PMP – Particle Measurement Program UNECE Informal Group
Non-exhaust particle emissions
Working Item 4
Development of a set of recommended measurement techniques and
sampling procedures
Questions related to the present document
Q1. Is the content of the document appropriate? Does it cover the main aspects discussed
during the last face-to-face meeting?
Q2. Is the template sufficient and easy to process? Do the tables cover the most important
aspects regarding methodologies?
Q3. Is there any additional information that needs to be added?
Please provide comments/suggestion
This document provides an overview of the main generation/sampling/measurement
techniques/methodologies described in publicly available studies and used to investigate
particle emissions from brake and tyre wear. All references used in this document can be
found in the survey of the available literature conducted by the JRC.
This document is intended to provide a basis for further discussion for the development of a
set of recommended methodologies and techniques with the final objective of improving
the comparability of future studies and their outcomes.
1. Generation and sampling of wear particles
1a. Brake wear particles
Brake wear particles generation and sampling can be performed in the laboratory by means
of a roller chassis bench (Full Chassis Dynamometer), a brake dynamometer or a pin-on-disc
configuration. Furthermore, mobile units can be employed in order to sample brake wear
particles on-road under “real world” driving conditions. Table 1 gives an overview of the
methods used for brake wear particles generation and sampling.
Table 1: Overview of methods used for brake wear particles generation and sampling
Code
Method
Note
Open
System
G1
Brake
Dynamometer
Enclosed
System
G2
G3
G4
G5
G6
G7
Pin-on-disc
method
Roller Bench
(Full Chassis
Dynamometer)
Mobile
Unit
Open
System
Enclosed
System
Open
System
Enclosed
System
Open
System









References
Iijima et al. 2007
Österle et al. 2008
Österle et al. 2010
Sanders et al. 2003
Garg et al. 2000
Gasser et al. 2009
Iijima et al. 2008
Kukutschová et al. 2009
Kukutschová et al. 2011
 Mosleh et al. 2004
 Wahlstrom et al. 2010a
 Wahlstrom et al. 2010b


 Kwak et al. 2013
 Mathissen et al. 2011
Figure 1a provides a schematic representation of two different brake dynamometer
assemblies (Iijima et al. 2007; Kukutschová et al. 2011). The most important difference
among the two assemblies is that the second one is enclosed in an environmental chamber.
In Figure 1b an enclosed pin-on-disc assembly is depicted (Wahlstrom et al. 2010b). Close
systems have several advantages over open ones. One advantage is the knowledge that the
particles collected and measured originate from the wear of the brake assembly and not
from the surroundings. The background concentration could be in the same order or higher
than the concentration produced by the disc brake contact, especially if urban driving
conditions are studied. This also means that resuspension of existing particles is ruled out,
thus no under- or over- estimation of wear particles due to resuspension occurs. With close
systems is easy to provide the right conditions for isokinetic sampling and a high particles
collection efficiency, as industrial benches have big safety chambers where proper piping
systems can be installed. Another advantage of close over open systems is that it is possible
to control the cleanness of the incoming air. Furthermore it is possible to precisely control
the temperature and humidity levels. On the other hand, determined particle size
distribution in open systems cannot deviate from the original due to particle aggregation or
deposition as a result of the interaction between the particles and the chamber wall. It is
true that the real brake system does not work in a completely free environment either,
because on one side there is the rim and on the other side the mudguard, therefore the
influence of the close chamber (or the lack of it) cannot be evaluated.
Figure 1a: Schematic representation of different brake dynamometer assemblies [Left Iijima et al. 2007; Right - Kukutschová et al. 2011]
Regarding mobile units, Mathissen et al. 2011 equipped a vehicle with five stainless steel
sampling tubes of 0.4 cm in diameter inside the front right wheel housing. The different
positions allow the localization of the particle source. Conductive tubing with an inner
diameter of 0.8 cm and an average length of 6 m was used to connect the sampling ports
with the measurement devices inside the vehicle. The setup is not designed for isokinetic
sampling. However, there is no correction necessary since non-isokinetic sampling losses
would have affected larger particles only. The residence time for the aerosol can be
estimated to be smaller than 0.4 s at a flow rate of 50 l min-1. Thermophoresis can be
neglected because the measurements were performed at ambient temperature. On the
other hand, Kwak et al. 2013 equipped a vehicle with three sampling inlets, one in front of
the vehicle to measure background concentrations, one close to the tire/road interface to
measure tyre particles, and one close to the brake pad to sample brake particles. All
sampling inlets were connected to sampling plena, which had an inner diameter of 48 mm,
enabling the sampling air-flow to be well mixed. Flow velocity of sampling air was 0.58 m/s,
and the Reynold's number was 1858, thus satisfying laminar flow. Sampling particles were
sucked in at a flow rate of 63 l min−1. Conductive tubing with an inner diameter of 10 mm
and length of 1 m was to line the tubes running from the plena to the particle monitors.
Isokinetic sampling design was adopted.
Figure 1b: Schematic representation of a pin-on-disc assembly. (A) Room air; (B) fan; (C)
flow rate measurement; (D) filter; (E) flexible tube; (F) inlet for clean air, measurement
point; (G) closed chamber; (H) pin-on-disc machine; (I) pin sample; (J) air outlet,
measurement points; (K) displacement gauge; (L) dead weight; (M) rotating disc sample;
(N) air inside chamber, well mixed [Wahlstrom et al. 2010b]
1b. Tyre wear particles
Tyre wear particles generation and sampling can be performed either by directly in the
laboratory using a wheel simulator or on-road, under “real world” driving conditions, by
means of mobile units. In general, road simulation laboratory studies are employed in order
to study the contributions from tyre and road wear in an isolated environment, under
controlled laboratory conditions, whereas the mobile units usually measure additionally the
contribution from resuspended dust present under ambient conditions. Finally, cryogenic
production of tyre wear particles can be performed if pieces of tread are crushed under
cryogenic conditions and sieved to 180 μm. However, this methodology generates only very
large particles and fails to represent actual wear conditions.
Figure 2 provides a schematic representation of three different road simulators (Gustafsson
et al. 2008; Aatmeeyata et al. 2010; Kreider et al. 2010). Details on all simulators are
provided in the annex. The set-up depicted on the left was used in Aatmeeyata et al. 2010
and is designed to utilize vertical space and thus reduce space requirement and enable
complete enclosure of the entire set-up (1.8 x 0.71 x 1.28 m). The fork/wheel assembly is
also equipped with a brake, while an odometer is used to measure the speed of rotation
and (linear) distance traveled by the tire. At the top of the assembly, there is a provision for
applying a load on the tire. On the other hand, sampling in the VTI simulator hall makes it
possible to sample pure wear particles, with very low contamination from ambient particles
and no influence from tail-pipe emissions. The VTI road simulator is possible to run with four
wheels around a circular track. A linear track simulation is accomplished even though the
tires are running in a circle, because no radial force is acting on the tires as the wheels are
bolted to the axles of the road simulator. To make the wheels move radically across the
entire track, an eccentric movement can be activated above 50 km h-1. The simulator track
can be equipped with any type of pavement. The dimensions of the simulator are 10 m x 8
m x 5 m. Lastly the Bundesanstalt für Straßenwesen (BASt), the German Federal Highway
Research Institute, operates an interior drum testing system (IPS) that consists of an
enclosed drum that contains pavement casks against which a tire can roll. The IPS has an
internal diameter of 3.8 m and is electronically programmable to mimic a variety of driving
conditions by varying speed, temperature, acceleration, braking, and steering. Tire wear
particles are generated without the influence from other road surface contaminants such as
brake dust, vehicle exhaust, oil/grease, salts, soil, vegetation, etc. For both the VTI and BASt
road simulators, the pavement is not subjected to weathering or other natural conditions,
and as such a polishing effect can occur that causes the surface becomes smoother.
Therefore, the pavement is ‘sharpened’ between runs to maintain representative surface
textures.
Table 2: Overview of methods used for tyre wear particles generation and sampling
Code
Method
G8
Road - Wheel
Simulator
G11
Open
System
Enclosed
System
G9
G10
Note
References
Dahl et al. 2006
Gustafsson et al. 2008
Kupiainen et al. 2005
Panko et al. 2009
Sjodin et al. 2010
Aatmeeyata et al. 2009
Aatmeeyata et al. 2010
Kreider et al. 2010
 Kreider et al. 2010
 Rogge et al. 1993
Cryogenic
Production
Mobile
Unit








