Environmental Engineering Reference
In-Depth Information
(Sierra/Marple Model 210). Therefore, when using the MFM one requires less measure-
ments that is important from the point of view of time and cost reduction for conducting
a study.
3. Productivity of sampling
Theoretically, there are no limitations on the productivity of the MFM. What is limited it
is linear velocity but not the iltering surface. In reality one managed to reach productivity
up to 20,000 m
3
/h and using standard sampling devices. Productivity of the most powerful
impactors is considerably (approximately 300 times) lower.
4. Range of determined sizes
The MFM realized on the base of iber materials having diameter of about 7 μm enables to
determine
d
0
in the size range of 0.04-7 μm. The error of LND parameters determination
is higher at both ends of the size range than in its center and the best results are received in
the range of 0.1-5 μm. None of the existing impactor marks allows for covering of such a
wide range: MFM has advantages here giving way to the majority of impactor marks in the
area of micron sizes, especially, at
d
0
> 5 μm.
5. Auxiliary equipment and sampling procedures
Devices intended for sampling for ibrous ilters are quite appropriate for use with the
MFM method. Impactor being a rather complicated design having high aerodynamic resis-
tance requires the use of powerful high-head air blowers to achieve a required low rate. In
that respect MFM method is simpler and cheaper in operation.
17.11.4 MFM a
PPlication
Application of the MFM method of multilayer ilters for determination of size distribution of aero-
sols enabled us to receive a number of interesting scientiic results. Namely, starting with 1986 this
method is the main one for the study of radioactive aerosols produced during Chernobyl accident
(see Chapter 18).
During the course of a full scale study of aerosols' transfer from the Aral Region [130] one and
the same atmospheric aerosol has been analyzed using an impactor, a laser aerosol spectrometer and
the MFM method. Value deviations of mass median aerodynamic diameter (MMAD) accounted
for no more than 20%. The method was used to study the sizes of natural radioactive aerosols of
7
Be,
212
Pb [131], atmospheric aerosol over Moscow [132], for evaluation of size distribution of some
speciic aerosols in process communications of industrial plants [133], nuclear reactors [134] and for
complex study of other aerodispersed systems [135].
Recently [136] experiments were accomplished, which compare results of determination of sizes
of NaCl and Se particles, produced by laboratory generators. The results received by the MFM prac-
tically coincide with those received by other known methods realized in the TSI installation and by
a laser aerosol spectrometer (difference between calculated and measured values does not exceed
0.02 μm for particles having their size of about 0.30 μm).
17.12 FILTERS FOR CAPTURING GASEOUS SUBSTANCES
Some chemical compounds of substances (iodine, ruthenium, tellurium, cesium, mercury and
others) exist in the atmosphere both in aerosol and gaseous state simultaneously. It is known that
ibrous ilters are effective in capturing aerosols but are “transparent” for vapors. For that reason
two-component FP (SFM) sorption-iltering materials were developed that consist of ibers and
sorbent particles introduced into the intra-iber space [137]. Such materials are seldom used in the
process puriication systems due to their relatively low sorption capacity, but as analytical means
they have a number of advantages as compared to other analytical means (carbon cartridges, sorp-
tion columns, etc.). First of all, that is suficiently high effectiveness and low resistance to air low.
Second, such analytical ilters can be accommodated in standard sampling devices operating with
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