Question

If an average \(\mathrm{O}_{3}\), molecule "lives" only \(100-200\) seconds in the stratosphere before undergoing dissociation, how can \(\mathrm{O}_{3}\) offer any protection from ultraviolet radiation?

Short answer

Ozone (O3) offers protection from ultraviolet radiation in the stratosphere despite its short lifespan due to the constant formation and dissociation processes it undergoes. The balance between these processes creates a steady-state concentration of ozone, which effectively absorbs harmful UV radiation. When ozone absorbs UV radiation, it dissociates into oxygen molecules and atoms, which then participate in further ozone formation processes, maintaining the protective ozone layer in the stratosphere.

Step-by-step solution

Understand the role of ozone in the stratosphere

First, it's important to grasp the role that ozone molecules play in the stratosphere. Ozone absorbs harmful ultraviolet (UV) radiation from the sun, preventing it from reaching the Earth's surface. UV radiation is divided into three types: UVA, UVB, and UVC. Ozone primarily absorbs UVB and UVC radiation, which can harm living organisms and cause skin cancer in humans.

Describe the formation and dissociation of ozone molecules

Ozone is formed through a series of chemical reactions involving oxygen molecules (O2) and individual oxygen atoms (O): 1. Oxygen molecules (O2) absorb UV radiation, which dissociates them into two oxygen atoms (O): \[ O_2 + \text{UV} \rightarrow 2O \] 2. The free oxygen atoms (O) then react with other oxygen molecules (O2) to form ozone (O3): \[ O + O_2 \rightarrow O_3 \] 3. Ozone molecules (O3) can also absorb UV radiation, causing them to dissociate back into an oxygen molecule (O2) and an oxygen atom (O): \[ O_3 + \text{UV} \rightarrow O_2 + O \] The balance between the formation and dissociation of ozone creates a steady-state ozone concentration in the stratosphere.

Explain how ozone offers protection despite its short lifespan

Ozone's short lifespan in the stratosphere indicates that ozone molecules are constantly undergoing formation and dissociation processes. When ozone absorbs UV radiation, it dissociates to form oxygen molecules and atoms, which in turn participate in further ozone formation processes. As a result, despite the short lifespan of individual ozone molecules, there is always a steady-state concentration of ozone in the stratosphere that effectively absorbs and blocks harmful UV radiation from reaching the Earth's surface. In conclusion, the constant formation and dissociation of ozone in the stratosphere ensure that there is always a sufficient concentration of ozone to protect the Earth from harmful ultraviolet radiation, despite the short lifespan of individual molecules.

Key concepts

UV Radiation Protection

The ozone layer plays a crucial role in safeguarding life on Earth from the sun's harmful ultraviolet (UV) radiation. This invisible shield is located in the stratosphere, and it mainly absorbs and filters out UVB and UVC rays. These types of UV radiation can be particularly damaging:

• UVB rays: Can lead to skin cancer and cataracts in humans, and they also harm marine ecosystems and crops.
• UVC rays: The most harmful type of UV radiation, but fortunately, it is almost entirely absorbed by the ozone layer and doesn’t reach the Earth’s surface.

By blocking these dangerous rays, the ozone layer protects all living organisms, ensuring the planet remains a thriving habitat.

Ozone Formation and Dissociation

Ozone creation and destruction in the stratosphere is a fascinating dance of molecules reacting to UV light.

Ozone (O_3) forms via a two-step process:

• First, UV radiation breaks apart an oxygen molecule (O_2) into two individual oxygen atoms (O): \[ O_2 + \text{UV} \rightarrow 2O \ \]
• These free oxygen atoms then react with other O_2 molecules to form ozone: \[ O + O_2 \rightarrow O_3 \ \]

Ozone, however, doesn't stick around for long. It also absorbs UV radiation, breaking back down into an O_2 molecule and an O atom: \[ O_3 + \text{UV} \rightarrow O_2 + O \ \]
Though each ozone molecule's lifespan is short, this continuous cycle maintains a stable concentration of ozone, creating a dynamic equilibrium that protects Earth from UV radiation constantly.

Stratospheric Chemistry

The chemistry of the stratosphere involves complex interactions that maintain the balance of ozone. This region, about 10 to 50 kilometers above Earth's surface, hosts these critical processes of molecular transformations.

Ozone is key to the photochemical reactions that define stratospheric chemistry. Here are some fascinating points:

• Photodissociation: UV light splits molecules, which is the basic mechanism for both O_2 breaking into O and for O_3 dissociating.
• Ozone balance: The rapid cycle of ozone formation and decomposition ensures that ozone levels remain stable, effectively absorbing harmful UV rays.
• Role in climate: Ozone also influences temperature in the stratosphere since its formation and breakdown release heat, affecting weather patterns and climate.

Understanding these chemical processes helps us appreciate the delicate balance that keeps our planet shielded from excessive UV radiation, highlighting the importance of preserving the ozone layer.