CEN/TR 16013-3:2012

Workplace exposure - Guide for the use of direct-reading instruments for aerosol monitoring - Part 3: Evaluation of airborne particle concentrations using photometers

This Technical Report describes the use of photometers for the determination of airborne particles belonging to the respirable fraction and gives details on their limitations and possible uses in the field of occupational hygiene.
NOTE   Photometers can also be used to detect other size fractions of airborne particles after aerodynamic pre-separation, but these are not the focus of this Technical Report.
The method complements existing conventional long-term aerosol particle sampling and can be used for:
-   instantaneous (direct-reading) measurement,
-   time-related monitoring,
-   investigation of space-related aerosol evolution (mapping), and
-   exposure visualization.
The method enables e.g.:
-   detection and relative quantification of concentration peaks due to specific operations (bagging, sanding, etc.);
-   identification of most exposed workers with a view to more detailed studies of risks and prevention measures to be applied; and
-   detection of dust emission sources and their relative magnitudes.

Exposition am Arbeitsplatz - Leitfaden für die Anwendung direkt anzeigender Geräte zur Überwachung von Aerosolen - Teil 3: Bewertung der Konzentration luftgetragener Partikel mit Photometern

Exposition au poste de travail - Guide d'utilisation des instruments à lecture directe pour la surveillance des aérosols - Partie 3 : Évaluation des concentrations de particules en suspension dans l'air à l'aide de photomètres

Le présent Rapport technique décrit l’utilisation de photomètres pour la détermination des particules en suspension dans l’air appartenant à la fraction alvéolaire et en précise les limites et les utilisations possibles dans le cadre de l’hygiène du travail.
NOTE   Des photomètres peuvent également être utilisés pour détecter d’autres fractions de taille de particules en suspension dans l’air après une séparation aérodynamique préalable, mais ils ne font pas l’objet du présent Rapport technique.
Complémentaire de l’échantillonnage classique existant de longue durée des particules d’aérosol, cette méthode peut être utilisée pour :
-   un mesurage quasi instantané (lecture directe) ;
-   une surveillance dans le temps ;
-   un examen des variations spatiales des aérosols (cartographie) ; et
-   une visualisation de l’exposition.
A titre d’exemples, cette méthode permet :
-   la détection et la quantification relative des pics de concentration dus à des opérations spécifiques (ensachage, ponçage, etc.) ;
-   l’identification des travailleurs les plus exposés en vue d’études plus approfondies des risques et des mesures de prévention à appliquer ; et
-   la détection des sources d’émission de poussières et leurs importances relatives.

Izpostavljenost na delovnem mestu - Vodilo za uporabo instrumentov z neposrednim odčitavanjem za monitoring aerosolov - 3. del: Vrednotenje koncentracij lebdečih delcev s fotometri

To tehnično poročilo opisuje uporabo fotometrične metode za določitev delcev v zraku, ki pripadajo vdihani frakciji, in zagotavlja podrobnosti o njihovih omejitvah in možnih načinih uporabe na področju higiene dela.

General Information

• Status: Published
• Publication Date: 16-Oct-2012
• ICS: 13.040.30 - Workplace atmospheres
• Technical Committee: CEN/TC 137 - Assessment of workplace exposure
• Drafting Committee: CEN/TC 137/WG 3 - Particulate matter
• Current Stage: 9093 - Decision to confirm - Review Enquiry
• Start Date: 12-Jun-2015
• Completion Date: 14-Apr-2025
• Ref Project: SIST-TP CEN/TR 16013-3:2012 - Workplace exposure - Guide for the use of direct-reading instruments for aerosol monitoring - Part 3: Evaluation of airborne particle concentrations using photometers

Standards Content (Sample)

SLOVENSKI STANDARD
01-december-2012
,]SRVWDYOMHQRVWQDGHORYQHPPHVWX9RGLOR]DXSRUDERLQVWUXPHQWRY]
QHSRVUHGQLPRGþLWDYDQMHP]DPRQLWRULQJDHURVRORYGHO9UHGQRWHQMH
NRQFHQWUDFLMOHEGHþLKGHOFHYVIRWRPHWUL
Workplace exposure - Guide for the use of direct-reading instruments for aerosol
monitoring - Part 3: Evaluation of airborne particle concentrations using photometers
Exposition am Arbeitsplatz - Leitfaden für die Anwendung direkt anzeigender Geräte zur
Überwachung von Aerosolen - Teil 3: Ermittlung der Konzentrationen luftgetragener
Partikel mit Photometern
Exposition au poste de travail - Guide d'utilisation des instruments à lecture directe pour
la surveillance des aérosols - Partie 3 : Évaluation des concentrations de particules en
suspension dans l'air à l'aide de photomètres
Ta slovenski standard je istoveten z: CEN/TR 16013-3:2012
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.

