Aerosols (Encyclopedia of Environmental Issues, Revised Edition)
An aerosol is a multiphasic system consisting of tiny liquid and solid particles and the gas in which they are suspended. In unpolluted areas such as New Zealand, aerosols contain impurities from natural sources; acidity comes from carbonic acid (H2CO3). In central Europe and other industrialized areas throughout the world, fossil-fuel combustion contributes large amounts of oxides of sulfur (SOx) and oxides of nitrogen (NOx) to the atmosphere, leading to the formation of sulfuric acid and nitric acid aerosols. In these polluted areas, acidity levels are much higher in fog than in rain, and dry deposition of sulfuric and nitric acid particulates from impactions of acid fog may be more damaging to buildings and the environment than acid rain. Forest canopies tend to scavenge acid aerosols; on conifer-covered mountains, cloud droplets are the major source of acid deposition. Dry deposition on canopies rapidly affects root systems and increases soil acidification over the long term. Soil acidification has been linked to a number of adverse effects on vegetation, especially tree dieback and forest decline in Europe.
Aerosols in industrialized areas often contain heavy metals—including chromium (Cr), iron (Fe), copper (Cu), cadmium (Cd), cobalt (Co), nickel (Ni), and lead (Pb)—latex, surfactants, and asbestos. When tetraethyl lead was used as a gasoline additive, inhalation of lead aerosols contributed a substantial fraction of the body...
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Further Reading (Encyclopedia of Environmental Issues, Revised Edition)
Colbeck, Ian, ed. Environmental Chemistry of Aerosols. Ames, Iowa: Blackwell, 2008.
Cotton, William R., and Roger A. Pielke, Sr. Human Impacts on Weather and Climate. 2d ed. New York: Cambridge University Press, 2007.
Katsouyanni, K., et al. “Short-Term Effects of Ambient Sulphur Dioxide and Particulate Matter on Mortality in Twelve European Cities: Results from Time Series Data from the APHEA Project.” British Medical Journal 314 (June 7, 1997).
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Background (Encyclopedia of Global Warming)
Effects of aerosol pollutants such as volcanic dust have been debated for a long time. A 1783 eruption of a volcanic fissure in Iceland seemed related to an unusually cool summer in France that year. In 1883, the volcanic dust from the explosion of Krakatoa in the East Indies dimmed the sunlight for months, as had the 1815 eruption of Tambora. Some scientists perceived a pattern of temporary cooling from such events. Others asked if pollutants should be expected to warm, rather than cool, the atmosphere.
Aerosols are minute airborne solid or liquid particles suspended in the atmosphere, typically measuring between 0.01 and 10 microns. They may be of either natural or anthropogenic origin. Natural aerosol sources include salt particles from sea spray; clay particles from the weathering of rocks; volcanically produced sulfur dioxide, which oxidizes to form sulfuric acid molecules; and desert dust. Anthropogenic (human-produced) aerosol sources include industrial pollutants such as sulfates, created by burning oil and coal; smoke from large-scale burning of biomass, such as occurs in slash-and-burn clearing of tropical forests; and pollution from naval vessels’ smokestacks.
Normally, most aerosols rise to form a thin haze in the troposphere; rain washes these out within about a week’s time. Some aerosols, however, are found in the higher stratosphere, where it does not rain. They can remain in this atmospheric layer for...
(The entire section is 551 words.)
Early Speculation About Aerosols (Encyclopedia of Global Warming)
Long before there was much interest in aerosols as a factor in climate change or any equipment capable of adequately analyzing aerosol data, a few individuals speculated about a possible aerosol-climate connection. The first man credited with reporting his ideas was Mourgue de Mondtredon, a French naturalist who in 1783 documented the eight-month-longLaki eruption in southern Iceland. The eruption caused the grass to die: Three-quarters of the region’s livestock and one-quarter of its people starved to death. For months, a haze hovered over western Europe. When Benjamin Franklin was visiting in France in 1783, he experienced an unseasonably cold summer and speculated that the Laki volcanic “fog” had noticeably dimmed the sunlight.
A century later, in 1883, the eruption of the Indonesian volcano Krakatoa (Krakatau) sent up a veil of volcanic dust that reduced sunlight globally for months. Scientists were unable to determine what effect the eruption might have had on the average global temperature, but scientists thereafter acknowledged volcanoes as a possible natural influence on Earth’s climate.
A few scientists who examined temperatures after major volcanic eruptions between 1880 and 1910 perceived a pattern of temporary cooling. Only later would older records reveal that the 1815 eruption of Tambora in Indonesia had affected the climate more severely than had the Krakatoa eruption....
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Early Twentieth Century Aerosol Research (Encyclopedia of Global Warming)
Throughout the first half of the twentieth century, it was known that volcanic aerosols could affect climate. As a result, some scientists suspected that other kinds of dust particles could have similar climatic effects. Physics theory seemed to support the notion that these particles should scatter radiation from the Sun back into space, thereby cooling the Earth. These ideas remained largely speculative, though some researchers began to focus on the possibility that human activity might be a major source of atmospheric particles.
