Atmospheric particles INDEX

Because the single-scattering albedo depends sensitively on the imaginary part of the refractive index there has been keen interest in determining optical constants of atmospheric particles. These are used to calculate the important parameters in the heat balance problem for present and predicted aerosol... 

Figure 14.1 Imaginary part of the refractive index of several solids and liquids that are found as atmospheric particles.

Light scattering and absorption techniques have also been used, for example to obtain the index of refraction of the particles and then to compare these atmospheric measurements to laboratory measurements of NAT, NAD, etc. determined in laboratory studies. Adriani and co-workers (1995), for example, using light scattering in the visible, report four types of particles... 

Lindberg, J. D., and J. B. Gillespie, 1977. Relationship between particle size and imaginary refractive index in atmospheric dust, Appl. Opt., 16, 2628-2630. 

Table 3.2 shows measurements of particulate and gaseous stable iodine in the atmosphere. Moyers et al. (1971) used membrane filters and activated charcoal to collect the particulate and gaseous fractions in air at Boston, and found the ratio Ip/Ig to be correlated with the concentration of particulate lead in the air. It was not inferred that Ip was combined with particles of lead, but rather that the concentrations of lead served as an index of the total airborne particulate. Moyers et al. expressed their results as... 

Single-particle optical analyzers are especially useful for continuous measurement of particles of uniform physical properties. However, as discussed earlier, uncertainties develop in the measurement of particle clouds that are heterogeneous in composition because the refractive index may vary from particle to particle. Thus, in making atmospheric aerosol measurements, workers have assumed an average refractive index characteristic of the mixture to estimate a calibration curve or have reported data in terms of the equivalent particle diameter for a standard aerosol, such as suspended polystyrene latex spheres. 

Since however a large fraction of the scattering is in the forward direction, the depletion of solar radiation reaching the ground is not as large as expected merely on the basis of extinction. In addition the presence of the absorbing aerosol modifies the infrared characteristics of the atmosphere. The net effect depends on the size and refractive index of the particles. 

Gennings S.C., Effect of the particulate complex refractive index and particle size distribution variations on atmospheric extinction and absorption for visible through middle IR wavelengths. Appl. Opt. , 17 (24), 3922-3929 (1978). 

CONTENTS 1. Basic Principles (J. W. Robinson). 2. Instrumental Requirements and Optimisation (J. E. Cantle). 3. Practical Techniques (J. E. Cantle). 4a. Water and Effluents (B. J. Farey and L A. Nelson). 4b. Marine Analysis by AAS (H. Haraguchi and K. Fuwa). 4c. Analysis of Airborne Particles in the Workplace and Ambient Atmospheres (T.J. Kneip and M. T. Kleinman). 4d. Application of AAS to the Analysis of Foodstuffs (M. Ihnat). 4e. Applications of AAS in Ferrous Metallurgy (K. Ohis and D. Sommer). 4f. The Analysis of Non-ferrous Metals by AAS (F.J. Bano). 4g. Atomic Absorption Methods in Applied Geochemistry (M. Thompson and S. J. Wood). 4h. Applications of AAS in the Petroleum Industry W. C. Campbell). 4i. Methods forthe Analysis of Glasses and Ceramics by Atomic Spectroscopy (W. M. Wise et al.). 4j. Clinical Applications of Flame Techniques (B.E. Walker). 4k. Elemental Analysis of Body Fluids and Tissues by Electrothermal Atomisation and AAS (H. T. Delves). 4I. Forensic Science (U. Dale). 4m. Fine, Industrial and Other Chemicals. Subject Index. (All chapters begin with an Introduction and end with References.)... 

Polarimetry is a powerful method for studying solar-system bodies. It has allowed the determination of such parameters as the complex refractive index of particles in planetary atmospheres, the size distribution functions of these particles, the methane concentrations, the atmospheric pressure values above the cloud layers, etc. Independent spectral analyses of linear P) and circular (V) polarization observational data also may facilitate the determination of physical characteristics of particles at different heights in a planetary atmosphere. Polarimetiy enables us to make qualitative conclusions about... 

Sobolev [66] hypothesized that the formation of polarization properties of planetary atmospheres takes place in the highest atmospheric layers (where the optical depth does not exceed values of about 1). It is then sufficient to consider only the first-order scattering in the calculation of the second Stokes parameter, Q. Sobolev considered two models of the atmospheric vertical stracture 1) a single-layer model in the form of a semi-infinite cloud layer, and 2) a two-layer model, in which an optically thin gas layer is put on top of the semi-infinite cloud layer. Comparisons of the phase dependence of the degree of linear polarization observed in the visible with calculations for two values of the real part of the refractive index = 1-33 and 1.50) and for varying particle radii showed the best agreement for monodisperse particles with rir= 1.5 and a radius of 1 micrometer. 

The great interest in this topic was further demonstrated by the paper of Kattawar et al. [23], Several models of the vertical stractme of the cloud layer were analyzed using the Monte-Carlo method and polarimetric observations. Using homogeneous and inhomogeneous atmosphere models yielded the same real part of the refractive index and the same particle size. This fact seems to confirm Sobolev s hypothesis that linear polarization is mostly formed by single scattering within an optically thin top atmospheric layer. 

---