Light extinction coefficient

Light extinction coefficients per unit mass of chemical constituent are constant for growing aerosols for certain forms of the growth laws and particle size distributions. Constant coefficients simplify source allocation analyses for visibility degradat ion. 

In a separate study ( ) aerosol species mass distributions were successfully used to calculate the contribution of each species to the extinction coefficient. Unfortunately, such detailed data is not usually available. At most air monitoring stations, only the total aerosol species mass concentrations, M -, are determined from filter samples. Statistical methods have been used to infer chemical species contributions to the particle light extinction coefficient ( ). For such analyses it is assumed that bgp can be represented as a linear combination of the total species mass concentrations, M-j, viz.. 

These limitations on the statistical inference of species contributions to the particle light extinction coefficient raise several questions (i) Is the statistical analysis of filter data a valid method for determining species contributions to the extinction coefficient of atmospheric aerosols (ii) Can we place confidence limits on the quality of the statistical results and (iii) Can the quality of the statistical results be enhanced through improved sampling techniques ... 

China Lake Light Extinction Coefficient Budget... 

The ratio of the light extinction coefficient of flame-generated smoke to the mass concentration of soot in the smoke is approximately constant and equal to os = 8.7 1.1 m2/g.64 The implication of this nearly universal value is that the soot yield, i.e., the mass of soot generated per mass unit of fuel burnt, can be estimated from light extinction measurements as follows ... 

Canopy light extinction coefficient (k) Calculated using the function LI = 1 — exp( t LAI), where LI is the fraction of light intercepted by the canopy and LAI is leaf area index (m2 leafm-2 land) Varies3 ... 

Light extinction coefficient (k) Extinction coefficient for a particular substance is a measure of how well it absorbs electromagnetic radiation at particular wavelengths 0.78-1.01 Allirand et al., 1988... 

Particle light-extinction coefficient Long-path transmittance Beer s law measurement -h... 

Changes in SSA will affect light penetration in the snowpack. The light extinction coefficient depends on Sc, and therefore on SSA . If the SSA increases from 100 to 200 cm. g, the e-folding depth and the light intensity integrated over the whole snowpack will decrease by a factor of 1.4. 

All of the gravity sedimentation techniques, with the exception of photo-sedimentometers which detect the projected area of the particles (which in turn is proportional to particle surface) measure size distribution by mass. Photosedimentometers can only give useful results for particles coarser than around 5 pm because for finer particles the wavelength of light becomes comparable to the particle size, the laws of geometric optics break down and the so-called light extinction coefficient becomes highly size dependent. 

The intensity of a spectral absorption band at a given wave length is expressed in terms of absorption or extinction coefficients, dehned on the basis of the Beer-Lambert law. The latter states that the fraction of incident light absorbed is proportional to the number of molecules in the light path, i.e., to the concentration (c) and the path length (1). The law may be expressed mathematically as ... 

Indicators There are certain compounds that are suitable as indicators for sensitive and specific clinical analysis. Nicotinamide adenine dinucleotide (NAD) occurs in oxidized (NAD" ) and reduced (NADH) forms. Nicotinamide adenine dinucleotide phosphate (NADP) also has two states, NADP" and NADPH. NADH has a very high uv—vis absorption at 339 nm, extinction coefficient = 6300 (M cm) , but NAD" does not. Similarly, NADPH absorbs light very strongly whereas NADP" does not. 

The molecular extinction coefficients (at various wavelengths) of the four main components of the irradiation are shown in Table 5. The absorption of light above 300 nm is favored by tachysterol. A yield of 83% of the previtamin at 95% conversion of 7-dehydrocholesterol can be obtained by irradiation first at 254 nm, followed by reirradiation at 350 nm with a yttrium aluminum garnet (YAG) laser to convert tachysterol to previtamin D. A similar approach with laser irradiation at 248 nm (KrF) and 337 nm (N2) has also been described (76). 

This facile reaction involves a modest change in the absorption of visible light, largely because of the visible absorption band of <7 -azobenzene [1080-16-6] having a larger extinction coefficient than azobenzene [17082-12-1]. Several studies have examined the physical property changes that occur upon photolysis of polymeric systems in which the azobenzene stmcture is part of the polymer backbone (17). 

The extinction coefficient is dependent on the presence of gases and molecules that scatter and absorb light in the atmosphere. The extinction coefficient may be considered as the sum of the air and pollutant scattering and absorption interactions, as shown in Eq. (10-4) ... 

The Rayleigh scattering extinction coefficient for particle-free air is 0.012 km for "green" light (y = 0.05 /rm) at sea level (4). This permits a visual range of —320 km. The particle-free, or Rayleigh scattering, case represents the best visibility possible with the current atmosphere on earth. 

A transmissometer is similar to a telephotometer except that the target is a known light source. If we know the characteristics of the source, the average extinction coefficient over the path of the beam may be calculated. Transmissometers are not very portable in terms of looking at a scene from several directions. They are also very sensitive to atmospheric turbulence, which limits the length of the light beam. 

Extinction Coefficient a measure of the ability of particles or gases to absorb and scatter photons from a beam of light a number that is proportional to the number of photons removed from the sight path per unit length. See absorption. Extinction Cross Section the amount of light scattered and absorbed by a particle divided by its physical cross section. 

The UV absorber (UVA) class (e.g., 2-hydroxy-benzophenones and benzotriazoles, see AO 23-27 in Table lb) are stable to UV light and have high extinction coefficients in the region 330-360 nm. They operate pri-... 

Peroxides are used most commonly either as thermal initiators or as a component in a redox system. While peroxides are photochemically labile, they seldom find use as photoinitiators other than in laboratory studies because of their poor light absorption characteristics. They generally have low extinction coefficients and absorb in the same region as monomer. Kinetic parameters for decomposition of some important peroxides are given in Table 3.5,... 

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