Exams
Test Series
Previous Year Papers
Syllabus
Books
Cut Off
Latest Updates
Eligibility
Acid Rain Definition, Formation, Causes, Effects and Prevention
IMPORTANT LINKS
Environmental Chemistry
Have you ever heard about rain that can actually harm trees, buildings, and even people? That’s acid rain. It may look like normal rain, but it contains harmful chemicals that come from pollution in the air. When gases like sulfur dioxide and nitrogen oxides mix with rainwater, they form acids that fall to the ground with rain, snow or fog. In this article, we’ll help you understand what acid rain is, how it forms, what causes it, and what we can do to stop it.
What is Acid Rain?
Acid rain is a form of precipitation characterised by high concentrations of acidic compounds, usually in the form of dissolved ions or molecules. Acid rain contains sulphur dioxide (SO2) and nitrogen oxides (NOx) which are emitted from fossil fuel combustion. Acidic pollutants can also be discharged from the smokestacks of ships and coal-fired power plants.
Chemistry Notes Free PDFs
| Topic | PDF Link |
|---|---|
| Class 11 Chemistry Short Notes PDF | Download PDF |
| Class 12 Chemistry Complete Notes | Download PDF |
| Study Notes for Physics | Download PDF |
| Class 11 Biology Short Notes PDF | Download PDF |
| Class 12 Biology Short Notes PDF | Download PDF |
Formation of Acid Rain
Acid rain is formed when oxides of nitrogen and sulphur combine with water vapour in the atmosphere. The result is a chemical reaction that produces acidity. Acid rain can occur in many places worldwide, most often in industrial areas where there are polluting factories which cause pollution.
Causes of Acid Rain
The primary causes of acid rain are sulphur dioxide (SO2) emitted from coal-fired power plants. Sulphur dioxide combines with oxygen to form sulphuric acid (H2SO4), which dissolves with the water droplets and rains down as acid rain. Nitrogen oxides emitted by automobiles also contribute to the formation of acid rain.
Other sources include industrial emissions and biomass burning. Industrial emissions like chlorofluorocarbons (CFC), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are the main contributors. These chemicals deplete the ozone layer in the stratosphere, which absorbs ultraviolet radiation from the sun before reaching Earth’s surface. Biomass burning includes forest fires, agricultural fires, and fossil fuels for heating or cooking purposes.
Natural Causes
Natural sources of acid rain include:
- Volcanic eruptions – When volcanoes erupt, they release sulphur dioxide, which mixes with water vapour in the atmosphere to form sulphuric acid. It then reacts with rainwater and releases (H+), which causes the water to turn acidic.
- Seaspray – When waves crash against rocks or the shoreline, they release aerosols into the atmosphere. These aerosols also decrease the pH level of rainwater.
- Lightning – Lightning is one of the most common natural sources of acid rain. This is because when it strikes, it creates an electrical discharge that travels from the ground to the air. This process creates nitrogen oxides (NOx) and sulphur dioxide (SO2) gases that are released into the atmosphere.
- Wildfires – Wildfires are a natural part of the ecosystem, but they can cause acid rain by releasing sulphur dioxide into the air. When wildfires occur, they release large amounts of carbon dioxide and methane as well. These greenhouse gases can cause global warming, which leads to more wildfires.
Human Activities
Following are some human activities that contribute to the formation of acidic rain.
- The major sources of human-induced acid rain are sulphur dioxide (SO2) emissions from the combustion of fossil fuels such as coal power plants.
- Nitrogen oxides (NOx) emissions such as those from petrol/ diesel-powered automobiles and other internal combustion engines.
- Industrial usage of chlorine and fluorine compounds such as refrigerants and aerosol propellants.
- When trees are cut down, they release carbon dioxide into the atmosphere, reacting with water vapour to form carbonic acid. The acid, when reacting with rainwater vapours, releases (H+) ions, further making it acidic.
Which Gases are Responsible for Acid Rain?
The gases responsible for acid rain are carbon dioxide, nitrous oxide, and fluorinated gases such as hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs). Acid rain reaction with these gases has been explained below.
