How Acid Rain Develops, Spreads, and DestroysAcid rain is environmentally damaging rainfall that occurs after fossil fuelsburn, releasing nitrogen and sulphur oxides into the atmosphere. Acid rain,simply stated, increases the acidity level of waterways because these nitrogenand sulphur oxides combine with the airs normal rainfall.
Acid rain is asilent threat because its effects, although slow, are cumulative. This analysisexplains the cause, the distribution cycle, and the effects of acid rain. Most research shows that power plants burning oil or coal are the primarycause of acid rain. The burnt fuel is not completely expended, and some residueenters the atmosphere.
Although this residue contains several potentially toxicelements, sulphur oxide and, to a lesser extent, nitrogen oxide are the majorproblem, because they are transformed when they combine with moisture. Thischemical reaction forms sulphur dioxide and nitric acid, which then rain down toearth. Once fossil fuels have been burned, their usefulness is over. Unfortunately,it is here that the acid rain problem begins. Fossil fuels contain a number ofelements that are released during combustion.
Two of these, sulphur oxide andnitrogen oxide, combine with normal moisture to produce sulphuric acid andnitric acid. The released gases undergo a chemical change as they combine withatmospheric ozone and water vapour. The resulting rain or snowfall is moreacidic than normal precipitation. Acid level is measured by pH readings.
The pH scale runs from 0 through 14 –a pH of 7 is considered neutral. (Distilled water has a pH of 7. ) Numbers below7 indicate increasing alkalinity. (Household ammonia has a pH of 11. ) Numbersbelow 7 indicate increasing acidity. Movement in either direction on the pHscale, however, means multiplying by 10.
Lemon juice, which has a pH value of 2,is 10 times more acidic than apples which have a pH of 3, and is 1000 times moreacidic than carrots, which have a pH of 5. Because of carbon dioxide (an acidic substance) normally present in air,unaffected rainfall has a pH of 5. 6. At this time the pH of precipitation in thenortheastern United States and Canada is between 4. 5 and 4. In Massachusetts,rain and snowfall have an average reading of 4.
1. A pH reading below 5 isconsidered to be abnormally acidic, and therefore a threat to aquaticpopulations. Although it might seem that areas containing power plants would be mostseverely affected, acid rain can in fact travel thousands of miles from itssource. Stack gases escape and drift with the wind currents. The sulphur andnitrogen oxides are thus able to travel great distances before they return toearth as acid rain.
For an average of two to five days after emission, the gases follow theprevailing winds far from the point of origin. Estimates show that about 50percent of the acid rain that affects Canada originates in the United States; atthe same time, 15 to 20 percent of the US acid rain originates in Canada. The tendency of stack gases to drift makes acid rain a widespread menace. More than 200 lakes in the Adirondacks, hundreds of miles from any industrialcentre, are unable to support life because of their water has become so acidic. Acid rain causes damage wherever it falls. It erodes various types ofbuilding rock such as limestone, marble, and mortar, which are gradually eatenaway by the constant bathing in acid.
Damage to buildings, houses, monuments,statues, and cars is widespread. Some priceless monuments and carvings alreadyhave been destroyed, and even trees of some varieties are dying in largenumbers. More important, however, is acid rain damage to waterways in the affectedareas. Because of its high acidity, acid rain is dramatically lowers the H inlakes and streams.
Although its effect is not immediate, acid rain eventuallycan make a waterway so acidic that it dies. In areas with natural acid-bufferingelements such as limestone, the dilute acid has less effect. The northeasternUnited States and Canada, however, lack this natural protection, and so arecontinually vulnerable. The pH level in an affected waterway drops so low that some species cease toreproduce. In fact, a pH level of 5. 1 to 5.
4 means that fisheries arethreatened; once a waterway reaches a pH level of 4. 5, no fish reproductionoccurs. Because each creature is part of the overall food chain, loss of oneelement in the chain disrupts the whole cycle. In the northeastern United States and Canada, the acidity problem iscompounded by the run-off from acid snow. During the cold winter months, acidsnow sits with little melting, so that by spring thaw, the acid released isgreatly concentrated.
Aluminum and other heavy metals normally present in soilare also released by acid rain and run-off. These toxic substances leach intowaterways in heavy concentrations, affecting fish in all stages of development. Acid rain develops from nitrogen and sulphur oxides emitted by industries andpower plants burning fossil fuels. In the atmosphere, these oxides combine withozone and water to form acid rain: precipitation with a lower than average pH. This acid precipitation returns to earth many miles form its source, severelydamaging waterways that lack natural buffering agents.
The northeastern UnitedStates and Canada are the most severely affected areas in North America.Category: Science
