13th Conference on Atmospheric Radiation
13th Conference on Cloud Physics

JP2.11

Experimental studies of the structure and optical scattering/absorption properties of aerosols generated from combustion sources

PAPER WITHDRAWN

Eranda I. Perera, National Institute for Occupational Safety and Health, Pittsburgh, PA; and C. D. Litton

Aerosols generated from combustion are a primary source of carbonaceous particles in the earth's atmosphere and their absorption and scattering properties play a significant role in assessing climate affects at both regional and global levels. Yet the chemistry, size, and morphology of these aerosols can vary over an exceedingly wide dynamic range, resulting in absorption/scattering efficiencies and their albedos that may easily vary by factors of two to three, thus producing significant uncertainties in their contribution to climate forcing. To quantify these effects, detailed theoretical and experimental investigations were undertaken that encompass a large range of aerosol properties generated from various combustion sources relevant to radiative transfer with the intent of validating or defining the regions of applicability of commonly accepted approximations, such as Rayleigh-Debye-Gans, used in many climate forcing models. This paper discusses some of the initial results of the experimental portions of the research.

In this phase of the research, experiments were conducted to study and quantify the optical scattering properties of aerosols generated from both flaming and smoldering fires of different combustion sources including pulverized coal, Douglas Fir wood chips and different rubber samples namely, styrene butadiene, polyvinyl chloride and neoprene. In the experiments, the aerosol produced from the burning samples were flowed from a small combustion chamber into a larger smoke chamber and mixed via two circulating fans to achieve a uniform mixture. Samples were then extracted from the chamber and flowed to various measuring instrumentation used to characterize the scattering and absorption properties of the fractal-like particles. Data acquired included discrete angular scattering at four forward and two backward angles, mass concentration, broad-band light extinction simulating the response of the human eye, along with light extinction at 3 discrete wavelengths (450 nm, 630 nm, and 1000 nm). During these experiments smoke samples were also collected for imaging and characterized using both the Scanning Electron Microscope (SEM) and the Transmission Electron Microscope (TEM). The experimental data obtained for both smoldering and flaming combustion particles were compared with the microscopic data in order to understand differences in size, shape, radius of gyration, mean diameter, fractal dimension, extinction coefficient, albedo, etc.

Analysis of the data indicated that most of the smoldering fires yielded fractal-like aggregates with similar properties while all flaming fires produced fractal-like aggregates with similar characteristics but distinctly different from those produced during smoldering. Interestingly, the particles generated from smoldering pulverized coal showed no fractal structure, with these particles almost perfect spheres with sizes distributed in a logarithmic normal manner. Except for this one aerosol, all of the other sources produced aerosols with a fractal-like structure. For instance, fractal-like aggregates from smoldering fires were composed of primary particles with diameters in the range of 0.06 m to 0.08 m whereas aggregates from flaming fires were composed of smaller primary particles with diameters in the range of 0.01 m to 0.03 m; the number of primary particles per aggregate was higher in the case of flaming than for smoldering; and the albedo for aggregates from smoldering was significantly greater than the albedo for aggregates from flaming. These results compared quite favorably with visual images from the TEM and the SEM with regard not only to number and size of primary particles per aggregate but also with regard to the aggregate shape and the resultant fractal dimensions. Additional data and analysis are presented along with the implication of these results to aerosol radiative transfer. mbol">£ZzE8ޥx52#B_;#thcttM}jNR*k$ɹ N;ftJ>;~~֟^tem}rS-ן;%gqonxSVz)=(£Ew/lSP'm'([ڝ|]_l,, 4&ݤ"9£Ef׏]fˇ{{W&5'_zC;:רhgQ 9yw9*h@R'tjN 82]Au%;C%"MtM5ouVM\c@; c( m 8W~Nq'P71X3"³,P"tiJ嚲x2B2RĐha0;£IB%"'BSh4E2Fhz6s@5q)2"vS_6Yp³ @Sy6es/L),/ƌlD:5{zSx|g }6&ةEXwixhbBG ?gK|CNµDaz#'3Mz>

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Joint Poster Session 2, Optical and Radiative Properties of Clouds Posters
Wednesday, 30 June 2010, 5:30 PM-8:30 PM, Exhibit Hall

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