Aerosols and the environment
Aerosols are tiny particles, both solid and liquid, suspended in the atmosphere, significantly impacting environmental air quality globally. In unpolluted regions like New Zealand, aerosols contain natural impurities, whereas industrialized areas often see pollution from fossil-fuel combustion resulting in the production of harmful compounds like sulfuric and nitric acid. This heightened acidity can damage buildings and ecosystems more severely than acid rain, as seen with the detrimental effects on soil and forest health in Europe. Aerosols also contain heavy metals and other pollutants, contributing to health issues such as asthma and respiratory problems, particularly in urban populations. Historical episodes of severe smog, like the infamous 1952 London smog, have highlighted the lethal effects of aerosols, prompting regulatory action to improve air quality. Furthermore, aerosols can influence visibility and weather patterns, contributing to phenomena like fog formation and reducing air travel safety due to low visibility conditions. Overall, the interplay of aerosols with both environmental and health factors underscores the complexity of their role in our atmosphere.
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Aerosols and the environment
DEFINITION: Aggregations of small particles, both liquid and solid, and the atmospheric gases in which they are suspended
Atmospheric aerosols are responsible for the diminishment of environmental air quality throughout much of the world.
An 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 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 burden of lead in urban dwellers. Recognition of this hazard led to a ban on leaded gasoline. Dry deposition of heavy metals in aerosols can have adverse effects on ecosystems; CdSO4 and CuSO4 are known to reduce root elongation in trees. Fluorides released by heavy industry contribute to tree dieback.
The adverse impact of aerosols on air quality has been noted by many writers since the time of John Evelyn, who, on January 24, 1684, recorded a marked decrease in atmospheric visibility and increased respiratory problems associated with London smog. During the late nineteenth and early twentieth centuries, the lethal effects of aerosols were evident in the greatly increased that occurred during London smog episodes. A historic episode in 1952, during which smog in London reduced visibility to zero, caused an estimated four thousand excess deaths, doubling the normal death rate for children and for adults ages forty-five to sixty-four. This episode led to legislation regarding emissions controls, and by the late 1960’s, the health effects related to burning were reduced to minimal levels.
Urban aerosols—with their mix of latex, soot, hydrocarbons, SOx and NOx, and other pollutants—have been implicated in the growing prevalence of asthma. In the United States, the National Institutes of Health (NIH) estimated that asthma prevalence rose 34 percent between 1983 and 1993. About 4.8 million children in the United States were estimated to suffer from asthma in 1993. Asthma deaths have rapidly increased in the United States, rising from 0.9 per 100,000 people in 1976 to 1.5 per 100,000 people in 1986. Deaths from asthma among African Americans of all ages rose from 1.5 per 100,000 in 1976 to 2.8 per 100,000 in 1986. African Americans between the ages of fifteen and twenty-four had an asthma death rate of 8.2 per one million in 1980; by 1993, the rate had increased to 18.8 per one million.
Aerosols also increase the and scattering of light in the atmosphere, reducing visibility. When particle concentrations exceed 80-100 milligrams per cubic meter (mg/m3), visibility falls below 1 kilometer (0.62 miles). Smoke palls can travel considerable distances; for example, during the spring of 1998, agricultural burning in the Yucatán in Mexico created a pall that markedly diminished visibility in Dallas, Texas.
Particulates in aerosols serve as condensation nuclei and may enhance fog formation. Visibility reductions by hygroscopic (moisture-retaining) air pollutants are noticeable at relative humidities of about 50 percent. A number of multicar chain-reaction accidents have occurred downwind of industrial plants when hygroscopic plumes have passed over cooling ponds adjacent to highways, creating abrupt reductions in visibility. When drivers of cars and trucks moving at high speeds suddenly become engulfed in an area with visibility of only a few feet, they often respond erratically, causing accidents.
Extremely low air temperatures can lead to the formation of ice fogs—known as “arctic haze”—over cities; such fogs, which are entirely (caused by humans), are fed by moisture and by particles given off by combustion. They are composed of minute ice crystals that substantially reduce visibility to the point where air travel is restricted. Ice fogs last for several days at a time and are frequent during winters in Fairbanks, Alaska, and many Canadian cities. The Siberian city of Irkutsk reports an average of 103 days of fog yearly, all during winter.
Bibliography
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