Question

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

Short answer

In conclusion, individual ozone (O₃) molecules have a short lifetime of 100-200 seconds in the stratosphere, but their ability to absorb harmful UV radiation remains effective due to the continuous formation and dissociation process. This dynamic system allows for the constant regeneration of ozone molecules, keeping a balanced and protective ozone layer for life on Earth.

Step-by-step solution

Understanding Ozone molecules and their role in UV radiation absorption

Ozone (O₃) is a molecule made up of three oxygen atoms. It is mainly found in the Earth's stratosphere, where it plays a crucial role in absorbing harmful ultraviolet (UV) radiation emitted by the Sun. UV radiation can cause various health problems such as eye damage and skin cancer. Thus, the presence of ozone in the stratosphere is important for the protection of life on Earth.

Formation and dissociation of Ozone molecules

Ozone is formed by the high-energy sunlight in the stratosphere splitting O₂ molecules into individual oxygen atoms, which further react with O₂ molecules to form O₃. This process can be represented by the following reactions: 1. Formation of O₃: \(O_2 + O \rightarrow O_3\) 2. Dissociation of O₃: \(O_3 + UV \rightarrow O_2 + O\) When a high-energy UV photon interacts with an ozone molecule, it causes the molecule to dissociate back into an oxygen molecule (O₂) and a free oxygen atom (O). Even though each ozone molecule has a relatively short lifetime (100-200 seconds) before undergoing dissociation, the continuous formation and dissociation of ozone molecules allow them to provide constant protection against UV radiation.

Constant regeneration of Ozone molecules

Ozone molecules in the stratosphere constantly undergo formation and dissociation cycles, wherein new ozone molecules are formed as the existing ones dissociate. As a result, the ozone layer remains in a dynamic state, replenishing the ozone molecules that absorb UV radiation and protect life on Earth. This constant regeneration process helps maintain a balance between the creation and dissociation of ozone molecules.

Conclusion

In conclusion, even though individual ozone (O₃) molecules have a short lifetime of 100-200 seconds in the stratosphere, their ability to offer protection from harmful UV radiation is made possible by the continuous formation and dissociation process. This dynamic system allows the regeneration of ozone molecules, which in turn helps maintain a balanced and protective ozone layer in the Earth's stratosphere.

Key concepts

Ozone Molecule Formation and Dissociation

Ozone, often symbolized as O₃, is a protective layer found high above the Earth in the stratosphere, crucial for shielding life on our planet from the Sun's ultraviolet (UV) rays. This molecule consists of three oxygen atoms, and its life cycle is key to understanding its protective role. The formation of ozone is a sunlight-driven process; high-energy UV light splits an oxygen molecule (O₂) into two separate oxygen atoms. These highly reactive atoms then collide and bind with O₂ molecules to form ozone (O₃). This process can be succinctly expressed by the reaction: \(O_2 + O \rightarrow O_3\).
The cycle does not end with formation; ozone molecules are not permanent fixtures in the stratosphere. They undergo dissociation, or breaking apart, when they absorb UV radiation. When a UV photon hits an ozone molecule, one oxygen atom breaks away, leaving behind an O₂ molecule. This interaction is illustrated by the reaction: \(O_3 + UV \rightarrow O_2 + O\). Despite what might seem like a vulnerability, the constant formation and breakdown of ozone is actually a cycle that maintains the balance of ozone in the stratosphere, providing enduring protection against UV radiation.

Ultraviolet Radiation Absorption

The absorption of ultraviolet (UV) radiation by the ozone layer is a natural phenomenon of paramount importance. UV radiation is a type of energy released by the Sun which includes different wavelengths, some of which are harmful to life on Earth. The ozone layer predominantly absorbs the shorter wavelengths, known as UV-B and UV-C radiation. These wavelengths are harmful to biological organisms as they can cause skin cancer, cataracts, and damage to DNA.

• UV-C radiation is almost completely absorbed by ozone and oxygen in the stratosphere.
• UV-B radiation is partially absorbed, with some reaching the Earth's surface, but significantly reduced in intensity.

Each time an ozone molecule absorbs UV radiation, it dissociates into an O₂ molecule and a free oxygen atom as mentioned earlier. The energy from the UV radiation is effectively converted during this reaction, drastically reducing its potential to damage organic material on Earth's surface. While individual ozone molecules are sacrificed during this process, the dynamic equilibrium in the stratosphere ensures a steady supply of ozone, continuously safeguarding our planet.

Stratosphere Ozone Dynamics

Within the stratosphere, the dynamics of ozone are marked by a delicate balance between production and destruction. This balance is governed by complex chemical reactions and is influenced by various factors including temperature, altitude, and the presence of other chemicals. In regions with more intense sunlight, such as near the equator, ozone formation rates are higher. Conversely, in areas with less UV radiation, such as the poles, ozone forms at a slower pace.
Despite the ongoing formation and dissociation, the overall quantity of ozone is maintained because for each ozone molecule that is broken down by UV light, another is formed from the released oxygen atom and the surrounding O₂ molecules. Man-made chemicals like chlorofluorocarbons (CFCs) have the potential to upset this balance by releasing chlorine atoms that catalyze the breakdown of ozone. This can lead to what's known as ozone depletion, the effects of which are seen in phenomena such as the 'ozone hole'. Awareness of these dynamics and efforts to control the emission of ozone-depleting substances are vital for the protection of the ozone layer, which, in turn, protects all life on Earth from the Sun's harshest UV rays.