In stratosphere most of the ozone formation is assisted by
(a) cosmic rays
(b) gamma-rays
(c) ultrav

Q: Why don't visible or infrared radiations form ozone?

Visible and infrared radiations have lower energy and longer wavelengths compared to UV radiation. They simply do not possess enough energy to break the strong double bond of the $O_2$ molecule, which is the crucial first step in ozone formation.

Q: Does ozone formation happen in the troposphere (where we live) too?

Yes, but the mechanism is entirely different. In the troposphere, ozone is formed as a secondary pollutant through complex photochemical reactions involving nitrogen oxides ($NO_x$) and volatile organic compounds (VOCs), not directly from $O_2$ splitting by UV.

Q: If UV creates ozone, why do we always hear that UV is harmful?

UV radiation is harmful to living tissues because it carries enough energy to damage DNA and cause skin cancer. The beauty of the ozone layer is that it acts as a sacrificial shield; the sun's harmful UV-B and UV-C radiation is absorbed and used up in the very process of creating and destroying ozone, preventing it from reaching the Earth's surface.

Q: What exactly is a 'nascent' oxygen atom?

A nascent oxygen atom is a single, uncombined atom of oxygen ($O$). It is highly reactive because it has unpaired electrons and strongly seeks to bond with other molecules to achieve a stable electron configuration.

Q: Is ozone destruction also caused by UV radiation?

Yes! The ozone-oxygen cycle (Chapman cycle) is a continuous, dynamic process. UV radiation not only creates ozone by splitting $O_2$, but it also destroys ozone by splitting $O_3$ back into $O_2$ and $O$. This dynamic equilibrium is what maintains the steady concentration of the ozone layer.

Question

In stratosphere most of the ozone formation is assisted by

Options:

(A) cosmic rays

(B) $\gamma$-rays

(C) ultraviolet radiations

(D) visible radiations

Sigma Percentile · Accepted Answer

Imagine you are floating high up in the Earth's atmosphere, about 15 to 30 kilometers above the surface. You have entered the **stratosphere**, a region characterized by thin air and a very special chemical drama that protects all life on Earth.

In this article, we will explore the fascinating mechanism of how the ozone layer is formed, answering a classic question from Environmental Chemistry.

### The Stage: The Stratosphere

The stratosphere is populated by an abundance of diatomic oxygen molecules, denoted as $O_2$. Under normal conditions, these molecules are quite stable. The two oxygen atoms are held together by a strong double bond, floating peacefully in the upper atmosphere. However, the stratosphere is the Earth's first major line of defense against the harsh environment of space, meaning it is constantly bombarded by high-energy radiation from the sun.

### The Catalyst: Ultraviolet Radiation

Among the various types of electromagnetic radiation emitted by the sun, **ultraviolet (UV) radiation** plays the starring role in our story. UV radiation carries a significant amount of energy—much more than visible light or infrared radiation.

When a powerful UV photon collides with an $O_2$ molecule, it transfers its energy to the molecule. This energy is sufficient to overcome the strong double bond holding the oxygen atoms together.

### The Climax: Photodissociation

The breaking of the $O_2$ bond by light is a process known as **photodissociation**. The chemical equation for this step is elegantly simple:

$$O_2(g) \xrightarrow{	ext{UV radiation}} O(g) + O(g)$$

The molecule splits apart, resulting in two highly reactive, single oxygen atoms. These are often referred to as **nascent oxygen**. Because they have unpaired electrons, they are chemically unstable and desperately seek out other molecules to bond with to achieve a stable electron configuration.

### The Resolution: The Birth of Ozone

These lone, highly reactive oxygen atoms don't stay single for long. When one of these nascent oxygen atoms bumps into an intact $O_2$ molecule nearby, a rapid chemical reaction occurs. They combine to form a triatomic molecule:

$$O(g) + O_2(g) ightarrow O_3(g)$$

This newly formed $O_3$ molecule is **ozone**!

If we trace the entire process back to its origin, it becomes crystal clear that the formation of ozone in the stratosphere is fundamentally driven and assisted by **ultraviolet radiations**. Without the initial high-energy UV light to split the stable oxygen molecules, the entire cycle (known as the Chapman cycle) would never begin. Therefore, ultraviolet radiation is the correct answer.

Animated Solution for Chemistry - Environmental Chemistry: In stratosphere most of the ozone formation is assisted by

Select Answer:

Visualized Solution

$O_{2}$ \text{ in Stratosphere}

\text{Role of UV Radiation}

\text{Photodissociation of } O_2

\text{Formation of Ozone}

\text{Conclusion}

The Sigma Insight: Atmospheric Pollution

The Stage

The Catalyst

The Climax

The Resolution

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