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Acid rain is rain that is more acidic thannormal. Acid rain is a complicated problem.Caused by air pollution, acid rain's spreadand damage involves weather, chemistry,soil, and the life cycles of plants and animalson the land and from acid rain in the water. Scientists have discovered that air pollutionfrom the burning of fossil fuels is the majorcause of acid rain. Power plants andfactories burn coal and oil. Power plants usethat coal and oil to produce the electricity weneed to heat and light our homes and to runour electric appliances. We also burnnatural gas, coal, and oil to heat our homes. The smoke and fumes from burning fossilfuels rise into the atmosphere and combinewith the moisture in the air to form acid rain.The main chemicals in air pollution thatcreate acid rain are sulfur dioxide andnitrogen oxides. Acid rain usually forms highin the clouds where sulfur dioxide andnitrogen oxides react with water, oxygen,and oxidants.
This forms a mild solution ofsulfuric acid and nitric acid. Sunlightincreases the rate of most of thesereactions. Rainwater, snow, fog, and otherforms of precipitation containing those mildsolutions of sulfuric and nitric acids fall to theearth as acid rain. Water moves through every living plant andanimal, streams, lakes, and oceans in thehydrologic cycle. In that cycle, waterevaporates from the land and sea into theatmosphere. Water in the atmosphere thencondenses to form clouds. Clouds releasethe water back to the earth as rain, snow, orfog.
When water droplets form and fall to theearth they pick up particles and chemicalsthat float in the air. Even clean, unpollutedair has some particles such as dust orpollen. Clean air also contains naturallyoccurring gases such as carbon dioxide.The interaction between the water dropletsand the carbon dioxide in the atmosphere,and to a lesser extent, from chlorine which isderived from the salt in the sea, gives rainan average pH of about 5.6, making evenclean rain slightly acidic. Other naturalsources of acids and bases in theatmosphere may lower or raise the pH ofunpolluted rain. However, when raincontains pollutants, especially sulfur dioxideand nitrogen oxides, the rain water canbecome very acidic. Acid rain does not account for all of theacidity that falls back to earth frompollutants. About half the acidity in theatmosphere falls back to the earth throughdry deposition as gases and dry particles.The wind blows these acidic particles andgases onto buildings, cars, homes andtrees.
In some instances, these gases andparticles can eat away the things on whichthey settle. Dry deposited gases andparticles are sometimes washed from treesand other surfaces by rainstorms. When thathappens, the runoff water adds those acidsto the acid rain, making the combinationmore acidic than the falling rain alone. Thecombination of acid rain plus dry depositedacid is called acid deposition. The chemical reactions that change airpollution to acid rain can take from severalhours to several days. Years ago, whensmokestacks were only a few stories high,pollution from smokestacks usually stayednear the ground and settled on land nearby.This caused unhealthy conditions for plantsand animals near the smokestacks.
Toreduce this pollution, the governmentpassed a law permitting the construction ofvery tall smokestacks. At that time, peoplethought that if the pollution were sent highinto the air it would no longer be a problem.Scientists now know that this is incorrect.Sending pollution high into the skyincreases the time that the pollution stays inthe air. The longer the pollution is in the air,the greater are the chances that thepollutants will form acid rain. In addition, thewind can carry these pollutants for hundredsof miles before they become joined withwater droplets to form acid rain. For thatreason, acid rain can also be a problem inareas far from the polluting smokestacks.Dry deposition is usually more abundantnear the cities and industrial areas wherethe pollutants are released. There are also natural sources of acids suchas volcanoes, natural geysers and hotsprings.
Nature has developed ways ofrecycling these acids by absorbing andbreaking them down. These natural acidscontribute to only a small portion of theacidic rainfall in the world today. In smallamounts, these acids actually help dissolvenutrients and minerals from the soil so thattrees and other plants can use them forfood. The large amounts of acids producedby human activities overload this naturalacidity.Acid rain is poorly understood and we willprobably spend billions on research endingup with two opposing groups of experts.One of the biggest money contributers toour congressmen is a lobby groupdedicated to defeating or diluting any acidrain controls.'Acid Rain,' or more precisely acid precipitation, isthe word used to describe rainfall that has a pH levelof less than 5.6. This form of air pollution is currentlya subject of great controversy because of it'sworldwide environmental damages. For the last tenyears, this phenomenon has brought destruction tothousands of lakes and streams in the UnitedStates, Canada, and parts of Europe. Acid rain isformed when oxides of nitrogen and sulfite combinewith moisture in the atmosphere to make nitric andsulfuric acids.
