Acid Rain (3433 words) Essay Example For Students

Acid Rain (3433 words) Essay Acid RainWhat is acid rain? Acid rain is the term for pollution caused when sulfur andnitrogen dioxides combine with atmospheric moisture. The term acid rain isslightly misleading, and would be more accurate if deemed enhanced acid rain,as rain occurs acidic naturally. Acidity is measured on what is know as the pHscale. Fourteen is the most basic, seven is the most neutral, and zero is themost acidic. Pure rain has a pH level of 7, which is exactly neutral. Theacidity of rain is determined by the pH of pure water in reaction withatmospheric concentrations of carbon dioxide, resulting in carbonic acid. Theseparticles partly dissociate to produce hydrogen ions and bicarbonate ions. Abicarbonate atom is an ion formed by one hydrogen atom, one carbon at atom, andthree oxygen atoms, and is very effective in natural waters at neutralizinghydrogen ions and reducing acidity. The dissociation results in the naturalacidity of pure rain, which is moderately acidic at a pH of 5.7. Rain less than 5.7 is considered acid rain, meaning it has reacted with acidic atmosphericgases other than carbon dioxide, such as sulfur dioxide and nitrogen dioxide. Sulfur dioxide is produced by electric utilities, industrial, commercial andresidential heating, smelters, diesel engines and marine and rail transport,which creates sulfuric acid in rain. Nitrogen dioxide will also react with therain, caused largely by transportation (cars, trucks, planes, etc.) and electricutilities, producing nitric acid. There is a certain degree of naturallyoccurring acidity in rain water. This acid is from reaction with alkalinechemicals, found in soils, lakes and stream, and can occasionally occur when avolcano erupts as well. Bacterial action in soils and degasing from oceanicplankton also contribute to the acidity found in rain. More than 90% of thesulfur and 95% of the nitrogen emissions which occur in North America are due tothe pollution created by humans.1 How Is Acid Rain Formed? Acid rain consistsmainly of acids formed in the atmosphere. It consists of the oxides of sulfur,SO2 and SO3, and of nitrogen NO and NO2. Let us examine the major contributor to acid rain, sulfur oxides. Natural sources which emit sulfur dioxide includevolcanoes, sea spray, plankton and rotting vegetation. Despite these naturaloccurrences, the burning of fossil fuels (such as coal and oil) can be largelyblamed for the emissions. The chemical reactions begin as energy from sunlight,in the form of photons, hit ozone molecules (O3) to form free oxygen (O2), aswell as single reactive oxygen atoms (O). The oxygen atoms react with watermolecules (H2O), producing electrically charged, negative hydroxyl radicals(HO). These hydroxyl radicals are responsible for oxidizing sulfur dioxide andnitrogen dioxide, which produces sulfuric acid and nitric acid. Some particleswill settle to the ground (in the form of acid deposition) or vegetation canabsorb some of the SO2 gas directly from the atmosphere. When sulfur dioxidecomes in contact with the atmosphere, it oxidizes and forms a sulfate ion. Itbecomes sulfuric acid as it joins with hydrogen atoms in the air and falls do wnto earth. Oxidation occurs most in clouds, especially in heavily polluted air,where other compounds such as ammonia and ozone help to catalyze the reaction,increasing the amount of sulfur dioxide changing to sulfuric acid. Not all ofthe sulfur dioxide is converted to sulfuric acid, and it is not uncommon for asubstantial amount to float up into the atmosphere, move to another area, andreturn to earth as sulfur dioxide, unconverted. S (in fossil fuels) + O2 =* SO22 SO2 + O2 =* 2 SO3 Much of the sulfur dioxide is converted to sulfur trioxidein the atmosphere SO3 + H2O =* H2SO4 The sulfur trioxide can then dissolvewithin water to form sulfuric acid Nitric oxide and nitric dioxide are mainlyfrom power plants and exhaust fumes. Similar to sulfur dioxide, reactions areheavily catalyzed in heavily polluted clouds where iron, manganese, ammonia andhydrogen peroxide are present. Also, the formation of nitric acid can triggerfurther reactions which release new hydroxyl radicals to generate more sulfuricacid. The following is a typical reaction, which is direct combination ofnitrogen and oxygen at the high temperature inside a car engine. N2 + O2 + heat=* 2NO 2NO + O2 =* 2NO2 This nitrogen monoxide immediately reacts with oxygenand forms nitrogen dioxide in the following reaction 3NO2 + H2O =* 2HNO3 (aq) +NO The nitrogen will then dissolve in water in the atmosphere and produce nitricacid There are several other potential contributors to acid rain. These includeoxidation by products of alkene-ozone reactions, oxidation by reactions of NxOyspecies and oxidation by peroxy radicals. Each of these reactions, however proveto be minor contributors and are rather insignificant. How Is Acid Rain Harmful?Environmental Hazards Aquatic Ecosystems Acid rain has an effect on virtuallyall ecosystems it touches. Perhaps the most prominent, and equally as troublingis the harmful results it produces when in contact with lakes, streams andponds. Scientists studying the effects of acid r ain went to a lake about 135 kmaway from the Ontario- Manitoba border called Lake 223. This lake, so far northacid rain did not reach it, was extremely healthy, and was a perfect setting toexplore