`SO_2` is considered as an air pollutant because

Options

A. Its concentration increases with temperature increases of atmosphere.
B. It is used as an insecticide which is air pollutant
C. It reacts with `O_2 and H_2O` to produce acid rain
D. It is a strong oxidant and oxidant oxidizes other components of atmosphere

Answer

To determine why sulfur dioxide (SO₂) is considered an air pollutant, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Definition of Air Pollutant**:
An air pollutant is any substance in the air that can cause harm to humans, animals, or the environment.

2. **Sources of SO₂**:
Sulfur dioxide is primarily produced from the burning of fossil fuels, such as coal and oil, in thermal power plants, industries, and automobiles.

3. **Chemical Reactions Involving SO₂**:
When SO₂ is released into the atmosphere, it can react with oxygen (O₂) and water (H₂O) present in the air. The reaction can be represented as:
\[ 2 \text{SO}_2(g) + \text{O}_2(g) + 2 \text{H}_2\text{O}(l) \rightarrow 2 \text{H}_2\text{SO}_4(aq) \]
This reaction produces sulfuric acid (H₂SO₄), which is a key component of acid rain.

4. **Formation of Acid Rain**:
The sulfuric acid formed from the reaction of SO₂ with water contributes to acid rain. Acid rain occurs when rainwater becomes acidic due to dissolved sulfuric acid and other pollutants.

5. **Environmental Impact**:
Acid rain can have detrimental effects on aquatic ecosystems, soil, vegetation, and human-made structures. It can harm aquatic life by lowering the pH of water bodies, making it inhospitable for many species.

6. **Conclusion**:
Therefore, SO₂ is considered an air pollutant because it contributes to the formation of acid rain, which poses significant risks to the environment and public health.