Short Answer

Acid rain is caused by the release of sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) into the atmosphere, which react with water, oxygen, and other chemicals to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃).

Major sources include burning fossil fuels in power plants, vehicles, and industries. Natural sources like volcanic eruptions and lightning also contribute, but human activities are the primary cause of modern acid rain.

Detailed Explanation :

Definition of Acid Rain

Acid rain refers to any form of precipitation — rain, snow, sleet, fog, or hail — that has a higher acidity than normal, typically with a pH below 5.6. It forms when pollutants in the air dissolve into water droplets, making the precipitation acidic.

Normal rain is slightly acidic due to carbon dioxide (CO₂) forming carbonic acid, but acid rain has stronger acids like sulfuric and nitric acids, which are more harmful.

1. Human Causes of Acid Rain

1. Burning Fossil Fuels
   • Power plants, factories, and vehicles burn coal, oil, and gas, releasing SO₂ and NOₓ into the atmosphere.
2. Industrial Emissions
   • Industries like metal smelting, oil refining, and chemical manufacturing emit sulfur and nitrogen compounds.
3. Vehicle Exhaust
   • Cars, trucks, and airplanes produce nitrogen oxides, contributing significantly to acid rain.

Human activities are the largest contributors to acid rain in modern times.

2. Natural Causes of Acid Rain

1. Volcanic Eruptions
   • Release SO₂ and other gases into the atmosphere.
2. Lightning and Natural Fires
   • Produce nitrogen oxides through high-temperature reactions with air.

Although natural sources exist, they contribute less to the overall acid rain compared to human sources.

3. Chemical Reactions Leading to Acid Rain

1. Formation of Sulfuric Acid

 

1. Formation of Nitric Acid

These acids dissolve in rainwater, snow, or fog, producing acid rain.

4. Types of Acid Rain

1. Wet Deposition
   • Acidic precipitation in the form of rain, snow, or sleet.
2. Dry Deposition
   • Acidic gases and particles settle on surfaces without precipitation.

Both types lead to environmental damage, including soil acidification, water pollution, and damage to structures.

5. Effects of Acid Rain

• Environmental Effects: Acidifies lakes and rivers, harms aquatic life, and damages forests.
• Material Damage: Corrodes buildings, monuments, and statues, especially those made of limestone and marble.
• Health Effects: Indirectly affects humans by contaminating water and food, and respiratory issues can occur from polluted air.

6. Summary of Causes

• Primary causes: Human activities — burning fossil fuels, industrial emissions, vehicle exhaust.
• Secondary causes: Natural sources — volcanic eruptions, lightning, forest fires.
• SO₂ and NOₓ react with water in the atmosphere to form strong acids, leading to acid rain.
• Human activities are the major contributors to modern acid rain problems.

Conclusion

Acid rain is mainly caused by human-induced emissions of sulfur dioxide and nitrogen oxides, which react with atmospheric water to produce strong acids. Although natural processes contribute, industrialization, vehicles, and fossil fuel burning are the primary causes today. Understanding the sources of acid rain is essential for reducing air pollution, protecting ecosystems, and preventing damage to buildings and human health. Effective measures include reducing emissions, using cleaner energy, and international regulations.