Aerosol Particle Counters
FRANK T GUCKER
Professor of Chemistry
Indiana University
Bloomington, Indiana
Two general methods have been used for determining particulate
concentration in aerosols. The first involves the collection of the particulate matter, usually by precipitation on suitable slides, and the counting of the particles; the second involves direct counting in the aerosol
phase.
A special method of counting aerosol particles is applicable only to
viable microorganisms. In this case a known volume of the aerosol is
passed through a suitable cotton plug filter or better through a capillary
impinger jet operating under water as described by T. Rosebury.30 If
the organisms washed from the filter or collected in the impinger are
deposited on agar and incubated, a colony count will give the number
of particles. Beside its limited applicability, the process is slow and involves the uncertain viability of the organisms. More generally, the
particles may be precipitated by settling or by means of a thermal or
electrostatic precipitator. The slide may then be examined visually or
photographically with the help of an optical or electron microscope.
Ingenious automatic electronic methods of scanning and counting have
been recently introduced to determine the number, size, and sometimes
even the shape of the particles. Most of these methods have been developed in England and were described at the Conference on the Physics of
Particle Size Analysis held at the University of Nottingham in 1954.16
A discussion of these methods is beyond the scope of the present article
which is confined to counting in the aerosol phase.
The ultramicroscope was used for studying particles in the aerosol
phase by P. V. Wells and R. H. Gerke in 1919 and later by R. Whyt-
law-Gray and his collaborators at the beginning of their long series of
studies of aerosols. In 1927 the latter group developed a special dark-
field cell for visual counting of aerosol particles without the difficulties
encountered in the Zsigmondy slit ultramicroscope. In 1927 also H. L.
Green adapted the Wilson-Shimizu cloud chamber to condense moisture
upon small aerosol particles and thus increase their size so that they
can be photographed. In 1949 A. L. Chaney developed a dust camera
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