Open
System




Hussein et al. 2008
Kreider et al. 2012
Kwak et al. 2014
Mathissen et al. 2011
Figure 2: wheel simulators used in different studies [Up-left: Aatmeeyata et al. 2010; Upright: Gustafsson et al. 2008; Below: Kreider et al. 2010]
Regarding mobile units, those developed by Mathissen et al. 2011 and Kwak et al. 2013
were described in 1a section. Hussein et al. 2008 equipped a vehicle with three metal tube
inlets: two behind the front tires and one underneath the van as a background. The front
inlet was 0.4 cm in diameter and 3 m long; the flow rate in this inlet was 1.7 l m-1. Both
inlets behind the front tires were mounted symmetrically and they were 1.9 cm in diameter
and 2.3 m long. Flow rates through these two inlets were 75 l m-1. Measurements behind
the tires during motion indicated that along the center of the tire, the air speed is not
significantly influenced by the ambient wind direction at distances of 10 cm from the tire.
Each inlet behind the left and right tires fed into a 60-cm-long torpedo-shaped manifold that
had an inner diameter of 7.5 cm. A specially designed baffle ensured that the flow through
the manifold was uniform and well mixed. A single carbon vane pump drew the necessary
air through both the manifolds. The manifold was used to distribute the sampled air to as
many as five instruments which were connected to the manifold via 100-cm-long tygon
tubes.
2. Physicochemical characterization of wear particles
2a. Mass Size distribution measurement systems
The most commonly used instruments for assessing mass weighted size distribution are
cascade impactors, which operate on the basis of inertial classification of particles. Even if
different kinds of impactors have been employed for assessing wear particles, they all
operate based on the same principal. Another commonly used method for assessing mass
weighted size distribution involves the use of an Optical Particle Counter. Table 3 gives an
overview of the methods used in the literature. More details for each method can be found
in the Annex.
Table 3: Overview of methods used for mass size distribution of wear particles
Code
M1
M2
M3
M4
Instrument
Principle
Optical Particle
Counter
(DustTrak)
Light
scattering
with
electrical
detection
 Wahlstrom et al. 2010a
 Wahlstrom et al. 2010b






Inertia
impaction




 Harrison et al. 2012
Micro Orifice
Uniform Deposit
Impactor
(MOUDI)
Small deposit area
low-pressure
cascade impactor
(SDI)
Low Pressure
Impactor
(LPI)
Brakes
Garg et al. 2000
Gietl et al. 2010
Harrison et al. 2012
Sanders et al. 2003




Inertia
impaction
Inertia
impaction
Tyres
Gustafsson et al. 2008
Hussein et al.2008
Kreider et al. 2012
Kwak et al. 2013
Panko et al. 2009
Sjödin et al. 2010
Gustafsson et al. 2008
Kupiainen et al. 2005
Panko et al. 2009
Sjödin et al. 2010
 Kukutschová et al. 2011
 Österle et al. 2008
 Österle et al. 2010
2b. Number Size distribution measurement systems
Particle size measurement can be based on the following properties: geometrical size
(Microscopy), inertia (Impactors), electrical mobility (Differential Mobility Analysers), and
optical properties (Optical Particle Counters). These properties have been used by
researchers for assessing PN distribution of wear particles. Table 4 gives an overview of the
methods used in the literature. More details for each method can be found in the Annex.
Table 4: Overview of methods used for number size distribution of wear particles
Code
N1
Instrument
Laser Scattering
Particle Size
Analyzer
(LSA)
N2
Aerodynamic
Particle Sizer
(APS)
N3
Engine Exhaust
Particle Sizer
(EEPS)
N4
Condensation
Nucleus Counter
(CPC)
N5
Aerosol
Spectrometer –
Optical Particle
Counter
(OPC)
N6
Scanning Mobility
Particle Sizer
(SMPS)
N7
Electrical Low
Pressure Impactor
(ELPI)
Principle
Brakes
Light
scattering
 Kukutschová et al. 2009
 Mosleh et al. 2004
Inertia
impaction
with light
scattering
detection
Differential
mobility
analysis with
electrical
detection
Condensation
of particles
with light
scattering
detection




Light
scattering
with electrical
detection




Electrical
mobility
analysis with
electrical
detection
Electrical
impaction
with electrical
detection
Iijima et al. 2007
Iijima et al. 2008
Kukutschová et al. 2011
Sanders et al. 2003
Tyres





