Absorption-coefficient-determination method for particulate materials

Abstract

A method is presented for determining the optical absorption coefficient, or the imaginary refractive index, of particulate material that has been collected from aerosols or hydrosols by means of filtration. The method, based on the Kubelka-Munk theory of diffuse reflectance, is nondestructive and requires no other knowledge of the sample than the amount present, the specific gravity, and an estimate of the real index of refraction. The theoretical development of the method is discussed along with an analysis of photometric and gravimetric errors. We test the method by comparing results obtained for powdered didymium glass with measurements made before the glass was crushed. An example of the method's application to the determination of the absorption coefficient of atmospheric dust at UV, visible, and near-IR wavelengths is also presented.

An Empirical Method for the Determination of the Complex Refractive Index of Size-Fractionated Atmospheric Aerosols for Radiative Transfer Calculations

“…The bulk absorption coefcient (¾ a ) and the mass-speci c absorption (B a ) for the ANL, PSC, and UPRA samples are presented in Table 5. The absorption coef cient was calculated from the relation k D (¸=4¼ )¾ a (Gosse et al 1997;Lindberg et al 1994), and the mass-speci c absorption was calculated by assuming black carbon to be the major absorbing component of the aerosol, with a density of 1,200 kg/m 3 (Horvath 1993). The mass-speci c absorption coef cients ranged from 5.7 to 16 m 2 /g.…”

Multi-angle absorption photometry—a new method for the measurement of aerosol light absorption and atmospheric black carbon

“…H anel (1987,1994) applied radiative transfer schemes to deal with the radiative transfer problem for a plane layer that both scatters and absorbs radiation. Lindberg, Douglass, & Garvey (1994) employed a variation of the Kubelka-Munk theory of di use re ectance and considered a single layer consisting of an aerosol-powder mixture.…”

Mean Particle Diameters. From Statistical Definition to Physical Understanding

“…(24) to relate estimates of the median diameters of various distribution functions in order to overcome the limitations of Eq. (38), is doubtful.…”

“…In the German (DIN) notation, however, the mean diameter r k x , is expressed only in terms of the median and the geometrical standard deviation of its density function ) (x q r , see Eq. (38). Using an equation similar to Eq.…”

“…Values of the real component of refractive indices have been published for many bulk materials [37]. The imaginary refractive component (i.e., the absorption part) is more difficult to find in the literature [38,39]. Mie theory, which describes scattering of light by homogeneous spheres of arbitrary size, is the most rigorous scattering model available, and is used in many commercial instruments.…”