TECHNICAL REPORT
CEN/TR 16013-3
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
October 2012
ICS 13.040.30
English Version
Workplace exposure - Guide for the use of direct-reading
instruments for aerosol monitoring - Part 3: Evaluation of
airborne particle concentrations using photometers
Exposition au poste de travail - Guide d'utilisation des Exposition am Arbeitsplatz - Leitfaden für die Anwendung
instruments à lecture directe pour la surveillance des direkt anzeigender Geräte zur Überwachung von Aerosolen
aérosols - Partie 3 : Évaluation des concentrations de - Teil 3: Bewertung der Konzentration luftgetragener
particules en suspension dans l'air à l'aide de photomètres Partikel mit Photometern

This Technical Report was approved by CEN on 10 June 2012. It has been drawn up by the Technical Committee CEN/TC 137.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 16013-3:2012: E
worldwide for CEN national Members.

Contents Page
Foreword . 3
Introduction . 4
1 Scope . 5
2 Operating Principle . 5
2.1 General . 5
2.2 Light scattering . 5
2.3 Instrument response — Effects of airborne particle properties . 6
3 Instrument types . 8
3.1 General . 8
3.2 Passive aerosol monitors . 9
3.3 Active aerosol monitors . 9
3.4 Size-selective aerosol monitors . 9
4 Calibration . 10
4.1 General . 10
4.2 Factory calibration . 10
4.3 Optical reference element . 11
4.4 Gravimetric reference . 11
5 Choice of aerosol monitor . 12
5.1 General . 12
5.2 Active or passive aerosol monitors . 12
5.3 Mass concentration range . 12
5.4 Hazardous work environments . 13
5.5 Size selection. 13
6 Procedure for making aerosol measurements using photometers . 13
6.1 Instrument operating procedure. 13
6.2 Sampling strategies . 14
7 Limitations of use and sources of error . 15
8 Cleaning and maintenance . 15
Annex A (informative) Influence of physical parameters of aerosol particles and their
polydispersity on photometer measurement . 17
A.1 General . 17
A.2 Bias maps . 17
Annex B (informative) Currently available photometers . 21
Bibliography . 24

