Acid rain, its causes, effects and remedies
Acid Rain: Causes, Effects, and Remedies
H₂CO₃(aq) → H⁺ + HCO₃⁻
The ionization of H₂CO₃ at pH 5.6 produces H⁺ ions, which naturally brings the pH of rainwater to 5.6. However, when the pH value falls below 5.6, making the water more acidic, it is termed “Acid Rain.”
Causes of Acid Rain:
To improve modern living standards, industrial production has increased, causing industrial chimneys to emit massive amounts of flue gas day and night. These gases contain harmful substances like hydrogen sulfide, sulfur dioxide (SO₂), and sulfur trioxide (SO₃). Nearly 60% of sulfur dioxide is emitted from thermal power plants. Additionally, oil refineries and sulfuric/nitric acid production plants contribute significantly to the emission of SO₂ and NO₂. Furthermore, the excessive use of urea fertilizer for increased food production leads to the release of nitrogen oxides into the atmosphere through decomposition.
These oxides of nitrogen and sulfur dissolve in rainwater to form acids, resulting in acid rain.
SO₂ + H₂O → H₂SO₃
SO₃ + H₂O → H₂SO₄
Effects of Acid Rain:
- 1. Acid rain can lower the pH of water bodies from the neutral pH 7 to as low as 3. This intensity disrupts the ecosystem, killing fish and destroying crop fertility.
- 2. Buildings and monuments are severely eroded. For example, sulfur dioxide emissions from the Mathura oil refinery have caused the white marble of the Taj Mahal, located 250 km away, to turn yellow and corrode.
- 3. Bridges, ships, and vehicles made of metal are not spared from the corrosive effects of acid rain.
- 4. Acid rain causes gradual deforestation, leading to environmental disasters. A prominent example occurred in Virginia, USA, and Sweden, where pH levels dropped below 2, devastating local forests.
- 5. High acidity interferes with the germination of seeds and the hatching of fish eggs in water bodies.
- 6. Essential soil minerals like Ca, Mg, Al, and Zn are leached away by acid rain, leaving the soil barren.
Remedies for Acid Rain:
The adverse effects of acid rain can be significantly reduced through the following measures:
1. Treatment Plants:
Before emission, harmful sulfur dioxide gas from industrial chimneys is passed through Flue-Gas Desulfurization (FGD) plants, where limestone or lime absorbs the SO₂.
CaO(s) + SO₂(g) → 2CaSO₃(s)
2CaSO₃(s) + O₂(g) + 4H₂O(l) → 2(CaSO₄.2H₂O)
2. Recycling:
Waste gases can be recycled instead of being released. For instance, SO₃ and NO₂ can be redirected into manufacturing processes to produce acids. Also, SO₂ can be converted into sulfur using Fe₂O₃ catalyst for further H₂SO₄ production.
NO₂ + O₂ + H₂O → HNO₃
SO₂ + CH₄ → CO₂ + H₂S
H₂S + SO₂ → S + H₂O
3. Auto Exhaust Treatment:
Carbon monoxide (CO) and Nitrogen oxides (NOx) produced by incomplete combustion in automobile engines are converted into less harmful CO₂ and N₂ using catalytic converters with V₂O₅ catalyst.
4. Public Awareness:
Environmental movements (like BELA or BAPA in Bangladesh) play a crucial role in raising public awareness. By educating individuals and compelling government authorities and industrial owners to adopt eco-friendly measures, we can one day protect our environment from the devastating effects of acid rain.
