Light scattering and absorption by fractal-like carbonaceous chain aggregates: comparison of theories and experiment.
This study compares the optical coefficients of size-selected soot particles measured at a wavelength of 870 nm with those predicted by three theories, namely, Rayleigh-Debye-Gans (RDG) approximation, volume-equivalent Mie theory, and integral equation formulation for scattering (IEFS). Soot particles, produced by a premixed ethene flame, were size-selected using two differential mobility analyzers in series, and their scattering and absorption coefficients were measured with nephelometry and photoacoustic spectroscopy. Scanning electron microscopy and image processing techniques were used for the parameterization of the structural properties of the fractal-like soot aggregates. The aggregate structural parameters were used to evaluate the predictions of the optical coefficients based on the three light-scattering and absorption theories. Our results show that the RDG approximation agrees within 10% with the experimental results and the exact electromagnetic calculations of the IEFS theory. Volume-equivalent Mie theory overpredicts the experimental scattering coefficient by a factor of approximately 3.2. The optical coefficients predicted by the RDG approximation showed pronounced sensitivity to changes in monomer mean diameter, the count median diameter of the aggregates, and the geometric standard deviation of the aggregate number size distribution.
Chakrabarty
Rajan K
RK
Chemical Physics Program, Department of Physics, University of Nevada, Reno 89557, USA. rajan@dri.edu
Moosmüller
Hans
H
Arnott
W Patrick
WP
Garro
Mark A
MA
Slowik
Jay G
JG
Cross
Eben S
ES
Han
Jeong-Ho
JH
Davidovits
Paul
P
Onasch
Timothy B
TB
Worsnop
Douglas R
DR