APPENDIX D
A&WMA 2001 CONFERENCE - Student Poster Session
DESIGN AND EVALUATION OF A SEMI HI-VOL AIR SAMPLER FOR PM2.5 CHEMICAL
ANALYSIS IN DOWNTOWN TORONTO
by
Julia Tsai, Janet Ma, Greg J. Evans*
M. A. Sc. Candidate
University of Toronto, Chemical Engineering & Applied Chemistry
200 College Street, Toronto, Ontario, Canada, M5S 3E5
INTRODUCTION
Originally, interest in the environmental impact of particulate matter (PM) focussed on total
particulate matter (TSP); however, this focus shifted to PM10 (particle size  10m), as smaller
particles are capable of long-range and trans-boundary transport. Over the last ten years greater
attention has been placed on the identifying any relationships between PM 10, and PM2.5 in particular,
and adverse health effects. Epidemiological studies have attempted to demonstrate a particle size, the
chemical composition and particle toxicity relationship, but the results are still inconclusive.
Therefore, it is important to continue studying both the size and composition of airborne PM to better
evaluate and understand the factors that affect the particles’ toxicity and health risks.
The fractionation of particulates into inhalable PM10 and respirable PM2.5 is commonly
practiced for PM monitoring1. This paper describes a semi hi-vol dichotomous air sampler that was
developed in our laboratory. The flowrate was purposely set to semi hi-vol to minimize the exhaust
air volume flow into the laboratory. Two distinct PM10 and PM2.5 impactors units provide size
fractionation to PM10 and PM2.5.
Another feature of this air sampler is that the sampling duct is
equipped with six sampling outlets, which allows simultaneous analysis by multiple instruments
within the laboratory to facilitate comparison between results. The air sampler achieved PM2.5
sampling using a single stage multi-nozzle PM10 impactor and a second stage PM2.5 commercial
impactor.
After-filter analysis was done by inductively coupled plasma – optical emission spectrometry
(ICP-OES), instrumental neutron activation analysis (INAA) and ion chromatography (IC).
ICP-OES and INAA are fast and sensitive techniques for elemental analysis2.
Both
The chemical
information is being used for ongoing research into source apportionment via receptor modeling, the
fate of transport of PM in the atmosphere, and health risk studies.
MATERIALS AND METHODS
Description of the Sampler
The in-house sampler consisted of a 4 sampling duct located 4 m off the ground, a multinozzle PM10 impactor, six sampling outlets, six isokinetic probes, a second stage PM2.5 commercial
impactor, a filter distributor and holder, and a flow controller (Figure 1). All components were made
of aluminium.
The first stage of the sampler was an inertial impactor that removed particles larger than 10
m. These were collected on a multi-nozzle circular Vaseline®-coated Whatman cellulose filter.
Before the second stage, the sampling duct was equipped with four ½  and two 1 sampling
collection outlets. Six isokinetic sampling probes were also designed to collect representative PM
samples from the centre of the sampling duct. The second stage of the sampler was a commercial
impactor. This impactor was the No. 2 plate from a Sierra-235 five-stage cascade impactor and
removed PM that was less than 10 m and greater than 2.5 m. These PM sizes were collected on a
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slotted coarse Whatman cellulose filter. All cellulose collection substrates were coated with 1:7
Vaseline®: hexane mixture to minimize particle bounce and re- entrainment.
Sample Inlet
PM10
Impactor
Sampling Duct and
Sample Outlets
PM2.5 Impactor
Sample
Distributor
Filter Holder
Flow
Controller
Hi-Vol. Motor
Blower
Figure 1: PM Sampling System
Finally, PM2.5 was collected through a 7diameter circular opening on a fine uncoated 8 
10 Whatman 41 cellulose after-filter. This facilitated division of the filter sample and reduced the
amount of filter digested in the subsequent PM elemental analysis. Cellulose filter paper was used in
the study because it was low in cost and was easily digested. The sampler was operated between 40
L/min and 280 L/min and a constant flow was maintained using a digital mass flow controller
(Model G312-LF, Andersen Instruments Inc.).
