Exam Question

### (a) Ozone Depletion and its Effects
Ozone depletion refers to the gradual thinning of the Earth's ozone layer, primarily in the stratosphere, which is approximately 10 to 50 kilometres above the Earth's surface. The ozone layer is a region of high ozone (O₃) concentration that plays a crucial role in absorbing most of the Sun's harmful ultraviolet (UV) radiation, particularly UV-B and UV-C, before it reaches the Earth's surface.
Naturally, ozone is formed when ultraviolet radiation from the sun splits molecular oxygen (O₂) into two free oxygen atoms (O). These free oxygen atoms then rapidly combine with other O₂ molecules to form ozone (O₃). The depletion occurs when certain anthropogenic chemicals, known as Ozone Depleting Substances (ODS), are released into the atmosphere. These substances, when they reach the stratosphere, are broken down by UV radiation, releasing highly reactive halogen atoms (e.g., chlorine and bromine). These halogen atoms then act as catalysts to destroy ozone molecules in a chain reaction, meaning a single chlorine atom can destroy thousands of ozone molecules before it is eventually removed from the stratosphere.
**Effects of Ozone Depletion:**