Question

Explain why ozone destruction via the reaction of \(\mathrm{O}_{3}\) with atomic oxygen does not occur to a significant extent in the lower stratosphere.

Short answer

The reaction of ozone with atomic oxygen is limited in the lower stratosphere due to low temperatures and low atomic oxygen concentrations.

Step-by-step solution

Understand Ozone Destruction Reaction

The reaction where ozone ( 703) is destroyed by atomic oxygen can be represented as: \(\mathrm{O}_{3} + \mathrm{O} \rightarrow 2\mathrm{O}_{2}\). This reaction involves collision between an ozone molecule and an oxygen atom, leading to the formation of two oxygen molecules.

Analyze Temperature Conditions

The lower stratosphere is relatively cold compared to other parts of Earth's atmosphere. The temperature affects the kinetic energy of atmospheric particles, influencing their movement and the likelihood of collisions occurring between ozone molecules and atomic oxygen.

Examine Concentration of Atomic Oxygen

In the lower stratosphere, the concentration of atomic oxygen is low because it mainly comes from the photodissociation of molecular oxygen, which primarily occurs higher up in the stratosphere, where ultraviolet (UV) radiation is more intense.

Consider Reaction Rate Factors

The rate of the reaction between \(\mathrm{O}_{3}\) and \(\mathrm{O}\) depends on the frequency and energy of collisions, which, as we saw, are affected by temperature and concentrations of \(\mathrm{O}_{3}\) and \(\mathrm{O}\). In the lower stratosphere, these conditions are not favorable for a high reaction rate.

Conclusion on Reaction Occurrence

Due to low temperatures and a low concentration of atomic oxygen in the lower stratosphere, the reaction between ozone and atomic oxygen does not occur to a significant extent, making it an ineffective pathway for ozone destruction in that region.

Key concepts

Lower Stratosphere

The lower stratosphere is a unique part of Earth's atmosphere, located just above the troposphere. It spans from about 10 to 20 kilometers above the Earth's surface. Here, environmental conditions differ significantly from those found at other altitudes.

• The lower stratosphere contains the bulk of the ozone layer, which protects life on Earth from harmful ultraviolet (UV) radiation.
• Temperatures in this part of the atmosphere are colder compared to environments higher up, where sunlight interacts more directly with atmospheric particles.

This chilled environment affects chemical reactions, including those involving ozone. Understanding these dynamics is crucial for comprehending the mechanisms of ozone depletion.

Atomic Oxygen

Atomic oxygen, denoted by the symbol \(O\), is a critical component in atmospheric chemistry. In its reactive form, atomic oxygen is a single oxygen atom, as opposed to molecular oxygen (\(O_2\)), which consists of two oxygen atoms bonded together.

• Unlike molecular oxygen, atomic oxygen is extremely reactive and short-lived.
• Its formation in the atmosphere primarily results from the photodissociation of molecular oxygen by high-energy UV light, particularly in the mid to upper parts of the stratosphere.

The concentration of atomic oxygen is significant because it determines the occurrence and rate of reactions with ozone. However, in the lower stratosphere, this concentration is typically much lower, limiting its role in ozone destruction.

Photodissociation

Photodissociation is a process where molecules are broken down into smaller components by photons, particularly those in the ultraviolet spectrum. This process plays a crucial role in atmospheric chemistry, especially in the destruction and formation of ozone.

• Molecular oxygen (\((O_2)\)) absorbs UV radiation, leading to its dissociation into two atomic oxygen atoms.
• This photodissociation primarily occurs in the higher stratosphere due to the greater availability of UV light, resulting in more atomic oxygen there.

In the lower stratosphere, less UV light penetrates, so photodissociation occurs at a reduced rate. This is why there is less atomic oxygen available to interact with ozone, limiting the extent of ozone destruction through this pathway.

Reaction Rate

The rate of any chemical reaction is influenced by several factors, including the concentration of reactants, the temperature, and the energy of collisions. These principles apply to the reaction between ozone (\(O_3\)) and atomic oxygen (\(O\)).

• A higher concentration of reactants and increased temperature often lead to more frequent and energetic collisions, speeding up the reaction.
• In the lower stratosphere, the concentration of atomic oxygen is low, and the ambient temperature is relatively cool.

These conditions result in fewer effective collisions between ozone and atomic oxygen, leading to a slow reaction rate. Consequently, the pathway for ozone destruction via this reaction in the lower stratosphere is minimal.

Temperature Conditions

Temperature plays a fundamental role in determining the kinetics of atmospheric reactions. In the lower stratosphere, temperatures can dip to extremely low levels, creating a unique environment for chemical interactions.

• Low temperatures reduce the kinetic energy of molecules.
• Reduced kinetic energy results in fewer and less forceful collisions between molecules, affecting reaction rates negatively.

In the case of ozone destruction by atomic oxygen, these cold conditions in the lower stratosphere mean that even when atomic oxygen is present, its interaction with ozone is limited. This significantly reduces the probability of ozone molecules being broken down in this region, preserving the ozone layer from this specific destructive pathway.