Gustafsson et al. 2008
Kreider and Panko, 2012
Kwak et al. 2013
Panko et al. 2009
Sjödin et al. 2010
 Mathissen et al.2011
 Österle et al. 2010
 Wahlstrom et al. 2010a
 Wahlstrom et al. 2010b
Österle et al. 2008
von Uexküll et al. 2005
Wahlstrom et al. 2010a
Wahlstrom et al. 2010b
 Kukutschová et al. 2011
 Österle et al. 2008
 Wahlstrom et al. 2010b
 Aatmeeyata et al. 2009
 Hussein et al.2008




Dahl et al. 2006
Gustafsson et al. 2008
Panko et al. 2009
Sjödin et al. 2010
 Garg et al. 2000
 Sanders et al. 2003
An important issue to be taken into account when studying particle size distributions is that
in order to fully describe the distribution it is necessary to use instruments that cover the
whole range of the particles’ size. For instance in case of PN distribution a combination of a
SMPS and an optical counter would cover the whole range of diameters between a few nm
to several μm. On the other hand, studies that use instruments with specific limitations at
their measurement range may result in misleading conclusions like those previously
recorded at the PMP group (i.e. APS or other optical counters with a detection limit of
around 0.3 µm).
Figure 3 depicts an idealized size distribution (upper line) in which SMPS measurements of
ultrafine particles together with APS measurements (bottom separated lines) have been
combined. Since APS has a detection limit of 300-400 nm it gives an artificial mode in this
size fraction. The same occurs with SMPS alone for the coarser size fractions. To avoid these
artefacts close to the edge of the coarser and finer detection limits, the size distributions
have to be recalculated to give a continuous size distribution (upper one).
Figure 3. Size distribution in which SMPS measurements of ultrafine particles together
with APS measurements are combined (upper line) or separated (bottom lines)
2c. Chemical and morphology characterization
Table 5 gives an overview of the methods used in the literature for the chemical and
morphology characterization of particles emitted as a result of brake and tyre wear. Most of
these methods refer to the chemical characterization of the inorganic part of wear particles
(i.e. trace elements and heavy metals). Very few studies tried to identify specific organic
compounds into wear particles and this remains a field where there is still a lack of
information. Like in case of size number distribution, in order to fully characterize wear
particles it is necessary to combine two or more analytical methods, since each one of them
comes with specific limitations. More details for each method, as well as for the
combinations found in the literature are given in the Annex.
Table 5: Overview of methods used for chemical characterization of wear particles
Code
Instrument
Principle
Brakes
C1
Scanning Electron
Microscope
(SEM)
Electron
interaction with
visual detection






C2
Transmission Electron
Microscope
(TEM)
Electron
interaction with
visual detection





C3
X-Ray Fluorescence
(XRF)
Detection of
X-Ray
fluorescence
C4
C5
C6
C7
C8
C9
C10
C11
C12
Kukutschová et al. 2009
Kukutschová et al. 2011
Österle et al. 2008
Österle et al. 2010
Peikertová et al. 2013
Wahlstrom et al. 2010a
Gasser et al. 2009
Kukutschová et al. 2011
Österle et al. 2008
Österle et al. 2010
Peikertová et al. 2013







Tyres
Adachi et al. 2004
Camatini et al. 2001
Gustafsson et al. 2008
Kreider et al. 2010
Kupiainen et al. 2005
Panko et al. 2009
Sjödin et al. 2010
 Kukutschová et al. 2011
 Sanders et al. 2003
 Harrison et al. 2012












Karlsson et al. 2011
Kukutschová et al. 2009
Mosleh et al. 2004
Österle et al. 2008
Österle et al. 2010
Wahlstrom et al. 2010a
Adachi et al. 2004
Camatini et al. 2001
Gustafsson et al. 2008
Kupiainen et al. 2005
Panko et al. 2009
Sjödin et al. 2010
Energy Dispersive XRay Spectroscopy
(EDX or EDS)
Detection of XRay dispersive
energy
X-Ray Diffraction
Spectroscopy
(XRD)
Proton Induced
X-Ray Emission
(PIXE)
X-Ray diffraction
patterns
for detection
 Peikertová et al. 2013
 von Uexküll et al. 2005
X-Ray
detection
 Garg et al. 2000
 Kukutschová et al. 2011
 Gustafsson et al. 2008
 Panko et al. 2009
 Sjödin et al. 2010
Oxidation of PM
with optical
detection
Conversion to
plasma and
atomic emission
detection
 Garg et al. 2000
 Kukutschová et al. 2011
 Aatmeeyata et al. 2010
 Kupiainen et al. 2005
 Iijima et al. 2007
 Iijima et al. 2008
 Kreider et al. 2010
Conversion to
plasma and m/z
detection
 Iijima et al. 2007
 Iijima et al. 2008
 Sjodin et al. 2010
 Rogge et al. 1993




