🌧️ What is Acid Rain?

Acid rain refers to rain (or snow, fog, or dust) that has a lower pH than normal, making it acidic. Normal rain has a pH of around 5.6, but acid rain can be as low as 4.0 or even lower.

🧪 Causes of Acid Rain

🔥 Emission of Acidic Gases

Burning of fossil fuels (coal, oil, gas) in:

• Factories
• Power plants
• Vehicles

Releases:

• Sulfur dioxide (SO₂)
• Nitrogen oxides (NOₓ)

☁️ Reactions in the Atmosphere

These gases react with water, oxygen, and other chemicals in the air to form acids:

Key Chemical Reactions:

\[\text{SO}_2 + \text{O}_2 \rightarrow \text{SO}_3\]

\[\text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4\ (Sulfuric\ acid)\]

\[2\text{NO} + \text{O}_2 \rightarrow 2\text{NO}_2\]

\[4\text{NO}_2 + 2\text{H}_2\text{O} + \text{O}_2 \rightarrow 4\text{HNO}_3\ (Nitric\ acid)\]

🌍 Effects of Acid Rain

🌳 Environment

• Damages leaves, slows plant growth
• Lowers soil pH, making important nutrients (like calcium and magnesium) harder to access
• Harms aquatic life; ocean acidification dissolves calcium carbonate shells of corals, mollusks, and similar organisms

🏛️ Buildings

• Corrodes metals and limestone
• Reacts with calcium carbonate in marble: \[\text{CaCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{CaSO}_4 + \text{H}_2\text{O} + \text{CO}_2\]

🧑‍🔬 Human Impact

• Does not burn skin like strong lab acids, but can cause:
• Breathing problems (from the pollutants)
• Contamination of drinking water

⚙️ Prevention and Control

🧼 Clean Technology

• Scrubbers in factories remove SO₂
• Catalytic converters in cars reduce NOₓ

💡 Use of Alternative Energy

• Solar, wind, hydro reduce fossil fuel use

🌿 International Agreements

• Countries agree to limit emissions (e.g., Clean Air Acts)

🔁 Bonus: Natural Buffers

Some areas resist acid rain due to alkaline soil or rocks (like limestone), which neutralize acids:

\[\text{CaCO}_3 + 2\text{H}^+ \rightarrow \text{Ca}^{2+} + \text{CO}_2 + \text{H}_2\text{O}\]

✅ Key Points for IJSO:

• Acid rain is mainly caused by SO₂ and NOₓ
• Leads to sulfuric acid and nitric acid in the air
• Damages plants, animals, water, and buildings
• Prevented by reducing fossil fuel emissions
• Some natural materials (e.g., limestone) neutralize the acid

Written by Kasiban Parthipan