What is Acid Rain and why it occurs?

We’ve heard about acid rain since we were little. Many of us have ideas that this kind of rain happens in the past or a particular region of the world.

Surely that rain is terrible, and wherever it is, everything burns in acid, burns, and crumbles. In fact, in countries like ours, where the atmosphere is rich in Sulphur (S) oxides and nitrogen (N) oxides, there is a constant rain of acid rain.

When the P^H value of rainwater reaches less than 4 (four) or 4 (four), then that rain is called acid rain.

P^H is the amount of concentration of hydrogen ions (H⁺) in a liquid. It is expressed by the negative logarithm of hydrogen ion concentration, the chemical formula of which is given below: –

P^H = log₁₀ ^(1/H+) বা  -log₁₀H⁺

It is expressed by a scale called the P^H scale. P^H scales range from 0 to 14. The P^H value of clean drinking water is considered 7. If the P^H of a liquid is less than 7, it is called acid, and if it is more than 7, it is called alkali or alkaline or basic.

From the chemical formula, we understand that if H⁺ in a liquid increase by 10-fold, the value of P^H decreases by 1, and if the amount of H⁺ decreases by 10-fold, the value of P^H increases by 1.

Below is a P^H scale.

Cities or regions that rich in industries, automobiles, or wood or coal brick kilns, usually have high levels of sulphur and nitrogen oxides in the atmosphere and rainfall in those areas are acidic.

The chemical reactions of sulphur (S) and nitrogen (N) with oxygen in the presence of sunlight to form oxide then reaction with rainwater or fog water is given below: –

(1) Sulphur (S) with oxygen (O2) and Sulphur dioxide with rainwater or fog water:

S + O₂ → SO₂
SO₂ +1/2 O₂ + H₂O = H₂SO_4↓

(2) Nitrogen (N) with oxygen (O2) and Nitrate with rainwater or fog water:

N + O₂ → NO
NO + O₂ + H₂O  → HNO₃

Disadvantages of acid rain:

• Contaminates drinking water.
• Damage Aquatic lives and Vegetations.
• Destroys soil fertility by changing the P^H value. Soil P^H is usually 7-8. But as a result of acid rain, it decreases and destroys soil chemical equilibrium. When its accumulation in soil called Wet Deposition.
• Erode Buildings and sculptures.
• Cause Deforestation.
• The reasons for the increase in sulphur dioxide and nitrogen oxide in the air are as follows:

Sulphur Dioxide (SO₂): –

• As a result of the burning/busting of fossil fuels like petrol, diesel, octane, coal, etc. in industries, vehicle, brick kiln, especially coal burning in industries or power plants (75%).
• Industrial process (25%).

Nitrogen oxide (NO):

• As a result of burning/busting of fossil fuels like petrol, diesel, octane, etc. in the vehicle (52%).
• As a result of the burning of petrol, diesel, coal, etc. in industries, brick kilns. (44%).
• Agriculture process and others (4%).

An industrial area in Raisa (source of NO and SO₂)

Remedy:

1. Stopped using small vehicles for one or two passengers carrying such as taxis, car. Instead of that big vehicles that carrying more passengers like long buses should introduce.
2. For long-distance traveling long buses, trains should use instead of cars.
3. Use bicycles instead of vehicles, develop the habit of walking for short distances like offices, markets, playgrounds, parks, etc.
4. Gradually reduce the use of petrol, diesel, octane, and introduce green energies.
5. Stop burning coal and wood completely.
6. Industrial factories to be set up away from the cities.
7. For Particulate Matter, harmful gases removal in Chimney, Settling Chamber, Cyclone Collectors, Electrostatic Precipitous, Coal burring PP, Wet cleaning process should be used.
8. Stop burning objects or hay that cause smoke in agricultural work and cooking etc.
9. Those areas that experience Acid rains, should use lime or alkaline from time to time in ponds, water bodies, fish culture projects.

References:

1. Atmospheric Pollution, History, Science and Regulation, Mark Z. Jacobson, Cambridge Uni. Press, 2003
2. Environment: Problems and Solutions, DK Asthana, Meera Asthana, Chand Pub. India, 1999.
3. Environmental Chemistry, AK De, 4th Edition, New Age International (Pvt)Ltd, India, 2000
4. Air Pollution, MN Rao, HVN Rao, Tata-McGraw-Hill, India, 1989.
5. Wikipedia.

Source: GreenPage Bangla