Visibility, degradation

A survey by national park personnel indicates that large areas of the United States are subject to varying degrees of visibility degradation (1). The middle portion of the eastern half of the country and the Florida Gulf Coast are subject to widespread hazy air masses associated with stagnation conditions. Large portions of the western half of the country are subject... 

Describe the impact of future visibility degradation on your area (e g, on specific areas of scenic attraction). 

Optical measurements permit the quantification of visibility degradation under different conditions. Several instruments are capable of measuring visual air quality, e.g., cameras, photometers, telephotometers, transmis-someters, and scattering instruments. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

Figure 16. Photocurrent/cell potential difference for n-type GaP anode and p-type GaP cathode in O.IM HfSOi, illuminated as in Figure 15. Hydrogen evolution occurred at the GaP cathode without visible degradation, but in this cell the anodic reaction is oxidation of P to HsPOs and dissolution of the anode material (16).

The basic theoretical equation ( ) relating source contributions and chemical composition is a mass balance which requires no consideration of rate processes. In this paper, the theory is extended to the resolution of the visibility degrading components of the aerosol and to chemically reactive families of chemical compounds. These extensions require new theoretical analyses which take into account the dynamics of aerosol growth and chemical kinetics, respectively. The extension to these rate processes are the subject of this paper. 

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. 

The aerosol scattering coefficient distribution was calculated from the aerosol volume distribution, using the method described in Friedlander (] ] ). The resultant distribution is plotted in Figure 3. The contribution of the fine aerosol to visibility degradation at China Lake is seen in this figure. 

Secondary NAAQS are set to protect public welfare. This includes economic losses due to damage to agricultural crops, forests, and materials as well as aesthetic effects, including visibility degradation. 

A fourth example of data showing the particle distribution was a study that used the DRUM sampler at Grand Canyon National Park in 1984 (22). Recording the size distribution of sulfur was necessary in helping to understand the effects of sulfur on visibility degradation because there were two size modes one near 0.3 xm and one around 0.1 xm. These modes were not present simultaneously but appeared somewhat anticorrelated (see August 14 in Figure 7). 

Long-term Tests of Operating Display Panels. Life tests were being carried out at room temperature and at 80 °C to study the long-term stability of unshielded devices in contact with GH LC. The devices have been tested for over 1 year without visible degradation. 

Atmospheric aerosols are multicomponent particles ranging from 0.001 to 10 pm in diameter. Particles are introduced into the atmosphere by combustion processes and a variety of other anthropogenic and natural sources. They evolve by gas-to-particle conversion and coagulation, are augmented due to the formation of fresh particles by nucleation, and are removed by deposition at the earth s surface and scavenging by airborne droplets. Atmospheric aerosols are the main cause of the visibility degradation accom-... 

Bessekhouad, Y., N. Chaoui, M. Trzpit, N. Ghazzal, D. Robert and J.V. Weber (2006). UV/Vis versus visible degradation of acid orange II in a coupled CdS/Ti02 semiconductors suspension. Journal of Photochemistry and Photobiology A-Chemistry, 183(1-2), 218-224. 

Thus, atmospheric research in the eastern U. S. has been dominated by the need for a better understanding of sulfur species, first because of presumed human health effects of S02, then because of human health effects of sulfates, and now because of effects of sulfate and acid upon plant and animal life (and, to a lesser extent, on building materials, statues, etc.) in the East, and because of visibility degradation in the West. 

In August, 1983, members of the Research Staff of Ford Motor Company carried out a field experiment at two rural sites in southwestern Pennsylvania involving various aspects of the acid deposition phenomenon. This presentation will focus on the wet (rain) deposition during the experiment, as well as the relative importance of wet and dry deposition processes for nitrate and sulfate at the sites. Other aspects of the experiment have been discussed elsewhere the chemistry of dew and its role in acid deposition (1), the dry deposition of HNO3 and SO2 to surrogate surfaces (2), and the role of elemental carbon in light absorption and of the latter in visibility degradation (3). 

Phenyl vinyl sulfide prepared using this procedure is stable at room temperature under a nitrogen atmosphere for months. The submitters have kept samples for over nine months at ambient temperature without any visible degradation. 

Shah J. J., Measurements of carbonaceous aerosol across the US Sources and role in visibility degradation, Ph. D. thesis, Oregon Graduate Center, Beaverton, Oregon (1981). 

Fig. 5 Surface of blend of natural rubber and butadiene rubber (45 55) after UV exposure while under tensile stress (applied parallel to the vertical). The lower part of the sample was shielded from the UV illumination and suffered very much less visible degradation than the upper zone. (See also RQfP )...

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