Radiometric Model of the Transmission Cell-Reciprocal Nephelometer.
Radiometric Model of the Transmission Cell-Reciprocal
Nephelometer.
(1387 K)
Mulholland, G. W.; Bryner, N. P.
Atmospheric Environment, Vol. 28, No. 5, 873-887, 1994.
Sponsor:
National Aeronautics and Space Administration,
Washington, DC
Keywords:
absorption; aerosols; agglomerates; extinction;
scattering coefficient; smoke
Abstract:
A radiometric model has been developed to assess the
effects of angular truncation, finite size of the
detector, and angle response characteristics of the
cosine sensor on the measurement of the total scattering
coefficient by a transmission cell-reciprocal
nephelometer. These effects are computed for
monodisperse polystyrene spheres over the size range
0.02-8 mum based on Mie theory and for smoke
agglomerates ranging from 10 to 10(7) primary units
based on the Fisher-Burford approximation. The accuracy
of the model calculations is determined by comparison
with exact solutions for the case of a detector with an
infinitesimal area and for a finite area detector with a
diffuse scattering function. The predicted results are
compared with measured results for six different sizes
of monodisperse polystyrene sphere aerosols with
particle diameters in the range 0.1-2.35 mum. The
measurements were carried out as a function of the
distance between the laser beam and detector for 1.3 and
2.7 cm diameter cosine sensors. A table of design
parameters for making accurate total scattering
measurements is obtained for both spheres and
agglomerates. An accuracy of +5% was obtained for
spherical particles with diameters <1.1 mum with our
TCRN, and we estimate that similar performance would be
obtained for smoke agglomerates with up to 3 x 10(3)
primary spheres per agglomerate.
