Ozone absorbs ultraviolet (UV) light through a process called photodissociation, where UV radiation breaks the ozone molecule apart.
The Process Explained
When an ozone molecule (O3) encounters ultraviolet (UV) radiation, specifically UV-B and UV-C, the energy from the UV photon is absorbed. This absorption causes the ozone molecule to split apart into:
- An ordinary oxygen molecule (O2)
- A free oxygen atom (O)
Here's a breakdown of the process:
- Absorption: The ozone molecule absorbs a UV photon.
- Dissociation: The absorbed energy breaks the bond between one of the oxygen atoms and the O2 molecule. This results in the separation of O3 into O2 + O.
- Reformation (Optional): The free oxygen atom can then collide with another oxygen molecule (O2) to reform ozone (O3). This reformation process releases heat, which warms the stratosphere. Alternatively, the free oxygen atom can react with another ozone molecule.
Why This is Important
This absorption of UV light by ozone in the stratosphere is crucial because:
- It prevents harmful levels of UV-B and UV-C radiation from reaching the Earth's surface. These types of UV radiation can cause skin cancer, cataracts, and damage to plant life.
- The energy absorbed in the dissociation process warms the stratosphere, playing a role in the temperature profile of the atmosphere.
Simplified Analogy
Think of ozone as a sponge that soaks up dangerous UV light. When it soaks up too much, it breaks into smaller pieces (oxygen molecule and oxygen atom). These pieces can sometimes come back together to form the sponge (ozone) again.
Types of UV Radiation and Ozone Absorption
| UV Radiation Type | Wavelength (nm) | Ozone Absorption | Effects |
|---|---|---|---|
| UV-C | 100-280 | Almost completely | Absorbed in the atmosphere; does not reach Earth |
| UV-B | 280-315 | Significantly | Partially absorbed; can cause sunburn and skin cancer |
| UV-A | 315-400 | Weakly | Least energetic; reaches Earth's surface |
Ozone is most effective at absorbing UV-C radiation. While it also absorbs a significant portion of UV-B, some still reaches the Earth's surface. UV-A is only weakly absorbed by ozone.