Foreword
This document (CEN/TR 16013-3:2012) 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 [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
CEN/TR 16013 consists of the following parts, under the general title Workplace exposure — Guide for the use
of direct-reading instruments for aerosol monitoring:
 Part 1: Choice of monitor for specific applications;
 Part 2: Evaluation of airborne particle concentrations using Optical Particle Counters;
 Part 3: Evaluation of airborne particle concentrations using photometers.
Introduction
All photometer-based direct-reading aerosol monitors use the principle of light scattering to determine airborne
particle concentration. Here, a light source (usually produced by a laser or diode) is collimated and illuminates
airborne particles entering a sensing volume. The instrument optics are usually designed such that the intensity
of the light scattered at a particular angle is proportional principally to the respirable fraction of the airborne
particle concentration. Other physical properties of the aerosol such as particle size, refractive index and
particle shape, will affect their response by varying degrees (see [7]) although this can be minimised by careful
design of the photometer. Therefore, photometer-based direct-reading aerosol monitors are not ideal for the
measurement of worker exposure or to check whether threshold limit values of industrial dust concentrations
are exceeded. Their main advantage is that they give an almost instantaneous measure of airborne particle
concentration, thereby reducing considerably the time and effort associated with standard gravimetric methods.
They are also better at measuring aerosols with high vapour pressures that would normally evaporate during
standard gravimetric analysis. Some instruments include a pre-classifier on the inlet (cyclone or impactor) to
make the overall response closer to the respirable dust definition.
Photometers are therefore best suited to assess variations of airborne particle concentration in time or space
and to check for any sudden change of concentration. Typical applications are:
 walk-through surveys;
 background sampling to assess concentration variations and mean concentration during a working
shift period;
 assessment of the effectiveness of dust control systems;
 measurement of indoor air quality;
 as part of exposure video visualization systems.
For measurement of personal exposure they should be considered as complementary to conventional filter-
based gravimetric methods (see [2]), although with careful calibration, they can also give an accurate measure
of respirable dust exposure, i.e. that which enters the mouth and nose and passes to the lower regions of the
respiratory system (see EN 481).
1 Scope
This Technical Report describes the use of photometers for the determination of airborne particles belonging to
the respirable fraction and gives details on their limitations and possible uses in the field of occupational
hygiene.
NOTE Photometers can also be used to detect other size fractions of airborne particles after aerodynamic pre-
separation, but these are not the focus of this Technical Report.
The method complements existing conventional long-term aerosol particle sampling and can be used for:
 instantaneous (direct-reading) measurement,
 time-related monitoring,
 investigation of space-related aerosol evolution (mapping), and
 exposure visualization.
The method enables e.g.:
 detection and relative quantification of concentration peaks due to specific operations (bagging,
sanding, etc.);
 identification of most exposed workers with a view to more detailed studies of risks and prevention
measures to be applied; and
 detection of dust emission sources and their relative magnitudes.
2 Operating Principle
2.1 General
A laser or light emitting diode is used to produce a high intensity source of light, which is usually in the visible
near-infrared spectrum. This is collimated and illuminates airborne particles entering the sensing volume of the
instrument. The optical sensing volume is created by intersection of illuminating and detecting light beams as
shown in Figure 1. The intensity of the light scattered at a particular angle is proportional to the airborne particle
concentration and is detected using sensitive photomultipliers or photodiodes with response spectra covering
approximately the source emission spectra.
2.2 Light scattering
Interaction of a light beam with an airborne particle in suspension can cause several effects: absorption of part
of the light, reflection, refraction or diffraction of the beam. These combined effects result in scattering of the
incident light in every direction. The illumination and collection optics are arranged inside a photometer so that
light scattered at a fixed range of angles reaches the detector (see Figure 1). Depending on the design, these
º º º
instruments can measure the scattered light in the region of θ = 90 , 45 or less than 30 . Choice of observation
angle plays a prominent part in detection. Front scattering is relatively insensitive to changing airborne particle
º