the effects of acid rain on aquatic ecosystems. In 1974, scientistsbegan to add sulfuric acid into the lake. The acid was added very slowly, and itwas four years later when they saw a major change. The freshwater shrimp beganto die out. Fathead minnows stopped reproducing and began to vanish. As thescientists continued adding acid to Lake 223 in low amounts, large algae matsbegan to form and crayfish became unhealthy and died. Seven years after thebeginning of the experiment, the lake trout stopped reproducing, and most of thefish species, leeches, crawfish and mayflies began to die. In 1984, thescientists stopped adding the acid. Without the addition of deadly sulfuricacid, the lake slowly began to recover. Some of the fish species began torecover, however some of the scientists estimated it would take one hundredyears for the lake to fully recover, even without the addition of any more acid. Fish can still live in a lake with a low acid level, however they will get sickand not grow to proper proportions. Often the fish will not reproduce, andeventually, as the acid level increases, all the fish will die. The acid willalso leach metals from the bottom of the lake. There are metals containedwithin the mud and rocks of the lake bottom, however they remain not dangerousas long as they are not released. The acid will draw out these harmful metalsand dissolve them in the water, resulting in the deterioration and disappearanceof a species. One of these damaging metals is aluminum, which will coat and burnthe gills of the fish as it intakes the polluted water. Some fish found inacidic lakes contain higher levels of mercury in their bodies, which is harmfulto humans, resulting in the government telling society to limit the amount offish they eat from certain lakes and rivers. If the numbers of one species orgroup of species changes in response to acidification, the ecosystem of t heentire body of water is likely to be affected through the predator-preyrelationships. Let us examine how acid rain is dangerous to fish. A freshwaterfishs respiration consists of a trade of hydrogen ions (H+) in their bloodfor sodium ions (Na+) from the water around them. If the concentration ofhydrogen ions in the water is increased, which is essentially what happens whenpH falls, there are (proportionally) fewer sodium ions. Fish are forced toabsorb more hydrogen while finding it harder to obtain sodium. The acidity oftheir blood increases, while the salt content drops. An experiment involvingbrown trout showed that at a pH of 5.2 or lower, this process was fatal to thisspecies, and is likely deadly to many other trout species. The following chartshows the steps typical to freshwater fish as the acidity increases. (Fig 1-1)ACIDITY LEVEL (pH) EFFECTS ON AQUATIC LIFE 7 Neutral, H+ and H- are in balance6.8 Shells of clams and snails become thinner, due to lack of hazardous calciumi ons in the water 6.6 The viability of eggs of the fathead minnow is reduced,rain can have and fewer eggs hatch 6.5 Lake trout begin to have difficultyreproducing, clams and snails become scarcer, green algae growth increases 6Several clam and snail species disappear, several trout species populationsdecrease, the smooth newt is gone, smallmouth bass, walleyes and spottedsalamanders have difficulty reproducing, several mayfly species cease to layeggs 5.8 Copepods (a critical link of crustaceans in the marine food chain) aregone, crayfish have trouble regrowing exoskeleton after molting 5.7 Severalalgae species decrease, while filamentous green algae increases, planktondecreases 5.5 Rainbow trout, fathead minnows and smallmouth bass loseconsiderable population, walleyes, brook trout, roach, lake trout and shinersdont reproduce, leeches and mayfly larvae vanish. 5.4 Crayfish reproductivityis impaired. 5 Snail and clams are extinct. All but one species of crayfish areextinct, brook trou t, walleyes and most bullfrogs are gone, most fish speciesexperience reproduction difficulties, zooplankton population begins to drop,green and green-blue algae mats have largely spread 4.8 Leopard frog numbersdecline 4.5 Mayflies and stoneflies vanish, a slowing in growth rate and oxygenuptake of bacteria is notable 4.2 The common toad disappears 4 The oxygen outputof Lobelia plants declines 75% 3.5 Virtually all clams, snails, frogs, fish andcrayfish vanish 2.5 Only a few species of acid-tolerant midges, bacteria andfungi are alive 2 In practical terms, the lake is sterile Two hundred and twentylakes in Ontario have been found acidified, meaning their pH is less that 5.1year round.2 Terrestrial Plant Life It is much more difficult to solve themystery of forest destruction compared to that of a lake. This is partiallybecause trees live so much longer than fish do, and acid rain damage in treesmay not show up for thirty or forty years. It is also very difficult toreplicate forest co nditions in a laboratory, such as insects, cold winters,pollution, elevation and abrupt changes in rainfall. Each of these conditionsput stress on the trees and can be considered variables. Many scientists areconvinced that because of the complexity of a forest ecosystem, it is nearlyimpossible to prove the death of forests is due to pollution in the form of acidrain, but deduce from many experiments it is a main factor in forestdestruction. Deciduous trees are like air filters, and screen particles thatpass