In the 1950’s, nuclear bomb tests provided improved data on aerosol behavior in the stratosphere. It was determined that stratospheric dust would remain for some years, but would stay in one hemisphere. Research in the early 1960’s indicated that large volcanic eruptions lowered average annual temperatures. Some researchers, however, deemed those results enigmatic, since temperatures had fallen during a period of few eruptions. Meteorologists acknowledged that other small, airborne particles could influence climate, but throughout the first half of the century, speculation fell short of conclusion.
Gradually, scientists shifted their focus to anthropogenic atmospheric particles. Measurements by ships between 1913 and 1929 noted that sea air showed an extended decrease in conductivity, apparently caused by stack smoke and gases from ships and possibly from...
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Aerosol Research in the Later Twentieth Century (Encyclopedia of Global Warming)
By the early 1960’s, the scientific community was beginning to pay more attention to the possibility that humans influenced clouds. One noted astrophysicist had long had an interest in aerosols after seeing the effects of the Dust Bowl in the 1930’s. He noticed changes in the skies over Boulder, Colorado, and pointed out jet airplane contrails, predicting correctly that they would spread, thin, and become indistinguishable from cirrus clouds. The apparent ability of aircraft to create cirrus clouds revealed the possibility that they might be causing climate changes along major air routes. Others questioned the possibility of anthropogenic activity as the source of pollution settling on polar ice caps. At the time, the theory did not receive much credence.
Around 1970, the British meteorologist Hubert Horace Lamb’s Dust Veil Index established a connection between dust and lower temperatures. While scientific studies at this time did not yet find strong evidence for an increase in global turbidity, they did document regional hazes that spread in a radius of up to one thousand kilometers or more from industrial centers. The scientific debate shifted from the existence of anthropogenic dust to the effects of that dust. It remained a subject of controversy whether and under what circumstances dust would cool or heat the climate, especially after a spacecraft on Mars in 1971 found that a large...
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Context (Encyclopedia of Global Warming)
A number of aerosol specialists have questioned whether they have underestimated the cooling effect of aerosols. If they had, they would have underestimated those aerosols’ restraint of greenhouse warming, significantly underestimating the extent of global warming in the absence of anthropogenic aerosol pollution. Much uncertainty remains, and each new study introduces new complexities. It seems clear that reducing sooty emissions would both delay global warming and benefit public health, yet nagging questions remain: Since aerosol and clouds, unlike gases, are not distributed evenly throughout the atmosphere, uniform samples cannot be obtained. Further, the properties of clouds and aerosols are incompletely understood, and scientists are only beginning to understand some of the interactions that take place between aerosols, clouds, and climate. Thus, these interactions have not yet been incorporated into their models.
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Further Reading (Encyclopedia of Global Warming)
Levin, Z., and William R. Cotton, eds. Aerosol Pollution Impact on Precipitation: A Scientific Review. New York: Springer, 2009. Discusses the principles of cloud and precipitation formation, the sources and nature of atmospheric aerosols and their distribution, techniques for measuring aerosols, effects of pollution and biomass aerosols on clouds and precipitation, and parallels and contrasts between deliberate cloud seeding and aerosol pollution effects.
Massel, Stanislaw R. Ocean Waves Breaking and Marine Aerosol Fluxes. Sapot, Poland: Institute of Oceanology of the Polish Academy of Sciences, 2007. Addresses the basic processes and mechanics of steep and breaking waves, experimental insights into wave-breaking mechanisms, wave-breaking criteria, and various aspects of marine aerosols and marine aerosol fluxes, especially in the Baltic Sea.
Spury, Kvetoslav R., ed. Aerosol Chemical Processes in the Environment. New York: Lewis, 2000. Five sections treat general aspects of aerosols, laboratory studies of aerosols, the synthetic chemistry of aerosols, aerosol deposits on buildings, and aerosols in the atmosphere.
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Aerosols (Encyclopedia of Science)
Aerosols are collections of tiny particles of solid and/or liquid suspended in a gas. The size of particles in an aerosol ranges from about 0.001 to about 100 microns. (A micron is one-millionth of a meter.) The most familiar form of an aerosol is the pressurized spray can, which can dispense anything from hair spray to enamel paint to whipping cream. Aerosols are produced by a number of natural processes and are now manufactured in large quantities for a variety of commercial uses. They are also at the root of a number of environmental problems, including air pollution and destruction of ozone, a natural component of Earth's atmosphere.
Aerosols are commonly classified into various subgroups based on the nature and size of the particles of which they are composed and, to some extent, the manner in which the aerosol is formed. Although relatively strict scientific definitions are available for each subgroup, these distinctions may become blurred in actual practical applications. The most important of these subgroups are fumes, dusts, mists, and sprays.
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