HR: 0800h
AN: A21B-0852    [Abstracts]
TI: In Situ Measurement Of Optical Properties Of Flame Generated Monodispersive Soot Particles And Comparison With Rayleigh-Debye-Gans Scattering Theory
AU: * Chakrabarty, R K
EM: Rajan.Chakrabarty@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 United States
AU: Moosmller, H
EM: hansm@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 United States
AU: Garro, M A
EM: garro@fas.harvard.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 United States
AU: Arnott, W P
EM: pat@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 United States
AU: Slowik, J G
EM: slowikja@bc.edu
AF: Boston College, Chestnut Hill, Massachusetts, MA 02467 United States
AU: Cross, E S
EM: espencer@aerodyne.com
AF: Boston College, Chestnut Hill, Massachusetts, MA 02467 United States
AU: Han, J H
EM: hanjg@bc.edu
AF: Boston College, Chestnut Hill, Massachusetts, MA 02467 United States
AU: Davidovits, P
EM: paul.davidovits@bc.edu
AF: Boston College, Chestnut Hill, Massachusetts, MA 02467 United States
AB: Fractal dimension, morphology, and optical properties of soot aerosol particles generated in an Ethane/O2 flame were determined at three fuel equivalence ratios -2.3, 2.8, and 3.5 respectively. Soot particles were first size-selected with a differential mobility analyzer (DMA) to achieve a monodispersive size distribution and then their properties were analyzed with an integrated photoacoustic-nephelometry instrument and a scanning electron microscope (SEM). The integrated photoacoustic-nephelometry instrument measures the total light extinction coefficient for a given size distribution of soot particles, and is built on the principle of combining two separate optical measurement techniques, namely the photoacoustic technique for measuring light absorption and the integrating nephelometry technique for measuring light scattering by particles. Soot particles were sampled on nucleopore clear polycarbonate filers for imaging with a high resolution SEM.The particle images from the SEM were analyzed for their fractal dimensions, projected area equivalent diameter distribution, and monomer size distribution using image processing software and algorithms. The projected area equivalent diameter of the soot particles was found to be almost identical to their mobility diameter and the monomer diameters of the primary particles ranged between 30 and 50 nm. The 3-dimensional mass-fractal dimension (Df) of the particles ranged between 1.02 and 1.78. Calibrated measurements of scattering and absorption coefficients of the soot particles for each of the three different fuel equivalent ratios were obtained by the integrated photoacoustic-nephelometry instrument. These measured values of the absorption and scattering coefficients were compared with calculations using the Rayleigh-Debye-Gans (RDG) theory for scattering and absorption by fractal aggregates, and very good agreement was found between experiment and the RDG theory. A sensitivity test on the performance of the Rayleigh-Debye-Gans scattering theory for fractal aggregates will also be discussed.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0360 Radiation: transmission and scattering
DE: 0619 Electromagnetic theory
DE: 0669 Scattering and diffraction
DE: 0694 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005