through the air around them. These particles collect on the leaves of thetree, and studies have shown that when these particles contain acid they cancause damage to the leaves. The leaves are the part of the tree that help makefood, hence any damage to the leaves will result in harm to the health of theentire tree. Coniferous trees are vulnerable to the harmful effects of acid rainas well. The trees needles are designed to nourish the tree after they fall tothe ground. Each need le houses whole colonies of microscopic bacteria and algaethat help the tree change nitrogen into food at the roots. Acid rain will oftenburn away this material, thereby reducing adequate food supply, and weakeningthe trees health. After the damage has been done to leaves and needles, acidrain harms the trees even more through the soil. Soil has a level of acid. Acidin the soil can do damage to the trees by releasing aluminum, which, once incontact with acid, becomes highly poisonous to forests. The aluminum will enterthe trees hairlike roots, choking them, and when these become clogged, theupper branches are no longer nourished. Even though there may be plenty ofmoisture in the soil, the tree can die of thirst. Scientists have discoveredthat the aluminum content in soil has tripled since the 1960s.3 Acid rain alsokills important organisms on the forest floor. The process of decomposition isinterrupted as the acid kills many of the bacteria and fungi that live on theforest floor. At a pH level of 4.0, the earthworm dies, further damaging thedecomposition process. Without earthworms and bacteria to decompose the debrisconsisting of animal and bird droppings, twigs and dead leaves, the materialscontinue to build on the forest floor. When debris builds up, seedlings from thetrees are not able to survive, because they can not work their way down to thesoil to root. This causes the forest to slowly disappear, as older trees die,and the forest will not be able to rejuvenate itself. Acid rain is hardest ontrees high up in mountains, because it is often covered in mist or fog,literally bathing the trees in an acidic atmosphere. Trees also suffer becauseof changes in the soil. Acid rains leach metals (draw metals out of mud androcks) in the soil, and the trees in turn intake these harmful metals throughtheir roots. Figure 1-2 shows the damage that acid rain can to do a forest HumanHealth It is known that the earth contains many metals that are potentiallydangerous to h umans, such as lead, mercury, and aluminum. Most of the time thesemetals are harmless because they are in the soil, bonded to other elements. Theproblem occurs when acid detaches these metals from the rocks and soils, and canbe carried deep into the ground and make their way to underground streams. Thesestreams eventually connect to our water sources. Medical researchers have foundthese metals can be dangerous, and on rare occasion, is even fatal. Aluminum hasbeen found to kill people who have kidney problems, and can also collect inbrain tissue. Some scientists even suspect that aluminum deposits on the braincause Alzheimers disease. (A disease that results in memory loss, nervoussystem problems, and death. Acid rain is known to irritate the whole respiratorysystem, beginning with mucous membranes in the nose and throat, all the way totissue in the lungs. Consequently, acid rain has an increased effect on peoplewith respiratory problems. The U.S. Council on Environmental Quality es timateshealth-related problems due to acid precipitation cost the United States $2billion per year.4 In August 1987, over one hundred people were treated for eye,throat, and mouth irritation when 1.8 metric tonnes of highly toxic sulfurdioxide gas leaked from an Inco plant near Sudbury, Ontario. Even Fig 1-2 Thispicture shows how a coniferous forest has been virtually destroyed. Acid rain isblamed for the destruction of terrestrial ecosystems around the world. withoutaccidents, the sulfur dioxide regularly emitted from Inco smokestacks has beenlinked to chronic bronchitis in Inco employees.5 Drinking Water Acid raindamages drinking water in various ways. Thus far, amounts of metals in drinkingwater have been minimal, however the fact that metals even leak into the wateris troubling to scientists. Since metals remain in the body once ingested, overtime, small amounts accumulate into large quantities, and it has yet to beconcluded how large an amount will prove to be harmful to humans . Acid raincauses damage by loosening metals off metal water pipes. Modern plumbing usesplastic tubing, but older systems have copper pipes. The copper pipes are heldtogether by a mixture of tin and lead. Lead is known to be extremely dangerousto humans, even in small amounts, and will cause damage to the brain and nervoussystem. A study that was done in Ontario found that water sitting in plumbingpipes for ten days contained hazardous levels of copper and lead. This discoverycould be a widespread danger, since often people will go on vacation and notshut off the plumbing, allowing water to sit and absorb these dangerous metals. Marriage And Aging EssayAcid rain can also dissolve the reinforcements that occur around large waterpipes. In some parts of the United States, asbestos is used to reinforce thecement bases that hold water pipes. Asbestos is not dangerous when bound to thecement, but is highly dangerous when separated, and