refractive index and so forward-scattering photometers with scattering angles < 30 are less sensitive to the
º
refractive index of the aerosol than instruments with a 90 scattering angle. However, at small scattering angles,
photometers overestimate particles smaller than 1,5 µm.
Key
1 light source
2 incident light
3 aerosol flow
4 lens
5 light detector
6 scattered light
7 scattering angle
8 light stop
9 sensing volume
10 lens
Figure 1 — Light scattering aerosol photometer
2.3 Instrument response — Effects of airborne particle properties
2.3.1 General
For spherical particles of known refractive index the instrument response can be calculated by applying Mie's
light scattering theory (see [13]). The calculated response for a typical light scattering photometer is shown in
Figure 2.
Key
X particle diameter, in micrometres (µm)
Y calculated relative response at constant mass concentration
1 coal dust
2 fused alumina
3 quartz
4 Arizona Road Dust
5 sampling convention for the respirable fraction
Figure 2 — Calculated size-dependent mass-sensitivity of a photometer for four dust materials along
with the conventional respirability (see EN 481)
The physical parameters of some aerosols measured are listed in Table A.1. The photometer parameters are
as follows:
 wavelength of incident light λ = 950 nm;
º
 angle of detection of scattered light θ = 70 ;
º
 semi-angle of light collection β = 10 .
Careful design of the photometer (observation angle, wavelength of the incident light etc., see [1]) allows
measurement of a certain particle size fraction of aerosol. Figure 2 shows a photometer-based dust monitor
that is essentially responsive to particle sizes within the respirable fraction of aerosol. In this case, the
photometer response increases up to a particle diameter of about 1 µm. This is followed by a decrease in
response for larger particles with a large drop in response for particles greater than 10 µm.
In reality the amount of light scattered by an airborne particle entering the detector is a complex function of the
particle size, shape, refractive index, wavelength of the light source and will therefore change for different dust
types. It also depends on the geometry of the photo-detecting optical system.
2.3.2 Particle density
The density of an airborne particle does not affect its light scattering properties and so a photometer's response
will not change with the density of the aerosol being measured. However, the mass concentration of an aerosol
does depend on the particle density and so concentration measurements made by the photometer should be
corrected for the difference between the densities of the actual dust measured (ρ ) relative to that of the
act
calibration dust (ρ ) (see 4.2), assuming that the density of the actual dust is known. To make the correction,
cal
the ratio of the two densities, ρ /ρ is applied to the photometer measurement (see [15]). Care should be
act cal
taken when applying a simple density correction factor since any changes in density (caused by a change of
aerosol type) will most likely be accompanied by changes in the particle size distribution and refractive index of
the aerosol being measured, which will affect the monitor response (see 2.3.3 and 2.3.4).
2.3.3 Particle size
Photometer response is strongly dependent on particle size (see [18] and [22]). For airborne particles, smaller
than the wavelength of the illuminating light, the intensity of the scattered light is proportional to d , where d is
p p
the particle diameter. For larger particles, typically greater than the wavelength of the illuminating light, the
. In the intermediate region where the particle
intensity of the scattered light is approximately proportional to d
p
size approximates to the wavelength of the illuminating light the intensity function can undergo oscillations,
depending on the optical properties of the airborne particles (see Figure 2).
2.3.4 Particle refractive index
Changes in refractive index produce a non-linear change in photometer response. Therefore, a correction
factor based on a simple ratio of the refractive indices of the aerosol being measured to the aerosol with which
the photometer was originally calibrated cannot be applied. However, there is evidence to suggest that the
majority of airborne particles has a refractive index very near to 1,5 (see [7] and [12]). Furthermore, most
º º
modern photometers measure forward-scattered light (sensing angle of 45 to 95 ), which is less sensitive to
changes in refractive index (see [16]). Therefore, any small difference between the refractive index of the
measured aerosol relative to the calibration aerosol can either be ignored or considered linear over that narrow
range and compensated for by a linear correction factor. For airborne particles with a refractive index
substantially different from 1,5 the effects on photometer response are largely unknown, but a photometer can
anyhow be recalibrated for particles with a constant refractive index.
2.3.5 Particle shape
Theoretical and experimental calibration curves of optical techniques for particle characterisation are usually
