Light extinction

This birefringence coupled with spherical geometry produces light extinction along the axis of each of the Polaroid filters, hence the 90° angle of the Maltese cross. 

Table 7. Light Extinction Budgets, excluding Mean Percentage Contribution...

Light Extinction Budget the percent of total atmospheric extinction attributed to each aerosol and gaseous component of the atmosphere. 

Natural Conditions conditions substantially unaltered by humans or human activities, as applied in the context of visibility, natural conditions include naturally occurring phenomena that reduce visibility as measured in terms of light extinction, visual range, contrast, or coloration. 

Regional Haze Visibility Impairment any humanly perceptible change in visibility (light extinction, visual range, contrast, coloration) from that which would have existed under natural conditions, caused predominantly by a combination of many sources from, and occurring over, a wide geographic area. 

Transmissometer an instrument that measures the amount of light extinction over a fixed, specified path length. 

Upon irradiation with a monochromatic visible light, extinction of the silver nanoparticles deposited on a... 

Extensions of receptor modeling theory to light extinction and to reactive chemical compounds require introduction of rate process concepts. 

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 future development of the chemical mass balance receptor model should include 1) more chemical components measured in different size ranges at both source and receptor 2) study of other mathematical methods of solving the chemical mass balance equations 3) validated and documented computer routines for calculations and error estimates and 4) extension of the chemical mass balance to an "aerosol properties balance" to apportion other aerosol indices such as light extinction. 

The species mass extinction efficiency. Eg, can be theoretically determined from Mie s classical solution to light extinction by a sphere in an infinite medium. Computer routines are available to calculate single particle extinction efficiencies, and, hence. Eg ( ). If the mass distribution of each species is... 

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 ... 

The calculated theoretical values were used to compute the 1979 China Lake light extinction budget shown in Table 9. 

China Lake Light Extinction Coefficient Budget... 

Type of Light Extinction Average Medi an 1 PM (est.) Average 1 Median PM (est.)... 

The quality of statistically inferred species extinction balances can be enhanced with proper aerosol sampling. Due to its important role in light scattering, only the fine aerosol should be sampled. A mass balance should account for all major fine particle species. Ideally the particle scattering coefficient should be measured directly at the location where aerosol is sampled by the filters. The importance of soot and other carbonaceous aerosol contributions to light extinction in arid regions should not be overlooked. 

The long-term average total extinction coefficient at downtown Los Angeles is 6.62 10 m (19) as inferred from daytime measurements of gjevailing visibility. Elemental carbon present at about 9 pgm with a specific absorption of 11.9 m g would account for about 17% of total light extinction at downtown Los Angeles. 

TABLE 9.8 Contribution of Light Absorption to Total Light Extinction Due to Particles in the Troposphere"... 

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