
Spectrometer to 0,3 µm (d , concentration ranges available,
depending on OAS
(OAS) high max. concentration means
model and
depending on OAS
(CEN/TR 16013-2 low accuracy at low
coincidence
model)
[4]) concentrations and vice versa.
correction
Determination of number
Number concentration from the
concentration integration of the number size
distribution is less accurate than
direct number concentration
measurements
Mobility Particle From 2,5 nm to Approximately Only suitable for constant or
9 3 13
Size Spectro-meter 1,2 µm, depending slowly changing number size
10 1/m to 10
(MPSS) on employed distributions
1/m
(ISO 15900 [12]) Differential
Based on mobility equivalent
Electrical Mobility
particle diameter
Classifier (DEMC)
Determination of number
concentration from the
integration of the number size
distribution is less accurate than
direct number concentration
measurements
Filter sampler for Any particle size Lower Only suitable for high
Mass
subsequent that passes a size concentration limit concentrations, unless sampling
concentration
gravimetric selective inlet dependent on times of at least several hours
Metric Instrument Size range Concentration Comments
range
analysis upstream, e.g. for quantification limit are feasible
the respirable of balance and
Method can only deliver time-
fraction sampling duration
integrated average
concentrations, no time-
resolved data
Tapered Element Any particle size Depending on More accurate the higher the
Oscillating that passes a size averaging time, e.g. concentration and the longer the
Microbalance selective inlet approximately > 10 averaging times; only suitable
(TEOM) upstream, e.g. for for constant or slowly changing
µg/m for 15 min
the respirable concentrations
averaging
fraction
Optical Aerosol Larger than Up to several Only instrument capable of
Spectrometer 0,18 µm to 0,3 µm measuring mass concentrations
mg/m , depending
(OAS) (d , depending on with high time resolution, but
on OAS model
requires individual calibration
OAS model)
of mass concentration
measurement for each test
aerosol
Mobility Particle From 2,5 nm to Approximately Only suitable for constant or
9 3 13
Size Spectrometer 1,2 µm, depending slowly changing number size
10 1/m to 10
(MPSS) on employed distributions
1/m
Differential
Based on mobility equivalent
Electrical Mobility
particle diameter
Classifier (DEMC)
13 3
Aerodynamic 25 nm to 5 µm Only suitable for constant or
Up to 10 1/m
Aerosol Classifier slowly changing number size
(AAC) with distributions
Condensation
Based on aerodynamic
Particle Counter
equivalent particle diameter
(CPC)
12 3
Optical Aerosol Larger than 0,1 µm Based on optical equivalent
Up to 10 1/m ,
Spectrometer to 0,3 µm (d , particle diameter
depending on OAS
(OAS)
model and
depending on OAS
Number size
coincidence
model)
distribution
correction
Aerodynamic 0,5 µm to 20 µm Usable up to Based on aerodynamic
10 3
Particle Sizer equivalent particle diameter
10 1/m ,
(APS)
depending on
acceptable
coincidence error
Electrical Low 6 nm to 10 µm Different for every Based on aerodynamic
Pressure Impactor size bin; equivalent particle diameter;
(ELPI) concentrations determined
e.g. 0,1 1/m to
10 3
based on current measurement
1,7 × 10 1/m at
at each impactor stage (unipolar
d = 5,3 µm;
particle charging at device inlet)
240 1/cm to
13 3
7,9 × 10 1/cm
= 6 nm
at d
Metric Instrument Size range Concentration Comments
range
Differential 2,5 nm to 1,2 µm n/a Classifies based on electrical
Electrical Mobility (mobility mobility; classified aerosol may
Classifier (DEMC) equivalent contain multiple peaks in the
diameter), size distribution due to multiply
depending on charged particles
Particle size
model
Aerodynamic 25 nm to 5 µm n/a Classifies based on particle
Aerosol Classifier (aerodynamic relaxation time
(AAC) equivalent
diameter)
7.2 Laboratory calibration and adjustment
7.2.1 General
Laboratory calibration can be performed at different levels of specificity, i.e. with monodisperse or
polydisperse particles of different sizes, shapes, refractive indices and concentrations. This is generally
required for a better understanding of a sensor’s performance and is recommended prior to making a
choice of a sensor type to be used for a specific measurement task. Since the concentration reading of an
optical aerosol measurement device will always depend on the prevailing particle and aerosol
properties, it can differ from workplace to workplace and thus an individual calibration and if necessary
adjustment for each workplace is advisable. Whereas laboratory calibrations can provide detailed
information on the overall performance of a low-cost PM sensor and its specific reactions to different
particle and aerosol properties, in many practical cases, it is circumvented in favour of carrying out an
individual calibration at the workplace for the prevailing specific aerosol instead.