confined to airborne particles of spherical shape, whereas most aerosol systems consist mainly of particles
having irregular shape. The Mie scattering patterns of a non-spherical object can differ considerably from those
of the sphere, especially when particle size is much larger than the wavelength of the scattered light. The
effects of particle shape on instrument response can be reduced by collecting scattered light produced by
º
diffraction alone. Therefore, monitors that measure scattered light at small sensing angles (< 30 ) i.e. in the
front diffraction lobe will be less sensitive to changes in particle shape.
3 Instrument types
3.1 General
There are many photometer-based direct-reading aerosol monitors available from a number of manufacturers.
They are available in various sizes and weights, which will determine their most appropriate area of application:
 small and lightweight for personal monitoring;
 portable for workplace surveys/mapping;
 bench mounted for static monitoring.
Photometer-based direct-reading aerosol monitors measure light scattering intensities that generally
3 3
correspond to aerosol concentrations from as low as 1 µg/m up to several hundred mg/m and often display
basic statistical information such as average, maximum and minimum concentration. Most incorporate data
logging facilities where measurements of concentration are stored inside the instrument's internal memory.
These measurements can be downloaded to a computer later on for detailed interpretation of the data. Many
photometers also have alarm set-points such that when the concentration exceeds a pre-programmed value,
an alarm is triggered thereby alerting the user.
Photometers can be classified into two distinct types depending on how the aerosol being measured enters the
instrument's sensing zone. The first is known as a “passive” aerosol monitor whereby airborne dust enters the
instrument by the natural air movement in the surrounding air (see 3.2). The second is known as an “active”
aerosol monitor whereby air is drawn into the sensing zone by an in-built pump (see 3.3).
A list of photometer-type aerosol monitors that are currently available is given in Annex B. This list does not
claim to be an exhaustive one, but it includes many of the types that are widely available and that are battery-
powered and therefore suitable for use in occupational settings.
3.2 Passive aerosol monitors
Passive aerosol monitors are generally of an open cell design in which the aerosol to be measured passes into
the optical sensing zone by the natural movement of the surrounding air. This means that they can under-
sample in low wind conditions where a proportion of the aerosol does not enter the instrument. In personal
sampling the movement of the worker will cause the airborne particles to enter the optical sensor cell, and this
is therefore not a problem. But it could be a problem for static sampling, however in these situations there is
usually air movement which will transport airborne particles into the sensing volume. A modulated infrared
monochromatic light source is often used to limit the influence of stray ambient light entering the open cell,
which is absorbed by a filter placed in front of the photodetector (see [3]).
Passive aerosol monitors can be susceptible to contamination of the optics with dust, because of the open cell
design. This can lead to a significant increase in the monitors “zero reading” throughout a measurement,
especially where the concentration of aerosol is high.
3.3 Active aerosol monitors
Active aerosol monitors draw the aerosol through an inlet nozzle and into the sensing chamber using an in-built
pump. These monitors sometimes utilise a sheath flow of air that isolates the aerosol in the chamber to help
keep the optics clean for improved reliability and lower maintenance (these are identified in Table B.1). Some
monitors also collect the airborne particles exiting the chamber onto an internal filter for subsequent gravimetric
or chemical analysis.
3.4 Size-selective aerosol monitors
A number of active aerosol monitors can be fitted with size-selective inlets that separate the aerosol into the
various health-related fractions prior to entering the instrument (see Table B.1). Examples of this type of
1)
aerosol monitor are the TSI Sidepak and TSI Dustrak monitors that use impactor or cyclone adaptors to
separate the aerosol into PM , PM , PM and respirable size fractions prior to entering the instrument's
1,0 2,5 10
sensing zone.
Some passive aerosol monitors can also be made to operate actively (see Table B.1) by drawing air through a
size-selective adaptor located on the inlet of the monitor, using a small personal sampling pump. The adaptor
usually consists of a personal cyclone or inlet containing size-selective porous foams that allow only respirable-
sized airborne particles to enter. The adaptors can be used together with a filter to capture the particles passing
through the monitor inlet, allowing a concurrent in-line gravimetric calibration to be carried out (see 4.4.2). The
adaptors also ensure that the aerosol monitor is only ever challenged with respirable-sized airborne particles so

