What chemical in the stratosphere is a key indicator of ozone depletion?

The presence of Chlorine Monoxide (ClO) in the stratosphere serves as a critical indicator of ozone depletion due to its direct involvement in the chemical reactions that deplete ozone molecules. Chlorine compounds, especially those stemming from substances such as chlorofluorocarbons (CFCs), are released into the atmosphere where they are eventually broken down by ultraviolet (UV) radiation, releasing chlorine atoms. These free chlorine atoms can then react with ozone (O3), leading to the breakdown of ozone into oxygen (O2).

Chlorine Monoxide (ClO) forms when chlorine reacts with ozone, and its detection in the atmosphere indicates ongoing ozone destruction. Monitoring ClO levels allows scientists to assess the extent of ozone depletion and the effectiveness of regulations put in place to phase out harmful substances like CFCs.

In contrast, while Carbon Dioxide (CO2), Methane (CH4), and Nitrous Oxide (N2O) are greenhouse gases that contribute to global warming and climate change, they do not significantly influence ozone depletion in the stratosphere like Chlorine Monoxide does. Thus, ClO is specifically associated with ozone layer degradation, making it the key indicator.