=Paper=
{{Paper
|id=Vol-1152/paper67
|storemode=property
|title=Environmental Control Systems for Defining the Activity Size Distribution of Radioactive Aerosols - a Case Study
|pdfUrl=https://ceur-ws.org/Vol-1152/paper67.pdf
|volume=Vol-1152
|dblpUrl=https://dblp.org/rec/conf/haicta/Ioannidou11
}}
==Environmental Control Systems for Defining the Activity Size Distribution of Radioactive Aerosols - a Case Study==
https://ceur-ws.org/Vol-1152/paper67.pdf
Environmental control systems for defining the activity
size distribution of radioactive aerosols - a case study
Alexandra Ioannidou
Aristotle University of Thessaloniki, Physics Department, Nuclear Physics & Elementary
Particle Physics Division, Thessaloniki 54124 Greece
Abstract. The 1ACFM cascade impactor and the High Volume cascade
impactors are the instruments that mainly used to define the activity size
distribution of radioactive aerosols in the environmental air. The impactors are
instruments designed to collect and separate particulate matter according to its
aerodynamic size, determining the penetration of particles in the human lung,
as well as the transport and diffusion of particles in the ambient air. An
example of the activity size distribution of the natural radionuclide tracer 7Be
is given, as this determined by a 20cfm cascade impactor.
Keywords: radioactive aerosols, impactor, AMAD, environmental
radioactivity
1 Introduction
The aerodynamic diameter of particles is a critical parameter in characterization of
suspension aerosols, while the aerodynamic size distribution defines the manner in
which the particles are deposited in the lung during inhalation.
The impactors are instruments designed to collect and separate particulate matter
according to its aerodynamic size, which is the most important size in particle work
because it determines the penetration of particles in the human lung, as well as the
transport and diffusion of particles in the ambient air. These samplers were calibrated
so that all particles collected, regardless of physical size, shape, or density, are sized
aerodynamically and can be directly related to human lung deposition.
In this study two cascade impactors are presented. Finally, the activity size
distribution of the natural radionuclide tracer 7Be in different inhalable fractions
(<0.39 m, 0.30-0.69 m, 0.69-1.3 m, 1.3-2.1 m, 2.1-4.2 m , 4.2-10.2 m and
>10.2 m) is given as this obtained by measurements with a 20cfm cascade impactor
in the region of the city of Thessaloniki, Greece.
2 Instrumentation
Measurements on aerodynamic sizes of atmospheric aerosols and associated
radionuclides are mainly carried out with Anderson 1-ACFM eight-stage cascade
impactors as well as with 20 cfm (six-stage) high-volume cascade impactors (HVI).
______________________________
Copyright ©by the paper’s authors. Copying permitted only for private and academic purposes.
In: M. Salampasis, A. Matopoulos (eds.): Proceedings of the International Conference on Information
and Communication Technologies
for Sustainable Agri-production and Environment (HAICTA 2011), Skiathos, 8-11 September, 2011.
765
The 1-ACFM eight stage cascade impactor (Fig. 1), is operating at a flow rate of
28 l min-1 (1 ft3 min-1). The stages had effective cutoff diameters (ECDs) of 0.4, 0.7,
1.1, 2.1, 3.3, 4.7, 5.8 and 9.0 m.
Fig. 1. The set-up of 1ACFM eight-stage Andersen Cascade Impactor
Each impactor stage contains multiple precision drilled orifices. Each stage has a
removable glass petri dish with a metal cover. By subsequently making the orifice
diameter smaller on each stage of the Cascade Impactor, the particles are increased in
velocity and the aerodynamic separation of particles over a large range can be
determined. (Fig. 2) Successively smaller particles are inertially impacted onto the
collection surfaces (http://www.labautomate.net/, http://www.globalspec.com/
FeaturedProducts/Detail/ThermoScientificAirQualityInstruments/The_Original_And
ersen_Cascade_Impactors/123307/0).
Fig. 2. By subsequently making the orifice diameter smaller on each Stage of the Cascade
Impactor, the particles are increased in velocity and the aerodynamic separation of particles
over a large range can be determined. Successively smaller particles are inertially impacted
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The High Volume Cascade Impactors HVI, are multi-stage cascade impactors
which attach to any standard high volume air sampler and fractionate particles into as
many as six size ranges (www.staplex.com, http://www.westechinstruments.com
/prodlist.asp? productCategory=Ambient Air Samplers).
The 20cfm High Volume six-stage Cascade Impactor (Fig. 3) has ECDs of 0.41,
0.73, 1.4, 2.1, 4.2, and 10.2 m. The impactor is operated at the flow rate of 20cfm
and collection occurred on impaction collection filters.
Fig. 3. The set-up of High Volume 20CFM Cascade Impactor (Staplex, Andersen)
Suspended particles enter the high volume air sampler and pass through the
parallel slots in the first impactor stage. Those particles larger than the particle cut-
off size of the first stage impact on a slotted collection substrate. The air stream
passes through the slots of the substrate and accelerates as it flows through the
narrower parallel slots of the following impactor stage and eventually most of the
particles acquire a sufficient momentum to impact on one of the collection substrates.