Carbon dioxide
\begin{aligned}
& \mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{H}_2 \mathrm{CO}_3 \\
& \mathrm{H}_2 \mathrm{CO}_3 \rightarrow \mathrm{H}^{+}+\mathrm{HCO}_3^{-}
\end{aligned}
Nitrous Oxide
\mathrm{NO}_2+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{HNO}_3+\mathrm{NO}
Sulphur Dioxide
\mathrm{SO}_2+\mathrm{O}_2 \rightarrow \mathrm{SO}_3+\mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{H}_2 \mathrm{SO}_4
- 168 Topic Specific
- 52 Weekly Revision
- 24 Monthly Digest
- 12 Need-to-Know NEWS
- 96 State Specific
- 10 Previous Year Questions
- 17 Revision 2024
- 52 Advanced Current Affairs
Effects of Acid Rain
Acid rain is a local environmental problem that can have a global effect. Acid rain effects may take years to show up, and it is difficult to determine the cause of various problems. It can negatively affect human health and wildlife and damage buildings and property. Some of these effects include the following.
Acidification of Lakes and Streams
The pH level of most water bodies is around 6-8, however, it can drop below 4 when exposed to high concentrations of acidic substances like sulphuric acid or nitric acid from coal-fired power plants or factories. Acidic water can kill fish eggs by burning through their shells or making them too weak.
Damage to Buildings and Monuments
Acid rain can erode stone statues, buildings, bridges, and other structures made of limestone or marble. It can also damage buildings made of brick or concrete.
Reduced Visibility
The particles in acid rain can reduce visibility by hindering our view of the sun on a bright sunny day, causing squinting or even temporary blindness if we are standing too close to a source when acid rain occurs.
Health Effects
Acidic deposition can harm human health by damaging the lungs and causing respiratory problems like asthma attacks. It may also cause irritation in the eyes, such as conjunctivitis (pink eye), in people who exercise or play outdoor sports.
Damage to Plants, Trees, and other Vegetation
Plants cannot thrive in an acidic environment because they require alkaline soil to grow properly. Acidic soil causes minerals such as calcium and magnesium to become less available for plant growth. This affects everything from root growth to flower development.
Oxidation or Rusting of Iron and Steel
Iron or steel come in contact with oxygen in acidic air and rust. This process is called oxidation or rusting. This is another effect of acid rain.
How to Prevent Acid Rain?
Now that you know the acid rain causes and effects, you should learn about the prevention of acid rain. The major acid rain prevention methods are:
- Use of renewable energy: Reducing fossil fuels by relying on renewable energy sources such as solar energy, wind energy, hydropower, etc.
- Energy conservation: Purchase energy-efficient electrical appliances and use public transportation, bicycles, or walking (especially short distances).
- Liming: Even if acid deposition has taken place, adding lime to water bodies and soil can help neutralize the pH.
- Planting trees: Trees absorb carbon dioxide from the air and release oxygen back into it again. This helps to balance out the effects of fossil fuels on our atmosphere.
- Use public transport more often: Reduce vehicle emissions by driving less often or using public transportation instead of driving alone.
Testbook has emerged as an ultimate platform for exam preparations. Learn with live classes from our top mentors, and choose from a wide range of mock tests, quizzes, and study material to practice. Download the Testbook App now to prepare for your next exam!
FAQs
How is acid rain formed? Which gas is responsible for acid rain?
Acid rain refers to rainfall and other forms of precipitation having high acidity levels. Acid rain is caused due to the reaction of carbon dioxide, nitrogen dioxide, and sulphur dioxide with water droplets in the air.
What should be the pH of the rain to call it acid rain?
Typical pH value of acid rain is 4.0, but any rainfall below 5.6 pH is considered acid rain.
What are the effects of acid rain?
Acid rain has harmful effects on freshwater bodies, soils, flora, and fauna. In addition, acid rain also damages non-living structures such as the peeling of paints, corrosion of metal structures, weathering of marble sculptures, etc.
What are the acid rain effects on humans?
Acid rain affects humans indirectly. The sulphur dioxide and nitrogen dioxide created in the atmosphere can cause respiratory disorders or worsen these conditions. For example, people with respiratory conditions like asthma or chronic bronchitis might suffer from difficulty breathing.
What are some effective ways to reduce acid rain?
An effective way to reduce acid rain is to reduce the usage of fossil fuels and use cleaner energy. For example, renewable energy like solar and wind power helps reduce acid rain because they produce little to no air pollution.