Atmospheric Pollution

and are formed over Antarctica.These are converted back into reactive atoms which start the chain reaction with causing its depletion.

Step 1: Ozone formation.
Ozone is formed in the upper atmosphere from oxygen molecules under the influence of ultraviolet (UV) light. UV light breaks apart the oxygen molecules, leading to the formation of ozone.
Thus, the correct answer is (2).

In presence of U.V. rays is converted into .

Step 1: Understand the greenhouse effect.
The greenhouse effect is primarily due to the presence of gases such as , , and water vapor in the atmosphere, which absorb infrared radiation and trap heat.
Step 2: Conclusion.
The greenhouse effect is caused by gases that absorb infrared radiation. Final Answer:

Step 1: During thunderstorm, nitrogen and oxygen combine to form oxides of nitrogen.
Step 2: These dissolve in rainwater forming nitric acid, lowering pH.

Step 1: Incomplete combustion of petrol and diesel occurs in automobile engines.
Step 2: Incomplete combustion mainly produces carbon monoxide.

Step 1: Hydrocarbons can act as carcinogens.
Step 2: Long-term exposure increases risk of cancer.

Photochemical smog is formed due to reactions of nitrogen oxides and hydrocarbons in sunlight producing ozone. SO₂ is mainly involved in classical smog.

Step 1: Ozone absorbs harmful ultraviolet radiation.
Step 2: It does not absorb infrared radiation significantly.

Complete combustion of fuel in automobile engines produces carbon dioxide as the major product.

Certain hydrocarbons are carcinogenic and prolonged exposure can cause cancer.

Step 1: Photochemical smog is formed due to reactions between: \beginitemize • Nitrogen oxides (NO, NO₂) • Hydrocarbons • Sunlight \enditemize Step 2: Ozone (O₃) is a major constituent formed during photochemical smog. Step 3: Sulphur dioxide (SO₂) is mainly responsible for classical (London) smog, not photochemical smog.