Question

How is the protective ozone shield formed? What causes its natural breakdown?

Short answer

The ozone shield is formed by conversion of molecular oxygen to ozone under the action of solar ultraviolet radiation. Its natural breakdown is catalyzed by various compounds, such as nitrogen oxides, hydroxyl, and halogens, which convert ozone back into molecular oxygen.

Step-by-step solution

Ozone Formation

Ozone is formed in the Earth's atmosphere through a process known as the ozone-oxygen cycle. This cycle begins when solar ultraviolet radiation breaks apart molecular oxygen (\(O_2\)) into individual oxygen atoms. One freed oxygen atom (\(O\)) then combines with an \(O_2\) molecule to form a molecule of ozone (\(O_3\)). This process is represented by the equation: \(O_2 + \text{Photon} (ultraviolet light) \to 2O\) and \(O_2 + O \to O_3\).

Ozone Degradation

Natural breakdown of the ozone happens through catalytic cycles, involving chemical compounds such as nitrogen oxides (\(NO_x\)), hydroxyl (\(OH\)), and halogens (like \(Cl\) and \(Br\)). These compounds catalyze the conversion of ozone back to molecular oxygen. For example, let's consider one of the simplest catalytic cycles, involving \(Cl\) atoms: \(Cl + O_3 \to ClO + O_2\) and \(ClO + O \to Cl + O_2\). In this cycle, a chlorine atom \(Cl\) reacts with an ozone molecule \(O_3\) to produce chlorine monoxide \(ClO\) and an \(O_2\) molecule. Then, the \(ClO\) reacts with another \(O\) atom, regenerating the \(Cl\) atom and producing another \(O_2\) molecule. The regenerated \(Cl\) atom can then participate in another cycle of ozone destruction.

Overall Process

In conclusion, the formation and breakdown of the ozone shield is a natural process primarily driven by sunlight and involves a complex cycle of chemical reactions. The ozone layer can be depleted by man-made chemicals like CFCs (chlorofluorocarbons), which are potent catalysts for ozone destruction and can remain in the atmosphere for a long time due to their stability.