Description of the Impactor
Three impactor designs for PM10 were proposed and evaluated. The final impactor design
featured the nozzles for the nozzle plate and the impaction plate arranged in a misaligned fashion;
commonly seen in commercial multi-nozzle impactors. The number of nozzles and the nozzle
diameter (W) were designed based on the desired cut point (Dp50) and the flow rate (Q) 3,4. The Dp50,
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the aerodynamic diameter of particles collected with 50% efficiency, was calculated from the Stokes’
number (Stk), as defined in equation (1). The value Stk50 is the critical value corresponding to Dp50
and is now commonly used to characterize impactor efficiency. Also, for the circular jet impactor,
the Dp50 corresponds to a Stk50 of 0.5.
pd p Cc vo
Stk =
9W
4 p C c d p Q
2
2
5
=
(1)
9W 3
where p is the particle density (g/cm3), dp is the diameter of the particle (m), W is the
nozzle diameter (cm), v0 is the jet velocity (cm/sec), Q is the sampler flow rate and Cc is the
Cunningham’s slip correction.
The key impactor design parameters are summarized in Table 1 and the principle of
impaction6 is illustrated in Figure 2. Two important dimensionless parameters are S/W and jet
(W) - Impaction Nozzle Diameter
W
Acceleration nozzle
T
(T) - Throat
Acceleration nozzle exit
(S) – Jet-to- Plate
Distance
S
Streamline
Impaction Plate
Trajectory of
impacted particle
Trajectory of particle
too small to impact
Figure 2. Principle of impaction
Reynold’s number (Rej), where S/W influences the Dp50 and Re influences the sharpness of cut.
The final nozzle plate design consisted of 30 nozzles, symmetrically patterned in three annuli
within the 10.16 cm (4 diameter) circle, as shown in Figure 3a. Similarly, the impaction plate
consisted of 56 holes arranged in a staggered fashion to the nozzle plate above, each with a diameter
of 0.5776 cm as shown in Figure 3b. Figure 3b illustrates the misaligned nozzle arrangement (A), the
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custom-made 4 greased cellulose filter paper (B) and the particle deposits from a 24-hour sampling
period (C).
Nozzle Diameter, D (cm)
Jet Velocity (cm/sec)
Re
S/W
L/W
Stk50
Cc
0.789
284
1523
1.61
1.9
0.47
1.0
Table 1. Final design characteristics of the impactors for flow rate = 280 L/min. Note: S, W, T are
expressed in cm (Figure 2).
A
B
C
Figure 3b: Impaction Plate of Impactor Design II
Figure 3a. Nozzles symmetircally patterned.
with Collection Substrate
Laboratory Characterization of the Sampler
The sampling system was evaluated with an
Aerodynamic Particle Sizer (APS) (Model 3320,
TSI Inc.).
The experimental set-up used for the
…
…
…
…
.
.
Incoming
particles from an
urban street
characterization of the impaction section is shown in
Figure 4. To evaluate Dp50, the concentration and
Impactor / TSP
Unit
Upstream
size distribution of particles were measured by the
APS for 30 min upstream, then 30 min downstream.
This cycle was repeated 6 times in each experiment.
The PM10 impactor plate and the TSP plate in the
first stage were alternated in each experiment. The
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PM2.5 impactor
TSI 3320
APS
Downstream
Hi-Vol Blower
Figure 4. Experimental set up for system
characterization
APS was used to measure particles in the size range 0.5-19 m and was operated at a flow rate of 5
L/min. Collection efficiency curves were used to determine the cut point. Collection efficiency was
determined as follows for each particle size and the number concentration of particles upstream and
downstream are denoted as Cup and Cdn, respectively:
Collection Efficiency =
C up  C dn
(2)
C up
PM2.5 Chemical Analysis
Each filter sample was divided into quarters for analysis by ICP-OES, INAA, and IC. Two of
the filter quarters were microwave (Perkin Elmer Multiwave) digested in a 50% concentrated nitric
acid (EM Science, OminiTrace®) for 36 min. and diluted to 10mL before ICP-OES analysis. The
duplicate analyses were used as a precision check. The remaining two filter quarters were analyzed
by INAA at the SLOWPOKE II Facility at the Royal Military College, Kingston, Ontario and by IC
at Philip Analytical Services Inc. The INAA samples were irradiated for 5 min. at 5.01011 n/cm2s
and then counted for 5 min. For IC, the filter paper was centrifuged in 25mL of water for 1 hour and
7 anions were analyzed: F-, Cl-, NO2-, Br-, NO3-, PO43-, and SO42-.