A back-up filter collects the remaining small particles passing through the last
impactor stage. All particles are collected allowing for determination of total particle
concentration.
The cascade impactor was designed as a substitute for the human respiratory tract
to collect and separate particulate matter according to its aerodynamic size and
property (Fig. 4). Stage distribution of collected particle mass will indicate the extent
to which the aerosol sampled would have penetrated the human respiratory system.
This information is vital to environmentalist, aerosol physicists and industrial
hygienists for determining health risk and epidemiological risk.
After sampling is completed, the sampling time is recorded and the collection
substrates are removed from the sampling instrument. Each substrate for each
cascade stage is counted in detectors for determining the radioactivity for each
radionuclide of interest in each stage. Knowing the air sampling flow rate and the
sampling time, the mean activity of a radionuclide per unit volume of air can be
calculated for each radionuclide of interest, and the percentage radioactivity in each
size range can be estimated.
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Fig. 4. The Cascade Impactor designed as a substitute for the human respiratory tract to
collect and separate particulate matter according to its aerodynamic size and property
3. A case study
Beryllium-7 (t1/2 = 53.3 d) is a natural occuring radionuclide with cosmogenic origin
with an important fraction of its production taking place in the upper troposphere.
Soon after its formation 7Be is attached to atmospheric aerosol particles
(Porstendörfer et al., 1991; Papastefanou & Ioannidou, 1995; Paatero and Hatakka,
2000; Eleftheriadis et al., 2007).
Our purpose is to define the aerodynamic size distributions of naturally occurring
radioactive aerosols of 7Be in the region of the city of Thessaloniki, Greece in the
temperate zones (40°N).
3.1 Aerosol Collection Procedure
Aerosol samplings were carried out in the open air by using a 20cfm high volume 6-
stage cascade impactor with a regulated air flow rate of about 0.57 m3 min!1 (20 cfm)
and Efficient Cutoff Diameters of 0.39, 0.69, 1.4, 2.1, 4.2 and 10.2 m.
The length of each collection period was 24 h and the collected air volume was
about 800m3. Glass fiber filters were used as impaction substrates. After the
collection procedure the filters were measured for 7Be activity (E"=477 keV) using a
high resolution (1.9 keV at 1.33 MeV), with 42% relative efficiency, low-background
HPGe detector (Fig.5). Activity Median Aerodynamic Diameters (AMAD) were
derived by calculating the percentage distribution in each size fraction and plotting
the cumulative frequency distribution on log probability paper.
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Fig. 5. A typical Ge detector for gamma-radioactivity and a gamma spectra, where the peaks of
some radionuclides are defined
3.2 Experimental Results
The activity median aerodynamic diameter (AMAD) of 7Be aerosols ranged from
0.58 m to 1.22 m (avg 0.80 m) (Table 1). More than 80% of the 7Be activity was
found to be associated with particles smaller than 1.3 m (Fig. 6). Finally, the age of
aerosol particles was defined in the order of week.
The local meteorological conditions seems to affect the activity size distribution of
7
Be, while increased relative humidity during the sampling period results in incresed
AMAD values (Ioannidou, 2011).
4. Conclusions
The 20cfm Cascade Impactor has been proved the ideal impactor for characterizing
the activity size distribution 7Be aerosols in a daily measurements. The estimation of
the AMAD values of 7Be aerosols allow us to detrmine the AMAD value of any
tropospheric aerosol of the same origin, and calculate the total residence time of
tropospheric aerososl in the order of a week.
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Table 1. Experimental Data for 7Be aerosols (Ioannidou, 2011)
7
Start of Be AMAD #s
sampling ( m)
17-Jun-09 0.74 2.54
07-Sep-09 0.91 3.63
22-Sep-09 0.58 1.86
13-Oct-09 0.62 2.23
16-Oct-09 1.22 2.85
20-Oct-09 0.75 2.41
13-Jan-10 0.83 2.21
1.4
1.2
R/ logDp, Be (mBq m )
-3
1.0
0.8
7
0.6
0.4
0.2
0.0
0.1 1 10
Aerodynamic Diemeter, !m
Fig. 6. Activity size distribution of 7Be aerosols
References
1. http://www.labautomate.net/
2. http://www.globalspec.com/FeaturedProducts/Detail/ThermoScientificAirQuality
Instruments/The_Original_Andersen_Cascade_Impactors/123307/0
3. http://www.staplex.com/
4. http://www.westechinstruments.com/prodlist.asp?productCategory=Ambient Air
Samplers
5. Porstendörfer, J., Butterweck, G., and Reineking, A. (1991). Atmospheric
Environment 25A (3/4), 709-713.
6. Papastefanou, C. and Ioannidou, A. (1995). Journal of Environmental
Radioactivity 26, 273-282.
7. Paatero, J. and Hatakka, J. (2000). Health Physics 79, 691-696.
8. Eleftheriadis, K., Karanasiou, A.A., Siskos, P.A., and Psomiadou,C. (2007).
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