Effects of Atmospheric Haze

The United States Clean Air Act of 1977 set as a national goal the prevention of any future degradation and the reduction of any existing impairment of visibility in mandatory class I federal areas caused by anthropogenic air pollution. The Clean Air Act Amendments of 1990 reinforce the support of these goals. (See Chapter 22 foj a discussion of federal classes of areas.) These areas include most of the major national parks, such as the Grand Canyon, Yosemite, and Zion Park. This portion of the Clean Air Act ad- 

All nations contain areas of exceptional scenic beauty. The value of these areas is largely determined by society. Many nations, determined to protect these areas, have established parks or preserves where only limited development can occur, in many instances limited to facilities such as food and lodging for visitors to the area. 

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 

Average airport visibilities over the eastern half of the United States have been determined over a period of approximately 25 years (1948-1974) (6). Although seasonal variations occur, the long-term trend has been decreased visual air quality over the time period. 

Holzworth and Maga (16) developed a technique for examining the trend in visibility and analyzed data for several California airports. Bakersfield s visibility deteriorated over the period 1948-1957, and Sacramento s visibility decreased over the period 1935-1958. Los Angeles had decreasing visibility from 1932 to 1947, with little change over the period 1948-1959. 

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Atmospheric Effects. The presence of fine particles (0.1-1.0 mm in diameter) or N02 in the atmosphere can result in atmospheric haze or reduced visibility due to light scattering by the particles. The major effect of atmospheric haze has been degradation in visual air quality and is of particular concern in areas of scenic beauty, including most of the major national parks such as Great Smoky Mountain, Grand Canyon, Yosemite, and Zion Parks. 

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