Acid Rain : Causes of Acid Rain

You must have heard the term acid rain before. Do you know acid rain is caused by air pollution? Air pollution is increasing day by day in the atmosphere and a matter of concern for all nations. Air pollution is the huge problem in front of our generation so as acid rains. In this article we will discuss acid rain in detail with its causes and impacts on us. 

The term acid rain was coined by Scottish Chemist Robert Angus Smith in 1852. Royal Society of Chemistry has given him the title of ‘Father of Acid Rain’. He wrote about his findings in his book ‘Air and Rain: The Beginnings of a Chemical Climatology’. He examined rainwater near industrial area of England and Scotland. 

What is Acid Rain? 

In simple words, if rainwater has pH lower than 5.7 then it is called acid rain. According to EPA (Environmental Protection Agency) acid rain is a broad term which includes any form of precipitation with acidic components (nitric acid, sulfuric acid etc.) that fall to the ground. It can be in the form of wet or dry forms. It includes rain, fog, hail or even dust that is acidic.

Chemistry Behind Acid Rain 

Industries, vehicles etc. emit gases such as sulfur dioxide, nitrogen oxides etc. which are transported by wind and air currents and reacts with rainwater. When sulfur dioxide and nitrogen oxides (NO2, NO3) react with water, form acids (such as sulfuric acid, nitric acid etc.). Other than sulfur dioxide and nitrogen oxides, carbon dioxide present in the atmosphere also contributes to acid rain. 

Reactions involved in formation of acid rain can be written as follows –

S + O2 🡪 SO2

N + O2 🡪 NO2

C + O2 🡪 CO2

SO2 + H2O 🡪 H2SO3

2H2SO3 + O2 🡪 2H2SO4

2NO2 + H2O 🡪 HNO3 + HNO2

2HNO2 + O2 🡪 2HNO3

CO2 + H2O 🡪 H2CO3 


Rainwater has pH of 5.7 which is slightly acidic because of carbonic acid formed by the reaction of carbon dioxide with water, present in it. It doesn’t lower the pH of water much as carbonic acid is a weak acid. But when sulfuric acid and nitric acid get merged with rainwater, they lower the pH of rainwater below 5.7 as these both are strong acids. 

Causes of Acid Rain 

All those mediums, instruments or reactions which emit gases such as sulfur dioxide, nitrogen oxides etc. are indirect causes of acid rain. Here we are listing few causes of acid rain –

  • Natural causes- Forest fires, volcanic eruptions etc. release some chemicals which cause acid rain. Although these natural incidents cause only 1% of total amount of acid rains. Major part of acid rain is caused by human activities only. 

  • Industries – Steel industry, cement manufacturing industry etc. emit sulfur dioxide, nitrogen oxides in large quantity which causes acid rain. 

  • Coal based power plants – Coal based power plants emit many gases which causes air pollution and acid rain. 

  • Burning of fossil fuels – Fuels which are produced by the anaerobic decomposition of dead organisms are called fossil fuels. Burning of fossil fuels such as coal, petrol etc. emit many gases which cause air pollution and air pollution is the main cause of acid rain.

  • Petrol and diesel-based vehicles – Petrol and diesel on burning produce a large amount of carbon dioxide, sulfur dioxide and nitrogen oxides which cause air pollution and acid rain.


Effects of Acid Rain 

Acid rain mainly affects our ecosystem, health, materials such as marble, visibility etc. We can list effects of acid rain by following points –

  • Effect of acid rain on our ecosystem- Ecosystem is a community made by interaction between living organisms and their physical environment. All living and non-living material is interlinked. If one part of it gets affected, then another part also gets the harmful effects of it. Due to acid rain organisms which live in the pond, sea etc. get affected at large level. If pH level goes below 5.7 then frogs, fishes, snails, clams, trout etc. die. 

  • Acid rainwater release aluminum from soil which goes into lakes, sea and ponds. Thus, more acid rain causes high amount of aluminum in water bodies while most of the plants and animals can tolerate a moderate amount of aluminum. So, many plants and animals get died due to this. 

  • Effect of acid rain on human health – Human health gets adversely affected by acid rain. Human beings are also a part of ecosystem. Acid rain causes imbalance in the ecosystem by affecting its many factors. It can cause lungs diseases, hair fall, lever diseases etc. 

  • Effects of acid rain on material – Acid rain affects the materials such as marble, cement buildings etc. Strong acids present in the acid rain react with calcium carbonate and other materials which cause damage on their surface. They get faint and deteriorate faster. 

  • Less Visisbility - Gases such as sulfur dioxide, carbon dioxide etc. cause fog, smog in the atmosphere which causes less visibility. 

  • Effect of acid rain on plants, trees and forests – Acid rain adversely affects forests, plants and trees. They die due to high amount of aluminum in the soil or acid in the water. Their roots get dry completely and ultimately the plant or tree dies. 


Effect of acid rain on monuments (Real – Life Examples)

  • Taj Mahal – Taj mahal is largely affected by the acid rain. Sulphuric acid reacts with marble or calcium carbonate and forms calcium sulfate. Which cause corrosion. Thus, white color of the marble gets brownish. Reaction can be written 

  • as follows – CaCO3 + H2SO4 🡪 CaSO4 + H2O + CO2

  • Statue of Liberty – It is made up of copper. It is becoming green in colour due to reaction with acid present in acid rain. Reaction can be written as follows –

            Cu + 2H2SO4 🡪 CuSO4 + SO2 + 2H2O


Prevention of Acid Rain 

Following measures should be taken for prevention of acid rain –

  • Air pollution should be reduced. 

  • Emission of air polluting gases such as sulfur dioxide, nitrogen dioxide etc. should be reduced or stopped. 

  • Electric vehicles should be used in place of fossil fuels-based vehicles. 

  • Industries must use different ways to prevent emission of air polluting gases. 

  • Burning of fossil fuels should be minimized.