ACID RAINThe term „acid rain‟ means any form of precipitation like rain, fog, snow, or hail that containsharmful substances such as nitrogen and sulfur oxides."Acid rain" is a broad term referring to amixture of wet and dry deposition (deposited material) from the atmosphere containing higherthan normal amounts of nitric and sulfuric acids. The precursors, or chemical forerunners, of acidrain formation result from both natural sources, such as volcanoes and decaying vegetation, andman-made sources, primarily emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx)resulting from fossil fuel combustion. In the United States, roughly 2/3 of all SO2 and 1/4 of allNOx come from electric power generation that relies on burning fossil fuels, like coal. Acid rainoccurs when these gases react in the atmosphere with water, oxygen, and other chemicals to formvarious acidic compounds. The result is a mild solution of sulfuric acid and nitric acid. Whensulfur dioxide and nitrogen oxides are released from power plants and other sources, prevailingwinds blow these compounds across state and national borders, sometimes over hundreds ofmiles.Wet DepositionWet deposition refers to acidic rain, fog, and snow. If the acid chemicals in the air are blown intoareas where the weather is wet, the acids can fall to the ground in the form of rain, snow, fog, ormist. As this acidic water flows over and through the ground, it affects a variety of plants andanimals. The strength of the effects depends on several factors, including how acidic the water is;the chemistry and buffering capacity of the soils involved; and the types of fish, trees, and otherliving things that rely on the water.Dry DepositionIn areas where the weather is dry, the acid chemicals may become incorporated into dust orsmoke and fall to the ground through dry deposition, sticking to the ground, buildings, homes,
cars, and trees. Dry deposited gases and particles can be washed from these surfaces byrainstorms, leading to increased runoff. This runoff water makes the resulting mixture moreacidic. About half of the acidity in the atmosphere falls back to earth through dry deposition.MEASURING ACID RAINAcid rain is measured using a scale called “pH.” The lower a substances pH, the more acidic itis. Pure water has a pH of 7.0. However, normal rain is slightly acidic because carbon dioxide(CO2) dissolves into it forming weak carbonic acid, giving the resulting mixture a pH ofapproximately 5.6 at typical atmospheric concentrations of CO2. As of 2000, the most acidic rainfalling in the U.S. has a pH of about 4.3.In USTwo networks, both supported by EPA, monitor acid rain‟s pH and the chemicals that cause acidrain. The National Atmospheric Deposition Programmeasures wet deposition and developedmaps of rainfall pH (follow the link to the isopleth maps) and other important precipitationchemistry measurements.The Clean Air Status and Trends Network (CASTNET) measures dry deposition. This EPA Website features information about the data collected, the measuring sites, and the types of equipmentused.HISTORYit began entering the atmosphere in large amounts during the Industrial Revolution and was firstdiscovered by a Scottish chemist, Robert Angus Smith, in 1852. In that year, he discovered therelationship between acid rain and atmospheric pollution in Manchester, England.Although it was discovered in the 1800s, acid deposition did not gain significant public attentionuntil the 1960s and the term acid rain was coined in 1972. Public attention further increased inthe 1970s when the New York Times published reports about problems occurring in the HubbardBrook Experimental Forest in New Hampshire.EFFECTS OF ACID RAINAcid rain causes acidification of lakes and streams and contributes to the damage of trees at highelevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. Inaddition, acid rain accelerates the decay of building materials and paints, including irreplaceablebuildings, statues, and sculptures that are part of our nations cultural heritage. Prior to falling tothe earth, sulfur dioxide (SO2) and nitrogen oxide (NOx) gases and their particulate matterderivatives—sulfates and nitrates—contribute to visibility degradation and harm public health.Surface Waters and Aquatic Animals
