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Chapter 19: Problem 18

How do CFCs affect the concentration of ozone in the stratosphere and contribute to the formation of the ozone hole?

Short Answer

Expert verified
CFCs, when released into the atmosphere, rise to the stratosphere where they are broken down by UV radiation, releasing chlorine. This chlorine acts as a catalyst to convert ozone into oxygen, starting a cycle that depletes the ozone layer. Concentrated depletions of ozone, referred to as 'ozone holes', form predominantly over the polar regions.

Step by step solution

01

Understanding CFCs

Chlorofluorocarbons (CFCs) are chemical compounds that were earlier widely used in industry, for example in air conditioning systems and refrigerators, aerosol propellants and electronic cleaning. These compounds are stable, non-toxic and fire-resistant, but are strong greenhouse gases and are not easily broken down in the lower atmosphere.
02

Emission and Ascension of CFCs

CFCs are released into the atmosphere through human activity. Due to their stability, they do not decompose in the lower atmosphere and gradually ascend to the stratosphere.
03

Interaction with UV Radiation and Release of Chlorine

In the stratosphere, CFCs are broken apart by solar radiation, specifically UV radiation, releasing chlorine atoms. The chemical reaction can be described as: \[ CFCl_{3} + UV Rays → CFCl_{2} + Cl \]
04

Role of Chlorine in Destruction of Ozone

The chlorine atom catalyses the conversion of Ozone (O3) back into Oxygen (O2), perpetuating a cycle that depletes the ozone layer. The chemical reactions involved are: \[ Cl + O3 → ClO + O2 \] and \[ ClO + O → Cl + O2 \] Through these reactions, one chlorine atom can destroy many ozone molecules before it is removed from the stratosphere.
05

Formation of the Ozone Hole

The 'ozone hole' is a term for a region of depleted ozone in the stratosphere, found mostly over Antarctica, but also observed over the Arctic. The depletion of ozone in these regions is primarily due to reactions on the surface of polar stratospheric clouds (PSCs), which form during the polar winter. This leads to a process known as the ozone hole.

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