Thermal/Optical
Carbon Analyzer
Inductively Coupled
Plasma – Atomic
Emission Spectroscopy
(ICP-AES)
Inductively Coupled
Plasma – Mass
Spectrometry
(ICP-MS)
Gas Chromatography
Mass Spectrometry
(GC-MS)
Column
separation and
m/z detection
High Pressure Liquid
Chromatography
Fluorescence Detector
(HPLC-FLD)
Pyrolysis with Gas
Column
separation and
fluorescence
detection
Thermal
Aatmeeyata et al. 2010
Kreider et al. 2010
Kwon et al. 2012
Rogge et al. 1993
 Sjodin et al. 2010
 Unice et al. 2012
Chromatography-Mass
Spectrometry
C13
Focused ion beam
microscopy
decomposition
of PM with m/z
detection
Ion interaction
with visual
detection
 Milani et al. 2004
Annex
A. Generation and sampling of wear particles
Brake wear particles
G1
Commercial name(s)
Type of instrument
Temperature tolerance
Braking Pressure or Deceleration
Speed variation
Inertial load
What can measure
What cannot measure
Main limitations
Main Characteristics / Advantages
G2
Commercial name(s)
Type of instrument
Temperature tolerance
Braking Pressure or Deceleration
Speed variation
Inertial load
What can measure
What cannot measure
Brake Dynamometer
Link full-scale brake dynamometer (2900); TecSA Intertia
Dynamometer
Brake Dynamometer
Up to 700-800°C
Up to 4.9 m s-2
0–90 km/h
45-90 kg m2
Can be coupled to size distribution instruments; Filters can
collect PM for characterization; Speed, Acceleration,
Deceleration, Pressure, Torque, Brake temperature, cooling
air speed, air temperature
Live wear value. It has to be done by getting pin/disc
dimensions before and after test; Not appropriate for
investigation of generation mechanism
Not possible to control the cleanness of the incoming air
and or precisely control the temperature and RH levels; Not
appropriate for investigation of generation mechanism;
Difficulty of reproducing the conditions and loads identical
as on real vehicle. Deviation from reality could come from:
air and rolling resistance, real torque (instantaneous)
distribution, air flow.
Open System / High repeatability, accuracy and automation
of the tests (no human factor affecting the test); Short time
of execution; Able to reduce the particle collection
efficiency and modify the dilution factor (especially from
high energy brakes which emits a PN which can create
instruments problems - overflow, unreliable currents)
Brake Dynamometer
Link Friction Test Machine (D); Link full-scale brake
dynamometer (2900); TecSA Intertia Dynamometer
Brake Dynamometer
Up to 400°C
Up to 4.9 m s-2
0–180 km/h
120-2000 kg
Can be coupled to size distribution instruments; Filters can
collect PM for characterization; Speed, Acceleration,
Deceleration, Pressure, Torque, Brake temperature, cooling
air speed, air temperature
Live wear value. It has to be done by getting pin/disc
dimensions before and after test; Not appropriate for
Main limitations
Main Characteristics / Advantages
investigation of generation mechanism
Particle size distribution may deviate (?) from the original
due to particle aggregation or deposition as a result of the
interaction between the particles and the chamber wall;
Not appropriate for investigation of generation mechanism;
Difficulty of reproducing the conditions and loads identical
as on real vehicle. Deviation from reality could come from:
air and rolling resistance, real torque (instantaneous)
distribution, air flow.
Close System / High repeatability, accuracy and automation
of the tests (no human factor affecting the test, no ambient
influence); Short time of execution; Can be a good mean to
understand if pin-on-disc studies are somehow significative
of a real system; Able to reduce the particle collection
efficiency and modify the dilution factor (especially from
high energy brakes which emits a PN which can create
instruments problems - overflow, unreliable currents)
G3
Pin-on-disc Tribometer
Commercial name(s)
Type of instrument
Temperature tolerance
Braking Pressure or Deceleration
Speed variation
Inertial load
Not applicable
Tribometer
What can measure
Up to 2-3 MPa depending on pin geometry
60 km/h
Not applicable
Can be coupled to size distribution instruments; Speed,
Acceleration, Deceleration, Pressure, Brake temperature,
air temperature, relative humidity
What cannot measure
Main limitations
Main Characteristics / Advantages
Not possible to reach speeds higher than those of urban
conditions; Not possible to control the cleanness of the
incoming air and or precisely control the temperature and
RH levels; Possible contamination from resuspension dust
Open System; Appropriate for investigation of generation
mechanism; Can be used to determine wear and airborne
wear coefficients which could be used in computer
simulations
G4
Pin-on-disc Tribometer
Commercial name(s)
Type of instrument
Temperature tolerance
Braking Pressure or Deceleration
Speed variation
Inertial load
Not applicable
Tribometer
What can measure
What cannot measure
Up to 2-3 MPa depending on pin geometry
60 km/h
Not applicable
Can be coupled to size distribution instruments; Speed,
Acceleration, Deceleration, Pressure, Applied torque, Brake
temperature, Air temperature, Relative humidity
Main limitations
Main Characteristics / Advantages
Not possible to reach speeds higher than those of urban
conditions; PN distribution may deviate from the original
due to particle aggregation or deposition as a result of the
interaction between the particles and the chamber wall
Close System; Appropriate for investigation of generation
mechanism; Can be used to determine wear and airborne
wear coefficients which could be used in computer
simulations
Tyre wear particles
G8
Road - Wheel Simulator
Commercial name(s)
Type of instrument
Temperature tolerance
Acceleration or Deceleration
Speed variation
Inertial load
VTI road simulator
Road simulator
Unlimited
What can measure
Up to 70 km/h
Axle load 450 kg
Can be coupled to size distribution instruments; Speed,
Acceleration, Deceleration, air temperature, relative
humidity
What cannot measure
Main Characteristics / Advantages
Not possible to control the cleanness of the incoming air
and or precisely control the temperature and RH levels
Open System; Appropriate any type of pavement
G9a
Road - Wheel Simulator
Commercial name(s)
Type of instrument
Temperature tolerance
Acceleration or Deceleration
Speed variation
Inertial load
Not applicable
Wheel simulator
Unlimited
Main limitations
What can measure
36 km/h
44.3 kg
Can be coupled to size distribution instruments; Speed,
Acceleration, Deceleration, air temperature, relative
humidity
What cannot measure
Main limitations
Main Characteristics / Advantages
Not possible to achieve high speeds; PN distribution may
deviate from the original due to particle aggregation or
deposition as a result of the interaction between the
particles and the chamber wall
Close System; Reduced space requirement; Complete
enclosure of the entire set-up that facilitates collection of
all generated particles
G9b
Road - Wheel Simulator
Commercial name(s)
BASt road simulator
Type of instrument
Temperature tolerance
Acceleration or Deceleration
Speed variation
Inertial load
What can measure
Road simulator
-10°C to 50°C
Acceleration: 0-63 m/s2; deceleration: 0.5 - >2 m/s2
Up to 160 km/h
Maximum wheel load 10kN
Can be coupled to size distribution instruments; speed,
acceleration, deceleration, air temperature, tire
temperature, camber angle, steering angle
What cannot measure
Main limitations
Main Characteristics
Complex ventilation system and airflows inside the drum
make real-time particle size distribution difficult
Closed System; Appropriate for any type of pavement;
ability to set variable driving par cour; cyclonic collection
device to collect bulk wear particulate can be mounted
inside near tire pavement interface
