Acid rain: Definition, Causes and Effects - Acid Rain Formula

•The term acid rain was first used by Robert Angus Smith (1872).
•It is described as ‘man’s chemical warfare on nature”.

•Also known as Acid precipitation

What is Acid Rain:

•Acid rain refers to the presence of excessive acid content in the atmosphere and also in the precipitation water(rain, snow, mist, fog etc).

•It is the rain fall and other forms of precipitation with a pH of less than 5 of normal rain is 5.6-6.5.

•Two forms: Wet and Dry

•Wet deposition: Rain, snow and fog

•Dry deposition: it is settle down of wind blown acidic gases and particles over trees, various articles and soil. about 50 of acidity is passed to earth as dry deposition.

Causes of Acid Rain: 

      1. Sulphuric acid and nitric acid are the major agents of acid rain.

a) Formation of Sulphuric acid:

2SO₂+O₂->2SO₃

SO₃+H₂O->H₂SO₄   (Sulphuric acid)

b) Formation of nitric acid

2NO+3[O]->N₂O₅

N₂O₅+H₂O->2HNO₃ (Nitric acid
2. Hydrochloric acid, nitrous acid and carbonic acid also contribute to acid rains.

a) Formation of carbonic acid

             CO₂+H₂O-> H₂CO₃ (Carbonic acid)

             b)Formation of nitrous acid

NO+O₃->NO₂+O₂

NO+NO₂->N₂O₃

                           N₂O₃+H₂O-2HNO₂ (Nitrous acid)
Oxides of nitrogen come from combustion of fuels in automobiles as well as in power plants.
Oxides of sulphur are released from smokestacks of coal fired power plants, smelters and other industries (oil furnaces).

Social issues and the environment :Climate change, Global warming and Acid rain, Green house effect, ozone layer depletion from Biology Exams 4 U

Effects of Acid Rain (Acid precipitation):

Acid rain is very harmful to agriculture, plants, and animals. It washes away all nutrients which are required for the growth and survival of plants. Acid rain affects agriculture by the way how it alters the composition of the soil.

Effect on nitrogen cycle: Nitrogen cycle is highly sensitive to the acidification of soil.  Acidity suppresses denitrification, high  pH increases the volatilization of ammonia, Alkalinity affects the survival of nitrogen fixing bacteria.

Effect on fresh water ecosystems: due to acid rain many lakes in Germany and other European countries have a pH of less than 5, an acidity level considered lethal for many species of fish. Acidic water can carry dissolved aluminum to lakes and streams which clogs the gills of fish and deprives them of oxygen.

Effects on soil: It causes leaching of essential minerals of soil

Effects  on terrestrial ecosystems: It causes extensive damage to forest trees and all vegetation.

Effects on buildings, stone structures (stone leprosy) etc: Acid rain corrodes metals, marble, painted surfaces, slate, stone etc. This phenomenon is called Stone leprosy. In Greece and Italy, valuable stone statues have been partially dissolved and Taj Mahal in India is affected by the acid rain.

. Acid rain has the following reaction with the marble (calcium carbonate):

                                 CaCO3 +  H2SO4 -> CaSO4  + H2O + CO2  

Acid rain damages plants  direct effect on foliage and growing point; necrosis, dieback, chlorosis, defoliation. It causes reduced rates of photosynthesis and growth, increased sensitivity to drought and disease.

Effects on human health: Acidification of soil may leads to the aluminum toxicity of drinking water, which may cause kidney failure, bone softening, Alzheimer’s disease  etc.