Acid Rain

Acid Rain

ACID RAIN

Acid rain is defined as rain or any other form of precipitation that has elevated levels of hydrogen ions (low pH), or in simple words is acidic. The cause of acid rain is emissions of sulphur dioxide and nitrogen oxide. These react with the water molecules in the atmosphere to produce acidic rain water. Nitrogen oxides are naturally produced by lightning strikes while volcanic eruptions are major source of sulphur dioxide production.

Causes of  Acid Rain

The causes of acid rain are the Sulfur and Nitrogen particles which get mixed with the wet components of rain. Sulfur and Nitrogen particles which get mixed with water are found in two ways either man-made i.e as the emissions given out from industries or by natural causes like how a lightning strike in the atmosphere releases nitrogen ions and sulphur is released from volcanic eruptions.

H2O (l) + CO2 (g) ⇌ H2CO3 (aq)

Sulphur dioxide and nitrogen dioxide undergo oxidation and then they react with water resulting in the formation of sulphuric acid and nitric acid respectively. The following reaction will clarify the acid formation reaction:

2SO2 (g) + O2 (g) + 2H2O (l) → 2H2SO4 (aq)
4NO2 (g) + O2 (g) + 2H2O (l) → 4HNO3 (aq)

FORMS OF ACID DEPOSITION

There are mainly two forms of acid deposition as discussed below-

• Wet Deposition:In places where the weather is wet, acids fall to the ground in forms which include fog, rain, mist or snow. It usually happens when the wind blows the acidic chemicals in the air. The acid is removed from the atmosphere and deposited on the earth’s surface. When this acid flows through the ground, it has harmful effects on animal, plant and aquatic life. It also affects marine life because the water from drain flows into rivers and canals and is then mixed up with sea water.
• Dry Deposition:In areas where the weather is dry, if the wind blows the acidic chemicals in the air, the acidic pollutants mix with smoke or dust and fall to the ground as dry particles. These may also stick to the ground and surfaces of trees, buildings or cars. Dry deposition gives birth to almost 50% of the acidic pollutants in the atmosphere. These deposited acidic pollutants are washed away from earth surface by rainstorms.
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Effects of acid rain:

• It causes respiratory issues in animals and humans.
• When acid rain falls down and flows into the rivers and ponds it affects the aquatic ecosystem. As it alters the chemical composition of the water, to a form which is actually harmful to the aquatic ecosystem to survive and causes water pollution.
• Acid rain also causes the corrosion of water pipes. Which further results in leaching of heavy metals such as iron, lead and copper into drinking water.
• It damages the buildings and monuments made up of stones and metal
• 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.

Real life examples:

• Taj Mahal, one of the 7 wonders of the world, is largely affected by acid rain. The city of Agra has many industries which emit the oxides of sulphur and nitrogen in the atmosphere. People continue to use low-quality coal and firewood as domestic fuel, adding to this problem. Acid rain has the following reaction with the marble (calcium carbonate):

CaCO3 +  H2SO4 → CaSO4  + H2O + CO2 

* Statue of Liberty which is made of copper has also been damaged by the cumulative action of acid rain & oxidation for over 30 years and is, therefore, becoming green in colour

How to prevent Acid Rain?

The only precaution that we can take against acid rain is having a check at the emission of oxides of nitrogen and sulphur. We have so far seen the details of acid rain and its harmful effect on animals, plants and the monuments. Being responsible citizens, one should be aware of the harmful effects they cause and of the industries which give out nitrogen and sulphur compound wastes unethically.