RESULTS and DISCUSSION
Air Sampler Evaluation
The sampler system was evaluated for its ability to deliver representative samples while the
impactors were evaluated in terms of their Dp50 and collection efficiency. The size distribution of
TSP samples taken from a street directly and from the sampler duct matched closely.
This
demonstrated that the isokinetic sampling was not creating any bias and that there were negligible line
losses.
The sampling duration of all the runs was kept constant for 30 min. to determine the
impactors’ Dp50. The samples were collected sequentially to minimize aerosol variations in the
ambient air. The results were presented as collection efficiency curves in Figure 5. Since the
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concentrations of 8-20 m particles were low and highly variable, the curve was only plotted up to 8
m. Some erratic transport of larger particles, possibly due to particle bounce, did occur and this
could not be eliminated despite substantial efforts. First, a combination of different plates from the 5stage commercial cascade impactor was tested. A PM2.5 cut off was attainable with plate No. 2 at a
flow rate of 280 L/min as illustrated in Figure 5. The cut point was next evaluated while sampling
with other instruments.
When the Laser Ablation Mass Spectrometer (LAMS) instrument was
operating at a flow rate of approximately 65 L/min, the cut point changed from 2.5 m by an
insignificant amount, as also illustrated in Figure 5. This demonstrated that a flow rate of 65 L/min
did not affect the cut point of the No. 2 plate.
To determine the effect of the sampling duration, one 10-min. sampling duration experiment
was performed and no obvious deviation in the sharpness in cut off was observed, as illustrated in
Figure 5. This is consistent with the results of Demokritou et.al.7 Finally, there was an insignificant
difference between the sharpness of the cut off when greased cellulose and glass fibre were used as
Collection Efficiency, %
the collection substrate.
100
90
80
70
60
50
40
30
20
10
0
0
1
2
3
10 min, greased cellulose
with LAMS
30 min, greased cellulose
30 min, glass fibre
4
5
6
7
8
9
10
Aerodynamic diameter, m
Figure 5. PM2.5 Collection efficiency of plate No.2 as a function of the aerodynamic diameter
Chemical Analysis and Comparison
A short sampling campaign was carried out everyday from December 11 to December 20,
2001. The PM2.5 sample was collected over a period of 24 hours starting from 6 am each day. The
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ICP-OES results showed that out of the 19 elements analyzed, Be, Cd, Co, Li, Ni, and V were usually
close to or below the detection limit (Figure 6). The analytical procedure was tested with NIST
Standard Reference Material 1648 Urban PM. Recoveries for all 15 certified elements were above
90% except Al, Cr, and Cd due to incomplete digestions. Duplicate analysis also showed good
agreement. Similarly, out of the 12 elements analyzed by INAA, only Al, Br, Ca, Cl, Mn, Na and V
were above detection limits (Table 2). IC results also revealed that only Cl -, NO3-, and SO42contributed to the PM concentrations in measurable amounts. Chloride was found to have high
concentrations, perhaps as a result of increased road salt use during the snow season (Figure 7).
Major constituents of Toronto PM for the 10-day December sampling campaign were mostly crustal
elements including: Al, Fe, Ca, K, Mg, and Na, with their concentrations ranging from 0.1 to 2
g/m3. Daily trends were constructed for some of the detectable elements, and complimentary
methods compared (Figure 7-9). The results between ICP-OES and INAA were agreeable with less
than 15% difference, and the LAMS results showed a similar trend with the filter results. Overall, the
data showed that sufficient PM2.5 was collected to carry out elemental analysis for most trace
elements.
