Acid Rain (Encyclopedia of Science)
Acid rain is a popular phrase used to describe rain, snow, fog, or other precipitation that is full of acids that collect in the atmosphere due to the burning of fuels such as coal, petroleum, and gasoline. Acid rain was first recognized in Europe in the late 1800s but did not come to widespread public attention until about 1970, when its harmful effects on the environment were publicized. Research has shown that in many parts of the world, lakes, streams, and soils have become increasingly acidic, prompting a corresponding decline in fish populations.
Acid rain occurs when polluted gases become trapped in clouds that drift for hundredsven thousandsf miles and are finally released as acidic precipitation. Trees, lakes, animals, and even buildings are vulnerable to the slow, corrosive (wearing away) effects of acid rain.
Acidification (the process of making acid) is not just caused by deposits of acidic rain but also by chemicals in snow and fog and by gases and particulates (small particles) when precipitation is not occurring.
The major human-made causes of acid deposition are (1) emissions of sulfur dioxide from power plants that burn coal and oil and (2) emissions of nitrogen oxides from automobiles. These emissions are transformed into sulfuric acid and nitric acid in the atmosphere, where they...
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Acid Rain (Science Experiments)
Why is acid rain a problem?
Acid Rain and Animals: How does acid rain affect brine shrimp?
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Did you know that acid rain can also be acid snow, acid fog, or even acid dust? is a form of precipitation that is significantly more acidic than neutral water. The pH scale offers a way to compare the acidity of substances, including rain. pH (the abbreviation for potential hydrogen) is a measure of the acidity or alkalinity of a solution. The symbol pH refers to the concentration of hydrogen ionsAn atom or groups of atoms that carry an electrical chargeither positive or negatives a result of losing or gaining one or more electrons. present in a liter of fluid. The pH scale ranges from 0 (greatest concentration of hydrogen ions and therefore most acidic) to 14 (least concentration of hydrogen ions and therefore most ). An alkaline solution is also called a baseA water-soluble compound that when dissolved in water makes an alkaline, or basic, solution with a pH of more than 7.. The number 7 represents a neutral solution, such as pure water.
Water with a pH of 4 is ten times more acidic...
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Acid Rain (Encyclopedia of Public Health)
"Acid rain" is the common term for a complex process more appropriately referred to as acid deposition. It includes the deposition of acidic compounds onto the ground and onto surface waters when it rains (wet deposition), and at other times as well (dry deposition). The acid compounds include both acidic gases, such as sulfur dioxide (SO2) and nitrogen dioxide (NO2), and acidic particles, such as sulfate and nitrate compounds. Acid deposition is believed to have adversely affected lakes and forests in the northeastern United States, Canada, and Europe, and to have caused material damage as well.
The primary anthropogenic source of airborne acidity is the burning of fossil fuels. Coal-and oil-fired electric utilities and industries emit gaseous SO2 and nitrogen oxides (NO and NO2) into the atmosphere. Automobiles and other mobile sources also contribute significant amounts of nitrogen oxides.
As these primary pollutants are transported by the wind, sometimes over long distances, they are slowly transformed through a variety of atmospheric reactions to secondary pollutants, such as nitric acid vapor and sulfuric acid droplets, which are strongly acidic. With further transport and reactions with ammonia gas (NH3) from biological decay processes at the ground level, they are transformed to less strongly acidic sulfate and nitrate particles. These atmospheric reaction products can remain suspended, impairing visibility, reducing air quality, and causing adverse human health effects or these products can be deposited directly onto surfaces at ground level.
The area affected by the emission sources is determined to a large extent by the time that pollutants stay in the atmosphere before removal through deposition.
Sulfur and nitrogen deposition have caused adverse impacts on highly sensitive forest ecosystems in the United States and northern Europe, such as high-elevation spruce and fir forests in the eastern United States. On the other hand, most U.S. forest ecosystems are not currently known to be adversely impacted. The gradual leaching of soil nutrients from sustained acid deposition can impede forest nutrition and growth. Potential risk depends on numerous factors, including rate of cation (positively charged ion) deposition, soil cation reserves, age of forest, weathering rates, species composition, and disturbance history. Dry deposition is now considered to be more damaging to stone than wet deposition.
Since sulfate significantly contributes to visibility-reducing particles in the eastern United States, reduced SO2 emissions will reduce sulfate concentrations and, in turn, their contribution to haze. In the 1990 U.S. Clean Air Act Amendments, Congress mandated reductions in annual emissions of SO2 by 1995 and nitrogen oxides from utilities burning fossil fuels starting in 1995.
As a result, statistically significant reductions in the acidity (represented by hydrogen ion content) and sulfate concentrations in precipitation were reported at deposition-monitoring sites in the Midwest, Mid-Atlantic, and northeast United States. Although utilities have significantly reduced their emissions, observable responses will lag due to inherent time lags between changes in emissions and responses by sensitive receptors, especially within ecosystems.
