MEASUREMENTS OF THE PARTICLE SIZE
DISTRIBUTION OF THE TROPOSPHERIC AEROSOL
WITH A ROTATING-DISK SAMPLER
S. K. FRIEDLANDER* and RALPH E. PASCERIT
Johns Hopkins University, Baltimore, Maryland
ABSTRACT
Measurements were made of the particle size distribution of the aero-
sol at Baltimore, Md. Particles smaller than a few tenths of a micron
in diameter were sampled by diffusion from room air to a rotating
disk with an electron-microscope grid attached. The rotating disk provides a known convective field with a number of desirable characteristics, Particle size distributions were calculated from the distribution
measured on the disk grid.
INTRODUCTION
As part of a study of the dynamics of the atmospheric aerosol,
measurements have been made of the size distribution of the aerosol
at Baltimore over the range between 70 A and 140 » in diameter.’ The
experimental data are reported in terms of asize-distribution function,
n(r), and the cumulative distribution function, N(r), defined as follows:
The quantity n(r) dr is the number of particles per unit volume with
radii between r and r+ dr. Then N(r), the total number of particles per
unit volume with radii greater than or equal to r, is given by
*Present address: W. M. Keck Engineering Laboratories, California Institute of Technology, Pasadena, Calif.
7+Present address: Allegany Ballistics Laboratory, Cumberland, Md.
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