Friday, 21 May 2010

Acid Rain and its Effect

Acid rain was first noticed in Scandinavia in the 1950s when large numbers of freshwater fish died. research showed that the water in which these fish had lived contained more than average amount of Acid. Later it was discovered that this extra Acid had been carried by rain, hence the term Acid rain. The Acid is formed in the air from sulfur dioxide (SO2) and nitrogen oxides (NOx) which are estimated by thermal power stations, industry and motor vehicles. These gases are either carried by prevailing winds across seas and national frontiers to be deposited directly into the earths surface or are converted in to acids which then fall to the ground in the rain.

Acid rain is measured using a scale called "pH." The lower a substance's pH, the more acidic it is. Pure water has a pH of 7.0. Normal rain is slightly acidic because carbon dioxide dissolves into it, so it has a pH of about 5.5. As of the year 2000, the most acidic rain falling in the US has a pH of about 4.3.

Acid rain causes acidification of lakes and streams and contributes to damage of trees at high elevations. For examples are:

** Acid deposition changes the chemistry of the environment. It affects water bodies such as ponds and lakes, river and streams, and bays and estuaries by increasing their acidity, in some cases to the point where aquatic animals and plants begin to die off.The acidity of lakes has increased large concentrations kill fish and plant life.

** Acid deposition damages vegetation as well.An increase in the acidity of soils reduces the number of crops that can be grown.

** Forests are being destroyed as important nutrients (calcium and potassium) are washed away (leached). These are replaced by manganese and aluminum which are harmful to root growth.In time the trees become less resistant to drought, frost and disease, and shed their needless.

** Water are more acidic and this could become a future health hazard. For example, the release of extra aluminum has been linked to Alzheimer's disease.

** Acid deposition damages man-made structures as well; marble,limestone, sandstone are susceptible to damage from acid deposition, as are metals, paints, textiles and ceramics. Repairing the damage caused by acid rain to buildings and monuments costs millions of dollars per year. The Acropolis in Athens and the Taj Mahal in India have both deteriorated rapidly in recent years.

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