Al
Ba
Be
ICP
X
X
X
INAA
X
X
Br
X
Ca
Cd
X
X
X
Cl
X
Co
Cu
Cr
Fe
K
Li
Mg
Mn
Na
Ni
Pb
Sr
V
Zn
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
100000
10000
1000
100
10
1
0.1
0.01
24 SO4 3
PO 3 O
N 2O
N
F
l
C
r
B
S
In
I
Sn
Ti
y
D
U
o
C
Zn
V
Sr
Pb
i
N
a
N
n
M
g
M
Li
K
Fe
u
C
r
C
d
C
a
C
a
B
l
A
Mass Concentration, ng/m3
Table 2. Elements investigated by ICP and INAA. The shaded X indicates below detection limit.
ICP
INAA
IC
Figure 6. Detection limits for ICP-OES, INAA, and IC instruments.
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Mass Concentration, ug/m3
18
16
14
12
10
8
6
4
2
0
Cl (avg) -INAA
Dec.11
Dec. 12
Dec. 13
Dec. 14
Dec. 15
Dec. 16
Cl-
Dec. 17
Dec. 18
Dec. 19
Dec. 20
Mass Concentration, ug/m3
Figure 7. Temporal trends of Chlorine from filter-collected Toronto PM: INAA vs. IC
10
Na
Al
1
Mn
0.1
0.01
Dec.11
Dec.12
Dec.13
Dec.14
Dec.15
ICP
Dec.16
Dec.17
Dec.18
Dec.19
Dec.20
INAA
Mass Concentration, ug/m3
Figure 8. Comparison of Na, Al, and Mn time trends: ICP vs. INAA.
0.06
0.05
LAMS
0.04
0.03
ICP-AES
0.02
0.01
0
Dec. 11 Dec. 12 Dec. 13 Dec. 14 Dec. 15 Dec. 16 Dec. 17
Dec. 18 Dec. 19 Dec. 20
Figure 9. Comparison of Pb analysis using LAMS and ICP-OES
CONCLUSIONS
A semi hi-vol air sampler for ambient PM2.5 monitoring was developed and evaluated. The
system allowed simultaneously sampling with other on-line instruments. The collection efficiency
experiments showed a Dp50 of 2.5 m was achieved at a flow rate of 280 L/min. Results also
indicated that other on-line instruments did not influence the cut point when in operation with the
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sampler. Preliminary chemical analysis by ICP-OES, INAA, and IC for the PM-collected filter
demonstrated that the sampler collected sufficient amounts of PM2.5 for trace elemental analysis. The
ICP-OES, INAA, and IC results were in reasonable agreement and followed the same temporal
trends. The LAMS results compared to that of the PM-collected filter showed that the sampler is able
to deliver the same PM to different instruments. The main limitation encountered in evaluating the
sampler efficiency was the high variability of the ambient PM concentrations.
ACKNOWLEDGEMENTS
The author wishes to acknowledge: Environment Canada and Toxic Substance Research
Initiatives for their financial support, the Perkin Elmer for their support of ANALEST Facility at the
University of Toronto, Patrick Lee for his advice on ICP-OES, and Phillip Tan for his technical
support.
REFERENCES
1. Jervis, R.E.; Tan, P.; and Evans, G.J. (1999). Biological Trace Element Research, 71-72: 223
2. Landsberger, S. and Creatchman, M. (1999). Elemental analysis of airborne particles. Gordon
and Breach Science Publishers, Canada.
3. Marple, V.A. (1970). Ph.D. Thesis, University of Minnesota, Minneapolis, MN.
4. Hinds, William C. (1999). Aerosol Technology Properties, Behaviour and Measurements of
Airborne Particles, John Wiley & Sons, Inc., New York.
