Subsection 10.1.1 Ozone Hole
The ozone hole refers to a severe depletion of the ozone layer in the Earth’s atmosphere over the Antarctic region, which occurs annually during September to November. The depletion is caused by the release of man-made chemicals, particularly chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), and other halogenated gases that have been used in refrigeration, air conditioning, and other industrial applications. These chemicals are transported into the upper atmosphere, where they are broken down by ultraviolet radiation from the sun, releasing chlorine and bromine atoms. These atoms then react with ozone molecules, breaking them down into oxygen molecules and causing a significant depletion of the ozone layer.
The most important reaction that leads to the depletion of ozone is as follows:
\begin{equation*}
CFCl_3 + UV radiation \rightarrow Cl· + CFCl_2
\end{equation*}
The chlorine radical (Cl·) produced in the above reaction reacts with ozone \((O_3)\) as follows:
\begin{equation*}
Cl· + O_3 \rightarrow ClO· + O_2
\end{equation*}
The ClO· radical then reacts with another oxygen molecule \((O_2)\) to form more chlorine radicals:
\begin{equation*}
ClO· + O \rightarrow Cl· + O_2
\end{equation*}
The chlorine radical produced in the second reaction then repeats the cycle, reacting with more ozone molecules to produce more chlorine radicals. This cycle continues until a large amount of ozone has been depleted. Another reaction that can also lead to ozone depletion involves bromine compounds, such as halons and methyl bromide, which are also released into the atmosphere from human activities.
\begin{equation*}
Br· + O_3 \rightarrow BrO· + O_2
\end{equation*}
\begin{equation*}
BrO· + O \rightarrow Br· + O_2
\end{equation*}
The bromine radical (Br·) produced in the first reaction then reacts with more ozone molecules, leading to further ozone depletion. These reactions are of particular concern because they can destroy large amounts of ozone in a short period of time.