7.2.2 Particle size dependence of sensor reaction
The intensity of light scattered by a particle has a strong dependence on the particle size (see Annex D).
For particles smaller than the wavelength of the light, i.e. in the Rayleigh regime, the intensity scales
with the sixth power, i.e. its decrease with decreasing particle size is very steep. In an optical aerosol
spectrometer this strictly limits the smallest detectable particle size, because scattered light pulses can
no longer be distinguished from background noise. In case of a photometer, even very small particles
can still be distinguishable from background noise, if they appear in sufficiently high concentrations.
The accuracy of the differentiation of different particle sizes further determines an advanced
photometer’s ability to distinguish different particle size fractions. For large particles, the detection
efficiency can be affected by particle losses due to sedimentation or impaction in bends of the aerosol
flow path inside the sensor.
The size dependent detection efficiency η(d ) is defined according to Formula (1) as:
p
Cd
( )
sen p
η d ×100 % (1)
( )
p
Cd
( )
ref p
where
η(d ) is the size dependent detection efficiency, in percent;
p
d is the particle diameter;
p
c (d ) is the particle concentration measured by the sensor for a given monodisperse particle size;
sen p
c (d ) is the corresponding concentration measured by the reference instrument.
ref p
=
For a well calibrated reference instrument (see Table 2), c (d ) is considered to be the “true”
ref p
concentration. Since besides the particle size, the light scattering intensity also depends on the
refractive index of the particle material, the detection efficiency is also a function of the particle
material. It is therefore commonly determined as a function of the optical equivalent particle diameter,
which refers to a particle material with well-known optical properties, usually polystyrene latex (PSL).
The sensors typically use internal algorithms to determine the number and/or mass concentrations in
different size fractions from the measured light intensity signals. These algorithms are usually not
disclosed by the manufacturer, but can result in different size dependent detection efficiencies for the
number and the mass concentration. Consequently, these two detection efficiencies shall be treated
separately.
Monodisperse particles of different sizes d and concentrations within the measurement range of
p
sensor and reference instrument are used to determine the particle size dependent detection efficiency
of a sensor. A suitable monodisperse particle generator shall be applied, e.g. utilizing a vibrating orifice
[13] or based on tailored condensation on nuclei [14]. Alternatively, the monodisperse aerosol
generator may comprise a generator for polydisperse aerosols, e.g. an atomizer or powder disperser,
and a suitable aerosol classifier, e.g. a differential electrical mobility classifier (DEMC) [15] for
submicron particles or an aerodynamic aerosol classifier (AAC) [16] for particle sizes up to 5 µm to
select monodisperse particles with different sizes. Care needs to be taken to avoid or correct for the
effect of larger multiply charged particles, when a DEMC is used. The monodisperse test aerosol shall be
conditioned upon classification, i.e. charge neutralized and dried if necessary. Whereas a potential
particle charge does not affect the measurement with a low-cost PM sensor, it can cause electrostatic
particle transport losses and thus affect the achievable precision that can be achieved with the
measurement setup. The monodisperse test aerosol is fed into a container, large enough to host all
sensors to be tested simultaneously (see Figure 3). Alternative experimental set ups like calm air
chambers are also applicable [17]. If the monodisperse test particles are produced with a classifier, the
number of sensors that can be tested is limited due to the low flow rate of the available classifiers.
Prior to any calibration using a DEMC or an AAC, the function of the classifier shall be checked by
dispersing monodisperse calibration particles of known size from a polystyrene latex (PSL) suspension.
Upon aerosolisation, the test aerosol needs to be dried to remove any particle-borne water. The size of
these particles shall be in the range from 100 nm to 300 nm to avoid interferences with residues from
the water and surfactants used to stabilize the PSL suspensions. According to CEN/TS 17434 [18], the
size detected with the classifier shall not deviate from the certified size of the PSL particles by more
than ± 3 %. If the deviation is in the range from 3 % to 10 %, the sheath flow rate of the classifier shall
be adjusted to achieve a more accurate sizing. If the deviation is > 10 %, then the entire classifier system
needs to be checked.
The sensors are completely placed inside the container rather than sampling from it to avoid interfering
with the sensor flow rate and flow direction. The air flow through the sensors is typically established by
means of a simple fan that cannot overcome a pressure difference. A reference instrument samples
from the container to determine the reference number or mass concentration and/or size distribution.
Depending on the flow rates of the monodisperse aerosol and the reference instrument, additional
filtered make up air shall be supplied at a flow rate that ensures the inlet flow to the container to be
higher than the flow rate exhausted from the container by the reference instrument. Whenever
necessary, the container shall have an opening to exhaust any excess flow. A small fan shall be us
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