Mass extinction coefficient

Reconstructed Extinction extinction estimate that results from summing up the product of the mass of each measured particle species and the appropriate absorption or extinction coefficient. 

Low-temperature, photoaggregation techniques employing ultraviolet-visible absorption spectroscopy have also been used to evaluate extinction coefficients relative to silver atoms for diatomic and triatomic silver in Ar and Kr matrices at 10-12 K 149). Such data are of fundamental importance in quantitative studies of the chemistry and photochemistry of metal-atom clusters and in the analysis of metal-atom recombination-kinetics. In essence, simple, mass-balance considerations in a photoaggregation experiment lead to the following expression, which relates the decrease in an atomic absorption to increases in diatomic and triatomic absorptions in terms of the appropriate extinction coefficients. 

In colorants, the spectral absorption pattern and the extinction coefficient are determined by the chromophore and rarely by side groups of the molecule, p-carotene and zeaxanthin contain the same chromophore but their molecular masses... 

Chemical methods for structure determination in diene pol3 mers have in large measure been superseded by infrared absorption techniques. By comparing the infrared absorption spectra of polybutadiene and of the olefins chosen as models whose ethylenic structures correspond to the respective structural units, it has been possible to show that the bands occurring at 910.5, 966.5, and 724 cm. are characteristic of the 1,2, the mns-1,4, and the m-1,4 units, respectively. Moreover, the proportion of each unit may be determined within 1 or 2 percent from measurements of the absorption intensity in each band. The extinction coefficients characteristic of each structure must, of course, be known these may be assigned from intensity measurements on model compounds. Since the proportions of the various units depend on the rates of competitive reactions, their percentages may be expected to vary with the polymerization temperature. The 1,2 unit occurs to the extent of 18 to 22 percent of the total, almost independent of the temperature, in free-radical-polymerized (emulsion or mass) poly butadiene. The ratio of trans-1,4 to cfs-1,4, however,... 

The density of Bronstcd and Lewis acid sites was determined by IR spectroscopy (Nicolet 710) of adsorbed pyridine, after desorption at 250°C, using the molar extinction coefficients previously obtained by Emeis [11]. The acid strength distribution of selected zeolites was studied by NH3-TPD in an Autochem 2910 Equipment (Micromeritics) coupled to a quadrupole mass spectrometer. First, NH3 was adsorbed at 175°C until saturation and then desorbed by increasing the temperature up to 800°C at a heating rate of 10°C/min. 

The depth-profile of photon absorption is analogous to that for UV-visible light, i.e. I = Io exp(-Ad), where the mass energy absorption coefficient, u/g is used instead of the extinction coefficient. Particulate energy absorption can be described by relative stopping powers. 

FIGURE 8.19 Peak extinction coefficient versus equivalence ratio of fuel/oxygen stream mixture in propane and ethene opposed-jet diffusion flames. /w is the fuel injection parameter. The greater the extinction coefficient, the greater the soot mass. From Ref. [93]. 

Prior to 1970 our understanding of the bonding of diatomic molecules to surfaces, and in many cases the type of adsorption (i.e., molecular or dissociative) was almost entirely dependent on indirect experimental evidence. By this we mean that deductions were made on the basis of data obtained from monitoring the gas phase whether in the context of kinetic studies based on gas uptake or flash desorption, mass spectrometry, or isotopic exchange. The exception was the important information that had accrued from infrared studies of mainly adsorbed carbon monoxide, a molecule that lent itself very well to this approach owing to its comparatively large extinction coefficient. 

Values of Y. vary for different aerosol components, the large values corresponding to the components with the highest extinction coefficients per unit mass of aerosol material. When Y. is constant, the extinction coefficient is linearly related through the coefficients Y. to the mass contributions of the various sources this considerably simplifies analyses relating visibility degradation to source contributions. 

Thus the use of a linear theory with constant coefficients to relate the extinction coefficient to source mass contributions can be justified for certain aerosol growth mechanisms. 

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. 

The contributions of aerosol chemical species to the extinction coefficient can be estimated from knowledge of their mass distributions, densities, and refractive indices. It is assumed that the particles can be represented as spheres. For a mixture in which the composition is a function of particle size and all particles of a given size have the same composition, defined here as a specific mixture, the contribution of species i becomes (4 ) ... 

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.. 

Table 3 summarizes the 1979 annual average particle extinction coefficient and the mass concentrations of the fine aerosol chemical species estimated by statistical analysis of the 61 filter samples. Organics and sulfates dominated the chemically determined fine aerosol mass at China Lake in 1979. A linear least squares fit between molar concentrations of NHt and SO gave a zero intercept, a slope of 1.87 and a correlation coefficient of 0.98. It is therefore assumed that the fine sulfate aerosol was in the form of ammonium sulfate. The mass concentration of carbonaceous and sulfate aerosols were, on the average, comparable in magnitude. 

Ozkaynak, H., A. D. Schatz, G. D. Thurston, R. G. Isaacs, and R. B. Husar, Relationships between Aerosol Extinction Coefficients Derived from Airport Visual Range Observations and Alternative Measures of Airborne Particle Mass, J. Air Pollut. Control Assoc., 35, 1176-1185 (1985). 

The measurement of screening performance of smokes is important because smoke screens are one of the countermeasures for IR surveillance systems. The performance of smoke formulations is decided in terms of total obscuring power (TOP), yield factor (Y), mass extinction coefficient (a) followed by calculation of obscuration effectiveness (a. Y. p). These parameters are defined in the following manner. 

The mass extinction coefficient (a)is a measure of screening effectiveness per unit mass of a material and is defined by the equation based on the Beer-Lambert law. It is related to the transmission of radiation through the smoke and is given by Equation 5.29 ... 

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