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The data on the complex refractive index (relative to air) of atmospheric aerosols have been obtained by using several methods.
Tafuro AM et al 2006 and Dubovik O et al 2002b both used radiative transfer modeling of radiance distributions in the atmosphere, obtained by an AERONET system of sun radiometers, in order to retrieve the complex (average) refractive index of the aerosol.
Volten H et al 2001 estimated the complex refractive index of Saharan and other aerosols by comparing scattering matrices obtained with geometric optics (ray tracing) for Gaussian random spheres to experimental data. This approach explicitly avoids assumptions about the sphericity of aerosol particles that has been used by other researchers, for example, Grams GW et al 1974. These latter researchers obtained an average complex refractive index of n = 1.525 - i0.005 at wavelengths of 488 and 514 nm for soil aerosol sampled in Texas, USA.
Lindberg JD and Laude 1974 used a diffuse-reflectance method for the determination of the imaginary part of the refractive index of aerosol which comprises diluting the sample aerosol in non-absorbing powder (BaSO4) and inferring, from the spectral reflectance of that composite sample a Kubelka-Munk absorption coefficient (Kortüm G 1969, Kubelka P and Munk 1931). They subsequently used Eq. 3 in Refractive index: Introduction with the "absorption coefficient" to derive m". obtained by applying the Kubelka-Munk theory of diffusive reflectance (for example, Kortüm G 1969) to samples of the dust diluted in BaSO4. As discussed by Lindberg and Laude, that coefficient may exceed the absorption coefficient defined in the Lambert law by a factor on the order of 2.
Bhardawaja PS et al 1974 proposed to use the dependence on the particle refractive index of the hemispherical backscattering ratio, Rbsca, (back-scattering coefficient to scattering coefficient) for dispersions with a power-law size.
On the other hand, Levin EJT et al 2009 (continental aerosol), Kocifaj M et al 2006b, and Stelson AW 1990 (urban aerosol), all used a volume-based average (a simple effective-medium theory, EMT) of the refractive index (see also, Yan B et al 2002) of the various aerosol components to obtain the complex refractive index of the aerosols. See also Chılek P et al 1988 for a comprehensive discussion of other EMTs.
Finally, Hänel G 1968 used a variation of the immersion refractometry technique to determine the real part of the refractive index and density of aerosol particles (see also Immersion refractometry).
Refractive index data for the various aerosol types are listed in separate tables: biomass burning, continental, desert, marine, urban and mixed. See also Refractive index databases.
| CITATION: Jonasz M. 2006. Refractive index of atmospheric aerosol (www.tpdsci.com/Tpc/RIAtmAer.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 24-Nov-2006 Modified: 20-Jan-2010 Peer-reviewed: 28-Nov-2006 |
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