B. Mass Size distribution measurement systems
M1) DustTrak aerosol monitor is a fast Optical Particle Counter (OPC) which measures the volume
concentration and reports the mass concentration of particles in mg/m3. It is based on light
scattering and can measure particle concentrations corresponding to the respirable size in the range
of 0.001–150 mg/m3 with 1 s time resolution (Kwak et al. 2013). The instrument is calibrated with a
standardized test dust having a different size distribution, density, and refractive index from those of
the particles measured here. A disadvantage of OPCs is that uncertainty in refractive index often
leads to significant variability in derived size distributions, even for the ideal case of homogeneous
spherical aerosol particles. Although the output of the DustTrak OPC can only be used as a relative
measure, it is useful for detecting changes over time in the generated particle mass (Wahlstrom et
al. 2010a; Wahlstrom et al. 2010b). It is not approved for air quality surveillance against air quality
guidelines but it is useful for monitoring of fast courses of events in homogenous aerosols (Sjodin et
al. 2010).
M2) Micro-Orifice Uniform Deposit Impactor (MOUDI) is a cascade impactor that separate particles
according to their aerodynamic size. It operates on the basis of inertial classification of particles. The
aerosol sample passes through a succession of stages, at each of which the aerosol is directed
through an array of nozzles situated above a solid substrate. Particles with aerodynamic diameters
above the design cut-point deposit by impaction, whereas smaller particles follow gas streamlines
around the collection plate. Impaction efficiency is a function of Stokes number. The narrower the
nozzle and the higher the air velocity, the finer are the particles that are collected. The smallest
particles passing through the final stage cannot be collected due to their small inertia, but often are
collected onto a final filter (Giechaskiel et al. 2014). MOUDI can be adjusted to operate with a
different number of collection stages (from 5 to 11) with the D50% cut points ranging from 56 nm to
18 μm. Aluminium foils are used for the collection of the particles. Foils are weighed before and
after collection of the wear debris to determine directly the mass-weighted size distribution. MOUDI
mainly deals with the non-volatile material leading at an overall underestimation due to particle loss
by vaporization (Harrison et al. 2011). Additionally, impactors in general are subject to errors due to
particle bounce which tends to reduce the measured particle size (Garg et al. 2000).
M3) Small deposit area low-pressure cascade impactor (SDI) is used to collect highly size-resolved
aerosol particle samples in several size fractions (aerodynamic cut-off diameter between 0.045 and
8.39 μm), with a sample flow rate of 11 l/min. Like all impactors it operates on the basis of inertial
classification of particles. The relatively high sample flow rate together with the small particle
collection area (Ø 8 mm), increase the sensitivity of the particle analysis even when the sample
concentration is low, while on the other hand low pressure makes this technique inappropriate for
volatile particles. Nuclepore polycarbonate membrane filters are usually employed as collection
substrates.
M4) Low Pressure Impactor (LPI) is a multi-stage cascade low pressure impactor which is used to
determine particle gravimetric mass size distribution. It operates on the basis of inertial classification
of particles. The size classification in LPI is made from few nm up to 10 µm with evenly distributed
impactor stages and can be extended down to 30 nm with an additional back-up filter. Aluminum
foils coated with a polycarbonate film and a thin layer of vacuum grease are used as impaction
substrates. In each size fraction the particles are collected on 25 mm collection substrates that are
weighed before and after the measurement to obtain gravimetric size distribution of the particles.
Other LPI characteristics include low inter-stage wall-losses and robust yet easy-to-use operation.
C. Number Size distribution measurement systems
N1) Laser Scattering particle size distribution Analyser (LSA) is used to measure particles with
diameters from 20 nm up to 1000 μm. The principle is based on measuring the angular variation in
intensity of light scattered as a laser beam passes through a dispersed particulate sample. Large
particles scatter light at small angles relative to the laser beam and small particles scatter light at
large angles. The angular scattering intensity data is then analysed to calculate the size of the
particles responsible for creating the scattering pattern, using the Mie theory of light scattering. The
shorter the wavelength of the irradiated light, the smaller the diameter becomes of particles that
can be measured. The particle size is reported as a factor of volume, area, length or particle number
(Kukutschová et al. 2009).
N2) The Aerodynamic Particle Sizer (APS) provides real-time aerodynamic measurements of particles
from 500 nm to 20 μm. The APS counts particles of all size fractions at each instant of the sampling
period and allows for the monitoring of particle size distribution and size variation during the entire
period of the test cycle. The particle size is calculated as the aerodynamic diameter from the time of
flight for passing between two laser beams. Since the APS spectrometer has high signal response, it
is possible to obtain the short-time profiles of particle size distribution (Iijima et al. 2007). APS
measures the number concentration as a function of the aerodynamic particle diameter. Mass
concentrations can also be calculated assuming a density of about 2,800 kg/m3 (Sjodin et al. 2010).
N3) An Engine Exhaust Particle Sizer (EEPS) consist of a particle charger, a classification column, and
a series of detectors and it is used for on-line measurement of particle size distributions in the range
from 5.6 to 560 nm. The instrument draws a sample of the particle flow into the inlet continuously.
Particles are positively charged to a predictable level using a corona charger. Charged particles are
then introduced to the measurement region near the centre of a high-voltage electrode column and
transported down the column surrounded by HEPA-filtered sheath air. A positive voltage is applied
to the electrode and creates an electric field that repels the positively charged particles outward
according to their electrical mobility. Charged particles strike the respective electrometers and
transfer their charge. A particle with higher electrical mobility strikes an electrometer near the top;
whereas, a particle with lower electrical mobility strikes an electrometer lower in the stack. This
multiple-detector arrangement using highly sensitive electrometers allows for simultaneous
concentration measurements of multiple particle sizes. The use of a corona discharge is necessary to
compensate for the lower detection sensitivity of electrometers versus CPCs. The drawback is that
the corona creates a significant fraction of multiply charged particles which are detected at
commensurately lower size. Hence, inversion of the current distribution becomes a complex process.
This explains the sometimes large differences between the results from these mobility
spectrometers as compared to SMPS derived size distributions. These differences can translate as
well to mass differences compared to filter or other mass based instruments. Mobility
spectrometers have lower sensitivity and size resolution than the SMPS, but their high time
resolution (0.1–1 Hz) is advantageous for transient measurement.