The ecological effects of acid rain are most clearly seen in the aquatic, or water, environments,such as streams, lakes, and marshes. Acid rain flows into streams, lakes, and marshes afterfalling on forests, fields, buildings, and roads. Acid rain also falls directly on aquatic habitats.Most lakes and streams have a pH between 6 and 8, although some lakes are naturally acidiceven without the effects of acid rain. Acid rain primarily affects sensitive bodies of water, whichare located in watersheds whose soils have a limited ability to neutralize acidic compounds(called “buffering capacity”). Lakes and streams become acidic (i.e., the pH value goes down)when the water itself and its surrounding soil cannot buffer the acid rain enough to neutralize it.In areas where buffering capacity is low, acid rain releases aluminum from soils into lakes andstreams; aluminum is highly toxic to many species of aquatic organisms.Acid rain causes a cascade of effects that harm or kill individual fish, reduce fish populationnumbers, completely eliminate fish species from a waterbody, and decrease biodiversity.Generally, the young of most species are more sensitive to environmental conditions than adults.At pH 5, most fish eggs cannot hatch. At lower pH levels, some adult fish die.FORESTSacid rain causes slower growth, injury, or death of forests. Acid rain has been implicated in forestand soil degradation in many areas. Forest floor: Differences in soil buffering capacity are animportant reason why some areas that receive acid rain show a lot of damage, while other areasthat receive about the same amount of acid rain do not appear to be harmed at all. Trees: Acidrain does not usually kill trees directly. Instead, it is more likely to weaken trees by damagingtheir leaves, limiting the nutrients available to them, or exposing them to toxic substances slowlyreleased from the soil. Quite often, injury or death of trees is a result of these effects of acid rainin combination with one or more additional threats. trees can be damaged by acid rain even if thesoil is well buffered. acidic water dissolves the nutrients and helpful minerals in the soil and thenwashes them away before trees and other plants can use them to grow. At the same time, acidrain causes the release of substances that are toxic to trees and plants, such as aluminum, into thesoil. Plants: Acid rain can harm other plants in the same way it harms trees.AUTOMOBILE COATINGThe reported damage typically occurs on horizontal surfaces and appears as irregularly shaped,permanently etched areas.MATERIALSAcid rain and the dry deposition of acidic particles contribute to the corrosion of metals (such asbronze) and the deterioration of paint and stone (such as marble and limestone). These effectssignificantly reduce the societal value of buildings, bridges, cultural objects (such as statues,monuments, and tombstones), and cars.VISIBILITYSulfates and nitrates that form in the atmosphere from sulfur dioxide (SO2) and nitrogen oxides(NOx) emissions contribute to visibility impairment, meaning we cannot see as far or as clearlythrough the air.
HUMAN HEALTHScientists have identified a relationship between elevated levels of fine particles and increasedillness and premature death from heart and lung disorders, such as asthma and bronchitis. Skinproblems.REDUCING EFFECTS OF ACID RAINUnderstand acid deposition‟s causes and effectsClean up smokestacks and exhaust pipesusing coal containing less sulfur, washing the coal, and using devices called “scrubbers” tochemically remove the SO2 from the gases leaving the smokestack.Power plants can also switch fuels—for example, burning natural gas creates much less SO2 thanburning coal.Similar to scrubbers on power plants, catalytic converters reduce NOx emissions from cars.Use alternative energy sourcesThere are other sources of electricity besides fossil fuels. They include nuclear power,hydropower, wind energy, geothermal energy, and solar energy. Nuclear and hydropower areused most widely in the United States, while wind, solar, and geothermal energy have not yetbeen harnessed on a large enough scale to make them economically-feasible alternatives.There are also alternative energies, such as natural gas, batteries, and fuel cells, available topower automobiles.Restore a damaged environmentegLimingTake action as individuals turn off lights, computers, and other appliances when youre not using them. Use energy-efficient appliances: lighting, air conditioners, heaters, refrigerators, washing machines, etc. Only use electric appliances when you need them. Keep your thermostat at 68°F in the winter and 72°F in the summer. You can turn it even lower in the winter and higher in the summer when you are away from home. Insulate your home as best you can. Carpool, use public transportation, or better yet, walk or bicycle whenever possible Buy vehicles with low NOx emissions, and properly maintain your vehicle. Be well informed.