It is still too early to determine whether changes in aquatic ecosystems have resulted from emission reductions. Over the last fifteen years, lakes and streams throughout many areas of the United States have experienced decreases in sulfate concentrations in response to decreased emissions and deposition of sulfur, and there is evidence of recovery from acidification in New England lakes. In contrast, the acidity levels of the majority of Adirondack lakes have remained fairly constant, while the most sensitive Adirondack lakes have continued to acidify.
The kind of damages seen in forests and lakes in the northeastern United States have also been witnessed in Scandinavia and other parts of northern Europe.
(SEE ALSO: Airborne Particles; Ambient Air Quality [Air Pollution]; Clean Air Act; Environmental Determinants of Health; Inhalable Particles [Sulfates]; Total Suspended Particles [TSP])
National Acid Precipitation Assessment Program (1998). National Acid Precipitation Assessment Program Biennial Report to Congress: An Integrated Assessment. Silver Spring, MD: Author.
Acid Rain (World of Earth Science)
Acid rain is rain with a pH (a logarithmic measurement of acidity or alkalinity) of less than 5.7. Acid rain usually results from elevated levels of nitric and sulfuric acids in air pollution. Acidic pollutants that can lead to acid rain are common by-products from burning fossil fuels (e.g., oil, coal, etc.) and are found in high levels in exhaust from internal combustion engines (e.g., automobile exhaust). Acidic precipitation may also occur in other forms such as snow.
Acid rain occurs when polluted gasses become trapped in clouds. The clouds may drift for hundreds, even thousands, of miles before finally releasing acidic precipitation. Trees, lakes, animals, and even buildings are vulnerable to the slow corrosive effects of acid rain, whose damaging components are emitted by power plants and factories, especially those burning low grades of coal and oil.
Acid rain was first recognized in 1872, approximately 100 years after the start of the Industrial Revolution in England, when an English scientist, Robert Angus Smith (1817884), pointed out the problem. Almost another century passed, however, before the public became aware of the damaging effects of acid rain. In 1962, the Swedish scientist Svante Oden brought the acid rain quandary to the attention of the press, instead of the less popular scientific journals. He compiled records from the 1950s indicating that acid rain came from air masses moving out of central and western Europe into Scandinavia.
After acid rain was discovered in Europe, scientists began measuring the acidity of rain in North America. Initially, they found that the problem was concentrated in the northeastern states of New York and Pennsylvania because the type of coal burned there was more sulfuric. By 1980, most of the states east of the Mississippi, as well as southeastern Canada, were receiving acidic rainfall. Acid rain falls in the West also, although the problem is not as severe. Acid rain in Los Angeles, California is caused primarily by local traffic emissions. Car emissions contain nitrogen oxide, the second highest problematic gas in acid rain after sulfur dioxide.
Acid rain is measured through pH tests that determine the concentration of hydrogen ions. Pure water has a neutral pH of approximately 7.0. When the pH is greater than 7, the material is thought to be alkaline. At a pH of 5.7, rain is slightly acidic, but when its pH is further reduced, the rain becomes an increasingly stronger acid rain. In the worst cases, acid rain has shown a pH of 2.4 (about as acidic as vinegar). When pH levels are drastically tipped in soil and water, entire lakes and forests are jeopardized. Evergreen trees in high elevations are especially vulnerable. Although the acid rain itself does not kill the trees, it makes them more susceptible to other dangers. High acid levels in soil causes leaching of other valuable minerals such as calcium, magnesium, and potassium. According to the World Watch Institute, in the late 1980s and early 1990s forest damage in Europe ranged from a low of 4% in Portugal to a high of 71% in Czechoslovakia, averaging 35% overall.
Small marine organisms cannot survive in acidic lakes and rivers, and their depletion affects larger fish and ultimately the entire marine life food chain. Snow from acid rain is also damaging; snowmelt has been known to cause massive, instant death for many kinds of fish. Some lakes in Scandinavia, for example, are completely devoid of fish. Acid rain also eats away at buildings and metal structures. From the Acropolis in Greece to Renaissance buildings in Italy, ancient structures are showing signs of slow corrosion from acid rain. In some industrialized parts of Poland, trains cannot exceed 40 miles (65 km) per hour because the iron railway tracks have been weakened from acidic air pollution.
New power plants in the United States are being built with strict emissions standards, but retrofitting older plants is difficult and expensive. Nevertheless, the United States Environmental Protection Agency requires most of the older and dirtier power plants to install electrostatic precipitators and baghouse filtersevices designed to remove solid particulates. Such devices are required in Canada, in industrialized countries in Western Europe, and in Japan. Scrubbers, or flue-gas desulfurization technology, are also being used because of their effectiveness in removing as much as 95% of a power plant's sulfur dioxide emissions. These devices are expensive, however, and there are clauses in pollution control laws that allow older plants to continue operation at higher pollution levels. Another way to reduce acid rain is for power plants to burn cleaner coal in their plants. This does not require retrofitting but it does increase transportation costs since coal containing less sulfur is mined in the western part of the United States, far away from where it is needed in the midwest and eastern part of the country.
See also Atmospheric pollution; Erosion; Global warming; Groundwater; Petroleum, economic uses of; Rate factors in geologic processes; Weathering and weathering series