N4) PTrak counter is a particle measurement instrument which use light scattering to count particles
in real time after they are grown to micron size range between 0.02 and 1 μm. The P-trak ultrafine
particle counter is a portable version of a condensation particle counter (CPC). The working principle
of PTrak is more or less the same of all CPCs. Particles are drawn through the instrument by a pump.
Upon entering the instrument, particles pass through a saturator tube where they mix with alcohol
vapours. The particle/alcohol mixture is then drawn into a condenser tube, which cools the
air/particle stream causing alcohol to condense on the particles and the particles grow into
detectable droplets. The droplets then pass through a focused laser beam, producing flashes of
scattered light. The scattered light flashes are sensed by photodetector and counted to determine
particle number concentration. The temperatures of the saturator and condenser and properties of
the working fluid determine the lower detectable size, which is typically in the range of 3–10 nm.
The CPCs in the European legislation must be full-flow (the total inlet flow must pass the counting
optics), and have a 50% counting efficiency at 23 nm.
N5) Optical Particle Counters (i.e GRIMM 1.108 and 1.109) are aerosol spectrometers with an
operating principle similar to that of photometers. The major difference is that the OPC optical
sensing volume, formed by the intersection of a focused light beam with a narrow particle beam, is
much smaller so that only one particle is illuminated at a time. The scattered light is detected by a
photo detector as an electrical pulse. The particle size is determined from the pulse height using a
calibration curve typically obtained from measurements with spherical particles of known size and
composition. The lower detection size limit is above 100 nm so it cannot be used for size distribution
in the lower nanoparticle range. For particles large enough to be detected, OPCs are capable of
measuring concentrations of up to 103 cm-3 before coincidence errors become too large. A
disadvantage of OPCs is that uncertainty in refractive index often leads to significant variability in
derived size distributions, even for the ideal case of homogeneous spherical aerosol particles
(Giechaskiel et al. 2014). This means that since an optical particle counter is sensitive to the shape
and refractive index of the particles, the measured particle sizes and thus the number distributions
are approximate (Wahlstom et al. 2010a).
N6) Scanning Mobility Particle Sizer (SMPS) is used to measure number size distributions for particles
in the mobility size range from 10 to 445 nm. It combines a differential mobility analyzer (DMA) for
size classification along with an electrometer or a condensation particle counter (CPC) for the
detection of the particles. The particles are charged in a controlled manner and then sequentially
classified according to their electrical mobility. With the controlled charging, particle electrical
mobility corresponds to particle size. The counter subsequently registers the particles in sequential
size classes. The counter is a condensation nuclei counter which uses condensation to optically count
particles down to 10 nm. A few inter-comparisons of size distributions with SMPS systems of the
same or different manufacturers have shown differences of the size distributions of 10%. However
differences of >20% can also be found, especially for non-spherical particles. Such differences can be
attributed to differences in particle charging efficiency, CPC counting efficiency, diffusion losses and
non-ideal DMA transfer functions. Despite the potential for variability, the SMPS is arguably the
most accurate instrument for high resolution size distributions of diluted exhaust aerosols
(Giechaskiel et al. 2014). Mass concentrations can also be calculated assuming a density of 1,000
kg/m3.
N7) Electrical Low Pressure Impactor (ELPI) is a cascade impactor which classifies particles according
to their aerodynamic diameter. It is used to collect second by second information on particle size
distributions. The ELPI operates by using a corona discharge to charge the particles prior to their
introduction into the cascade impactor portion of the instrument. This portion includes several
stages with D50% cut points in the size range of 16.5 nm to 7 μm. As the particles within specific size
ranges impact onto the corresponding stages, electrometers record the charge that is deposited. The
resulting currents are converted to particle number concentrations by dividing by the charging
efficiency, which depends on particle diameter, and correcting for particle losses on preceding
stages. These, can also be converted to mass-weighted size distributions using an approximate value
for the density of the particles. Integration over the size distribution gives the total number and
mass of wear particles generated per test. ELPI is used quite often for research in engine tests beds
and generally the agreement with the PM mass is within 10% for emissions in the range of non-DPF
vehicles. At low emission levels the agreement is not so good due to the filter artefact. With other
instruments (e.g. LII or PASS) the agreement at low levels (e.g. <3 mg/mi) is better than 10–20%
(Giechaskiel et al. 2014).
D. Chemical and morphology characterization
C1) Electron microscopy methods provide a means to examine the sizes and morphology of particles.
This applies mainly to solid particles since semi-volatile particles are difficult to detect because they
evaporate under vacuum and heating by the electron beam. Scanning Electron Microscope (SEM)
uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid
specimens. The signals that derive from electron-sample interactions reveal information regarding
morphology, chemical composition, and crystalline structure and orientation of materials making up
the sample, but they yield no information about the compounds constituting the wear particles. This
information is needed if we are to understand the chemistry of the wear particles (tyres and brakes)
and estimate the temperature in the contact (brakes). The method has other disadvantages like the
high time required for analyzing a sufficient number of particles in order to ensure statistical
representatives. Also, care must be taken to interpret 3 dimensional shapes and sizes from the 2
dimensional images. SEM is usually coupled with Energy Dispersive X-Ray Spectroscopy (EDX) for
chemical characterization of particles with diameters between 100-1000 nm (Österle et al. 2008).
C1
Scanning Electron Microscope (SEM)
Type of instrument
Measurement Principle
Output
Measuring range
What can measure
Electron Microscope
Electron interaction with visual detection
SEM images of wear particles
Not applicable
Morphology and size of wear particles; Focuses on the
sample’s surface and composition; Provides a three
dimensional image; Appropriate for nanoparticles
Quantitative analysis of elements; Organic compounds
Method good to be combined with other methods (EDX or
XRD or XRF) for quantitative analysis
What cannot measure
Main limitations
C2) Transmission Electron Microscopy (TEM) uses high energy electrons which are accelerated to
nearly the speed of light. When an electron beam passes through a thin-section specimen of a
material electrons are scattered. A sophisticated system of electromagnetic lenses focuses the
scattered electrons into an image or a diffraction pattern, or a nano-analytical spectrum, depending
on the mode of operation. Each of these modes offers a different insight about the specimen. The
imaging mode provides a highly magnified view of the micro- and nanostructure. The diffraction