1) TSI Sidepak and TSI Dustrak are examples of suitable products available commercially. This information is given for
the convenience of users of this Technical Report and does not constitute an endorsement by CEN of these products.
that any effects of large particles on instrument response are eliminated. This increases the accuracy of the
monitor in circumstances where the size distribution of the aerosol is likely to change.
2)
The Respicon TM particle sampler/monitor uses a single sampling head to model the human respiratory
tract and simultaneously determine the three health-related airborne particle fractions: inhalable, thoracic and
º
respirable. It combines both inertial classification with 90 light scattering photometric aerosol detection and so
offers time resolved concentration measurements of the three particle size fractions. The sampling head
comprises a multistage, virtual impactor that traps airborne particles onto three individual filters as collection
substrates. Coarse particles pass straight through to the lower collector while other particles are
aerodynamically separated onto the appropriate filter. The first virtual impactor stage separates out and collects
particles smaller than 4 µm. The second stage collects particles below 10 µm, while the third stage collects the
remaining coarse particles. The Respicon TM does not display “live” real-time measurements of airborne dust
concentration; instead the optical sensors are calibrated post-test using the mass concentrations measured
gravimetrically from the filter samples. The average photometer voltage measured at each impactor stage is
applied to the gravimetric measurements to give a photometer calibration for each particle size fraction. This
calibration is then applied to each data point to give a graph of dust mass concentration against time.
2)
The TSI Dustrak DRX , unlike the other dust monitors, does not use impactor or cyclone inlets to separate
the aerosol by inertial methods, but instead samples the entire aerosol and combines photometric
measurement with optical sizing of single particles in a single optical system to determine the various health-
related fractions of airborne particles (see [21]). The photometric signal is calibrated to approximate to the
PM fraction of the aerosol mass, the size range over which the photometric signal is most sensitive. The
2,5
electrical pulse heights from particles larger than 1 µm are calibrated to approximate the particle aerodynamic
diameter of an aerosol of given physical properties, from which the aerosol mass distribution can be inferred.
By combining the photometric and optical pulse measurements, the instrument can estimate aerosol mass
concentrations higher than typical single particle counting instruments while providing size information and
more accurate mass concentration information than traditional photometers.
4 Calibration
4.1 General
Most photometers are calibrated in the factory using a “standard test dust" and are adjusted to agree with
respirable dust concentration measurements made using reference gravimetric methods. Some aerosol
monitors are supplied with an optical reference element (so-called calibration element) that allows a single
point check of the factory calibration to be carried out (see 4.3). In practice, it is highly unlikely that the
“standard” test dust will exhibit the same physical properties (refractive index, density, particle size distribution,
shape as the airborne particles being measured which will introduce an uncertainty in the measurement (see
[4], [6], [17] and [18]). Therefore, a separate calibration should be carried out each time the monitor is exposed
to a different aerosol in order to obtain accurate quantitative measurements of the airborne particles. In order to
obtain an accurate measure of airborne particle concentration, the aerosol monitor should always be compared
to a reference gravimetric dust sampler placed alongside and adjusted accordingly.
4.2 Factory calibration
A test aerosol generated from Arizona Road Dust (ARD, see ISO 12103-1) is often used as the "standard test
dust" to calibrate dust-monitoring instruments because of its consistency in mineral content and particle size. It
also has a similar refractive index to many workplace aerosols. In practice, the manufacturer generates a
uniform atmosphere of the test dust inside an enclosure. The aerosol monitor and a reference gravimetric dust
sampler are placed alongside each other inside the enclosure and exposed for a period of time sufficient for a
weighable quantity of dust to be collected by the gravimetric sampler. The airborne dust concentration is
calculated for the reference sampler and the aerosol monitor and the process is then repeated over the
concentration range of the aerosol monitor. The aerosol monitor concentration is then plotted against reference

