Acid Rain: Definition, Causes, Harmful Effects and Prevention

Acid rain can be defined as the precipitation of acid in the form of rain.

• It is also known as acid deposition.
• It is a form of precipitation containing acidic components such as sulfuric and nitric acids.
• These components fall to the surface of the earth from the atmosphere in both wet and dry forms.
• This includes rain, snow, fog, hail, and even acidic dust.
• Normal rainwater has a pH value of around 5.7, making it slightly acidic.
• When rainwater interacts with pollutants such as sulfur dioxide or nitrogen oxides, it becomes more acidic.
• The pH value of acid rain is around 4.0.

Key Terms: Acid rain, Sulfuric acid, Nitric acid, Precipitation, Atmosphere, pH value, Nitrogen oxides, Sulfur dioxide

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What is Acid Rain?

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“Acid rain is precipitation containing high levels of acids formed when sulfur dioxide and nitrogen oxides react with normal rainwater.”

The term precipitation refers to any form of liquid or frozen water that condenses in the atmosphere and falls back to the Earth's surface. 

• The main forms of precipitation include drizzle, rain, snow, ice pellets, graupel, and hail.
• Normal rainwater reacts with pollutants like sulfur dioxide and nitrogen oxides in the atmosphere.
• This reaction between rainwater and pollutants converts them into sulfuric and nitric acids.
• The precipitation of these acids on the surface of the earth is known as acid rain.
• The word acid rain was coined first in 1852 by Scottish chemist Robert Angus Smith.
• The Royal Society of Chemistry considers him the “father of acid rain”.

Acid Rain

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Causes of Acid Rain

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Acid rain is formed by the reaction of sulfur and nitrogen compounds with rainwater. These can be caused by two main sources:

• Human activities: Emissions from factories, power plants, and vehicles release sulfur dioxide (SO₂) and nitrogen oxides (NO_x) into the atmosphere.
• Natural sources: Lightning strikes can produce nitrogen oxides, while volcanic eruptions release sulfur dioxide.

Regular clear rain is also not clean but less harmful because when it reacts with carbon dioxide, it forms weak carbonic acid. The reaction involved is

H₂O (l) + CO₂ (g) ⇌ H₂CO₃ (aq)

Acid rain is more harmful because when sulfur dioxide and nitrogen dioxide react with normal rain, it results in the formation of sulphuric acid and nitric acid, respectively. The reactions involved are

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

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Effects of Acid Rain

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The effect of acid rain can be seen on humans, plants, aquatic life, and also, on stone buildings and big metallic structures. 

• Acid rain washes away all the nutrients essential for plant growth and survival.
• It also alters the soil composition.
• It causes various respiratory issues in animals and humans.
• It alters the aquatic life as if it falls into the river, and changes the pH of river water.
• It is also responsible for the water pollution of the river.
• Acid rain corrodes water pipes, leaching harmful heavy metals into drinking water.
• It is also responsible for damaging various buildings and monuments which are made up of stones and metals.

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Harmful Effect of Acid Rain: Real-Life Examples

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Some of the harmful effects of acid rain on famous buildings and monuments are given below.

Effect on the Taj Mahal

Taj Mahal is in the city of Agra where many industries are using chemicals that emit oxide of sulphur and nitrogen.

• These oxides combine with atmospheric water and fall down as acid rain.
• This acid rain is causing corrosion on the marble of the beautiful white marble of the Taj Mahal.

Effect on The Statue of Liberty

The Statue of Liberty another famous monument is also getting damaged due to the acid rain. The Statue of Liberty is made up of copper, which is turning green by the slow action of acid rain.

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Prevention of Acid Rain

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The only thing that we can do to prevent acid rain is to keep a check on the emission of nitrogen and sulphur oxide from different industries and the burning of fossil fuels.

• To prevent acid rain, reduce the amount of sulphur dioxide and nitrogen oxide in the atmosphere.
• This can simply be done by using cleaner fuel and removing oxides of sulphur and nitrogen before releasing them.
• Use coal that contains less sulphur or wash the coal to reduce sulphur content or opt for natural gas.
• Use alternate energy resources such as geothermal, wind, and solar energy, to reduce sulphur and nitrogen oxides quantity.

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Things to Remember

• Any precipitation containing very high levels of nitric and sulfuric acid is called acid rain.
• Regular rainwater becomes more acidic when reacts with pollutants like sulfur dioxide or nitrogen oxides.
• The pH of acid rain is mainly about 4.0.
• The main reason for acid rain is mainly the combustion of fossil fuels.
• Acid rain is harmful to the fertility of the soil and contributes to the corrosion of soil surfaces.