Environmental Engineering Reference
In-Depth Information
3. A set of diffusion batteries or diffusion batteries composed of wire screen can be used for
collecting aerosol particles in the ultraine and nanometer range (Ruzer and Sextro, 1997).
4. An air Pump with regulated low rate.
5. High collection eficiency (99.999% for particle sizes <1000 nm) gravimetric air ilters.
The calibration procedure consists of the following measurements:
1. e
1
, e
2
—deposition coeficients of the unattached and attached radon progeny in diffusion
battery, respectively
2. e
3
, e
4
—detection eficiencies of the unattached and attached radon progeny deposited in
diffusion battery, respectively
3. e—detection eficiencies of the summary (unattached and attached radon progeny) air-
borne activity on the ilter
The procedure for measurement of the unattached fraction of radon progeny consists of measuring
the activity of radon progeny inside the diffusion battery, in the diffusing battery backing ilter, and
in the open ilter.
The unattached fraction of radon progeny, f, can be calculated as a ratio of the unattached
(q
u
) and sum [(q
u
+ q
a
), unattached +attached] concentration according to the formula (Ruzer and
Sextro, 1997):
q
[
eN 1 e
(
−
)
−
e e N
]
(16.3)
u
db
2
2 4
bf
f
=
=
[(
q
+
q
)
N e e 1 e
[
(
−
)
−
e e 1 e
(
−
)]
u
a
of
1 3
2
2 4
1
where N
db
, N
bf
, and N
of
are measured activity in the diffusion battery, backing ilter, and open ilter,
respectively.
A summary of the results for this approach is presented in Figure 16.2 (Ruzer, 2008), which
shows the measurement of unattached concentration of
218
Po relative to particle surface area
concentration in the range of 0.3-2.1 μm, made with monodisperse latex aerosols of different sizes
and concentrations (Dokukina and Ruzer, 1976). In each case, the measured aerosol concentration
was converted to the aerosol surface area concentration. These results suggest that for aerosols in the
size range covered by this calibration, 0.3-2.1 μm in diameter, the particle surface area concentration
is in the corresponding range from 10
−5
to 0.3 cm
−1
, and is related to the unattached fraction of
218
Po, f. The calibration procedure used is for monodisperse spherical particles, from which the
surface area can be directly calculated. In practice, for nonspherical and polydisperse aerosols an
“equivalent surface area” should be used, which is the surface area of a spherical aerosol having
the same diffusion deposition property as the real aerosol. Under actual measurement conditions
Aerosol particle
Positive
Cluster formation
Rn-Daughters
Attachment
Neutral
Cluster formation
FIGURE 16.2
Basic process of Rn decay product behavior in air deining “unattached” and “aerosol-
attached” activities.
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