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Acid rain is defined as any type of precipitation with a pH that is below 5.0. Normal rain has a pH which its range is between 4.5 and 5.6 with an average value of 5.0. This natural acidity is caused by dissolved carbon dioxide dissociating to form weak carbonic acid.
Acid rain is formed bythe oxidation of sulfur, carbon and nitrogen containing compounds which have both natural and human caused emissions. This oxidation occurs in both the gas phase and in raindrops ,then produces sulfuric acid, carbonic acid and nitric acid.
The resulting increased acidity in soil and waterways has proven to be harmful to fish and vegetation. Acid rain also accelerates weathering in carbonate rocksand accelerates building weathering. It also contributes to acidic rivers, streams, and damage to trees at high elevation. Efforts to combat this phenomenon are ongoing.
|2 History and trends |
|3 Adverse effects |
|3.1 Effects on lake ecology |
|3.2 Effects of acid rain on soil biology |
|3.3 Other adverse effects|
|4 Prevention Methods |
|5 References |
|6 See also |
The principal natural phenomena that contribute acid-producing gases tothe atmosphere are emissions from volcanoes and those from biological processes that occur on the land, in wetlands, and in the oceans. The effects of acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe.
The principal cause of acid rain is from human sources, such as industrial and power-generating plants and vehicles and electricity generation. Thegases can be carried hundreds of miles in the atmosphere before they are converted to acids and deposited. The origin of acid rain is the presence of SO2 and NOx released in the fuel burning processes and specially in the industrial areas. As water vapour condenses, it sweeps the acids formed between these compounds and water (HNO3 and H2SO4). Cloud particulates act as condensation nuclei ontowhich water condenses or ice is formed. This is one of way in which air self-cleans: the so called "rain out" effect. One alternative mechanism involves sweeping of atmosphere particulates by falling rain drops or snow that deposit them on the ground. This is called "washout" effect and is very effective for removing atmospheric particles. Smaller particles are swept out of the rain way by the wind.On the other hand, the rain-out effect is the origin of water acidity.
Industrial acid rain is a substantial problem in China, Eastern Europe, Russia and areas down-wind from them. Acid rain from power plants in the midwest United States has also harmed the forests of upstate New York and New England. These areas all burn sulfur-containing coal to generate heat and electricity.
History and trends
Acid rain was first reported in Manchester, England, which was an important city during the Industrial Revolution. In 1852, Robert Angus Smith found the relationship between acid rain and atmospheric pollution. The term "acid rain" was used by him in 1872. He observed that acid rain could lead to natural destruction.
Though acid rain was discovered in 1852, it wasn't until the...