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Wavelength Dependence of the Absorption of Black Carbon Particles: Predictions and Results from the TARFOX Experiment and Implications for the Aerosol Single Scattering AlbedoMeasurements are presented of the wavelength dependence of the aerosol absorption coefficient taken during the Tropical Aerosol Radiative Forcing Observational Experiment (TARFOX) over the northern Atlantic. The data show an approximate lamda(exp -1) variation between 0.40 and 1.0 micrometers. The theoretical basis of the wavelength variation of the absorption of solar radiation by elemental carbon [or black carbon (BC)] is explored. For a wavelength independent refractive index the small particle absorption limit simplifies to a lambda(exp -1) variation in relatively good agreement with the data. This result implies that the refractive indices of BC were relatively constant in this wavelength region, in agreement with much of the data on refractive indices of BC. However, the result does not indicate the magnitude of the refractive indices. The implications of the wavelength dependence of BC absorption for the spectral behavior of the aerosol single scattering albedo are discussed. It is shown that the single scattering albedo for a mixture of BC and nonabsorbing material decreases with wavelength in the solar spectrum (i.e., the percentage amount of absorption increases). This decease in the single scattering albedo with wavelength for black carbon mixtures is different from the increase in single scattering allied for most mineral aerosols (dusts). This indicates that, if generally true, the spectral variation of the single- scattering albedo can be used to distinguish aerosol types. It also highlights the importance of measurements of the spectral variation of the aerosol absorption coefficient and single scattering albedo.
Document ID
20020066544
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
Authors
Bergstrom, Robert W.
(Bay Area Environmental Research Inst. San Francisco, CA United States)
Russell, Philip B.
(NASA Ames Research Center Moffett Field, CA United States)
Hignett, Phillip
(Ministry of Defense London United Kingdom)
Date Acquired
August 20, 2013
Publication Date
February 1, 2002
Publication Information
Publisher: American Meteorological Society
Subject Category
Environment Pollution
Funding Number(s)
CONTRACT_GRANT: NCC2-1094
Distribution Limits
Public
Copyright
Other

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