mode displays accurate information about the local crystal structure. Nano-analytical modes (x-ray
and electron spectrometry) tell researchers which elements are present in the material. TEM has
much higher resolution compared to SEM. Furthermore it is able to provide details about the
internal composition of the sample. TEM is usually coupled with Energy Dispersive X-Ray
Spectroscopy (EDX) or Energy Filtered (EF) system for chemical characterization of particles with
diameters < 100 nm (Österle et al. 2008).
C2
Transmission Electron Microscope (TEM)
Type of instrument
Electron Microscope
Measurement Principle
Output
Measuring range
What can measure
What cannot measure
Main limitations
Electron interaction with visual detection
TEM images of wear particles
Not applicable
Morphology and size of wear particles; Elemental
composition; Appropriate for crystallites in the range of 21000 nm; Much higher resolution compared to SEM
Quantitative analysis of elements; Organic compounds
Method good to be combined with other methods (EDX or
XRD or XRF) for quantitative analysis; Provides a 2
dimensional image
C3) X-Ray Fluorescence (XRF) utilizes x-rays for qualitative and semi-quantitative inorganic chemical
analysis of unknown samples. X-Rays bombard atoms in the sample and electrons are removed or
ejected from inner shells. Electrons from outer shells of the atom drop down to fill the vacant
position and to return the atom to a more stable, ground state. When this occurs energy is
produced, some of which is in the form of X-Rays. Each element has its own unique X-Ray signature
meaning that X-Rays from a sample can provide detailed information about it. The main advantages
of XRF include easy sample preparation compared to other inorganic analysis methods, multielement determination (all elements between Na and U can be simultaneously analyzed), as well as
the possibility to screen completely unknown samples. On the other hand, XRF provides qualitative
analysis of elements without indicating the phases which are present in the sample, while
quantitative analysis of elements is not very accurate.
C3
X-Ray Fluorescence (XRF)
Type of instrument
Measurement Principle
Output
Measuring range
What can measure
Spectrometer
X-Ray fluorescence energy detection
Spectra of elements and quantification (counts/energy)
Down to ppm concentrations for most elements
All elements with atomic number greater than 11; Nondestructive method; Easy sample preparation; Possibility to
screen completely unknown samples
Organic compounds; Elements lighter than Na
No information about the phases of the element present;
Semi-quantitative method good to be combined with other
methods (XRD)
What cannot measure
Main limitations
C4) Energy Dispersive X-Ray Spectroscopy (EDX or EDS) is a variant of XRF which makes use of the Xray spectrum emitted by a solid sample bombarded with a focused beam of electrons to obtain a
localized chemical analysis. All elements from Be to U can be detected in principle, though not all
instruments are equipped for 'light' elements (Z < 10). High energy beam of charged particles may
excite an electron in an inner shell, ejecting it from the shell while creating an electron hole where
the electron was. An electron from an outer, higher-energy shell then fills the hole, and the
difference in energy between the higher-energy shell and the lower energy shell may be released in
the form of an X-ray. The number and energy of the X-rays emitted from a specimen can be
measured by an energy dispersive spectrometer. As the energy of the X-rays is characteristic of the
difference in energy between the two shells, and of the atomic structure of the element from which
they were emitted, this allows the elemental composition of the specimen to be measured. EDX is
usually coupled with SEM for chemical characterization of particles with diameters between 1001000 nm and allowing thus phase distinction (Österle et al. 2008).
C4
Energy Dispersive X-Ray Spectroscopy (EDX or EDS)
Type of instrument
Measurement Principle
Output
Measuring range
What can measure
Spectrometer
X-Ray dispersive energy detection
Spectra of elements and quantification (counts/energy)
Down to ppm concentrations for most elements
All elements with atomic number greater than 10; Nondestructive method
Organic compounds
No information about the phases of the element present;
EDX is usually coupled with SEM for phases characterization
of particles with diameters between 100-1000 nm; Not all
instruments are able to measure light elements (Z<10)
What cannot measure
Main limitations
C5) X-Ray Diffraction Spectroscopy (XRD) is an instrumental technique that is usually used to study
crystalline materials. Its main difference from XRF is that it can determine the presence and amounts
of minerals species in sample, as well as identify phases. The three-dimensional structure of nonamorphous materials is defined by regular, repeating planes of atoms that form a crystal lattice.
When a focused X-ray beam interacts with these planes of atoms, part of the beam is transmitted,
part is absorbed by the sample, part is refracted and scattered, and part is diffracted. When an X-ray
beam hits a sample and is diffracted, we can measure the distances between the planes of the
atoms that constitute the sample by applying Bragg's Law. The characteristic set of d-spacings and
theirs intensity generated in a typical X-ray scan provides a unique "fingerprint" of the phases
present in the sample. When properly interpreted, by comparison with standard reference patterns
and measurements, this "fingerprint" allows for identification of the material. XRD methods for
crystallite size determination are applicable to crystallites in the range of 2-100 nm. The diffraction
peaks are very broad for crystallites below 2-3 nm, while for particles with size above 100 nm the
peak broadening is too small. Due to the complexity of XRD data analysis, the chemical composition
of the sample must be known in advance by a semi-quantitative analysis (i.e. XRF) in order to
accurately pin point the phases present in your sample. XRD is not good for organic materials, as
they often have very similar signatures. Both XRD and XRF are non-destructive methods.
C5
X-Ray Diffraction Spectroscopy (XRD)
Type of instrument
Measurement Principle
Output
Spectrometer
X-Ray diffraction patterns for detection
Spectra of elements and their phases and quantification
(counts/energy)
Measuring range
What can measure
All elements with atomic number greater than 13 and their
What cannot measure
Main limitations
phases; Appropriate for crystallites in the range of 2-100
nm; Non-destructive method
Elements with atomic number smaller than 13; Organic
compounds
Chemical composition of the sample must be known in
advance by a semi-quantitative analysis
C6) Proton Induced X-Ray Emission (PIXE) has the same operating principle as the previously
described spectroscopy methods. In PIXE the incident beam particles (usually 3 MeV protons) eject
inner shell electrons from the target atoms which results in the emission of characteristic X-rays.
With a suitable x‑ray detector more than 70 elements with atomic number larger than 13 can be
detected. PIXE is similar to EDX only with electron microprobes. However, due to the complete
absence of primary bremsstrahlung the sensitivity of PIXE is enhanced by about a factor of 100
compared to EDX and is of the order of ppm for most elements. Quantitative analysis is also possible
with the appropriate corrections to absorption and x-ray yields. PIXE is often used together with
imaging nuclear microprobes for spatial elemental mapping.
C6
Proton Induced X-Ray Emission (PIXE)
Type of instrument
Measurement Principle
Output
Measuring range
What can measure
Spectrometer