5. Kim, H.T.; Kim, Y.J. and Lee, K.W. (1998). Aerosol Sci. and Technol. 29: 350.
6. Marple, V.A.; et .al. (1993). Inertial, Gravitational, Centrifugal and Thermal Collection
Techniques. In Aerosol Measurement: Principles, Techniques, and Applications, ed. K. Willeke
and Paul A.Baron. Chap. 11, p. 212. New York: Van Nostrand Reinhold
7. Demokritou, P.; Kavouras, I.G.; Harrison, D. and Koutrakis, P. (2001). Air & Waste Manage.
Assoc. 51: 514
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DESIGN AND EVALUATION OF A SEMI HI-VOL AIR SAMPLER FOR PM2.5 CHEMICAL
ANALYSIS IN DOWNTOWN TORONTO
Julia Tsai, Janet Ma, Greg J. Evans*
M.A.Sc. Candidate
University of Toronto, Chemical Engineering & Applied Chemistry
200 College Street, Toronto, Ontario, Canada M5S 3E5
Abstract
A semi hi-vol dichotomous air sampling system was designed and developed to collect particulate
matter (PM) at a flowrate of 280 L/min (10 ft3/min) from downtown Toronto for subsequent PM2.5
analysis in the Urban Aerosol Laboratory at the University of Toronto. After passing through an
initial PM10 impactor, small portions of this air stream are diverted to different instruments within the
laboratory such as an Aerodynamic Particle Sizer (APS) and an on-line Laser Ablation Mass
Spectrometer (LAMS). The bulk of the PM then passes through a PM2.5 impactor and is collected on
a 810 cellulose filter paper. The PM10 separation system consists of a custom-designed 30-nozzle
impactor plate and the PM2.5 stage consists of an Anderson Cascade impactor plate No.2. The
sampling system cut off was evaluated with the APS by determining the impactor collection
efficiency as a function of the particle diameter. Results indicated a Dp50 of 2.5 m was achieved and
some particle bounce was also observed. Chemical analyses of the filters were performed using ICPOES, INAA, and IC. The filter papers were divided into quarters. Two of the filter paper quarters
were microwave digested and analyzed by ICP-OES.
The remaining two filter quarters were
analysed by INAA and IC separately. Results showed that out of the 19 elements analyzed by ICPOES (Al, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, Sr, V, Zn), Be, Cd, Co, Li, Ni,
and V are usually below the detection limits. The ICP procedure was tested with NIST Standard
Reference Material 1648 Urban PM. The duplicate quarter PM samples also agreed well with each
other. In the INAA results, only Al, Br, Cl, Mn, Na, and V yielded detectable results and Cl -, NO3-,
and SO4-2 were the exclusive detectable ions by IC. The intercomparison between the different
analytical techniques yielded reasonable agreement. The advantage of this sampling system is that it
allows simultaneous analysis by multiple instruments within the laboratory to facilitate comparison
between the results. For example, elemental concentrations measured on the filter papers can be
compared to the single particle results from the LAMS.
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1
Jervis, R.E., Tan, P., and Evans, G.J. (1999). Biological Trace Element Research, 71-72: 223
2
S. Landsberger and M. Creatchman (1999). Elemental analysis of airborne particles. Gordon and
Breach Science Publishers, Canada.
3 Marple, V.A. (1970). Ph.D. Thesis, University of Minnesota, Minneapolis, MN.
4 Hinds, William C. (1999). Aerosol Technology Properties, Behaviour and Measurements of
Airborne Particles, John Wiley & Sons, Inc., New York.
5 Kim, H.T., Kim, Y.J. and Lee, K.W. (1998). Aerosol Sci. and Technol. 29: 350.
6
Marple, V.A., et .al. (1993). Inertial, Gravitational, Centrifugal and Thermal Collection Techniques.
In Aerosol Measurement: Principles, Techniques, and Applications, ed. K. Willeke and Paul A.Baron.
Chap. 11, p. 212. New York: Van Nostrand Reinhold
7
Demokritou, P., Kavouras, I.G., Harrison, D. and Koutrakis P. (2001). Air & Waste Manage.
Assoc. 51: 514
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