The two primary sources of acid rainare sulfur dioxide, and oxides of nitrogen. Sulfurdioxide is a colourless, prudent gas released as aby-product of combusted fossil fuels containingsulfur. A variety of industrial processes, such as theproduction of iron and steel, utility factories, andcrude oil processing produce this gas. In iron andsteel production, the smelting of metal sulfate ore,produces pure metal. This causes the release ofsulfur dioxide. Metals such as zinc, nickel, andcopper are commonly obtained by this process.Sulfur dioxide can also be emitted into theatmosphere by natural disasters.
Ten percent of allsulfur dioxide emission comes from volcanoes, seaspray, plankton, and rotting vegetation. Overall, 69.4percent of sulfur dioxide is produced by industrialcombustion. Only 3.7 percent is caused bytransportation The other chemical that is also chiefly responsiblefor the make-up of acid rain is nitrogen oxide.Oxides of nitrogen is a term used to describe anycompound of nitrogen with any amount of oxygenatoms. Nitrogen monoxide and nitrogen dioxide areall oxides of nitrogen. These gases are by-productsof firing processes of extreme high temperatures(automobiles, utility plants), and in chemicalindustries (fertilizer production). Natural processessuch as bacterial action in soil, forest fires, volcanicaction, and lightning make up five percent of nitrogenoxide emission. Transportation makes up 43percent, and 32 percent belongs to industrialcombustion. Nitrogen oxide is a dangerous gas byitself.
As mentioned before, any precipitation with apH level less than 5.6 is considered to be acidrainfall. The difference between regular precipitationand acid precipitation is the pH level. A pH scale isused to determine if a specific solution is acidic orbasic. Any number below seven is considered to beacidic. Any number above seven is considered to bebasic. The scale is color coordinated with the pHlevel. Most pH scales use a range from zero tofourteen.
Seven is the neutral point (pure water). ApH from 6.5 to 8, is considered the safe zone.Between these numbers, organisms are in very littleor no harm. Not only does the acidity of acid precipitationdepend on emission levels, but also on the chemicalmixtures in which sulfur dioxide and nitrogen oxidesinteract in the atmosphere. Sulfur dioxide andnitrogen oxides go through several complex steps ofchemical reactions before they become the acidsfound in acid rain. The steps are broken down intotwo phases, gas phase and aqueous phase. Thereare various potential reactions that can contribute tothe oxidation of sulfur dioxide in the atmosphereeach having varying degrees of success. The mostcommon process is when sulfur dioxide reacts withmoisture found in the atmosphere.
When thishappens, sulfate dioxide immediately oxidizes toform a sulfite ion. Afterwards, it becomes sulfuric acid when it joinswith hydrogen atoms in the air. A common reactionfor sulfur dioxide to becomes sulfuric acid is byoxidation by ozone. This reaction occurs at apreferable rate and sometimes is the maincontributor to the oxidation of sulfuric acid. There areother insignificant reactions that contribute to acidrain, but contribute to little to mention. Thesereactions unfortunately prove to be insignificant forvarious reasons. These reactions mentioned above,are gas phase reactions. Sulfur dioxide oxidation is most common in cloudsand especially in heavily polluted air wherecompounds such as ammonia and ozone are inabundance. These catalysts help convert more sulfurdioxide into sulfuric acid.
But not all of the sulfurdioxide is converted to sulfuric acid. In fact, asubstantial amount can float up into the atmosphere,transport to another area and return to earthunconverted. Like sulfur dioxide, nitrogen oxides rise into theatmosphere and are oxidized in clouds to form nitricor nitrous acid. These reactions are catalyzed inheavily polluted clouds where traces of iron,manganese, ammonia, and hydrogen peroxide arepresent. Nitrogen oxides rise into the atmospheremainly from automobile exhaust. In the atmosphereit reacts with water to form nitric or nitrous acid. Over the years, scientists have noticed that someforests have been growing more and more slowlywithout reason. Trees do not grow as fast as theydid before.
Leaves and pines needles turn brown andfall off when they are supposed to be green.Eventually, after several years of collecting andrecording information on the chemistry and biologyof the forest, researchers have concluded that thiswas the work of acid rain. A rainstorm occurs in aforest. The summer spring washes the leaves of thebranches and fall to the forest floor below. Some ofthe water is absorbed into the soil. Water run-offenters nearby streams, rivers, or lakes. That soilmay have neutralized some or all of the acidity in theacid rainwater.
This ability of neutralization is calledbuff ....
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