2) Respicon TM and TSI Dustrak DRX are examples of suitable products available commercially. This information is
given for the convenience of users of this Technical Report and does not constitute an endorsement by CEN of these
products.
concentration and the slope of the resultant graph is used to adjust the amplifier gain of the aerosol monitor so
that it measures the same as the reference sampler. Respirable samplers are often used as the reference
since photometers are most sensitive to this range of particle sizes, but also because respirable airborne dust
is the health-related fraction most commonly measured by occupational hygienists. Occasionally other
3)
reference samplers are used, an example being the Microdust Pro aerosol monitor that is calibrated using a
total suspended particulate sampler (TSP sampler). A TSP sampler collects nearly all of the airborne particles
(similar to the inhalable fraction) and so the response of the Microdust Pro is always higher than those of
aerosol monitors calibrated using respirable reference samplers, usually by a factor of about 2.
4.3 Optical reference element
At the same time as calibrating the aerosol monitor, certain manufacturers also produce an optical reference
element. This is usually in the form of an optical filter that is inserted into the monitor's sampling zone and
creates a fixed optical scattering effect. After the aerosol monitor has been calibrated with ARD (see 4.2) the
calibration element is inserted and the resulting concentration reading is recorded and is supplied with the
instrument on purchase. This can be used at any time as a single point check to confirm the factory calibration
for the monitor.
4.4 Gravimetric reference
4.4.1 General
The composition of the aerosol being measured is often unknown but is likely to have different physical
properties to the aerosol with which the instrument was originally calibrated in the factory. This is important
since photometer response can depend critically on the physical properties as well as the concentration of the
aerosol being measured. In order to make accurate quantitative measurements in the field, the average
photometer reading (C ) should always be compared to measurements made with a reference gravimetric
m
sampler (C ) during a given time period to give a correction factor (C /C ) that can be applied to the photometer
r r m
measurements. This is only valid for identical and stable aerosols and recalibration should be performed when
either the nature of the aerosol or its size distribution changes or the workplace site is changed.
4.4.2 Integral back up filter
Some active aerosol monitors include an integral back up filter onto which the aerosol passing through the
sensing zone is captured, and can be used to determine the reference gravimetric concentration. Also, as
mentioned in 3.4 some passive-type monitors can be fitted with in-line size-selective adaptors, which attach to
the inlet and can be used to determine the reference concentration. Aerosol is drawn into the adaptor using a
small personal sampling pump and passes through the monitor's sensing volume before being collected onto a
back up filter. The size selectivity of such a sampling system should be tested against EN 481 according to
EN 13205.
4.4.3 External gravimetric sampler
Some aerosol monitors do not include a back up filter to collect the measured aerosol or cannot be fitted with
an in-line size-selective adaptor. In these cases, the only option is to use an external gravimetric sampler to
measure the reference airborne particle concentration. These can use any pre-separator that selects the
respirable fraction of the airborne particles (for example cyclone, horizontal elutriator, foam, etc.). Aerosol
monitors can be calibrated to measure aerosols that deposit in other regions of the respiratory tract, such as
the inhalable fraction, by using reference samplers designed to measure this fraction (see [14] and [19]).
Special care should be taken in doing this to ensure that the aerosol is stable since the monitor calibration will
be very sensitive to changes in particle size. For example, if airborne particles greater than the size range of
the respirable particle fraction are produced, these will be measured by the reference gravimetric inhalable
sampler but will not be detected by the aerosol monitor (see [20]).

