What is believed to be responsible for ozone depletion?

• A. The increase of free chlorine in the upper atmosphere
• B. The decrease of O2 levels in the atmosphere
• C. The stabilization of CFCs in the stratosphere
• D. The reduction of UV rays reaching the earth

Answer: (A)

The correct choice highlights the significant role of free chlorine in the upper atmosphere in contributing to ozone depletion. Chlorofluorocarbons (CFCs), commonly used in refrigerants and aerosol propellants, release chlorine when they are broken down by ultraviolet (UV) radiation in the stratosphere. This free chlorine reacts with ozone (O3) molecules, leading to their destruction and significantly thinning the protective ozone layer.

The other choices do not effectively explain the primary mechanism behind ozone depletion. The decrease of O2 levels in the atmosphere does not have a direct impact on the concentration of ozone, as ozone is formed from oxygen molecules under UV light. The stabilization of CFCs in the stratosphere is misleading; while CFCs are stable, it is their breakdown that leads to the release of chlorine, which is harmful. Lastly, the reduction of UV rays reaching the Earth is a consequence of ozone depletion rather than a cause; a diminished ozone layer allows more UV radiation to penetrate, leading to various environmental and health issues. Therefore, the release of free chlorine is established as a primary factor in the ozone layer's depletion.