28 AEROSOLS
Two different types of electrical mobility analyzers
shown in Figure 11 have been widely used (Whitby, 1976).
On the left hand side in the figure is an integral type, which is
commercially available (EAA: Electrical Aerosol Analyzer).
That on the right hand side is a differential type, which is
also commercially available (DMA: Differential Mobility
Analyzer). The critical electrical mobility B ec at which a par-
ticle can reach the lower end of the center rod at a given
operating condition is given, respectively, for the EAA and
DMA asBQQ
LVr
ec r
()ac ⎛
⎝⎜⎞
2 ⎠⎟1
p 2ln (36)BQ
LVr
rBQ
LVr
ec rc
e
a
21
21
pp 2ln , ln⎛
⎝⎜⎞
⎠⎟⎛
⎝⎜⎞
⎠⎟ (37)B ec can be changed by changing the electric voltage applied
to the center rod. A set of data of the particle number con-
centration or current at every B ec can be converted into a size
distribution by data reduction where the number distribution
of elementary charges at a given particle size is taken into
account.
Electrical mobility analyzers are advantageous for
smaller particles because v e in Eq. (20) increases with the
decrease in particle size. The differential mobility analyzer
has been increasingly utilized as a sizing instrument and a
monodisperse aerosol generator of particles smaller than
1 m m diameter (Kousaka et al. , 1985).Diffusion BatteriesThe diffusion coefficient of a particle D is given by Eq. (15).
As shown in Figure 3, D increases with a decrease in par-
ticle size. This suggests that the deposition loss of particles
onto the surface of a tube through which the aerosol is flow-
ing increases as the particle size decreases. The penetration
(1–fractional loss by deposition) h p for a laminar pipe flow
is given as (Fuchs, 1964),hp 0 8191 0 009750 0325...exp 3.657 exp 22.3exp( ββ) ( )( ^57 β),.bpDL Q⁄ 0 0312(38)hbbbbp 1 2 56...,.^23 ⁄ 1 2 0 177^43 / 0 0312 (39)where L is the pipe length and Q is the flow rate. A diffusion
battery consists of a number of cylindrical tubes, rectangu-
lar ducts or a series of screens through which the gas stream
containing the particles is caused to flow. Measurement of the
penetration of particles out the end of the tubes under a number
of flow rates or at selected points along the distance from the
battery inlet allows one to obtain the particle size distribution
of a polydisperse aerosol. The measurement of particle number
concentrations to obtain penetration is usually carried out with
a condensation nucleus counter (CNC), which detects particles
with diameters down to about 0.003 m m.REFERENCESFlagan, R.C., Seinfeld, J.H. (1988) Fundamentals of Air Pollution Engi-
neering. Prentice Hall, Englewood Cliffs, NJ.
Fuchs, N.A. (1964) The Mechanics of Aerosols. Pergamon Press, New York,
204–205.
Hering, S.V., Friedlander, S.K., Collins, J.J., Richards, L.W. (1979) Design
and Evaluation of a New Low-Pressure Impactor. 2. Environmental Sci-
ence & Technology, 13, 184–188.
Kousaka, Y., Okuyama, K., Adachi, M. (1985) Determination of Particle
Size Distribution of Ultra-Fine Aerosols Using a Differential Mobility
Analyzer. Aerosol Sci. Technology, 4, 209–225.
Lodge, J.P., Waggoner, A.P., Klodt, D.T., Grain, C.N. (1981) Non-Health
Effects of Particulate Matter. Atmospheric Environment, 15, 431–482.
Marple, V.A., Liu, B.Y.H. (1974) Characteristics of Laminar Jet Impactors.
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Impactor for Particle Classification and Generation of Test Aerosols with
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Mazumder, M.K., Ware, R.E., Wilson, J.D., Renninger, R.G., Hiller, F.C.,
McLeod, P.C., Raible, R.W. and Testerman, M.K. (1979). SPART ana-
lyzer: Its application to aerodynamic size distribution measurement.
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Seinfeld, J.H. (1986) Atmospheric Chemistry and Physics of Air Pollution.
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Smith, W.B., Wilson, R.R. and Harris, D.B. (1979). A Five-Stage Cyclone
System for In Situ Sampling. Environ. Sci. Technology, 13, 1387–1392.
Stöber, W. (1976) Design, Performance and Application of Spiral Duct
Aerosol Centrifuges, in “Fine Particles”, edited by Liu, B.Y.H., Aca-
demic Press, New York, 351–397.
Van de Hulst, H.C. (1957) Light Scattering by Small Particles. Wiley,
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Whitby, K.T. (1976) Electrical Measurement of Aerosols, in “Fine Particles”
edited by Liu, B.Y.H., Academic Press, New York, 581–624.
Wilson, J.C. and Liu, B.Y.H. (1980) Aerodynamic Particle Size Measure-
ment by Laser-Doppler Velocimetry. J. Aersol Sci., 11, 139–150.
Yoshida, T., Kousaka, Y., Okuyama, K. (1975) A New Technique of Particle
Size Analysis of Aerosols and Fine Powders Using an Ultramicroscope.
Ind Eng. Chem. Fund., 14, 47–51.KIKUO OKUYAMA
YASUO KOUSAKA
JOHN H. SEINFELD
University of Osaka Prefecture and California Institute of TechnologyAGRICULTURAL CHEMICALS: see PESTICIDES
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