Problem 41 - A Complete Resource Book in Chemistry for JEE Main

Question

Ozone layer is present in (a) stratosphere (b) troposphere (c) mesosphere (d) exosphere

Step-by-Step Solution

Answer

The ozone layer is present in the stratosphere.

Step 1: Understanding Atmospheric Layers

The atmosphere is composed of several layers, starting from the Earth's surface up to outer space. The layers, in order from closest to the Earth, are: troposphere, stratosphere, mesosphere, and exosphere. The ozone layer is located in one of these layers.

Step 2: Identifying the Ozone Layer

The ozone layer is a protective layer in the Earth's atmosphere that absorbs most of the Sun's harmful ultraviolet radiation. This layer is crucial for life on Earth.

Step 3: Locating the Ozone Layer

The majority of the ozone layer exists in the stratosphere, which is the second layer of the atmosphere, just above the troposphere.

Step 4: Choosing the Correct Option

Since the ozone layer is primarily located in the stratosphere, option (a) "stratosphere" is the correct answer for where the ozone layer is present.

Key Concepts

Atmospheric Layers

The atmosphere is an invisible yet crucial part of our world. It is composed of layers that each have distinct characteristics and functions. Starting closest to the Earth's surface, we have the **troposphere**. This is where we live and where weather happens, extending up to about 8 to 15 kilometers above the Earth. Next is the **stratosphere**, which reaches about 50 kilometers high. It is home to the ozone layer, a vital shield against ultraviolet radiation. Above the stratosphere is the **mesosphere**, stretching up to about 85 kilometers. Here, temperatures drop significantly, and it serves as a barrier reducing meteors to dust. Finally, the outermost layer is the **exosphere**, which gradually fades into outer space. It is extremely thin and is where particles escape into space. As you rise through these layers, the properties such as temperature and pressure change, making each layer unique.

Stratosphere

The stratosphere is the second layer of the atmosphere, sitting just above the troposphere and stretching up to about 50 kilometers above the Earth's surface. This layer is particularly important because it houses about 90% of the Earth's ozone.
The stratosphere is distinct because it contains the ozone layer, which makes it crucial for protecting life on Earth.
- **Heating Phenomenon**: Unlike the troposphere, the stratosphere's temperatures increase with altitude due to the absorption of ultraviolet radiation by ozone. This creates a warm layer above a cooler one, resulting in little vertical mixing and stable conditions. - **Jet Aircraft**: Many commercial jets fly in the lower stratosphere to avoid turbulence found in the troposphere, thanks to its stability.
The stability and the presence of the ozone layer are two main reasons the stratosphere plays such a key role in making Earth a habitable planet.

Ultraviolet Radiation Absorption

Ultraviolet (UV) radiation from the Sun can be harmful to life on Earth, but fortunately, the ozone layer absorbs most of it before it can reach the surface. This absorption occurs primarily in the stratosphere, home to the majority of the Earth's ozone.

• **Role of Ozone**: Ozone molecules are made up of three oxygen atoms. They are highly effective at absorbing UV radiation, particularly UV-B and UV-C rays, which can cause skin cancer and cataracts in humans, as well as damage to plants and marine ecosystems.
• **Protection Mechanism**: As UV rays enter the stratosphere, they break apart ozone molecules. This process absorbs the energy from the UV rays, effectively reducing the amount that reaches the Earth's surface.

By absorbing UV radiation, the ozone layer acts as a protective shield, safeguarding all living organisms from potential harm. Without it, the intense UV rays could significantly increase the risk to the health of both ecosystems and humans alike.