Theory of Operation B-7
Charging Theory
The particle charge distribution used in the data reduction for the
SMPS
™ spectrometer is based on a theoretical model developed by
Wiedensohler [1986] and is an approximation of the Fuchs [1963]
diffusion theory for particle sizes in the submicrometer regime.
Figure B-5 shows the measured data of Wiedensohler [1986] and
theoretical curves based on the theory of Fuchs [1963] and
calculated by Wiedensohler [1988]. The theoretically determined
charge distribution agrees well with experimental data. It can be
seen from the figure that the fraction of positively charged particles
is different from the fraction of negatively charged particles.
Table B-1 lists the fractions of particles in air that carry +1, +2, +3,
+4, +5, and +6 charge units.
Figure B-5
Bipolar Particle Charge Distribution in Air [Wiedensohler and Fissan, 1988]
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