What do you mean by Acid Rain ?

Air pollution can be very dangerous when it comes to the Acid rains. Acid rains are very disasterous form of air pollution......
The term acid rain was first used by Robert Angus in 1872. It literally means presence of excessive acids in rain water. Natural rainfalls through unpolluted environment are very slightly acidic due to presence of CO2 in atmosphere , which forms carbonic acid (H2CO3) , by dissolving in rain water . This rain having pH value about 5.6 is not acidic.....
However due to presence of SO2 and NOx in atmosphere which forms acids like H2SO4 and HNO3 which are generally secondary pollutants , because they are made up of primary pollutants , due to this secondary pollutants pH value of rain lowers to as 2.4 and this type of precipitation is called Acid rain.....
Acid rain actually is a cocktail of mainly H2SO4 and HNO3. H2SO4 contributes 60-70 % of acid precipitation , HNO3 30-40 % and HCl very low.......

CAUSES OF ACID RAIN

There are various causes to Acid rains ..... In my previous post I have told you about ...What is Acid rain ? .... In this post I would tell you about how it is caused ?...The acidity in rain water is caused due to formation of secondary pollutants like H2SO4, HNO3,HCl etc. due to reaction of water vapour with SO2,NOx and HCl gas. The greater is the concentration of these primary pollutants , the greater would be the acidity.......The primary pollutant responsible for 2/3 rd of the acid rains, is SO2, which is chiefly produced by burning of coals and oils, largely used for generation of heat and power in industries as well as in domestic uses, besides the large scale use of petrol and diesel in automobiles. This SO2 pollutant released in the atmosphere by various sources , finally leads to H2SO4 acidity in rains.SO2 + 1/2 O2 + H2O ---->>> H2SO4Similarly another primary pollutant nitrogen oxides responsible for 1/3 of acid rains , is mainly produced by the auto emissions, nitrogeneous fertilizers , forests fires and grass lands etc. This NOx pollutant is finally responsible for HNO3 acidity in rains...Following reactions takes place : NO + O3-----> NO2 + O2NO2 + O3 ----> NO3 + O2NO3 + NO2 -----> N2O5N2O5 + H2O ----> 2HNO3Some of the industries may release hydrogen chloride gas into the atmosphere, which may cause HCl acidity , but this is generally on a very small scale........

EFFECTS OF ACID RAIN

There are various adverse effects of acid rain which create complex problems ... some of them are :

(1) On Human Health : There is no direct link between acid rain and human health , but acid rains decreases the pH value of ground water below 4.5. This acidic water may corrode the pipes and cause leaching of heavy metals into drinking water. These heavy metals can affects the human skin, lungs and hair. It is responsible for accumulation of toxic metals in the food chain such as Hg and Cd, these metals can affect human nervous system,respiratory system and digestive system, by making the person an easy prey to neurological diseases. It also reduce visibility due to smog.....
(2) On Aquatic Life : It is responsible for increasing the acidity of river , lake and streams. The acidic water having pH value below 4.5 is highly lethal to fishes. They can leach aluminium from soil , which can carry to rivers , lakes etc.This metal is toxic and can cause death by clogging gills of the fish and making them unable to breath. Many bacteria and green algae are killed due to acidification.....
(3) On Plants : Acid rains has the potential to convert forests into waste lands by damaging trees, plants and crops. Due to acid rains about 50% of the natural forests are damaged in the countries like Germany, Switzerland..... They carry various nutrients from soil such as Al, Ca ,Mg which can affect plant growth . Acid rains weakens the trees like pine , spruce , ashes and birch.......
(4) On Property : The minerals such as Al, Mn,Cd,Cu Pb carried by acid rain indirectly affect the buildings. Acid rains corrodes houses , monuments , statues , bridges , fences and railings..... Damages to the world's monuments such as in Rome , Venice , Athens ,London , India are quite visible......

CONTROLLING MEASURES OF ACID RAIN

Acid rain has become a big problem world wide . Due to its harmful effects it is much need for the humans to control it . This is not only affecting us but also to plants, aquatic life , property as well...
One of the simplest solution to the problem of acid rain may be to neutralize the acid with lime. But using the lime over a large bodies will be too expensive and it will too have its adverse effects . The another way or probably the best way to overcome this problem is to control the emissions of SOx and NOx from anthropogenic sources....
Efforts have however , started to provide expensive scrubbers in thermal power plants and other industries to check the emissions of SO2 and other pollutant gases ; to provide three way catalyst convertors in automobiles to check the emission of both SO2 and NOx ; to protect forests and lakes by taking emergency measures , such as spreading of lime on their surface ; by fertilising the damaged trees with nutrients , and so on.......

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