Proton bombarding followed by X-Ray detection
Spectra of elements and quantification (counts/energy)
Down to ppm concentrations for most elements
All elements with atomic number greater than 13; Higher
sensitivity compared to other spectroscopy methods
Elements with atomic number smaller than 13; Organic
compounds
No information about the phases of the element present;
Has to be used with other techniques to gain information
regarding the phases
What cannot measure
Main limitations
C7) Thermal/optical carbon analyzer working principal is separated into two steps: first, the sample
is heated in an inert atmosphere to volatilize organic material to CO2 or CH4. Carbon measured in this
step is designated as Organic Carbon (OC). After that oxygen is introduced to the remaining sample
and heated to higher temperatures (up to 900°C). The measured carbon in this step is designated as
Elemental Carbon (EC). In this process, OC may char in an oxygen free atmosphere and erroneously
be detected as EC. Some refractory OC may also be counted as EC. Finally, some EC may be counted
as OC due to the activity of catalytic or oxidizing species adsorbed in the PM. Hence, the split
between EC and OC with this method is not accurate. Different measurement protocols in terms of
heating rate and oxidation temperature, as well as optical correction methods for charring may be
used. Hence, the EC/OC split is operationally defined when thermal/optical analysis is involved.
Inter-laboratory comparison studies show that different thermal methods agree within 5–15% on
the total carbon (EC+OC) concentrations, but the EC and OC concentrations can differ by a factor of
more than two (Giechaskiel et al. 2014). One important benefit of using thermal-optical carbon
analysis is the availability of widely-accepted and extensively used calibration methods.
C7
Thermal/Optical Carbon Analyzer
Type of instrument
Measurement Principle
Output
Measuring range
Carbon analyzer
Oxidation of PM and optical detection
Flame Ionization Detector (FID) signal of CH4 quantification
Down to ppm concentrations for both EC and OC (less than
1 μg/m3 for atmospheric samples)
Elemental and Organic Carbon; Total Carbon
Specific organic compounds; Inorganic compounds
The split between EC and OC is not accurate; EC and OC
concentrations can differ from the actual in a factor of 2 or
more; Requires different filter for PM collection (quartz)
What can measure
What cannot measure
Main limitations
C8-C9) Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma
Atomic Emission Spectroscopy (ICP-AES) are analytical techniques used for the detection of trace
metals and elements. In both techniques the sample is typically introduced into the ICP plasma as an
aerosol where it is completely dissolved and the elements in the aerosol are converted first into
gaseous atoms and then ionized towards the end of the plasma. Excited ions and atoms can be
detected either by measuring the m/z ratio of the different ions formed (MS) or by measuring the
electromagnetic radiation which is emitted at wavelengths characteristic of each element (AES). In
both methods the sample has first to be digested. ICP-MS has detection limits for most elements
equal to or better than those obtained by Graphite Furnace Atomic Absorption Spectroscopy
(GFAAS). One advantage is the ability to handle both simple and complex matrices with a minimum
of matrix interferences due to the high-temperature of the ICP source. Also ICP-MS has superior
detection capability to ICP-AES with the same sample throughput, as well as the ability to obtain
isotopic information. None of these techniques can be used for organic compound determination.
C8-C9
Inductively Coupled Plasma – Atomic Emission
Spectroscopy/Mass Spectrometry (ICP-AES/MS)
Type of instrument
Measurement Principle
Output
Mass or Atomic Emission Spectrometry
Conversion to plasma & atomic emission or mass detection
Spectra of elements and quantification (counts/mass) or
(counts/wavelength)
Down to ppb concentrations for all elements
A wide range of metals and trace elements; Ability of
handling both simple and complex matrices; High sensitivity
and selectivity
Organic compounds
Requires difficult and time consuming digestion procedure;
Expensive instrumentation; MS detection has superior
detection capability to AES; MS analysis is much faster and
multi-element compared to AES
Measuring range
What can measure
What cannot measure
Main limitations
C10) GC-MS is an analytic technique which combines the separating power of Gas Chromatography
with the detection power of Mass Spectrometry. MS is a wide-ranging detecting technique, which
involves the production and subsequent separation and identification of charged species according
to their mass to charge (m/z) ratio. Identification of chemical species is accomplished by matching
both the gas chromatographic retention times to pure components and mass spectral fragmentation
patterns to standard MS libraries. GC uses a carrier gas to transport sample components through
either packed columns or hollow capillary columns containing the stationary phase. In general GC
columns have smaller internal diameter and are longer than HPLC columns. GC-MS is used for
determination of organic compounds of wear particles. In this method the sample has first to be
extracted through a difficult and time consuming procedure. Aatmeeyata et al. (2010) proposed the
following temperature program for PAHs separation: initial temperature of 70 °C (4 min), heated to
150°C at 15°C min−1, then to 210°C at 3°C min−1, then held at 210°C (8 min), and finally heated to
290°C at 2°C min−1 (5 min). GC-MS presents lower sensitivity for PAHs detection compared to HPLC
techniques coupled either with UV or FLD.
C10
Gas Chromatography Mass Spectrometry (GC-MS)
Type of instrument
Measurement Principle
Output
Measuring range
What can measure
What cannot measure
Main limitations
Gas Chromatography
Column separation followed by mass detection
Chromatogram of organic compounds and quantification
Down to 10 ng/ml for most PAHs
Full range of organic compounds
Requires difficult and time consuming extraction
procedure; Lower sensitivity for PAHs compared to HPLC
C11) High Performance Liquid Chromatography (HPLC) is an analytical method that yields high
performance and high speed compared with traditional column chromatography. It has the same
operating principle as GC with the major difference being at the sample condition during separation
(liquid instead of gas). It is based on the principal that under the same conditions, the time between
the injection of a component into the column and the elution of that component is constant.
Fluorescence detector (FLD) is probably the most sensitive among the existing HPLC detectors.
Typically, fluorescence sensitivity is 3 orders of magnitude higher than that of the UV detector for
strong UV absorbing materials. FLDs are very specific and selective among the others optical
detectors. This is normally used as an advantage in the measurement of specific fluorescent species
in samples like for example PAHs. HPLC-FLD has been used for determination of PAHs in tyre wear
particles with higher sensitivity compared to GC-MS.
C11
High Pressure Liquid Chromatography Fluorescence
Detector (HPLC-FLD)
Type of instrument
Measurement Principle
Output
Measuring range
Liquid Chromatography
Column separation followed by fluorescence detection
Chromatogram of selected PAHs and quantification
Down to 0.02 ng/ml for most PAHs
What can measure
What cannot measure
Main limitations
Organic compounds that fluorescence (PAHs); Higher
sensitivity compared to other detectors
Compounds without fluorescence radiation
Requires difficult and time consuming extraction procedure