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

Although individual ozone (O3) molecules have a short lifespan of 100-200 seconds, they continuously form and dissociate in the stratosphere, creating a protective ozone layer. Ozone molecules form when UV radiation breaks apart oxygen molecules (O2) into free oxygen atoms, which then collide with other O2 molecules to form O3. Ozone molecules dissociate when they absorb UV radiation, breaking down into O2 molecules and free oxygen atoms. This ongoing cycle of formation and dissociation maintains the ozone layer, enabling it to absorb harmful ultraviolet radiation and protect life on Earth.

Step-by-step solution

Understanding the ozone molecule#writer_sdk# An ozone molecule, also known as O3, consists of three oxygen atoms bonded together. Ozone molecules exist primarily in the Earth's stratosphere, which is located approximately 10-50 km above the Earth's surface. The ozone layer plays a vital role in protecting the Earth from harmful UV radiation, which can cause skin cancer, cataracts, and damage to the immune system as well as to marine and plant life.

Step 2: Formation of ozone molecules#writer_sdk# Ozone molecules are formed in the stratosphere when ultraviolet (UV) radiation breaks apart regular oxygen molecules (O2) into free oxygen atoms. When UV radiation with a wavelength shorter than 240 nm hits an O2 molecule, the radiation energy is strong enough to break the oxygen bond and produce two free oxygen atoms. These free oxygen atoms can then collide with other O2 molecules to form O3: \[ O_2 + UV_{<240 nm} \to 2O \] \[ O + O_2 \to O_3 \]

Dissociation of ozone molecules#writer_sdk# Ozone molecules are not very stable and can quickly dissociate (break apart) when they absorb ultraviolet radiation. When ozone molecules absorb UV radiation with a wavelength between 240 nm and 310 nm, they break apart into O2 molecules and free oxygen atoms. This dissociation process can be represented as follows: \[ O_3 + UV_{240-310 nm} \to O_2 + O \] The free oxygen atoms produced in dissociation can then react with more O2 molecules to form new ozone molecules, as described in Step 2.

Step 4: Explaining the protective role of ozone#writer_sdk# Although individual ozone molecules only "live" for 100-200 seconds before dissociating, the continuous cycle of ozone formation and dissociation helps to maintain an overall ozone presence in the stratosphere. By absorbing ultraviolet radiation (particularly the hazardous UV-C radiation), ozone molecules prevent that energy from reaching Earth's surface, effectively protecting life on Earth. Overall, despite the short lifespan of ozone molecules, the cycling processes of formation and dissociation maintain the ozone layer and enable it to offer continuous protection against harmful ultraviolet radiation.