3) Microdust Pro is an example of a suitable product available commercially. This information is given for the
convenience of users of this Technical Report and does not constitute an endorsement by CEN of this product.
During calibration, the reference sampler should be placed in close proximity to the aerosol monitor so that they
are both exposed to the same aerosol. This is especially important where sources of aerosol are localised and
not well mixed.
For 4.4.2 and 4.4.3 the following method is used to determine the reference gravimetric concentration:
 the filter is weighed before and after exposure to determine the mass of dust collected (m ). If the
d
mass is in grams, this is converted to milligrams by multiplying by 1 000;
 the total volume of air sampled (V) is determined by multiplying the pump (or aerosol monitor) flow
t
-1
rate, in litres per minute (l ⋅ min ) by the sampling time, in minutes (min). This is converted from litres
to cubic metres (m ) by dividing by 1 000;
-3
 the mass concentration, given in milligrams per cubic metres (mg ⋅ m ), is calculated from m /V .
d t
5 Choice of aerosol monitor
5.1 General
The choice of aerosol monitor will depend on the particular application. Certain types of aerosol monitors have
features that lend themselves better to some applications than others.
5.2 Active or passive aerosol monitors
5.2.1 Passive photometers
Passive photometers are probably best suited to measurements of relative changes in airborne dust
concentrations, e.g. for walk-through surveys and measurement of the effectiveness of dust control systems.
They are likely to underestimate airborne particle concentration for static measurements in low wind conditions
(see 3.2). In these situations they should be moved through the air to generate a relative air movement. The
addition of an in-line gravimetric adaptor and pump (see 4.4.3) for calibration purposes whilst allowing
quantitative measurements to be made adds appreciable mass and bulk to the aerosol monitor. Although this is
not a problem for static sampling it could prove uncomfortable to the worker during personal monitoring over
extended periods of time.
Passive photometers should not be used where they are likely to be exposed to high dust concentrations for
prolonged periods of time since as mentioned previously the optics can become contaminated with dust.
Because they have no in-built pump, passive aerosol monitors are silent in operation and also have much lower
power consumption resulting in longer measurement periods before the batteries need replacing or recharging.
This can prove advantageous in certain circumstances, e.g. where noise is an issue, or for prolonged
measurement periods where there is no access to a mains power supply.
5.2.2 Active photometers
Active photometers can be used for most applications and some have the added advantage of using a sheath
of clean air to protect the optics, meaning they can be operated for longer periods before they require cleaning.
They can also be used with size-selective inlets that allow different size fractions to be measured, e.g. cyclone
inlet for respirable and impactor inlets for PM and PM size fractions. Some active monitors also have an in-
1,0 2,5
built back up filter allowing for concurrent gravimetric calibration.
5.3 Mass concentration range
The mass concentrations of aerosol likely to be measured should be considered when choosing which type of
-3 -3
aerosol monitor to use. Most aerosol monitors measure mass concentrations as low as 1 µg ⋅ m or 10 µg ⋅ m ,
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but the upper limit can vary considerably between instruments from 10 mg ⋅ m to 2 500 mg ⋅ m (see
Table B.1).
5.4 Hazardous work environments
Photometers that are to be used in hazardous work environments containing flammable/explosive gases,
vapours, mists, dusts, or ignitable fibres need to be certified as intrinsically safe for that environment (ATEX
certified) (see EN 60079-0 and EN 60079-11). This will ensure that in normal use and in the event of electrical
failure, they will not present a source of ignition resulting in fire or explosion. Such work environments should
be evaluated and identified by a qualified health and safety professional prior to using any instrument in that
area.
5.5 Size selection
If the measurement of a certain fraction of the airborne particles is required, then aerosol monitors that use
size-selective inlets should be considered. Those typically separate the aerosol into PM , PM , PM and
1,0 2,5 10
respirable, thoracic and inhalable size fractions prior to entering the instrument's sensing zone. For maximum
accuracy they should be calibrated against reference gravimetric samplers that measure the size fraction of
interest.
6 Procedure for making aerosol measurements using photometers
6.1 Instrument operating procedure
6.1.1 General
The photometer should be operated in accordance with the instructions given in the manufacturer's operating
manual.
6.1.2 General instrument set-up
 The user should be fully familiar with the operation of the instrument prior to taking a measurement.
 If the instrument is to be used for personal or portable use, the internal batteries should have enough
capacity to last for the duration of the measurement. This can mean replacing disposable batteries
such as alkaline batteries or charging the instrument fully before use. Most modern aerosol monitors
have a battery status indicator, which should be checked prior to use.
 The aerosol monitor should be set to the most appropriate range of aerosol mass concentration and
resolution for the intended application. This will not apply if the monitor has an auto-ranging feature.
 Time and date should be correctly adjusted. This is particularly important when work activities are
being monitored over a period of time so that peak concentrations or exposures can be related to a
particular activity.
 The averaging period of the photometer should be adjusted to suit the task being monitored or aerosol
being measured. Aerosol monitors typically take a measurement every second. However, the time
over which the airborne particle mass concentration is averaged and displayed (the averaging period
or time constant) can usually be adjusted from typically one second up to several minutes. In
measurement applications where aerosol mass concentrations change rapidly, a longer averaging
time will offer increased stability for the displayed value. The averaging period should not be confused
with the logging interval.
6.1.3 Zeroing
The aerosol monitor should be zeroed prior to making a measurement, especially if it is to be used to make
quantitative rather than comparative measurements. Although methods differ slightly between instruments,
each relies on cleaning optical surfaces, and purging the instrument's measurement chamber with particle-free
air after which the monitor reading is adjusted to zero. The zeroing methods described in the instruments'
operating instructions should be followed.
6.1.4 Calibration
Photometer calibration methods are explained in detail in Clause 4. The type of calibration will depend on the
type of measurement being made. If the aerosol monitor is to be used to measure relative changes in
concentration then calibration is not essential. However, if the optical reference element is available, this can
be used to perform a single point check to ensure that the aerosol monitor is adjusted to the factory-set
calibration. If the aerosol monitor is to be used to accurately measure airborne dust concentrations then it
should be calibrated using a suitable reference gravimetric sampler. This calibration will only apply if the
properties of the aerosol do not change significantly during the duration of the measurement.
6.1.5 Evaluation of data
All modern aerosol monitors incorporate an on-board data logger for storage of aerosol mass concentration
measurement results. The maximum logging duration is determined by the capacity of the internal memory and
the logging interval. Therefore, the logging interval should be determined and adjusted such that the monitor
will log for the full length of the task. Certain monitors can be set to two logging modes. The first is “overwrite”
and in this case when the memory becomes full, the oldest measurements are overwritten. The second is “stop
when full” and as the name suggests, as soon as the memory becomes full the monitor stops logging. Care
should be taken when choosing which logging mode to use and the safest option is to choose a sufficient long
logging interval such that the memory does not become full during the duration of the measurement.
Most aerosol monitors also provide basic statistical information such as minimum, maximum and mean
concentration calculations and some will even display rudimentary graphical information. Measurements can
also be downloaded to a computer for more detailed interrogation of the data, allowing for peaks or rapid
changes in dust concentration to be identified. Each monitor is supplied with its own software and instructions
to which the operator should refer.
6.2 Sampling strategies
6.2.1 Personal monitoring
Generally, the aerosol monitor should be small and light enough to be worn within the breathing zone and
should not affect normal work activities. If using an additional reference gravimetric sampler (for example for
calibration), this should be placed in close proximity to the monitor so that they are both exposed to the same
aerosol. Likewise, any additional weight introduced by the reference gravimetric sampler and associated pump
should not adversely interfere with normal work activities. The monitor and/or pump(s) should be securely
attached using a suitable belt or harness.
Worker exposure measurements can focus on specific operations or mean exposure throughout the shift.
Where possible, sampling time should coincide w
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