has been linked to cancerand other serious diseases. Many health officials worry that loose asbestos willfind its way to the citys water when acid rain comes in contact with thecement. Effects On Man Made Structures Scientists are becoming increasinglyconcerned with acid rains destruction of the built environment. There areobjects in our built environment that are irreplaceable. Historic landmarks andstatues, old cathedrals and temples, paintings and sculpture all are part ofthe built environment and are slowly being damaged. Some of these objects arepractical, making life easier, safer or more comfortable. Many factors determinehow much damage acid rain will do, including the am ount of rain, the location,and direction of wind. All influence the amount of corrosion done. Areas thathave a large amount fog or humidity tend to suffer more than dry areas, which iswhy many steel bridges located over water get rusted and corroded by acid. Whenmetal is decayed, it cannot take the same amount of stress of weight as when itwas originally created. Acid rain has been blamed in several collapses ofbridges around the world. Acid rain corrodes the steel track used on railroads,thus the tracks must be constantly checked. Metal in air planes can also beeaten away by acid rain. The United States Air Force spends more that $1 billionevery year to repair or replace damaged parts.6 A study done in Sweden showedthat metal rusts four times faster in areas that receive a lot of acid rain. This figure is staggering, and yet, metal is not the only material damaged byacid rain. Houses and buildings made of brick and stone are affected as well. Acid rain can dissolve the mortar, which is used in cement to hold brickstogether. When the mortar is worn away, the bricks crumble more easily, becausethey shift and cannot stay intact against the heavy weight of the brickspressuring from above. The corrosive effects of acid rain are particularlyobvious on limestone, because it is composed of calcium carbonate, which ishighly reactive with acid rain. Tombstones made of marble (which ismetamorphosed or heated limestone) have been badly damaged, while oldertombstones made of slate remain intact. Famous buildings such as the Taj Mahal,The United States Capitol building and the Lincoln Memorial in Washington, areall being continually damaged by acid rain. Statues made of bronze and copperare particularly susceptible to corrosion. These statues turn green naturally,and this covering, called a patina, acts as a protective shield against theelements. Acid rain eats away at the patina, and where the acid dissolves thegreen covering, it leav es a streaky black coat. This process ruins statuesthroughout the world. How Does Acid Rain Affect the Economy? Canada/AmericanRelations Canada is particularly susceptible to the effects of acid rain. Itsgeographical location places it directly in the path of a large amount of U.S. emission, and the granite bedrock of the Canadian Shield has a poor bufferingquality. (A buffer is a material that can chemically weaken acid soil and isless harmful to the environment, such as lime or baking soda.) The lack of sucha quality renders Eastern Canada highly vulnerable to damage due to UnitedStates pollution. Canada suffers more from acid rain than the United Statesdoes, even though much of the pollution originates in the United States. Acidrain costs Canadians hundreds of millions of dollars every year. To try anddecrease the large amounts of money the pollution is costing tax payers, Canadahas passed laws to force its electrical companies to cut down on harmfulemissions. However, no matter what laws are passed in Canada, it is not possibleto stop U.S. power plants from sending acid in its direction. Figure 1-3displays amounts of emissions created by the United States and Canada. The Gavinpower plant is an excellent example of how the United States sends tonnes ofacid t o Canada every year. Every hour, this power plant burns 600 tonnes ofcoal. The higher the smokestack, the further the dangerous gases will travel,and the Gavin smokestack is 1 103 feet tall.7 Obviously, The Gavin can not besolely blamed for the pollution, but it is power plants such as these that havecaused trouble between the two countries. It is estimated that about 50% of thesulfate deposited in Canada derived from American sources.8 Sixty of the largestplants and thus largest polluters are located in the Ohio Valley, a shortdistance away from vulnerable Canadian land. In 1980, Canada and the UnitedStates signed a Memorandum of Intent, an agreement that both countries wouldmake acid rain control a priority. They both promised to focus on developingideas to cut down the amount of sulfur dioxide and nitrogen oxide emissionsbeing pumped into the air. In the past, Canada has presented devastatingly largefigures to the United States, in an attempt to have them change laws andregulatio ns regarding pollution. Unfortunately, the attempts thus far have beenunsuccessful, as the US government requests more testing and studies instead ofaltering laws. In the recent past, the negotiations between Canada and UnitedStates representatives have been hardly reminiscent of efforts put forth byCanadian officials. Many U.S. politicians still qualify acid rain as a minorproblem, and it is treated as such, according to Raymond Robinson, chairman ofthe Canadian Environmental Assembly.