Dust sometimes settles quickly on surfaces, but vast quantities are carried to the upper layers of the air and suspended there for long periods of time. The effects of a volcanic eruption such as that of Krakatoa in Indonesia have been observed three years after its occurrence. Large seasonal dust storms occur in the Sahara and neighboring W Africa and in the Taklimakan and Gobi deserts and neighboring NE Asia; Beijing is annually affected by such storms. Dust from large storms in Africa often travels as far as the S United States and the Caribbean, where it can affect air quality, and dust from the Gobi Desert in Asia has been carried as far east as Minnesota. Such dust storms, which are aggravated by desertification, can have negative health and economic effects; in addition to potentially harmful mineral particles, the dust may include bacteria, fungi, viruses, and various pollutants.
Hygroscopic dust particles (those to which water adheres) are the nuclei of condensation in free air; the nucleus of each droplet in a fog or cloud and of each raindrop and snowflake is one of these invisible particles of inorganic or organic dust. John Aitken, a Scottish physicist who in 1880 invented a device for counting particles in air, first correlated dust particles and condensation. Dust is also chiefly responsible, through its scattering effect upon light (diffusion), for one type of haze and for sunrise and sunset colors.
See also Dust Bowl.
Licensed from Columbia University Press
Licensed from Columbia University Press
See D. Worster, Dust Bowl: The Southern Plains in the 1930s (1979); T. Egan, The Worst Hard Time (2005).
Licensed from Columbia University Press
Any of a class of highly stable organic compounds prepared by the reaction of chlorine with biphenyl, a two-ring compound. The commercial product, a mix of several PCB isomers, is a colourless, viscous liquid that is almost insoluble in water, does not degrade under high temperatures, and is a good electrical insulator (see dielectric). PCBs became widely used as lubricants, heat-transfer fluids, and fire-resistant dielectric fluids in transformers and capacitors in the 1930s and '40s. In the mid 1970s they were found to cause liver dysfunction in humans and came under suspicion as carcinogens; their manufacture and use were consequently restricted in the U.S. and many other countries, though illegal dumping by manufacturers continued. They persist in the environment and have entered the food chain, causing great harm especially to invertebrates and fish.
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Section of the U.S. Great Plains that extended over southeastern Colorado, southwestern Kansas, the panhandles of Texas and Oklahoma, and northeastern New Mexico. The term originated after World War I, when the area's grasslands were converted to agricultural fields. In the naturally dry climate, overcultivation added to the effect of a severe drought in the early 1930s, when heavy winds blew the loose topsoil in “black blizzards” that blocked out the sun and piled dirt in drifts. Many farmers and ranchers left the region for California and elsewhere. The planting of windbreaks and grassland enabled the area to recover by the early 1940s.
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