Question

Define the term free radical, and give two examples relevant to stratospheric chemistry.

Short answer

Free radicals are highly reactive atoms or molecules with an unpaired electron. Examples in stratospheric chemistry include hydroxyl radical (OH) and chlorine monoxide radical (ClO).

Step-by-step solution

Define the Term 'Free Radical'

A 'free radical' is a molecule or atom that contains an unpaired electron in an open shell configuration. This unpaired electron makes free radicals highly reactive as they seek to pair up this lone electron by reacting with other substances.

Identify Free Radicals in Stratospheric Chemistry

In stratospheric chemistry, free radicals play a significant role, particularly in the processes that affect the ozone layer. They are involved in catalytic cycles that lead to ozone depletion.

Provide Examples

Two examples of free radicals relevant to stratospheric chemistry are the hydroxyl radical (OH) and chlorine monoxide radical (ClO). Both are instrumental in the breakdown of ozone. The hydroxyl radical can react with ozone to start a chain reaction that leads to ozone destruction, while the chlorine monoxide radical forms in reactions that also contribute to ozone layer depletion.

Key concepts

Stratospheric Chemistry

Stratospheric chemistry is the study of chemical processes that occur in the Earth's stratosphere, which is located between the troposphere and the mesosphere. It's particularly important because it impacts the ozone layer, a protective shield that absorbs harmful ultraviolet radiation from the sun. Key players in stratospheric chemistry include various free radicals and other reactive species.

One of the primary concerns within stratospheric chemistry is how these chemicals interact to either preserve or deplete the ozone layer. The presence of free radicals such as hydroxyl (OH) and chlorine monoxide (ClO) can lead to significant changes in the ozone concentration. Understanding these processes helps scientists assess the impact of human activities and natural events on the ozone layer.

• Stratosphere: Layer of atmosphere above the troposphere.
• Chemical processes: Involve free radicals that affect ozone concentration.
• Ozone layer: Absorbs harmful UV radiation.

Ozone Depletion

Ozone depletion refers to the thinning and reduction of the ozone layer in the Earth's stratosphere. This is caused by reactions involving free radicals, which are released by both natural processes and human activities. The most well-known human-made chemicals contributing to this depletion are chlorofluorocarbons (CFCs).

When these substances reach the stratosphere, they undergo photodissociation, a process where sunlight breaks chemical bonds. This releases free radicals, such as chlorine, which participate in reactions that destroy ozone molecules. The result is areas of significantly reduced ozone concentration, often referred to as "ozone holes."

• Chlorofluorocarbons: Human-made chemicals that harm the ozone layer.
• Photodissociation: Process releasing reactive radicals.
• Ozone holes: Regions of strong ozone depletion.

Hydroxyl Radical

The hydroxyl radical (OH) is a highly reactive free radical present in the atmosphere, playing a crucial role in stratospheric chemistry. It is often referred to as a "detergent" of the atmosphere due to its ability to react with and break down various pollutants and gases.

In the context of the stratosphere, the hydroxyl radical can initiate reactions that lead to the destruction of ozone molecules. When OH reacts with ozone (O extsubscript{3}), it starts a chain reaction, resulting in the depletion of the ozone. This makes the presence of hydroxyl radicals an important factor in understanding the dynamics of ozone depletion.

• Highly reactive: Quickly engages in chemical reactions.
• Ozone interactions: Can start ozone-depleting reactions.
• Atmospheric "detergent": Breaks down pollutants.

Chlorine Monoxide Radical

Chlorine monoxide (ClO) is a free radical that significantly contributes to stratospheric ozone depletion. It forms through the reaction of chlorine atoms with ozone molecules. Chlorine, usually released by the breakdown of CFCs, interacts with ozone to produce ClO and molecular oxygen.

This radical is notorious for its potential to perpetuate the ozone depletion cycle. In the polar stratosphere, ClO can agglomerate to create a powerful ozone-depleting compound that destabilizes multiple ozone molecules in a short period. This is especially concerning over regions like Antarctica, where the "ozone hole" phenomenon is annually observed.

• Derived from CFCs: Chlorine comes from human activity.
• Ozone reaction: Disrupts ozone balance.
• Polar stratosphere effects: Severe depletion observed in cold regions.